US3383872A - Device for producing cold with cold loss prevention means - Google Patents

Description

May 21, 1968 J. w. L. KGHLER DEVICE FOR PRODUCING COLD WITH COLD LOSS PREVENTION MEANS 3 Sheets-Sheet 1 Filed Nov.

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May 21, 1968 J. w. L. KOHLER DEVICE FOR FRODUCING COLD WITH COLD LOSS PREVENTION MEANS Filed Nov. 16, 1966 3 Sheets-Sheet 2 ,as F48 FIGA INVENTOR. JACOB w.:. .KOHLER ZLJVA A2 May 21, 1968 J. w. L. KOHLER 3,383,872

DEVICE FOR PRODUCING COLD WITH COLD LOSS PREVENTION MEANS Filed Nov. 16, 1966 3 Sheets-Sheet 3 a: I: D

1 A l 18 I 3 14 '1 a I I1 1 I li' l I II INVENTOR.

JACOB W.L.K5HLER United States Patent 3,383,872 DEVICE FOR PRODUCING COLD WITH COLD LOSS PREVENTION MEANS Jacob Willem Laurens Kohier, Emmasingel, Eindhoveu, Netherlands, assignor to North American Philips (30., Inc., New York, N.Y., a corporation of Delaware Filed Nov. 16, 1966, Ser. No. 594,745 Claims priority, application Netherlands, Dec. 5, 1965, 6515,725 6 Claims. (Cl. 62--6) ABSTRACT OF THE DISCLOSURE Cold gas refrigerator construction with means to prevent cold to be dissipated to the atmosphere through the walls surrounding a gap between the walls and the adjacent piston. This may be in the form of additional expansion spaces or in a duct system from one refrigerator to another refrigerator.

The invention relates to a device which comprises at least one cylinder having a piston-like member reciprocating therein, said piston-like member being capable of varying the volume of an expansion space in said cylinder, in which space, during operation, an average temperature prevails which is lower than the ambient temperature. Furthremore, a gap is present between said member and a cylinder Wall cooperating therewith and communicating on one side with said space, the said gap being bounded on its side remote from said space by a seal between the piston-like member and the cylinder wall.

Devices of this type are known and may be constructed, for example, as a piston expansion machine in which a high-pressure medium is reduced in pressure at low temperature.

Another example of such a device is a cold gas refrigerator operating according to the Stirling principle. Such a refrigerator comprises one or more compression spaces which have a variable volume and one or more expansion spaces communicating therewith which likewise have :a variable volume and in which, during operation, lower average temperatures prevail than in the said compression spaces. In the communication between each pair of the spaces a regenerator is arranged while for varying the volume of said spaces piston-like members are provided which are movable with a mutual phase difference.

In a further example of a device of the type to which the present invention relates a double-acting piston-like member reciprocates in a closed cylinder. The space on one side of the piston-like member has a lower average temperature than the space on the other side of said member. These two spaces communicate with one another through a regenerator in which the space which is at a higher temperature can be made to communicate alternately with a high-pressure container and with a low-pressure container. The communication with the low pressure container is effected when the volume of the coldest space is substantially at a maximum so that therein mainly expansion occurs.

In these machines the piston-like body which can vary the volume of the expansion space in general has thin walls and a rather large height. This is done to insulate the cold expansion space from the space on the other side of the piston-like member. It has the further advantage that the seal between the piston-like member and the cylinder cooperating therewith can be effected at a distance from the cold space and consequently at a higher temperature. At the area of the seal the piston-like member and the cylinder have a difference in diameter which is as small as possible. In known machines it is common 3,383,872 Patented May 21, 1968 practice to make the piston-like member have a somewhat smaller diameter between the working face and the seal than at the area of the seal as a result of which a gapis formed between the cylinder and the piston-like member. This is done because otherwise the possibility exists that, as a result of inaccuracies in the manufacture and tolerances, the long piston-like member binds in the cylinder.

However, in these known machines the drawback occurs that cold produced in the expansion space flows away to the ambient atmosphere through the walls which bound the said gap and through the medium in the gap, which consequently means a loss for the machine. A great drawback is that at the decreasing temperature at which cold must be produced, the production of cold decreases proportionally with the temperature while the said loss of cold increases proportionally with the decreasing temperature. So this loss becomes relatively larger and larger when the temperature at which the cold is produced becomes lower. As a result of the lower temperature, the temperature gradient from the expansion space to the seal becomes larger that a larger loss of cold from the expansion space will occur.

