JP4733842B2

JP4733842B2 - Superconducting material cooling device

Info

Publication number: JP4733842B2
Application number: JP2001039722A
Authority: JP
Inventors: 茂吉田; 孝一大橋; 泰晴上岡; 勇相良; 克哉堤; 博伸木村; 敬昭坊野; 雅行今野; 和夫船木; 成卓岩熊
Original assignee: Kyushu Electric Power Co Inc; Fuji Electric Co Ltd; Taiyo Nippon Sanso Corp; Kyushu TLO Co Ltd
Current assignee: Kyushu Electric Power Co Inc; Fuji Electric Co Ltd; Taiyo Nippon Sanso Corp; Kyushu TLO Co Ltd
Priority date: 2000-03-31
Filing date: 2001-02-16
Publication date: 2011-07-27
Anticipated expiration: 2021-02-16
Also published as: JP2001345208A

Description

【０００１】
【発明の属する技術分野】
この発明は、超電導トランスや超電導マグネット、そのほか各種の超電導コイル、あるいは超電導ケーブルなどの超電導部材、特に高温超電導部材を、液体窒素によって低温に冷却・保持するための超電導部材冷却装置に関するものである。
【０００２】
【従来の技術】
超電導コイルなどの超電導部材、特に高温超電導を利用した超電導部材を冷却するにあたっては、冷却媒体として比較的安価な液体窒素（ＬＮ₂ ）を使用することが多い。この場合一般には大気圧の飽和液体窒素、すなわち約７７Ｋの液体窒素が用いられている。すなわち、真空断熱されたクライオスタットと称される大気に実質的に開放された冷却容器に超電導部材を収容しておき、その冷却容器内に約７７Ｋの大気圧飽和液体窒素を注入してその液体窒素中に超電導部材を浸漬させ、冷却・保持するのが通常である。
【０００３】
ところで高温超電導部材においては、若干でも温度が下がれば、超電導特性が大幅に向上することが知られている。例えば臨界電流は、７７Ｋから７０Ｋに下がっただけでも数倍に大きくなることが知られている。
【０００４】
そこで大気圧の液体窒素を減圧して例えば６５Ｋ程度に温度降下させた液体窒素中に超電導部材を浸漬させて、超電導部材を７７Ｋよりも低い温度まで冷却することが考えられる。その場合、液体窒素中に超電導部材を浸漬させるための容器では、液体窒素の減圧状態を維持させる必要がある。一方、一般に使用されているクライオスタットでは、実質的に大気に開放させた状態での使用を前提としているため、この種の汎用クライオスタットを減圧した液体窒素に適用しようとすれば、蓋部や電流導入端子等の箇所における封止の点で不充分となり、外部から水分を含む大気圧の空気が内部に吸い込まれて、電流導入端子のガス抜穴での水分凍結による閉塞や超電導部材表面への氷の付着が生じたりし、実用上運転が不可能となるおそれがある。そのため前述の目的のためには、新たに特殊な容器を設計、製作しなければならず、その場合コストの大幅な上昇を招く問題があり、そのため実用化はためらわれていたのが実情である。
【０００５】
また一方、大気圧の飽和液体窒素中に超電導部材を浸漬させて超電導部材を作動させた場合、超電導部材の発熱によって飽和液体窒素が直ちに気化してガス気泡が発生するため、そのガス気泡によって電気絶縁性が低下したり、冷却効率が低下したりしてしまう問題があるが、前述のように減圧によって例えば６５Ｋ程度に温度降下された液体窒素中に超電導部材を浸漬させた場合も、減圧下では超電導部材の発熱によって前記同様に直ちに液体窒素が気化して気泡が発生するから、気泡発生に対する根本的な解決策とはならない。したがってこのことも減圧された液体窒素の使用がためらわれていた一因である。
【０００６】
そこで本発明者等は、既に特開平１０−５４６３７号において、液体窒素によって高温超電導部材を冷却するにあたって、特殊な真空封止などを行なわずに、大気に実質的に開放された極く一般的な汎用クライオスタットを超電導部材冷却容器として用いながらも、より低温に高温超電導部材を冷却して超電導性能を向上させ得るようにするとともに、高温超電導部材作動時における高温超電導部材の発熱による液体窒素からのガス気泡の発生を抑制するようにした超電導部材冷却装置を提案している。
【０００７】
上記提案の超電導部材冷却装置は、基本的には、超電導部材を収容してその超電導部材を冷却するための冷却容器を実質的に大気圧に開放した構成とし、かつ大気圧下で過冷却状態とした例えば６７Ｋ程度の液体窒素を、液面上に空間を残すように前記冷却容器内に収容し、かつその液面上の空間に窒素ガスを導入して大気圧に加圧し、その冷却容器内の大気圧下で過冷却状態の液体窒素によって超電導部材を冷却するようにしている。そしてまた上記提案の超電導部材冷却装置において、超電導部材に対する冷却媒体として機能させる大気圧下で過冷却状態の液体窒素は、次のようにして得ている。すなわち、前述の冷却容器とは別に減圧用容器を設けて、その減圧用容器内に熱交換器を配設しておき、減圧用容器内に熱交換用液体窒素（例えば約７７Ｋの大気圧の飽和液体窒素）を供給するとともに、その減圧用容器内の圧力を真空ポンプによって減圧して、減圧用容器内の液体窒素を大気圧から減圧させることによりその温度を例えば６５Ｋの低温に降下させる。一方、前記熱交換用液体窒素とは別に、大気圧の冷却用液体窒素（例えば約７７Ｋの飽和液体窒素）を前記熱交換器に導き、その熱交換器において減圧用容器内の６５Ｋの減圧された熱交換用液体窒素と熱交換させて、例えば６７Ｋ程度まで大気圧のまま冷却させ、大気圧下での過冷却状態とする。そしてこの大気圧下で過冷却状態の例えば６７Ｋの冷却用液体窒素を前述の冷却容器に導いて、超電導部材を６７Ｋに近い温度（例えば７０Ｋ）の低温に冷却することとしている。
【０００８】
このような特開平１０−５４６３７号の提案の超電導部材冷却装置においては、通常の７７Ｋ程度の大気圧下での飽和液体窒素を冷却媒体として用いた場合よりも超電導部材を確実に低温に冷却することができ、そのため超電導部材の性能を向上させることができ、しかもこの場合、冷却容器内の過冷却状態の冷却用液体窒素の液面上の空間が、大気圧の窒素ガスで満たされることにより、外部から水分を含む大気圧の空気が内部に吸い込まれるおそれを少なくして、冷却容器の蓋部や電流導入端子等の封止に厳密さが要求されないようにすることができ、さらには超電導部材を浸漬させた冷却用液体窒素が前述のように過冷却状態であるため、超電導部材の作動時において超電導部材が発熱しても、その発熱部位周辺で液体窒素が気化温度に達するには温度的余裕があり、そのため直ちにはガス気泡が発生せず、したがってガス気泡によって絶縁性が低下したり冷却効率が低下したりするおそれも少ないなどの利点がある。
【０００９】
しかしながら上記提案の超電導部材冷却装置については、未だ次のような問題があった。
【００１０】
すなわち、上記提案の超電導部材冷却装置においては、冷却用の液体窒素とは別に熱交換用液体窒素を減圧用容器内に供給し、真空ポンプによりその減圧用容器内を減圧して熱交換用液体窒素を温度降下させ、その温度降下した熱交換用液体窒素と冷却用液体窒素とを熱交換させることにより大気圧で過冷却状態の冷却用液体窒素を得るようにしているが、この場合減圧用容器内の熱交換用液体窒素は減圧によって徐々に蒸発気化し、かつその気化ガスがポンプにより排気されて行くから、減圧用容器内の液体窒素液面は急激に低下して行き、遂には減圧用容器内の熱交換器が露出してしまうことになる。このように熱交換器が液面から露出してしまえば、充分な熱交換能率が得られなくなって、冷却用液体窒素を充分な過冷却状態となるように冷却することが困難となるから、実際上は熱交換器が液面から露出する以前に、改めて減圧用容器内に液体窒素を補給しなければならず、またこの液体窒素補給時には運転を一旦停止させなければならない。
【００１１】
このように前記提案の超電導部材冷却装置では、減圧用容器内の液体窒素補給のために運転を停止する必要があるところから、長時間連続して運転することができないという問題があり、また液体窒素補給およびそのための運転停止−運転再開のための手間も煩雑となるという問題がある。もちろん短時間の運転の場合は特に問題とはならないが、超電導部材の実用化へ向けた実験・研究、測定等においては、長時間連続して運転することが求められることが多く、したがって減圧用容器への熱交換用液体窒素補給が前記提案の装置の普及に対する大きなネックとなっていたのが実情である。
【００１２】
そこで本発明者等は、前記提案に倣い、大気圧もしくは大気圧よりも高い圧力下で過冷却状態とした液体窒素を超電導部材に対する冷却用媒体として用いながらも、液体窒素を冷凍機によって大気圧下での過冷却となる温度まで冷却し、得られた過冷却状態の低温の液体窒素を、そのまま直接超電導部材を冷却するための冷却媒体として用いることとし、これにより前記提案の場合のような減圧用容器や熱交換器を用いないようにし、それに伴なって減圧用容器内への熱交換用液体窒素の補給のための運転停止を回避し得るようにして、長時間の連続運転を可能とした超電導部材冷却装置を、特許第２８５９２５０号において提案している。
【００１３】
上記特許による超電導部材冷却装置は、基本的には、超電導部材を収容してその超電導部材を冷却するための大気に実質的に開放された冷却容器と、前記冷却容器へ供給すべき液体窒素を収容するための大気圧に実質的に開放された供給側容器と、前記供給側容器へ液体窒素を供給するための液体窒素供給手段と、前記供給側容器内の液体窒素を、大気圧下での過冷却温度まで冷却するための冷凍機と、前記供給側容器内において大気圧下での過冷却温度まで冷却された液体窒素を前記冷却容器に移送するための移送手段とを有してなり、供給側容器および冷却容器の液面上の空間を大気圧とするかまたは大気圧よりも高い圧力とし、かつ前記移送手段によって前記冷却容器内に供給された過冷却状態の液体窒素中に前記超電導部材を浸漬させるようにしたことを特徴とするものであり、その具体例を図５に示す。
【００１４】
図５において、冷却対象となる超電導部材１は冷却容器３の底部に配置されている。この冷却容器３は、大気に実質的に開放された一般的な汎用のクライオスタットからなるものであって、その外周壁部および底壁部が真空断熱構造５とされ、また上端には開閉可能な蓋部７が設けられている。この蓋部７は、容器本体に対して真空封止されたものではなく、またこの蓋部７には汎用のクライオスタットと同様な電流導入端子等が設けられており、このような蓋部７と容器本体部分との間の隙間や電流導入端子等を通じて冷却容器３の内部は実質的に大気開放された状態となっている。なお蓋部７には安全弁１９が設けられているが、この安全弁１９は、内部圧力が外部の大気圧に対して例えば＋０．１ｋｇｆ／ｃｍ² を越えた場合に開放されて、内部圧力を大気圧〜大気圧＋０．１ｋｇｆ／ｃｍ² の範囲内、すなわち大気圧もしくは大気圧より若干高い圧力に保持するように機能する。そして超電導部材１は蓋部７から支持部材９Ａ，９Ｂによって吊下げた状態となっている。冷却容器３内の底部には、後述するようにトランスファチューブ４５を介して大気圧での過冷却状態の液体窒素（冷却用液体窒素）１１が供給されて、超電導部材１がその液体窒素１１に浸漬される。またその冷却容器３内における液体窒素１１の液面１１Ａよりもわずかに下方の位置には、水平横断面の外形形状が冷却容器３の水平横断面内周形状と実質的に相似の形状をなしかつ上下方向に所定の厚みを有する断熱部材１３が配設されている。この断熱部材１３は、要は全体として上下方向への熱伝導が液体窒素よりも格段に少ないものとなっていれば良く、通常はＦＲＰなど熱伝導率の小さい材料によって形成するか、あるいは中空構造としてその中空部分を真空断熱構造とする。なおこの断熱部材１３は、前述の支持部材９Ａ，９Ｂによって蓋部７から吊下げられており、またその断熱部材１３の周囲が冷却容器３の内周壁面に対して若干の隙間１４を保つように作られており、したがってこの隙間１４を液体窒素１１が移動し得ることになる。一方冷却容器３における冷却用液体窒素１１の液面１１Ａの上方に残された空間（蓋部７と液面１１Ａとの間の空間）１５には、外部の第１の窒素ガス供給源１６から窒素ガス供給管１８を経て大気圧の窒素ガスが供給される。また冷却容器３内における断熱部材１３の下面側の位置には、後述する還流管１７の一端側が開口している。
【００１５】
さらに前述のように大気に実質的に開放された冷却容器３とは別に、供給側容器２１が配設されている。
【００１６】
供給側容器２１は、前述の冷却容器３と同様に大気に実質的に開放されたものであって、その外周壁部および底壁部が真空断熱構造２３とされ、また上端には開閉可能な蓋部２５が設けられている。この蓋部２５は容器本体に対して真空封止されたものではなく、このような蓋部２５と容器本体部分との間の隙間などを通じて供給側容器２１の内部は実質的に大気に開放された状態となっている。この供給側容器２１には、外部の液体窒素供給源２７から、制御弁２９および供給管３１を介して液体窒素３３が供給されるようになっている。そして供給側容器２１内における液体窒素３３の液面３３Ａよりもわずかに下方の位置には、水平横断面の外形形状が供給側容器２１の水平横断面形状と実質的に相似の形状をなしかつ上下方向に所定の厚みを有する断熱部材３５が、蓋部２５から支持部材３７Ａ，３７Ｂによって吊下げられた状態で配設されている。この断熱部材３５も、前記冷却容器３内の断熱部材１３と同様のものであり、その断熱部材３５の周囲が供給側容器２１の内周壁面に対して若干の隙間３９を保持していて、その隙間３９を液体窒素３３が移動し得るように構成されていることも、冷却容器３内の断熱部材１３と同様である。
