EP2584294A1 - Cold-gas supply device for a RMN-appliance - Google Patents

Abstract

The subject of the present invention is a device for supplying cold gases to an installation or an NMR analysis apparatus equipped with a measuring probe, said cold gases ensuring the cooling of the sample contained in the probe. but also its lift and its rotational drive, said supply device essentially comprising an insulated tank containing liquid gas at boiling temperature and in which are arranged exchangers through which the gas flows to be cooled, these exchangers being connected to transfer lines conveying the cooled gases to the probe. Device (1) characterized in that it also comprises at least one additional heat exchanger (8, 8 ', 8 ") ensuring a pre-cooling of the gas flow concerned before it is conveyed to the exchanger (6, 6', 6") corresponding, each or each additional exchanger (8, 8 ', 8 ") being in the form of a double-flow exchanger fed either by the gaseous vapor (5') produced by the boiling of the liquid gas (5) in the tank (4), either by the cold gas discharged or escaping at the probe.

Description

The present invention relates to the field of measurement and imaging equipment and installations using nuclear magnetic resonance (NMR), in particular the so-called low temperature Magic Angle Spinning (LTMAS) NMR techniques (Magic Angle Spinning). temperature).

The invention more particularly relates to a cold gas supply device of a device or an NMR installation of the aforementioned type, and a corresponding installation.

Some LT MAS NMR probes operate with very cold gases at temperatures close to liquid nitrogen (77.3 K). These gases guide and rotate the sample generally contained in a small tube called a rotor inserted in a stator, but also the cooling of this sample.

For this purpose, three separate gaseous streams, generally designated by "VT" (sample cooling gas), "Bearing" (bearing) and "Drive" (drive) are used. These gases have traditionally pressures of 1 to 4 bar and typical flow rates vary from 20 to 60 Nl / min. The pressure and the flow rate depend on the speed of rotation of the sample programmed by the user.

Usually, these aforementioned gases, from bottles, cans or similar reservoirs at room temperature, are cooled by passing through three exchangers (one per gas) contained in three pressurized chambers filled in part with liquid nitrogen. The internal pressure of each chamber is regulated and kept constant by an electronic controller. The controller regulates the internal pressure of the chambers by acting on the heating power of heating resistors immersed in the liquid nitrogen of the chambers.

A constant pressure of the liquid nitrogen in the chamber in equilibrium with its vapor means that the temperature of the liquid nitrogen in the chamber is constant. In this way, the boiling temperature of the liquid nitrogen of each chamber is controlled. For correct rotation of the MAS rotor, it is essential to supply dry gases that do not contain liquefied gases.

This mechanical assembly constituted by these three exchangers is a cold gas supply device, commonly called LTMAS cooling device.

An example of such a device is described in the document FR-A-2 926 629 .

These known cooling devices work perfectly, but have the disadvantage of consuming a large amount of liquid nitrogen.

Thus, the consumption can reach 20 l / hr, or 480 liters per day when the rotational speed of the rotor is high. The total consumption of liquid nitrogen is directly proportional to the internal pressure of the chambers containing the exchangers.

However, the pressure of each chamber is a function of the speed of rotation of the rotor. A high rotational speed is achieved with higher gas flow rates especially for "Drive" and "Bearing" gases. The heat exchange surfaces of the chambers are dimensioned to be able to evacuate the maximum thermal power.

Of course, a significant consumption of liquid nitrogen causes a significant increase in the operating cost of the installation and requires frequent handling of liquid nitrogen tanks by the user of the device. To ensure the continuous operation of the device 24h / 24h, the user must typically set up twice a day a 200 liter can filled with liquid nitrogen, in order to maintain the constant level in the main nitrogen tank in which are arranged chambers enclosing the exchangers.

Although the document FR-A-2 926 692 evokes a possibility of pre-cooling, only the exploitation of gas leaks at the reservoir is evoked and no practical functional or constructive details are provided.

The present invention aims to overcome the aforementioned drawbacks, by proposing an optimized solution to significantly reduce the consumption of liquid nitrogen in the aforementioned devices, while taking into account the specificities of the different gaseous flows concerned.