The invention is based on the recognition of the fact that the flow of cold from the expansion space decreases when the temperature gradient is smaller in the axial direction.

In order to realize this the device according to the invention is characterized in that it comprises means for additionally cooling said wall of the piston-like member and/ or the cylinder which bounds the said gap over at least one part of the axial length along the whole circumference.

By this additional cooling the part of the wall in question will have a lower temperature so that the temperaure gradient between said part and the expansion space will be smaller than is the case without this additional cooling. By additionally cooling the walls which bound the gap at several places substantially any desired temperature gradient can be obtained. In this manner loss of cold produced in the expansion phase is minimized. The cold which is lost now is cold which is supplied to the walls of the gap and has been produced at a higher temperature than the temperature prevailing in the expansion space, but with a better efiiciency. As a result of this the device will produce cold with a better total efficiency.

In a favourable embodiment of the device according to the invention the walls of the piston-like member and of the cylinder which bound the gap have stepped constructions in such manner that, viewed in the axial direction, the gap is divided into at least two parts, one part of the gap being located nearer to the coldest expansion space having a smaller diameter than the part of the gap located farther remote from the said space, so that the volume of the space, influenced by the annular surfaces formed as a result of the stepped construction, can vary in phase with the volume of the coldest expansion space. A a result of this, cold is produced in the said spaces, so that the temperature gradient in the gap and its walls will be smaller than in the known refrigerators. The walls of the gap serve as regenerators for medium flowing into and out of the said spaces. In this manner a local cooling of the walls of the gap is obtained with very simple means.

In a further favourable embodiment of the device according to the invention, the wall of the piston-like member and the cylinder which bound the gap have conical constructions at least ever part of their axial length, the smallest diameter of said walls being located in the direction of the coldest expansion space. In this embodiment cold will be produced again in the space which is bounded by the conical walls so that said conical walls are cooled. As a result of this, the temperature gradient in the gap will be decreased.

In a further embodiment of the device according to the invention, one or more places of the wall of the cylinder and/or the piston-like member which also bounds said gap are each in a heatconducting relationship with a source of cold along the whole circumference, each of said sources of cold having a lower temperature than the place communicating therewith so that thermal energy can be withdrawn from these places.

In order that the invention may readily be carried into eifect, it will now be described in greater detail, by way of example, with reference to the accompanying drawings, in which:

FIGURE 1 is a diagrammatic cross-sectional view of a known cold-gas refrigerator.

FIGURE 2 is a diagrammatic cross-sectional view of a cold-gas refrigerator in which the walls of the displacer part, which influences the expansion space with the lowest temperature, and the cylinder cooperating therewith have stepped constructions.

FIGURE 3 is a diagrammatical cross-sectional view of a cold-gas refrigerator in which the walls of the displacer part, which influences the expansion space with the lowest temperature, and a cylinder cooperating therewith have a conical construction.

FIGURE 4 is a diagrammatic view of another coldproducing device in which the piston-like member which can vary the volume of the expansion space as well as the cylinder cooperating therewith have stepped constructions.

FIGURE 5 is a diagrammatic cross-sectional View of a cold-producing device comprising two cold-gas refrigerators which supply their cold at different temperatures and in which the cold part of the refrigerator which supplies its cold at the higher temperature is in a heatconducting relationship with a place of the part of the cylinder wall which cooperates with the last displacer stage.

FIGURE 1 shows a known cold-gas refrigerator which comprises a compression piston 1 which can vary with its working face the volume of a compression space 2. Reference numeral 3 denotes a displacer which consists of two parts 4 and 5 having different diameters. The worxing face of the displacer part 4 can vary the volume of an expansion space 6 while the annular surface 7 can vary the volume of an intermediate expansion space 8. The compression piston 1 and the displacer 3 are connected by means of a piston rod 9 and a displacer rod 10, respectively, to a gear not shown which can move said members with a mutual phase difference.

The compression space 2 communicates, through a cooler 11, a first regenerator 12, and a first freezer 13, with the intermediate expansion space 8. The intermediate expansion space 8 communicates with the expansion space 6 through a second regenerator 14 and a second freezer 15. The displacer part 4 is incorporated with some play in the cylinder part cooperating therewith so that between said displacer part and the cylinder a narrow gap 17 is formed which at its top side is in open communication with the expansion space 6 and is closed at its lower side by the seal 18 arranged on the displacer part 4. Said seal consequently is at a higher temperature than the expansion space 6. The displacer part 5 having the larger diameter is constructed in a corresponding manner.

