US2892308A - Water spray cooling method and apparatus for supersonic nozzle - Google Patents

Description

June 30, 1959 A. FERRI ET AL WATER SPRAY COOLING METHOD AND APPARATUS PoR sUPERsoNIc NozzLE Filed April 19, 1957 Q" A J xwh SY s/,v/ v6 Aza.

United States Patent WATER SPRAY COGLING METHOD AND APPA- RATUS FOR SUPERSONC NOZZLE Antonio Ferri, Rockville Centre, Paul A. Libby, Freeport, and Martin H. Bloom, Woodmere, N.Y., assignors to the United States of America as represented by the vSecretary of the Air Force Application April 19, 1957., Serial No. 654,049 Claims. (Cl. titl-35.6)

The present invention relates to a method and apparatus for the rapid and efficient cooling of a high speed How nozzle or conduit; and more particularly, -relates to the cooling of supersonic flow nozzles and the like by a coolant, low energy combined gas and liquid stream directed over the exterior surface of the nozzle wall,

In cooling high temperature wall structures, especially those forming conduits or nozzles for the high speed, high heat energy flow of compressiblelluids, the thermal and mechanical stresses developed in the wall by the high energyr stream present many difficulties. A high temperature on the inner surface of the wall tendingto expand the wall, countered by a low temperature on the cold'- side causing contraction of the wall, creates severe stresses across the wall which at high temperature and pressure diierential tend toV fracture or shear the wall structure. The use of an extremely thin Wall to eliminate the temperature gradient across the wall has been proposed; however, where a high pressure gradientexists between the main stream and cooling stream, it is not possible to use a thin wall structure. v

' Among other standard cooling methods, both regenerative and evaporative cooling have been proposed as a solution of the cooling problem, particularly in rocket motor construction. Unfortunately,'the boiling instability of liquid streams within aA high Vtemperaturevpassage renders the above types and other similar coolingliquid methods impractical for extremely high speed cooling.

` Cooling and efficient heat absorptionrbecorne an'especiallywaciite problem in supersonic ilow nozzles. .'Ihc. major design factor is concerned with the, heat transfer at' the throat area ofthenozzle. As an example, with an airV y"stre-am. entering the throat area of the nozzle at 3,"000 iR. and at 600 p.s.i. for acceleration up to sonic speeds 'followed by expansion up to supersonic and hypersonicspeeds, it is vnecessaryto Vtransfer exceedingly high amounts of heataway from avery small throat area. With a `greater wall thickness to .withstand the pressure, it isfirnpossibletov rapidly conductvthe heat away from the throat area. With a thin walled throat area, of course the pressure conditions become critical. Also, inf 'supersonic and, hypersonic ow nozzles the nozzle wall must `be. extremely rigid and smooth to prevent development of shock waves in the air flow.

. The present invention obviates the foregoing difficulties andproblerns and permits theuse of a thin walled nozzle or `conduit structure forthe high speed, high energy ow of iiuid with rapid and eiicient cooling in providing for a method, andan apparatus for the cooling and pressure equalization of theV thin walled structure by passing a low energystream over the outside surface of the nozzle at aMachnumber equivalent to the Mach number in tliefhigh energy stream, and simultaneously intermixing a liquid vspray coolant with the low energy stream, the liquid having a vaporization temperature below the Wall temperature vso as to establish additional cooling by evaporation. s, y

lt-is, accordingly, an object of the present invention to provide for the pressure equalizing, indirect cooling of a chamber or nozzle wall which is exposed to high s equalization, together with the indirect, rapid cooling of 'i a thin Walled, high temperature conduit exposed to high velocity, high energy fluid streams.

Itis an additional object to provide for a high velocity coolant stream adjacent to a supersonic flow nozzle for the convective and evaporative cooling of the nozzle walls together with the ow and pressure equalization of a high energy fluid stream flowing through the nozzle.

Itis another object to provide for a liquid saturated coolant air stream through a contoured passage along the exterior wall of a hypersonic flow nozzle with the coolant stream ow under conditions corresponding to conditions of a high energy stream through the nozzle.

It is anadditional object to provide for a method for cooling the walls of supersonic and hypersonic ow noz-v zles in such a way as to maintain the walls at a constant temperature with negligible mechanical stresses during high energy stream flow at high stagnation temperatures and stagnation pressures through the nozzle.

