Design, fabrication and test of liquid metal heat-pipe sandwich panels

NASA-TM-84631 NASA Technical Memorandum 84631 DESIGN,FABRICATIONAND TEST OF LIQUIDMETAL HEAT-PIPESANDWICHPANELS AL BASIULISAND CHARLESJ. CAHARDA APRI L 1983 NationalAeronauticsand Space Administration Langley ResearchCenter Hampton, Virginia 23665 19830014270 DESIGN_FABRICATION AND TEST OF LIQUID METAL HEAT-PIPE SANDWICH PANELS A. Basiulis HughesAircraft Company Torrance, California C. ]. Camarda NASA Langley ResearchCenter Hampton,Virginia Abstract Integral heat-pipe sandwich panels, which synergistically combine the thermal efficiency of heat pipes and the structural efficiency of honeycomb sandwich panel construction, were fabricated and tested. The designs utilize two different wickable honeycomb cores, facesheets with screen mesh sintered to the internal surfaces, and potassium or sodium as the working fluid. Panels were tested by radiant heating, and the results indicate successful heat pipe operation at temperatures of approximately 922K (1200°F). These panels, in addition to solving potential thermal stress problems in an Airframe-lntegrated Scramjet Engine, have potential applications as cold plates for electronic component cooling, as radiators for space platforms, and as low distortion, large area structures. LANGLEYSCRAMJET CONCEPT HONEYCOMB STRUCTU RE LARGEAT THROUGH HONEYCOMB Introduction Design studies of the NASA Langley Airframe-lntegrated Scramjet Enginel have indicated potential thermal stress problems. Excessive thermal stresses result from large transient temperature gradients across the honeycomb sandwich walls of the engine structure during engine startup and shutdown. Conventional heat-pipe panel designs can reduce the thermal gradients. However, inherent in these designs are problems associated with bonding the heat pipes to the honeycomb panels) the resultant thermal gradients due to contact resistances, and the probability of a substantial increase in panel mass. An alternate solution to these problems is the development of an integral heat-pipe sandwich panel 2 that synergistically combines the thermal efficiency of heat pipes with the structural efficiency of sandwich construction, with only a negligible increase in mass. A preliminary evaluation of such a concept was reported by Peeples. 3 )LING JACKET rOPWALL .SIDEWALL COOLEDSTRUCTURE In addition to the above application, heat-pipe sandwich panels have potential as cold plates for electronic and circuit card cooling) as radiators for space platforms, and as low distortion) large area structures (e.g., space antennas). To verify the feasibility of a heat-pipe sandwich panel, a program was initiated (NASA Contract NASI-16556) to fabricate several low mass liquid metal heat-pipe honeycomb panels, Fig. I Features of cooled scramjet structure. This paper describes the thermal environment that led to the investigation of a heat-pipe sandwich panel) illustrates the preliminary design considerations and testing, describes manufacturing and fabrication details, discusses preliminary performance testing, and comments on poten- surfaces exposed to aerodynamic flow are cooled regeneratively by the circulation of hydrogen fuel (prior to injection) through a cooling jacket. Inconel 718 was chosen for the honeycomb primary structure) with Hastelloy-X or Nickel-200 chosen for the cooling jacket. The honeycomb front facesheet is 0.15 cm (0.06 in.) thick) the back facesheet is 0.13 cm (0.05 in.) thick, and the honeycomb cell is a 0.6#-cm (0.25 in.) hexagonal arrangement constructed of 0.008-cm (0.003 in.) foil-gage ribbon. tial future applications. Environment Design of Heat-Pipe Sandwich Panels Temperature gradients through the honeycomb walls during transient operation (i.e., engine startup or shutdown) may very well control the structural design. A mission profile of a research-type vehicle was used by Buchmann1 to predict the thermal/structural response quantities. A finite-difference analysis model of a section of the sidewall-topwall (Fig. 2) was used to calculate the transient temperatures shown in Fig. 3. Note from Fig. 3(a) that at startup, the front facesheet quickly rises to 890K NASALangleyResearch Center has been involved in a research program for the development of AirframeIntegrated Scramjet Engine concepts. 