US2939316A - High vacuum device - Google Patents

Description

June 7, 1960 N. BEECHER ETAL HIGH VACUUM DEVICE Filed March 14, 1958 NN .Sl

INVENTORJ` Norman 5 ecLNk MN ON Amm G. u/JSL QLA CJ- nited States Patent i() i HIGH VACUUM DEVICE Norman Beecher and Milo P. Hnilicka, Jr., Concord,

Filed Mar. 14, 1958, Ser. No. 721,466

11 Claims. (Cl. 73-116) This invention relates to testing and more particularly to apparatus for testing rocket motors and the like under conditions encountered by such rocket motors at extremely high altitudes.

In order to test rocket motors which are to be fired at high altitudes (well above the altitudes presently encountered by manned aircraft) it has been necessary to fire the rocket from another rocket or ballon and to telemeter test data back to the ground. There have been some attempts to fire such rocket motors under simulated conditions of high altitude at ground level. So far as is known, such simulated tiring at ground level has not been successfully accomplished under conditions approximating those existing in the upper atmosphere.

Accordingly, it is a principal object of the present invention to provide testing apparatus which will permit firing of a rocket motor under conditions simulating those existing at altitudes from seventy-five to one hundred and' fifty miles.

.Still another object of the invention is to provide a testing apparatus which is capable of pumping millions of cubic feet per minute of gases resulting from the operation of a rocket motor in a high vacuum chamber.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the apparatus possessing the construction, combination or elements and arrangement of parts which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawing which is a diagrammatic, schematic, sectional View of a preferred embodiment of the invention.

When firing a rocket motor under conditions corresponding to an altitude of seventy-five to one hundred miles, it is necessary to maintain a pressure on the order of -5 to lO-G mm. Hg abs. 'Ihe test system must be capable of handling the enormous volume of low-pressure gas generated when the rocket is fired into an evacuated chamber.

In a preferred embodiment of the invention, this is accomplished by providing an elongated vacuum-tight chamber which includes a means for evacuating the chamber to a free air pressure of less than l mm. Hg abs. It also includes a means for holding the rocket motor to be tested adjacent the forward portion of the chamber in a position to introduce the combustion products into the chamber at high velocity in a direction generally parallel to the axis of the elongated chamber. Adjacent that forward portion of the chamberholding the rocket motor, there is provided a first condensing surface which, in a preferred embodiment, is the wall of the elongated chamber. Refrigerating means is associated with this l iii-st condensing surface which is capable of maintaining this surface at a temperature on the order of 77 K. to

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82 K. Further along the chamber there is provided a second condensing surface (also preferably part of the chamber wall) having an associated refrigerating mechanism for maintaining thisY surface at a temperature on the order of 65 K. Lastly, the chamber includes a third condensing surface and means for maintaining this third condensing surface at a temperature between 40 K. and 65 K.

The rst condensing surface is preferably maintained at a temperature of about 77 K. to 82 K. by means of a supply of liquid air or nitrogen at atmospheric pressure which is sprayed over the outside of the chamber wall by means of a circulating pump and distribution system. Evaporation of the liquid air or nitrogen at at- Inospheric pressure will maintain this wall at about 77 K. to 82 K.

- For covenience the invention will be initially described as employing liquid nitrogen. Accordingly, evaporation of liquid nitrogen at atmospheric pressure will maintain this wall at about 77 K. The second refrigerating surface is maintained at 65 K. by providing in contact therewith a supply of liquid nitrogen which is maintained at a pressure of about 200 mm. Hg abs., this pressure corresponding to a temperature of about 65 K. The third condensing surface is preferably maintained at the low temperature of between 4 K. and 65 K. by a refrigeration system utilizing gaseous helium. The gaseous helium refrigeration system preferably includes a compressor, counter-current heat exchanger, heat exchanger for utilizing cold nitrogen vapors and an expander. The helium refrigeration system is preferably maintained throughout the complete cycle at a temperature above the condensation temperature (4 K.) of helium so that it is not necessary to handle liquid helium.

The air or nitrogen system is preferably arranged so that during the initial cooling of the chamber from room temperature of about 300 K. to 77 K., total refrigera tion duty of the expander is used for removal of most of the sensible heat in the system by a gaseous nitrogen recirculation system. Accordingly, the nitrogen system is arranged so that a closed compression-expansion cycle gradually reduces the temperature of the gaseous nitrogen by recycling to the point where it approaches the desired, extremely low temperature of nitrogen liquefaction. Thereafter, before the test rocket is fired the excess refrigeration produced by the expander can be usedfor liquefaction of air and fractionation of nitrogen and liquid nitrogen can be stored in an insulated container. During l the actual rocket firing, when the heat load exceeds several times the expander duty, the accumulated inventory of liquid nitrogen is circulated to sprays or wiers and is used to supplement the expander duty.

