US3827252A

US3827252A - Method of regulation of the frigorific power of a joule-thomson refrigerator and a refrigerator utilizing said method

Info

Publication number: US3827252A
Application number: US00342672A
Authority: US
Inventors: P Chovet; C Rollin; H Galasso; R Prost
Original assignee: Air Liquide SA
Current assignee: Air Liquide SA; LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Priority date: 1972-03-23
Filing date: 1973-03-19
Publication date: 1974-08-06
Anticipated expiration: 1991-08-06
Also published as: JPS4935940A; FR2176544B1; FR2176544A1; DE2314003A1; GB1431333A

Abstract

The invention relates to a method of and apparatus for the regulation of the frigorific power supplied by a refrigerator utilizing the Joule-Thomson expansion of a refrigerant fluid at a temperature below its inversion temperature, in which the flowrate of the expanded refrigerant fluid is automatically regulated in dependence on the frigorific output to be supplied, and is regulated to a value higher than the flow-rate corresponding to the minimum frigorific power to be supplied, under steady operating conditions, by the expansion of said refrigerant fluid, so as to compensate for the thermal losses of said refrigerator under these operating conditions. The refrigerator comprises an expansion device consisting of an expansion orifice, a seating and a needle-valve, one of said two latter elements being fixed and the other movable, and a temperature-responsive detection device forming part of the regulation system and acting on said movable element in dependence on the temperature detected; the regulation may be effected by proportional action or by direct action, in the latter case, the temperature-responsive regulation chamber being constituted by a bellows member containing a charge of heat-expandable fluid.

Description

it States .111 ifi l 19] l10vet et al. 1 Aug. 6, 1974 METHUD Ull REGULATHUN UF THE 3,704,597 12/1972 Nicholas 62/222 FRHGURHq/C PQWER A 3 704,598 12/1972 Campbell 62/514 .lUULE-THOMSON nrrnrernnron AND 4. k j fg lj REFMGERATUR lUTHLllZiNG SAlD l k METHUD Primary Examiner-William J. Wye [75] inventors: Patrice Chovet, Bernin; Claude Attorney, g Firm-Young & p n

Railin, Grenoble; Honore Galasso, Echirolles; Roger Prost, Saint [57] ABSTRACT Egreeve all of France The invention relates to a method of and apparatus for [73] Assignee: lLAir Liquide, Somme A ny the regulation of the frigorific power supplied by a relPour LEtude Er LExploirari deg frigerator utilizing the Joule-Thomson expansion of a Procedes Georges Cla de, Pari refrigerant fluid at a temperature below its inversion France temperature, in which the flow-rate of the expanded refrigerant fluid is automatically re ulated in de en- [221 1973 dence on the frigorific output to bf supplied, an d is [21] Appl. No.; 342,672 regulated to a value higher than. the flow-rate corresponding to the minimum frigorific power to be supplied, under steady operating conditions, by the ex [30] Fmrelgn Apphcatwn Pnomy Data pansion of said refrigerant fluid, so as to compensate 1972 France 7210139 for the thermal losses of said refrigerator under these operating conditions. The refrigerator comprises an U-S- 14, expansion device consisting of an expansion rifice a 62/223 seating and a needle-valve, one of said two latter elellnt- Cl. 1 ments being fixed and the other movable and a Field 01fSearch 222, 1 56 temperature-responsive detection. device forming part of the regulation system and acting on said movable 1 References Cited element in dependence on the temperature detected; UNITED STATES PATENTS the regulation may be effected by proportional action 3,055,192 9/1962 Dennis 62/514 of y dirfict action, in the latter Case, the temperature 3 32 755 5 9 7 je 2 5 responsive regulation chamber being constituted by a 3.451730 7/1969 Berry 62/514 bellows member containing a charge of heat- 3,517,525 6/1970 Campbell 1. 62/514 expandable fluid. 3,590,597 7/1971 Campbell 62/514 3,640,091 2/1972 Buller 62 514 9 Clams, 7 Drawmg Figures PATENIEU AUG 6 I974 SHEET 1 OF 3 FIG.]

PATENTEB 3.827. 252

SHEET 2 OF 3 m2 F/G-J METIIUI) F REGULATION OF THE FRIGORIFIC POWER OF A JUIJLlE-TIIOMSUN REFRIGERATOR AND A REFRIGERATUR UTILIZING SAID METIIUD The present invention relates to a method of regulation of the effective refrigerating power delivered by a refrigerator utilizing the Joule-Thomson expansion of a refrigerant fluid from a high pressure to a low pressure, the said fluid being at a temperature lower than its inversion temperature. The invention is also con cerned with a Joule-Thomson refrigerator enabling the method of regulation forming the object of the invention to be carried into effect.

Refrigerators of the Joule-Thomson type have been employed for several years in various applications, especially in maintaining cold for devices detecting electro-magnetic radiation.

A refrigerator of this kind comprises a heat exchanger including a first passage for the refrigerant fluid under high pressure, and a second passage for the said fluid under low pressure, in heat-exchange relation with each other; an expansion member, the upstream side of which communicates with the first passage; a chamber for the refrigerant fluid under low pressure, communicating with the downstream side of the expansion member and the second passage.

When a refrigerator of this type is utilized in keeping cold a device for detecting electromagnetic radiation, this latter is generally arranged on the outside of the chamber under low pressure of the refrigerator, in thermal contact with the metal wall of this latter facing the expansion member along the mean direction of ejection of the refrigerant fluid.

When a refrigerator of this type is working in steady conditions, that is to say when the level of temperatures which can be reached by the refrigerant fluid at low pressure in the expansion chamber of the said refrigerator, remains substantially constant and equal to a cold reference temperature, substantially equal to the boiling point of the refrigerant fluid at the low pressure, there is thus produced by Joule-Thomson expansion of the refrigerant fluid at a temperature lower than its inversion temperature, a refrigeration power at least necessary to compensate the calorific power injected into the refrigerator, resulting in particular from the heat losses of the refrigerator under continuous working conditions, that is to say heat leakages towards the interior of the refrigerator, and eventually resulting from heat given off by a thermal load (a detector of electromagnetic radiation for example) in heat-exchange relation with the refrigerant fluid at low pressure.