For this purpose, the subject of the invention is a device for supplying cold gases to an installation or an NMR analysis apparatus equipped with a measuring probe, said cold gases ensuring the cooling of the sample contained in the probe, but also its lift and its rotation drive,
said supply device essentially comprising an insulated tank containing liquid gas at boiling temperature and in which are arranged exchangers traversed by the gas streams to be cooled, these exchangers being connected to one or more transfer lines carrying the cooled gases towards the probe,
said device also comprising at least one additional exchanger ensuring a pre-cooling of the relevant gas flow before it is conveyed to the corresponding exchanger, the said or each additional exchanger being in the form of a double-flow exchanger,
characterized in that each exchanger is associated, upstream with respect to the gaseous flow concerned, an additional pre-cooling exchanger, supplied either by the gaseous vapor produced by the boiling of the liquid gas in the tank, or by the cold gas discharged from the probe or escaping at the probe,
in that the additional exchanger ensuring the pre-cooling of the cold gas for cooling the sample is supplied with gaseous vapor produced by the boiling of the liquid gas in the reservoir and
in that the additional heat exchangers for pre-cooling the cold gases intended to respectively provide the lift and the rotation of the sample are fed with the gases discharged or escaping at the level of the probe.

• la figure 1 est une représentation schématique et de principe du dispositif d'alimentation selon l'invention ;
• la figure 2 est une vue en élévation latérale et en coupe d'un dispositif d'alimentation selon un mode de réalisation avantageux de l'invention ;
• la figure 3 est une vue en coupe de l'unité structurelle formée par l'arrangement des échangeurs additionnels selon une variante préférée du dispositif représenté figures 1 et 2 (seul l'échangeur additionnel pour le gaz de refroidissement de l'échantillon est représenté en totalité) ;
• la figure 4 est une représentation schématique partielle d'une installation de mesure RMN (seule la structure enveloppante de la sonde est représentée et non l'appareil RMN lui-même), montrant les branchements fluidiques la reliant à un dispositif d'alimentation tel que représenté aux figures 1 et 2, et,
• la figure 5 est une représentation partielle plus détaillée et à une échelle différente de la partie de la sonde entourant l'échantillon, faisant partie de l'installation représentée figure 4, avec indication symbolique des flux de gaz.

The invention will be better understood, thanks to the following description, which refers to preferred embodiments, given by way of non-limiting examples, and explained with reference to the appended diagrammatic drawings, in which:

• the figure 1 is a schematic and basic representation of the feeding device according to the invention;
• the figure 2 is a side elevation and sectional view of a feeder according to an advantageous embodiment of the invention;
• the figure 3 is a sectional view of the structural unit formed by the arrangement of additional exchangers according to a preferred variant of the device shown figures 1 and 2 (only the additional exchanger for the sample cooling gas is represented in full);
• the figure 4 is a partial schematic representation of an NMR measuring installation (only the enveloping structure of the probe is shown and not the NMR apparatus itself), showing the fluidic connections connecting it to a feed device as shown in FIGS. figures 1 and 2 and,
• the figure 5 is a more detailed partial representation on a different scale of the part of the probe surrounding the sample, forming part of the installation shown figure 4 , with symbolic indication of gas flows.

The figures 1 and 2 show a cold gas supply device 1 of an installation or an NMR analysis apparatus 2 equipped with a measurement probe 3, said cold gases ensuring the cooling of the sample 3 'contained in the probe 3 but also its lift and rotation training. This feed device 1 essentially comprises an insulated tank 4 containing liquid gas 5 at boiling temperature and in which are arranged exchangers 6, 6 ', 6 "traversed by the streams of gas to be cooled, these exchangers being connected to one or more transfer lines 7, 7 ', 7 "(isolated or under vacuum) conveying the cooled gases towards the probe 3.

According to the invention, this device 1 also comprises at least one additional heat exchanger 8, 8 ', 8 "ensuring a pre-cooling of the gas flow concerned before its routing to the corresponding exchanger 6, 6', 6", said or each additional exchanger 8, 8 ', 8 "in the form of a double-flow (or counter-current) heat exchanger supplied either by the gaseous vapor 5' produced by the boiling of the liquid gas 5 in the tank 4, either by the cold gas 9 discharged out of the probe or escaping at the probe 3.

