US3130562A - Cryogenic pumping apparatus - Google Patents

Description

April 28, 1964 N. H. WOOD ETAL 3,130,562

CRYQGENIC PUMPING APPARATUS Filed Nov. 2. 1960 3 Sheets-Sheet -l Ffgj.

Inventor-s: Norman H- Wo Loyd B.Nesbit.t,

by 4; x. M

Their- Attorney- April 28, 1964 Filed Nov. 2, 1960 N. H. WOOD ETAL CRYOGENIC PUMPING APPARATUS 3 Sheets-Sheet 2 Inventors.-

Nor'man H. Wood,

Loyd B. Nesbitt,

The/P Attorney- A ril28, 1-964 N. H. WOOD ETAL 3,130,562

CRYOGENIC PUMPING APPARATUS Filed Nov. 2; 1960 3 Sheets-Sheet 3 Inventors: Nor-man H. Wood, Lo cl B.Nesbit t,

by 73/ f, M

Their- Attor'n e United States Patent 3,130,562 CRYOGENTC PUMPTNG APPARATUS Norman H. Wood, Schenectady, and Loyd B. Neshitt, Alplaus, N.Y., assignors to General Electric Company, a corporation of New York Filed Nev. 2, 196a, Ser. No. 66,324 8 Ciaims. (Cl. 624tl4) The present invention relates to improved cryogenic pumping apparatus and, more particularly, to improved cryogenic pumping apparatus for use in space simulating chambers.

In the copending application of D. l. Santeler, entitled Cryogenic Pumping Apparatus, filed September 30, 1960, Serial No. 59,642, assigned to the assignee of the present application, there is disclosed a cryogenic pumping apparatus for use in space simulating chambers which will substantially permit the duplication of cold black space and the pressure conditions existing the spatial environment. It is noted in the Santeler application that the molecules being distributed from the surface of a vehicle in space rarely collide with one another and return to the vehicle. To duplicate this effect in a confining chamber, it is necessary that the walls of the chamber substantially absorb all the molecules being emitted by the space vehicle or the test member. To simulate spatial pressure conditions a pressure less than 1 1() mm. of mercury should be maintained. This may be achieved by a three-fold pumping arrangement including mechanical pumping, diffusion pumping, and cryogenic pumping. Another requirement for simulating outer space is that the temperature of an energy absorbing wall within the chamber be maintained less than approximately 100 K. (Kelvin).

The Santeler application discloses a cryogenic pumping construction which includes radiant energy absorb'mg means in the form of a battle fin which is in heat exchange relation with a gaseous or liquid refrigerant, such as nitrogen, to maintain the temperature of the bafi le fin less than approximately 100 K., the baffle fin further shielding a condensing fin maintained at a lower temperature, for example, 20 K. In this manner, radiant energy is absorbed substantially only by the baffle fin and condensation of gases or cryogenic pumping is performed substantially only by the condensing fin. The term condensing as utilized herein denotes the substantial liquefication or solidification of certain gases on the condensing means, these gases not condensing on the radiant energy absorbing means because of their low boiling points.

The present invention envisions a construction wherein the absorption of radiant energy is substantially achieved only by bafie means and cryogenic pumping is substantially performed only by a condensing means to achieve the advantages of the Santeler construction, and also further including extended surfaces which assure improved absorption characteristics to the bafile means with respect to radiant energy while simultaneously making more effective use of the condensing means to assure rapid and effective cryogenic pumping.

The chief object of the present invention is to provide an improved space simulating chamber.

Another object of the invention is to provide improved cryogenic pumping means.

A further object of the present invention is to provide an improved cryogenic pumping member for use in space simulators including a bafile fin which will substantially absorb radiant energy in a manner so that a minimum amount of such energy is reflected to the test member and further including therewith a condensing fin which will assure rapid cryogenic pumping.

These and other objects of our invention may be more readily perceived from the following description:

Briefly stated, the present invention relates to cryogenic pumping of evacuated chambers wherein bafile means absorb radiant energy and also shield condensing means from sources of radiant energy, the bafile means having surfaces defining passages for substantially directing gas molecules located in the chamber toward the condensing means.