Usually, the refrigerant fluid in the gaseous state and at high pressure is cooled and at least partly liquefied by the Joule-Thomson expansion. There is thus obtained in the expansion chamber of the refrigerator, at low pressure, a liquid phase and a gaseous phase of the refrigerant fluid, distinct and separated from each other, or mixed together in a homogeneous orheterogeneous manner, depending on the position of the refrigerator or its conditions of operation. The thermal load is then maintained at a cold temperature level, substantially equal to the boiling point of the refrigerant fluid at low pressure.

However, in steady working conditions, it is generally impossible to maintain the effective frigorific power at a nominal value, due to the following disturbances in the operation of the refrigerator:

1. The calorific power injected into the refrigerator may vary within certain limits, independently ofthe expanded flow-rate. This may be due to an intermittent evolution of heat from the thermal load to be cooled, or to variations of the surrounding temperature, external to the refrigerator.

2. Certain impurities of the refrigerant fluid utilized may be condensed at the level of the expansion de vice, thus causing an obstruction of this latter and resulting in a reduction of the frigorific power delivered.

3. In the case where the refrigerator is supplied with refrigerant fluid from a gaseous source of constant volume under high pressure, for a substantially constant low pressure (atmospheric pressure for example) at the beginning of the stable operating period, the frigorific power delivered is greater than the nominal frigorific power, by reason of the very high pressure, whereas at the end of the stable operating period the frigorific power delivered is lower than the nominal frigorific power due to the lower high pressure. In this case, for the high pressures, refrigerant fluid is therefore wasted and the autonomy of the refrigerator is correspondingly reduced for a gaseous source of given volume.

For all these reasons, it appears necessary to regulate the useful frigorific power delivered by the refrigerator under stable conditions, in order to maintain this latter at its nominal value. For that purpose, by means of an appropriate regulation system, it is chosen to adjust automatically the flow-rate of the expanded refrigerant fluid.

In a similar manner, under the transient conditions of starting-up or stopping of the refrigerator, with the same system of regulation, it is possible to vary automatically the frigorific power delivered between the nominal power of the stable period and an initial frigorific power greater than the said nominal power, corresponding to the power delivered during the starting-up of the refrigerator.

In the cases where the Joule-Thomson refrigerator employed is regulated, the expansion device is capable in addition of adjusting the flow-rate of the refrigerant fluid and is provided for that purpose with a seating having an expansion orifice and a needlevalve defining, with the said orifice, an adjustable expansion passage for the refrigerant fluid, one of these two members being movable with respect to the other which is fixed. The system of regulation chosen then effects the movement of the moving member of the expansion device in dependence on a detected quantity representing the discrepancy of the useful frigorific power delivered by the refrigerator, with respect to its nominal value.

The regulation systems employed may be of different types:

1. They may be of the indirect action type. For example, the system of regulation comprises a detection element responsive to temperature (for example a thermo-couple), mounted inside the refrigerator, in the expansion chamber of the refrigerant fluid, in heat-exchange relation with the circuit of the refrigerant fluid under low pressure obtained after expansion.

The electricl signal obtained at the output of the thermo-couple, representing the temperature detected depending on the instantaneous useful frigoritic power delivered, is transmitted to a measuring device outside the refrigerator. In this latter, the electric signal transmitted is algebraically added to a reference signal corresponding to the nominal frigorific power in order to obtain an error signal. The error signal thus obtained is transmitted to an electro-pneumatic valve external to the refrigerator and finally operating the displacement of the moving member of the expansion device as a function of the detected temperature.

2. They may also be of the direct action type. In this case, the regulation system is entirely disposed in the refrigerator, and comprises a regulation chamber responsive to temperature, containing a charge of a fluid expandable under the effect of tempera ture, consisting at least partly of a bellows having one extremity fixed while the other movable extremity actuates the displacement of the moving member of the expansion device, in heat exchange relation with the refrigerant fluid at the low pressure.

In these two cases, the position of the moving element of the expansion device is thus adjusted in dependence on the discrepancy of the net delivered frigorific power with respect to its nominal value, and this under the effect of the temperature reached by the detection element responsive to the temperature:

Thermo-couple for an indirect action system;

chamber for a direct-action system, the volume of which varies under the effect of temperature.

In the direct-action regulation systems previously described, the quantity detected by the regulation system is generally a temperature (that reached by the detection element responsive to temperature, for example by the chamber of expandable fluid) depending on the frigorific power of the refrigerator.

In fact, according to the foregoing, it should be noted that under steady working conditions, the detection element is in heat-exchange relation, on the one hand with the expanded refrigerant fluid, that is to say with all or part of the circuit under low pressure of the said fluid from the downstream side of the expansion device (chamber under low pressure and second passage of the exchanger, in the case of the refrigerator previously specified), and on the other hand with the hot part of the refrigerator, in particular by heat conduction.

The result is that the temperature reached by the regulation member corresponds to the equilibrium between the flow of heat reaching the said device from the hot part of the refrigerator, and the flow of cold reaching the said device from the circuit under low pressure of the refrigerant fluid.

Thus, any variation of the frigorific power delivered, or of the calorific power injected, or both, is thus indicated by a variation of the temperature reached by the detection element.

According to a first proposal, in which there is described a Joule-Thomson refrigerator comprising a direct action regulation system as previously described, the chamber containing the sealed charge of fluid expandable under the effect of temperature is entirely enclosed by the bellows, and the moving extremity of this latter actuates the displacement of the seating of the expansion device.

The bellows is capable of being expanded and contracted in a housing substantially isolated from the lowpressure circuit of the expanded refrigerant fluid. In this case, under steady conditions, due to the total inertia of the regulation system (essentially thermal), it is impossible to stabilize the frigorific power delivered at a nominal value.