【００１７】
さらに供給側容器２１には、その供給側容器２１内の液体窒素３３を、大気圧下での飽和液体窒素の温度よりも低い過冷却温度（約７７Ｋよりも低い温度、例えば６５〜７０Ｋ）に冷却するための冷凍機４１が配設されている。この冷凍機４１は、冷凍媒体ガス（通常はヘリウムガス）を圧縮するための圧縮部（コンプレッサ）４１Ａと、圧縮された高圧の冷凍媒体ガスを膨張させて低温を得るとともににその低温を冷却対象（液体窒素）と熱交換するための冷却ヘッド４１Ｂと、圧縮部４１Ａからの高圧の媒体ガスと冷却ヘッド４１Ｂから戻る膨張された低圧の媒体ガスの流れを切替えるためのモーターバルブ等の切替部４１Ｃと、その切替部４１Ｃと冷却ヘッド４１Ｂとの間で冷凍媒体ガスを往復させる通路を内部に形成したシリンダ部４１Ｄとからなるものであり、その切替部４１Ｃが供給側容器２１の蓋部２５上に配置され、シリンダ部４１Ｄが切替部４１Ｃから蓋部２５を下方へ貫通して供給側容器２１内の液体窒素の液面３３Ａ上の空間４７を通り、その下端が液体窒素中に浸漬され、その部分すなわち液体窒素中に浸漬された部分に冷却ヘッド４１Ｂが設けられている。ここで、シリンダ部４１Ｄは一般にステンレス鋼により作られている。また冷却ヘッド４１Ｂは、その外面に銅等の良伝熱材料からなる伝熱ブロックを設けた構成とされている。なお圧縮部４１Ａは通常は供給側容器２１から離れた位置に配置され、その圧縮部４１Ａと切替部４１Ｃとの間が、高圧ガス管路４１Ｅ、低圧ガス管路４１Ｆによって結ばれている。
【００１８】
また供給側容器２１内には、蓋部２５から吊下げられた状態で送液ポンプ４３が配設されている。この送液ポンプ４３は、その取入口（汲出口）が供給側容器２１における断熱部材３５よりも下方（通常は供給側容器２１の底部近く）に位置するように配設されている。そしてこの送液ポンプ４３の出口側はトランスファーチューブ４５に接続されており、このトランスファーチューブ４５は前述のように冷却容器３内に導かれている。さらに前記冷却容器３からの還流管１７が供給側容器２１内へ導かれており、その還流管１７の先端側開口端が供給側容器の底部（前記冷凍機４１の冷却ヘッド４１Ｂよりも下方の位置）において開口している。
【００１９】
また供給側容器２１における液体窒素３３の液面３３Ａの上方に残された空間（蓋部２５と液面３３Ａとの間の空間）４７には、外部の第２の窒素ガス供給源４９から窒素ガス供給管５１を経て大気圧もしくは大気圧以上の圧力の窒素ガスが供給されるようになっている。
【００２０】
ここで、液体窒素供給源２７、制御弁２９、および供給管３１は、供給側容器２１に液体窒素を供給するための液体窒素供給手段６３を構成している。さらに送液ポンプ４３およびトランスファチユーブ４５は、供給側容器２１内において大気圧で過冷却状態に冷却された液体窒素を冷却容器３に移送するための移送手段６５を構成している。一方第１の窒素ガス供給源１６、窒素ガス供給管１８は、冷却容器３における液面上の空間１５に大気圧もしくは大気圧以上の圧力の窒素ガスを供給するための第１の窒素ガス供給手段６７を構成しており、また第２の窒素ガス供給源４９、窒素ガス供給管５１は、供給側容器２１における液面上の空間４７に大気圧もしくは大気圧以上の圧力の窒素ガスを供給するための第２の窒素ガス供給手段６９を構成している。
【００２１】
以上のような図５に示される先行技術による超電導部材冷却装置の全体的な機能について以下に説明する。
【００２２】
液体窒素供給手段６３の液体窒素供給源２７から供給側容器２１に供給される液体窒素は、７７Ｋ程度のものであるが、その液体窒素は供給側容器２１内において、冷凍機４１の冷却ヘッド４１Ｂによって大気圧もしくは大気圧以上の圧力のもとで冷却されて、大気圧下での飽和液体窒素温度（７７Ｋ程度）よりも低い温度、例えば６５〜７０Ｋ程度まで温度降下される。そしてその６５〜７０Ｋ程度に過冷却された大気圧もしくは大気圧より高い圧力の液体窒素３３は、送液ポンプ４３によって供給側容器２１の底部付近から汲み上げられ、トランスファチューブ４５を介して、大気に実質的に開放された冷却容器３内に導かれる。冷却容器３内に導かれた過冷却状態の液体窒素を図５では符号１１で示しており、これが冷却用液体窒素に相当する。
【００２３】
冷却容器３内においては、前述のような例えば６５〜７０Ｋの過冷却状態の液体窒素１１によって超電導部材１が例えば６７〜７２Ｋ程度に冷却・保持される。また冷却容器３内において超電導部材１からの熱などによって例えば７０Ｋ程度以上に温度上昇した液体窒素は、還流管１７を介して供給側容器２１へ戻る。このようにして供給側容器２１へ還流された流体窒素は、冷凍機４１の冷却ヘッド４１Ｂにより再び６５〜７０Ｋ程度まで大気圧もしくは大気圧以上の圧力のもとで冷却され、前述のように送液ポンプ４３によって冷却容器３に再び送られることになる。
【００２４】
ここで、冷却容器３内における冷却用液体窒素１１の液面１１Ａの上方の空間１５には窒素ガス供給管１８を介して大気圧もしくは大気圧以上の圧力の窒素ガスが導入される。したがって冷却容器３の液面上の空間１５は大気圧もしくは大気圧以上の圧力の窒素ガスで満たされることになる。そのため冷却容器３内の圧力が大気圧もしくは大気圧以上の圧力に維持され、蓋部７の封止部分や電流導入端子部分などを介して外部から空気が引き込まれて侵入することが防止される。
【００２５】
また冷却容器３内における冷却用液体窒素１１の液面下には断熱部材１３が配設されているから、冷却用液体窒素１１の液面（気液界面であるため約７７Ｋ）とその断熱部材１３よりも下側、特に超電導部材１が位置している冷却容器底部との間で熱勾配を与えることができる。またその断熱部材１３の存在によって液面１１Ａ付近に底部側との間での対流撹拌が阻止される。そしてこれらの結果、超電導部材１が位置する底部の冷却用液体窒素１１を、６５Ｋ程度の低温の過冷却状態に維持することができる。そしてこのように超電導部材１が例えば６５〜７０Ｋの過冷却状態の低温の液体窒素１１によって取囲まれるため、超電導部材１の作動時において超電導部材１が発熱しても、その周囲の液体窒素が大気圧下での気化温度（約７７Ｋ）以上となるまでには１０Ｋ程度の余裕があり、そのため超電導部材１の発熱によってその周囲の液体窒素が直ちに気化してガス気泡が発生してしまうことを有効に防止できる。
【００２６】
なお供給側容器２１内における液体窒素３３の液面３３Ａの上方の空間４７にも、窒素ガス供給管５１を介して大気圧もしくは大気圧以上の圧力の窒素ガスが導入されて、その大気圧もしくは大気圧以上の圧力の窒素ガスで満たされることになる。そのため供給側容器２１内の圧力が大気圧もしくは大気圧以上の圧力に維持され、蓋部２５の封止部分などを介して外部から空気が引き込まれて侵入することが防止される。
【００２７】
また冷却容器３と同様に、供給側容器２１内における液体窒素３３の液面下にも断熱部材３５が配設されており、そのため液体窒素３３の液面（気液界面であるため約７７Ｋ）とその断熱部材３５よりも下側、特に冷凍機４１の冷却ヘッド４１Ｂ付近との間で熱勾配を与えることができる。またその断熱部材３５の存在によって液面３３Ａ付近と断熱部材３５よりも下側の部分との間での対流撹拌が阻止される。そしてこれらの結果、送液ポンプ４３の取入口付近の液体窒素３３を、６５〜７０Ｋ程度の低温の過冷却状態に維持して、その６５〜７０Ｋ程度の低温の過冷却状態の液体窒素を冷却容器３へ送り込むことができる。
【００２８】
【発明が解決しようとする課題】
図５に示される装置においては、前述のように供給側容器２１内における液体窒素３３の液面下にＦＲＰなどの低熱伝導率材料からなる断熱部材３５を配置することによって、液面付近（約７７Ｋ）と冷却ヘッド４１Ｂ付近（６５〜７０Ｋ）との間で熱勾配を形成している。しかしながらこのようなＦＲＰなどからなる断熱部材を液面下に設けた場合、次のような問題があることが判明した。
【００２９】
すなわち、供給側容器２１内においては、液体窒素３３の液面３３Ａは、大気圧もしくは大気圧以上の圧力の窒素ガスと液体窒素３３が接する気液界面となっており、そのため液面近傍の液体窒素は、定常時は飽和液体となっている。そしてその液面近傍の液体窒素の温度は、大気圧もしくは大気圧より高い圧力下での飽和温度となっている。なおここで“大気圧よりも高い圧力”も、実際上は既に述べたように大気圧よりもわずかに高い程度であるから、以下では、説明の簡単化のため、一律に大気圧と記すこととし、液面近傍の液体窒素の温度も、一律に大気圧での飽和温度（約７７．４Ｋ）と考えることとする。
【００３０】
一方、供給側容器２１内における液体窒素の液面３３Ａよりも下方に離れた位置、特に冷凍機４１の冷却ヘッド４１Ｂの位置やそれよりも下方の位置では、前述のように液体窒素が冷却ヘッド４１Ｂにより冷却されて、大気圧下での飽和温度よりも低い６５〜７０Ｋ程度の温度の過冷却状態となっている。そのため液体窒素中の冷却ヘッド４１Ｂより上方の領域では、液面から下方へ向かって温度勾配が形成されている。そしてこのような温度勾配を安定して維持するため、前記提案の装置では断熱部材３５を設けており、またこの断熱部材３５によって対流撹拌を阻止するようにしているのであるが、実際の運転時には、送液ポンプ４３の作動状況や熱負荷の変動などによる擾乱が液体窒素中に生じて、液体窒素に対流が発生したり撹拌されたりしてしまうことがある。その場合、温度勾配が乱されて、たとえ前述のような断熱部材３５を設けていても、運転状況が不安定化し、また液面での液体窒素の気化や逆に窒素ガスの凝縮が生じたりして、液面位置が変動してしまい、それに伴なって温度勾配の不安定化が一層激しくなり、ますます運転状況が不安定化し、冷却効率の低下、システムの信頼性の低下を招いてしまうおそれがある。
【００３１】
特に前述の従来技術の場合、断熱部材３５を配置した領域では、その断熱部材３５の体積によって液体窒素が排除されていて、断熱部材３５の周囲のわずかな狭い空隙３９の部分のみを液体窒素が移動し得る状況となっているから、わずかに液体窒素の蒸発もしくは窒素ガスの凝縮が生じただけで、液面の位置が大きく変動し、そのため温度勾配が大きく変動してしまうおそれがある。したがって従来技術のような断熱部材３５を設けた場合は、実際の運転時においては運転状況の安定化、信頼性の向上を図るには未だ不充分であった。
【００３２】
なお上述の説明では供給側容器２１内の断熱部材３５を例にとって説明したが、冷却容器３内の断熱部材１３についてもほぼ同様な問題がある。
【００３３】
さらに、既に述べたように特開平１０−５４６３７号に示される超電導部材冷却装置、すなわち超電導部材を収容した冷却容器とは別に減圧容器を設けておいて、減圧用容器内の液体窒素を減圧して例えば６５Ｋの低温に降下させ、かつその低温の液体窒素と大気圧の冷却用液体窒素とを熱交換させて、得られた大気圧下で６５Ｋ程度の低温の液体窒素（すなわち大気圧下での過冷却液体窒素）を冷却容器に導き、その冷却容器内の超電導部材を６５Ｋ近くまで冷却するようにした装置の場合も、冷却容器内に外部から大気圧の窒素ガスを導入するようにしており、また冷却容器内の液体窒素の液面下にＦＲＰ等からなる断熱部材を配置することが考えられており、この場合も前記と同様な問題があった。
【００３４】
結局、液面上に空間を残して液体窒素を収容しかつその液面上の空間に大気圧もしくは大気圧以上の圧力で窒素ガスが導入される液体窒素容器（例えば特許第２８５９２５０号の装置における供給側容器２１もしくは冷却容器３、あるいは特開平１０−５４６３７号の装置における冷却容器）内の液体窒素を、大気圧下での過冷却温度とし、かつその液体窒素容器内の液体窒素の液面下にＦＲＰ等からなる断熱部材を設けておき、大気圧下での過冷却温度の液体窒素によって超電導部材を冷却するようにした装置では、すべて前述のような問題が生じるおそれがあったのである。
【００３５】
この発明は以上の事情を背景としてなされたもので、液面上に空間を残して過冷却温度の液体窒素を収容する液体窒素容器の液面上の空間を大気圧もしくは大気圧以上の窒素ガス圧力で加圧し、大気圧下での過冷却温度の液体窒素によって超電導部材を冷却するようにした装置において、主として液面下の温度勾配を確実かつ安定して保つことができるようにし、これによって運転状況の安定化、冷却効率の向上、信頼性の向上を図ることを目的としたものである。
【００３６】
【課題を解決するための手段】
前述のような課題を解決するため、この発明においては、基本的には液体窒素容器内の液面よりも下方の位置から液面よりも上方の位置までの間にわたって、連続気泡タイプのウレタン発泡体の如く、連続孔（連続気泡）を有する多孔質断熱材からなる対流阻止部材を配置することとした。
【００３７】
すなわち請求項１の発明は、液面上に空間を残して液体窒素を収容しかつその液面上の空間に大気圧もしくは大気圧以上の窒素ガス圧力が加えられる液体窒素容器内の液体窒素を、大気圧下での過冷却温度とし、その大気圧下での過冷却温度の液体窒素によって超電導部材を冷却するように構成した超電導部材冷却装置において、前記液体窒素容器内の液体窒素の液面よりも下方の位置から、液面上方の位置までの間にわたって、連続孔を有する多孔質断熱材からなる対流阻止部材を配置したことを特徴とするものである。
【００３８】
このような請求項１の発明の超電導部材冷却装置においては、対流阻止部材は連続孔を有する多孔質断熱材によって作られているため、液体窒素容器内の液体窒素が液面に近い位置において対流阻止部材の連続孔に入り込むことになり、したがって液体窒素容器内の液面は、対流阻止部材の上下方向中間位置（上端面と下端面との間の中間の位置）において対流阻止部材の内部の連続孔部分に位置することになる。そして液面近傍の位置において液面下の液体窒素が、前述のように対流阻止部材の内部の連続孔内に入り込んでいるため、運転時に送液ポンプや熱負荷の変動などによって容器内の液体窒素に対流や撹拌が生じても、液面近傍の液体窒素はその移動（対流、撹拌）が阻止され、その結果上述のような対流や撹拌に起因する上下方向の温度勾配が崩れたり、乱れたりすることを未然に防止することができる。
