US3908397A - Cooling system - Google Patents

Abstract

A cooling system including a cooling element placed in the space to be cooled and provided with a blocking device comprising a restriction for blocking the flow of cooling fluid through the cooling element in the case of an intolerable temperature rise in said cooled space.

Description

United States Patent [191 Prast et al.

[4 1 Sept. 30, 1975 COOLING SYSTEM [75] Inventors: Gijsbert Prast; Jan Mulder, both of Emmasingel, Eindhoven, Netherlands [73] Assignee: U.S. Philips Corporation, New

York, N.Y.

[22] Filed: Mar. 27, 1974 [211 App]. No.: 455,399

[30] Foreign Application Priority Data Apr. 9. 1973 Netherlands 7304884 [52] US. Cl. 62/514; 62/200; 62/525 [51] Int. Cl. F25B 19/00 [58] Field of Search 62/115, 200, 467, 498, 62/514, 525

[56] References Cited UNITED STATES PATENTS 350.896 l 1/1967 Hamish 62/200 Primary E.\'aminerWilliam F. ODea Assistant E.\'aminerRonald C. Capossela Attornqv. Agent, or F inn-Frank R. Trifari 5 7 1 ABSTRACT A cooling system including a cooling element placed in the space to be cooled and provided with a blocking device comprising a restriction for blocking the flow of cooling fluid through the cooling element in the case of an intolerable temperature rise in said cooled space.

7 Claims, 2 Drawing Figures COOLING SYSTEM BACKGROUND OF THE INVENTION The invention relates to a cooling system for cooling to a lower temperature at least one space which is closed in operation. The system comprises at least one cooling element which' is placed in said space and through which a cooling fluid can flow, and the inlet of which is connected to a fluid supply pipe passed through a wall of the space, while the outlet is connected to a fluid discharge pipe passed through a wall of the space.

Cooling systems of the type referred to are described in British Pat. No. 521,792 and in US. Pat. No. 2,753,691, FIG. 4. In these known cooling systems the cooling elements are in the form of cooling coils placed in storage containers for liquefied gas. The cooling coils by recondensing liquid vaporized by heat leakage into the container or by direct cooling of the liquid, prevent the pressure in the storage containers from exceeding a given value.

The known cooling systems have a disadvantage which manifests itself in the case of increased heat flow from the ambient atmosphere into the cooled container as a result of leakage, for example when the evacuated sheath of the container has leaks due to mechanical shock or vibration. The increased heat leakage results in a substantial rise of the temperature in the container so that the cooling fluid flowing through the cooling coil is heated. This means that a considerable part of the available cooling power is wasted.

In addition, the heat leaking into the container spreads to the remainder of the cooling system. When the system comprises further containers equipped with cooling elements, cooling of these containers also is jeopardized.

The rise in temperature in the leaking container is accompanied by a rise in pressure. In cooling systems in which the amount of cooling fluid supplied to the cooling coil is regulated in accordance with the pressure prevailing in the container, leakage even involves additional losses of cooling power. This state of affairs is not improved by a vent valve opening at a given maximum pressure.

It is an object of the present invention to provide a cooling system of the type referred to in which the said above-described disadvantage is avoided.

SUMMARY OF THE INVENTION A cooling system according to the invention is characterized in that a blocking device is provided which completely or partly blocks the flow of fluid to the cooling element in response to an intolerable rise in temperature of the cooled space.

This ensures that in the case of heat leakage into the cooled space, which shows itself by a considerable rise in temperature, the supply of cooling fluid is completely or partly blocked. Thus substantially no cooling power is wasted, and further cooled spaces which form part of the cooling system are unaffected by the leakage.

The blocking device may be a temperature sensor which is placed in the space to be cooled and operates a valve in the fluid supply pipe. However, moving parts are involved, which increases the complexity of the system.

Especially in systems which are required to operate unattended for comparatively long periods of time and hence have to satisfy very exacting reliability requirements, moving parts are undesirable. Moreover they are subject to wear.

These disadvantages are obviated by the invention. Accordingly an advantageous embodiment of the cooling system according to the invention is characterized in that the blocking device comprises a restriction included in the part of the fluid supply pipe situated within the cooled space and by a heat exchanger included on the one hand in the fluid supply pipe on the side of the restriction remote from the cooling element and on the other hand in the fluid discharge pipe.

In normal operation of the cooling system with normal heat leakage, the temperature of the cooling fluid issuing from the cooling element is substantially equal to the temperature at which it enters the element. In this case the heat exchanger in the fluid supply and discharge pipes is passive. When however the cooling fluid is considerably heated in the cooling element owing to heat leakage into the respective container, the cooling fluid flowing towards the cooling element is heated in the heat exchanger by warm cooling fluid flowing from the cooling element, possibly after vaporization. Thus the restriction, primarily because of the reduced density (transition from liquid to gas) or because of the reduced density and the increased viscosity (gas) of the cooling fluid, abruptly offers a flow resistance such to the cooling fluid that substantially no fluid is allowed to pass.

