US3648473A

US3648473A - Pumping system for low-density gas flow in space chambers and wind tunnels

Info

Publication number: US3648473A
Application number: US65048A
Authority: US
Inventors: William B Stephenson
Original assignee: US Air Force
Current assignee: US Air Force
Priority date: 1970-08-19
Filing date: 1970-08-19
Publication date: 1972-03-14
Anticipated expiration: 1989-03-14

Abstract

A low-density cryopumping system for pumping high velocity high temperature, directed gas flow from a wind tunnel and/or rocket nozzle by means of condensation on a structure consisting of a series of condensing surfaces positioned downstream of the nozzle, and oriented in spaced-apart relation to each other and parallel to the gas flow to thereby permit the flow to initially bypass therethrough for direct impingement against a precooling structure positioned further downstream from the condensation structure. The gas is thereby cooled and thereafter deflected upstream in diffused manner for its subsequent impingement against, and condensation and collection on, the condensing surfaces.

Description

United States Patent Stephenson [54] PUMPING SYSTEM FOR LOW-DENSITY GAS FLOW IN SPACE CHAMBERS AND WIND TUNNELS [72] Inventor: William B. Stephenson, Tullahoma, Tenn.

[73] Assignee: The United States of America as represented by the Secretary of the Air Force (22] Filed: Aug. 19, 1970 [21] Appl.No.: 65,048

3,149,775 9/1964 Pagan0.... ..62/55.5 3,286,531 11/1966 Shapiro ..62/55.5

Primary Examiner-William J. Wye Attorney-Harry A. Herbert, Jr. and Arthur R. Parker [5 7] ABSTRACT A low-density cryopumping system for pumping high velocity high temperature, directed gas flow from a wind tunnel and/0r rocket nozzle by means of condensation on a structure con sisting of a series of condensing surfaces positioned downstream of the nozzle, and oriented in spaced-apart relation to each other and parallel to the gas flow to thereby permit the flow to initially bypass therethrough for direct impingement against a precooling structure positioned further downstream from the condensation structure. The gas is thereby cooled and thereafter deflected upstream in diffused manner for its subsequent impingement against, and condensation and collection on, the condensing surfaces.

10 Claims, 4 Drawing Figures PUMPING SYSTEM FOR LOW-DENSITY GAS FLOW IN SPACE CHAMBERS AND WIND TUNNELS BACKGROUND OF THE INVENTION This invention relates generally to the field of cryopumps and, in particular, to their use in pumping high-velocity directed gas flows by means of condensation.

Although cryopumping systems have been extensively utilized in the removal of static gases from vacuum systems, their use in the pumping of highvelocity directed flows has, however, been somewhat limited since the direct application thereto of the static pumping data for condensation has not been immediately obvious. In this regard, both molecular beam and supersonic low-density wind tunnel experiments have shown that, for relatively low-energy fluxes, practically all of the incident flux or flow is condensed on a surface normal to the stream, provided the surface temperature remains low enough. However, when the total enthalpy of the stream is high, as for rocket exhausts, it may be impossible to maintain the pumping surface temperature low enough, unless, as taught by the present invention, some kind of two-step system is utilized in which a precooling stage is used to initially extract the bulk of the sensible heat before the gas reaches the pumping (condensing) surface. In this connection, it has been determined that the precooling stage should be placed downstream of the condensing stage, since its positioning upstream thereof may result in large pumping losses.

Where a hot multispecies directed gas stream is present, the pumping system should comprise successively colder stages which (I) remove heat and (2) condense or absorb the various components thereof in a series of steps. In the case of rocket exhaust streams, the components thereof are usually condensable on liquid nitrogen cooled surfaces at a temperature of 80 K., conventional gaseous helium cooled surfaces at 20 K., and further absorbable on lower temperature surfaces at 420 K.