【００３９】
また対流阻止部材は容器内の液面上の空間中へも延出しているため、液面上の空間における窒素ガスの対流や撹拌も阻止され、そのため液面上の気相における温度勾配も安定化し、このことも運転状況の安定化、信頼性の向上に寄与する。
【００４０】
さらに、対流阻止部材として、その空隙率（気孔率）が高いもの（例えば連続気泡ウレタン発泡体では９０％程度の空隙率を有する）を用いれば、仮に液面での液体窒素の気化や窒素ガスの凝縮によって液量の増減が生じたとしても、それが液位の変動に及ぼす影響は小さく、このことも温度勾配の安定化に寄与する。
【００４１】
なおここで、対流阻止部材に使用される多孔質断熱材としては、可及的に熱伝導率が低いものが望ましいが、液体窒素とそれほど熱伝導率が変わらないものを用いても、前述のように液体窒素の対流、撹拌を阻止する結果として、見掛け上大きな断熱効果を示すことになる。したがって断熱材としては前述のような連続気泡ウレタン発泡体の如く、極く一般的な材質のものを用いることができるのである。
【００４２】
また請求項２の発明は、前述の特許第２８５９２５０号の超電導部材冷却装置に準じて、容器内の液体窒素を直接冷凍機によって大気圧下での過冷却温度まで冷却するようにした場合に、前記同様に連続孔を有する多孔質断熱材からなる対流阻止部材を設けることを規定したものである。
【００４３】
具体的には、請求項２の発明は、液面上に空間を残して液体窒素を収容しかつその液面上の空間に大気圧もしくは大気圧以上の窒素ガス圧力が加えられる供給側容器と、その供給側容器内の液体窒素を大気圧下での過冷却温度まで冷却するために冷却ヘッドを液体窒素の液面よりも下方の位置まで浸漬させた冷凍機とを備え、供給側容器内の過冷却温度の液体窒素を冷却対象の超電導部材へ導いてその超電導部材を冷却するように構成された超電導部材冷却装置において、前記供給側容器内の液体窒素の液面よりも下方の位置から、液面上方の位置までの間にわたって、連続孔を有する多孔質断熱材からなる対流阻止部材を配置したことを特徴とするものである。
【００４４】
このように冷凍機の冷却ヘッドを容器内の液体窒素中に直接浸漬させて、大気圧下での過冷却温度の液体窒素を得る場合には、その容器内に通常配設されている送液ポンプの動作などによって液体窒素の対流や撹拌が生じ易く、また温度勾配の乱れがシステム全体に与える影響も大きいが、既に述べた請求項１の発明と同様に、連続孔を有する多孔質断熱材からなる対流阻止部材を設けておくことによって、液面下の温度勾配、液面上の温度勾配を安定化することができる。
【００４５】
なお請求項２の構成の場合、多孔質断熱材からなる対流阻止部材は、請求項３で規定しているように、供給側容器の液面よりも下方でかつ冷凍機の冷却ヘッドの上端部以上の位置から液面上方の位置までの間にわたって配置しても、あるいは請求項４で規定しているように、供給側容器の液面よりも下方でかつ冷凍機の冷却ヘッドにおける上下方向中間位置から液面上方の位置までの間にわたって配置しても良い。
【００４６】
さらに請求項５の発明は、請求項４に記載の超電導部材冷却装置において、冷凍機の冷却ヘッドが供給側容器の底面近くの位置まで延伸されていることを特徴とするものである。
【００４７】
ここで、冷凍機のシリンダ部の内部には常温付近の高圧の媒体が流れるが、請求項５で規定するような構成としておけば、冷凍機のシリンダ部の外周面に断熱部が設けられているため、そのシリンダ部における液体窒素中に浸漬された部分でも、シリンダ部内の常温付近の媒体ガスから液体窒素への熱侵入量が少なく、そのため冷凍機の冷却効率が低下することが防止され、またシリンダ部からの熱侵入による液体窒素の蒸発自体も少なくなるため、液体窒素の液面レベルの変動も少なくなる。
【００４８】
さらに請求項６発明は、請求項４もしくは請求項５に記載の超電導部材冷却装置において、前記冷凍機のシリンダ部の外周面に断熱部が設けられ、かつその断熱部が、冷凍機の冷却ヘッドの外周面における上下方向の中間位置まで延長されていることを特徴とするものである。
【００４９】
このような請求項６の発明の超電導部材冷却装置では、シリンダ部外周面の断熱部が冷凍機の冷却ヘッドの外周面の上下方向中間位置まで延長されているため、供給容器内における液面、すなわち気液界面から冷凍機の冷却ヘッドへの熱侵入が少なくなり、冷却効率を一層向上させることができる。
【００５０】
【発明の実施の形態】
【００５１】
【実施例】
図１において、供給側容器２１における液体窒素３３の液面３３Ａを挟んで上下の領域には、連続気泡ウレタン系発泡体の如く、連続孔（連続気泡）を有する多孔質断熱材からなる対流阻止部材７７が配設されている。この対流阻止部材７７は、その下面７７Ａが液面３３Ａより所定距離だけ下方の位置（図１の例では冷凍機４１の冷却ヘッド４１Ｂの上端）に位置するように、またその上面７７Ｂが蓋部２５よりも若干下方の位置に位置するように配置されている。そして液体窒素３３は、その液面３３Ａ近傍において対流阻止部材７７の内部の連続孔に入り込んで、液面３３Ａが対流阻止部材７７の上面７７Ｂと下面７７Ａとの中間に位置することになる。なお対流阻止部材７７の外周面の形状・寸法は、供給側容器２１の内周面と実質的に同一形状でほぼ同一寸法に作られ、供給側容器２１の内周面に嵌め込まれた状態とされている。
【００５２】
一方冷却容器３における液体窒素１１の液面１１Ａを挟む上下の領域にも、連続気泡ウレタン系発泡体の如く、連続孔（連続気泡）を有する多孔質断熱材からなる対流阻止部材７９が配設されている。この対流阻止部材７９は、その下面７９Ａが液面１１Ａより所定距離だけ下方の位置、望ましくは冷却対象となる超電導部材１の上端よりも上方の位置に位置し、かつ上面７９Ｂが蓋部７の下面よりも若干下方に位置するように定められている。そして液体窒素１１がその液面１１Ａの近傍において対流阻止部材７９の内部の連続孔部分に入り込み、その液面１１Ａが対流阻止部材７９の上面７９Ｂと下面７９Ａとの中間に位置することになる。なお対流阻止部材７９の外周面の形状・寸法は、冷却容器３の内周面と実質的に同一形状でほぼ同一寸法に作られ、冷却容器３の内周面に嵌め込まれた状態となっている。
【００５３】
以上のような図１に示される実施例において、液体窒素供給源２７から供給側容器２１内に供給された７７Ｋ程度の液体窒素は、冷凍機４１の冷却ヘッド４１Ｂによって大気圧もしくは大気圧以上の圧力のもとで冷却されて、大気圧下での飽和液体窒素温度（７７Ｋ程度）よりも低い温度（過冷却温度）、例えば６５〜７０Ｋ程度まで温度降下され、過冷却された液体窒素３３が、送液ポンプ４３によって供給側容器２１の底部付近から汲み上げられ、トランスファチューブ４５を介して、冷却容器３内に導かれ、超電導部材１を例えば６７〜７２Ｋ程度に冷却・保持する。また冷却容器３内において超電導部材１からの熱などによって例えば７０Ｋ程度以上に温度上昇した液体窒素は、還流管１７を介して供給側容器２１へ戻る。このようにして供給側容器２１へ還流された液体窒素は、冷凍機４１の冷却ヘッド４１Ｂにより再び６５〜７０Ｋ程度まで大気圧もしくは大気圧以上の圧力のもとで冷却され、前述のように送液ポンプ４３によって冷却容器３に再び送られることになる。また供給側容器２１における液面３３Ａ上の空間４７および冷却容器３における液面１１Ａ上の空間１５には、大気圧もしくは大気圧以上の圧力の窒素ガスが導入されて、供給側容器２１内の圧力および冷却容器３内の圧力が大気圧もしくは大気圧以上に維持され、蓋部２５の封止部分などおよび蓋部７の封止部分や電流導入端子部分などを介して外部から空気が引込まれることを防止している。以上の動作状況は図５に示す従来技術と実質的に同様である。
【００５４】
ここで、供給側容器２１においては、液体窒素３３中における冷凍機４１の冷却ヘッド４１Ｂよりも上方の部分、すなわち液面３３Ａ近傍の領域では、液体窒素３３が対流阻止部材７７の連続孔中に入り込んでいるため、送液ポンプ４３の作動などの何らかの原因により容器２１内の下部の領域で対流や撹拌が生じても、その対流や撹拌による液体窒素の流動が対流阻止部材７７の連続孔の壁部によって妨げられ、結局液面３３Ａの近傍の領域では対流や撹拌が阻止されて、液面３３Ａから下方へ向かっての温度勾配が安定して維持される。
【００５５】
また、液面３３Ａ上の空間４７においても、液面下の液体窒素３３の対流や撹拌に附随して、気相（窒素ガス）に対流や撹拌が生じる可能性があるが、その場合でも対流阻止部材７７が液面上まで存在しているため、窒素ガスの対流や撹拌が生じることを防止し、蓋部２５から液面３３Ａに至るまでの気相領域の温度勾配を安定化することができる。
【００５６】
さらに、仮に液面３３Ａからの液体窒素の気化や液面３３Ａ上の空間からの窒素ガスの凝縮によって、液体窒素の量が変動したとしても、一般に連続気泡ウレタン系発泡体などの連続孔多孔質断熱材は、その水平横断面における気孔部分（空隙部分）の面積（すなわち液体窒素３３が入り込んでいる部分の水平横断面面積）が図５に示す従来技術における断熱部材３５の周囲の空隙３９の水平横断面積に比べて格段に大きいのが通常であり、そのためわずかの液量の変動が液面位置の変動に大きな影響を及ぼしてしまうことを回避して、液面位置を安定して維持することができる。
【００５７】
また冷却容器３内においても、連続孔を有する多孔質断熱材からなる対流阻止部材７９が配設されているため、上記と同様な作用、効果を得ることができる。すなわち冷却容器３の側では、冷却対象である超電導部材１の動作による熱負荷の変動によって冷却容器３内の下部で液体窒素１１の対流や撹拌が生じることがあるが、これを対流阻止部材７９によって阻止して、液面１１Ａの近傍での液体窒素１１の対流や撹拌を有効に防止し、温度勾配を安定化することができる。また冷却容器３内における液面１１Ａ上の空間の気相（窒素ガス）に対しても同様であって、蓋部７から液面１１Ａまでの気相領域における温度勾配を安定化することができる。
【００５８】
そしてまた、冷却容器３の側の対流阻止部材７９も、水平横断面の気孔部分の面積が図５に示す従来技術の断熱部材１３の周囲の空隙１４の水平横断面面積に比較して格段に大きいのが通常であり、そのため前記同様にわずかな液量の変動が液面位置の変動に及ぼす影響を小さくして、液面位置を安定化することができる。
【００５９】
ここで、図１に示される実施例においては、供給側容器２１内における対流阻止部材７７を、その下面が冷凍機１の冷却ヘッド４１Ｂの上端に位置するように配置しているが、対流阻止部材７７は、その下面が冷凍機１の冷却ヘッド４１Ｂの上下方向の中間位置に達するように配置しても良く、その場合の例を示したのが図２の実施例である。
【００６０】
図２の実施例では、冷凍機４１の冷却ヘッド４１Ｂは、その下端が供給側容器２１の底面近くまで延長されている。そしてこのように下方へ延長された冷却ヘッド４１の上下方向の中間位置に相当するレベルに、連続孔を有する多孔質断熱材からなる対流阻止部材７７の下面７７Ａが位置している。もちろん対流阻止部材７７の上面７７Ｂは液面３３Ａよりも上方（蓋部２５に近い位置）に位置している。なおこの実施例では、常温付近の温度の冷凍機媒体ガスが内部を流通する冷凍機４１のシリンダ部４１Ｄから液体窒素中への熱侵入を可及的に防止するため、シリンダ部４１Ｄの外周面を取囲むように、真空断熱構造あるいは適宜の断熱材からなる断熱部８０が設けられている。
【００６１】
図２に示す実施例の場合、対流阻止部材７７は液面上方から冷凍機４１の冷却ヘッド４１Ｂの上下方向中間位置にまで及んでいるため、図１の例の場合よりも対流阻止部材７７における液面下の部分の厚みが大きくなっている。これは対流阻止に有効な領域が広いことを意味し、そのため図１の例の場合よりも対流や撹拌による液体窒素１１の流動を防止する効果が大きく、したがって温度勾配をより一層安定化させる効果が得られる。またここで、図２の例では冷凍機４１の冷却ヘッド４１Ｂの下端が供給側容器２１の底面近くまで延長されているため、より一層対流阻止部材７７の液面下の厚みを増すことが可能となって、前述の効果をより一層大きくすることが可能となっている。なお冷却ヘッド４１Ｂの上部（前記中間位置よりも上方の部分）の外周面は対流阻止部材７７によって取囲まれているが、冷却ヘッド４１Ｂの下部の外周面は液体窒素１１に直接接触しているため、冷却ヘッド４１Ｂと液体窒素１１との間の熱交換効率を低下させるおそれは少ない。
【００６２】
また図２の実施例では、冷凍機４１のシリンダ部４１Ｄの外周面に断熱部８０が設けられており、そのため内部を高圧で常温付近の温度の冷凍機媒体ガスが流通するシリンダ部４１Ｄからその外側の液体窒素１１への熱侵入をも防止することができる。
【００６３】
なおこのように冷凍機４１のシリンダ部４１Ｄの外周面に断熱部８０を設ける場合、図３に示すようにその断熱部８０を冷却ヘッド４１Ｂの上下方向中間位置まで延長させておいても良く、このようにすれば冷却ヘッド４１Ｂの上部の外周面が液体窒素に直接接触することを防止でき、そのため熱勾配の安定化に一層寄与することができる。
【００６４】
なお以上の各実施例においては、対流阻止部材を供給側容器２１と冷却容器３との両者に設けているが、場合によっては供給側容器２１のみに設けても良い。
【００６５】
以上の各実施例は、特許第２８５９２５０号において提案されている従来技術の超電導部材冷却装置を改良したものとして示したが、特開平１０−５４６３７号で提案されている従来技術の超電導部材冷却装置、すなわち冷凍機を用いずに、減圧用容器および熱交換器を用いて大気圧下での過冷却液体窒素を得て超電導部材を冷却する装置に準じて、この発明を適用し得ることはもちろんである。その場合の実施例を図４に示す。
