US3256712A - Cryostat heat exchanger - Google Patents

Description

June 21, 1966 M. J. MAKOWSKI 3,256,712

CRYOSI'AT HEAT EXCHANGER Filed Dec. 4, 1963 4 Sheets-Sheet 2 U IO (D 1.00 3; emu

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r l l wulma June 21, 1966 M. J. MAKOWSKI 3,256,712

CRYOSTAT HEAT EXCHANGER Filed Dec. 4, 1963 4 Sheets-Sheet 5 FIG. 4

w INVENTOR. 5 MACIEJ JERZY MAKOWSKI ATTORNEYS June 21, 1966 M. J. MAKOWSKI CRYOSTAT HEAT EXCHANGER 4 Sheets-Sheet 4 Filed Dec. 4, 1963 830i mm E 5250 v INVENTOR. MACIEJ JERZY MAKOWSKI BY 9? h? ATTORNEYS United States Patent ice 3,256,712 CRYOSTAT HEAT EXCHANGER Maciej J. Makowski, Torrance, Califi, assignor to Fairchild Hiller Corporation, a corporation of Maryland Filed Dec. 4, 1963, Ser. No. 328,449

1 Claim. (Cl. 62-514) This invention relates to heat exchangers and more particularly to a heat exchanger for use with a cryostat to cool fluids at low temperatures.

The present invention relates to a heat exchanger which is particularly adapted for use in a cryostat, although it has numerous other applications. In accordance with the invention the heat exchanger is formed by two counter-current type exchanger units. Each unit has two helical passages for the inflow and outflow of a separate cooling fluid. The first unit is provided at its input with a first fluid at a high pressure which is to be used to cool an object. This high pressure fluid travels down one of the helical passages and is permitted to expand into a chamber. The low pressure cooler fluid is then returned to the source through the second helical passage. A common wall is provided between the first and second helical passages to effect a heat exchange to cool the incoming high pressure fluid.

The second unit also has two helical passages, one of which is provided with a second fluid at a high pressure which is to be used to precool the first fluid. The second fluid expands into a chamber and the cooler lower pressure fluid is returned to the source through the second helicalpassage of the second unit. A common member is provided to effect heat exchange between the high pressure input second fluid and the low pressure output, to further cool the second fluid. In accordance with the invention a common heat conductive member is also provided between the high pressure input passage for the first fluid and the low pressure output passage for the second fluid. This arrangement provides additional precooling for the high pressure input first fluid which is to do the actual cooling of the object.

The heatexchanger of the present invention has several advantages. First of all, a large heat exchange surface area is possible between the fluid in the two passages in each unit because of the helical formation of the fluid passages. This gives a high cooling capacity for a heat exchanger of relatively small overall volume. Additionally, the location of the two units to permit heat exchange therebetween further precools the cooling fluid to increase the capacity of the exchanger.

It is an object of this invention to provide'a heat exchanger of the counter-current type in which the fluid to be cooled and the cooling fluid travel in helical passages having a common wall for heat transfer purposes.

A further object of the invention is to provide a heat exchanger for a cryostat, the heat exchanger being formed by two counter-current units having a common mem her for heat transfer purposes.

Another object of the invention is to provide a heat exchanger for-med by two counter-current units which carry respective cooling fluids in which both units have two helical passages for the input and output of the respective fluid and a common member between the two passages for transfer ofvheat, the two units also having a common heat transfer member between the input passage of the first unit and the output passage of the second to provide further cooling for the fluid in the first unit input passage by the fluid in the output passage of the second unit.

Still another object of the invention is to provide a heat exchanger for a cryostat in which the heat exchanger is formed by two counter-current exchanger 3,256,7l2 Patented June 21, 1966 units, the units being constructed to precool the fluid in meet the units.

Other objects and advantages of the present invention Will become more apparent upon reference to the following specification and annexed drawings, in which:

FIGURE 1 is a plan view taken partially in section of a cryostat vessel showing the heat exchanger contained therein;

FIGURE 2 is a plan view taken partially in section of one of the support members to hold the exchanger within the cryostat vessel;

FIGURES 3, 4 and 5 are sectional views to be laid end-to-end of various portions of the cryostat vessel and the heat exchanger.