Y Referring now to the drawing, there is shown a schematic, diagramma-tic sectional View of one preferred embodiment of the invention. The apparatus comprises an elongated, stainless steel chamber 10 defining there Withman elongated space 12. Adjacent one end of chamber 10, there is positioned an insulated plug 14 arranged to provide an effective heat break between test chamber tempera-ture and room temperature and to support a lrocket motor schematicallyv indicated at 16. The end of chamber 10 in front of plug 14 is at room temperature and is closed by a rubber gasketed vacuum door 18. A

valve 22 and a charging port are provided so that a sequence of rocket motors to be tested can be introduced into the space 12 after evacuation `without disturbing the test chamber vacuum. A plurality of vacuum pumps 24 distributed along the length of the chamber `are employed for evacuating space 12 to the requisite low pressure. In a preferred embodiment, these pumps include combinations of steam ejectors and diusion pumps so as vtcrncenitive .substantially alllof `the air system to remove most of the sensible heat. Vtern preferably includes a `nitrogenvent'66 arranged to "vent both chambers 25 'and 27 'during initial cooling of Vthe. system. During this initial coolingthese two chama f. 3 Y Y Y* from the interior of the chamber as Well as the noncondensible residue of combustiony products near the point of hrst impinge- Y ment-.offthes'e moncondensible zgasesonfthe wall of the chambenlll. While only i2 such pumps are shown, it. is anticipated that Ias many as one hundred 16inoh highvacuum.idiiusionpumps willY be positioned along the chamber.Y and around thepperipher'y of a test chamber 12 Yfeet in diameter and 100 feet long.

` and .27, respectively, Vthese two wiers being fed liquid nitrogenfromjpipes y36 yand 38. Liquid nitrogen overflows from the wiersandcovers the'outer surface of test chamber 10 with afiln'i of liquid. Liquid nitrogen vapo- .rizingfrom the iilmintothe spaces 25 and 27 provides a high .heat transfer and maintains the inside walls of the Vtest chamber 10 at the requisite low ltemperature corre- Y :sponding tothe nitrogen vapor pressure in the spaces'25 and 27,.respeotively. The liquid'nitrogen is fed through `pipe 40 'from a storage tank 42'by means of a recirculating pump 46. Excessrliquid nitrogen owing around the sides of -test chamber'l) is fed back to the storage tank 42 bymeans of drainpipes 48V and '50. Makeup liquid nitrogen Vintroduced to the system 'by means of pipes Y 52 and v92.

"Nitrogen vapors at Y--32()" F. (77 K.) escape from space `25 adjacent' the front end of chamber' 10 through Apipe 60, a compressed helium gas cooler' 84 and then are vented to atmospheric pressure. VThe sensible heat of i the vent gases at lofwV temperature level can be used in vregenerative heat exchangers, if economically desirable. 'Nitrogenvapors from the space'27, adjacent the far end of theclramber 10, escape from vent 62 which is preferably arranged, Vvby means of vacuum pump 64, to maintain la *pressure onthe' order of l0() to 200 mm. Hg abs. Yinetlrie'space', corresponding to nitrogen boiling points of'63 K.to68'K. y

"Whileliquid'nitrogen orliquid air can be utilized to cool-thetestchamber 10 fromv about 300 K. to 77 K., itismuch preferred to utilizeA a gaseous 'nitrogen recycle 'Ihis sysbers "25land l27 preferably-both operate at about atmospheric pressure. Nitrogenmvapms in pipe 66 pass 'through a countercurrent heat'exchanger 70 into Va com- Y' A 2,939,316 e' E, -v -Y heat exchanger 91, the chilled helium vapors are passed through expander 86 Where further heat is removed as mechanical energy. 'Ihe chilled helium vapors then pass through a condensing coil schematically indicated at 88 which is positioned inside ofthe test chamber 10 at the far end thereof from therockt motor-16. 'I'he cold helium will maintain the -coil at la .temperature between 4 and 65 K.' VSince'the coil "88 is completely surrounded by cold,(.65"jK.-77 K.) Walls, it will pick up very little lheat by radiation. VAccordingly .thereis substantially no loss of refrigeration-capacity of coil 88 due to radiation. If desired, liquid nitrogen'or l65" K. nitrogen vapors can be used as refrigerant for the helium vapors. Y Y

In addition to the above-described pumping system, there is also preferably included anadsorbent mass 96, preferably charcoal or silica gel, which is conned in a relatively ,thin layer around the periphery of the .tank witha'large .exposed area to permit adsorption of noncondensible gases, such `ashydrogen and nitrogen. This adsorbent mass 96 Yis chilled to 65 `K. or thereabouts Vby the low temperature of the chamber 10 adjacent space 27.