The attached drawings illustrate preferred embodiments of the invention in which:

FIGURE 1 is a view in section of a space simulating chamber employing the present invention;

FIGURE 2 is a sectional view of the diffusion pump utilized in the apparatus shown in FIGURE 1;

FIGURE 3 is a sectional view of a cryogenic member which may be utilized in the apparatus shown in FIG- URE 1;

FIGURE 4 is another embodiment of the cryogenic member illustrated in FIGURE 3 FIGURE 5 is an enlarged plan view of the baffle member used in FIGURE 4;

FIGURE 6 is a sectional view of a third embodiment of the cryogenic member shown in FIGURE 3; and

FIGURE 7 is a sectional view of a fourth embodiment of the cryogenic member illustrated in FIGURE 3.

In FIGURE 1 there is shown a space simulator 2 which comprises an outer housing including an upper hemispherical shell 3, a lower hemispherical shell 4 and a centnal cylindrical shell 5 which defines the evacuated chamber within which a test member 12 is to be tested. Shield 6 located within the chamber is intended to absorb radiant energy. A suitable solar radiation source 7 is also located in the upper portion of the chamber. A substantially spherical cryogenic member 8 is mounted in the lower portion of the chamber. Shield 6 is supported by a plurality of gusset plates 10, spherical member 8 being supported by rods 11 extending from gusset plates 15}.

As initially noted, evacuation of chamber 2 may be achieved by the combination of mechanical, diffusion, and cryogenic pumping means. The mechanical and diffusion pumping means are located externally of simulator chamber 2 and are connected thereto by means of conduit elbows 17 and 18. Elbows 17 and 18 extend through cylindrical portion 5 of the housing and one end of each extends through radiant energy absorbing shield 6. The opposite ends of the elbows are connected to suitable diffusion pumps 24 and 21 which are further connected to mechanical pumping means 22 and 23. The construction and manner of operation of diffusion pumps 20 and 21 are described more fully hereinafter.

The upper portion of chamber 2 has located therein the previously noted radiant energy absorbing shield 6 which comprises a frusto-conical shaped portion 14 and a cylindrical portion 16. These portions may be fabricated of plate material and suitably connected to form a structure which envelops light source 7 and a portion of the substantially spherical cryogenic pumping member 8. Suitable heat exchange coils 15 are fastened and thermally connected to the plates comprising shield 6. A refrigerant, such as liquid nitrogen, may be circulated in coils 15. As previously noted, it is desired that a temperature less than approximately K. be maintained within the space simulating chamber. This is readily achieved by the use of liquid nitrogen which may provide a shield temperature of approximately 77 K. The function of the radiant energy absorbing shield 6 is to absorb photons in a manner that no randomly reflected energy in any uncontrolled manner passes into the lower portion of the chamber. For this reason, the plates are preferably fabricated to provide an energy absorbing means of high absorbtivity. Gas molecules in the upper portion of the chamber striking shield 6 either condense and stay, condense and re-evaporate, or diffusely reflect essentially instantly depending upon their species. Those not condensing eventually make their way to either the diffusion pumps or a colder condensing panel.

Cryogenic pumping member 3 comprises a plurality of panels 25 which are fabricated to form a substantially spherical enclosure having an opening through which the radiant energy from the light source 7 may pass. A test member 12 may be mounted in the center portion of the cavity substantially defined by cryogenic pumping member 8. Cryogenic pumping member 8 is provided with suitable refrigerant coils 26 through which a suitable fluid such as nitrogen is passed. The nature of the inner surface of cryogenic pumping member 8 is described more fully hereinafter.

A sectional view of diffusion pump 20 which may be used with the apparatus is illustrated in FIGURE 2. Diffusion pump 26 comprises a cylindrical casing 30 having a connecting flange 31 adapted to be suitably connected to the space simulating chamber. Cylindrical casing 30 is in heat exchange relation with coil 32 through which coolant is passed for the purpose of cooling inner surface 44 thereof. In the lower portion of the pump suitable heating means 33, such as an electric heater, may be provided which is associated with a boiler 34 in which an organic oil or pumping fluid is purified by crude fractionation. The oil vapor from the boiler passes upwardly through three concentric annular passages defined by cylindrical members 35, 36, and 37. The ends of the cylindrical members cooperate with suitable deflectors 38, 39, and 46 to define annular orifices 41, 42, and 43. These orifices direct the vapor annularly toward cooled surface 44.