Referring to FIGURE 1, the cryostat is shown as having an outer generally cylindrical housing 10. Since the housing is to be evacuated, it is sealed at one end thereof by a removable cap 11 which is fastened to an end fitting 12 by a number of fasteners such as the bolts 13. The end fitting 12 is in turn held to the housing 10 by a number of other suitable fasteners 14. Located within the cap 11 and the end fitting 12 are suitable bellows, sealing rings, and other similar elements which facilitate the attachment of evacuation apparatus to evacuate the interior of the housing 10. Since these elements and theevacuation apparatus form no part of the present invention they are not shown or described in detail.

The heat exchanger 15 is held within the evacuated housing 10 by a number of support members which are described in detail below. The exchanger 15 contains the fluid for cooling an object (not shown), the object being held in a support 16. The object can be of any type, for example, a piece of semiconductor material. A portion of the exchanger 15 is covered by a heat radiation shield 18 made of highly conductive material Whose purpose is to keep incident radiant heat energy away from the portion of the exchanger that it covers. The radiation shield 18 has a bell-shaped piece 18a which extends into the shield 18 so that the object to be cooled can be placed within the shield adjacent the cooling portion of the exchanger (see FIGURE 5). The housing 10, also has a sealed window or other suitable feed through 17 so that the object can be placed within the housing adjacent the cooling fluid in the heat exchanger 15 without destroying the vacuum in the housing.

The end of the shield 18 nearest the cap 11 tapers down to a nose piece 19 having a number of openended slots therein. This end of shield 18 is held spaced from the inside of the housing 10 by a number of support members 19a. One end of each support member 1 is held in a respective slot and the other end of each member is held by suitable fastening means (not shown), such as a threaded end on the member and a mating nut, to a collar 20 formed on the inside of the housing 10. The heat exchanger 15 is supported at its right end within the heat shield in a manner to be described below. The left end of the shield 18 is fastened to a portion of the heat exchanger, as shown in FIG- URE 4.

The left portion of the heat exchanger, which is not covered by the shield 18, includes an outer tube 23. One end of tube 23 is held to the inside of the housing 10 within an end fitting 30. The other end of the outer tube 23, which is closer to the center of the exchanger, is provided with a collar 22 made of a material having poor heat conductive properties. Connected to the collar 22 at points spaced therearound are a number of fastening spacer members 24 which are also made of a material having poor heat conduction properties. As shown best in FIGURE 2, one end of each member 24 has a head thereon to hold it to the collar while the other end has a screw and nut. The screw and nut end of each member 24 rests on a ridge 26 formed in a cylindrical cap member 25. The cap members 25 are fastened to holes in the housing 10. By moving members 24 the outer tube 23 of the exchanger may be positioned, within limits, within housing 10. Each cap 25 is closed off by an end piece 27 to maintain the vacuum within the housing 10. The right end of the heat exchanger is supported within the heat shield in a manner to be described below. Thus, the heat exchanger is rigidly supported at three points within the housing to prevent it from moving or vibrating.

The left end of housing is sealed by a fitting 30 which is closed off by a plug 31 (see FIGURE 3) to maintain the vacuum in the housing. As explained before, the left end of the heat exchanger inner tube 23 is supported within this fitting. The end fitting 30 also accommodates two sets of input and output pipes for the two fluids to be used in the heat exchanger. Thefirst set of pipes includes a high pressure input pipe 34 and a low pressure output pipe 35. The first set of pipes carries the fluid for cooling the object and the fluid may be, for example, hydrogen. The second set of pipes has a high pressure input pipe 37 and low pressure output pipe 38. This second set of pipes carries another fluid, such as nitrogen for example, which is used as a heat exchange medium to further reduce the temperature of the main cooling fluid carried by the first set of pipes 34 and 35. As can be seen, the high pressure input pipes 34 and 37 have smaller diameters than the low pressure output pipes 35 and 38.