Previous attempts to maintain a low pressure in a space environment where a high-temperature jet introduces gas into a chamber have involved (1) allowing the chamber pressure to rise by several orders, which obviously is a disadvantage, (2) the provision of a very large capacity refrigeration system for the removal of both the sensible heat and the condensation heat of the jet and (3) the introduction of a precooling array of surfaces ahead of the condensing surface to extract the bulk of the sensible heat. Both the methods of (1) and (3) above have proven unsatisfactory, the method of (I) obviously allowing an unfavorable increase in chamber pressure, and the precoolers involved in the method of (3) above, that have been designed to date, having transmitted no more than fifty (50) percent of the flow, the remainder being returned, again, to unfavorably increase the chamber pressure. Solution (2) above has proven not feasible because of the high cost of refrigeration capacity at low temperatures. The present invention avoids the aforementioned unsatisfactory aspects by utilizing the directional character of the jet flow to minimize heat transfer to the condensing surfaces. The stream is cooled and rendered diffuse so that it is readily pumped by the relatively long passages inherently formed by and between the condensing surfaces, as will be further described hereinafter. In particular, the concept of the present invention maintains a low-environmental chamber pressure and, furthermore, minimizes the low-temperature refrigeration requirements by a unique and yet simplified arrangement to be hereinafter disclosed in the following summary and detailed description thereof.

SUMMARY OF THE INVENTION The present invention consists briefly in a cryopumping system for a wind tunnel or rocket which has as its principal object the pumping of a high-velocity, directed gas flow by the use of condensing surfaces incorporated downstream of the tunnel or rocket nozzle. The temperature of the flow is initially lowered by a precooling system located further downstream from the condensing surfaces. The latter are spaced apart and oriented parallel to the stream to thereby permit the flow to initially bypass therethrough for its direct impingement against, and precooling by, the precooling system, which includes separate precooling portions for both the axial and radial flow components. The precooled gas is thereby deflected, in diffused manner, back upstream for substantial impingement against, and condensation and collection on the condensing surfaces. A separate set of condensing surface are used for condensing both the precooled radial and axial components of the gas flow.

Other objects, as well as advantages, of the invention will become readily apparent from the following disclosure thereof, taken in connection with the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 represents a schematic illustration of the elementary two-stage cryopumping system concept utilized in the present invention, as it may be applied to one series of condensing surfaces;

FIG. 2 is another schematic view, showing the basic configuration incorporating the concept of the present invention, as it may be applied to the hot multispecies, directed gas stream of a rocket, for example;

FIG. 3 is a perspective view, partly schematic and brokenaway, illustrating details of the preferred form of the inventive cryopump; and