It is therefore impossible to stabilize the flow-rate at a nominal value corresponding to the nominal useful frigorific power; this flow-rate continually oscillates about this nominal flow-rate between zero flow-rate and a maximum flow, without being damped, which corresponds to a hunting phenomenon. In a corresponding manner, the volume of the bellows oscillates in an insufficiently damped manner between a minimum volume corresponding to a zero useful section of expansion passage and a maximum volume corresponding to a maximum useful section of the said expansion passage. In consequence, according to this proposal, the regulation of the flow-rate of expanded refrigerant fluid is of the on/off type. This has considerable disadvantages.

The expanded flow-rate of refrigerant fluid thus oscillates between a maximum flow-rate and a flow-rate substantially zero. The period of the corresponding oscillations depend on the one hand on the thermal inertia and on the other hand on the mechanical inertia of the regulation system employed. In this connection, it must be observed that the heat exchange rate effected between the refrigerant fluid under low pressure and the sealed charge of expandable fluid, contained in the regulation chamber, is relatively low.

An important part of this exchange is in fact effected between the fluid under low pressure circulating in the cold zone of the second passage under low pressure of the exchanger, and the expandable fluid, through the wall of the bellows housing, the interstitial gaseous atmosphere between this latter and the wall of the bellows and this latter. This contribution to the cold thermal exchange towards the regulation chamber is thus defective, since the interstitial gaseous atmosphere plays in a way the part of a thermal insulation layer. The result is that the period of the oscillations of the expanded flow-rate is relatively long (from one to several minutes).

This means that the flow-rate of refrigerant fluid remains substantially zero during non-negligible periods of time (one to several seconds), corresponding to the troughs of the oscillations of the expanded flow. In consequence, during these periods of time, the temperature reached by the refrigerant fluid under low pressure is capable of increasing substantially with respect to the nominal cold temperature of operation of the refrigerator.

This presents a serious difficulty when these refrigerators are utilized to keep detectors of electromagnetic radiations and especially infra-red detectors in a cold state. In fact, it is known that such detectors have maximum sensitivity and selectivity for a given wave-length over a narrow zone of temperatures. In consequence, any heating during the periods of closure of the expansion device causes the selectivity and the sensitivity of the detectors employed to fall at once.

In a subsequent proposal, there have been described various refrigerators regulated by direct action as previously, which are for example similar to the refrigerator described in the first proposal. For these latter, ac-

cording to this second proposal, the regulation chamber containing the sealed charge of expandable fluid may be entirely defined by the wall of the bellows or partly defined by the wall of the bellows and additionally by the wall of the housing in which the bellows is mounted.

The regulation chamber may further comprise a bulb forming an appendice arranged at least partly beyond the expansion device with respect to the remainder of the chamber. The said chamber may be partly transferred to a hot zone of the refrigerator, in which case another portion remains in a cold zone of this latter in the form of a bulb, or it may be entirely located in a cold zone of the refrigerator.

In all cases, the moving extremity of the bellows actuates the displacement of the moving needle-valve of the expansion device. In operation, in these types of refrigerators, the refrigerant fluid is expanded and condensed and is then separated into a liquid phase collected at the bottom of the chamber at low pressure, and a gaseous phase occupying the remainder of the said chamber, which thus implies operation of the refrigerator in a vertical position, and the production of a level of refrigerant fluid in liquid form.

For the refrigerators described in this second proposal, as distinct from that described in the first proposal, the regulation chamber is always in heatexchange relation directly with the refrigerant fluid at the low pressure. In fact, when due to the construction, it is impossible to arrange the regulation chamber in direct contact with the refrigerant fluid under the low pressure, there are provided in a first case in which the chamber is arranged in a housing separate from the main chamber at low'pressure, communication passages from the said main chamber towards the said chamber, pierced in the wall of the said housing, and in the second case for which the regulation chamber is separate from the main chamber under low pressure, by at least one part of its own wall, a bulb comstituting an appendice of the said chamber, arranged in the lowpressure chamber of the refrigerator.

In this case, as previously there is obtained a hunting phenomenon during regulation. In consequence, it is impossible under steady operation to stabilize the flowrate of the expanded refrigerant fluid at a nominal value corresponding to the nominal useful frigorific power of the refrigerator.

Under the effect of variations in the volume of the regulation chamber, the flow-rate thus oscillates, in an undamped manner, on each side of the nominal flowrate, that is to say between a zero flow-rate and a maximum flow-rate. However, the period of the oscillations is less than the period of the oscillations of the flow-rate obtained for a refrigerator in accordance with the previous proposal. In fact, due to direct heat exchange will all or part of the regulation chamber, the total inertia of the regulation system is smaller.

On the other hand, the amplitude of the oscillations, that is to say the upper limit (maximum flow-rate) of the expanded flow is very large, due to the nature of the expandable fluid chosen for filling the regulation chamber. In fact, according to this second proposal, it is chosen to fill the regulation chamber with a fluid identical with the refrigerant fluid (nitrogen for example) or a fluid such as methane, the boiling point of which at the pressure existing under steady operating conditions in the expansion chamber, is at least equal to the boiling point of the refrigerant fluid at the low pressure of the refrigerator.

The result is that the operation of the regulation chamber can be compared with that of a vapourtension bulb, since the expandable fluid is partly in the condensed form at the nominal temperature of operation of the refrigerator.

According to this second proposal, if the variations of temperature of the regulation capacity correspond well to the variations of useful frigorific power delivered, the quantity detected in order to regulate the frigorific power delivered corresponds in fact to the measurement of the level of the liquid phase of the refrigerant fluid in the chamber under low pressure.

