US3589138A - Device for transporting thermal energy from a lower to higher temperature level - Google Patents

Abstract

A method and apparatus operating with normal and superfluid 4He at temperatures below the -point of liquid helium, for cooling wherein a first superleak through which passes only superfluid 4He, produces a fountain-pump effect which is applied to a second superleak which provides cooling an object within a second enclosure.

Description

United States Patent 1 3,589,138

[72] Inventors Adrianus Petrus Severijns; [50] Field of Search .r 62/467, Frans Adrianus Staas, both of Emrnasingel, 5 14 56 Eindhoven, Netherlands 7 211 Appl. No. 830,068 References Cited [22] Filed June 3, 1969 UNITED STATES PATENTS I 1 Patented 29, 1971 3,195,322 7/1965 London 62/467 [73] Assignce [15. Philips Corporation 33767 12 4/1968 London 62/514 3,472,038 10/1969 Staas 62/467 [32] Priority June 5,1968 I [33] Netherlands Primary Examiner-W 1lha m .lv Wye [31] 6,807,903 A!t0rney-F rank R. Trlfari DEVICE FOR TRANSPORTING THERMAL ENERGY Q A ER To A HIGHER ABSTRACT: A method and apparatus operating with normal E E Y and superfluid He at temperatures below the A-point of liquid rawmg helium, for cooling wherein a first superleak through which .[52] US. Cl 62/56, passes only superfluid "He, produces a fountain-pump effect 62/457, 62/514 which is applied to a second superleak which provides cooling [51] Int. Cl F25d an object within a second enclosure.

IA I4A PATENTEHJUNZQIHH 3.589.138

SHEET 1 OF 2 fig] INVENTORS ADRIANUS P. SEVERIJNS FRANS A STAAS BY Jam/e a 1T AGE PATENTEUJUNZYQIQ?! 3.589.138

SHEET 2 CF 2 INVENTOR ADRIANUS P. SEVERUNS FRANS A. STAAS iiwa If- AGENT DEVICE FOR TRANSPORTTM; THERMAL ENERGY FROM A LOWER TO A HIGHER TEMPERATURE LEVEL This invention relates to a device for transporting thermal energy from a lower to a higher temperature level. In a prior art device the two temperature levels lie below the temperature of the )t-point of helium and the device comprises a circu lating duct which is filled with He, and in which at least one material mass is situated having the property that normal "He cannot pass said mass and superfluid He can pass said mass without turbulence occurring during the flow. This material mass extends over a part of the circulation duct and fully covers the passage thereof. The circulation duct further comprises a pump which during operation can maintain a pressure difference across the said material mass. The material mass and at least the part of the circulating duct situated on the lower pressure side of said mass are thermally insulating, and the part of the circulation duct which communicates with the higher pressure side of the said material mass is in thermal contact with a cooler, for example, a helium bath, having a temperature which is lower than that of the A-point of He. The dimensions of the passage in the circulation duct and the pump are chosen such that the helium therein exceeds its criti cal speed and turbulence occur.

In the following description the material mass having the property substantially bars passage of normal "He and permits passage of only the superfluid He without turbulence occuring during said flow will be referred to as superleak."

In this known device a continuous cooling process is obtained in that turbulence occurs in the circulation duct. Actually it holds according to Landau for a duct comprising helium at a temperature below the h-point, that a driving force 66;). on said helium satisfies the relation where Ap pressure difference across the duct.

p the density of the helium.

S= the entropy of the helium and AT= the temperature difference between the two sides of the duct.

Further data about this can be found in Fluid Mechanics" L.D. Landau and E.M. Lifshitz Pergamon Press 1959, and in Quantam Fluids D.F. Brewer Proceedings of the Sussex University Symposium l620 Aug. 1965. Furthermore, according to Anderson, Au=hn where h is Planck's constant and n is the number of quanticized turbulence in the superfluid which are formed at the wall of the duct.

During starting the known device, a driving force A t is exerted on the medium in the circulation duct due to the action of the pump. At that instant, the temperature in the device still is the same everywhere, so AT=0. This means that the said An according to the above formula is translated in a pressure difference Ap across the part of the circulation duct which com municates with the suction side of the pump (since no turbulence can occur in the superleak, Ap. across the superlealt will be zero). As a result of this pressure difference, normal helium will flow through said part of the duct to the pump. With this flow of normal helium a stream of thermal energy is also obtained from one side of the superleak to the pump and the cooler. As a result of this a temperature difference AT is formed across the superleak which has for its result that the pressure difference Ap across the part of the duct communicating with the suction side of the pump becomes smaller. Across the superleak a pressure difference will start prevailing, in which because no turbulence occurs in the superleak, Ap=P AT.

