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CN112816518A - Method and device for testing supercooling degree thermal boundary in solidification process in circular tube - Google Patents

Method and device for testing supercooling degree thermal boundary in solidification process in circular tube Download PDF

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CN112816518A
CN112816518A CN202110011258.1A CN202110011258A CN112816518A CN 112816518 A CN112816518 A CN 112816518A CN 202110011258 A CN202110011258 A CN 202110011258A CN 112816518 A CN112816518 A CN 112816518A
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CN112816518B (en
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高玉国
安建才
阿古斯.萨斯弥多
徐铭汉
郭朋彦
范以撒
郭树满
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North China University of Water Resources and Electric Power
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    • G01N25/20—Investigating or analyzing materials by the use of thermal means by investigating the development of heat, i.e. calorimetry, e.g. by measuring specific heat, by measuring thermal conductivity
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Abstract

本发明公开一种测试圆管内凝固过程过冷度热边界的方法和装置，该装置包括待测液体圆管，待测液体圆管放入相变材料恒温容器内，在相变材料恒温容器内设置有第四温度计，紧贴待测液体圆管外壁上设置有第二温度计，第一温度计设置在待测液体圆管内。变相材料恒温容器内设置有制冷装置和搅拌装置。还公开测试圆管内凝固过程过冷度热边界的方法。本发明采用在无外界冲击和震动等较强扰动的条件下，通过测试壁面外侧相变材料固液共存时的自然对流传热系数的方法可以解决上述问题。采用本方法可以在外壁面不使用外部隔热材料，不仅避免了使用外部隔热材料带来的不便，也可以避免由于和外界热交换产生的温度波动的影响。

Figure 202110011258

The invention discloses a method and a device for testing the thermal boundary of subcooling degree in a solidification process in a circular tube. The device comprises a circular tube of liquid to be tested. A fourth thermometer is arranged, a second thermometer is arranged close to the outer wall of the liquid circular tube to be measured, and the first thermometer is arranged in the liquid circular tube to be measured. A refrigeration device and a stirring device are arranged in the thermostatic container of the phase-change material. Also disclosed is a method for testing the thermal boundary of subcooling during solidification in a circular tube. The present invention can solve the above problems by testing the natural convection heat transfer coefficient when the phase change material on the outside of the wall coexists with solid and liquid under the condition of no strong disturbance such as external impact and vibration. By adopting the method, no external heat insulating material is used on the outer wall surface, which not only avoids the inconvenience caused by using the external heat insulating material, but also avoids the influence of temperature fluctuations due to heat exchange with the outside world.

Figure 202110011258

Description

Method and device for testing supercooling degree thermal boundary in solidification process in circular tube
Technical Field
The invention relates to a method for over-testing a thermal boundary of a solidification supercooling degree in a round pipe, and also relates to a method for testing a thermal boundary of a solidification supercooling degree in a round pipe.
Background
Supercooling means the difference between the theoretical crystallization temperature (freezing point) of a substance (e.g. metal, alloy, crystal) and the actual crystallization site temperature. Many phase change materials exhibit supercooling during crystallization, i.e., crystallization does not proceed when the temperature drops to the freezing point. Crystallization only occurs after a certain temperature below the theoretical freezing point, as the temperature continues to decrease. The size of the supercooling degree of the phase-change material and the influence factors of the supercooling degree have very important influence on the performance of the phase-change material in practical application, but because the influence factors are more during the formation of crystal nuclei in the crystallization process and the duration is very short, the difficulty of the supercooling degree test and the theoretical research is greatly increased.
The research method of the supercooling degree comprises experiments, theoretical analysis and numerical simulation. At present, when theoretical analysis and numerical simulation methods are adopted for research, thermal boundary conditions need to be accurately obtained through an experimental method, and a mathematical model can be established and solved. There are three common thermal boundary conditions used: the first type of thermal boundary condition is wall temperature; a second type of thermal boundary wall heat flow; the third type of thermal boundary is the convective heat transfer coefficient of the outer wall and the ambient temperature.
A number of studies have found that wall temperatures are difficult to measure accurately and directly. If the mode of forced convection heat transfer outside the wall surface is adopted, the liquid flow process can generate large speed fluctuation and impact and vibration to the wall of the test tube, and the measurement accuracy of the supercooling degree is greatly influenced by external disturbance such as the impact and the vibration. And the heat flow in the cooling process and the heating process is different in test, and the heat flow in the heating process can be obtained by directly testing the current and the voltage heated by the heating belt. But the heat flow in the cooling process is difficult to directly obtain by adopting the method.
Disclosure of Invention
The invention provides a method and a device for testing supercooling thermal boundary in a solidification process in a round pipe, which can solve the problems by testing the natural convection heat transfer coefficient when solid and liquid of a phase change material on the outer side of a wall surface coexist under the condition of no strong disturbance such as external impact, vibration and the like. By adopting the method, no external heat insulation material is used on the outer wall surface, so that the inconvenience caused by using the external heat insulation material is avoided, and the influence of temperature fluctuation caused by heat exchange with the outside is also avoided.
The purpose of the invention is realized by the following technical scheme:
the utility model provides a device of test pipe in-process subcooling degree thermal boundary, includes the liquid pipe that awaits measuring, and in phase change material thermostatic container was put into to the liquid pipe that awaits measuring, be provided with the fourth thermometer in phase change material thermostatic container, hug closely and be provided with the second thermometer on the liquid pipe outer wall that awaits measuring, first thermometer setting is in the liquid pipe that awaits measuring. A refrigerating device and a stirring device are arranged in the phase change material constant temperature container.
According to the device for testing the supercooling thermal boundary in the solidification process in the round pipe, the phase change material constant temperature container is a constant temperature water bath, the fourth thermometer is arranged in the constant temperature water bath, the second thermometer is arranged to be attached to the outer wall of the round pipe of the liquid to be tested, and the first thermometer is arranged in the round pipe of the liquid to be tested.