This level varies in the same direction as the frigorific power delivered. In fact, if the operation of refrigerators according to the second proposal is examined, it is found that when the liquid phase of the refrigerant fluid under low pressure is in direct thermal contact with all or part of the regulation chamber, this causes the closure of the expansion device (expanded flow-rate zero), while when the gaseous phase of the refrigerant fluid is in direct thermal contact with all or part of the regulation chamber, this causes the opening of the expansion device (expanded flow-rate maximum).

The heat-exchange coefficients of the regulation chamber'with the liquid pahse and the gaseous phase of the refrigerant fluid being substantially different (in a ratio of for example), it follows that a small variation of the level (quantity detected) corresponds to a very large variation of the volume of the regulation capacity and therefore a very large variation of the expanded flow-rate (regulating quantity). For the same mechanical inertia of the regulation system, due to the great sensitivity of the regulation system, there results a very large maximum flowrate with respect to the previous case.

In conclusion, as compared with the first proposal, a refrigerator according to the second proposal thus has a regulation of the expanded flow-rate of the on/off type characterized by a very short period or a high frequency and oscillations of large amplitude.

Operation of this kind, of a perfectly discontinuous nature, is absolutely unsuitable for obtaining a good thermal efficiency of the exchanger of the refrigerator. Its efficiency is therefore defective, or in other words, in order to obtain the same nominal useful frigorific power, it is necessary to expend rriore refrigerant fluid. In consequence, in the case of a refrigerator associated with a source of gas of given volume, its autonomy is low.

In consequence, none of the regulation systems above referred to appears satisfactory, according to whether the temperature level is detected in the cold zone of the exchanger (first proposal) or the level of refrigerant fluid in the liquid form (second proposal).

The present invention thus proposes to define a new method of regulation of a Joule-Thomson refrigerator which makes it possible to overcome the disadvantages of the regulation systems discussed above. More precisely, the invention proposes to define a method of regulation different from the method of regulation by on/off of the expanded flow-rate, and reducing substantially the oscillations of the expanded flow.

The conception of the system and method of regulation according to the invention, is characterized by the fact that by means of the system of regulation chosen, the flow-rate of the expanded refrigerant fluid is automatically adjusted, above a minimum flow-rate other than zero corresponding to the minimum frigorific power which is to be delivered under steady conditions by the expansion of the refrigerant fluid in order to compensate for the heat losses of the refrigerator under those conditions.

By regulation system there is meant according to the present invention, the regulation systems previously considered, whether they are of the indirect or direct action type, and whether the quantity detected in order to correct the flow-rate of the expanded refrigerant fluid is the level of the refrigerant fluid in the liquid form in the expansion chamber of the refrigerator, or the temperature existing in the cold zone of the exchanger of the refrigerator, or any other significant quantity of the variations of the useful frigorific power delivered.

The heat losses of the refrigerator in steady operation may be easily evaluated by calculation or experiment, for example by filling the expansion chamber with a given quantity of the refrigerant fluid in liquid form and measuring as a function of time the quantity of refrigerant fluid in the gaseous form escaping from the refrigerator.

Starting from these heat losses, knowing the nature of the refrigerant fluid, the high and low pressures of operation of the refrigerator, it is easy to deduce the minimum flow-rate which produces by expansion the frigorific power necessary to compensate for these heat losses. According to the invention, the expanded flowrate is constantly regulated above this rate of flow.

By minimum flow-rate, there is thus meant a flowrate of expanded refrigerant fluid permitting the compensation under steady operation of the heat losses of the refrigerator. This flow-rate does not necessarily remain constant; it is for example capable of varying as a function of variations in the rate of expansion of the refrigerant fluid. Thus, to a reduction of the high pressure there will correspond an increase of the minimum flow-rate. These same remarks are equally valid for the expression nominal flow-rate wherever this term may be employed.

In practice, a system of regulation functioning according to the invention may carry out its action under two conditions of operation:

I. A transient state of starting-up or stopping of the refrigerator, during which the useful frigorific power delivered does not remain constant but on the contrary varies between a nominal useful frigorific power, greater than the minimum frigorific power previously referred to, and an initial useful frigorific power greater than the said nominal frigorific power, corresponding to the frigorific power delivered during the starting-up of the refrigerator.

For this state of operation, the system of regulation adjusts in a corresponding manner the flow-rate of the expanded refrigerant fluid between the minimum flow-rate and an initial flow-rate higher than the minimum flow.

2. A steady operating state during which the useful frigorific power delivered is maintained at a nominal and constant value, higher than the minimum frigorific power. In this case, in a corresponding manner, by means of the system of regulation chosen as a function of the disturbances caused to the operation of the refrigerator (variations of the rate of expansion, etc.), the flow-rate of the expanded refrigerant fluid is regulated above the minimum flow-rate previously defined, so as to maintain the useful frigorific power delivered at its nominal value.

In practice, in the case of a Joule-Thomson refrigerator as previously defined, the minimum flow-rate corresponds to a so-called minimum position of the moving element of the expansion device, in which the total section of passage of the refrigerant fluid through the expansion device is a minimum.

In consequence, with respect to the state of the prior art previously discussed, the regulation of the expanded flow-rate is thus of the all-or-little type. In this way, the disadvantages previously indicated, associated with a regulation of the on/off type are eliminated. Irrespective of the period of the oscillations of the regulated flow-rate, or the amplitude of these oscillations, and whatever may be the conditions of operation of the re frigerator, a minimum frigorific power, guaranteeing the maintenance of the cold reference temperature of the refrigerator is always ensured under steady operating conditions.

When the regulation system as described previously is of the direct action type and comprises for that purpose a regulation chamber responsive to temperature, containing a charge of fluid expandable under the effect of temperature, of which at least a part is in heatexchange relation with the refrigerant fluid at low pressure (preferably with this latter circulating in the cold zone of the second passage of the refrigerator exchanger), the invention has the following preferred procedure. The nature of the expandable fluid is chosen in such manner that this latter remains gaseous at the boiling temperature of the refrigerant fluid at the low pressure. Thus, when the refrigerant fluid is nitrogen, the expandable fluid is chosen from hydrogen, helium, neon, and mixtures of these gases.