1 Results of that study indicate that an all-honeycomb primary structure, illustrated in Fig. 1, has less deflection and complexity than beam and honeycomb combinations of equal mass. Hence, an all-honeycomb configuration was chosen as the best structural concept. All internal and external engine i TOP- -___S WALL _IEl'l • I,_ _ CORNERBRACKtI TYPICAL TEMPERATUI_[ -- -- -BA _I J_ • • • • f.J_ : ....: FRONTFACESHEET--I_ OF COOLINGJACKET i I SIDEI! WALL II Fig. 2 If I_ NODE honeycomb core could be a foil-gage or to reduce thermal gradients in the woven faces. mesh The screen wiekable CK FACESHEET flow. The tohoneycomb is notched at each end to aliquid screen sintered foil ribbons; this allows face-to-face OF HONEYCOMB ZONE allow intracellular liquid flow by capillary action. This design allows tothetheentire to be screen also is sintered internalsurface faces ofof the the facing sandwich to wetted by liquid and thus aid in evaporation and also help 1 II II Mathematical model for transient thermal anal_Isis of honeycomb topwall-sidewall corner section. _ allow intracellular liquid flow and perforated enableof intracellular vapor flow. Although the primary tomode heat transfer is in the transverse direction (face to face) for the present application, the choice of other design alternatives can enable varying degrees of in-plane heat transfer. Critical Element Evaluation To accommodate the heat-pipe sandwich panel requirements, the structure must consist of two facings with internally wickable faces bonded to a perforated, wickable honeycomb core material (as shown in Fig. 5). Several (ll#0°F), resulting in a front-to-back AT of 667K (1200°F) for a Hastelloy-X core. At engine shutdown, whether caused by normal occurrences or an abnormality [ MAXIMUM such as a flameout, the temperature relationships of the front of the cooling jacket and the back of the honeycomb are reversed, as shown in Fig.than 3(b). front-to-back AT developed is somewhat less at The startup--on the order of 5561< (1000°F) for the Hastelloy-X core. These thermal premature fatigue failure.l Solutions noted in Ref. l result in concepts that complex or heavier, or both. gradients result in excessive thermal to this problem are either more stresses _ (HASTELLOY-X) _ | F r _'"FRONT v _ emerged as a solution to the above problem, The heat-pipe sandwich panels fabricated in the past met unique requirements of unilorm temperature over a large surface area. The basic idea for the heat-pipe sandwich panel _ field,4 uniform have temperature over operation a large area5 (0.5x6 These panels demonstrated in a zero-g meters (1.64x19.7 ft.)) and an isothermal surface6 (within 0.0IK (0.02°F)). However, all these panels were built by welding or furnace brazing by highly skilled technicians and, although they met all the technical requirements, they were very costly to manufacture. The primary objective was to fabricate a heat-pipe l_oneycomb sandwich using a wickable honeycomb core, appropriate working fluid, and wickable internal faces that would enhance the transverse heat transfer capability of ihe honeycomb. During operation, heat would be absorbed at the heated face by the evaporation of working fluid, The heated vapor flows, due to a pressure differential, to the cooler face, where it condenses and gives up its stored heat. The cycle is completed with the return flow of liquid condensate back to the heated face by the capillary pumping action of the wickable core. A schematic of the heat-pipe sandwich panel concept is shown in Fig. 5. A F(N_// 900 | and The objective during this program was to design and fabricate a cost- and mass-effective sandwich panel using existing manufacturing techniques and equipment. The upper and lower ends of the core have flanges that enable spot welding to the faces. The entire sandwich panel can be constructed by simultaneously spot welding the core ribbons to each other and to the faces using the manufacturing technique illustrated in Fig. 4. The spot welds are so close together that they form an almost continuous bond. Since the entire panel is spot welded, this eliminates _he need for bonding and possible materials compatibility problems. MAXIMUMAT 700t _ 800I- I t / _ ! /HAST.-X 300_ 120 / I I I 60o I080 TIME (SECONDS) (a)$TARTUP MAXIMUM •.&T (Ni) 900 " __ \ MAXIMUM /(HASTELLOY-X) _T / .\. _. BACK o_ - 700 LU :E 500 _ ., 300 l 0 [ ] ] 80 120 TIME (SECONDS) (b) SHUTDOWN Fig. 3 Honeycomb temperature histories at zone I. 1 WHEELS E TRODE STRIP CORE RIBBON _.. 