The details of the heat exchanger 15 are explained by referring to FIGURES 3-5. The exchanger is formed by two counter-current type heat exchanger units. The first unit runs substantially the entire length of the heat exchanger 15 and carries the cooling fluid supplied by pipe 34 to cool the object in support 16. The second countercurrent unit runs for only a portion of the first and is concentric with the first to provide a heat exchange medium from pipe 37 for further cooling the fluid in the first unit.

The first unit of the exchanger includes an inner hollow tube 40 of poorly conductive material which extends for substantially the entire length of the exchanger 15. The right end of the tube 40 terminates in a narrow or tapered portion 42 (FIGURE 5) having a number of open-ended slots 44 at its end. The end portion 42 of tube 40 is held within the shield 18 by a plurality of supports 43 of poorly conductive material having heads 45 at one end thereof to hold the supports within slots 44. The supports 43 protrude through respective tubular extensions 46 in the radiation shield 18 where they are held by a fastening means such as a nut 47 placed on top of a washer 48. This arrangement forms the support for the right end of the exchanger.

Referring back to FIGURE 3, the wider end of inner tube 40 is held in the fitting 30 by the support flange 50. Fitting 30 has a cavity portion 51 sealed by the plug 31 and a bore in which the end of outlet pipe 35 is mounted. A passage 52 is provided for the pipe 35 to communicate with the interior of tube 40 through the cavity 51. The outer wall of the tube 40 to the right of the flange is unbroken for a short distance and then a number of through bores 53 are provided. The remainder of the interior of the tube 40 is sealed off by a plug 54 to the right of these bores.

To form the counter current heat exchanger portion for the first unit, a continuous, helically wound fin 60 is formed on the outer wall of tube 40. Fin 60 extends from the right of the holes 53 to near the beginning of the narrowed down inner tube section 42 (FIGURE 5). The tube 40 is surrounded over most of its length by a wall 63 formed in two sections 63a and 63b (FIGURES 4 and 5) which are joined together by a spirally grooved capillary restricter tube support member 62 (FIGURE 4). The wall 63 is made of material having poor heat conductive properties. The left end of wall section 63a is held on the inside of a flange support member 6011 mounted in the interior of end fitting 30. Communication is provided to the inside of wall section 63a from high pressure fluid input pipe 34 by a passage and cavity 59. A filter screen 58 is provided to trap out any solid particles from the incoming fluid stream. It should be noted that passage 59 is sealed off from cavity 51 by the internal construction of the fitting.

The wall sections 63a and 63b and the capillary tube support member 62 have fastened on the insides thereof or held in close proximity thereto the top walls 65 of a first crenelated helically formed finned structure 64. The crenelated structure 64 is concentric with the helical fin 60, so that one fin threads through the passage formed by each top wall 65 and the side walls of the structure depending from each side therefrom. One end of the structure 64 is fastened to the outside of tube 40 by the flap 66 at a point to the left of the bores 53 so that the bores are covered.

As can be seen, two fluid passages are provided between the wall 63 and the tube 40. The first of these passages, called the outer helical passage 67, is formed between the inside of wall sections 63a and 63b and the space formed by bottom and side walls of the crenelated structure 64. This outer passage 67 accommodates the incoming fluid from pipe 34 and extends from the input passage 59, through the space between wall section 63a and the flap 66, and then along the entire length of the tube 40. As explained before, the top wall 65 of the crenelated structure is also fastened or maintained in close proximity to the inside of the support piece 62 and the inside of wall section 63.

As shown in FIGURE 5, the end of wall section 63b near the narrow tube end 42 is formed with an opening 68 to provide communication between the end of the first helical passage 67 and an annular cavity 69 in a sealed ring member 70 mounted on the end of tube 40. The large open end of a mounting pad support 71 of high heat conductive material surrounds and is fastened to the outside of the ring 70. The other end of support 71 covers a portion of the narrow tube section 42 which has a capillary restricter tube 73 coiled thereover. This end of the pad support 71 form the base of the mounting 16 for holding the object to be cooled.