The action of the pump depends on the myriad individual collisions of oil-vapor molecules with molecules of air or other gas being pumped. Jets of oil-vapor molecules are emitted from orifices 41, 42, 43 at velocities approximating the speed of sound. The jets are shaped to make the emitted oil vapor thrust strongly downward and outward. Air molecules traveling in a comparatively random fashion enter the region occupied by the jets and suffer collisions with the much heavier oil molecules. The driving rain of oil molecules propel the air generally downward, thus compressing it. The three orifices define three stages of compression. In the lower portion of the pump, the oil is returned to the boiler as a film while the highly compressed gas is passed through a foreline 45 connected to a suitable mechanical pump 22 which discharges the gas from the system. Deflector 46 acts as a check valve to maintain the fluid flow pattern in the pump. The oil returning to the boiler is again vaporized and passed through the previously mentioned orifices to further compress the gas thereby substantially evacuating the chamber. A pressure of IX 10* mm. of mercury may be readily achieved by such a diffusion pump.

In FIGURE 3, there is shown an enlarged sectional view of a portion of cryogenic pumping member 8. This member comprises a spherical wall portion 50 which is associated with heat exchange coil 26 also shown in FIG- URE 1. Coil 26 is soldered or thermally attached in another conventional manner to wall 5! so that the refrigerant within the tube is in heat exchange relation with said well. A plurality of baflle fins 51 extend angularly from wall 50 and are thermally connected thereto. In this manner, the temperatures of the wall and bafiie fins are substantially that of coils 26 through which refrigerant is circulated.

As previously noted, the major portion of the heat load in the apparatus is due to radiant heat which may be partially absorbed by radiant energy absorbing shield 6 located in the upper portion of the apparatus shown in FIGURE 1. The energy which is reflected or emitted from the test member in FIGURE 1 is substantially absorbed by baffle fins 51 shown in FIGURE 3. The high absorbent qualities of the surface of the panels which. comprise cryogenic pumpingmember 8 and radiant energy absorbing shield 6 supply the cold black space required for the absorption of radiant energy.

It has been found that to simulate space, a pressure less than approximately 1x10 mm. of mercury is desirable. With the present invention, a pressure of 1X l0 mm. of mercury may be achieved in the chamber. A high capacity is necessary to maintain desired pressure while the test member is being outgassed. A substantially low pressure may be achieved by the use of mechanical and diffusion pumps. However, the present invention envisions combining therewith cryogenic pumping of certain gases. Cryogenic pumping in the present invention may cause the condensation of molecules of gases having boiling points above the temperature of suitable surfaces provided therein in order to achieve the desired low pressure.

The present invention in a manner similar to that disclosed in the copending Santeler application provides means for absorbing radiant energy while shielding the surfaces upon which it is intended to condense gases.

In the embodiment shown in FIGURE 3, baflie fins 5t absorb radiant energy, that is, substantially all photons reaching the surface of the bafiie fins are absorbed by the refrigerant cooled surface which may be less than approximately K. In the case of randomly moving gas molecules, these molecules either condense on the surface or are predominantly diffusely reflected. A portion of these strike condensing fins 54 and others are returned to the chamber. In addition, however, many other molecules enter openings 52 in the bafiie fin and are reflected along walls 53 or openings 52 in such a manner as to be directed toward condensing fin 54 on which the gas condenses. molecule is shown in FIGURE 3. It is noted that the openings in the bafiie fins are of a size in relation to the thickness of the bafiie fins that the condensing fins 54 are substantially optically shielded from the source of radiant energy, that is, the test member except for that energy whose axis of emission is almost coincident with the axis of the opening. I

In FIGURE 4 there is shown another embodiment of the cryogenic pumping means in which a planar wall member 69 is provided with an indentation 61 adapted to receive a portion of coil 26 which is either soldered or in some other suitable manner thermally connected to the wall member. The shape of wall member may be either arcuate or planar depending on the nature of the chamber. Bafiie fin 62 extends from the indented portion 61; a plan view of halide fin 62 is shown in FIGURE 5. Baflle fin 62 may comprise a plurality of corrugated sheets 62 having the undulating portions of each sheet connected to adjacent sheets in a manner to define a plurality of openings 64. In this embodiment the bafile fins are almost entirely perforated and provide very little reflecting surfaces for gas molecules and photons to be reflected back to the test member. A condensing fin 65 having substantially planar surfaces is mounted between bafile fin 62 and wall member 60. Condensing fin 65 is in heat exchange relation with tube 67 through which a low temperature refrigerant is passed. The temperature of fin 65 is intended to be much lower than baflie fins 62. Photons impinge on the surfaces of the sheets 63 which define the walls of the openings 64 in bafiie fin 62 and are absorbed. Gaseous molecules enter the openings and either condense or may ultimately be directed through openings 64 toward condensing fin 65 which is in heat exchange with the refrigerant coil 67.