The device for testing the supercooling thermal boundary of the circular tube in the supercooling process comprises a constant temperature water bath, wherein a solid-liquid phase change material container is sleeved in the constant temperature water bath, a liquid circular tube to be tested is sleeved in the solid-liquid phase change material container, a first thermometer is arranged in the middle of the liquid circular tube to be tested, a second thermometer is arranged at the position, close to the liquid circular tube to be tested, of the solid-liquid phase change material container, a third thermometer is arranged at the position, close to the constant temperature water bath, of the inner wall of the solid-liquid phase change material container, a fourth thermometer is arranged in the constant temperature water bath, and a refrigerating device and a stirring device are arranged.
The method for testing the supercooling thermal boundary in the process of solidification in the round pipe comprises the following steps of: a. injecting liquid to be measured into a liquid round pipe to be measured, wherein the liquid to be measured is kept at an initial temperature which is higher than a theoretical freezing point and lower than a theoretical boiling point;
d. loading secondary refrigerant into the phase-change material constant-temperature container, starting a refrigerating device and stirring equipment of the phase-change material constant-temperature container to cool the secondary refrigerant until the phase secondary refrigerant in the phase-change material constant-temperature container is in a solid-liquid coexisting state, namely when the temperature of the fourth thermometer is constant, closing the refrigerating setting and the stirring setting, and recording the count;
e. b, placing the round liquid tube to be measured in the step a into a phase-change material constant-temperature container, and simultaneously recording the values of the temperature of the first thermometer and the temperature of the second thermometer along with the time change;
f. stopping when the duration time is up to the time when the temperatures of the first thermometer and the second thermometer are kept stable and unchanged, monitoring the fourth thermometer, and ensuring the count of the fourth thermometer to be unchanged during a temperature reduction experiment;
g. the temperature variation curve with time during the supercooling degree test is divided into three parts: a liquid region, a solid-liquid coexisting region, and a solid region.
The method for testing the supercooling thermal boundary in the process of solidification in the round pipe comprises the following steps of:
a. injecting liquid to be measured into a liquid round pipe to be measured, wherein the liquid to be measured is kept at an initial temperature which is higher than a theoretical freezing point and lower than a theoretical boiling point;
b. filling liquid with a freezing point lower than that of the liquid to be detected as a secondary refrigerant into the constant-temperature water bath, starting the constant-temperature water bath, cooling to a temperature below the actual crystallization temperature of the liquid to be detected, and keeping the temperature of the constant-temperature water bath constant;
c. placing a solid-liquid phase change material container into a constant-temperature water bath, and filling a phase change material into the phase change material container to enable the phase change material to generate a solid-liquid mixture; the temperature of the solid-liquid mixture is consistent with the temperature of the secondary refrigerant in the constant-temperature water bath;
d. starting the thermostatic water bath of the thermostatic water bath to cool the secondary refrigerant until the phase change material in the solid-liquid phase change material container is in a solid-liquid coexisting state, namely when the temperature of the third thermometer is consistent with that of the fourth thermometer, closing the refrigeration setting and the stirring setting, and recording the count of the first thermometer, the second thermometer, the third thermometer and the fourth thermometer;
e. b, placing the round liquid pipe to be measured in the step a into a solid-liquid phase change material container, and simultaneously recording the numerical values of the temperature changes of the first thermometer and the second thermometer along with time;
f. stopping when the duration time is up to the time when the temperatures of the first thermometer and the second thermometer are kept stable and unchanged, monitoring the third thermometer, and ensuring the count of the third thermometer to be unchanged during a temperature reduction experiment;
g. the time-varying curve of the supercooling degree test transition is divided into three parts: a liquid region, a solid-liquid coexisting region, and a solid region.
In the method for testing the supercooling thermal boundary in the solidification process in the round tube, the calculation formula of the average heat flux density of the three regions and the calculation of the average convective heat transfer coefficient in the period of time are disclosed as follows:
(1) pure liquid and pure solid zones:
certain time period t of pure liquid and pure solid cooling areaiMean heat flow density Q ini(W) and the average convective heat transfer coefficient h in the periodi(W/m2In. degree. C.) is as follows:
Qi＝m.cp,j.(T0,i-Tl,i)/ti； (1)
Hi＝Q1,i/A/(Tw1,i-Tm)； (2)
wherein, T0,i,Tl,iAre respectively the tiAverage initial temperature and average final temperature of the test cross section in the sample tube in a time period; the two average temperatures are calculated by: the central temperature T of the cylinder obtained by the test of the first thermometercentAnd the temperature T of the inner wall surface at the radius calculated according to the transient heat conduction methodRIs calculated as the arithmetic mean of the average of the values,
namely T0,i＝(T0,i,cent+T0,i,R)/2,Tl,i＝(Tl,i,cent+Tl,i,R)/2
Subscripts cent and R denote the location of the test section center and radius, respectively;
the analytical solution for the temperature at the cylinder radius can be obtained from the transient heat conduction process
TR＝(Tcent-Tm).cos(βi)+Tm (3)
βiIs the transcendental equation tan betai＝Bi/βiThe root of (a) is,
specific pile number Bi ═ h at radiusi.R/λj (4)
Solving for h due to implicit functioniFirstly, the initial temperature and the final temperature of the second thermometer at the outer wall of the sample cylinder are read in a time period i, and a value T slightly larger than the initial temperature and the final temperature is assumed0,i,R' and Tl,i,R', then calculating T0,iAnd Tl,iAnd respectively calculating according to equation (1) and equation (2) to obtain Qi' and hi'; then h is addediAfter substituting equation (4), equation (3) is used to solve a new T0,i,R"and Tl,i,R"; then respectively comparing the initial assumed value and the difference between the two newly obtained parameters, i.e. | T0,i,R’-T0,i,R"| and | Tl,i,R’-Tl,i,R"|, if the difference is greater than 0.01, with T0,i,R"and Tl,i,R"separately replace the initially assumed value T0,i,R' and Tl,i,R' recalculating until the iterative calculation ends with the difference less than 0.01, thereby finally obtaining hi; in addition, at the initial time immediately after the liquid sample is put into the system and the test is started, since the temperature of the entire initial sample is uniform, T is set to be equal to0,iDirectly equal to the core temperature T of the sample0,i,cent；