[n this manner a simple device is obtained to produce cold at a lower temperature starting from a temperature which lies below the h-point of helium. In this device a pump is required for creating the driving force Au. This pump may be, for example, a centrifugal pump or a piston pump. No temperature difference occurs across said pump, so AT=0, and hence A t= Ap/p. A difficulty is that this pump operates at temperatures in the proximity of l K. which, of course, involves structural problems. Furthermore such a pump should be coupled to a driving device which operates at room temperature. Through the coupling, thermal energy will flow towards the pump, which energy is dissipated in that a quantity of liquid helium evaporates from the helium bath surrounding the pump. So this means a loss.

it is the object of the invention to provide a device of the above-described type having a better action and a simpler construction than that of the prior art device, in which the pump operates according to the principle of the fountain ef feet. The device according to the invention is characterized in that both temperature levels lie below the temperature of the A-point of helium and the device comprises a circulation duct which during operation of the device is filled with He, The duct is constructed from a first superleak which communicates at one end with a supply of He at a temperature which lies below the )i-point and communicates at its other end with a first space in which thermal energy can be supplied to the helium; this space communicates, through a first duct and a cooler in which thermal energy can be withdrawn from the helium at a temperature which lies below the )t-point, with a second superleak which at its other end is bounded by a second space in which thermal energy can be supplied to the helium and with which space a second duct communicates A heating device with which thermal energy can be supplied to the helium at a temperature higher than that which prevails during operation in the cooler is disposed in the first and/or second space, the first and the second duct being proportioned so that during operation the medium therein exceeds its critical speed and turbulence occurs, the device being thermally insulated.

in this manner a device is obtained :in which by supplying thermal energy to the He in the first or second space at a higher temperature than prevails in the cooler, a fountain pump effect occurs across the first and the second superleak, respectively, so that a driving force Au. on the helium in the circulation duct is obtained. This means, as already explained above, that in this case a pressure difference and a temperature difference are obtained across the other superleak. When, for example, thermal energy is supplied in the second space at the higher temperature, the fountain pump effect occurs across the second superleak, while a pressure difference and temperature difference are obtained across the first superleak, as a result of which a lower temperature prevails in the first space. At this lower temperature an object can be cooled which hence supplies thermal energy at this lower temperature to the helium. Since as a result of the pressure difference across the first duct, both superfluid and normal helium will flow through it, the thermal energy supplied to the first space will be transferred to the cooler with this normal helium. 0n the other hand it is also possible to supply thermal energy at a higher temperature in the first space, a fountain pump effect occurring across the first superleak and a pressure difference and temperature difference being obtained across the second superleak, which results in the production of cold at a lower temperature in the second space.

In this manner a device is obtained having one or two pumps without moving components which are connected to a motor which is at room temperature. The heating devices may comprise, for example, a small electric heating coil which communicates with the atmosphere through two thin wires so that inleak of thermal energy by conduction will be small. It is alter natively possible to construct the heating devices in the form of a plate or rod of readily conducting material which can be made to communicate with the atmosphere through a thermal conductor. In this manner a refrigerator is obtained in which by supplying thermal energy to one heating device cold is produced at a low temperature at another location, in which heating can be carried out optionally in the first or the second space and hence the cold can also be obtained optionally in the second or the first space.

1 duct empty outside said vacuum space and in which the vacuum space, with the device accommodated therein, can be immersed in a bath containing liquid die at a temperature which lies below the A-point, the cooler being in a heat con ducting contact with the liquid He bath.

A further favourable embodiment of the device according to the invention is characterized in that the side of the second duct remote from the second space communicates, through a further cooler in which thermal energy can be withdrawn from the helium at a temperature which lies below the A point, with one side of the first superleak. In this embodiment the device is constituted by a closed circulation duct having two superleaks, two spaces and two coolers. This assembly according to a further embodiment may be accommodated in a vacuum space which can be immersed in a bath containing liquid helium at a temperature below the A-point, the two coolers being in thermal contact with the helium bath.

In order that the invention may be readily carried into effect, two embodiments of devices for transporting thermal energy between two temperature levels lying below the A- point of helium will now be described in greater detail, by way of example, with reference to the diagrammatic FIGS. 1 and 2, which are not drawn to scale.

FIG. 1 is an elevation view in section of an apparatus according to the present invention.

FIG. 2 is a view similar to FIG. 1 of another embodiment of the invention.