If desired, a bafile 68 similar in construction to the baffle fins 62 may be thermally connected to wall 60. In this manner, the absorbent qualities of the wall may be enhanced in that photons will enter into the open A typical path 57 of such a ings of baffle 68 with less opportunity for reflection of energy.

In this embodiment shown in FIGURE 4, it is desirable that the bafile fin 62 be also maintained at a temperature less than 100 K. In the preferred embodiment, coil 26 has passing therethrough liquid nitrogen so that a temperature of approximately 77 K. is maintained. In this manner, the function of the baflle fins to absorb radiant energy is performed. A refrigerant such as hydrogen, neon, or helium may be circulated through coil 67 to maintain the condensing surface at approximately 20 K. By maintaining the temperature at this level, gases, such as nitrogen, oxygen, argon, carbon monoxide, and carbon dioxide, are cryogenically pumped, that is, these gases are diffusely reflected from the surfaces of the baflle fins or are directed to condensing fins 65 where they are condensed. If desired, helium at sufficiently low temperature may be supplied to coil 67 in which case all gases in equilibrium, excepting helium, condense.

In FIGURE 6 there is shown a third embodiment of the invention. The wall construction is similar to that shown as 69 in FIGURE 4. However, in this embodiment baflle fin 70 is fabricated to supply a plurality of passages 72 which have a general arcuate shape, that is, there is a change of direction of the paths through the baflle fin. This type of construction is provided to assure impingement of radiant energy on the surfaces 71 which define passages 72. By providing a tortuous path there is less opportunity of energy being reflected to the test member or to the condensing fin from the bafiie fin. The function of these passages is the same as those shown in FIGURES 3 and 4, that is, the gas molecules are directed therethrough to condensing fin 65 upon which they may be condensed.

In FIGURE 7 there is shown a fourth embodiment of the invention especially adapted for situations where in all gases except helium may be cryogenically pumped. Wall member 60 preferably is placed in heat exchange relation with a refrigerant being circulated in coil 26. The refrigerant is also in heat exchange relation with bafile fin 30 having suitable passages 81 therein through which gas molecules may be passed. Bafile fin 80 also performs the function of optically shielding condensing fins S2 and 84 Which are located between baffle fin 80 and wall member 60. First condensing fin 82 is located adjacent baflle fin 80 and is in heat exchange relation with coil 86 through which a low temperature refrigerant such as liquid hydrogen may be passed to maintain the temperature of the surface at, for example, 20 K. Located between wall member 60 and first condensing fin 82 is a second condensing fin 84 which is in heat exchange relation with coil 87 through which a lower temperature refrigerant such as liquid helium having a temperature of approximately 4 K. may be passed. It is noted that bafile fin 80 is provided with passages 81, first condensing fin 82 is provided with passages 83 which are angularly disposed with respect to the passages 81 and similarly there are passages 85 in fin 84. Passages 85 also are angularly disposed with respect to passages 83 in fin 82.

In operation of this embodiment to FIGURE 7, the action of the bafile fin is similar to those in the previously described embodiments, that is, photons may be absorbed by this fin, however gas molecules may ultimately be directed through the passages 81 toward first condensing fin 82 which is shielded by bafile fin 80. First condensing fin 32 provides a plurality of passages 83 into which the gas molecules may be directed. Molecules of nitrogen, oxygen, argon, carbon monoxide, and carbon dioxide may condense on the surfaces defining the passages. Molecules of hydrogen and neon may also condense, however, they will re-evaporate and pass through the openings 83 and are further directed toward the second condensing fin 84 passing into openings 85 thereof. Since the temperature of this surface may be less than the condensing temperatures of gases such as hydrogen and neon, these gases condense on the surfaces defining openings 85. Helium gas may also condense and be re-evaporated. Since the helium constitutes such a small portion of the earths atmosphere, that is, 4 parts per million, the chamber is substantially pumped free of the gas molecules located therein, depending on their rate of emission from a test member.