【００６６】
図４において、冷却容器３は図１に示される実施例の冷却容器と同様に大気に実質的に開放された汎用のクライオスタットからなるものであって、過冷却液体窒素１１が液面上に空間を残すように注入されており、かつその底部に冷却対象となる超電導部材１が配置されている。この冷却容器３の具体的構成は、図１の実施例の場合と同様であり、その詳細な説明は省略する。もちろん冷却容器３内の液体窒素１１の液面１１Ａを挟んでその上下にわたって連続孔を有する多孔質断熱材からなる対流阻止部材７９が配置されている点も、図１に示される実施例の冷却容器３と同様である。なお冷却容器３内の液体窒素１１の液面上の空間１５には、窒素ガス供給源７１から窒素ガス供給管７３Ａ，７３Ｃ、開閉弁７５Ｂを経て大気圧もしくは大気圧以上の圧力の窒素ガスが供給されるようになっている。また冷却容器３内における冷却用液体窒素１１の液面１１Ａのわずか下方の位置には、後述する還流管１７の一端側開口端が開口している。
【００６７】
さらに前述のように大気に実質的に開放された冷却容器３とは別に、供給側保持容器８１および減圧用容器８３が配設されている。
【００６８】
供給側保持容器８１は、冷却容器３と同様に大気に実質的に開放されたものであって、この供給側保持容器８１には、外部の液体窒素供給源８５から、制御弁８７および供給管８９を介して大気圧の液体窒素９０が供給される。その供給量は供給側保持容器８１内に設けた液面計９１および前記制御弁８７によって制御される。また供給側保持容器８１内には、送液ポンプ９３が配設されており、この送液ポンプ９３によって供給側保持容器８１内の大気圧もしくは大気圧以上の圧力の液体窒素９０が、第１トランスファチューブ９５を介して減圧用容器８３内の後述する熱交換器１１７へ輸送されるようになっている。また供給側保持容器８１内における液体窒素９０の液面の上方の空間には、外部の窒素ガス供給源７１から窒素ガス供給管７３Ａ，７３Ｂ、開閉弁７５Ａを経て大気圧もしくは大気圧以上の圧力の窒素ガスが導かれるようになっている。なお供給側保持容器８１内の液面下には、前述の冷却容器３から導かれる還流管１７の先端が開口している。
【００６９】
一方減圧用容器８３には、外部の液体窒素供給源１０５から、制御弁１０７および供給管１０９を介して熱交換用液体窒素１１１が供給される。その供給量は、減圧用容器８３内に設けた液面計１１３および制御弁１０７によって制御されるようになっている。またこの減圧用容器８３には、減圧手段としてロータリーポンプ１１５が接続されており、このロータリーポンプ１１５によって内部の熱交換用液体窒素１１１が大気圧よりも所定の圧力だけ低い圧力（例えば２０ｋＰａ）に減圧され、またそれに伴なって温度降下されるようになっている。さらに減圧用容器８３内には、熱交換用液体窒素１１１に浸漬される位置に熱交換器１１７が配設されている。この熱交換器１１７の入口側には、前述の供給側保持容器８１から第１トランスファチューブ９５を介して大気圧もしくは大気圧以上の圧力の飽和液体窒素９０が供給されて、その液体窒素９０が、減圧用容器８３内の減圧された低温の熱交換用液体窒素１１１と熱交換されて、温度降下する。また熱交換器１１７の出口側は第２トランスファチューブ１１９に接続されていて、熱交換により温度降下した液体窒素９０が前述の冷却容器３に、冷却用液体窒素１１として導かれるようになっている。
【００７０】
ここで減圧用容器８３の側の液体窒素供給源１０５、制御弁１０７、供給管１０９は、減圧用容器８３へ熱交換用液体窒素を供給するための熱交換用液体窒素供給手段１２１を構成している。また液体窒素供給源８５、制御弁８７、供給管８９、供給側保持容器８１、送液ポンプ９３、第１トランスファチューブ９５は、熱交換器１１７に大気圧もしくは大気圧以上の圧力の液体窒素を供給するための冷却用液体窒素供給手段１２３を構成している。さらに第２トランスファチユーブ１１９は、熱交換器１１７を通過した大気圧下での過冷却温度の冷却用液体窒素を冷却容器３に移送するための移送手段１２５を構成している。なおこの実施例では、冷却容器３が請求項１で規定する液体窒素容器に相当する。
【００７１】
以上のような図４に示される第２の実施例の超電導部材冷却装置の全体的な機能について以下に説明する。
【００７２】
供給側保持容器８１から送液ポンプ９３により第１トランスファチューブ９５を介して減圧用容器８３内の熱交換器１１７へ送られる液体窒素９０は、運転開始の初期においては７７Ｋ程度の温度の大気圧下での飽和状態のものとなっている。一方減圧用容器８３内は、減圧手段、例えばロータリーポンプ１１５によって大気圧よりも低い圧力に減圧され、そのため液体窒素供給源１０５から減圧用容器８３に供給された液体窒素１１１は、大気圧で下の飽和温度（７７Ｋ程度）から例えば６５Ｋ程度まで温度降下される。そして供給側保持容器８１から熱交換器１１７へ送られて来た大気圧もしくは大気圧以上の圧力の液体窒素９０は、減圧用容器８３内の例えば６５Ｋの液体窒素１１１と熱交換されて、６７Ｋ程度まで温度降下する。すなわち過冷却状態となる。なおこの熱交換器１１７においては、液体窒素９０の圧力は特に変化せず、大気圧もしくは大気圧以上の圧力の状態を維持する。
【００７３】
上述のようにして６７Ｋ程度に過冷却された大気圧もしくは大気圧以上の圧力の液体窒素９０は、第２トランスファチューブ１１９を介して、大気に実質的に開放された冷却容器３内に導かれる。冷却容器３内に導かれた過冷却状態の大気圧の液体窒素を図４では符号１１で示しており、これが冷却用液体窒素に相当する。ここで、冷却容器３内における冷却用液体窒素１１の量は、液面１１Ａ上に空間１５が残るように還流管１７によって調整される。
【００７４】
冷却容器３内においては、図１に示した実施例と同様に６７Ｋの過冷却状態の大気圧もしくは大気圧以上の圧力の液体窒素１１によって超電導部材１が例えば７０Ｋ程度に冷却・保持される。ここで、冷却容器３内における冷却用液体窒素１１の液面１１Ａの上方の空間１５には、窒素ガス供給源７１から窒素ガス供給管７３Ａ，７３Ｃ、開閉弁７５Ｂを介して大気圧もしくは大気圧以上の圧力の窒素ガスが導入される。そのため冷却容器３内の圧力が確実に大気圧もしくは大気圧以上の圧力に維持され、蓋部７の封止部分等を介して外部から大気圧の空気が引き込まれて侵入することが確実に防止される。
【００７５】
ここで、冷却容器３内においては、既に述べた図１の実施例の場合と同様に、連続孔を有する多孔質断熱材からなる対流阻止部材７９を液面１１Ａの上下にわたって設けているため、何らかの原因による擾乱によって冷却容器３内の下部で液体窒素１１の対流や撹拌が生じても、液面近傍の液体窒素や液面上の窒素ガスに対流や撹拌が生じるおそれが少なく、温度勾配を安定化できるとともに、液面位置を安定化することができる。
【００７６】
なお、運転が進んで定常状態となれば、還流管１７を経て冷却容器３から供給側保持容器８１に７０Ｋ程度の液体窒素が戻されることにより、供給側保持容器８１内の液体窒素９０も７０Ｋ近い温度、すなわち大気圧下での過冷却温度となる。そこで供給側保持容器８１についても冷却容器３と同様に、連続孔を有する多孔質断熱材から成る対流阻止部材を、液面９０Ａの上下にわたって配設しておくことが望ましい（但し図４中では示していない）。このように供給側保持容器８１の液面９０Ａの上下にわたって対流阻止部材を設けておけば、冷却容器３と同様に、何らかの原因による擾乱によって供給側保持容器８１内の下部で液体窒素９０の対流や撹拌が生じても、液面近傍の液体窒素に対流や撹拌が生じるおそれが少なく、温度勾配を安定化し得るとともに、液面位置を安定化することができる。
【００７７】
なお図１〜図４に示される各実施例のいずれにおいても、対流阻止部材７７，７９に用いる連続孔を有する多孔質断熱材としては、連続気泡ウレタン系発泡体のほか、例えば連続気泡ポリエチレン系発泡体、アクリロニトリルーブタジエンゴム系発泡体、エチレンプロピレンゴム系発泡体等を使用することができる。
【００７８】
さらに、以上の説明では、特許第２８５９２５０号の超電導部材冷却装置に準じた実施例（図１〜図３）における供給側容器２１および冷却容器３、また特開平１０−５４６３７号の超電導部材冷却装置に準じた実施例（図４）の冷却容器３（あるいは冷却容器３および供給側保持容器８１）について、その液面の上下にわたって連続孔を有する多孔質断熱材からなる対流阻止部材を設けることとしたが、これらの容器に限らず、要は液面上に空間を残して液体窒素を収容しかつその液面上の空間に大気圧もしくは大気圧以上の窒素ガス圧力を加え、容器内の液体窒素を大気圧下での過冷却温度とし、その大気圧下での過冷却温度の液体窒素によって超電導部材を冷却する場合にはすべて適用可能である。
【００７９】
【発明の効果】
前述の実施例からも明らかなように、この発明は、液面上に空間を残して液体窒素を収容しかつその液面上の空間に大気圧もしくは大気圧以上の窒素ガス圧力が加えられる液体窒素容器内の液体窒素を、大気圧下での過冷却温度とし、その大気圧下での過冷却温度の液体窒素によって超電導部材を冷却するように構成した超電導部材冷却装置において、液体窒素容器内の液体窒素の液面の下方の位置から液面の上方の位置までの間にわたって、連続孔を有する多孔質断熱材からなる対流阻止部材を設けているため、容器内の下部において何らかの擾乱により液体窒素に対流や撹拌が生じても、液面近傍においては液体窒素の対流、撹拌が有効に阻止され、そのため液面から下方へ向かっての温度勾配が安定に維持されるとともに、液面上の気相の温度勾配も安定して維持され、さらには液体窒素の蒸発や窒素ガスの凝縮により液体窒素の液量に若干の変動が生じても、その変動が増幅されて液面位置が大きく変動されてしまうことも防止でき、したがって運転状況の安定化を図って冷却効率を常に安定させるとともに信頼性を向上させることができる。
【図面の簡単な説明】
【図１】この発明の第１の実施例の超電導部材冷却装置の全体構成を示す略解図である。
【図２】この発明の第２の実施例の超電導部材冷却装置の全体構成を示す略解図である。
【図３】この発明の第３の実施例の超電導部材冷却装置の全体構成を示す略解図である。
【図４】この発明の第４の実施例の超電導部材冷却装置の全体構成を示す略解図である。
【図５】従来の超電導部材冷却装置の全体構成を示す略解図である。
【符号の説明】
１超電導部材
３冷却容器（液体窒素容器）
１１液体窒素
３３液体窒素
１１Ａ液面
１５液面上の空間
３３Ａ液面
４７液面上の空間
２１供給側容器（液体窒素容器）
１６，４９，７１窒素ガス供給源
４１冷凍機
４１Ｂ冷却ヘッド
７７対流阻止部材
７９対流阻止部材[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a superconducting member cooling apparatus for cooling and holding a superconducting member such as a superconducting transformer, a superconducting magnet, various other superconducting coils, or a superconducting cable, particularly a high-temperature superconducting member at a low temperature with liquid nitrogen.
[0002]
[Prior art]
When cooling a superconducting member such as a superconducting coil, particularly a superconducting member using high-temperature superconductivity, a relatively inexpensive liquid nitrogen (LN) is used as a cooling medium. ₂ ) Is often used. In this case, saturated liquid nitrogen at atmospheric pressure, that is, liquid nitrogen of about 77K is generally used. That is, a superconducting member is accommodated in a cooling container substantially open to the atmosphere called a cryostat that is thermally insulated from a vacuum, and about 77 K of atmospheric pressure saturated liquid nitrogen is injected into the cooling container. Usually, the superconducting member is immersed therein, and cooled and held.
[0003]
By the way, in a high-temperature superconducting member, it is known that the superconducting characteristics will be greatly improved if the temperature is slightly lowered. For example, it is known that the critical current increases several times even if it falls from 77K to 70K.