In the operation of .fthe device as shown, steam'is introduced to the'interior of the test chamber-10 by means Vof a pipe A90, the steam serving to displaceair from the interior of the chamber and to heat the chamber walls -to facilitate evaporation of moisture and other condensed vapors. While the steam is being introduced, the vacuum system 1 is operated to continuously Yor intermittently remove a mixture of steam and air. When the Sinner surface of the Walls of the chamber '10 have been heated to the .requisite degree (eg. 200 F.) and most of the air has been displaced from the interior ofthe -chamber, introduction of steam is stopped andV evacualtion of the chamber proceeds by means of pumps24. During this evacuation, hot air or steam can be recirculated through the spaces 25 and 27 .to maintain the chamber 10`at arelatively high temperature to degas thewalls commenced. lThe nitrogen atmosphere in spaces 25 and 27 is Y recirculated Vthrough `the pipe 66, heat exchanger 7 0,compressor 72 and'expander 76 from which it is introduced back through the spaces 25 and 27. Since this pressor '7215through an after ycooler 74 and return back .Y

through-the vheaty countercurrent exchanger 70. Thereafterfthe compressed cooled nitrogen vapors are Vrun ,through Van expander 76 where the heat is removed as mechanical-:energy and the stream temperature drops 30 fC. or more. From the expander Athe cooled gases y'arefedibyrneans of pipe 78 back to spaces 25 and 27 "--to cool the chamber 10, andV the insulating Vtank 23. Conventional Vmeans such as a reversing countercurrent heataexchangerfor an adsorbent 'filter is used to avoid foulingA of Vthe countercurrent heat exchangers by ice or -.(U.S. Ratent No. 2,584,381, Dodge et al., February 5,1952.)

The;helium system includes a compressor 80 for com- .pressing .helium gas, and a heat exchanger 84 where the compressed 'helium gas is passed in heat-exchange rela- -V`tionship lvvithlcolcl (77 'K.) vnitrogen vapors passing f-thrpuehlnipa, @fte-racing through .a countercurrent Vrecirculation of nitrogen removes largequantities of heat from the spaces 25' and 27, it will serveto cool the Wall 1t? of the'testchamben'the inner wall 26 and the insulation 30 of the insulating tank 23. By this means,

`the temperature `of the Walls 10 and 26 can be'reduced to VYabout 'K. Thereafter the nitrogen vapor recycle system can be' discontinued and liquid nitrogen is introducedjthroughpipe '36 and 38 to wiers 34 and 35 so as tospray liquid nitrogen over the outer surface of test Vbrought into operation to Vbring the temperature'of the condensing coil 88 down to a Vtemperature substantially lbelow'65 K., but above 4'K. A'suitable rocket motor is Vplaced inthe charging port .26, which charging portis evacuated. VThe rocket is then introducedinto the holder i4 and. is red. The gaseous products Yof combustion l pass down the-space 12 and condense on the inner Surface of chamber. 10.V Some of the, products of combus-tion will condcnseinean the rocket Ymotor 4where the Walla is about 77 K. Most of the remainder .of the reaction products will condense at the far end of the chamber which is maintained at 65 K., while carbon monoxide and nitrogen will condense at lthe surface of cooling coil 88 which is maintained between 4 K. and 65 K. Hydrogen and helium in the reaction products will be pumped out by a multiplicity of ports distributed along the chamber the vacuum pumps 24, backed by suitable forepumps.

Some of the hydrogen, helium and nitrogen will also be adsorbed by the very cold adsorption medium 96 so as to decrease the pumping load on the pumps 24.