It is a further object to providefor a low energy air stream over the exterior surface of an inner lining for a ow passage at a velocity and stagnation pressure equivalent to the velocity and pressure ow of a high energy stream owing through the passage.

A still further object is the provision of a Water sprayed, selectively controlled coolant air stream along the outer` surface of an axially symmetrical nozzle wall at` avelocity and stagnation pressure equivalent to the velocity and pressure of a high energy air stream owing through the nozzle.

-Other objects and features of the present invention will become apparent in View of the following description considered inconnection with the accompanying drawings in which:VV

,Fig lis a sectional view of a hypersonic ow nozzle I disposed in a wind tunnel to receive high stagnation temperature Vand pressure air from a heater section; and

Fig. 2 is a detailed,-fragmentary view of the throat section of the preferred form of nozzle. In Fig. 1 there is shown a preferred embodiment of a supersonic, axially symmetrical flow nozzle 10 disposed within a Wind tunnel housing 11 with a forced air sup` ply system 12 including a heater (not shown) disposed at right angles to the wind tunnel and nozzle.

-As more particularly set forth in our copending application,..SerialeNurnber 645,878, led March 13, 1957, it is now possible to supply air lfor hypersonic flow purpose at 600 p.s.i. and 3,000" R. These conditions have been found necessary in order to simulate free-flight conditions for Mach numbers ranging from 5 to l5; that is, to obtain full stagnation temperatures and pressures at the corresponding Mach number desired. In accelerating such a high temperature, high pressure air stream up to the de sired Mach number, thepresent invention provides for the elongated,` thin walled, axiallyV symmetrical nozzle or effusor 10 consisting of a convergent entrance 15 at the entrance to the wind tunnel to receive the air from the` exhaust section'of the heater, followed by a throat section- 16 and a gradually divergent test section 17 to further accelerate the air up to hypersonic speeds. For interconnection ofthe nozzle to the wind tunnel and to an outer wall Z0, to be'described, support means are integrally formed with the nozzle including a forward, peripheral lip 13 verging radially outwardly then rearwardly from the entrance 15 and a circumferential shoulderportion 14 located adjacent the Mach 3 section of the Patented June 30, 1959 test section 17. The nozzle wall is composed of a suitable low carbon steel with a smooth, uniform nickel plating covering the inner surface thereof. Of course, other suitable, high temperature materials may'be utilized, such as stainless steel.-

Spaced between thetunnel housing 11 and the nozzle wall is the annular cooling jacket or outer wall 20 with inner surface 21 of the cooling jacket fo'rming'a-specially designed, contoured cooling passage 22. The annular passage 22, whichl is defined by the exterior surface of the nozzle wall and the inner surface of the cooling jacket', `is contoured so that the height of the passage varies proportionally with the diameter of the main ow passage at corresponding points along the nozzle and passage. The effective height and arca of the cooling passage thus correspond with the effective diameter and area of the nozzle to obtain equivalent flow characteristics inthe iluid streams. This construction is consideredunique in. that iluid flow in the cooling passage and main nozzle can be controlled to ow at equivalent Mach numbers and stagnation pressures; it is thereby possible to equalize the high pressure flow of the main stream through the nozzle by means of the coolant stream in the passage. At the same time, the coolant stream is conducting heat from the cold Wall side o f the nozzle substantially as rapidly as it is being transferred to the wall by the high energy main stream.

In that heat transfer conditions are critical along the nozzlewallfrom a point just ahead ofthe throat section up to the Mach 3 section in the nozzle, the cooling ,passage is'extended-substantially half-way along the divergent test section from the entrance into the nozzle. The cooling passage 22 is therefore formed of an annular manifold opening 23 which extends peripherally about the nozzle entrance 15 between the nozzle wall and outer wall, then converges rearwardly and inwardly into a restricted annular throat section 24 and diverges rearwardly along the nozzle' test section and is terminated adjacentV the Mach 3 section.

To obtain a rigid connection between the outer wall 20V and the nozzle, the outer wall is constructed in sections and positioned between the lip 13 and shoulder 14 of the nozzle. The sections are preferably welded to form'thecomplete wall structure and connected to the outer end ofthe lip 13 and to the forward surface of the shoulder 14 by means of suitable Weld or bolted connections. The entire assembly is then inserted into the Wind tunnel housing and positioned adjacent the discharge chamber from the supply system 12.