Tw1,iIs the tiAverage temperature of the sample tube wall over a period of time; when the sample is in a pure liquid state Cp,j，λjSpecific heat capacity (J/kg. ℃) and thermal conductivity (W/m.K) of the liquid, respectively, and C when the sample is in a pure solid statep,j，λjThe specific heat capacity (J/kg. ℃) and the thermal conductivity (W/m.K) in the solid state respectively;
(2) average heat flux Q of liquid cooling zone in phase change process2(W) and the average convective heat transfer coefficient h in the period2(W/m2In. degree. C.) is as follows:
Q2＝Lt.m/tls；
H2＝Q2/A/(Tw,ls-Tm)；
setting the material of a slender straight pipe (cylinder) as thin-wall stainless steel, the outer diameter D (m) and the inner diameter d (m) of the straight pipe, the liquid level height of the liquid to be measured poured into the straight pipe is L (m), the heat conductivity coefficient lambda (W/m.K) of the metal pipe, and the temperature of a third thermometer is the temperature T of solid-liquid coexistencem；
Density of liquid sample rho (kg/m)3) Initial temperature T of the sample0Minimum temperature point T of supercooling phasecTheoretical freezing point of sample solution is TsLt (J/kg) is the liquid-solid phase transition latent heat; in the solid-liquid coexisting stage, the time period from the lowest point to the complete solidification starting point of the sample is tl,sThe average temperature of the outer side wall of the sample cylinder in the time period is Tw,ls(ii) a Final stable temperature in solid phase of Te(ii) a All the related temperature units are in centigrade degrees, and the time unit is in seconds;
volume V (m) of liquid to be measured3)：V＝π(d/2)2L；
Mass m (kg) of liquid to be measured: m ═ ρ V;
convective heat transfer area A (m)2)：A＝πDL。
By adopting the technical scheme, the invention has the beneficial effects that:
the technical problem that the forced convection heat transfer mode generates large original speed fluctuation to impact and vibrate the wall of the test tube can be solved by adopting a method for testing the natural convection heat transfer coefficient when solid and liquid of the phase-change material on the outer side of the wall surface coexist under the condition of no strong disturbance such as external impact and vibration. The invention can avoid using external heat insulation material on the outer wall surface, thereby not only avoiding the inconvenience caused by using the external heat insulation material, but also avoiding the influence of temperature fluctuation caused by heat exchange with the outside.
Drawings
FIG. 1 is a schematic view of the structure of the apparatus of the present invention.
Fig. 2 is a graph of temperature versus time for the supercooling test.
Detailed Description
The structure and method of the present invention are described in detail below with reference to fig. 1 and 2.
The utility model provides a device of test pipe in-process subcooling degree thermal boundary, includes the liquid pipe that awaits measuring, and in phase change material thermostatic container was put into to the liquid pipe that awaits measuring, be provided with the fourth thermometer in phase change material thermostatic container, hug closely and be provided with the second thermometer on the liquid pipe outer wall that awaits measuring, first thermometer setting is in the liquid pipe that awaits measuring. A refrigerating device and a stirring device are arranged in the phase change material constant temperature container. In the invention, the phase-change material constant-temperature container is a constant-temperature water bath, the fourth thermometer is arranged in the constant-temperature water bath, the second thermometer is arranged close to the outer wall of the liquid round pipe to be measured, and the first thermometer is arranged in the liquid round pipe to be measured.
The method for testing the supercooling thermal boundary of the circular tube in the solidification process comprises the following steps:
a. injecting liquid to be measured into a liquid round pipe to be measured, wherein the liquid to be measured is kept at an initial temperature which is higher than a theoretical freezing point and lower than a theoretical boiling point;
d. loading secondary refrigerant into the phase-change material constant-temperature container, starting a refrigerating device and stirring equipment of the phase-change material constant-temperature container to cool the secondary refrigerant until the phase secondary refrigerant in the phase-change material constant-temperature container is in a solid-liquid coexisting state, namely when the temperature of the fourth thermometer is constant, closing the refrigerating setting and the stirring setting, and recording the count;
e. b, placing the round liquid tube to be measured in the step a into a phase-change material constant-temperature container, and simultaneously recording the values of the temperature of the first thermometer and the temperature of the second thermometer along with the time change;
f. stopping when the duration time is up to the time when the temperatures of the first thermometer and the second thermometer are kept stable and unchanged, monitoring the fourth thermometer, and ensuring the count of the fourth thermometer to be unchanged during a temperature reduction experiment;
g. the temperature variation curve with time during the supercooling degree test is divided into three parts: a liquid region, a solid-liquid coexisting region, and a solid region.
The second structure of the device for testing the supercooling thermal boundary in the solidification process in the round pipe is as follows: including the liquid pipe 3 that awaits measuring, the liquid pipe that awaits measuring is put into phase change material thermostatic vessel, is provided with fourth thermometer 7 in phase change material thermostatic vessel, hugs closely to be provided with second thermometer 5 on the liquid pipe outer wall that awaits measuring, and first thermometer setting is in the liquid pipe that awaits measuring. A refrigerating device and a stirring device are arranged in the phase change material constant temperature container. The phase change material constant temperature container comprises a constant temperature water bath tank 1, a solid-liquid phase change material container 2 is sleeved in the constant temperature water bath tank, a liquid round pipe to be detected is sleeved in the solid-liquid phase change material container 3, a first fourth thermometer is arranged in the middle of a liquid round pipe to be detected, a second thermometer 5 is arranged at the position, close to the liquid round pipe to be detected, of the solid-liquid phase change material container, a third thermometer 6 is arranged at the position, close to the constant temperature water bath tank, of the inner wall of the solid-liquid phase change material container, a fourth thermometer 7 is arranged in the constant temperature water bath tank, and a refrigerating device and a stirring.