Thus a cooling system is obtained having a blocking device which operates automatically and reliably and comprises no moving parts, and in the case of heat leakage into the cooled container substantially blocks the flow of cooling fluid to this container, with the re sult that substantially no cooling power is wasted and the remainder of the system is unaffected by the heat leakage into the said container.

According to the invention the cooling system in which in operation gaseous cooling fluid is supplied to the fluid supply pipe, is characterized in that the restriction is a laminar restriction.

For a laminar restriction the following formula approximately applies where:

m fluid mass flow through the restriction AP pressure drop across the restriction T= absolute temperature of the fluid at the location of the restriction C constant.

Because AP is determined by the cooling system and may be considered as a constant we have:

where C, is a new constant.

Thus a small rise in temperature of the gas used as a cooling fluid which flows towards the restriction results in a considerable reduction in the gas flow allowed to pass through the restriction. The laminar restriction may for example comprise a system of small-diameter passages.

In the cooling device in which in operation liquid cooling fluid is supplied to the fluid supply pipe, the restriction according to the invention is a turbulent restriction. A turbulent restriction, such as a diaphragm provides the advantage that in general its manufacture is simpler than that of a laminar restriction.

The fact that in the present case, a turbulent restriction is sufficient and hence no costlier laminar restriction is required, is due to the circumstance that owing to the large change in density which occurs at the transition of the cooling fluid from the liquid to the gaseous state as a result of heating in the heat exchanger, the flow resistance of the cooling fluid in the restriction is greatly increased. Consequently the flow of cooling fluid through the restriction is greatly reduced.

The invention will now be explained more fully with reference to the accompanying drawings in which two exemplary embodiments of the cooling system are shown schematically and not to scale.

BRIEF DESCRIPTION OF THE DRAWINGS DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, a Dewar flask 1 contains liquid hydrogen. In a vapor space 2 of the flask a cooling coil 3 is placed, the inlet of which is connected to a supply pipe 4 for cooling fluid andthe outlet of which is connected to a discharge pipe 5. A heat exchanger 6 for heat exchange with the cold head 7 ofa cold gas refrigerator 8 is connected at one end to the supply pipe 4 and at the other end to the discharge pipe 5. Said supply and discharge ducts 4 and have a first part 4a, 5a, respectively extending from the refrigerator 8 to said flask or closed space 1, and a second part 4a, 5a, respectively within said space, with adjacent portions of said second parts forming said heat exchanger. A pumping device 9 connected in the supply pipe 4 serves to circulate the cooling fluid, in this case pressurized gaseous helium.

The part of the supply pipe 4 situated within the vapor space 2 of the Dewar flask 1 includes a laminar restriction 10, while outside the Dewar flask a heat exchanger l 1 is included in the supply pipe 4 and also in the discharge pipe 5. The restriction or first means 10 and the heat exchanger or second means 11 together form a blocking device.

During normal operation the gaseous helium at a pressure of for example 20 atmospheres Which circulates in the pipe system is cooled in the heat exchanger 6 to for example 15 K. In the Dewar flask l the cold gaseous helium just ensures recondensation of hydrogen vaporized by heat leakage. Hence the hydrogen pressure remains at a value below atmospheric pressure. The temperature of the helium gas streams entering and leaving the cooling coil are nearly equal. Hence the temperatures of the two helium gas streams which pass through the heat exchanger 11 are substantially equal also. Thus this heat exchanger 11 plays no active part.

If owing to leakage of the Dewar flask there is increased heat leakage into the system, the temperature in the flask rises and the helium gas is heated in the cooling coil 3.

As a result, in the heat exchanger 11 the hot helium gas issuing from the Dewar flask heats the cold helium stream from the cold head 7. Mainly because of the ensuing increase in viscosity of the helium of the latter current, and to a lesser extent because of the reduced helium density, the laminar restriction 10 allows only a fraction of the initial helium stream to pass. I-Ience substantially no thermal energy is wasted in the Dewar flask l, and at the same time heating of the cold head 7 of the cold gas refrigerator 8 is prevented.