Leading into the manifold 23 at circumferential, spaced intervals are coolant air supply pipes or hoses 26 which are passed through bores 25, each bore extending the length of the wall and through the shoulder 14 as shown. Each pipe is supplied with air from a suitable pressurized air storage supply source or chamber 29. At the rearward end of the cooling passage 22, a series of bores 27 are passed through the shoulder adjacent the nozzle wall for extension of exhaust pipes 28 into the exhaust end of the cooling passage to act as disposal outlets for the pressurized air stream leaving the cooling passage.

In high speed flow through supersonic speeds the heat transfer rates, particularly across the nozzle Wall in the throat area can be eiciently absorbed by the coolant air stream alone and it is possible to maintain a low, constant' wall temperature throughout the length of the passage. However, in hypersonic flowVthe heat transfer rates become so critical that the wall thickness at the throat area would have to be impractically small in order to establish the necessary cooling by the air coolant stream alone. A unique manner of additional cooling isprovided in the present invention to maintain the desired wall temperature, while at the same time making it possible to retain a reasonable wall thickness. For this purpose, a series of tube receiving openings 30 are spaced' at axial and circumferential intervals. through the outer wall 20 which project radially inwardly from the outer surface to the inner surface of the wall along the entrance and throat section. Extending through each of the openings 30 is a liquid-conducting tube 31 for projection into the cooling passage 22 with a small orifice or spray nozzle 32 connected'to the passage end of each tube 31'l The spray orifices are preferably fitted with an elbow iitting so that in connected position to the tubes, the orifices will be directed down stream in the direction of ow ofthe coolant air. of each tube 31 a water supply system including a chamber 33 is provided to supply Water in pressurized form to the liquid conducting tubes. The supply chamber 33'is regulated to force water through the orifices at a pressure of to 250 psi. greater than thepressure of the coolant air stream at that point; In this way, finely divided droplets of water are sprayed evenly across the coolant stream so as to thoroughly intermix with the stream and provide optimuml cooling by evaporation. thorough intermixing can also be obtained by impinging the atomized Water transverselyV across the cooling passage into the coolant stream ow. Furthermore, it is to be noted that the combined air and liquid coolingv achieved diifers substantially from normal evaporative cooling in that the liquid which is forced in the form of a mist into the cooling passage is rapidly carried away by the high velocity, low energy coolant stream ow through the coolant passage. Thus, any excess liquid in the cooling passage is not permitted to remain in the high temperature area in order to prevent excessive heat build-up and-boiling instability. In addition, it is possible to provide an excess amount of atomized water; since the pressure at each axial station is constant the wall temperature throughout the cooling passage will remain constant over a wide latitude of heat transfer rates, only4 the amount of Vaporized water changing. In addition,

since the discharge of the cooling passage is open to the atmosphere and the throat area flow is supersonic, the cooling is self-stabilizing over a wide range of heat transfer rates with little control necessary except for the amount of excess water.

In performing test operations the test model (not shown) is positioned in the tunnel housing at the rearward end of the divergent test section of the nozzle, In a nozzle designed for tests between Mach numbers 5 and 6 a high energy stream of air is prepared in the air supply system 12; for example, a stagnation temperature of 3,000 R. and stagnation pressure of 600 p.s.i. can be prepared for flow through the nozzle at a Mach number of 6 where the nozzle is one foot in diameter at the test section. For the required acceleration of a high energy air stream up to transonic speeds in the throat area upon discharge from the heater, the nozzle entrance convergesinto a throat diameter of 1.5 inches with a wall thickness of 0.120 inch and a throat passage diameter of 0.070 inch. Cool, ambient air is then directed from the air storage chamber through the hoses 26 into the coolingpassage entrance or manifold Z3 at a pressure corresponding to the high energy air stream pressure at the entrance to the throat section, thus defining a low energy aii stream flowing through the cooling passage insubstantially the same direction as the main stream. Due to the effectively similar contour of the cooling passage and main nozzle section, equalized pressure and flow ina substantially parallel, common direction is maintained between the main, high energy stream and the coolant,

At the opposite end- Ofv course,

in that the static temperature'of the air stream has gradually been reduced through expansion to a temperature below the critical wall temperature, and the wall thickness is sufficient to withstand the reduced pressure of the high energy stream; t

As the air coolant stream 'is directed through the coolant passage 2v2, a nely divided water spray is simultaneously introduced into the" cooling passage in the direction of ow ofthe stream and outwardlyiinto it. The control of th'eamouut of water atomized into the cooling passagel not being critical, due to the continuous exchange and removal of water, it is only important that a sufficient amount of water be sprayed into the passage which will be in excess of the amount evaporated. This can be easily determined by considering the heat transfer across the wall for a given wall thickness and the amount of heat required to be absorbed over that amount ab-V sorbed by the air coolant stream.