The invention thus makes it possible to recover at least part of the cold gas frigories that are not currently exploited and intended to be discharged into the atmosphere.

The precooling resulting from the gas concerned results in a reduction in the heat power to be transferred by the corresponding exchanger 6, 6 ', 6 "and therefore a reduction in the refrigeration requirement by the liquid nitrogen 5 (in which the exchangers 6, 6' 6 "are arranged, generally inside chambers 6" 'controlled in temperature and pressure).

This basic concept of the invention is preferentially applied to the three cold gases.

Thus, according to the invention, it is provided that each exchanger 6, 6 ', 6 "is associated, upstream with respect to the gaseous flow in question, an additional pre-cooling exchanger 8, 8', 8", as shown the figure 1 .

Also in accordance with the invention, the additional exchanger 8 providing the precooling of the cold gas for cooling the sample 3 'is supplied with gaseous vapor 5' produced by the boiling of the liquid gas 5 in the tank 4 and the exchangers additional 8 'and 8 "ensuring the precooling of the cold gases intended to respectively provide lift and rotation of the sample 3' are fed by the gases 9 evacuated or escaping at the probe 3.

This ensures the supply of dry gases for the lift and the rotation of the probe 3, even after a prolonged shutdown of the installation 2 (due to the interdependence between the flow rates of the gases 9 and lift gases and rotation as explained below).

According to one embodiment of the invention, resulting in an effective heat transfer and emerging from the figure 3 of the accompanying drawings, each additional exchanger 8, 8 ', 8 "is constituted by an arrangement of two concentric ducts or tubes 10, 10', one of which is traversed by the flow of the gas to be pre-cooled (primary circuit), preferably the inner tube or conduit, and the other 10 '(secondary circuit) is traversed by the flow of the cooling gas formed by the gaseous vapor 5' of boiling liquid gas 5 of the tank 4 or by the gases 9 evacuated or s escaping from the level of the probe 3.

With a view to achieving optimum utilization of the refrigerating power of the gaseous vapors 5 'and the exhaust gases 9, with progressive pre-cooling, each additional exchanger 8, 8', 8 "is advantageously a counter flow or flow exchanger opposed.

According to an advantageous constructive variant of the invention, figures 2 and 3 , and resulting in a simple, compact and thermally optimized solution, the three additional exchangers 8, 8 ', 8 "are grouped into a single structural unit 11, for example in the form of a single coil 11 consisting of a interlaced arrangement of three helical tubular formations 10, 10 'each corresponding to one of the three additional exchangers 8, 8', 8 ".

Preferably, as shown in figure 2 the additional exchangers 8, 8 ', 8 ", preferentially grouped structurally into one only unit 11 housed in an insulated housing 11 'are at least partially arranged in the upper part 4' of the tank 4 enclosing the liquid gas 5 and the exchangers 6, 6 ', 6 ", advantageously being mounted in a cover 4" closing said reservoir 4.

An exemplary non-limiting practical embodiment will now be described in detail and in relation to the Figures 1 to 4 attached drawings.

As indicated above, the aim of the invention is to reduce the consumption of liquid gas (generally nitrogen) in NMR installations, in particular those using LTMAS probes, and to this end the general method used consists in pre-cooling all MAS gas before passing them through the different exchangers 6, 6 ', 6 ".

For this purpose, the invention exploits the hitherto unused cooling power of all the cold gases produced during the operation of the feed device 1 and the NMR probe 3.

1. 1) Lors du fonctionnement du dispositif d'alimentation 1, il se produit en permanence une ébullition de l'azote liquide 5 dans le réservoir principal 4, provoquée par le refroidissement des gaz MAS dans les chambres 6"' et le transfert de chaleur vers l'extérieur de ces chambres. Ce gaz (azote) très froid, est communément appelé « boil-off ». Il est inutilisé dans la construction actuelle de ces dispositifs d'alimentation et il est simplement rejeté à l'air libre par des tubes débouchant sur le haut du dispositif.
2. 2) Dans la sonde RMN LTMAS, les gaz froids "VT", "Bearing" et "Drive" en quittant le stator 3" se mélangent dans le volume interne de l'enveloppe externe 2' de la sonde 3. Le mélange gaz froid résultant est rejeté hors de la sonde à l'atmosphère par un tube d'échappement débouchant du boitier de base de la sonde. L'enveloppe constituant l'enveloppe externe 2' de la sonde est bien isolée thermiquement et par conséquent le gaz d'échappement reste à basse température. La température du gaz en sortie, simplement évacué dans l'air actuellement, peut être comprise entre 120 à 140K en fonctionnement permanent.