The method for testing the supercooling thermal boundary of the circular tube in the solidification process comprises the following steps:
a. injecting liquid to be measured into a liquid round pipe to be measured, wherein the liquid to be measured is kept at an initial temperature which is higher than a theoretical freezing point and lower than a theoretical boiling point;
b. filling liquid with a freezing point lower than that of the liquid to be detected as a secondary refrigerant into the constant-temperature water bath, starting the constant-temperature water bath, cooling to a temperature below the actual crystallization temperature of the liquid to be detected, and keeping the temperature of the constant-temperature water bath constant;
c. placing a solid-liquid phase change material container into a constant-temperature water bath, and filling a phase change material into the phase change material container to enable the phase change material to generate a solid-liquid mixture; the temperature of the solid-liquid mixture is consistent with the temperature of the secondary refrigerant in the constant-temperature water bath;
d. starting the thermostatic water bath of the thermostatic water bath to cool the secondary refrigerant until the phase change material in the solid-liquid phase change material container is in a solid-liquid coexisting state, namely when the temperature of the third thermometer is consistent with that of the fourth thermometer, closing the refrigeration setting and the stirring setting, and recording the count of the first thermometer, the second thermometer, the third thermometer and the fourth thermometer;
e. b, placing the round liquid pipe to be measured in the step a into a solid-liquid phase change material container, and simultaneously recording the numerical values of the temperature changes of the first thermometer and the second thermometer along with time;
f. stopping when the duration time is up to the time when the temperatures of the first thermometer and the second thermometer are kept stable and unchanged, monitoring the third thermometer, and ensuring the count of the third thermometer to be unchanged during a temperature reduction experiment;
g. the time-varying curve of the supercooling degree test transition is divided into three parts: a liquid region, a solid-liquid coexisting region, and a solid region.
In the method for testing the supercooling thermal boundary in the solidification process in the round tube, the calculation formula of the average heat flux density of the three regions and the calculation of the average convective heat transfer coefficient in the period of time are disclosed as follows:
(1) pure liquid and pure solid zones:
certain time period t of pure liquid and pure solid cooling areaiMean heat flow density Q ini(W) and the average convective heat transfer coefficient h in the periodi(W/m2In. degree. C.) is as follows:
Qi＝m.cp,j.(T0,i-Tl,i)/ti； (1)
Hi＝Q1,i/A/(Tw1,i-Tm)； (2)
wherein, T0,i,Tl,iAre respectively the tiAverage initial temperature and average final temperature of the test cross section in the sample tube in a time period; the two average temperatures are calculated by: the central temperature T of the cylinder obtained by the test of the first thermometercentAnd the temperature T of the inner wall surface at the radius calculated according to the transient heat conduction methodRIs calculated as the arithmetic mean of the average of the values,
namely T0,i＝(T0,i,cent+T0,i,R)/2,Tl,i＝(Tl,i,cent+Tl,i,R)/2
Subscripts cent and R denote the location of the test section center and radius, respectively;
the analytical solution for the temperature at the cylinder radius can be obtained from the transient heat conduction process
TR＝(Tcent-Tm).cos(βi)+Tm (3)
βiIs the transcendental equation tan betai＝Bi/βiThe root of (a) is,
specific pile number Bi ═ h at radiusi.R/λj (4)
Solving for h due to implicit functioniFirstly, the initial temperature and the final temperature of the second thermometer at the outer wall of the sample cylinder are read in a time period i, and a value T slightly larger than the initial temperature and the final temperature is assumed0,i,R' and Tl,i,R', then calculating T0,iAnd Tl,iAnd respectively calculating according to equation (1) and equation (2) to obtain Qi' and hi'; then h is addediAfter substituting equation (4), equation (3) is used to solve a new T0,i,R"and Tl,i,R"; then respectively comparing the initial assumed value and the difference between the two newly obtained parameters, i.e. | T0,i,R’-T0,i,R"| and | Tl,i,R’-Tl,i,R"|, if the difference is greater than 0.01, with T0,i,R"and Tl,i,R"separately replace the initially assumed value T0,i,R' and Tl,i,R' recalculating until the iterative calculation ends with the difference less than 0.01, thereby finally obtaining hi; in addition, at the initial time immediately after the liquid sample is put into the system and the test is started, since the temperature of the entire initial sample is uniform, T is set to be equal to0,iDirectly equal to the core temperature T of the sample0,i,cent；
Tw1,iIs the tiAverage temperature of the sample tube wall over a period of time; when the sample is in a pure liquid state Cp,j，λjSpecific heat capacity (J/kg. ℃) and thermal conductivity (W/m.K) of the liquid, respectively, and C when the sample is in a pure solid statep,j，λjThe specific heat capacity (J/kg. ℃) and the thermal conductivity (W/m.K) in the solid state respectively;
(2) average heat flux Q of liquid cooling zone in phase change process2(W) and the calculation formula of the timeAverage convective heat transfer coefficient h2(W/m2In. degree. C.) is as follows:
Q2＝Lt.m/tls；
H2＝Q2/A/(Tw,ls-Tm)；
setting the material of a slender straight pipe (cylinder) as thin-wall stainless steel, the outer diameter D (m) and the inner diameter d (m) of the straight pipe, the liquid level height of the liquid to be measured poured into the straight pipe is L (m), the heat conductivity coefficient lambda (W/m.K) of the metal pipe, and the temperature of a third thermometer is the temperature T of solid-liquid coexistencem；
Density of liquid sample rho (kg/m)3) Initial temperature T of the sample0Minimum temperature point T of supercooling phasecTheoretical freezing point of sample solution is TsLt (J/kg) is the liquid-solid phase transition latent heat; in the solid-liquid coexisting stage, the time period from the lowest point to the complete solidification starting point of the sample is tl,sThe average temperature of the outer side wall of the sample cylinder in the time period is Tw,ls(ii) a Final stable temperature in solid phase of Te(ii) a All the related temperature units are in centigrade degrees, and the time unit is in seconds;
volume V (m) of liquid to be measured3)：V＝π(d/2)2L；
Mass m (kg) of liquid to be measured: m ═ ρ V;
convective heat transfer area A (m)2)：A＝πDL。
When the invention is used for experiments, water is used as liquid to be tested for experiments, and the specific experiments are as follows:
in order to test the supercooling degree of water during freezing, firstly, water is used as liquid to be tested to be injected into a clean and dry slender cylinder (the cylinder needs to keep a larger length-diameter ratio to reduce the influence of natural convection on radial heat transfer when the inner wall surface of the cylinder is cooled), and the cylinder is kept at an initial temperature which is higher than a theoretical freezing point for a period of time to achieve thermodynamic equilibrium. The initial temperature of the liquid water to be measured is higher than the theoretical freezing point of 0 ℃ under normal pressure and lower than the boiling point of 100 ℃, and the selection of the specific initial temperature can be determined according to actual conditions so as to avoid the evaporation of liquid with too high temperature or the over-high heat which can not be reduced to the temperature required by supercooling.