FIG. 4 is an additional partially schematic and broken-away view, showing further details of the cooling system utilized for both the precooling and condensing stages of the inventive arrangement of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring generally to the drawings, and, in particular, to FIG. 1 thereof, the basic or elementary two-stage system involved in the present invention is indicated generally at 10 as including a cooling surface at 11 and a condensing surface at 12, the latter being formed into a tubelike configuration. The two-stage system was developed, in accordance with the teaching of the present invention, when it became evident that, although relatively low-energy fluxes may be satisfactorily pumped by condensation alone, for relatively highenergy fluxes, a large fraction of the heat must be extracted, before the gas reaches the condensing surface, by means of a precooling surface. It has been determined that, if the said precooling surface is placed upstream of the condensing surface, the directed character of the flow is destroyed, and at least half of the scattered gas is reflected upstream. To obviate this difficulty, the precooling surface, as at Ill, for the present invention, may be located downstream of the condensing surface, as at 12, and thereby effectively blocks or closes the downstream end thereof. Moreover, since the axis of the tube configuration formed by the said condensing surface 11 is oriented parallel to the flow vector, the incident flux or flow, indicated generally at 13, is permitted to bypass therethrough and impinge directly against the cooling surface 11, where it is precooled. Thereafter the uniform incident flow impinging against the surface 11 is converted into random flux and diffuses upstream from section A" (Note FIG. 1), as is schematically indicated at the reference numeral 14. Part of this flux is thereby transmitted and then intercepted and condensed on the walls of the tube or condensing surface 12, and a part thereof, corresponding to the efflux at outlet or upstream end at the section marked Bf represents the fraction thereof not condensed and therefore not captured by the pump 10. Very little of the incoming flow from the incident flux I3 is intercepted by the condensing surface 12 due to the latters previously noted parallel orientation. However, because of its unique orientation, the latter surface I2 offers a large interception area to the diffusely returning flux, after the latter has initially impinged against, and been precooled by the configuration is to a high-enthalpy stream composed of 5 several species that are most efficiently condensed or absorbed on different surfaces. The cryogenies available may be used to supply cooling to surfaces at about 80 I(., l2-25 K., and 2-5 I(., respectively, for liquid nitrogen, gaseous helium, and liquid helium. In addition to direct condensation, cryogenic adsorption appears to be feasible for pumping hydrogen. In FIG. 2, for example, there is illustrated a schematic array of cooling and condensing surfaces, indicated generally at 15, that is designed to pump a hot gas stream comprising species which may, for example, condense at the aforementioned temperatures of 80 K., 20 K., and 4.5 I(., respectively. Thus, if these three cryogenic media are made available at the respectively lower temperatures, T,, T T as indicated above, the three-stage pumping arrangement of FIG. 2 is made effective for pumping a stream comprising components N., N and N; which may comprise the aforesaid coolants and which respectively condense at the three successively lower temperatures of T,,=80 K., T =2O K., and T =4.5 K. Thus, with the arrangement of FIG. 2, all the incident flow at 16 comprises components N N and N passes through the array until it is arrested and cooled at the 80 K. temperature section (T indicated at 17, which is at the extreme downstream end of the array. At this surface 17, the first condensable component, N is condensed and pumped. The remaining species, N and N diffuse upstream into the 20 K. temperature (T array at station A, as depicted at 18, where the major part of the second species N is condensed and pumped. However, a fraction, F of the 20 K. condensable species, N is transmitted through section B, as indicated at 19, as well as all of the third species N;,, as indicated at 20. The 4.5 temperature condensing surface transmits and condenses a fraction, F of the third species, N plus most of the 20 K., second species N leaving a portion or fraction F of the second species N and a fraction of F N to be rejected at the section C" and therefore not pumped, as indicated generally at 21.

The arrangement of the condensing surfaces through which the directed stream passes may be in the form of rectangular or hexagonal cells, concentric cones, or parallel plates, like a venetian blind. The specific embodiment of the invention to be hereinafter disclosed in connection with FIGS. 3 and 4 is an example of one such configuration which is currently utilized in a test facility. As viewed particularly in the aforesaid FIG. 3, the unique pumping system of the present invention is indicated generally at 22 as being enclosed within an outer wall surface 23, which may represent the chamber wall of a low density-research wind tunnel and/or space propulsion test facility. Pumping system 22 may comprise a first, pair of cooling surfaces 24 and respectively, for cooling the radial and axial components of the gas flow. Surfaces 24 and 25 may be maintained, for example, at the previously mentioned temperature of 80 K. or T Said pumping system 22 may further comprise a second, pair of condensing plate surface structures at 26 and 27, respectively, which correspond to the appropriately positioned cooling surface 24 and 25. On the one hand, cooling surface 24 is concentrically arranged within the outer research chamber wall 23 and is further positioned in surrounding relation to the condensing plate surface structure 26. Moreover, cooling surface 24 is further oriented normal to, and is utilized to intercept and initially cool the radial component of a high-velocity gas flow, indicated generally and schematically at 28, which is being emitted or exhausted from a nozzle at 29, the latter constituting either the wind tunnel or rocket nozzle. On the other hand, the cooling surface 25, which is mounted in blocking position downstream of the downstream ends of the condensing surface structure 27, is likewise further oriented normal to, and thereby intercepts and initiallycools the axial component of the aforesaid gas flow 28. After its initial precooling by the said cooling surfaces 24 and 25, the gas flow is then returned upstream in greatly diffused form.