In operation of the space simulating chamber, test member 12 is suitably suspended therein and is substantially enveloped by the cryogenic pumping member 8. The access openings to the chamber are sealed and as a result of the action of the mechanical and diffusion pumps, a substantially low pressure is achieved. A refrigerant such as liquid nitrogen may be circulated through coils 15 which are in heat exchange relation with shield 6 thereby absorbing radiant energy in the upper part of the chamber while condensing gas molecules whose condensing temperatures are above that of shield 6. The random movement of gas molecules continues in the area of the test member accompanied by a degassing of the test member resulting in a distribution of gas molecules. Reflected energy also passes toward cryogenic pumping member 8. Cryogenic pumping member 8 supplements the efforts of the mechanical and diffusion pumping means previously described and with the construction illustrated in FIGURE 3, photons are absorbed by baffle fins 51 which substantially shield condensing fins 54. Gas molecules randomly moving in the chamber are either reflected from the baflle fins or pass into the openings 52, the molecules impinging on surfaces 53 which define openings 52 until the molecules reach the area of condensing fins 54. Since the condensing fin is in heat exchange relation with a low temperature refrigerant, for example, maintained at a temperature less than approximately 20 K., gases whose condensing temperatures are above 20 K. substantially condense on the condensing fin surface.

In the embodiment of FIGURE 4, the particular construction of the baffle fin assures that many of the gas molecules pass through the passages 64 with little reflection of the molecules or of radiant energy toward test member 12. The gas molecules pass toward the condensing fin 65 on which they are substantially condensed.

In FIGURE 6, gas molecules and photons also impinge on surfaces 71 which define openings 72 with little return reflection of the photons or gas molecules. In this embodiment because of the arcuate shape of passages 72, there is greater opportunity for the photons and gas molecules to impinge on the passage surfaces.

In FIGURE 7, photons are absorbed by the surfaces of openings 81 of batfle fins with the gas molecules being directed through the opening 81 toward the first condensing fin 82. By maintaining condensing fin 82 at a lower temperature than the bafile fin, for example, 20 K., gases whose condensing temperatures are above 20 K., such as nitrogen, oxygen, argon, and carbon monoxide, condense. The remaining gases, helium, hydrogen, and neon, pass through passages 83 toward second condensing fin 84 and impinge substantially on the surfaces of openings 85. In this embodiment it is preferable that coil 87 and thus the second condensing fin may be substantially maintained at a temperature of approximately 4 K., and in this instance the hydrogen and neon substantially condense leaving only helium as the only noncondensed gas.

The present invention is directed to improved cryogenic pumping means in which the energy absorbing function is substantially isolated and performed by improved bafile fins. Radiant energy is absorbed on the improved surface which contributes toward the desired result of having a minimum amount of energy and gas molecules re-directed toward the test member. Cryogenic pumping is performed by low temperature refrigerants placed in heat exchange relation with condensing fins.

While the present invention has been described with particular reference to space simulators, it will be appreciated that the cryogenic pumping means may find use in other devices such as in arc melting furnaces and other environments wherein radiant energy is evident and high pumping speeds are required.

While we have described preferred embodiments of our invention, it will be understood that our invention is not limited thereto, since it may be otherwise embodied within the scope of the appended claims.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. In a space simulator, the combination of means defining a chamber, a pump connected to and adapted to evacuate the chamber, a substantially spherically shaped cryogenic pumping member located in said chamber and being adapted to substantially envelop a test member in said chamber, said cryogenic member comprising bafile means for absorbing radiant energy, means for condensing gases located in said chamber, the gas condensing means being maintained at a temperature substantially less than the temperature of the baffle means, said baffle means substantially shielding the gas condensing means and including passage means for directing gas molecules in the chamber toward the gas condensing means.

2. In a space simulator, means defining a chamber, a pump connected to and adapted to substantially evacuate said chamber, a substantially spherical cryogenic member being located in said chamber and being adapted to substantially envelop a test member in said chamber, said cryogenic member comprising a wall member, a plurality of bafile fins extending from said wall member and being angularly disposed with respect to said wall member, said wall member and baflle fins being thermally connected, a plurality of condensing fins being located between the bafiie fins and the wall member whereby the condensing fins are substantially shielded from the test member, said bafiie fins including means defining passages therein for directing gas molecules located in the chamber toward the condensing fins, and means for maintaining the condensing fins at a temperature substantially less than the temperature of the wall member.