In the current installations, two sources of easily exploitable cold gases have been identified by the inventor:

1. 1) During the operation of the feed device 1, liquid nitrogen 5 is continuously boiled in the main tank 4, caused by the cooling of the MAS gases in the chambers 6 "'and the heat transfer to The outside of these chambers, which is very cold, is commonly called "boil-off." It is unused in the actual construction of these feeders and is simply vented to the open by tubes. leading to the top of the device.
2. 2) In the LTMAS NMR, the cold gases "VT", "Bearing" and "Drive" leaving the stator 3 "are mixed in the internal volume of the outer shell 2 'of the probe 3. The cold gas mixture The resultant is discharged from the probe into the atmosphere by an exhaust pipe opening from the base housing of the probe, the envelope constituting the outer shell 2 'of the probe is well thermally insulated and therefore the gas of Exhaust remains at low temperature The temperature of the gas outlet, simply vented into the air at present, can be between 120 to 140K in continuous operation.

As shown by figures 2 and 4 , there is provided according to the invention a transfer rod 12 'MAS gas to the probe 3 which is fixed on the housing 11' isolated by an internal vacuum. Advantageously, between lid and the tank is a seal and the lid is held on the liquid nitrogen tank by flanges.

In its preferred embodiment, the invention provides three pre-coolers 8, 8 ', 8 "for the gases" VT "," Bearing "and" Drive ".

Each additional exchanger forming gas pre-cooler is a countercurrent heat exchanger, the construction of which is called "tube in tube" and which has a helical shape. In the inner tube 10 (for example 8 mm) circulates the gas to be cooled from top to bottom ( Figures 1 and 3 ). In the annular section between the inner tube 10 and the outer tube 10 '(for example 16 mm) circulates the cold precooling gas from bottom to top. For example, the gas "VT" enters at room temperature and the cold pre-cooling gas is vented to the air at the top of the coil of the figure 3 . The precooled gas VT exits the bottom of the coil 11 and then passes into the exchanger 6. The three pre-coolers 8, 8 ', 8 "for the gases" VT "," Bearing "and" Drive "are contained in the housing 11' .

On the figure 3 , G1 represents the VT gas flow at ambient temperature, G1 'represents the precooled gas flow VT, G2 represents the gas vapor flow 5' discharged from the upper part 4 'of the tank 4 and G2' represents the vapor flow gas 5 'escaping into the environment.

1. 1) Le gaz "VT" est prérefroidi par le gaz (azote) froid "boil-off " 5' produit dans le réservoir 4 d'azote liquide 5 dans lequel sont plongés les échangeurs 6, 6', 6". Ce gaz froid 5' passe par l'entrée 13 du conduit externe 10' de prérefroidissement. Dès que le contrôle de la pression des chambres 6"' est activé, c'est-à-dire dès que les pressions des chambres sont constantes, il se produit une ébullition dans le réservoir 4 autour des chambres et le gaz froid produit (vapeur gazeuse 5') passe par le circuit formé par le tube externe 10' de l'échangeur additionnel 8.
2. 2) Les gaz froids en sortie des échangeurs 6, 6', 6" sont dirigés vers la sonde par la canne de transfert 12' qui est accouplée à une ligne de transfert interne isolée 14, logée dans la partie basse de la structure de sonde 3. Les gaz ressortent de la ligne interne près du stator 3". Le gaz "BEARING" assure la sustentation, le gaz "DRIVE" l'entraînement du rotor et le gaz "VT" refroidit la partie centrale du tube échantillon 3'.
3. 3) La sonde RMN 3 est isolée thermiquement par une double paroi sous vide 2' (Dewar). En ressortant du stator 3", les trois gaz se mélangent dans le volume interne de la sonde 3 et sortent mélangés par le tube d'échappement 15, débouchant à l'extérieur du boitier fermant la partie basse de la structure de la sonde 3 (Figure 4).