(2) The water tank of the constant temperature water bath is filled with liquid with low freezing point as secondary refrigerant, such as water and glycol mixed liquid with freezing point of-30 ℃. And starting the thermostatic water bath to ensure that the highest temperature of the refrigerating medium in the water bath is at least reduced to be below the actual crystallization temperature of the liquid to be measured, wherein the temperature is selected according to the experimental condition and needs to be adjusted to-14 ℃. The cold energy is provided by the latent heat of phase change of the cold-carrying agent, and the temperature of the external environment far away from the outer wall side of the sample cylinder to be tested is kept constant for a long time after the refrigerating unit is shut down and the experiment is finished.
(3) And (3) putting a solid-liquid phase change material container filled with a phase change material into the constant-temperature water bath tank (if the secondary refrigerant is in a solid-liquid mixed state in the second step, the solid-liquid phase change material container is not arranged, and the round liquid pipe to be detected is directly put into the constant-temperature water bath tank), adjusting the proportion of the phase change material according to specific experimental conditions to generate a solid-liquid mixture, keeping the temperature of the solid-liquid mixture after initial stabilization consistent with the stable temperature of the secondary refrigerant in the external water bath, then releasing latent heat through phase change to make up the loss of external heat dissipation, and finally keeping the temperature of at least the accessory at the inner wall side of the solid-liquid phase change material container. The amount of the phase-change material in the solid-liquid coexisting state in the container and the amount of the solid generated by crystallization of the phase-change material need to be in a solid-liquid mixed state all the time in the whole experiment period, and when the external temperature changes, a stable external temperature environment is provided for the liquid to be tested in the experiment, and the phenomenon that the external environment temperature of the liquid to be tested changes greatly due to the fact that all the solid melts cannot occur. For example, about 28% of water and glycol mixed solution can be filled, so that enough solid ice particles appear at-14 ℃ to ensure that the temperature is increased after the solid in the solid-liquid mixture is completely melted when the external refrigerating medium refrigerating cycle is stopped in order to avoid vibration and impact in the experimental process.
(4) During the experiment, the thermostatic water bath is started, so that the temperature of the refrigerating medium at the outermost layer is reduced to a certain proper low temperature (the temperature can be adjusted according to the experiment requirement), and after a period of stable heat transfer, the phase-change material in the solid-liquid phase-change material container is in a solid-liquid coexisting state with proper solid content. And when the temperature of the third thermometer of the solid-liquid phase change material container far away from the liquid round tube to be measured (the third thermometer can be near the inner side wall of the solid-liquid phase change material container, but does not need to be tightly attached to the inner side wall, so that the third thermometer is in a solid-liquid coexisting region) and the fourth thermometer of the constant-temperature water bath is stable, the reading is recorded. The refrigeration and agitation system of the thermostatic waterbath was then turned off to eliminate external shocks. And then placing the liquid round tube with stable initial temperature to be measured into a solid-liquid phase-change material container in a solid-liquid coexisting state, and simultaneously recording the temperature changes of a first thermometer of the round tube to be measured and a second thermometer attached to the outer side wall of the tube wall along with the time. The experiment lasts for a while until the temperatures of the two thermometers 1 and 2 are kept basically stable, the temperature of the third thermometer is monitored, and the third thermometer is ensured to be in the solid-liquid coexisting region and the temperature of the third thermometer is kept unchanged in the temperature reduction experiment process.
(6) The method for calculating the heat flow density in a certain period of time comprises the following steps: the change curve of the temperature with time in the supercooling degree test is shown in the following graph, and is generally divided into three parts, namely a liquid region, a solid-liquid coexisting region and a solid region, as shown in fig. 2.
Setting the material of a slender straight pipe (cylinder) as thin-wall stainless steel, the outer diameter D (m) and the inner diameter d (m) of the straight pipe, the liquid level height of the liquid to be measured poured into the straight pipe is L (m), the heat conductivity coefficient lambda (W/m.K) of the metal pipe, and the temperature of a third thermometer is the temperature T of solid-liquid coexistencem；
Density of liquid sample rho (kg/m)3) Initial temperature T of the sample0Minimum temperature point T of supercooling phasecTheoretical freezing point of sample solution is TsAnd Lt (J/kg) is the latent heat of liquid-solid phase transition. In the solid-liquid coexisting stage, the time period from the lowest point to the complete solidification starting point of the sample is tl,sThe average temperature of the outer side wall of the sample cylinder in the time period is Tw,ls(ii) a Final stable temperature in solid phase of Te. All temperature units referred to are given in degrees celsius and time units are given in seconds.
Volume V (m) of liquid to be measured3)：V＝π(d/2)2L；
Mass m (kg) of liquid to be measured: m ═ ρ V;
convective heat transfer area A (m)2)：A＝πDL；
(1) Pure liquid and pure solid zones:
certain time period t of pure liquid and pure solid cooling areaiMean heat flow density Q ini(W) and the average convective heat transfer coefficient h in the periodi(W/m2In. degree. C.) is as follows:
Qi＝m.cp,j.(T0,i-Tl,i)/ti； (1)
Hi＝Q1,i/A/(Tw1,i-Tm)； (2)
wherein, T0,i,Tl,iAre respectively the tiAverage initial and final temperatures of the test cross-section within the sample tube over the time period. The two average temperatures are calculated by: the central temperature T of the cylinder obtained by the test of the first thermometercentAnd the temperature T of the inner wall surface at the radius calculated according to the transient heat conduction methodRIs calculated as the arithmetic mean of the average of the values,
namely T0,i＝(T0,i,cent+T0,i,R)/2,Tl,i＝(Tl,i,cent+Tl,i,R)/2
The subscripts cent and R denote the location of the test section center and radius, respectively.