It is to be understood, of course, that the cooling method as described has wide application to other areas of high temperature or high speed ow. Also for other purposes, it is entirely within the scope of the present invention to utilize other gases as the cooling stream and other liquids such as alcohol as the liquid coolant stream for the coolingof al1-types of compressible fluids and liquids. It is, ofcourse, important that the evaporating temperatures of the liquidbe lower than the wall temperature of 'the Ynozzle or conduit to be cooled. Therefore the above cooling method and apparatus is clearly conformable for jet, rocket motor and missile structures. In addition it is to be understood that the nozzle and Wall construction can be very easily modified without departing from the principles of operation of the invention. For instance, other means for rigidly connecting the nozzle and cooling jacket together can be utilized, such as an outer shell or casing provided with means for delivery of the coolant air and liquid into the cooling passage. Furthermore, the above method, broadly, can be utilized for the cooling of any type of fluid iioW conduit and either with or without the liquid spray dependent upon the heat transfer rates across the wall of the conduit. Therefore, other forms of construction may be very easily utilized, in place of the apparatus as described, to effect the desired coolant air and combined liquid spray streams, although the apparatus as described has been found to be particularly advantageous and efficient in carrying out the cooling operation.

Summarizing the advantages and primary features of the present invention, a method and apparatus for cooling the exterior surfaces of thin walled conduits or nozzles is provided which is particularly adaptable for the cooling of supersonic and hypersonic fluid flow conduits or nozzles by directing a low energy stream preferably in the direction of the high energy stream llow through a contoured passage adjacent the exterior surface of the conduit wall and at a Mach number corresponding to the Mach number in the high energy stream, and where necessary, simultaneously directing a liquid coolant into the low energy stream to cooperate with the low energy stream to maintain a constant wall temperature and pressure throughout the critical heat transfer portion of the conduit. With the method and apparatus as described, it is to be noted that the pressure equalization keeps the mechanical stresses at a minimum, permits a thinner wall structure and thus the higher wall temperature required for water evaporation. Furthermore, the heat of vaporization of the water is so high that large rates of heat transfer with small coolant ows can be brought about. In addition, the regulation of the cooling is greatly simplied in that the air is introduced at the same stagnation pressure as the main stream, and the amount of atomized water introduced is larger than necessary for cooling. Since the discharge of the cooling passage is open to the atmosphere and the throat area is in the sonic and supersonic flow range, the cooling is stabilized 6A. over a wide range of heat transfer rates with no 4control means necessary except for the amounts of excess water supply. t Y 1 While we have described the preferred forms of our invention, it is to be observed that additional modificacations may be devised utilizing the principle of cooling as set forth. Consequently, we wish to be limited not by the foregoing description which was given solely for purposes of illustration but only by the scope of the appended claims.

What is claimed is:

1. A cooling apparatus for a flow conduit through which a compressible uid is directed at a high temperature and pressure, said cooling apparatus comprising: an outer wall having an inner surface disposed in predetermined, spaced relation to the exterior walls of the conduit to define a contoured, annular passage between the conduit and the outer wall conforming substantially to the contour of the conduit to include equivalent diameters in the annular passage and the conduit at predetermined points along the length of said passage, means for spacing said outer wall and the conduit in predetermined relation, means adapted to pass a low energy, coolant gas stream through said passage at rates of ow corresponding to the rates of ow of the high energy stream through the conduit at said predetermined points, and liquid conducting means communicating With said annular passage forY spraying nely divided liquid into the coolant gas stream whereby the Acoolant gas and liquid spray are cooperable to maintain a constant temperature through the length of the passage.

