Heat Transfer & Materials Development Research

1. Heat Transfer & Materials Development Research R.A. Wirtz Mechanical Engineering Department University of Nevada, Reno Rawirtz@unr.edu (775) 784-6714 August 18, 2000 Wirtz, NASA Glenn

2. Research Focus Temperature Control of Electronics & Sensors High Performance Coolers and Heat Exchangers • Enhanced surfaces • Porous media applications • Hybrid TES Coolers • Phase change materials (PCM) • Multifunctional Materials/Devices • Heat Transfer Augmentation • Grooved Channels • Thermal Characterization of Devices and Systems • Infrared Imagery Wirtz, NASA Glenn

3. Research Sponsors • BMDO/AFOSR (Nevada EPSCoR) • Intel Corporation • National Science Foundation • Nevada Applied Research Initiative • Sierra Nevada R & D Inc, Incline Village • Anacapa Technology Inc, Reno Wirtz, NASA Glenn

4. Representative Project Activity • MCM Coolers • Woven-Mesh Heat Exchangers • Thermal Energy Storage Systems • Multi-Functional Materials Wirtz, NASA Glenn

5. MCM CoolersAir Cooling, 2” x 2” Footprint Wirtz, NASA Glenn

6. Porous Heat Sink 60mm x 60mm x 35mm 48 C Rise @ 150 W, .25 in H20 air Wirtz, NASA Glenn

7. High-Performance Woven Mesh Heat Exchange Wirtz, NASA Glenn

8. High Performance Woven MeshHeat Exchange Motivation: An anisotropic porous matrix having large  and large ke in a particular direction will result in a very effective heat exchange surface. • Porous Media (uniform particles) • High Surface Area per Volume,  • Fixed Porosity,   0.4 • Effective thermal conductivity, ke 20% kparticle • Isotropic Characteristics • Woven/Braided (3-D) Mesh • High (variable)  • Variable Porosity,  • Anisotropic (k and p) Wirtz, NASA Glenn

9. t Mesh wall FLOW FLOW OUT Thickness, t 5.5” FLOW IN Woven-Mesh Exchanger Concept Wirtz, NASA Glenn

10. Project Objectives & Methodology Develop Woven Mesh Heat Exchanger Technology for single-fluid, parallel plate exchangers. • Analytical Modeling • Thermal/fluid performance • Parametric studies • Fabrication Technology • Weaving with metal yarn / wire bonding • Pyrolytic graphite yarn • Weave Characterization • , , ke, R”, U, P • Modeling & measurement • Prototyping (build and test, benchmark) Wirtz, NASA Glenn

11. Analytical Modeling Thin Porous Wall Geometry Wirtz, NASA Glenn

12. Analytical Modeling, cont. Thin Porous Wall Heat Transfer Model Solid – new model Dash – Wirtz, 1998 Wirtz, NASA Glenn

13. Pout  FLOW OUT D Go(y) y 5.5” FLOW IN Gin Pin Passage Flow Modeling Wirtz, NASA Glenn

14. Analytical Modeling, cont. Flow Distribution Model A 4 taper of the inlet/outlet flow passages results in an approx. uniform flow distribution through the porous wall. Wirtz, NASA Glenn

15. Fabrication Methodology • Rigimesh • Simple construction • Anisotropic • Relatively high porosity • 3-D weave • Low porosity • Complex (learning curve) Wirtz, NASA Glenn

16. Fabrication Methodology, 3-D Weave An Iterative Process Wirtz, NASA Glenn

17. Fabrication Methodology, 3-D WeaveWire Bonding Options Wirtz, NASA Glenn

18. Mesh Characterization, Rigimesh Solid – present dash – Koh & Fortini, 1973 Wirtz, NASA Glenn

19. Mesh Characterization, Cont. • Pressure Drop Correlations • Armour & Cannon [1968], single screens • Rigimesh: current • Heat Transfer Coefficient • Rigimesh, 3-D weave: current Wirtz, NASA Glenn

20. TES-Systems Wirtz, NASA Glenn

21. Motivation • Hybrid Thermal Energy Storage (TES) coolers for variable power MCM’s • Cooler sized for intermediate heat load • TES component stores/releases heat during high/low power operation • Smaller, simpler, less power consuming cooler • Utilize “dry” Phase Change Materials • g-load, orientation insensitive operation • Simple packaging • Passive, reliable (no moving parts) Wirtz, NASA Glenn

22. Heat Source COOLANT A, C = Metalized Storage Volumes B = Heat Exchange Volume C B A TES Hybrid Coolers Wirtz, NASA Glenn

23. Hybrid SEM-E FTM PAO flow rate = 2.5 #m/min Nominal load = 1000 watt Load factor = 1.5, Duty cycle = 30% Wirtz, NASA Glenn

24. PCM Options • Utilize “dry” Phase Change Materials • g-load, orientation insensitive operation • Simple packaging • Passive, reliable (no moving parts) Wirtz, NASA Glenn

25. PG/NPG phase diagram. Latent heat and transition temperature of PG/NPG. Polyalcohol Solid Solutions Wirtz, NASA Glenn

26. 105 d t s 100 C] 95 0 90 Temperature [ 85 Test data Simulation data 80 75 0 10 20 30 40 50 60 70 80 Time [min] Comparison of simulation and experimental data TES-System Design Finite Volume Heat Transfer Model + Design Optimization Algorithm Wirtz, NASA Glenn

27. Multi-Functional Materials for Thermal Control of Sensors and Electronics • Space-Economy Dual Functionality • TES + Structural Wirtz, NASA Glenn

28. Methodology Encapsulate Phase Change Materials to form structural elements • Macro-encapsulations • Composite plates • PCM in honeycomb, metal foam, Rigimesh • Structural + k-enhance • Aluminum, graphite/epoxy skin • Micro-encapsulations • molded components • Metal encapsulate + sintering • K-enhance • Molecular deposition (CVD, etc.) • Polymer encapsulation • Epoxy, silicone, thermo-plastic matrix • Nano-precipitation Wirtz, NASA Glenn

29. Research Tasks • Characterization of PCM’s • Fabrication methodology • Low temp brazing, Micro-coating, Powder-in-matrix uniformity • Composite Thermo/mechanical characterization • Thermodynamic properties • Thermal diffusivity, conductivity • Material properties (static, dynamic) Wirtz, NASA Glenn

30. Preliminary Results Macro-EncapsulationPG, Foam Al, Al-sheet 118 j/cc heat storage capacity Potentially, a 40-fold increase in keff Wirtz, NASA Glenn

31. Conductivity Enhanced TES-Composites Wirtz, NASA Glenn

32. Polyalcohol solid solution in water/alcohol added to a liquid blended polymer and heated to precipitate the nanocrystalline S-S particles encapsulated in a polymer shell. Heater Micro-encapsulation Methodology Precipitated Nanocrystals of Polyalcohols Advantages Small nanocrystalline particles will be formed, on which a polymer coating will deposit due to presence of nuclei with large surface area. There will be other plasticizers present in liquid polymers. If necessary, it will be possible apply a metallic or alloy coating on top of this polymer coating. Stirrer Nanocrystals of polyalcohol Wirtz, NASA Glenn

33. Preliminary ResultsMicro-Encapsulation  Moldable Composite25% (vol) Cerrolow powder in Silicone50 j/cc heat storage capacity at 60C Wirtz, NASA Glenn

34. DMA testing for the Cerrolow-140-3250-1 / silicone composite. Preliminary Results Micro-Encapsulation25% (vol) Cerrolow powder in Silicone Wirtz, NASA Glenn

35. The End Wirtz, NASA Glenn