1. FLANGE WELD J | . "-.... ELECTRODE PANEL FABRICATION MACHINE TIPS 2. NODE WELD Fig. # _"_ Honeycomb panel welding machine and manufacturing technique (courtesy of Astech). Fig. 6 techniques were considered for internal facesheet wicking: sintering a screen to the facing, spot welding a screen to the facesheet, and grooving or roughening the facesheet by grid blasting. Grooving and roughening were rejected because of facesheet warping and the poor surface left for subsequent welding. Sintering the metal screen to the facing was chosen as having more structural integrity than spot welding. Figure 6 shows a photomicrograph of the sintered screen facesheet, Photomicrograph showing diffusion screen sintered to facesheet. bonding of assembly for process testing and preliminary performance testing; and a machine-assembled resistance-welded prototype for delivery and final testing. The proof-pressure test specimen was assembled, vacuum leak checked_ pressure tested up to 3.45 MPa (500 psi), and vacuum leak checked again. During and after testing, the honeycomb panel assembly retained structural and vacuum integrity. A hand-built, spot-welded core assembly was fabricated, processed with potassium working fluid and, after preliminary test at I075K (1475°F), was delivered to NASA Langley Research Center for further testing. Two designs for the honeycomb core were considered: a foil-gage sintered screen material (shown in Fig. 7) and a metal screen sintered to foil-gage stainless steel material, Both designs met structural and wicking requirements, with the former offering better wicking and the latter providing a stronger structural design. Figures 8 and 9 show performance limits for a heat-pipe honeycomb sandwich panel constructed with Regimesh K material for sodium and potassium working fluids, Fabrication of Test Models Sandwich panels were fabricated by Astech using an automated procedure for simultaneously resistance welding honeycomb ribbons to the facesheets. Completed sandwich Sample honeycomb ribbons were formed by Astech* using standard equipment, and test samples were fabricated for evaluation. Both samples, sintered screen and screen on foil_ met strength and wicking requirements. Three different designs of honeycomb sandwich panels were fabricated: a resistance-welded core assembly for proof-pressure testing; a handmad% spot-welded core * A division of TRE Corporation, j , Santa Ana, CA. TOP FACESHEET // WlCKABLE TO HONEYCOMB NOTCHED ALLOW LIQUID FLOW, PERFOR ATED TO ALLOW VAPOR FLOW ,._,. SCREEN SIN'I'ERED TO INTERNAL FACES TO ALLOW IN PLANE FLOWOF LIQUID ALONG FACES Fig. 5 Heat pipe sandwich panel concept. Fig 7 Photomicrograph 3 of Regimesh K sintered screen. I WICK OPERATING 10,000---- I TEMPERATURE.._I l DETAIL _ 10o0 _ if" Z < - < 00 f-/ ENTRAIN / / / o.// r I !I / U" /_S°N'C ! ! /" ? ! /? _-3....... fi 4- 400 -+-- 600 800 TEMPERATURE 1000 (OK) Fig. 8 Performance limits vs. temeprature for RegimeshK and soduim fluid. panels were delivered to Hughes for further processing. Figure 10 shows the completed honeycomb panel. To eliminate potential contamination, panels were degreased, then fired in dry hydrogen at 1173K (1652°F). At this point the sidewalls Fig. l0 Completed honeycomb panel prior to processing and final assembly. and processing tube were welded in place) completing the heat pipe assembly. Figure 11 shows the complete heat pipe assembly. The panel was then fired in dry hydrogen at 1173K (1652°F) to remove oxides which were formed during final assembly. After leak check_ the panel was placed in a vacuum chamber and heated to 1273K (1832°F) for final cleaning and outgassing. After _ OPERATING TEMPERATURE_I -- _ WICK .._.._L_--." • _" -• 10.000_---- _r"" _" -'_'--J_'l ,_ d / I J 1- 1000 ENTRAINMENT o / Z F- F- final processed. leak check, During the panel was chargedtests, with the working fluid and preliminary heat-pipe panel was isothermal over the active surface but did show some excess fluid in the processing tube. Figure 12 shows the heat-pipe panel during preliminary test. " / 100 -r SONIC 10 I / / 1 I 400 I 600 TEMPERATURE Fig. 9 I 'I I I, 800 1000 (°K) Performance limits vs. temeprature Regimesh K and potassium fluid. for Fig. l 1 Completed 4 heat pipe assembly prior to processing. L_--_ 2.54cm (1.0 in.) 10 16cm (4.0in.) ---.-,_ T 2.54 cm (1.0 in.) 5.08 cm (2.0 in.) • 1 S 5.08 cm (2.0 in.) !