3. A space simulator according to claim 2 wherein the means defining passages in the baffle fins define paths having at least one change of direction.

4. A cryogenic member comprising a wall member, a batfie fin thermally connected to said wall member and being angularly disposed with respect thereto, a condensing fin located between the baffle fin and the wall member whereby the condensing fin is substantially shielded, said baifie fin having a plurality of passages therein for direcing gas molecules to pass therethrough to the condensing fin, said condensing fin being adapted to be maintained at a temperature substantially less than the temperature of the bafiie fin.

5. The cryogenic member according to claim 4 wherein the passage means in the bafile fin have at least one change in direction.

6. A cryogenic member comprising a wall member; a bafiie fin thermally connected to and angularly disposed with respect to said wall member, a condensing fin being located between the bafile fin and the wall member and being thermally insulated from the baffle fin and the wall member, said bafile fin substantially shielding the condensing fin, said wall member and bafile fin being adapted to be maintained at a temperature less than approximately K., said condensing fin being adapted to be maintained at a temperature substantially less than the bafiie fin whereby radiant energy is substantially absorbed by the bafiie fin, said baffle fin including a plurality of passage means extending therethrough whereby gas molecules are directed to the condensing fin.

7. The cryogenic member according to claim 6 further including a second condensing fin located between the first mentioned condensing fin and the wall member, the second condensing fin being maintained at a lower temperature than the first mentioned condensing fin.

8. A cryogenic member comprising a wall member, a batfie fin thermally connected to and angularly disposed with respect to said Wall member, a first condensing fin being located between the baifie fin and the wall member and being thermally insulated from the bafile fin and the wall member, said baffle fin substantially shielding the first condensing fin, said bafile fin having a plurality of passages therein, said first condensing fin also having a plurality of passages therein, a second condensing fin being located between the wall member and the first condensing fin, said baifie fin being adapted to be maintained at a temperature less than approximately 100 K., said first condensing fin being adapted to be maintained at a temperature substantially less than the temperature of the baffie fin, said second condensing fin being adapted to be maintained at a temperature substantially less than a temperature of the first condensing fin whereby radiant energy is substantially absorbed by the bafile fin, gaseous molecules being directed through the passages in the baffie fin to the first condensing fin, a substantial portion of molecules being condensed on the firstcondensing fin, molecules not condensing on the first condensing fin being directed through the passages in the first condensing fin to the second condensing fin.

References Cited in the file of this patent UNITEDSTATES PATENTS 2,379,215 Brinkmann June 26, 1945 2,465,229 Hipple Mar. 22, 1949 2,939,316 Beecher et al. June 7, 1960 2,985,356 Beecher May 23, 1961 3,010,220 Schueller Nov. 28, 1961 OTHER REFERENCES 1959 Vacuum Symposium Transactions, American Vacuum Society, Incorporated, published by Pergamon Press, New York, 1960, pages 129-133 of interest.

Advances in Cryogenic Engineering, Timrnerhaus, pubished by Plenum Press, Incorporated, New York, 1960, Proceedings of 1954 Cryogenic Engineering Conference, Stearns et al., article on pages 35-40 relied on.

Claims (1)

1. IN A SPACE SIMULATOR, THE COMBINATION OF MEANS DEFINING A CHAMBER, A PUMP CONNECTED TO AND ADAPTED TO EVACUATE THE CHAMBER, A SUBSTANTIALLY SPHERICALLY SHAPED CRYOGENIC PUMPING MEMBER LOCATED IN SAID CHAMBER AND BEING ADAPTED TO SUBSTANTIALLY ENVELOP A TEST MEMBER IN SAID CHAMBER, SAID CRYOGENIC MEMBER COMPRISING BAFFLE MEANS FOR ABSORBING RADIANT ENERGY, MEANS FOR CONDENSING GASES LOCATED IN SAID CHAMBER, THE GAS CONDENSING MEANS BEING MAINTAINED AT A TEMPERATURE SUBSTANTIALLY LESS THAN THE TEMPERATURE OF THE BAFFLE MEANS, SAID BAFFLE MEANS SUBSTANTIALLY SHIELDING THE GAS CONDENSING MEANS AND INCLUDING PASSAGE MEANS FOR DIRECTING GAS MOLECULES IN THE CHAMBER TOWARD THE GAS CONDENSING MEANS.

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