The inputs of the three additional exchangers forming pre-coolers are fed by the two cold gas sources indicated above. More precisely :

1. 1) The gas "VT" is pre-cooled by the gas (nitrogen) cold "boil-off" 5 'produced in the tank 4 of liquid nitrogen 5 in which the exchangers 6, 6', 6 "are immersed. 5 'passes through the inlet 13 of the external pre-cooling duct 10. As soon as the control of the pressure of the chambers 6''is activated, that is to say, as soon as the pressures of the chambers are constant, it occurs. a boiling in the tank 4 around the chambers and the cold gas produced (vapor gas 5 ') passes through the circuit formed by the outer tube 10' of the additional exchanger 8.
2. 2) The cold gases leaving the exchangers 6, 6 ', 6 "are directed towards the probe by the transfer rod 12' which is coupled to an insulated internal transfer line 14, housed in the lower part of the probe structure 3. The gases emerge from the inner line near the stator 3 ". The gas "BEARING" provides the lift, the "DRIVE" gas the rotor drive and the "VT" gas cools the central part of the sample tube 3 '.
3. 3) The NMR probe 3 is thermally insulated by a double vacuum wall 2 '(Dewar). Coming out of the stator 3 ", the three gases mix in the internal volume of the probe 3 and exit mixed by the exhaust tube 15, opening out of the housing closing the lower part of the structure of the probe 3 ( Figure 4 ).

The vacuum-insulated flexible return rod 12 inserted in the exhaust tube 15 of the NMR measuring probe is held for example by a nut and an O-ring. The other end of the rod can be fitted into an adapter 16 fixed under the cover 4 "of the tank 4 of liquid nitrogen 5. It is held in place for example by a nut and a seal.

• 4) La surface d'échange thermique de chaque chambre 6"' est la partie supérieure non isolée thermiquement qui sert à transférer la puissance thermique vers l'extérieur de la chambre, c'est-à-dire vers l'azote liquide 5 du réservoir 4. La surface d'échange de chaque chambre 6"' a pu être réduite de 50 % environ par rapport à la version d'origine sans pré refroidissement. Cette diminution de surface à été rendue possible car la puissance thermique à évacuer dans chaque chambre est plus faible, en raison du pré-refroidissement des gaz MAS.

The adapter 16 distributes the cold gas (gas mixture discharged from the probe 3) to the two inlets of the two pre-coolers 8 'and 8 "by two plastic tubes.

• 4) The heat exchange surface of each chamber 6 "'is the non-thermally insulated upper part which serves to transfer the thermal power to the outside of the chamber, that is to say to the liquid nitrogen 5 of the tank 4. The exchange area of each 6 "chamber could be reduced by about 50% compared to the original version without pre-cooling. This surface reduction has been made possible because the thermal power to be evacuated in each chamber is lower, because of the pre-cooling of the MAS gases.

The specific allocation of the cold sources ("boil off" gas 5 'and gas mixture 9 evacuated by the probe 3) respectively to the various pre-coolers 8, 8', 8 "is essential for the proper functioning of the installation 4.

Thus, and as already mentioned before and illustrated by the figures 1 , 2 , 4 and 5 in particular, the cold gas 9 from the probe 3 is used to pre-cool the gases "BEARING" and "DRIVE". This cold gas ("exhaust") 9 coming out of the probe 3 is in fact a gas resulting from the mixing of all the cold gases (VT, Bearing and Drive) leaving the stator 3 ".

The gas VT is (at the level of the 6/8 assembly) pre-cooled only by the gas 5 'called "boil-off" of the tank LN ₂ (reference 4). This "boil-off" gas of the LN ₂ tank is produced continuously, said gas flow being created by the total thermal power dissipated in the liquid nitrogen. This is the sum of the thermal losses of the reservoir LN ₂ 4 and the thermal powers dissipated by each chamber 6 "'containing an exchanger 6, 6', 6" (the power released by each chamber depends solely on the internal pressure of this chamber). bedroom).