The device shown in FIG. ll comprises a duct 1 in which a first superleak 2 is accommodated. At its upper side the duct 1 is in open communication with a liquid helium bath 3 which is arranged in a Dewar vessel 4. By drawing off the vapor above the helium bath 3 by means ofa vacuum pump indicated by l- A, the temperature of the helium bath 3 is kept lower than the temperature of the A-point. The temperature of the helium bath 3 may be, for example l.3 K. At its other end the duct 1 opens into a space 5 in which an object 6 to be cooled is arranged. A first duct 7 communicates with the first space 5 and at its other end communicates with a second superleak 9 through a cooler 8. The superleak 9 is bounded at its other end by a second space 10. The space Ml communicates with a second duct 12, which opens into the helium bath 3. An electric heating device 11 is arranged in the space lltl and is connected to a current source not shown through current supply wires 13. The superleak 2, space 5, duct 7, cooler 8, superleak 9, space and duct 12 are arranged in a vacuum space 14 which communicates, through duct l5, with a vacuum pump indicated by M-A which maintains the vacuum. Furthermore, the heating device 11' may be arranged in the space 5, while in the space 10 an object 6 to be cooled may also be present.

The operation of this device is as follows: By supplying current to the heating device 11, the temperature in the space 10 will become slightly higher than the lower side of the superleak 9 in the cooler 8, where the temperature (l.3 K.) of the helium bath 3 prevails. On the assumption that in the cooler 8 a temperature T and pressure p,, prevail and in the space MD a temperature T,,+AT is effected. a pressure ,,+A will adjust in the space 11 in accordance with the formula Ap.=Ap/p-5 AT and as a result of the fact that Au,- across the superleak 9 is zero. the pressure difference across the superleak being The driving force on the helium in the second duct l2 now is Ay =66p,Jp+SAT A's a result of the fact that turbulence occurs in the second duct 12, Ap, =O. Since the second duct 12 on its side remote from space It opens into the helium bath, the temperature there will be equal to the temperature T,, in the cooler 8. This means that the temperature difference across the superleak and the temperature difference across the second duct are equal to each other. so AT AT As a result of this Au =A 'lZ/ +A ,-/p or the driving force ofthe pump is A;1.=AP total/P, which is in agreement with the formula of the driving force supplied, for example, by a liquid pump between two equal temperatures.

As a result of the above obtained fountain pump effect, helium is pumped from the cooler 8 to the helium bath 3. This means that a lower pressure will start to prevail in the cooler 8 than in the space 5, so that a pressure difference Ap is obtained across the first duct 7. As a result of this pressure difference, a driving force will be exerted on the medium in said duct, in such manner that superfluid and normal helium flow through the cooler 8. With the normal helium flow, corresponds a flow of thermal energy from space 5 to cooler 8. As a result of this the temperature in the space S will fall. In consequence of this a temperature difference A'I is formed across the superleak 2, which has for its result that a pressure difference will also start to prevail across the said superleak 2, in which again, because no turbulence occurs in the superleak 2, Ap,, SA'l',,. An equilibrium state will adjust in which the driving force on the medium supplied by the pump (superleak 9, space It), heating device 11 and duct I2) is just equal to the driving force necessary to cause the medium to flow through the part of the device (superleak 2, space 5, and duct 7). A lower temperature of, for example, 0.7 K. will start to prevail in the space 5.

An object 6 to be cooled is arranged in the space 5 and will supply thermal energy to the helium at that temperature. This supplied thermal energy will be transferred to the cooler 8 with the flow of normal helium through the duct 7. So in this manner a cooling power for the object 6 is obtained. The cooler 8 is constructed as a part of a duct which, to obtain a large heat-exchanging surface, is filled with a sintering material, for example, copper balls sintered together, the outer wall hereof being in contact with a copper plate 13 which extends in the helium bath with cooling fins. As a result of this the helium which flows from the duct 7 into the cooler 8 is cooled to the temperature of the helium bath 3.

Instead of supplying current to the heating device 11, current may be supplied to the heating device 11 in the space 5, if desirable. The result of this is that now a fountain pump effeet will occur across the superleak 2, in which the pressure in the space 5 will be higher than in the cooler 8. The helium then flows from the space 5 through the duct 7 to the cooler 8, in which it is cooled to the temperature of the helium bath 3. In the same manner as described above, a pressure difference and temperature difference will be obtained across the superleak 9, while a pressure difference exists across the duct 12 which causes the medium to flow from the space 10 to the helium bath. with the resulting flow of normal helium, thermal energy will be dissipated to the helium bath from the reservoir 10 which is at a low temperature. Cold is then produced in the space 10 at, for example, 0.7K. This production of cold can be used to cool, for example, an object 6'. So in this manner a refrigerator for extremely low temperatures is obtained in which by supplying thermal energy at one place a production of cold is obtained at another place.