The gaseous nitrogen recycle system can be employed as part of the facility in manufacturing liquid air or liquid nitrogen during times when it is not required for cooling the chamber 10. In this case, cold gas coming from the expander 716 can be passed through pipe 95 to heat exchanger 94 where it cools the interior of the heat exchanger to liquid air orl liquid nitrogen temperatures. It then passes through the counter-current heat exchanger 70, through the compressor 72, the after cooler 74, through the heat exchanger 70 again and a portion of the high pressure gases are then diverted to the heat Y exchanger 94 where liquid air or liquid nitrogen is condensed. The remainder of the stream passes through the expander 76 for removing further heat. lf the system is operated at atmospheric pressure at the outlet of the expander 76, liquid air will be produced in the heat exchanger 94. If it is operated at sub-atmospheric pressure, liquid nitrogen can be condensed in condenser 94.

Numerous changes in the above apparatus can be made without departing from the spirit of the invention. For example, sprays can be used instead of wiers -34 and 35. 'Equally the refrigeration cycle can be modied by including high pressure systems as well as low pressure systems.

Since certain changes can be made in the above method and apparatus without departing from the scope of the inventionherein involved, it is intended that all matter contained in the above description, or shown in the accompanying drawings, shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. Testing apparatus comprising an elongated vacuumtight chamber, means for evacuating said chamber to a pressure less than 1 mm. Hg abs., means for positioning a rocket motor adjacent the forward portion of the chamber in position to introduce its products of combustion into the chamber at high velocity, first refrigeratng means for maintaining a rst condensing surface in the chamber at a temperature on the order of 77 K., said first condensing surface comprising a surface adjacent the forward portion of said chamber, second refrigerating means for maintaining a second condensing surface in the chamber at a temperature on the order of 65 K., said second condensing surface comprising a surface adjacent the backward portion of said chamber, and third refrigerating means for maintaining a third condensing surface in the chamber at a temperature between 4 K. and 65 K, said third condensing surface comprising a coil positioned within the backward portion of said chamber.

2. Testing apparatus comprising an elongated vacuumtight chamber, means for evacuating said chamber to a pressure less than 1 mm. Hg abs., means for positioning a rocket motor adjacent the forward portion of the chamber in position to introduce the vapors therefrom into the chamber at high velocity, a first refrigerating means for maintaining a rst condensing surface in the chamber at a temperature on the order of 77 K., said first condensing surface comprising a surface adjacent the forward portion of said chamber, second refrigerating means for maintaining a second condensing surface in the chamber at a temperature on theorder of 65 K., said second condensing surface comprising a surface adjacent the backward portion of said chamber, and third refrigerating means for maintaining a third condensing surface in the chamber at a temperature between 4 K. and 65 K., said third condensing surface comprising a coil positioned within the backward portion of said chamber, said iirst refrigerating means including means for providing a supply of liquid nitrogen at about 760 mm. Hg. abs., and said second refrigerating means including means for providing a supply of liquid nitrogen at about 200 mm. Hg abs.

3. The apparatus of claim 2 wherein the third refrigerating means includes means for compressing helium and removing heat from the compressed helium by heat exchange with nitrogen vapors in one of said other refrigerating means.

4. The apparatus of claim 2`wherein one of said rst two refrigerating means includes means for owing a thin layer of liquid nitrogen over the outer surface of the chamber-defining wall. y

5. The apparatus of claim 2 wherein said first refrigerating system includes means for compressing nitrogen,v

means for expanding the compressed nitrogen to do work and remove heat therefrom and means for passing the expanded nitrogen in heat exchange relation to the first condensing surface to cool the first condensing surface.

6. IIfhe apparatus `of claim 2 wherein means are includcd for introducing a condensible vapor into the chamber to displace non-condensible and atmospheric gases from the chamber and thus facilitate initial pump down'of the system to a relatively high vacuum on the order of the few microns or less Hg abs.

7. The apparatus of claim 2 wherein the first condens- Y ing surface is nearer to the source of vapors than is the second or third condensing surface. y

8. The apparatus of claim 2 wherein the third refrigerating means includes meansY for compressing helium and removing heat from the compressed helium by `heat exchange with nitrogen vapors.

9. The apparatusr of claim 2 wherein an adsorbent medium ispositioned, in heat exchange relation to the cold chamber walls, inside of the chamber in position to adsorb large quantities of gases at low absolute pressures and temperatures. Y

10. `The apparatus of claim 9 wherein the adsorbent is supported as a cylinder around the inner periphery of the chamber.

ll. The apparatus of claim 2 wherein a plurality of diffusion pumps are distributed along the chamber to pump non-condensibles so that the non-condensibles will be pumped out of the system near the point of iirst impingement thereof on the chamber wall.

References Cited in the file of this patent UNITED STATES PATENTS 2,615,331 Lundgren Oct. 28, 1952 FOREIGN PATENTS 1,002,071 France oct. s1, 1951

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