[0004]
Therefore, it is conceivable to cool the superconducting member to a temperature lower than 77K by immersing the superconducting member in liquid nitrogen whose pressure is reduced to about 65K by reducing the pressure of liquid nitrogen at atmospheric pressure. In that case, in a container for immersing the superconducting member in liquid nitrogen, it is necessary to maintain the reduced pressure state of liquid nitrogen. On the other hand, since a cryostat that is generally used is assumed to be used in a state of being substantially open to the atmosphere, if this type of general-purpose cryostat is applied to liquid nitrogen that has been decompressed, a lid or current introduction Sealing at locations such as terminals is inadequate, atmospheric air containing moisture from outside is sucked into the inside, clogging due to moisture freezing in the vent hole of the current introduction terminal, and ice on the surface of the superconducting member May occur, and operation may become impossible in practice. Therefore, for the above-mentioned purpose, a special container must be newly designed and manufactured. In this case, there is a problem that causes a significant increase in cost, so that practical use is hesitant. .
[0005]
On the other hand, when the superconducting member is operated by immersing the superconducting member in saturated liquid nitrogen at atmospheric pressure, the saturated liquid nitrogen is immediately vaporized by the heat generated by the superconducting member and gas bubbles are generated. Although there is a problem that the insulating property is lowered or the cooling efficiency is lowered, as described above, even when the superconducting member is immersed in liquid nitrogen whose temperature has been lowered to about 65K by depressurization as described above, Then, since the liquid nitrogen is immediately vaporized and bubbles are generated by the heat generation of the superconducting member, it is not a fundamental solution for the bubble generation. Therefore, this is also one of the reasons why hesitated to use liquid nitrogen with reduced pressure.
[0006]
Therefore, the present inventors have already disclosed in JP-A-10-54637 that a very high temperature superconducting member is cooled by liquid nitrogen, and is very general that is substantially open to the atmosphere without performing special vacuum sealing or the like. While using a general-purpose cryostat as a superconducting member cooling vessel, it is possible to improve the superconducting performance by cooling the high-temperature superconducting member at a lower temperature, and from high-temperature superconducting member heat generation during operation of the high-temperature superconducting member A superconducting member cooling device that suppresses the generation of gas bubbles is proposed.
[0007]
The proposed superconducting member cooling device basically has a structure in which a superconducting member is accommodated and a cooling container for cooling the superconducting member is substantially opened to atmospheric pressure, and is supercooled under atmospheric pressure. For example, about 67K of liquid nitrogen is accommodated in the cooling container so as to leave a space on the liquid surface, and nitrogen gas is introduced into the space on the liquid surface to pressurize to atmospheric pressure, and the cooling container The superconducting member is cooled by liquid nitrogen in a supercooled state under atmospheric pressure. In the proposed superconducting member cooling apparatus, liquid nitrogen in a supercooled state under atmospheric pressure that functions as a cooling medium for the superconducting member is obtained as follows. In other words, a decompression vessel is provided separately from the above-described cooling vessel, and a heat exchanger is disposed in the decompression vessel, and the heat exchange liquid nitrogen (for example, an atmospheric pressure of about 77 K) is provided in the decompression vessel. Saturated liquid nitrogen) is supplied, and the pressure in the decompression vessel is reduced by a vacuum pump, and the liquid nitrogen in the decompression vessel is reduced from atmospheric pressure to lower the temperature to a low temperature of, for example, 65K. On the other hand, separately from the liquid nitrogen for heat exchange, liquid nitrogen for cooling at atmospheric pressure (for example, saturated liquid nitrogen of about 77K) is led to the heat exchanger, and 65K in the decompression vessel is depressurized in the heat exchanger. Heat exchange with the liquid nitrogen for heat exchange is performed, for example, cooling to about 67K with atmospheric pressure, and a supercooled state under atmospheric pressure is obtained. Then, for example, 67K cooling liquid nitrogen in a supercooled state under the atmospheric pressure is led to the above-mentioned cooling container, and the superconducting member is cooled to a low temperature close to 67K (for example, 70K).
[0008]
In such a superconducting member cooling apparatus proposed in Japanese Patent Laid-Open No. 10-54637, the superconducting member can be cooled to a lower temperature more reliably than when saturated liquid nitrogen at atmospheric pressure of about 77 K is used as a cooling medium. Therefore, the performance of the superconducting member can be improved, and in this case, the space on the liquid surface of the cooling liquid nitrogen in the cooling state in the cooling vessel is filled with nitrogen gas at atmospheric pressure. , Reducing the risk of atmospheric air containing moisture from the outside being sucked into the interior, so that rigorous sealing is not required for the lid of the cooling container, current introduction terminals, etc. Since the cooling liquid nitrogen in which the member is immersed is in a supercooled state as described above, even if the superconducting member generates heat during the operation of the superconducting member, the liquid nitrogen is vaporized around the heat generating part. To reach there is a temperature margin, therefore immediately have advantages such as fear less not generated gas bubbles, thus the cooling efficiency lowered insulating property by gas bubbles or drops.
[0009]
However, the proposed superconducting member cooling device still has the following problems.
[0010]
That is, in the proposed superconducting member cooling device, heat exchange liquid nitrogen is supplied into the decompression container separately from the cooling liquid nitrogen, and the inside of the decompression container is decompressed by a vacuum pump, and the heat exchange liquid is supplied. The temperature of the nitrogen is lowered, and the liquid nitrogen for cooling and the liquid nitrogen for cooling are subjected to heat exchange to obtain liquid nitrogen for cooling in an overcooled state at atmospheric pressure. The liquid nitrogen for heat exchange in the container is gradually evaporated and evaporated by decompression, and the vaporized gas is exhausted by the pump, so the liquid nitrogen liquid level in the decompression container is rapidly lowered and finally decompressed. The heat exchanger in the container will be exposed. If the heat exchanger is exposed from the liquid surface in this way, sufficient heat exchange efficiency cannot be obtained, and it becomes difficult to cool the cooling liquid nitrogen so as to be in a sufficiently subcooled state. In practice, before the heat exchanger is exposed from the liquid level, liquid nitrogen must be replenished into the decompression vessel, and the operation must be temporarily stopped when the liquid nitrogen is replenished.
[0011]
As described above, the proposed superconducting member cooling device has a problem that it cannot be operated continuously for a long time since it needs to be stopped for replenishment of liquid nitrogen in the decompression vessel. There is a problem that the trouble of replenishing nitrogen and stopping the operation and resuming the operation becomes complicated. Of course, there is no particular problem in the case of short-time operation, but it is often required to operate continuously for a long period of time in experiments, research, measurements, etc. for practical application of superconducting members. The fact is that the supply of liquid nitrogen to the vessel for heat exchange has become a major bottleneck for the spread of the proposed apparatus.
[0012]
Accordingly, the present inventors follow the above proposal and use liquid nitrogen that has been supercooled at atmospheric pressure or higher than atmospheric pressure as a cooling medium for the superconducting member, but liquid nitrogen is used by the refrigerator to achieve atmospheric pressure. Then, the liquid is cooled to a temperature at which it is supercooled below, and the obtained supercooled low-temperature liquid nitrogen is directly used as a cooling medium for cooling the superconducting member as it is. Long-term continuous operation is possible by avoiding the use of a decompression vessel or heat exchanger and avoiding the need to shut down the supply of liquid nitrogen for heat exchange in the decompression vessel. Japanese Patent No. 2859250 proposes a superconducting member cooling device.
[0013]
The superconducting member cooling apparatus according to the above-mentioned patent basically includes a cooling container that contains the superconducting member and is substantially open to the atmosphere for cooling the superconducting member, and liquid nitrogen to be supplied to the cooling container. A supply-side container that is substantially open to atmospheric pressure for containing; liquid nitrogen supply means for supplying liquid nitrogen to the supply-side container; and liquid nitrogen in the supply-side container under atmospheric pressure. A refrigerating machine for cooling to the supercooling temperature, and a transfer means for transferring the liquid nitrogen cooled to the supercooling temperature under atmospheric pressure in the supply side container to the cooling container. The space on the liquid level of the supply side container and the cooling container is set to atmospheric pressure or higher than atmospheric pressure, and the liquid nitrogen in the supercooled state supplied into the cooling container by the transfer means Soaked superconducting member And characterized in that it has a so that shows a specific example in FIG.
[0014]
In FIG. 5, the superconducting member 1 to be cooled is disposed at the bottom of the cooling vessel 3. The cooling container 3 is composed of a general-purpose cryostat that is substantially open to the atmosphere. The outer peripheral wall and the bottom wall of the cooling container 3 have a vacuum heat insulating structure 5 and can be opened and closed at the upper end. A lid 7 is provided. The lid portion 7 is not vacuum-sealed with respect to the container body, and the lid portion 7 is provided with a current introduction terminal similar to a general-purpose cryostat. The interior of the cooling container 3 is substantially open to the atmosphere through a gap between the container main body part and a current introduction terminal. In addition, although the safety valve 19 is provided in the cover part 7, as for this safety valve 19, internal pressure is +0.1 kgf / cm, for example with respect to external atmospheric pressure. ² The internal pressure is released from atmospheric pressure to atmospheric pressure +0.1 kgf / cm. ² In the range of, i.e., atmospheric pressure or slightly higher than atmospheric pressure. The superconducting member 1 is suspended from the lid portion 7 by support members 9A and 9B. As will be described later, supercooled liquid nitrogen (cooling liquid nitrogen) 11 at atmospheric pressure is supplied to the bottom of the cooling container 3 via a transfer tube 45 as described later, and the superconducting member 1 is supplied to the liquid nitrogen 11. Soaked. Further, the outer shape of the horizontal cross section is substantially similar to the inner peripheral shape of the horizontal cross section of the cooling container 3 at a position slightly below the liquid surface 11A of the liquid nitrogen 11 in the cooling container 3. And the heat insulation member 13 which has predetermined | prescribed thickness in the up-down direction is arrange | positioned. The heat insulating member 13 may be formed of a material having a low thermal conductivity such as FRP or a hollow structure, as long as the heat conduction in the vertical direction is significantly less than that of liquid nitrogen as a whole. The hollow portion has a vacuum heat insulating structure. The heat insulating member 13 is suspended from the lid portion 7 by the support members 9A and 9B described above, and the space around the heat insulating member 13 keeps a slight gap 14 with respect to the inner peripheral wall surface of the cooling container 3. Therefore, the liquid nitrogen 11 can move through the gap 14. On the other hand, a space (space between the lid 7 and the liquid surface 11A) 15 left above the liquid surface 11A of the cooling liquid nitrogen 11 in the cooling container 3 is supplied from an external first nitrogen gas supply source 16. Atmospheric pressure nitrogen gas is supplied through the nitrogen gas supply pipe 18. Further, one end side of a reflux pipe 17 to be described later is opened at a position on the lower surface side of the heat insulating member 13 in the cooling container 3.
[0015]
Further, a supply side container 21 is provided separately from the cooling container 3 that is substantially open to the atmosphere as described above.
[0016]
The supply side container 21 is substantially open to the atmosphere like the cooling container 3 described above, and the outer peripheral wall part and the bottom wall part thereof are the vacuum heat insulating structure 23, and the upper end can be opened and closed. A lid portion 25 is provided. The lid portion 25 is not vacuum-sealed with respect to the container body, and the inside of the supply-side container 21 is substantially opened to the atmosphere through such a gap between the lid portion 25 and the container body portion. It is in the state. The supply side container 21 is supplied with liquid nitrogen 33 from an external liquid nitrogen supply source 27 through a control valve 29 and a supply pipe 31. The outer shape of the horizontal cross section is substantially similar to the horizontal cross sectional shape of the supply side container 21 at a position slightly below the liquid level 33A of the liquid nitrogen 33 in the supply side container 21 and A heat insulating member 35 having a predetermined thickness in the vertical direction is disposed in a state of being suspended from the lid portion 25 by support members 37A and 37B. This heat insulating member 35 is also the same as the heat insulating member 13 in the cooling container 3, and the periphery of the heat insulating member 35 holds a slight gap 39 with respect to the inner peripheral wall surface of the supply side container 21, It is the same as that of the heat insulating member 13 in the cooling container 3 that the liquid nitrogen 33 can move through the gap 39.
[0017]
Further, in the supply side container 21, the liquid nitrogen 33 in the supply side container 21 is brought to a supercooling temperature (a temperature lower than about 77K, for example, 65 to 70K) lower than the temperature of the saturated liquid nitrogen under atmospheric pressure. A refrigerator 41 for cooling is disposed. The refrigerator 41 includes a compression unit (compressor) 41A for compressing a refrigeration medium gas (usually helium gas), expands the compressed high-pressure refrigeration medium gas to obtain a low temperature, and cools the low temperature. A cooling head 41B for exchanging heat with (liquid nitrogen), and a switching unit 41C such as a motor valve for switching the flow of the high-pressure medium gas from the compression unit 41A and the expanded low-pressure medium gas returning from the cooling head 41B And a cylinder part 41D formed therein with a passage for reciprocating the refrigeration medium gas between the switching part 41C and the cooling head 41B. The switching part 41C is provided on the lid part 25 of the supply side container 21. The cylinder portion 41D passes through the lid portion 25 downward from the switching portion 41C and passes through the space 47 on the liquid nitrogen liquid surface 33A in the supply side container 21, End is immersed in liquid nitrogen, the cooling head 41B is provided in the immersion portion in its portion or in liquid nitrogen. Here, the cylinder portion 41D is generally made of stainless steel. The cooling head 41B has a configuration in which a heat transfer block made of a good heat transfer material such as copper is provided on the outer surface thereof. Note that the compression unit 41A is normally disposed at a position away from the supply side container 21, and the compression unit 41A and the switching unit 41C are connected by a high-pressure gas pipeline 41E and a low-pressure gas pipeline 41F.
[0018]
In addition, a liquid feed pump 43 is disposed in the supply side container 21 while being suspended from the lid portion 25. The liquid feed pump 43 is disposed such that its intake (pump outlet) is located below the heat insulating member 35 in the supply side container 21 (usually near the bottom of the supply side container 21). The outlet side of the liquid feed pump 43 is connected to a transfer tube 45, and the transfer tube 45 is guided into the cooling container 3 as described above. Further, the reflux pipe 17 from the cooling container 3 is led into the supply side container 21, and the opening end of the reflux pipe 17 is at the bottom of the supply side container (lower than the cooling head 41 B of the refrigerator 41). Position).