FIG. 2 shows an embodiment of the device which differs slightly from that shown in FIG. 1. In this embodiment the first superleak 2, the first space 5, the first duct 7, the cooler 8, the second superleak 9 and the second duct 12 are constructed in the same manner and connected together in the same manner as in the device shown in FIG. 1. Only in this case the end of the duct 12 remote from the space It) communicates, through a duct 17 and a further cooler 18, to the side of the superleak 2 remote from the space 5. The duct 17 and the cooler 18 which is constructed as a fin cooler, are arranged outside the vacuum space in contact with the helium bath 3. So in this manner a closed circulation duct is obtained which is filled with He. The operation of this device is quite similar to that of the device shown in FIG. 1.

It will be obvious that, structurally, a large number of variations not shown are possible while maintaining the principle on which the invention is based, namely the creation ofa pressure difference across a first superleak by applying a temperature difference across a second superleak and the intercommunication through ducts which are proportioned so that the superfluid therein exceeds its critical speed.

We claim:

l. A device for transporting thermal energy from a lower to a higher temperature level, characterized in that both temperature levels lie below the temperature of the )t-point of helium and the device is operable with a supply of He at below the )\-point thereof, the device comprising a circulation duct including a first superleak having one end in communication with the supply of He at a temperature which lies below the A-point and its remote end in communication with the first space for cooling, said space communicates, through a first duct and a cooler in which thermal energy can be withdrawn from the helium at a temperature which lies below the )t-point, with a second superleak which at its remote end is bounded by a second space in which thermal energy can be supplied to the helium and with which space a second duct communicates, a heating device being arranged in the second space, with which thermal energy can be supplied to the helium at a temperature which is higher than that which prevails in the cooler during operation, the first and the second duct being proportioned so that during operation the medium therein exceeds its critical speed and turbulence occurs, the device being thermally insulated.

2. Apparatus for producing cold to cool an object, the cold produced in a temperature range where both the high and low temperature levels are below the A-point of liquid helium, the device operable with a supply of liquid helium maintained at a temperature below the A-point thereof whereby said liquid is fonned into a mixture of normal He and superfluid He, the device comprising:

a. a first superleak through which passes only superfluid He from said liquid helium supply,

b. a first enclosure defining a first space in which said object to be cooled is disposable, and into which said superfluid He from the superleak is flowable to transfer cold to said object, and wherein said superfluid He then becomes a mixture of normal He and superfluid He,

C. a cooler for receiving said mixture from the first space and the withdrawing thermal energy from said mixture,

d. a second superleak through which superfluid He is flowable from the cooler,

e. a second enclosure defining a second space into which superfluid He from the second superleak is flowable,

f. heating means in the second space for supplying thermal energy at a temperature higher than that in the cooler, for establishing a temperature differential across said second superleak, and

g. a discharge duct from said second space to the liquid heli um supply, whereby, the thermal energy supplied in the second space results in a fluid flow of superfluid He through the second superleak and a fountain pump effect to flow superfluid He through the first superleak to the first space for cooling the object therein.

3. Apparatus according to claim 2 further comprising a first duct connecting the first space and the cooler wherein said discharge and first ducts have internal dimensions proportioned such that the liquid flow therein will be turbulent.

4. Apparatus according to claim 2 further comprising a vacuum-chamber containing said first. and second superleaks, said first and second spaces, said heating means and said cooler means.

5. Apparatus according to claim 4 further comprising a reservoir of liquid He at a temperature below the )\-point thereof, the vacuum-chamber being immersed in said reservoir liquid.

6. Apparatus according to claim 5, further comprising vacuum pump means for establishing a partial vacuum in said reservoir of liquid He.

7. A method of cooling an object with a circulation duct including sequentially a first superleak, a first space in which an object to be cooled is disposable, a cooler, a second superleak, and a second space comprising the steps:

a. cooling a mixture of liquid helium into components of normal He and superfluid He,

b. heating the second space and thereby establishing a temperature differential across the second superleak, c. maintaining the temperature differential across said second superleak by cooling said cooler at the remote end of the second superleak, thereby causing superfluid He to flow through said second superleak, said flow establishing a fountain pumping effect on liquid in the first superleak,

d. flowing only the superfluid He through the first superleak and thus separating superfluid He from normal He,

e. flowing the superfluid He from the first superleak into a first space,

. cooling an object in said first space by transferring thermal energy from said object to said superfluid He, the su perfluid He by absorbing thermal energy then becoming a mixture with normal He, and

g. flowing said mixture to a cooler and cooling same, with superfluid He from said cooler then being flowed through said second superleak.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. LESLlBB Dated June 29, 1971 ADRIANUS P. SEVERIJ'NS ET AL Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

(301. 1, line 33, "66 should be A Col. 2, line 27, after "communicates" insert Col. 3, line 65, "66p should be A p IN THE CLAIMS Claim 2, line 15, "C. should be c.