Condensing plate surface structure 26 may consist of a plurality of horizontally and circumferentially disposed relatively elongated plate elements arranged in spaced apart and parallel relation to each other. Moreover, they may be concentrically arranged relative to, and within and in slightly spaced relation to the said cooling surface 24, as clearly depicted in the aforesaid FIG. 3. Condensing plate surface structure 27 likewise may consist of a plurality of vertically disposed, spaced apart and parallel plate elements positioned in front and upstream of the cooling surface 25. An important feature of both condensing surface structure-plate elements 26 and 27 resides in their parallel orientation relative to the gas flow 28 which ensures the initial bypass of the flow through the latter structure for its initial direct impingement on, and precooling by the cooling surfaces 24 and 25. In this manner, the present invention uniquely provides for the extraction of considerable heat from the gas flow prior to the latters condensation on the condensing surface structures 26 and 27. Moreover, the relatively elongated configuration of said condensing surface structures 26 and 27 provides what is, in effect, a series of long ducts ensuring a greater interception area and therefore much improved condensation to the gas flow, after the latter has been precooled and thereafter diffusely returned upstream.

The gas flow 28 to be cooled and condensed, which corresponds to the previously described incident flow of FIG. 2, may be composed of a single species N,, as in the case of the wind tunnel, or multiple species N,+N N,,, as in the case of a rocket exhaust plume. A suitable first, low temperature coolant at the previously described temperature T and consisting, for example, either of gaseous helium at 20 K., or liquid hydrogen, may be supplied to the condensing surface structures 26 and 27 from a first refrigeration system (not shown), through a supply or inlet line at 30 in the direction indicated by the arrow A, by way of a first, intake manifold at 31. Said low-temperature coolant may be thereafter collected by a second manifold at 32 for its subsequent return to the said first refrigeration system by way of the return line at 33, the direction of said coolant flow being indicated at the arrow A suitable second coolant at the previously suggested higher temperature, T K., may be similarly supplied to the cooling surfaces 24, 25 from a second refrigeration system (not shown) by means of the supply line at 34 in the direction indicated at the arrow C, through third and fourth manifolds, indicated at 35 and 36, respectively, and thereafter collected by a fifth and a sixth manifold, indicated at 37 and 38, respectively, for return to the said second refrigeration system by means of the return line at 39 in the direction of flow indicated at the arrow D."

With particular reference to FIG. 4, which illustrates only the cooling surface 24 and the condensing surface structure 26 for the sake of clarity, it is clearly illustrated that the previously described relatively high temperature T. 80 K., for example, coolant is transferred between the

manifolds

35 and 37 by means of coolant channels, indicated at 40, which may be integrally formed to the outer circumference of the said cooling surface 24 and interconnected therebetween. For the transfer of the previously noted, low temperature, T 20 I(., coolant between the

aforementioned manifolds

31 and 32, the coolant channels indicated at 41 as being integrally or otherwise formed within the individual elements comprising the condensing surface structure 26 may be utilized for interconnection between said last-named manifolds. Similarly designed interconnecting coolant channels (not shown) may also be utilized for transferring coolant between the

manifolds

36 and 38, respectively, used for the cooling surface 25 and condensing surface structure 27 (Note FIG. 3).

In operation, as seen in both FIGS. 3 and/or 4, both radial and axial components of the high-velocity gas flow 28 from the nozzle 29 passes between the condensing surfaces 26 and 27 and impinges directly on cooling surfaces 24 and/or 25 (cooling surface 24 and condensing surface structure 26 only are shown in FIG. 4), due to the parallel and spaced-apart orientation of the said condensing surface structures 26 and 27 to the direction of flow, where, according to classical slip flow, or molecular flow theory with an accommodation of unity, the molecules leaving the cooling surfaces 24 and 25 will be at a temperature in equilibrium with that of the surfaces 24, 25. To ensure the diffuse flow of the intercepted gas flow from the surface of each of the cooling surfaces 24 and 25, the latter may be formed with a grooved surface configuration, as indicated, for example, at 24a in FIG. 4 for the surface 24.