One end of the capillary restricter tube 73 extends into and communicates with the cavity 69 while the other end is open to discharge fluid to cool the pad support 71 and the object. The support 71 is sealed to tube section 42 at point 72 and a fluid discharge space 75 is left between the restricter tube 73 and the inside of the support. A larger chamber 74 is also left within the support in communication with space 75 to provide for a further pressure drop of the cooling fluid as it escapes from restricter 73.

The chamber 74 also communicates with an inner helical passage 76 extending the length of tube 40 between the inside of crenelated structure 64 and the fin 60. This inner passage is continuous from the end of the wall section 63b, where it communicates with chamber 74, back to the holes 53 at the end of the inner tube 40. As can be seen, the flap 66 covers the holes 53 so passage 76 is in communication therewith. It also should be noted that the bottom and side Walls of the first crenelated structure 64 are common to the outer and inner helical passages 67 and 76.

The operation of the first counter unit of the heat exchanger is as follows. High pressure cooling fluid enters through pipe 34 and travels down the outer helical passage 67 to the annular cavity 69 in ring 70 (FIG. 5). The fluid in this cavity passes into the end of restricter tube 73, travels through the coiled tube and is discharged in the space and chamber 74-75 formed by pad support 71. Because of the pressure drop encountered in going from a higher pressure in the passage 67 to a lower pressure in the space and chamber 7475 and the throttling effect of restricter 73, the discharged fluid becomes colder. This cooling fluid cools the pad support 71 and the object to be cooled.

After being discharged, the low pressure cooling fiuid in chamber 74 travels back down the tube 40 through the inner helical passage 76. The flow ends (FIGURE 3) as the outgoing fluid emerges from passage 76, passes through the holes 53 into the inside of tube 40 and then passes back to the source through outlet pipe 35. Heat exchange takes place between the incoming and outgoing fluid by conduction through the walls of the crenelated structure 64. Thus, the incoming fluid traveling towards restricter 73 is cooled by the cooler fluid flowing toward outlet pipe 35 along the entire length of the tube 40.

A second counter-current exchanger unit is provided to further cool the fluid flowing in the passage 67. This second unit is formed by a continuous helical fin 78 formed on the outside of wall section 63a. The outer tube 23 is concentric with and surrounds the wall section 63a. Tube 23 has a second crenelated helically wound structure 82 fastened or held in close proximity to its inner wall. One end of the tube 23 is held within the housing by the fitting 30 and a ring 83 (FIGURE 3) and the other end is fastened to the inside of the collar 22 (FIGURE 4) by the internal ridges 84 which form an annular cavity 85 therebetween. The end piece 86 of the crenelated structure 82 (FIGURE 3) is sealed to the inside of the left end of tube 23 while the other end piece 87 is sealed to the inside of the right end of the tube (FIGURE 4).

A continuous helical outer helical passage 90 is formed I between the inner wall of outer tube 23 and the side and bottom walls of the econd crenelated structure 82. Communication is made between the input end of passage 90 and the second fluid input pipe 37 between an annular passage 91 in the fitting 30 and a number of holes 92 in the tube 23. A filter screen 93 is provided in cavity 91 to trap any particles in the incoming fluid. The output end of passage 90 communicates with the annular cavity 85 (FIGURE 4) in the collar 22 through a plurality of holes 95 in the wall of tube 23.

An inner continuous helical passage 94 is formed between the fin 78 and the inside of crenelated structure 82 opposite the fin. Communication is made directly between'the passage 94 and the outlet pipe 38 by the end piece 86 of structure 82 which opens into a passage 96 formed in fitting 30. Outlet passage 96 is sealed off'from inlet passage 91 by the ring 83.