Signed and sealed this 19th day of December 1972.

(SEAL) ttest:

EDWARD M.FLEI'CI-IER, JR ROBERT GOTI'SCHALK Attesting Officer Commissioner of Patents FORM PO-IOSO (10-69) sco M DC 0376 P6g 1! US GOVERNMENT PRINTING OFFICE IID 0-305-334.

Claims (7)

1. A device for transporting thermal energy from a lower to a higher temperature level, characterized in that both temperature levels lie below the temperature of the lambda -point of helium and the device is operable with a supply of 4He at below the lambda -point thereof, the device comprising a circulation duct including a first superleak having one end in communication with the supply of 4He at a temperature which lies below the lambda point and its remote end in communication with the first space for cooling, said space communicates, through a first duct and a cooler in which thermal energy can be withdrawn from the helium at a temperature which lies below the lambda -point, with a second superleak which at its remote end is bounded by a second space in which thermal energy can be supplied to the helium and with which space a second duct communicates, a heating device being arranged in the second space, with which thermal energy can be supplied to the helium at a temperature which is higher than that which prevails in the cooler during operation, the first and the second duct being proportioned so that during operation the medium therein exceeds its critical speed and Turbulence occurs, the device being thermally insulated.

2. Apparatus for producing cold to cool an object, the cold produced in a temperature range where both the high and low temperature levels are below the lambda -point of liquid helium, the device operable with a supply of liquid helium maintained at a temperature below the lambda -point thereof whereby said liquid is formed into a mixture of normal 4He and superfluid 4He, the device comprising: a. a first superleak through which passes only superfluid 4He from said liquid helium supply, b. a first enclosure defining a first space in which said object to be cooled is disposable, and into which said superfluid 4He from the superleak is flowable to transfer cold to said object, and wherein said superfluid 4He then becomes a mixture of normal 4He and superfluid 4He, C. a cooler for receiving said mixture from the first space and the withdrawing thermal energy from said mixture, d. a second superleak through which superfluid 4He is flowable from the cooler, e. a second enclosure defining a second space into which superfluid 4He from the second superleak is flowable, f. heating means in the second space for supplying thermal energy at a temperature higher than that in the cooler, for establishing a temperature differential across said second superleak, and g. a discharge duct from said second space to the liquid helium supply, whereby, the thermal energy supplied in the second space results in a fluid flow of superfluid 4He through the second superleak and a fountain pump effect to flow superfluid 4He through the first superleak to the first space for cooling the object therein.

3. Apparatus according to claim 2 further comprising a first duct connecting the first space and the cooler wherein said discharge and first ducts have internal dimensions proportioned such that the liquid flow therein will be turbulent.

4. Apparatus according to claim 2 further comprising a vacuum-chamber containing said first and second superleaks, said first and second spaces, said heating means and said cooler means.

5. Apparatus according to claim 4 further comprising a reservoir of liquid 4He at a temperature below the lambda -point thereof, the vacuum-chamber being immersed in said reservoir liquid.

6. Apparatus according to claim 5, further comprising vacuum pump means for establishing a partial vacuum in said reservoir of liquid 4He.

7. A method of cooling an object with a circulation duct including sequentially a first superleak, a first space in which an object to be cooled is disposable, a cooler, a second superleak, and a second space comprising the steps: a. cooling a mixture of liquid helium into components of normal 4He and superfluid 4He, b. heating the second space and thereby establishing a temperature differential across the second superleak, c. maintaining the temperature differential across said second superleak by cooling said cooler at the remote end of the second superleak, thereby causing superfluid 4He to flow through said second superleak, said flow establishing a fountain pumping effect on liquid in the first superleak, d. flowing only the superfluid 4He through the first superleak and thus separating superfluid 4He from normal 4He, e. flowing the superfluid 4He from the first superleak into a first space, f. cooling an object in said first space by transferring thermal energy from said object to said superfluid 4He, the superfluid 4He by absorbing thermal energy then becoming a mixture with normal 4He, and g. flowing said mixture to a cooler and cooling same, with superfluid 4He from said cooler then being flowed through said second superleak.

Images