In the system shown in FIG. 2 three Dewar flasks 20, 21 and 22 contain liquid helium. In vapor spaces 23, 24 and 25 respectively of these flasks cooling coils 26, 27 and 28 respectively are placed which via supply pipes 29, 30 and 31 and discharge pipes 32, 33 and 34 respectively are connected in parallel relationship to a common supply pipe 35 and a common discharge pipe 36. Turbulent restrictions 38, 39 and 40 are included in the parts of the supply pipes 29, 30 and 31 situated within the Dewar flasks 20, 21 and 22 respectively. Outside the Dewar flasks heat exchangers 41, 42 and 43 are included in the associated supply and discharge pipes 29, 32; 30, 33; and 31, 34 respectively. Each assembly comprising a restriction and a heat exchanger 38, 41; 39, 42; 40, 43 constitutes a blocking device.

The three turbulent restrictions have substantially equal internal cross-sectional areas so that in normal operation they also ensure that substantially equal cooling fluid streams flow to the cooling coils.

The common discharge pipe 36 opens into a container 45 the vapor space 46 of which communicates via heat exchangers 47, 48 and 49 with the suction inlet 50 of a low-pressure compressor 51 the outlet of which is coupled to the inlet of a high-pressure compressor 52. The outlet 53 of the high-pressure compressor 52 is connected to the common supply pipe 35 via, in the enumerated order, a cooler 54, heat exchangers 49, 55, 48, 56 and 47, a throttle valve 57 and a heat exchanger 58 arranged in the container 45.

A cold source 60 forms part of the heat exchanger 55, and a cold source 61 forms part of the heat exchanger 56. The two cold sources may be the cold areas of a two-stage cold gas refrigerator. The cooling device uses helium as the cooling fluid. In operation gaseous helium is compressed to a high pressure in the compressors 51 and 52 and then supplied via the outlet 53 to the cooler 54 in which the compressed helium gives off the heat of compression. In the heat exchanger 49 the compressed helium then gives off heat to helium at a lower pressure and temperature. In the heat exchanger the high-pressure helium is cooled by the cold source to a temperature of, for example, 60K

'and then in the heat exchanger 48 again gives off heat to helium at a low pressure and temperature. Subsequently in the heat exchanger 56 the compressed helium is cooled further to a temperature of, for example, l5K by the cold source 61. Finally in the heat exchanger 47 the high-pressure helium again gives off hcat to helium at a lower pressure and temperature. The high-pressure helium then enters a throttle valve 57 in which it expands isenthalpically to below the critical pressure of 2.26 atmospheres and to below the critical temperature of 5.3K, so that about 50 percent of the gaseous helium is liquefied. In the heat exchanger 58 the remaining 50 percent of gaseous helium is condensed by the liquid helium in the container 45, so that substantially only liquid helium is supplied to the cooling coils 26, 27 and 28. In these cooling coils about one-half of the helium flowing through them is vaporized. In the container 45 helium in the gaseous state is separated from helium in the liquid state. The 50 percent of liquid helium then are used to condense the 50 percent of gaseous helium in the helium stream from the throttle valve 57. The helium vapor in the container 45 is sucked into the compressor 51.

In the process of cooling the latent heat (heat of evaporation) of the liquid helium is utilized. This means that the temperatures of the two helium streams flowing through each of the heat exchangers 41, 42 and 43 normally are equal, so that these heat exchangers then are passive.

When however heat leakage into one of the Dewar flasks occurs, for example into the middle flask 21, the temperature in it rises. As a result all the liquid helium flowing through the cooling coil 27 evaporates and the resulting helium gas is heated. In the heat exchanger 42 the hot helium gas gives off heat to the liquid helium flowing through the supply pipe 30, so that this liquid helium evaporates. The turbulent restriction 39 then sees gaseous helium instead of liquid helium, the density of this gaseous helium being far less than that of liquid helium. Mainly because of this difference in density the turbulent restriction 39 allows much less helium to pass. Thus very little thermal energy is wasted in the Dewar flask 21, while the Dewar flasks and 22 are not affected by the heating of the leaky Dewar flask 21.

Although the embodiments described relate to the cooling of cryostats filled with liquefied gas, obviously there are many other possible applications, such as the cooling of chambers in freeze-drying systems, the cooling of evacuated spaces in high-vacuum technology or in vapor deposition apparatus, the cooling of deepfreeze containers, and so on.

What is claimed is:

1. In a cooling system operable with a source of cooled fluid for refrigerating a closed space, including a cooling element which is situated in said space and through which said fluid is flowable for refrigerating said space, a supply duct for communicating said fluid from said source to said cooling element, a discharge duct for communicating said fluid from said element to said source, and means for circulating said fluid through said system, the improvement in combination therewith, wherein said supply and discharge ducts each comprise a first part extending from said source to said closed space and a second part within said closed space extending to said cooling element, said first part of said supply and discharge ducts having adjacent portions in heat exchange relationship forming a heat exchanger, the improvement being a blocking device comprising said heat exchanger and a fluid flow restriction means in said second part of the supply duct, whereby a heat leak into said closed space causing a temperature rise therein causes heat transfer into fluid in said cooling element and in said discharge duct, and further heat transfer from fluid in said discharge duct to fluid in said supply duct via said heat exchanger, and wherein said restriction means restricts flow in said supply duct of fluid to which said heat has been added.