A second capillary restricter tube 97 open at both ends is wound in the helical grooves of the support member 62. Several of the grooves in the support 62 are left vacant to provide an empty space into which the fluid can discharge. The restricter 97 is enclosed by a cover piece 99 which is fastened at one end to the outside of collar 22 and at the other end to the outside of support member 62 and the inside of the radiation shield 18. The cover piece 99 i shaped to form an expansion chamber 100 for the fluid escaping from tube 97. One end of the restricter tube 97 extends into the cavity 85 and communicates with the outer helical passage 90 while the other end discharges the fluid from this passage into the space between the cover and support members 99 and 62. The throttling action of restricter 97 and the expansion of the fluid into chamber 100 produces a pressure drop which cools the fluid discharged from restricter 97. The discharged fluid passes through slots 102 in the support member 62 back to. a chamber 103 formed by the cover piece 99 and the ridge 84 of cavity 85. Chamber 103 is in communication with the inner .helical passage 94. The cooled low pressure fluid in passage 94 is discharged into outlet pipe 38 and goes back to the source.

, The operation of the second counter-current unit is as follows. The second cooling fluid enters pipe 37 under high pressure and travels down the outer helical passage to the cavity 85 and then into the restricter 97 from which it is discharged into chamber to cool support member 62. The throttling action and the pressure drop cools the second fluid and the lower pressure cooled fluid returns through slots 102 to the inner helical passage 94 and thence to the outlet pipe 38. Heat exchange takes place between the incoming and outgoing second fluids through the walls of crenelated structure 82 so that the incoming high pressure fluid is precooled by the outgoing lower pressure fluid.

As should be understood from the foregoing description, the second fluid also serves to precool the incoming high pressure first fluid in the outer helical passage 67 associated with the first tube 63. This occurs because the wall section 63a is common both to high pressure input passage 67 of the first counter-current unit and .to the low pressure return passage 94 of the second countercurrent unit for the second fluid. Thus, the first fluid flowing in passage 67 which is actually used for cooling the object, is precooled in the first exchanger unit by the low pressure return fluid in passage 76 by heat exchange through crenelated structure 64 and is additionally precooled in the second exchanger unit by the low pressure return of the second fluid in passage 94 through the heat conduction of wall section 63a. It should also be clear that additional precooling of the first fluid or reboiling of the second fluid takes place-through the support member 62 whose inner wall is in proximity with the first crenelated Therefore, it can be seen that a heat exchanger has been structure 64 and the incoming high pressure fluid in passage 67. I provided whichnses two separate exchanger units having helical passages therein. The separate units are so constructed and located that cooling of an input fluid in one is effected by the output fluid of that unit and also by the output fluid of the other unit. This arrangement provides for eflicient precooling of the high pressure input fluid of the first unit, this fluid being eventual-1y used to cool an object.

What is claimed is:

A heat exchanger for a cryostat vessel operating with sources of first and second cooling fluids comprising first, second and third tubes mounted coaxially in increasing radius,

a helically formed first structure in close proximity to the inner wall of said second tube and forming a first helical input passage between said first tube outer wall and said structure and a first helical output passage between said structure and the inner wall of said second tube, a helical fin on said first tube outer wall extending into said first output passage,

means for supplying the first fluid from its source to said first input passage at a relatively high pressure,

means forming a first discharge chamber in communication with said first output passage and capillary restrictor means in communication with said first output passage and said first discharge chamber, said first capillary restrictor means and said first discharge chamber reducing the pressure of the first fluid in said first input passage to produce cooling of said first fluid and for conveying the reduced pressure fir t fluid into said first output passage for return to its source, heat exchange taking place between the first fluid at the higher and lower pressures through said first structure,

a helically for-med second structure in close proximity to the inner wall of said third tube and forming a' second helical input passage between the inner wall of said third tube and said second structure and a second helical output passage between the outer wall of said second tube and said second structure, a helical fin on said second tube outer wall extending into said second output passage,

means for supplying the second fluid from its source to said second input passage at a relatively high pressure,

means forming a second discharge chamber in communication with said second output passage and second capillary restrictor means in communication with said second input passage and said second discharge chamber, said second discharge chamber and said second capillary restrictor means reducing the pressure of the second fluid in said second input passage to produce cooling of said second fluid and for conveying the reduced pressure second fluid to said second output passage for return to its source, heat exchange occurring between the reduced pressure second fluid in said second output passage and the higher pressure first and second fluids in said first and second input passages through said second structure and said second tube respectively.

References Cited by the Examiner UNITED STATES PATENTS MEYER PERLIN, Primary Examiner.

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