2. A water spray, cooling apparatus for a hypersonic oW nozzle and the like wherein the nozzle is provided with a convergent entrance, a supersonic throat section and a divergent, hypersonic test section adaptable for accelerating a high energy gas stream through the nozzle to hypersonic speeds, said cooling apparatus comprising: an outer, cylindrical wall encircling the nozzle with the inner surface of the wall in predetermined relation with respect to the nozzle so as to define an annular passage surrounding the nozzle wall, said passage being selectively contoured in such a way that the axial Mach number distributions in said passage are substantially equivalent to that throughout the throat and divergent regions of the nozzle to equalize the high pressure ow through the nozzle; support means interconnecting the nozzle and said outer wall in rigid spaced relation, a series of air delivery hose members communicating with the forward end of said passage and adapted to deliver air under pressure into said passage, said outer wall including a series of radially inwardly extending tube receiving openings adjacent the throat section of the nozzle; and a series of liquid conducting tubes extending through said tube receiving openings and adapted to deliver liquid into said annular passage, each tube including a spray oriiice at the passage end thereof for directing a liquid into said passage in the direction of coolant gas flow and at a pressure exceeding the pressure of the coolant air stream in the throat, whereby the coolant gas and liquid are adaptable to selectively reduce the lwall temperature of said nozzle.

3. In a cooling apparatus for a supersonic ow nozzle and the like wherein the nozzle is provided with a convergent entrance, a restricted supersonic throat section and a divergent hypersonic test section adaptable for accelerating a high energy gas stream through the nozzle at supersonic and hypersonic speeds: an outer wall encircling the nozzle with the inner surface of the wall in predetermined, spaced relation with respect to the nozzle so as to define a contoured passage adapted to receive a low energy gas stream and surrounding the entrance and throat regions of the nozzle wall with the effective passage height conforming substantially to the nozzle diameter along the length thereof to equalize the flow of the low energy gas stream therethrough to the flow of the high energy gas stream through the nozzle; means for interconnecting the nozzle and said passagein predetermined spaced relation, and aA series of gas delivery hose members communicating with and adapted to deliver' 10W energy gas intothe fonward end of said'passage adjacent the entrance end of the nozzle at a pressure corresponding to'the pressure of the high energy gasv stream entering the nozzle.

4. In a-cooling apparatus for a thin walled supersonic ilow nozzle and the like comprising: inclosed means surrounding the nozzle wall so constructed and arranged as to `dene a contoured passageway between the nozzle and said outer wall, said passageway having an effective area along the length thereof conforming substantially tothe nozzle area toV effect a corresponding equivalent Mach number and stagnant pressure at various predetermined pointsA therebetween along the passageway, means for connecting said inclosing means' and the nozzle wall in predetermined, spaced relation; and means to direct a coolant gas through said passageway at a velocity and pressure corresponding to the velocity and pressure of the stream flowing through the supersonic flow nozzle.

5. InV a high speed, thin-walled, axially symmetrical ow nozzle disposed within a wind tunnel housing adapted t'o contain'a vforced air supplyand a heater andhaving a main ow passage including a convergent entrance adjacent to the wind tunnel entrance adapted to receive air under high pressure from the heater, a restricted throat section to accelerate the air received to supersonic speeds and al gradually divergent .testts'ec'tio'n tofurthei accelerateA the air to hyp'ers'onic' speeds, meansi for cooling' the yexterior'wa'lls of the nozzle; saidneanscomp'rising 'an an# nular outer wallvv surrounding the'n'ozzle wall' in spaced relation thereto to form an annular passage ybetween the exterior surface of the nozzle wall and the interior surface of said outer wall andcontoured in substantial conformance with the lcontour of said main How passage at predeterminedintervals therealong'to etfect equivalent Mach numbers therebetween on admission of coolant gas throughA said contoured'passage'at a ratecorresponding to the rater of flow of compressible fluid into said main flow passage, and liquid conducting means in communication'withsaid contoured passage to introduce liquid thereinto for intermixing with' said coolant gas to absorb heat from the exterior'walls of the nozzle and'maintain a constant temperature.

References Cited inthe le oftliis patent UNITED STATES PATENTS 2,354,151 skogiund July 18, 1944 2,439,473 Kalitinsky 1 ..Y.. Apr. 13, 1948 2,520,751 Zucrow Aug. 29, 1950 2,671,313 Laramee Mar. 9, 1954 FOREIGN PATENTS? 22,028 Great Britain Nov. 1, 1901

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