[0019]
Further, in the space 47 (the space between the lid portion 25 and the liquid surface 33A) 47 left above the liquid surface 33A of the liquid nitrogen 33 in the supply side container 21, nitrogen is supplied from the external second nitrogen gas supply source 49. Nitrogen gas having a pressure equal to or higher than atmospheric pressure is supplied through the gas supply pipe 51.
[0020]
Here, the liquid nitrogen supply source 27, the control valve 29, and the supply pipe 31 constitute liquid nitrogen supply means 63 for supplying liquid nitrogen to the supply side container 21. Further, the liquid feed pump 43 and the transfer tube 45 constitute transfer means 65 for transferring the liquid nitrogen cooled to the supercooled state at atmospheric pressure in the supply side vessel 21 to the cooling vessel 3. On the other hand, the first nitrogen gas supply source 16 and the nitrogen gas supply pipe 18 are a first nitrogen gas supply for supplying nitrogen gas having a pressure equal to or higher than atmospheric pressure to the space 15 above the liquid level in the cooling container 3. The second nitrogen gas supply source 49 and the nitrogen gas supply pipe 51 constitute means 67 and supply nitrogen gas having a pressure equal to or higher than atmospheric pressure to the space 47 on the liquid level in the supply side vessel 21. The second nitrogen gas supply means 69 for this purpose is configured.
[0021]
The overall function of the prior art superconducting member cooling device shown in FIG. 5 as described above will be described below.
[0022]
The liquid nitrogen supplied from the liquid nitrogen supply source 27 of the liquid nitrogen supply means 63 to the supply side container 21 is about 77K, and the liquid nitrogen is supplied to the cooling head 41B of the refrigerator 41 in the supply side container 21. Is cooled under atmospheric pressure or a pressure higher than atmospheric pressure, and the temperature is lowered to a temperature lower than the saturated liquid nitrogen temperature (about 77 K) under atmospheric pressure, for example, about 65 to 70 K. Then, the liquid nitrogen 33 that is supercooled to about 65 to 70 K or at a pressure higher than atmospheric pressure is pumped from the vicinity of the bottom of the supply side container 21 by the liquid feed pump 43, and is returned to the atmosphere via the transfer tube 45. It is led into the cooling vessel 3 which is substantially open. The supercooled liquid nitrogen introduced into the cooling vessel 3 is indicated by reference numeral 11 in FIG. 5 and corresponds to the cooling liquid nitrogen.
[0023]
In the cooling container 3, the superconducting member 1 is cooled and held at, for example, about 67 to 72K by the liquid nitrogen 11 in the supercooled state of 65 to 70K as described above. In addition, the liquid nitrogen whose temperature has risen to, for example, about 70 K or more due to heat from the superconducting member 1 in the cooling container 3 returns to the supply side container 21 through the reflux pipe 17. The fluid nitrogen refluxed to the supply-side container 21 in this manner is cooled again to about 65 to 70K by the cooling head 41B of the refrigerator 41 under atmospheric pressure or a pressure higher than atmospheric pressure, and sent as described above. It is sent again to the cooling container 3 by the liquid pump 43.
[0024]
Here, nitrogen gas having a pressure equal to or higher than atmospheric pressure is introduced into the space 15 above the liquid surface 11 A of the cooling liquid nitrogen 11 in the cooling vessel 3 through the nitrogen gas supply pipe 18. Therefore, the space 15 on the liquid surface of the cooling container 3 is filled with nitrogen gas having a pressure equal to or higher than the atmospheric pressure. Therefore, the pressure in the cooling container 3 is maintained at atmospheric pressure or a pressure higher than atmospheric pressure, and air is prevented from being drawn in from outside through the sealing portion of the lid portion 7 or the current introduction terminal portion. .
[0025]
Further, since the heat insulating member 13 is disposed under the liquid level of the cooling liquid nitrogen 11 in the cooling vessel 3, the liquid level of the cooling liquid nitrogen 11 (about 77K because it is a gas-liquid interface) and its heat insulating member. A thermal gradient can be applied to the lower side than 13, particularly the bottom of the cooling vessel where the superconducting member 1 is located. Further, the presence of the heat insulating member 13 prevents convective stirring between the bottom surface near the liquid surface 11A. As a result, the cooling liquid nitrogen 11 at the bottom where the superconducting member 1 is located can be maintained in a supercooled state at a low temperature of about 65K. Thus, since the superconducting member 1 is surrounded by the low-temperature liquid nitrogen 11 in a supercooled state of, for example, 65 to 70K, even if the superconducting member 1 generates heat during operation of the superconducting member 1, the surrounding liquid nitrogen remains. There is a margin of about 10K before the vaporization temperature under atmospheric pressure (about 77K) or higher, so that the heat generation of the superconducting member 1 immediately vaporizes the surrounding liquid nitrogen and generates gas bubbles. It can be effectively prevented.
[0026]
Note that nitrogen gas having a pressure equal to or higher than the atmospheric pressure is introduced into the space 47 above the liquid surface 33A of the liquid nitrogen 33 in the supply side container 21 via the nitrogen gas supply pipe 51, and the atmospheric pressure or It will be filled with nitrogen gas at a pressure higher than atmospheric pressure. Therefore, the pressure in the supply-side container 21 is maintained at atmospheric pressure or a pressure equal to or higher than atmospheric pressure, and air is prevented from being drawn from the outside through the sealing portion of the lid portion 25 and the like.
[0027]
Further, similarly to the cooling container 3, a heat insulating member 35 is also disposed below the liquid nitrogen 33 level in the supply side container 21, so that the liquid level of the liquid nitrogen 33 (about 77K because it is a gas-liquid interface). A thermal gradient can be applied to the lower side of the heat insulating member 35, particularly between the vicinity of the cooling head 41B of the refrigerator 41. Further, the presence of the heat insulating member 35 prevents convective stirring between the vicinity of the liquid surface 33 A and a portion below the heat insulating member 35. As a result, the liquid nitrogen 33 in the vicinity of the inlet of the liquid feed pump 43 is maintained in a low-temperature supercooled state of about 65 to 70K, and the low-temperature supercooled liquid nitrogen of about 65 to 70K is cooled. It can be fed into the container 3.
[0028]
[Problems to be solved by the invention]
In the apparatus shown in FIG. 5, as described above, the heat insulating member 35 made of a low thermal conductivity material such as FRP is disposed below the liquid surface of the liquid nitrogen 33 in the supply-side container 21, so that the vicinity of the liquid surface (about 77K) and a thermal gradient between the vicinity of the cooling head 41B (65 to 70K). However, it has been found that there is the following problem when such a heat insulating member made of FRP or the like is provided below the liquid surface.
[0029]
That is, in the supply-side container 21, the liquid surface 33A of the liquid nitrogen 33 is a gas-liquid interface where the nitrogen gas having a pressure equal to or higher than the atmospheric pressure and the liquid nitrogen 33 are in contact with each other. Nitrogen is a saturated liquid at steady state. The temperature of liquid nitrogen in the vicinity of the liquid surface is a saturation temperature under atmospheric pressure or a pressure higher than atmospheric pressure. Note that “pressure higher than atmospheric pressure” here is actually slightly higher than atmospheric pressure as already described, so in the following, for simplicity of explanation, it will be described as atmospheric pressure. The temperature of the liquid nitrogen near the liquid surface is also considered to be the saturation temperature (about 77.4 K) at atmospheric pressure.
[0030]
On the other hand, at the position in the supply side container 21 that is below the liquid nitrogen liquid level 33A, particularly at the position of the cooling head 41B of the refrigerator 41 or at a position below it, the liquid nitrogen is cooled by the cooling head as described above. It is cooled by 41B and is in a supercooled state at a temperature of about 65 to 70K, which is lower than the saturation temperature under atmospheric pressure. Therefore, in the region above the cooling head 41B in liquid nitrogen, a temperature gradient is formed downward from the liquid level. In order to stably maintain such a temperature gradient, the proposed apparatus is provided with a heat insulating member 35, and the heat insulating member 35 prevents convective stirring. In addition, disturbances due to fluctuations in the operating condition of the liquid feed pump 43 and the heat load may occur in the liquid nitrogen, and convection may be generated or stirred in the liquid nitrogen. In that case, the temperature gradient is disturbed, and even if the heat insulating member 35 as described above is provided, the operating situation becomes unstable, and liquid nitrogen vaporization or condensing nitrogen gas occurs on the liquid surface. As a result, the liquid surface position fluctuates, and the temperature gradient becomes more unstable, resulting in increasingly unstable operating conditions, leading to reduced cooling efficiency and reduced system reliability. There is a risk that.
[0031]
In particular, in the case of the above-described prior art, in the region where the heat insulating member 35 is disposed, the liquid nitrogen is excluded by the volume of the heat insulating member 35, and only a small portion of the narrow gap 39 around the heat insulating member 35 is liquid nitrogen. Since the liquid can be moved, the liquid level position fluctuates greatly even if the liquid nitrogen is slightly evaporated or the nitrogen gas is condensed, so that the temperature gradient may fluctuate greatly. Therefore, when the heat insulating member 35 as in the prior art is provided, it is still insufficient to stabilize the operation state and improve the reliability during actual operation.
[0032]
In the above description, the heat insulating member 35 in the supply-side container 21 has been described as an example, but the heat insulating member 13 in the cooling container 3 has substantially the same problem.
[0033]
Further, as already described, a superconducting member cooling device disclosed in JP-A-10-54637, that is, a decompression vessel is provided separately from the cooling vessel containing the superconducting member, and the liquid nitrogen in the decompression vessel is decompressed. For example, the temperature is lowered to a low temperature of 65K, and the low-temperature liquid nitrogen and the cooling liquid nitrogen at atmospheric pressure are subjected to heat exchange, and the obtained low-temperature liquid nitrogen at about 65K under the atmospheric pressure (that is, under atmospheric pressure) In the case of an apparatus in which the superconducting liquid nitrogen) is led to a cooling vessel and the superconducting member in the cooling vessel is cooled to close to 65K, nitrogen gas at atmospheric pressure is introduced from the outside into the cooling vessel. In addition, it has been considered that a heat insulating member made of FRP or the like is disposed below the liquid nitrogen surface in the cooling container. In this case, there is a problem similar to the above.
[0034]
Eventually, a liquid nitrogen container (for example, in the apparatus of Japanese Patent No. 2859250) in which liquid nitrogen is accommodated while leaving a space on the liquid surface and nitrogen gas is introduced into the space on the liquid surface at a pressure equal to or higher than atmospheric pressure. The liquid nitrogen in the supply-side container 21 or the cooling container 3 or the cooling container in the apparatus of Japanese Patent Laid-Open No. 10-54637) is set to a supercooling temperature under atmospheric pressure, and the liquid nitrogen level in the liquid nitrogen container In the apparatus in which a heat insulating member made of FRP or the like is provided below and the superconducting member is cooled by liquid nitrogen at a supercooling temperature under atmospheric pressure, all of the above-described problems may occur. .
[0035]
The present invention has been made in the background of the above circumstances, and a nitrogen gas at atmospheric pressure or above atmospheric pressure is left in the space on the liquid surface of the liquid nitrogen container that stores liquid nitrogen at a supercooling temperature while leaving a space on the liquid surface. In a device that pressurizes with pressure and cools the superconducting member with liquid nitrogen at a supercooling temperature under atmospheric pressure, the temperature gradient mainly below the liquid level can be maintained reliably and stably. The purpose is to stabilize operating conditions, improve cooling efficiency, and improve reliability.
[0036]
[Means for Solving the Problems]
In order to solve the above-described problems, in the present invention, an open-cell type urethane foam basically extends from a position below the liquid level in the liquid nitrogen container to a position above the liquid level. Like the body, a convection prevention member made of a porous heat insulating material having continuous pores (open cells) was arranged.
[0037]
That is, the invention of claim 1 is provided with liquid nitrogen in a liquid nitrogen container in which liquid nitrogen is accommodated leaving a space on the liquid level, and a nitrogen gas pressure is applied to the space on the liquid level. In the superconducting member cooling device configured to cool the superconducting member with liquid nitrogen at the supercooling temperature under atmospheric pressure, the liquid level of liquid nitrogen in the liquid nitrogen container A convection prevention member made of a porous heat insulating material having continuous pores is disposed from a position below the position to a position above the liquid level.
[0038]
In such a superconducting member cooling device according to the first aspect of the present invention, since the convection preventing member is made of a porous heat insulating material having continuous holes, the liquid nitrogen in the liquid nitrogen container is convected at a position close to the liquid surface. Therefore, the liquid level in the liquid nitrogen container is in the middle of the convection preventing member in the vertical direction (the intermediate position between the upper end surface and the lower end surface). It will be located in the continuous hole part. Since the liquid nitrogen below the liquid level has entered the continuous hole inside the convection prevention member as described above at a position near the liquid level, the liquid in the container is caused by fluctuations in the liquid feed pump or thermal load during operation. Even if convection or agitation occurs in nitrogen, the movement (convection or agitation) of liquid nitrogen in the vicinity of the liquid surface is prevented, and as a result, the temperature gradient in the vertical direction due to convection and agitation as described above is disrupted or disturbed. Can be prevented in advance.
[0039]
In addition, the convection prevention member extends into the space above the liquid level in the container, so that convection and stirring of nitrogen gas in the space above the liquid level is also prevented, so the temperature gradient in the gas phase above the liquid level is stable. This also contributes to the stabilization of the driving situation and the improvement of reliability.
[0040]
Further, if a member having a high porosity (porosity) is used as the convection prevention member (for example, the open-cell urethane foam has a porosity of about 90%), liquid nitrogen vaporization or nitrogen gas on the liquid surface is assumed. Even if the amount of liquid increases or decreases due to condensation, the effect on the fluctuation of the liquid level is small, which also contributes to stabilization of the temperature gradient.
[0041]
Here, as the porous heat insulating material used for the convection blocking member, it is desirable that the thermal conductivity is as low as possible, but even if using a material whose thermal conductivity is not so different from liquid nitrogen, Thus, as a result of preventing liquid nitrogen convection and stirring, an apparently large heat insulating effect is exhibited. Therefore, as the heat insulating material, an extremely general material such as the open-cell urethane foam as described above can be used.