The operation of this known device is known and will consequently not be described.

During operation, for example, a temperature of 100 K. will prevail in the intermediate expansion space 8 and a temperature of 20 K. will prevail in the expansion space 6. As shown in FIGURE 1, a temperature gradient from 20 to 100 K. will be across the gap 17. As a result of this a quantity of cold will leak away to the intermediate expansion space 8 through the walls which bound the gap 17 and also through the medium in the gap. Considering that the production of cold is proportional to the temperature at which expansion takes place, therefore only a small amount of cold production will be achieved at this low temperature. It will be clear that the loss of cold from said space very adversely influences the production, even in such manner that in circumstances it is impossible to produce cold at the desired low temperature and that it may even be impossible to reach the desired low temperature. This will surely be the case in the machine shown in the drawing, a displacer having a stepped construction but a cylindrical displacer having a uniform diameter is used, the side of which is remote from the space 6 being at room temperature (300 K.).

FIGURE 2 shows a cold-gas refrigerator which in outline corresponds to the cold-gas refrigerator shown in FIGURE 1. The difference between these two refrigerators is that the displacer part 4 and the cooperating cylinder wall have stepped constructions so that annular surfaces 20 and 21 are formed which can vary the volume of the spaces 22 and 23. These spaces communicate with the expansion space 6 through the parts 17 and 17" of the narrow gap. Since the volume variations of the spaces 22 and 23 are in phase with those of the expansion space 6, said spaces also constitute expansion spaces so that cold will be produced therein, the walls of the parts 17' and 17" of the gap serving as regenerators for the medium which flows into and out of the spaces 22 and 23, respectively. As a result of this production of cold, a temperature will prevail in said spaces which is lower than the temperature at the corresponding places in the refrigerator shown in FIGURE 1. The temperature variation of the space 6 (20 K.) to the space 8 K.) is shown in FIGURE 2. From this figure it appears that in the first part the temperature gradient is far less steep than in FIGURE 1. As a result of this the loss of cold from the space 6 is smaller. Naturally, since the temperature difference between the space 22 and the space 8 is large, a considerable transport of cold in the direction of the space will occur there. The resulting lost cold, however, has been produced at a higher emperature (40 K.) and consequently with a better efficiency, so that loss of said cold is less heavy than loss of cold from the space 6. Consequently said cold-gas refrigerator operates with a better efiiciency, that is to say, supplies niore cold at a given temperature or can reach a lower temperature than the known cold-gas refrigerator shown in FIGURE 1.

Instead of giving the displacer part 4 a stepped construction it may also be given a conical construction as shown in the cold-gas refrigerator of FIGURE 3.

In this refrigerator the volume of the space 25 influenced by the conical part of the displacer, will vary in phase with the volume of the space 6, so that the space 25 also is an expansion space. So in this space also cold will be produced but not at the low temperature which prevails in the space 6 but at a higher temperature. The loss of cold from the space 6 will consequently be smaller than in the refrigerator shown in FIGURE 1, while the cold leakage from the space 25 has been produced at a higher temperature and consequently with a better efiiciency.

FIGURE 4 diagrammatically shows a cold-producing device which comprises a double-acting piston-like member 31 reciprocating in a closed cylinder 30. The two spaces 32 and 33 on either side of the piston-like member 31 communicate with one another. In this communication a regenerator 34 is included. The piston-like member 31 is connected to a gear not shown, through a piston rod 35.

A duct 36 and a duct 37 communicate with the space 33. Controllable valves 38 and 39 are included in said ducts. The duct 36 communicates with the inlet of a compression device 42 through a storage container 40 and a heat exchanger 41. The duct 37 commmunicates with the outlet of the compressor 42 through a buffer container 43 and the heat exchanger 41.

This device operates as follows: When the piston 31 is substantially in its lowest position (the volume of the space 33 then is substantially at a maximum) the valve 39 is opened and the whole system is filled with the highpressure medium. In the opened condition of the valve 39 the piston 31 moves upwards. When the piston 31 has reached its uppermost condition (the volume of the space 32 then is at a maximum) the valve 39 is closed and the valve 38 is opened. If desired, the operation in the said manner of the valves is possible during the upward stroke of the piston 31. At the decrease in pressure caused by opening the valve 38, the medium will become colder so that in space 32 a given production of cold is obtained. A very low average temperature, for example, K. will adjust in the space 32. In order to check loss of cold produced in said space, the piston 31 has a stepped construction. As a result of this stepped construction the piston 31 comprises annular surfaces 45 and 46 which vary the volume of the spaces 47 and 48 in the same phase as the volume of the space 32. So these spaces also are expansion spaces so that therein cold is also produced but at a higher temperature and consequently with a better efficiency. So in this device loss of cold from the space 32 will be checked in the same manner as in the cold-gas refrigerator shown in FIGURE 2.