This particular assignment has, surprisingly, the advantage of avoiding problems related to uncontrolled variations in the rotation and possibly the lift of the rotor 3 'integrating the sample.

Indeed, during the periodic filling of the reservoir 4 of liquid nitrogen to maintain its substantially constant level, the internal pressure of the reservoir increases substantially.

If, under these conditions, the boil-off gas 5 'were to be used, possibly in admixture with the gas 9, to pre-cool the DRIVE and BEARING gases, the DRIVE and BEARING gas pressures would be disturbed further upstream. in the probe 3. These variations would then cause fluctuations in the speed of rotation of the rotor 3 'which would therefore become difficult to control. In addition, the cold gas 9 discharged from the probe 3 is at a higher temperature (of the order of 120-140 K), which would increase the consumption of liquid nitrogen and the boil-off of the tank 4.

When in the primary circuit 10 of a pre-cooler 8, 8 ', 8 "does not circulate any gas, or if the flow rate of the gas concerned is low, it is recommended to stop the flow of cold gas in the secondary circuit 10' because a partial liquefaction of the gas of the primary circuit 10 could occur.Thus, if the boil-off gas (whose temperature is estimated at about 80 K) was to be used to pre-cool the gas DRIVE or BEARING, which are under at a pressure of 1 to 3 bar, these gases could be partially liquefied, but this would seriously impair the good operation of the rotor 3 'because the BEARING and DRIVE gases must be absolutely free of droplets of liquefied nitrogen gas.

In addition, during the insertion or ejection phases of the sample, the rotor 3 'is stopped and all the flow rates of the gases in the probe 3 are zero. Consequently, the secondary flows of the BEARING 6 'and DRIVE 6 "exchangers are also zero and the BEARING and DRIVE gases present in the pre-coolers 8' and 8" can not be liquefied. On the contrary, if boil-off gas 5 'was used in the secondary 10' BEARING 6 'and DRIVE 6 "pre-coolers, there would be a possibility effective liquefaction of these gases. The construction according to the invention thus avoids possible problems of rotating the sample rotor 3.

In addition, in the particular case of the pre-cooler exchanger 8 for the gas VT, when the flow rate of the primary gas is stopped, the gas 5 'boil-off always circulates in the secondary circuit 10'. However, partial liquefaction of the VT gas is never observed in this pre-cooler 8, since the pressure of the gas VT is then low (P << 0.5 bar) while the boil-off gas temperature is 80 K or more. In addition, if liquefaction were to occur, this would not create any particular problem for the proper functioning of the probe 3 because the VT gas does not influence the rotation or the levitation of the sample.

Thanks to the specific provisions of the invention, it has been possible to very significantly reduce the consumption of liquid nitrogen, while ensuring the quality and characteristics of the gases transmitted to the probe 3.

With a prototype, the inventor was able to measure a consumption of 6.5 l / LN2 per hour (with a 3.2 mm rotor rotating at 8 KHz). This gives a reduction of more than about 50% compared to the consumption measured on a known equivalent supply device, not having the characteristics of the invention as apparent from the description above.

Reducing the consumption of liquid nitrogen reduces the number of manipulations of auxiliary liquid nitrogen cans used to maintain the constant level of liquid nitrogen in the main tank.

Thanks to the invention, there is therefore less implementation operations and connections of cans to be made every day. Thus, a single can of 200 liters of LN2 is sufficient to ensure continuous operation for 24 hours for moderate rotational speeds of the rotor, that is to say less than 10 KHz with a probe equipped with a rotor of 3 , 2 mm.

Another subject of the invention is an NMR measuring installation 2, in particular of the LT MAS probe type, in which the probe 3 is supplied with cold gases providing cooling (VT), lift (BEARING) and rotation (DRIVE ) of the sample (rotor 3 '), said installation 2 comprising and / or being fluidly connected to a supply device 7, 7', 7 "in cold gases, conveying these gases via feed lines corresponding respectively ( Fig. 4 and 5 ).

This installation 2 is characterized in that the feed device is a feed device 1 as described above.