- + + 2.54 cm (1.0 in.) Fig. 12 Heat-pipe panel during preliminary testing. _L SIDE VIEW TOPANDBOTTOMVIEW Preliminary Radiant Heat Tests Two prototype Fig. I# Thermocouple locations. panels) one empty and the other contain- ing potassium as the working fluid) were heated simultaneously by radiant heat lamps) as shown in Fig. 13. The heaters are quartz lamps with a heated length of 6.35 cm (25 in.) and having a rated power of 2500 watts (2.37 Btu/s) at 500 volts. Each lamp bank contains eight lamps. Six lamp banks were energized for each test. One of the panels was located directly under one lamp bank and the other panel was located the same vertical distance from the heaters but under another lamp bank. The distance of the panels from the lamp banks and the voltage to the lamps were varied. Power was applied as a step voltage input to the lamps. Power was applied for approximately 5 to 10 minutes and then abruptly shut off. Five thermocouples were located on the top and five on the bottom surfaces of the panels to measure temperature gradients) and four thermocouples were located along one side to study heat pipe startup performance. Thermocouple locations are shown in Fig. 14. The panels were tested with and without insulation covering the bottom and sides of the panels. The insulation prevents heat loss by free convection and simulates the adiabatic boundary conditions described in Ref. I. The panels were tested nine times) and results of those tests are summarized in Table I. Comparisons of temperature histories of a heat-pipe and non-heat-pipe sandwich panel with insulated and uninsulated surfaces are shown in Fig. 15. For the insulated panel tests shown in Fig. 15(a)) the temperatures of the back face of the non-heat-pipe panel and the heat-pipe panel temperatures continue to rise and slowly approach the temperature of the front facesheet of the non-heat-pipe panel as expected. Results of the uninsulated panel tests (Fig. 15(b))indicate that all temperatures level off and appear to reach a steady-state condition. As mentioned in Refs. 8 and 9, during heat-pipe startup from the frozen state) a nearly constant temperature continuum region propagates from the evaporator to the condensor section of the heat pipe. As shown in AIR\ COOLANTLINE FOR LAMPS HEAT LAMPS_ Table I Summary of radiant heat tests of heat-pipe sandwich panel MAX _ T DIST. FROM HEATERS RUN VOLTAGE NO INSULATED CM (IN.) V 1 NO 10.5 (4.125) 380 2 460 J t PANEL NON-HEAT- Fig. 13 Sandwich panels in position under radiant heat lamps. 5 NON HEAT PIPE PIPE 338 (809) 403 (725) 352 474 HEAT PIPE 891 (1145) 916 NON HEAT PIPE 926 (1208) 970 (1287) 250 313 (564) 407 (733) 803 (986) 863 (1093 4 300 343 (617) 467 (841) 856 (1081) 920 (1197) 5 358 353 (635) 487 877) 804 (1167) 984 (1312) 250 319 (575) 467 (840) 842 (1056) 894 (1150 354 490 923 974 (638) (882) (1202) (1293) 535 968 1020 5.1 (2.0) YES LEADS PIPE PANEL HEAT (1189) 6 / THERMOCOUPLE (OF) (854) ) _[. K (OF) (634) 3 HEAT_PIPE MAX T K 7 307 8 356 9 463 378 (680) (963) (1283)(1376 422 587 1073 1078 (750) (1056)(1472)(1480) NONHEAT 1000 -__+ 80C / o PANEL 800 THERMOCOUPLE / LOCATIONS v 600 II i / # ," 4 / / 400 _ TOPSURFACE .... BOTTOMSURFACE I 100 ',.'I/ 600 I til _ ..... _ -- _ .... 400 I I 300 TIME (SECONDS) w 500 100 1 z 0.51cm(0.2 in.) 1.02cm(0.4 in.) 1.52cm(0.6in.) 2.03cm(0.8in.) I I 300 TIME (SECONDS) 500 (a) WITH INSULATION Fig. 16 Temperature histories along the side of the heat-pipe panel, illustrating startup performance. 1000 -- o_ _- _ .......... ? H 600 --" 400 ] 100 J I 300 TIME (SECONDS) I 500 Initial studies indicate the heat-pipe honeycomb sandwich panels can be fabricated. The technology and commercial equipment are available to construct all-welded machine-assembled honeycomb panels. At present, such shapes for use in airframe structures. Calculations and experiments with subscale test specimens indicate the feasibility of full-scale heat-pipe sandwich structures. Potential applications for heat-pipe sandwich panels include= alleviating excessive thermal stresses in jet engines, cooling electronic components and circuit cards, limiting thermal distortions in large structures such as space antennas, and as radiators for space platforms. (b) WITHOUTINSULATION Acknowledgements Fig. 15 Comparison of temperature histories of a heatwithout pipe andinsulation. non-heat-pipe sandwich panel with and Fig. 15, once this continuum front reaches the back facesheet, the temperature there rises very rapidly as compared to the back facesheet of the non-heat-pipe panel. The temperature at which continuum flow begins and the rate at which the continuum front propagates depend on sonic flow limit of the vapor. the working fluid, the temperature, using a potassium heat-pipe The authors wish to acknowledge T.R. Lamp, H. Tanzer and 3.T. Burdette of Hughes Aircraft Co., who supported the design, fabrication, processing and testing of the honeycomb heat pipe sandwich panels, and T. Bernard of Astech for his support and for the fabrication of honeycomb sandwich segments. 