In the devices shown in the above figures, loss of cold from the coldest expansion stage is checked by producing cold at a higher temperature and cooling the walls of the gap with said cold. This additional cold is produced by the machine itself.

Of course, it is alternatively possible to produce said additional cold by means of another refrigerator.

This is diagrammatically shown in FIGURE 5.

This figure shows two cold-gas refrigerators A and B, arranged beside one another. In the expansion space 6 of the refrigerator A cold is produced at a temperature of 20 K. In the expansion space 6 of the refrigerator B cold is produced at a temperature of, for example, K. The 7 cold expansion space 6 of the refrigerator B communicates, through a system of ducts 50 containing a medium, with a place 51 of the cylinder wall which also bounds the gap 17. The said space 51 is chosen to be so that without additional cooling it would have a temperature exceeding 30 K. The medium in the duct system 50 is chosen to be so that at 20 K. it will condense against the walls of the expansion space 6 of the refrigerator B and evaporate at the place 51, thus cooling the cylinder wall. In this manner the temperature gradient in the refrigerator A between the space 6 and the place 51 is smaller than when no cooling would take place. As a result of this the loss of cold from the space 6 of refrigerator A will be smaller than in the known cold-gas refrigerator shown in FIGURE 1.

The duct system 50 may be replaced, if desired, by another heat-conducting connection, for example, a copper tube.

What is claimed is:

1. A device provided with at least one cylinder, a piston reciprocating in said cylinder and together defining an expansion space, said piston being capable of varying the volume of said expansion space in said cylinder, the average temperature in said space being lower than the ambient temperature, a gap located between said piston and adjacent cylinder wall and communicating with said expansion space, a seal bounding said gap at a location remote from said space and positioned between said piston and adjacent cylinder wall, and means for additionally cooling the wall of said piston and/or cylinder which bounds said gap over at least one part of the axial length along the entire annular area.

2. A device as claimed in claim 1 wherein the walls of said piston and adjacent cylinder bounding said gap are stepped in construction to form a plurality of expansion spaces of varying degrees of cold whereby when viewed in an axial direction said gap is divided into at least two parts, one part being located nearer to the coldest expansion space having a smaller diameter than the part of the gap which is farther remote from said coldest expansion space whereby the volume of the spaces influenced by the annular surfaces formed as a result of the stepped construction can vary in phase with the volume of said coldest expansion space.

3. A device as claimed in claim 1 wherein the walls of said piston and the adjacent cylinder wall which bound said gap are conical in cross-section at least over part of their axial length, and the smallest diameter of said walls being located in the direction of said coldest expansion space.

4. A device as claimed in claim 1, wherein at least one location on the wall of said cylinder and/ or piston which bounds said gap are each in heat-conducting relationship throughout said circumference with a cold source, each cold source having a lower temperature than the location communicating therewith so that thermal energy can be withdrawn from said location.

5. A device as claimed in claim 4 having two spaced cylinders, each of said cylinders being provided with a piston therein adapted for reciprocation, and a duct system connecting one expansion space in one of said cylinders to said location in the other of said cylinders.

6. A device as claimed in claim 4 having two spaced cylinders, each of said cylinders being provided with a piston therein adapted for reciprocation, and a copper tube connecting one expansion space in one of said cylinders to said location in the other of said cylinders.

References Cited UNITED STATES PATENTS 2,857,220 10/1958 Jonkers 626 2,907,175 10/1959 Kohler 626 3,145,629 8/1964 Gottzmann 626 3,214,924 11/ 1965 Van Geuns 626 3,218,815 ll/1965 Chellis 626 3,292,501 12/1966 Verbeek 626 WILLIAM J. WYE, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,383,872 May 21, 1968 Jacob Willem Laurens Kohler It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

In the heading to the printed specification, line 8,

Dec 5, 1965" should read Dec. 3, 1965 Column 1, line 29, "Furthrem0re" should read Furthermore Column 4, line 55, after "higher" insert average Signed and sealed this 7th day of October 1969.

(SEAL) test:

MI. Fletcher, Jr.

Attesting Officer Commissioner of Patents WILLIAM E. SCHUYLER, JR.

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