In consequence, according to this essential characteristic of the invention, there is utilized as the expandable fluid a gas which is non-condensable at the nominal working temperature of the refrigerator. The regulation chamber then behaves in operation like a gas thermometer and not like a vapour tension bulb, as shown by the state of the art.

It has been discovered according to the invention that by filling the chamber with a permanent gas there is correlatively obtained a linear variation of the displacement of the moving element of the expansion device, as a function of the variation of the temperature reached by the regulation chamber. In consequence, if the useful section of the expansion passage varies linearly as a function of the displacement of the said moving element, the flow-rate of expanded refrigerant fluid becomes proportional to the temperature reached by the regulation chamber. It then becomes possible to carry out under steady working conditions, a regulation of the expanded flow-rate by proportional action. In fact, the correction of the expanded flow is proportional to the difference between the useful frigorific power delivered and the nominal useful frigoriflc power. The position of the moving element of the expansion device is associated step-by-step with the difference to be corrected.

In addition, it must be emphasized that the choice of a gas as the expandable fluid for the regulation chamber makes it possible to reduce substantially the amplitude of the oscillations of the expanded flow-rate. In fact, the regulation chamber has a greater heat inertia than in the case of a filling with a gas-liquid mixture (vapour-tension bulb); the coefficient of internal exchange utilized is lower than in the previous case.

The result is that for the same externalimpulse (instantaneous variation of temperature resulting from an instantaneous variation of frigorific power), the impulse induced in the regulation chamber is not so large as in the previous case. In consequence, for the same mechanical inertia, there results a lower amplitude of the oscillations of the moving element of the expansion device and therefore a smaller amplitude of the oscillations of the expanded flow-rate.

The refrigerators which enable the invention to be carried into effect are similar to those previously described for the first and second proposals.

According to the invention, the total minimum section of the passage through the expansion device, of the first passage of the exchanger towards the expansion chamber, is not zero. It is preferably equal to at least 2 percent of the section of the orifice of the seating of the expansion device. This minimum total section may be represented by a calibrated leakage passage.

According to the invention, the regulation chamber may be formed entirely by the wall of the bellows or partly formed by the wall of this latter and additionally by the wall of the housing in which the bellows is arranged.

The invention will now be described with reference to the accompanying drawings, in which:

FIG. I represents a view in longitudinal section of the cold portion of a Joule-Thomson refrigerator according to the invention;

FIG. 2 represents a view in cross-section taken along the line Il-II of FIG. ll, of the same refrigerator;

FIG. 3 represents a view in crosssection, taken along the line III-III of FIG. I, of the same refrigerator;

FIG. 4- represents diagrammatically the expansion device of the refrigerator shown in FIGS. l to 3, and illustrates a method of regulation of the expanded flow-rate in the said device, according to the invention;

FIG. 5 shows diagrammatically another expansion device according to the invention, and illustrates a method of regulation of the expanded flow-rate according to the invention;

FIG. 6 shows diagrammatically a further expansion device according to the invention, and illustrates a method of regulation of the expanded flow-rate according to the invention;

FIG. 7 shows graphically the variations of the flowrate Q of the refrigerant fluid expanded, as a function of the time t. The curve shown indicates these variations for a refrigerator having its flow-rate regulated according to the invention, as described with reference to FIGS. d to 6.

The Joule-Thomson refrigerator shown in accordance with FIGS. I to 3, comprises a heat-exchanger 1, an expansion device 2, a regulation system 3, arranged in the interior of a heat-insulating wall 4 comprising an internal wall 5 and an external wall 6 between which a vacuum has been created.

The heat-exchanger 1 comprises a tube 50 of great length, arranged in the form of a coil between the cylindrical inner wall 5 and a cylindrical casing 7, and constituting a first passage for a refrigerant fluid under high pressure. The interstitial space 8 comprised between the tube 50, the inner wall 5 and the casing 7, constitutes a second passage for the refrigerant fluid under low pressure, in heat-exchange relation with the first passage 50 specified above.

The expansion device 2, capable of adjusting the flow-rate of the expanded refrigerant fluid, comprises a fixed seating 9 of stainless steel provided with an expansion orifce Ill and a moving needle-valve lltl defining with the said orifice 11, an expansion passage for the refrigerant fluid. The needle-valve It} is constituted by a sapphire stuck on a metal piece. The seating 9 comprises a channel 12, the upstream side of which communicates with the first passage 50 of the exchanger 1, while the downstream side communicates with the expansion orifice ill.

The seating 9 is fixed to a collar 13 by means of a pin M; the collar 13 is itself fixed by welding to one extremity of the cylindrical casing 7. There exists however a certain play between the pin 14 and the seating 9 in order to permit a self-centering action of the needle-valve it) inside the seating 9. The needle-valve 10 is fixed on a perforated plug 15 engaged inside and at one extremity of a movable split tube 16.

The internal space formed by the inner wall 5 is therefore partly occupied by the exchanger l and the expansion device 2. The remaining portion constitutes a chamber 17 for the refrigerant fluid under low pressure, communicating with the downstream side of the expansion orifice Ill and the second passage 8 of the exchanger 1, as previously defined.

A thermal load 18 constituting the sensitive portion of a detector of electro-magnetic radiation is fixed to the exterior of the inner wall 5, in thermal contact with this latter, opposite the expansion device 2, in the mean direction of ejection of the refrigerant fluid out of the expansion orifice Ill.

The direct-action regulation system 3 comprises a regulation chamber 19 sensitive to the temperature, defined by a bellows 20. As will be seen below, in operation this chamber constitutes, as for an indirect action regulation system, the detection element of a temperature representing the useful frigorific power delivered by the refrigerator.

The chamber 119 is in heat-exchange relation, on the one hand with the circuit of the refrigerant fluid under low pressure (chamber 17 and the second passage 8 of the exchanger I), and more particularly with the cold portion of the second passage of the heat-exchanger 2, and on the other hand with the hot part of the refrigerator by thermal conduction.