600 -- AT the heat input and the sandwich panel instead of a non-heat-pipe panel is 27 percent. It is possible that this reduction can be increased by using cesium as the working fluid; this is currently being investigated. Figure 16 gives some idea of the rate of continuum region growth. The results are characteristic of startup of liquid metal heat pipes as presented in Ref. 9. A typical comparison of temperature gradients through the depth of the honeycomb is shown in Fig. 17. As shown, the non-heat-pipe panel temperature gradient peaks slightly after that of the run. heat-pipe panel and is 29 percent higher for this particular _ _} o 200 # I 100 _J I 300 TIME (SECONDS) [ 500 Fig. 17 Comparison of temperature gradients for a heat-pipe and non-heat-pipe sandwich panel. References h Buchmann, O. A., "Thermal-Structural Design Study of an1979. Airframe-Integrated Scramjet,"NASA CR 3141, Oct. 2. Feldman, K. T., 3r., "Flat Plate Heat Pipe With Structural Wicks," U.S. Patent Appl. No. 803,582. 3. Peeples, M.E., Reeder, 3. C., and Sontage, K.E., "ThermostructuralApplicationsof Heat Pipes," NASA CR 150906,3une 1979. 4. 6. Fleishman, G.L., Loose 3. P., and Scallon, T., 3r., "Vapor Chambers for Atmospheric Cloud Physics Laboratory," Third International Heat Pipe Conference, Palo Alto, CA, May 22-24, 1978. 7. Dunn, P. and Reay, D.A., Press, 1976. 8. Cotter, T.P., "Heat Pipe Startup Dynamics," Heat Pipes, AIAA SelectedReprint Series,Sept. 1973, VoL XVI, pp. 42-45. 9. Camarda, C. 3., "Analysis and Radiant Heating Tests of a Heat-Pipe-Cooled Leading Edge," NASA TN D-8468, Aug. 1977. Fleishman, G. L. and Marcus,B. D., "Flat Plate (Vapor Chamber/Heat Pipes,"AIAA Paper No. 75-7728, AIAA t0th ThermophysicsConference,May 1975. 5. Heat Pipe Conference, Palo Alto, CA, May 22-24, 1978. Basiulis, A. and Formiller D. 3, "Emerging Heat Pipe Applications," Proceedings of the Third International Heat Pipes, Pergamon 1. Report No. 2. Government Accession No. 3, Recipient's Catalog No, NASATM84631 4. Title and Subtitle 5. Report Date Design,Fabrication and Test of LiquidMetalHeat-Pipe Sandwich Panels April1983 6. PerformingOrganizationCode 506-53-53-07 7. Author(s) 8. Performing Organization Report No. A1 Basiulis and Charles J. Camarda 10. Work Unit No. 9. Performing Organization Name and Address NASALangleyResearchCenter Hampton,VA 23665 11. Contract or Grant No. 13. Type of Report and Period Covered 12 Technical Memorandum ....... t4 Sponsoring Agency Code Sponsoring Agency Name and Address National Aeronautics and SpaceAdministration Washington, DC20546 15. Supplementary Notes Al Basiulis:HughesAircraftCompany Presentedat AIAA/ASME3rd JointThermophysics, Fluids,Plasmaand Heat Transfer Conference, June 7-11,1982,St. Louis_Missouri. 16. Abstract Integral heat-pipe sandwich panels, which synergistically combinethe thermal efficiency of heat pipes and the structural efficiency of honeycomb sandwich panel construction, were fabricated and tested. The designs utilize two different wickable honeycomb cores, facesheets with screen meshsintered to the internal surfaces, and potassium or sodiumas the working fluid. Panels were tested by radiant heating, and the results indicate swccessful heat pipe operation at temperatures of approximately 922K (1200VF). These panels, in addition to solving potential thermal stress problems in an Airframe-Integrated ScramjetEngine,have potentialapplications as cold platesfor electronic componentcooling,as radiatorsfor spaceplatforms,and as low distortion, largeareastructures. 17. Key Words (Sugg_ted by Author(s)) HeatPipes SandwichPanels 18. Distribution Statement ThermalStress ElevatedTemperature ScramjetEngine SubjectCategory34 19. Security Classif,(of this report) Unclassified N-305 Unclassified - Unlimited 20. SecurityClassif.(of this page) Unclassified 21. No. of Pages 8 22. Price A02 ForsalebytheNationalTechnicalInformation Service,Springfield,Virginia22161 View publication stats