The analytical solution for the temperature at the cylinder radius can be obtained from the transient heat conduction process
TR＝(Tcent-Tm).cos(βi)+Tm (3)
βiIs the transcendental equation tan betai＝Bi/βiThe root of (a) is,
specific pile number Bi ═ h at radiusi.R/λj (4)
Solving for h due to implicit functioniFirstly, the initial temperature and the final temperature of the second thermometer at the outer wall of the sample cylinder are read in a time period i, and a value T slightly larger than the initial temperature and the final temperature is assumed0,i,R' and Tl,i,R', then calculating T0,iAnd Tl,iAnd according to the equation(1) And equation (2) to obtain Qi' and hi'; then h is addediAfter substituting equation (4), equation (3) is used to solve a new T0,i,R"and Tl,i,R"; then respectively comparing the initial assumed value and the difference between the two newly obtained parameters, i.e. | T0,i,R’-T0,i,R"| and | Tl,i,R’-Tl,i,R"|, if the difference is greater than 0.01, with T0,i,R"and Tl,i,R"separately replace the initially assumed value T0,i,R' and Tl,i,R' recalculating until the iterative calculation ends with a difference of less than 0.01, thereby finally obtaining hi. In addition, at the initial time immediately after the liquid sample is put into the system and the test is started, since the temperature of the entire initial sample is uniform, T is set to be equal to0,iDirectly equal to the core temperature T of the sample0,i,cent。
Tw1,iIs the tiAverage temperature of the sample tube wall over time. In the case where the sample is in a pure liquid state Cp,j，λjthe specific heat capacity (J/kg. ℃) and the thermal conductivity (W/m.K) of the liquid, respectively, Cp,j，λjthe specific heat capacity (J/kg. ℃) and the thermal conductivity (W/m.K) in the solid state are shown.
(2) Average heat flux Q of liquid cooling zone in phase change process2(W) and the average convective heat transfer coefficient h in the period2(W/m2In. degree. C.) is as follows:
Q2＝Lt.m/tls；
H2＝Q2/A/(Tw,ls-Tm)。
the foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various changes and modifications can be made without departing from the overall concept of the invention, and these should be considered as the protection scope of the present invention, which will not affect the effect of the implementation of the present invention and the practicability of the patent.

Claims (6)

1.一种测试圆管内凝固过程过冷度热边界的装置，包括待测液体圆管，其特征在于：待测液体圆管放入相变材料恒温容器内，在相变材料恒温容器内设置有第四温度计，紧贴待测液体圆管外壁上设置有第二温度计，第一温度计设置在待测液体圆管内。1. a device for the thermal boundary of solidification process in the test circular tube, comprising the liquid circular tube to be tested, it is characterized in that: the liquid circular tube to be tested is put into the phase change material constant temperature container, and is set in the phase change material constant temperature container There is a fourth thermometer, a second thermometer is set close to the outer wall of the liquid circular tube to be tested, and the first thermometer is set in the liquid circular tube to be tested. 2.根据权利要求1所述的测试圆管内凝固过程过冷度热边界的装置，其特征在于：所述相变材料恒温容器为恒温水浴槽，第四温度计设置有恒温水浴槽内，第二温度计紧贴待测液体圆管外壁设置，第一温度计设置在待测液体圆管内。2. The device for testing the supercooling degree thermal boundary of the solidification process in the test circular tube according to claim 1, is characterized in that: the phase change material constant temperature container is a constant temperature water bath, and the fourth thermometer is provided with in the constant temperature water bath, and the second The thermometer is set close to the outer wall of the liquid circular tube to be tested, and the first thermometer is set in the liquid circular tube to be tested. 3.根据权利要求1所述的测试圆管内凝固过程过冷度热边界的装置，其特征在于：所述相变材料恒温容器包括恒温水浴槽，恒温水浴槽内套设有固液相变材料容器，待测液体圆管套设在固液相变材料容器内，在待测液体圆管中部设第一温度计，在固液相变材料容器靠近待测液体圆管位置设置有第二温度计，在固液相变材料容器内壁靠近恒温水浴槽的位置设置第三温度计，在恒温水浴槽内设置有第四温度计。3. The device for testing the supercooling degree thermal boundary of the solidification process in the circular tube according to claim 1, wherein the phase change material constant temperature container comprises a constant temperature water bath, and the constant temperature water bath is sleeved with a solid-liquid phase change material The container, the liquid circular tube to be tested is sleeved in the solid-liquid phase change material container, the first thermometer is set in the middle of the liquid circular tube to be tested, and the second thermometer is set at the position of the solid-liquid phase change material container close to the liquid circular tube to be tested, A third thermometer is arranged on the inner wall of the solid-liquid phase change material container near the constant temperature water bath, and a fourth thermometer is arranged in the constant temperature water bath. 4.根据权利要求1所述的测试圆管内凝固过程过冷度热边界的方法，其特征在于：包括以下步骤：4. the method for testing the supercooling degree thermal boundary in the solidification process in the test circular tube according to claim 1, is characterized in that: comprise the following steps: a.将待测液体注入到待测液体圆管内，待测液体保持高于理论凝固点以上且低于理论沸点的初温；a. Inject the liquid to be tested into the circular tube of the liquid to be tested, and keep the initial temperature of the liquid to be tested higher than the theoretical freezing point and lower than the theoretical boiling point; d.