One extremity of the bellows 2: 1) is fixed and con nected to a cylindrical member 21 arranged inside the casing 5, and the other extremity of which is movable and is connected to a block 22 fixed to the split tube 16. The moving extremity of the bellows 20, rigidily fixed to the block 22, thus controls the movement of the needle-valve 10 of the expansion device 2, through the intermediary of the split tube 16 sliding on each side of the guiding pin 14.

The chamber 19 contains a sealed charge of a fluid expandable under the effect of temperature, introduced into the bellows 20, by means of a tube 23 passing through the member 21. As previously indicated, the nature of this charge is determined in dependence on the refrigerant fluid chosen, on the low-pressure existing in the expansion chamber, in such manner that this charge will remain gaseous during operation.

It is thus a matter of constitutent remaining gaseous at the boiling temperature of the refrigerant fluid under the low pressure. When nitrogen is chosen as the refrigerant fluid, the expandable fluid is chosen from the group consisting of helium, hydrogen, neon, or a mixture of these gases.

The cylindrical casing 7, the collar 3 and the member 21 define a compartment enclosing the bellows 20, substantially insulated from the chamber 17 under low pressure.

It will be noted that the refrigerator which has just been described has the following advantages:

The needle-valve it) and the seating 9 are accurately centered with respect to each other by virtue of the sliding of the split tube 16 on each side of the pin 14;

The robust nature of this refrigerator is ensured, since the working parts of the expansion device 2 (needle-valve l and seating 9) are protected by the split tube 16.

Under steady operating conditions, a suitable refrigerant fluid (nitrogen for example) at a temperature lower than its inversion temperature under high pressure, circulates in the first passage or the conduit 50 of the exchanger 1 and is cooled to a low temperature. It is then expanded at low pressure in the expansion device 2, and the flow-rate of expanded refrigerant fluid delivers the frigorific power necessary to compensate at least for the calorific power injected into the refrigerator.

The refrigerant fluid is at least partly liquefied by expansion from the high pressure to the low pressure, and

there is obtained in the chamber 17 an entirely separate liquid phase and a gaseous phase, or in a homgeneous or heterogenous mixture, depending on the position of the refrigerator or its conditions of operation.

In all these cases, the presence of the refrigerant fluid at low pressure enables a cold reference temperature to be maintained in the chamber 17 which is substantially constant and equal to the boiling point of the refrigerant fluid employed at the said pressure. The charge 18, in heat-exchange relation with the said fluid, is therefore maintained at a substantially constant cold temperature.

The vaporized refrigerant fluid at low pressure then circulates in the second passage 8 of the exchanger 1, in which it is heated by heat-exchange with the refrigerant fluid at high pressure, in course of cooling in the first passage 50.

Under steady operating conditions, the regulation system 3 employed, or more particularly the expandable chamber 19, is subjected on the one hand to an additional supply of heat coming from the hot part of the refrigerator, and on the other hand to a supply of cold coming from the immediate and cold surroundings of the said device, that is to say from the circuit under low pressure of the expanded refrigerant fluid (chamber 17 and second passage 8 of the exchanger 1).

The regulation chamber 19 is therefore brought to an intermediate temperature, higher than the boiling point of the refrigerant fluid at the low pressure, correspond ing to an equilibrium between the calorific and frigorific fluxes which reach the chamber 19. The calorific flux generally remains substantially constant, while on the other hand the frigorific flux varies in dependence on the variations in the liquid-gas proportion of the refrigerant fluid under low pressure, collected in the chamber 17.

The greater the quantity of frigorific power delivered by the Joule-Thomson expansion, the richer becomes the mixture obtained in the chamber 17 in the liquid phase; the greater the quantity of frigorific flux transmitted to the regulation system 3, the greater the fall of temperature in the regulation chamber 19. The variations of the temperature of the said device thus follow the variations of useful frigoriflc power delivered.

As the chamber 19 contains a sealed charge of a gas which is expandable under the effect of temperature, it is therefore possible to effect a direct-action regulation of the useful frigorific power delivered, as a function of the temperature obtained at the level of the regulation system, and more precisely an automatic adjustment of the expanded flow-rate in dependence on the said temperature.

In accordance with the explanation given above, the operation of the regulation capacity as a gas thermometer makes it possible to obtain a linear relation between the temperature detected by the regulation chamber 19 and the displacement of the moving element of the expansion device (needle-valve 10). As by construction there exists a linear relation between this displacement and the flow-rate of expanded refrigerant fluid, there may thus be obtained a servo-control of the useful frigorific power delivered to the temperature detected by the regulation system.

The operation of the regulation system according to the invention is described below with reference to FIGS. 4 to 7.

The minimum frigorific power which is to be delivered under steady operating conditions by the expansion of the refrigerant fluid in order to compensate for the heat losses of the refrigerator under those conditions, is shown by the minimum flow-rate QMIN. This flow-rate is not necessarily constant, as has been previously indicated, especially if the rate of expansion of the refrigerant fluid varies with time. The flow-rate QMIN corresponds to the minimum position 24 of the needlevalve 10 (see FIG. 4), in which the total section of passage of the refrigerant fluid through the expansion device is a minimum but not zero.

From the instant 0 to the instant T, the refrigerator according to the invention is working under the transient conditions of starting-up. During the time T, by means of the regulation system utilized, the useful frigorific power delivered varies automatically from an initial useful frigorific power delivered by the intitial flowrate QI, greater than the minimum frigorific power delivered by the flow-rate QMIN, to the nominal useful frigorific power of the refrigerator, delivered by the nominal flow-rate ON.

The initial flow-rate 01 corresponds to the frigorific power delivered during the starting-up of the refrigerator, when the needle-valve 10 is in the intitial position 26 (see FIG. 4), that is to say when this latter liberates the full section of the expansion orifice.