2. Apparatus according to claim 1 wherein said restriction means comprises a laminar flow restriction means.

3. Apparatus according to claim 1 wherein said restriction means comprises a turbulent flow restriction means.

4. Apparatus according to claim 1 wherein said source of cooling fluid comprises continuous duct means including as parts thereof said supply and discharge ducts, a quantity of helium in said duct means, and a cold gas refrigerator for cooling said helium in said duct means.

5. Apparatus according to claim 1 wherein said closed space comprises a Dewar flask.

6. In a cooling system operable with a source of fluid for refrigerating a closed space, including a cooling element which is situated in said space whereby said fluid becomes heated and through which said fluid is flowable for refrigerating said space, a supply duct for communicating said fluid from said source to said cooling element, a discharge duct forcommunicating said fluid from said element to said source, and means for circulating said fluid through said system, the improvement in combination therewith, comprising first means in said closed space, and second means for transferring heat from said fluid heated in said cooling element to fluid in said supply duct upstream of said space, said first means operable to restrict flow in the supply duct of said fluid when it has been heated by said second means.

7. Apparatus according to claim 6 wherein said second means comprises a heat exchanger formed of adjacent portions of said discharge and supply ducts whereby heat from said fluid when heated in said cooling element is transferred to fluid in said supply duct, which fluid then becomes less dense and flow thereof is restricted by said first means.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,908,397 Dated Sept. 30, 1975 (S) GIJS BERT PRAST and JAN MULDER It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 3, line 47, after "second part" delete "4a, 5a", and

insert -4b, 5b-

Col. 4, line 53, "In operation gaseous helium" should be a new paragraph Col. 6, lines '34 and 35, after "in said space" delete "whereby said fluid becomes heated" line 36, after "said space" insert -whereby said fluid becomes heated-- Signed and Scaled this A ttes t:

RUTH C. MASON Allesting Officer C. MARSHALL DANN Commissioner ufParents and Trademarks

Claims (7)

1. In a cooling system operable with a source of cooled fluid for refrigerating a closed space, including a cooling element which is situated in said space and through which said fluid is flowable for refrigerating said space, a supply duct for communicating said fluid from said source to said cooling element, a discharge duct for communicating said fluid from said element to said source, and means for circulating said fluid through said system, the improvement in combination therewith, wherein said supply and discharge ducts each comprise a first part extending from said source to said closed space and a second part within said closed space extending to said cooling element, said first part of said supply and discharge ducts having adjacent portions in heat exchange relationship forming a heat exchanger, the improvement being a blocking device comprising said heat exchanger and a fluid flow restriction means in said second part of the supply duct, whereby a heat leak into said closed space causing a temperature rise therein causes heat transfer into fluid in said cooling element and in said discharge duct, and further heat transfer from fluid in said discharge duct to fluid in said supply duct via said heat exchanger, and wherein said restriction means restricts flow in said supply duct of fluid to which said heat has been added.

2. Apparatus according to claim 1 wherein said restriction means comprises a laminar flow restriction means.

3. Apparatus according to claim 1 wherein said restriction means comprises a turbulent flow restriction means.

4. Apparatus according to claim 1 wherein said source of cooling fluid comprises continuous duct means including as parts thereof said supply and discharge ducts, a quantity of helium in said duct means, and a cold gas refrigerator for cooling said helium in said duct means.

5. Apparatus according to claim 1 wherein said closed space comprises a Dewar flask.

6. In a cooling system operable with a source of fluid for refrigerating a closed space, including a cooling element which is situated in said space whereby said fluid becomes heated and through which said fluid is flowable for refrigerating said space, a supply duct for communicating said fluid from said source to said cooling element, a discharge duct for communicating said fluid from said element to said source, and means for circulating said fluid through said system, the improvement in combination therewith, comprising first means in said closed space, and second means for transferring heat from said fluid heat in said cooling element to fluid in said supply duct upstream of said space, said first means operable to restrict flow in the supply duct of said fluid when it has been heated by said second means.

7. Apparatus according to claim 6 wherein said second means comprises a heat exchanger formed of adjacent portions of said discharge and supply ducts whereby heat from said fluid when heated in said cooling element is transferred to fluid in said supply duct, which fluid then becomes less dense and flow thereof is restricted by said first means.

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