As indicated above, this installation 2 advantageously comprises a transfer rod 12 thermally insulated and preferentially flexible, intended to convey the gases 9 discharged or escaping from the probe 3 to the exchanger (s) additional (s) 8 ', 8 "concerned (s) and connecting the exhaust tube 15 of the probe 3 to the tank 4 of liquid gas 5.

Of course, the invention is not limited to the embodiments described and shown in the accompanying drawings. Modifications are possible, particularly from the point of view of the constitution of the various elements or by substitution of technical equivalents, without departing from the scope of protection of the invention.

Claims (7)

Device for supplying cold gases from an NMR analysis equipment or apparatus equipped with a measuring probe, said cold gases ensuring the cooling of the sample contained in the probe, but also its levitation and its entrainment in rotation,
said feed device (1) essentially comprising an insulated tank (4) containing liquid gas (5) with a boiling temperature and in which are arranged exchangers (6, 6 ', 6 ") traversed by the gas streams to cool, these exchangers being connected to one or more transfer lines (7, 7 ', 7 ") conveying the cooled gases towards the probe,
said device (1) also comprising at least one additional exchanger (8, 8 ', 8 ") ensuring a pre-cooling of the gas flow concerned before it is conveyed to the corresponding exchanger (6, 6', 6"), said or each additional exchanger (8, 8 ', 8 ") in the form of a double flow exchanger,
device (1) characterized in that each exchanger (6, 6 ', 6 ") is associated, upstream with respect to the gaseous flow in question, with an additional pre-cooling exchanger (8, 8', 8"), supplied with either by the gaseous vapor (5 ') produced by the boiling of the liquid gas (5) in the tank (4), or by the cold gas (9) discharged from the probe or escaping at the probe (3) )
in that the additional exchanger (8) providing the precooling of the cold gas for cooling the sample (3 ') is supplied with gaseous vapor (5') produced by the boiling of the liquid gas (5) in the reservoir ( 4) and
in that the additional heat exchangers (8 'and 8 ") for pre-cooling the cold gases intended to respectively provide the lift and the rotation of the sample (3') are fed by the gases (9) discharged or escaping from the level of the probe (3). Device according to claim 1, characterized in that each additional exchanger (8, 8 ', 8 ") is constituted by an arrangement of two concentric ducts or tubes (10, 10'), one of which (10) is traversed by the flow of the gas to be pre-cooled, preferably the inner tube or duct, and the other (10 ') is traversed by the flow of the cooling gas formed by the gaseous vapor (5 ') of boiling the liquid gas (5) of the tank (4) or by the gases (9) evacuated or escaping at the probe (3). Device according to any one of claims 1 and 2, characterized in that each additional exchanger (8, 8 ', 8 ") is a countercurrent or opposite flow exchanger. Device according to any one of claims 1 to 3, characterized in that the three additional exchangers (8, 8 ', 8 ") are grouped into a single structural unit (11), for example in the form of a single coil (11) constituted by an interlace arrangement of three helical tubular formations (10, 10 ') each corresponding to one of the three additional exchangers (8, 8', 8 "). Device according to any one of claims 1 to 4, characterized in that the additional exchangers (8, 8 ', 8 "), preferably structurally grouped in a single unit (11) housed in an isolated housing (11'), are at least partially arranged in the upper part (4 ') of the tank (4) enclosing the liquid gas (5) and the exchangers (6, 6', 6 "), advantageously being mounted in a lid (4") closing said tank (4). NMR measuring device, in particular of the LT MAS probe type, in which the probe is fed with cold gases providing the cooling, the levitation and the rotation of the sample, said installation comprising and / or being fluidly connected to a device of supply of cold gases, conveying these gases via respectively corresponding feed lines,
installation (2) characterized in that the feed device is a feed device (1) according to any one of claims 1 to 5. Installation according to claim 6, characterized in that it comprises a transfer rod (12) thermally insulated and preferably flexible, for conveying the gases (9) evacuated or escaping from the probe (3) to the exchanger or exchanger (s) additional (8 ', 8 ") concerned (s) and connecting the exhaust tube (15) of the probe (3) to the tank (4) liquid gas (5).

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