相变材料恒温容器内装入载冷剂，使载冷剂降温，直到相变材料恒温容器内的相载冷剂处于固液共存状态，即第四温度计温度恒定不变时，记录计数；d. Load the refrigerant into the thermostatic container of the phase change material to cool the refrigerant until the phase change material in the thermostatic container of the phase change material is in a state of coexistence of solid and liquid, that is, when the temperature of the fourth thermometer is constant, record the count; e.将步骤a的待测液体圆管放进相变材料恒温容器内，同时记录第一温度计和第二温度计温度随时间变化的数值；e. Put the liquid circular tube to be measured in step a into the phase-change material thermostatic container, and simultaneously record the time-varying values of the temperature of the first thermometer and the second thermometer; f.持续时间到第一温度计和第二温度计的温度保持稳定不变时停止，监控第四温度计，在降温实验时保证第四温度计的计数不变；f. Stop when the temperature of the first thermometer and the second thermometer remain stable and constant, monitor the fourth thermometer, and ensure that the count of the fourth thermometer remains unchanged during the cooling experiment; g.过冷度测试时的温度随时间变化曲线分为三个部分：液态区、固液共存区和固态区。g. The temperature variation curve during the subcooling test is divided into three parts: liquid region, solid-liquid coexistence region and solid region. 5.根据权利要求3所述的测试圆管内凝固过程过冷度热边界的方法，其特征在于：包括以下步骤：5. the method for testing the supercooling degree thermal boundary in the solidification process in the test circular tube according to claim 3, is characterized in that: comprise the following steps: a.将待测液体注入到待测液体圆管内，待测液体保持高于理论凝固点以上且低于理论沸点的初温；a. Inject the liquid to be tested into the circular tube of the liquid to be tested, and keep the initial temperature of the liquid to be tested higher than the theoretical freezing point and lower than the theoretical boiling point; b.恒温水浴槽内装入凝固点低于待测液体的液体作为载冷剂，开启恒温水浴，降温到待测液体实际结晶温度以下，保持恒温水浴温度恒定；b. The constant temperature water bath is filled with a liquid whose freezing point is lower than the liquid to be tested as the refrigerant, the constant temperature water bath is turned on, the temperature is lowered to below the actual crystallization temperature of the liquid to be tested, and the temperature of the constant temperature water bath is kept constant; c.将固液相变材料容器放置到恒温水浴槽内，相变材料容器装入相变材料，使相变材料出现固液混合物；固液混合物的温度与恒温水浴槽内的载冷剂温度一致；c. Place the solid-liquid phase change material container in the constant temperature water bath, and the phase change material container is filled with the phase change material, so that a solid-liquid mixture appears in the phase change material; the temperature of the solid-liquid mixture is the same as the temperature of the refrigerant in the constant temperature water bath. consistent; d.开启恒温水浴槽的恒温水浴，使载冷剂降温，直到固液相变材料容器内的相变材料处于固液共存状态，即第三温度计和第四温度计温度一致时，关闭制冷设置和搅拌设置，记录第一温度计、第二温度计、第三温度计和第四温度计的计数；d. Turn on the constant temperature water bath of the constant temperature water bath to cool the refrigerant until the phase change material in the solid-liquid phase change material container is in a state of solid-liquid coexistence, that is, when the temperature of the third thermometer and the fourth thermometer are the same, turn off the refrigeration setting and Stir the setting, record the counts of the first thermometer, the second thermometer, the third thermometer and the fourth thermometer; e.将步骤a的待测液体圆管放进固液相变材料容器内，同时记录第一温度计和第二温度计温度随时间变化的数值；e. Put the liquid circular tube to be measured in step a into the solid-liquid phase change material container, and simultaneously record the numerical values of the temperature of the first thermometer and the second thermometer that change with time; f.持续时间到第一温度计和第二温度计的温度保持稳定不变时停止，监控第三温度计，在降温实验时保证第三温度计计数不变；f. Stop when the temperature of the first thermometer and the second thermometer remain stable and constant, monitor the third thermometer, and ensure that the count of the third thermometer remains unchanged during the cooling experiment; g.过冷度测试时渡随时间变化曲线分为三个部分：液态区、固液共存区和固态区。g. The time-dependent curve of the subcooling degree test is divided into three parts: the liquid region, the solid-liquid coexistence region and the solid region. 6.根据权利要求4或5所述的测试圆管内凝固过程过冷度热边界的方法，其特征在于：所述三个区平均热流密度的计算公式以及该段时间内的平均对流换热系数的计算公开如下：6. The method for testing the supercooling degree thermal boundary of the solidification process in a circular tube according to claim 4 or 5, characterized in that: the calculation formula of the average heat flux density of the three zones and the average convective heat transfer coefficient during this period of time The calculation of is exposed as follows: (1)纯液态和纯固态区：(1) Pure liquid and pure solid regions: 纯液态和纯固体降温区的某时间段ti内的平均热流密度Qi(W)的计算公式以及该段时间内的平均对流换热系数hi(W/m2.℃)的计算公式如下所示：The calculation formula of the average heat flux density Q i (W) and the average convective heat transfer coefficient h i (W/m 2 .℃) in a certain period of time t i in the pure liquid and pure solid cooling zone As follows: Qi＝m.cp,j.(T0,i-Tl,i)/ti； (1)Q i =mc p,j .