[0042]
According to the invention of claim 2, according to the superconducting member cooling device of the above-mentioned Patent No. 2859250, when liquid nitrogen in the container is directly cooled to a supercooling temperature under atmospheric pressure by a refrigerator, As described above, provision of a convection preventing member made of a porous heat insulating material having continuous pores is provided.
[0043]
Specifically, the invention of claim 2 includes a supply-side container that stores liquid nitrogen leaving a space on the liquid level and that is applied with atmospheric pressure or a nitrogen gas pressure equal to or higher than atmospheric pressure in the space on the liquid level. A refrigerator having a cooling head immersed in a position below the liquid nitrogen level in order to cool the liquid nitrogen in the supply side container to a supercooling temperature under atmospheric pressure. In a superconducting member cooling apparatus configured to guide liquid nitrogen at a supercooling temperature of the superconducting member to be cooled to cool the superconducting member, the liquid nitrogen in the supply-side container from a position below the liquid level of the liquid nitrogen A convection prevention member made of a porous heat insulating material having continuous pores is disposed over the position above the liquid level.
[0044]
In this way, when the cooling head of the refrigerator is directly immersed in the liquid nitrogen in the container to obtain the liquid nitrogen at the supercooling temperature under atmospheric pressure, the liquid feeding usually disposed in the container Although the convection and stirring of liquid nitrogen are likely to occur due to the operation of the pump and the influence of the temperature gradient disturbance on the entire system is large, the porous heat insulating material having continuous pores is the same as the invention of claim 1 already described. By providing the convection prevention member comprising the above, the temperature gradient below the liquid level and the temperature gradient above the liquid level can be stabilized.
[0045]
In the case of the configuration of claim 2, the convection preventing member made of a porous heat insulating material is lower than the liquid level of the supply side container and the upper end of the cooling head of the refrigerator as defined in claim 3. Even if it is arranged from the above position to the position above the liquid level, or as defined in claim 4, it is below the liquid level of the supply side container and in the middle in the vertical direction in the cooling head of the refrigerator. You may arrange | position from the position to the position above a liquid level.
[0046]
Further, the invention according to claim 5 is the superconducting member cooling device according to claim 4, wherein the cooling head of the refrigerator is extended to a position near the bottom surface of the supply side container.
[0047]
Here, although a high-pressure medium near room temperature flows inside the cylinder portion of the refrigerator, a heat insulating portion is provided on the outer peripheral surface of the cylinder portion of the refrigerator if it is configured as defined in claim 5. Therefore, even in the part immersed in liquid nitrogen in the cylinder part, the amount of heat penetration into the liquid nitrogen from the medium gas near normal temperature in the cylinder part is small, so that the cooling efficiency of the refrigerator is prevented from being lowered, Further, since the evaporation of liquid nitrogen due to heat intrusion from the cylinder portion is also reduced, the fluctuation of the liquid nitrogen level is also reduced.
[0048]
Further, a sixth aspect of the present invention is the superconducting member cooling device according to the fourth or fifth aspect, wherein a heat insulating portion is provided on the outer peripheral surface of the cylinder portion of the refrigerator, and the heat insulating portion is a cooling head of the refrigerator. It is extended to the intermediate position of the up-down direction in the outer peripheral surface.
[0049]
In such a superconducting member cooling device according to the invention of claim 6, since the heat insulating portion of the outer peripheral surface of the cylinder portion is extended to the intermediate position in the vertical direction of the outer peripheral surface of the cooling head of the refrigerator, the liquid level in the supply container, That is, heat penetration from the gas-liquid interface into the cooling head of the refrigerator is reduced, and the cooling efficiency can be further improved.
[0050]
DETAILED DESCRIPTION OF THE INVENTION
[0051]
【Example】
In FIG. 1, the convection prevention which consists of a porous heat insulating material which has a continuous hole (open cell) in the upper and lower area | regions on both sides of the liquid level 33A of the liquid nitrogen 33 in the supply side container 21 like an open cell urethane type foam. A member 77 is provided. The convection prevention member 77 has a lower surface 77A positioned at a position below the liquid level 33A by a predetermined distance (in the example of FIG. 1, the upper end of the cooling head 41B of the refrigerator 41), and the upper surface 77B has a lid portion. It is arrange | positioned so that it may be located in the position slightly lower than 25. Then, the liquid nitrogen 33 enters the continuous hole inside the convection preventing member 77 in the vicinity of the liquid surface 33A, and the liquid surface 33A is positioned between the upper surface 77B and the lower surface 77A of the convection preventing member 77. The shape and dimensions of the outer peripheral surface of the convection preventing member 77 are substantially the same shape and substantially the same size as the inner peripheral surface of the supply-side container 21, and are fitted into the inner peripheral surface of the supply-side container 21. Has been.
[0052]
On the other hand, a convection prevention member 79 made of a porous heat insulating material having continuous pores (open cells), such as an open cell urethane foam, is also disposed in the upper and lower regions sandwiching the liquid surface 11A of the liquid nitrogen 11 in the cooling vessel 3. Has been. The lower surface 79A of the convection preventing member 79 is positioned at a position below the liquid surface 11A by a predetermined distance, preferably at a position higher than the upper end of the superconducting member 1 to be cooled, and the upper surface 79B is at the lid portion 7. It is determined to be located slightly below the lower surface. Then, the liquid nitrogen 11 enters the continuous hole portion inside the convection preventing member 79 in the vicinity of the liquid surface 11A, and the liquid surface 11A is positioned between the upper surface 79B and the lower surface 79A of the convection preventing member 79. The shape and size of the outer peripheral surface of the convection preventing member 79 are substantially the same shape and substantially the same size as the inner peripheral surface of the cooling vessel 3 and are fitted into the inner peripheral surface of the cooling vessel 3. Yes.
[0053]
In the embodiment shown in FIG. 1 as described above, liquid nitrogen of about 77K supplied from the liquid nitrogen supply source 27 into the supply side container 21 is at atmospheric pressure or higher than atmospheric pressure by the cooling head 41B of the refrigerator 41. The liquid nitrogen 33 is cooled under pressure and lowered to a temperature (supercooling temperature) lower than the saturated liquid nitrogen temperature (about 77K) under atmospheric pressure, for example, about 65 to 70K. Then, the liquid is pumped from the vicinity of the bottom of the supply-side container 21 by the liquid feed pump 43 and guided into the cooling container 3 through the transfer tube 45 to cool and hold the superconducting member 1 to about 67 to 72K, for example. Also, the liquid nitrogen whose temperature has risen to, for example, about 70 K or more due to heat from the superconducting member 1 in the cooling container 3 returns to the supply side container 21 through the reflux pipe 17. The liquid nitrogen refluxed to the supply side container 21 in this manner is cooled again to about 65-70K by the cooling head 41B of the refrigerator 41 under atmospheric pressure or a pressure higher than atmospheric pressure, and sent as described above. It is sent again to the cooling container 3 by the liquid pump 43. Further, nitrogen gas having a pressure equal to or higher than atmospheric pressure is introduced into the space 47 on the liquid level 33A in the supply side container 21 and the space 15 on the liquid level 11A in the cooling container 3 so that the inside of the supply side container 21 The pressure and the pressure in the cooling container 3 are maintained at atmospheric pressure or above atmospheric pressure, and air is drawn from the outside through the sealing portion of the lid portion 25 and the sealing portion of the lid portion 7 and the current introduction terminal portion. Is prevented. The above operation situation is substantially the same as the prior art shown in FIG.
[0054]
Here, in the supply side container 21, in the portion above the cooling head 41 B of the refrigerator 41 in the liquid nitrogen 33, that is, in the region near the liquid level 33 A, the liquid nitrogen 33 is in the continuous hole of the convection preventing member 77. Therefore, even if convection or agitation occurs in the lower region in the container 21 due to some reason such as the operation of the liquid feed pump 43, the flow of liquid nitrogen due to the convection or agitation is caused by the continuous holes of the convection prevention member 77. In the region near the liquid level 33A, which is hindered by the wall, convection and agitation are prevented, and the temperature gradient downward from the liquid level 33A is stably maintained.
[0055]
Also, in the space 47 on the liquid surface 33A, convection and stirring may occur in the gas phase (nitrogen gas) following the convection and stirring of the liquid nitrogen 33 below the liquid surface. Since the blocking member 77 exists up to the liquid level, it is possible to prevent the convection and stirring of the nitrogen gas and to stabilize the temperature gradient in the gas phase region from the lid 25 to the liquid level 33A. it can.
[0056]
Furthermore, even if the amount of liquid nitrogen fluctuates due to vaporization of liquid nitrogen from the liquid surface 33A or condensation of nitrogen gas from the space on the liquid surface 33A, generally an open pore porous material such as an open-cell urethane foam is used. In the heat insulating material, the area of the pore portion (gap portion) in the horizontal cross section (that is, the horizontal cross sectional area of the portion in which the liquid nitrogen 33 enters) is the air gap 39 around the heat insulating member 35 in the prior art shown in FIG. It is usually much larger than the horizontal cross-sectional area, so that it is possible to avoid the slight fluctuation of the liquid volume from having a great influence on the fluctuation of the liquid surface position, and to maintain the liquid surface position stably. be able to.
[0057]
Further, since the convection prevention member 79 made of a porous heat insulating material having continuous pores is also disposed in the cooling container 3, the same actions and effects as described above can be obtained. That is, on the cooling container 3 side, convection and agitation of the liquid nitrogen 11 may occur in the lower part of the cooling container 3 due to fluctuations in the thermal load caused by the operation of the superconducting member 1 to be cooled. Therefore, the convection and stirring of the liquid nitrogen 11 in the vicinity of the liquid surface 11A can be effectively prevented, and the temperature gradient can be stabilized. The same applies to the gas phase (nitrogen gas) in the space above the liquid surface 11A in the cooling vessel 3, and the temperature gradient in the gas phase region from the lid 7 to the liquid surface 11A can be stabilized. .
[0058]
Further, the convection preventing member 79 on the cooling container 3 side is also markedly different from the horizontal cross-sectional area of the void 14 around the heat insulating member 13 of the prior art shown in FIG. Usually, the liquid level is large, and as described above, the influence of the slight change in the liquid amount on the change in the liquid level can be reduced, and the liquid level can be stabilized.
[0059]
Here, in the embodiment shown in FIG. 1, the convection prevention member 77 in the supply side container 21 is arranged so that the lower surface thereof is located at the upper end of the cooling head 41 B of the refrigerator 1. The member 77 may be arranged so that the lower surface thereof reaches the intermediate position in the vertical direction of the cooling head 41B of the refrigerator 1, and an example of such a case is shown in the embodiment of FIG.
[0060]
In the embodiment of FIG. 2, the lower end of the cooling head 41 B of the refrigerator 41 is extended to near the bottom surface of the supply side container 21. The lower surface 77A of the convection preventing member 77 made of a porous heat insulating material having continuous holes is located at a level corresponding to the intermediate position in the vertical direction of the cooling head 41 extending downward in this way. Of course, the upper surface 77B of the convection preventing member 77 is located above the liquid level 33A (position close to the lid portion 25). In this embodiment, the outer peripheral surface of the cylinder part 41D is used in order to prevent heat intrusion into the liquid nitrogen from the cylinder part 41D of the refrigerator 41 in which the refrigerator medium gas having a temperature near room temperature flows. The heat insulation part 80 which consists of a vacuum heat insulation structure or a suitable heat insulating material is provided so that it may surround.
[0061]
In the case of the embodiment shown in FIG. 2, the convection prevention member 77 extends from above the liquid level to the intermediate position in the vertical direction of the cooling head 41B of the refrigerator 41, and therefore in the convection prevention member 77 than in the example of FIG. The thickness of the portion below the liquid level is increased. This means that the effective region for preventing convection is wide, so that the effect of preventing the flow of the liquid nitrogen 11 due to convection and agitation is greater than in the case of the example of FIG. 1, and thus the effect of further stabilizing the temperature gradient. Is obtained. Here, in the example of FIG. 2, since the lower end of the cooling head 41B of the refrigerator 41 is extended to the vicinity of the bottom surface of the supply side container 21, it is possible to further increase the thickness below the liquid level of the convection preventing member 77. Thus, the above-described effect can be further increased. The outer peripheral surface of the upper portion of the cooling head 41B (the portion above the intermediate position) is surrounded by the convection prevention member 77, but the lower outer peripheral surface of the cooling head 41B is in direct contact with the liquid nitrogen 11. Therefore, there is little possibility that the heat exchange efficiency between the cooling head 41B and the liquid nitrogen 11 is lowered.
[0062]
Further, in the embodiment of FIG. 2, a heat insulating portion 80 is provided on the outer peripheral surface of the cylinder portion 41D of the refrigerator 41. Therefore, from the cylinder portion 41D through which a refrigerator medium gas having a high temperature and a temperature near room temperature circulates. Heat intrusion into the outer liquid nitrogen 11 can also be prevented.
[0063]
When the heat insulating portion 80 is provided on the outer peripheral surface of the cylinder portion 41D of the refrigerator 41 as described above, the heat insulating portion 80 may be extended to the middle position in the vertical direction of the cooling head 41B as shown in FIG. In this way, it is possible to prevent the outer peripheral surface of the upper portion of the cooling head 41B from coming into direct contact with liquid nitrogen, which can further contribute to stabilization of the thermal gradient.
[0064]
In each of the above embodiments, the convection prevention member is provided in both the supply side container 21 and the cooling container 3, but may be provided only in the supply side container 21 depending on the case.
[0065]
Each of the above embodiments is shown as an improvement of the prior art superconducting member cooling device proposed in Japanese Patent No. 2859250, but the prior art superconducting member cooling device proposed in Japanese Patent Laid-Open No. 10-54637. That is, of course, the present invention can be applied in accordance with a device for obtaining supercooled liquid nitrogen under atmospheric pressure using a decompression vessel and a heat exchanger and cooling a superconducting member without using a refrigerator. It is. An embodiment in that case is shown in FIG.