As previously indicated with particular reference to FIG. 2, a large portion of the diffuse flow leaving the cooling surfaces 24, 25 will impinge on the condensing surface structures 26 and 27 where it will be condensed and captured, provided, of course, the condensing surface temperature is maintained at the condensing temperature in the manner hereinbefore described for the unique arrangement of the present invention. Moreover, to facilitate both the transfer of the coolant flow between the manifolds, such as at 31 and 32, as well as to foster or improve the condensing action of each of the said condensing surface structures 26 and 27, the latter may be each fabricated from a flat central plate element, as at 26a in FIG. 4, each of which plate element may be integrally formed with a coolant channel, such as was previously described at 41. Furthermore, the said central plate element may be further formed with an outer surface portion that incorporates a continuous configuration comprising a plurality of triangular, or other suitably shaped outwardly projecting pointed elements, as at 42, which collectively form a series of condensation-collecting channels interspersed therebetween and thereby greatly improves the condensing and collecting of the said condensation surface structures 26 and 27 Although the foregoing description of the operation of the inventive pumping system was based on an assumed accommodation coefiicient of unity; in actual practice, this coefficient will not be unity, but may approach it and values of 0.8 to 0.9 have been quite common. Furthermore, when the flow is composed of rocket exhaust gases, or other multicomponent gases, some components having higher condensation temperatures and therefore more easily condensable, the cooling surfaces 24 and 25 of the improved mechanism of the present invention will condense such more easily condensed constituents, thus reducing the heat load that must be handled by the more expensive low-temperature condensing surfaces 26 and 27.

Thus, a new and improved high-velocity gas flow pumping system has been developed wherein the low-temperature condensing surfaces 26 and 27 thereof are not required to accept the heat load of gases that will condense at higher temperatures; the gas flow is precooled before striking the said low temperature condensing surfaces, thereby even further reducing the refrigeration requirements for the required condensation; and the arrangement of the condensing surfaces 26 and 27 in a series of long duct configurations insures that a large fraction of the steam is condensed.

We claim:

1. A cryopumping system for application in a low-density research chamber-wind tunnel and/or space propulsion test facility having a high-speed nozzle for emitting a high-energy gas flow therefrom, and comprising; condensing means located in the chamber downstream of the nozzle and incorporating open-ended passageways oriented in a first, predetermined manner relative to the chamber axis, and corresponding to a first position in direct communicating and parallel relation with, and thereby initially receiving and bypassing therethrough the expanding flow of the high-energy gas being emitted from said nozzle, without any substantial condensation resulting therefrom; cooling means positioned within the chamber at a position therein downstream of the condensing means and being further oriented in a second, predetermined manner corresponding to a second position directly in the path of, and thereby ensuring the initial interception and substantial precooling of the gas flow being initially bypassed through the said open-ended passageways of said condensing means; said initially intercepted gas flow being thereby and thereafter returned upstream in a diffused condition, and therefore at a substantial angle to its original flow, after its initial, direct impingement with said cooling means, for its subsequent and substantial interception by, and condensation on, a substantial intercepting area of, the open-ended passageways of said condensing means; and separate coolant supply and return means adapted to respectively supply coolant at successively lower temperatures to said cooling and condensing means.

2. In a cryopumping system as in claim 1, wherein the openended passageways of said condensing means includes separate, first and second condensing-passageway portions perpendicularly-arranged relative to each other and respectively oriented in parallel relation to both radial and axial-flow components inherent in the expanding gas being emitted from said nozzle.

3. In a cryopumping system as in claim 2, wherein said first condensing-passageway portion comprises a first, plurality of horizontally extending and circumfierentially-disposed, condensing plate elements arranged in spaced-apart relation to each other, and in parallel relation to the radial component of the said gas flow resulting from its radially outward expansion after leaving the chamber nozzle; said condensing plate elements thereby forming said first condensing-passageway portion into a plurality of gas flow-bypassing ducts aligned in substantially parallel relation to, and thus ensuring the bypass therethrough of the radial component of said gas flow.

4. In a cryopumping system as in claim 2, wherein said second condensing-passageway portion comprises a second, plurality of vertically disposed, condensing plate elements oriented in both spaced apart and parallel relation to each other, and in parallel manner to the axial component of the said gas flow.

5. In a cryopumping system as in claim 4, wherein said cooling means comprises a first, precooler device oriented outwardly of, and at a first predetermined angular relation to said first, plurality of horizontally disposed, condensing plate elements to thereby ensure the deflection of the radial component of said precooled initial gas flow against a relatively large interception area formed by said condensing means.