(T 0,i -T l,i )/t i ; (1) Hi＝Q1,i/A/(Tw1,i-Tm)； (2)H i =Q 1,i /A/(T w1,i -T m ); (2) 其中，T0,i,Tl,i分别为该ti时间段内的试样管内的测试横截面的平均初温和平均末温；这两个平均温度的计算方法是：温度计1测试得到的圆筒中心温度Tcent和按照瞬态导热法计算的半径处的内壁面温度TR的算术平均值，Among them, T 0,i , T 1,i are the average initial temperature and average final temperature of the test cross-section in the sample tube in the time period t i respectively; the calculation methods of these two average temperatures are: The arithmetic mean of the cylinder center temperature T cent and the inner wall surface temperature T R at the radius calculated according to the transient thermal conductivity method, 即T0,i＝(T0,i,cent+T0,i,R)/2,Tl,i＝(Tl,i,cent+Tl,i,R)/2That is, T 0,i =(T 0,i,cent +T 0,i,R )/2,T l,i =(T l,i,cent +T l,i,R )/2 下标cent和R分别表示测试截面中心和半径的位置；The subscripts cent and R represent the position of the center and radius of the test section, respectively; 按照瞬态导热过程可以得到在圆筒半径处温度的分析解为According to the transient heat conduction process, the analytical solution of the temperature at the radius of the cylinder can be obtained as TR＝(Tcent-Tm).cos(βi)+Tm (3)T R =(T cent -T m ).cos(β i )+T m (3) βi是超越方程tanβi＝Bi/βi的根，β i is the root of the transcendental equation tanβ i =Bi/β i , 半径处的比渥数Bi＝hi.R/λj (4)The specific number at the radius Bi=hi .R/ λ j ( 4) 由于是隐函数，求解hi时，首先参考试样筒外壁处温度计2在时间段i内初温和末温的读数，假设一个略大于上述读数的一个值T0,i,R’和Tl,i,R’，然后计算T0,i和Tl,i，并根据方程(1)和方程(2)分别计算得到Qi’和hi’；然后再将hi’带入方程(4)后再用方程(3)求出新的T0,i,R”和Tl,i,R”；再分别比较初始假设值和计算新得到的两个参数的差别，即|T0,i,R’-T0,i,R”|和|Tl,i,R’-Tl,i,R”|，如果差别大于0.01，用T0,i,R”和Tl,i,R”分别替代初始假设的值T0,i,R’和Tl,i,R’，重新计算，直到差别小于0.01迭代计算结束，由此可以最终得到hi；另外，在液态试样刚放入系统开始测试时的初始时刻，由于初始试样整体温度均匀，所以T0,i直接等于试样中心温度T0,i,cent；Since it is an implicit function, when solving h i , first refer to the readings of the initial temperature and final temperature of the thermometer 2 at the outer wall of the sample cylinder in the time period i, assuming a value T 0, i, R ' and T l that are slightly larger than the above readings ,i,R ', then calculate T 0,i and T l,i , and calculate Q i ' and hi ' according to equation (1) and equation (2) respectively; then bring hi ' into equation ( 4) Then use equation (3) to find the new T 0,i,R ” and T l,i,R ”; then compare the difference between the initial assumed value and the newly calculated two parameters, namely |T 0 ,i,R '-T 0,i,R ”| and |T l,i,R '-T l,i,R ”|, if the difference is greater than 0.01, use T 0,i,R ” and T l, i, R "respectively replace the initial assumed values T 0, i, R ' and T l, i, R ', and recalculate until the difference is less than 0.01. The iterative calculation ends, and hi can be finally obtained. In addition, in the liquid sample At the initial moment when it is just put into the system to start the test, since the overall temperature of the initial sample is uniform, T 0,i is directly equal to the central temperature of the sample T 0,i,cent ; Tw1,i为该ti时间段内的试样管壁面的平均温度；在试样为纯液态时Cp,j，λj分别为液体的比热容(J/kg.℃)和导热系数(W/m.K)，当试样为纯固态时，Cp,j，λj分别为固态时的比热容(J/kg.℃)和导热系数(W/m.K)； Tw1,i is the average temperature of the wall surface of the sample tube in the time period t i ; when the sample is pure liquid, C p,j , λ j are the specific heat capacity of the liquid (J/kg.℃) and thermal conductivity ( W/mK), when the sample is a pure solid state, C p,j , λ j are the specific heat capacity (J/kg.℃) and thermal conductivity (W/mK) of the solid state, respectively; (2)相变过程的液态降温区的平均热流密度Q2(W)的计算公式以及该段时间内的平均对流换热系数h2(W/m2.℃)的计算公式如下所示：(2) The calculation formula of the average heat flux density Q 2 (W) in the liquid cooling zone of the phase change process and the calculation formula of the average convective heat transfer coefficient h 2 (W/m 2 .℃) during this period are as follows: Q2＝Lt.m/tls；Q 2 =L tm /t ls ; H2＝Q2/A/(Tw,ls-Tm)；H 2 =Q 2 /A/( Tw,ls −T m ); 设细长直管(圆柱体)材料为薄壁不锈钢，直管外径D(m)，内径d(m)，待测液体倒入直管后的液面高度为L(m)，金属管的导热系数λ(W/m.K)，第三温度计的温度为固液共存的温度Tm；Suppose the material of the slender straight pipe (cylinder) is thin-walled stainless steel, the outer diameter of the straight pipe is D (m), the inner diameter is d (m), the liquid level height of the liquid to be measured after pouring into the straight pipe is L (m), and the metal pipe The thermal conductivity λ (W/mK) of , the temperature of the third thermometer is the temperature T m of the coexistence of solid and liquid; 液态试样的密度ρ(kg/m3)，试样的初始温度T0，过冷阶段的最低温度点Tc,试样溶液的理论凝固点为Ts，Lt(J/kg)为液固相变潜热；在固液共存阶段，从最低点到试样完全凝固始点的时间段为tl,s，此时间段内试样筒外侧壁的平均温度为Tw,ls；固态阶段最终稳定温度为Te；所涉及到的所有温度单位都取摄氏度，时间单位为秒；The density ρ (kg/m 3 ) of the liquid sample, the initial temperature T 0 of the sample, the lowest temperature point T c in the supercooling stage, the theoretical freezing point of the sample solution is T s , and Lt (J/kg) is the liquid-solid latent heat of phase transition; in the solid-liquid coexistence stage, the time period from the lowest point to the start point of complete solidification of the sample is t l,s , and the average temperature of the outer wall of the sample tube during this time period is Tw,ls ; the solid-state stage is finally stable The temperature is Te ; all the temperature units involved are in degrees Celsius, and the time unit is seconds; 待测液体的体积V(m3)：V＝π(d/2)2L；The volume of the liquid to be measured V(m 3 ): V=π(d/2) 2 L; 待测液体的质量m(kg)：m＝ρV；Mass m(kg) of liquid to be tested: m=ρV; 对流换热面积A(m2)：A＝πDL。Convective heat transfer area A (m 2 ): A=πDL.
CN202110011258.1A 2021-01-05 2021-01-05 Method and device for testing supercooling degree thermal boundary in solidification process in circular tube Active CN112816518B (en)

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