During these transient conditions, the flow-rate of the expanded refrigerant fluid is thus caused to vary automatically between the initial flow-rate 01 for which the temperature of the regulation chamber 19 is the ambient temperature, and the nominal flow-rate QN for which the regulation chamber is at a temperature close to but higher than the nominal temperature of operation of the refrigerator (77K for example).

Starting from the instant T, the refrigerator according to the invention operates under steady conditions. From the instantT, the frigorific power delivered is maintained at its nominal value, by virtue of the regula tion system employed. Correspondingly, as a function of the disturbances caused in the operation of the refrigerator (variations of the rate of expansion for exam ple), the flow-rate of expanded refrigerant fluid is automatically adjusted regulated to a nominal value QN greater than the minimum flow-rate QMIN previously defined.

The flow-rate ON corresponds to the nominal position 70 of the needle'valve in which the total nominal section of the expansion passage is greater than the total minimum section of passage previously defined.

Due to the thermal inertia of the regulation system the expanded flow-rate is not stabilized at its nominal value but continually oscillates about that value, that is to say between an upper limit (maximum flow-rate QMAX) and a lower limit. According to the invention, there is chosen as the lower limit of the oscillations of the flow-rate, the minimum flow-rate QMIN previously defined, corresponding to the minimum frigorific power of the refrigerator. In consequence, under continuous steady conditions, the expanded flow-rate is continuously adjusted above this flow-rate QMIN which is a minimum but not zero.

Consequently, according to the invention, the volume of the regulation chamber is automatically regulated under continuous steady conditions and under the effect of the temperature reached by the expandable fluid, in dependence on the frigorific power to be delivered. More precisely, this volume is automatically adjusted between:

A minimum volume corresponding to a minimum temperature reached by the expandable fluid (gas) of the regulation chamber, at least equal to the boiling point of the refrigerant fluid under the low pressure, that is to say, according to the invention, corresponding to the minimum frigorific power previously defined, for which the needle-valve (moving element) of the expansion device 2 is in the minimum position 24 corresponding to a minimum total section of passage of the refrigerant fluid through the expansion device;

a maximum volume corresponding to a maximum temperature reached by the expandable fluid and therefore corresponding to a maximum frigorific power for which the needle-valve 10 of the expan sion device 2 is in the maximum position 25 corresponding to a maximum total section of passage of the refrigerant fluid through the expansion device.

This maximum total section of passage is lower under steady conditions than the initial total section of passage of the refrigerant fluid through the expansion desteady operating conditions, for refrigerators of the state of the art, the nominal frigorific power is maintained at a value substantially equal to the minimum frigorific power contemplated by the present invention.

In consequence, the expanded flow-rate is automatically regulated to a nominal value substantially equal to the minimum flow-rate QMIN shown in FIG. 7. Thus, for a refrigerator prior to the present invention, the flow-rate oscillates continually about the nominal flowrate QMIN, whereas for the refrigerator according to the invention, it oscillates continually about a nominal flow-rate QN greater than the flow-rate QMIN.

It should be noted that the minimum flow-rate QMIN is always greater than the residual! leakage flow e which is substantially zero, resulting from imperfections of construction of the expansion device 2, flowing away when the needle-valve l0 completely closes the expansion orifice 111 in order to annul the useful section of the expansion passage between the needle-valve I0 and the orifice Ill.

It should be observed that according to the invention, the frigorific power delivered is always in excess of the frigorific power strictly required. However, this does not result in a very large excess consumption of refrigerant fluid. In fact, due to the particular selection according to the invention, of the expandable fluid (gas) for the regulation chamber, permitting the amplitude of the oscillations of the expanded flow-rate to be considerably reduced, the nominal flow-rate QN (representing the mean expanded flow-rate) is very little higher than the minimum flow-rate QMIN.

The result according to the invention is to facilitate a very good thermal efficiency of the exchanger of the refrigerator (the expanded flow-rate is not regulated by all-or-nothing) while consuming a. flow-rate of refrigerant fluid which is very close to that of refrigerators of the prior art. In consequence, fora source of refrigerant fluid of a given volume, the autonomy of a Joule- Thomson refrigerator is considerably improved.

According to FIG. 4, the minimum section of passage through the expansion device is substantially equal to the minimum useful section of the expansion passage, existing between the needle-valve l0 and the expansion orifice lll when the needle-valve I0 is in the minimum position 24. The whole of the minimum flow-rate QMIN is thus expanded through the said minimum useful section. In accordance with FIG. 4, it is possible to regulate the value of this minimum useful section and correlatively the value of the maximum useful section corresponding to the maximum flow-rate, in different ways. First of all, it is possible to act at the level of the expansion device by regulating either the position of the needle-valve 10 with respect to its supporting plug 15, or the position of the seating 9. Action can then be taken at the level of the regulation device, either by regulating the position of the fixed extremity of the bellows (part 21), for example from the hot part of the refrigerator, or by regulating the characteristics of the expandable chamber 19.

In this latter case, either the elasticity of the bellows 20 may be suitably chosen (choice of the constituent material and its dimensions), or action may be taken on the characteristics of the sealed charge of the expandable fluid (by choosing for example a suitable filling pressure for the gas chosen as the: expandable fluid).

According to FIGS. and 6, when the needle-valve is in the minimum position 24, the minimum corresponding useful section of the expansion passage is substantially zero. The whole of the minimum flow-rate QMIN is therefore expanded through a calibrated passage 28. The expansion device comprises a calibrated leakage passage 28, located as shown in FIG. 5 in the seating 9 of the expansion device or located, as shown in FIG. 6, in the needle-valve 10 of the expansion device. The section of the leakage passage 28 is substantially equal to the total minimum section previously referred to.

Preferably by construction, the minimum total section previously defined is comprised between 2 and 5% of the section of the expansion orifice 11.