[0066]
In FIG. 4, the cooling vessel 3 is composed of a general-purpose cryostat substantially open to the atmosphere, like the cooling vessel of the embodiment shown in FIG. 1, and the supercooled liquid nitrogen 11 is placed on the liquid surface. The superconducting member 1 to be cooled is disposed at the bottom thereof. The specific configuration of the cooling container 3 is the same as that in the embodiment of FIG. 1, and detailed description thereof is omitted. Of course, the convection prevention member 79 made of a porous heat insulating material having continuous holes on the upper and lower sides of the liquid surface 11A of the liquid nitrogen 11 in the cooling vessel 3 is also arranged in the cooling of the embodiment shown in FIG. Similar to the container 3. In addition, in the space 15 on the liquid surface of the liquid nitrogen 11 in the cooling container 3, nitrogen gas having a pressure equal to or higher than atmospheric pressure is supplied from the nitrogen gas supply source 71 through the nitrogen gas supply pipes 73 A and 73 C and the opening / closing valve 75 B. It comes to be supplied. In addition, at the position slightly below the liquid surface 11A of the cooling liquid nitrogen 11 in the cooling vessel 3, an opening end on one end side of the reflux pipe 17 described later is opened.
[0067]
In addition to the cooling container 3 that is substantially open to the atmosphere as described above, a supply-side holding container 81 and a decompression container 83 are provided.
[0068]
The supply-side holding container 81 is substantially open to the atmosphere like the cooling container 3. The supply-side holding container 81 includes a control valve 87 and a supply pipe from an external liquid nitrogen supply source 85. The liquid nitrogen 90 at atmospheric pressure is supplied through 89. The supply amount is controlled by a level gauge 91 provided in the supply-side holding container 81 and the control valve 87. In addition, a liquid feed pump 93 is disposed in the supply-side holding container 81, and the liquid nitrogen 90 in the supply-side holding container 81 at a pressure equal to or higher than the atmospheric pressure is supplied to the first side by the liquid supply pump 93. It is transported to a heat exchanger 117 (described later) in the decompression vessel 83 through the transfer tube 95. Further, in the space above the liquid level of the liquid nitrogen 90 in the supply-side holding container 81, the pressure from the external nitrogen gas supply source 71 through the nitrogen gas supply pipes 73A and 73B and the open / close valve 75A is atmospheric pressure or a pressure higher than atmospheric pressure. Nitrogen gas is introduced. Note that, under the liquid level in the supply-side holding container 81, the leading end of the reflux pipe 17 led from the cooling container 3 is opened.
[0069]
On the other hand, the liquid container 111 for heat exchange is supplied with liquid nitrogen 111 for heat exchange from an external liquid nitrogen supply source 105 through a control valve 107 and a supply pipe 109. The supply amount is controlled by a liquid level gauge 113 and a control valve 107 provided in the decompression vessel 83. The decompression vessel 83 is connected with a rotary pump 115 as decompression means, and the rotary pump 115 causes the internal heat exchange liquid nitrogen 111 to a pressure lower than the atmospheric pressure by a predetermined pressure (for example, 20 kPa). The pressure is reduced and the temperature is lowered accordingly. Furthermore, a heat exchanger 117 is disposed in the decompression vessel 83 at a position immersed in the heat exchange liquid nitrogen 111. The inlet side of the heat exchanger 117 is supplied with saturated liquid nitrogen 90 having a pressure equal to or higher than atmospheric pressure from the supply-side holding container 81 through the first transfer tube 95, and the liquid nitrogen 90 is supplied to the heat exchanger 117. Then, heat is exchanged with the reduced-pressure low-temperature heat exchange liquid nitrogen 111 in the decompression vessel 83, and the temperature drops. The outlet side of the heat exchanger 117 is connected to the second transfer tube 119 so that the liquid nitrogen 90 whose temperature has dropped due to heat exchange is led to the cooling container 3 as the cooling liquid nitrogen 11. .
[0070]
Here, the liquid nitrogen supply source 105, the control valve 107, and the supply pipe 109 on the decompression container 83 side constitute a heat exchange liquid nitrogen supply means 121 for supplying the heat exchange liquid nitrogen to the decompression container 83. ing. The liquid nitrogen supply source 85, the control valve 87, the supply pipe 89, the supply side holding container 81, the liquid feed pump 93, and the first transfer tube 95 are supplied with liquid nitrogen having a pressure equal to or higher than atmospheric pressure to the heat exchanger 117. The liquid nitrogen supply means 123 for cooling for supplying is comprised. Further, the second transfer tube 119 constitutes a transfer means 125 for transferring the cooling liquid nitrogen at the supercooling temperature under the atmospheric pressure that has passed through the heat exchanger 117 to the cooling vessel 3. In this embodiment, the cooling container 3 corresponds to a liquid nitrogen container defined in claim 1.
[0071]
The overall function of the superconducting member cooling device of the second embodiment shown in FIG. 4 as described above will be described below.
[0072]
The liquid nitrogen 90 sent from the supply-side holding container 81 to the heat exchanger 117 in the decompression container 83 via the first transfer tube 95 by the liquid feed pump 93 is an atmospheric pressure having a temperature of about 77 K at the beginning of the operation. Saturated below. On the other hand, the inside of the decompression vessel 83 is decompressed to a pressure lower than the atmospheric pressure by a decompression means, for example, a rotary pump 115. Therefore, the liquid nitrogen 111 supplied from the liquid nitrogen supply source 105 to the decompression vessel 83 is reduced to the atmospheric pressure. The temperature is lowered from the saturation temperature (about 77K) to about 65K, for example. Then, the liquid nitrogen 90 having a pressure equal to or higher than the atmospheric pressure sent from the supply-side holding container 81 to the heat exchanger 117 is heat-exchanged with, for example, 65K liquid nitrogen 111 in the decompression container 83 to obtain 67K. The temperature drops to the extent. That is, it becomes a supercooled state. In this heat exchanger 117, the pressure of the liquid nitrogen 90 is not particularly changed, and maintains a state of atmospheric pressure or a pressure higher than atmospheric pressure.
[0073]
As described above, the liquid nitrogen 90 that is supercooled to about 67K or higher than atmospheric pressure is guided through the second transfer tube 119 into the cooling vessel 3 that is substantially open to the atmosphere. . The supercooled atmospheric pressure liquid nitrogen introduced into the cooling vessel 3 is indicated by reference numeral 11 in FIG. 4 and corresponds to cooling liquid nitrogen. Here, the amount of the cooling liquid nitrogen 11 in the cooling vessel 3 is adjusted by the reflux pipe 17 so that the space 15 remains on the liquid surface 11A.
[0074]
In the cooling container 3, the superconducting member 1 is cooled and held at, for example, about 70K by the liquid nitrogen 11 having a pressure of 67K in a supercooled state or a pressure equal to or higher than the atmospheric pressure as in the embodiment shown in FIG. Here, in the space 15 above the liquid surface 11A of the cooling liquid nitrogen 11 in the cooling container 3, the atmospheric pressure or the atmospheric pressure is supplied from the nitrogen gas supply source 71 through the nitrogen gas supply pipes 73A and 73C and the on-off valve 75B. Nitrogen gas at the above pressure is introduced. Therefore, the pressure in the cooling container 3 is reliably maintained at atmospheric pressure or a pressure higher than atmospheric pressure, and atmospheric air is reliably prevented from being drawn from the outside through the sealing portion of the lid portion 7 or the like. Is done.
[0075]
Here, in the cooling vessel 3, as in the case of the embodiment of FIG. 1 already described, the convection prevention member 79 made of a porous heat insulating material having continuous holes is provided over and below the liquid surface 11A. Even if convection or agitation of the liquid nitrogen 11 occurs in the lower part of the cooling vessel 3 due to disturbance due to some cause, there is little possibility that convection or agitation occurs in the liquid nitrogen near the liquid surface or nitrogen gas on the liquid surface, and the temperature gradient is reduced. While being able to stabilize, a liquid level position can be stabilized.
[0076]
If the operation proceeds to a steady state, liquid nitrogen of about 70 K is returned from the cooling container 3 to the supply-side holding container 81 through the reflux pipe 17, so that the liquid nitrogen 90 in the supply-side holding container 81 is also 70 K. Near temperature, that is, the supercooling temperature under atmospheric pressure. Therefore, it is desirable that the convection preventing member made of a porous heat insulating material having continuous pores is also provided on the upper and lower sides of the liquid level 90A in the supply side holding container 81 as in the cooling container 3 (however, in FIG. 4). Not shown). If the convection prevention member is provided over the liquid level 90 A of the supply-side holding container 81 as described above, the convection of the liquid nitrogen 90 is caused in the lower part of the supply-side holding container 81 due to disturbance due to some cause, as in the cooling container 3. Even if agitation occurs, there is little possibility that convection or agitation occurs in the liquid nitrogen near the liquid surface, the temperature gradient can be stabilized, and the liquid surface position can be stabilized.
[0077]
In addition, in any of each Example shown by FIGS. 1-4, as a porous heat insulating material which has the continuous hole used for the convection prevention members 77 and 79, in addition to an open cell urethane type foam, for example, an open cell polyethylene type Foams, acrylonitrile-butadiene rubber foams, ethylene propylene rubber foams, and the like can be used.
[0078]
Further, in the above description, the supply-side container 21 and the cooling container 3 in the embodiment (FIGS. 1 to 3) according to the superconducting member cooling apparatus of Japanese Patent No. 2859250, and the superconducting member cooling apparatus of JP-A-10-54637 For the cooling container 3 (or the cooling container 3 and the supply-side holding container 81) according to the embodiment according to the above (provided with a convection prevention member made of a porous heat insulating material having continuous pores above and below the liquid surface; However, it is not limited to these containers, the point is that liquid nitrogen is stored leaving a space on the liquid level, and nitrogen gas pressure of atmospheric pressure or atmospheric pressure is applied to the space on the liquid level to The present invention is applicable to all cases where nitrogen is used as a supercooling temperature under atmospheric pressure and the superconducting member is cooled with liquid nitrogen at the supercooling temperature under atmospheric pressure.
[0079]
【The invention's effect】
As is apparent from the above-described embodiments, the present invention is a liquid in which liquid nitrogen is accommodated while leaving a space on the liquid level, and nitrogen gas pressure equal to or higher than atmospheric pressure is applied to the space on the liquid level. In the superconducting member cooling apparatus configured to cool the superconducting member with the liquid nitrogen at the supercooling temperature under the atmospheric pressure, the liquid nitrogen in the nitrogen container is set to the supercooling temperature under the atmospheric pressure. Since a convection prevention member made of a porous heat insulating material having continuous pores is provided from a position below the liquid level of the liquid nitrogen to a position above the liquid level, the liquid is caused by some disturbance in the lower part of the container. Even if convection or agitation occurs in the nitrogen, the convection or agitation of liquid nitrogen is effectively prevented in the vicinity of the liquid level, so that the temperature gradient from the liquid level downward is maintained stably, and spirit The temperature gradient of the liquid nitrogen is also maintained stably, and even if there is some fluctuation in the liquid nitrogen volume due to evaporation of liquid nitrogen or condensation of nitrogen gas, the fluctuation is amplified and the liquid level position is greatly changed. Therefore, it is possible to stabilize the operation status and to constantly stabilize the cooling efficiency and improve the reliability.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing the overall configuration of a superconducting member cooling device according to a first embodiment of the present invention.
FIG. 2 is a schematic diagram showing an overall configuration of a superconducting member cooling device according to a second embodiment of the present invention.
FIG. 3 is a schematic diagram showing an overall configuration of a superconducting member cooling device according to a third embodiment of the present invention.
FIG. 4 is a schematic diagram showing an overall configuration of a superconducting member cooling device according to a fourth embodiment of the present invention.
FIG. 5 is a schematic view showing an entire configuration of a conventional superconducting member cooling device.
[Explanation of symbols]
1 Superconducting material
3 Cooling container (liquid nitrogen container)
11 Liquid nitrogen
33 Liquid nitrogen
11A liquid level
15 Space above the liquid level
33A liquid level
47 Space above the liquid level
21 Supply side container (liquid nitrogen container)
16, 49, 71 Nitrogen gas supply source
41 refrigerator
41B Cooling head
77 Convection prevention member
79 Convection blocking member

Claims

Liquid nitrogen in a liquid nitrogen container in which liquid nitrogen is stored leaving a space on the liquid level, and nitrogen gas pressure is applied to the space above the liquid level at atmospheric pressure or higher is subcooled under atmospheric pressure. In the superconducting member cooling apparatus configured to cool the superconducting member with liquid nitrogen having a supercooling temperature under atmospheric pressure, the liquid nitrogen container has a liquid from a position lower than the liquid nitrogen level in the liquid nitrogen container. A superconducting member cooling apparatus, wherein a convection preventing member made of a porous heat insulating material having continuous pores is disposed over a position above the surface.

A supply-side container in which liquid nitrogen is stored leaving a space on the liquid level and a nitrogen gas pressure is applied to the space on the liquid level or greater than atmospheric pressure, and the liquid nitrogen in the supply-side container is at atmospheric pressure In order to cool down to the supercooling temperature below, the cooling head is immersed in a position below the liquid nitrogen level, and the superconductivity to be cooled is supplied to the liquid nitrogen at the supercooling temperature in the supply side container. In a superconducting member cooling device configured to guide to a member and cool the superconducting member,
A superconductivity characterized in that a convection prevention member made of a porous heat insulating material having continuous holes is arranged from a position below the liquid level of liquid nitrogen in the supply side container to a position above the liquid level. Member cooling device.

The superconducting member cooling device according to claim 2,
The superconductivity in which the convection preventing member made of the porous heat insulating material is disposed between a position below the liquid level of the supply side container and a position above the upper end of the cooling head of the refrigerator to a position above the liquid level. Member cooling device.

The superconducting member cooling device according to claim 2,
A superconducting member in which the convection preventing member made of the porous heat insulating material is disposed below the liquid level of the supply side container and from the intermediate position in the vertical direction in the cooling head of the refrigerator to the position above the liquid level. Cooling system.

The superconducting member cooling device according to claim 4,
A superconducting member cooling device in which a cooling head of a refrigerator is extended to a position near a bottom surface of a supply-side container.

In the superconducting member cooling device according to claim 4 or 5,
Superconducting member cooling, characterized in that a heat insulating portion is provided on the outer peripheral surface of the cylinder portion of the refrigerator, and the heat insulating portion extends to an intermediate position in the vertical direction on the outer peripheral surface of the cooling head of the refrigerator. apparatus.