6. In a cryopumping system as in claim 5, wherein said cooling means further comprises a second precooler device positioned downstream of, and oriented at a second predetermined angular relation relative to said second, plurality of vertically disposed, condensing plate elements to thereby ensure the deflection of the precooled gas flow against the maximum area of interception of said last-named condensing plate elements.

7. In a cryopumping system as in claim 5, wherein said first precooler device comprises a grooved and arcuate-shaped, cooling surface circurnferentially disposed in spaced relation to, and radially outwardly of, said first-named condensing surface and thereby being in normal intercepting relation to the radial component of the expanding gas flow to thereby ensure the maximum diffusion of the said gas flow being impinged thereon and returned thereby to said first-named condensing surface.

8. In a cryopumping system as in claim 6, wherein said second precooler device comprises a. grooved inner surfaceplatelike element disposed normal to the gas flow immediately downstream of said second-named condensing surface to thereby intercept, precool, and ensure the return of the incoming flow in diffused manner to said last-named condensing surface.

9. In a cryopumping system as in claim 6, wherein said separate coolant supply and return means comprises a first, inlet coolant supply line adapted to supply a first coolant at a first, predetermined cooling temperature; a first manifold in contact with and thereby providing coolant to said first,

than that of said first-named, cooling temperature and further corresponding to the condensation temperature of the gas being condensed thereby; a third manifold in communication between said second, inlet coolant supply line and said first condensing portion; a fourth manifold for cooling said second condensing portion; and interconnecting coolant transfer line means extending between said third and fourth manifolds for ensuring the transfer of the said coolant therebetween.

Claims

2. In a cryopumping system as in claim 1, wherein the open-ended passageways of said condensing means includes separate, first and second condensing-passageway portions perpendicularly-arranged relative to each other and respectively oriented in parallel relation to both radial and axial-flow components inherent in the expanding gas beinG emitted from said nozzle.

3. In a cryopumping system as in claim 2, wherein said first condensing-passageway portion comprises a first, plurality of horizontally extending and circumferentially-disposed, condensing plate elements arranged in spaced-apart relation to each other, and in parallel relation to the radial component of the said gas flow resulting from its radially outward expansion after leaving the chamber nozzle; said condensing plate elements thereby forming said first condensing-passageway portion into a plurality of gas flow-bypassing ducts aligned in substantially parallel relation to, and thus ensuring the bypass therethrough of the radial component of said gas flow.

7. In a cryopumping system as in claim 5, wherein said first precooler device comprises a grooved and arcuate-shaped, cooling surface circumferentially disposed in spaced relation to, and radially outwardly of, said first-named condensing surface and thereby being in normal intercepting relation to the radial component of the expanding gas flow to thereby ensure the maximum diffusion of the said gas flow being impinged thereon and returned thereby to said first-named condensing surface.

8. In a cryopumping system as in claim 6, wherein said second precooler device comprises a grooved inner surface-platelike element disposed normal to the gas flow immediately downstream of said second-named condensing surface to thereby intercept, precool, and ensure the return of the incoming flow in diffused manner to said last-named condensing surface.

9. In a cryopumping system as in claim 6, wherein said separate coolant supply and return means comprises a first, inlet coolant supply line adapted to supply a first coolant at a first, predetermined cooling temperature; a first manifold in contact with and thereby providing coolant to said first, precooler device and in communication with said first, inlet supply line; a second manifold in contact with and thereby providing coolant to said second precooler device; and interconnecting coolant-supply means disposed in open communication between said first and second manifolds to thereby ensure the transfer of the said coolant therebetween.

10. In a cryopumping system as in claim 9, wherein said separate coolant supply and return means further comprises a second, inlet coolant supply line adapted to supply a second coolant at a second, predetermined cooling temperature lower than that of said first-named, cooling temperature and further corresponding to the condensation temperature of the gas being condensed thereby; a third manifold in communication between said second, inlet coolant supply line and said first condensing portion; a fourth manifold for cooling said second condensing portion; and interconnecting coolant transfer line means extending between said third and fourth manifolds for ensurinG the transfer of the said coolant therebetween.