In conclusion, irrespective of the conditions of operation of the refrigerator, it is thus ensured to maintain in the chamber 17 at low pressure, a cold temperature which is substantially constant and equal to the boiling point of the refrigerant fluid utilized, under the low pressure. This is verified whatever the thermal and me: chanical inertia of the regulation system may be, and is therefore irrespective of the period of oscillations of the flow-rate of expanded refrigerant fluid.

What we claim is:

l. A Joule-Thomson refrigerator for the isenthalpic expansion of a refrigerant fluid at a temperature below the inversion temperature thereof, from a high pressure to a low pressure, comprising:

a heat-exchanger including a first passage for said fluid under high pressure, and a second passage for said fluid under low pressure, in heat-exchange relation with one another,

an expansion device to adjust the flow rate of the expanded refrigerant fluid, the upstream side of which is in fluid communication with said first passage, said expansion device comprising a seating having an expansion orifice, and a needle valve defining with said expansion orifice an adjustable expansion passage for said refrigerant fluid, one of said seating and said needle valve being movable in a longitudinal direction while the other remains fixed,

a reception chamber for said refrigerant fluid under low pressure, in fluid communication with the downstream side of said expansion device and with said second passage,

direct-action regulating means comprising a temperature-responsive regulation chamber containing a charge of fluid expandable under the effect of temperature, at least partly in heat-exchange relation with at least part of the low-pressure circuit of said refrigerant fluid, a bellows member comprising at least part of a wall of said chamber and extending in said longitudinal direction, one extremity of which is fixed, whereas the other extremity is movable along said longitudinal direction and actuates the movable element of said expansion device in said longitudinal direction,

said expandable fluid being at least one member selected from the group consisting of hydrogen, helium and neon.

2. A refrigerator according to claim ll, wherein at least one of said regulating means and said expansion means adjusts the total expansion section through said expansion device, from said first passage toward said reception chamber, above a minimum expansion section, different from a substantially zero section.

3. A refrigerator according to claim 2, wherein said expansion section is equal to at least 2 percent of the section of said expansion orifice.

4. A Joule-Thomson refrigerator for the isenthalpic expansion of a refrigerant fluid at a temperature below the inversion temperature thereof, from a high pressure to a low pressure, comprising:

regulating means comprising a temperatureresponsive detection element at least partly in heatexchange relation with at least part of the lowpressure circuit of said refrigerant fluid, for moving the movable element of said expansion device in said longitudinal direction in response to the temperature detected by said detection element,

at least one of said regulating means and said expansion means adjusting the total expansion section through said expansion device, from said first passage toward said reception chamber, above a minimum expansion section, different from a substantially zero section.

5. A refrigerator according to claim 4, wherein said expansion section is equal to at least 2 percent of the section of said expansion orifice.

6. A refrigerator according to claim 4, wherein at least one of said regulating means and said expansion means adjusts the section of said expansion passage above a substantially zero section, and wherein said expansion device comprises a calibrated leakage passage having a section corresponding to said minimum expansion section.

7. A refrigerator according to claim 6, wherein said calibrated leakage passage is located inside said needle valve of the expansion device.

8. A refrigerator according to claim 6, wherein said calibrated leakage passage is located inside said seating of the expansion device.

9. A refrigerator according to claim 4, wherein said at least one of said regulating means and said expansion means adjusts the section of said expansion passage above said minimum expansion section.

Claims

1. A Joule-Thomson refrigerator for the isenthalpic expansion of a refrigerant fluid at a temperature below the inversion temperature thereof, from a high pressure to a low pressure, comprising: a heat-exchanger including a first passage for said fluid under high pressure, and a second passage for said fluid under low pressure, in heat-exchange relation with one another, an expansion device to adjust the flow rate of the expanded refrigerant fluid, the upstream side of which is in fluid communication with said first passage, said expansion device comprising a seating having an expansion orifice, and a needle valve defining with said expansion orifice an adjustable expansion passage for said refrigerant fluid, one of said seating and said needle valve being movable in a longitudinal direction while the other remains fixed, a reception chamber for said refrigerant fluid under low pressure, in fluid communication with the downstream side of said expansion device and with said second passagE, direct-action regulating means comprising a temperatureresponsive regulation chamber containing a charge of fluid expandable under the effect of temperature, at least partly in heat-exchange relation with at least part of the low-pressure circuit of said refrigerant fluid, a bellows member comprising at least part of a wall of said chamber and extending in said longitudinal direction, one extremity of which is fixed, whereas the other extremity is movable along said longitudinal direction and actuates the movable element of said expansion device in said longitudinal direction, said expandable fluid being at least one member selected from the group consisting of hydrogen, helium and neon.

2. A refrigerator according to claim 1, wherein at least one of said regulating means and said expansion means adjusts the total expansion section through said expansion device, from said first passage toward said reception chamber, above a minimum expansion section, different from a substantially zero section.

4. A Joule-Thomson refrigerator for the isenthalpic expansion of a refrigerant fluid at a temperature below the inversion temperature thereof, from a high pressure to a low pressure, comprising: a heat-exchanger including a first passage for said fluid under high pressure, and a second passage for said fluid under low pressure, in heat-exchange relation with one another, an expansion device to adjust the flow rate of the expanded refrigerant fluid, the upstream side of which is in fluid communication with said first passage, said expansion device comprising a seating having an expansion orifice, and a needle valve defining with said expansion orifice an adjustable expansion passage for said refrigerant fluid, one of said seating and said needle valve being movable in a longitudinal direction while the other remains fixed, a reception chamber for said refrigerant fluid under low pressure, in fluid communication with the downstream side of said expansion device and with said second passage, regulating means comprising a temperature-responsive detection element at least partly in heat-exchange relation with at least part of the low-pressure circuit of said refrigerant fluid, for moving the movable element of said expansion device in said longitudinal direction in response to the temperature detected by said detection element, at least one of said regulating means and said expansion means adjusting the total expansion section through said expansion device, from said first passage toward said reception chamber, above a minimum expansion section, different from a substantially zero section.