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Thermal Management Concepts

Thermal Management Concepts. Richard Wirtz Mechanical Engineering Department University of Nevada, Reno August 20, 1999. Overview. Current Technology Hybrid Fan Sinks and Spot Coolers Performance Increasing Strategies Variable Load Coolers. “Passive” Heat Sinks. Results and Comparison.

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Thermal Management Concepts

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  1. Thermal Management Concepts Richard Wirtz Mechanical Engineering Department University of Nevada, Reno August 20, 1999

  2. Overview • Current Technology • Hybrid Fan Sinks and Spot Coolers • Performance Increasing Strategies • Variable Load Coolers

  3. “Passive” Heat Sinks

  4. Results and Comparison Ducted Flow Rs-a[oC/watt] 28 cfm 130mm x 70mm x 40mm Note: R = 0.4 oC/watt  Q(ideal) = 11.2 cfm

  5. Bypass Effect Wirtz, Chen and Zhou (1994) JEP, Vol. 116, pp206 - 211

  6. Fan Sinks R.A. Wirtz and Ning Zheng (1998) “Methodology for Predicting Pin-Fin Fan-Sink Performance”, Proc. Sixth Intersociety Conference on Thermomechanical Phenomena in Electronic Systems, pps 303 – 309

  7. Typical Fan-Sink Operating Point

  8. ImplicationstoFan-Sink Design b = best fan efficiency a = best H.S. performance

  9. Higher Performance DevicesAir Cooling, 2” x 2” Footprint

  10. Folded-Fin HS Design Concept

  11. Folded-Fin Performance2” x 2” x 2” Device

  12. Helical-Fin Design Concept

  13. Helical-Fin Performance50mm dia x 20mm high

  14. Porous Heat Sink60mm x 60mm x 30mm

  15. Porous Heat Sinkcut-away

  16. Porous Heat Sink Performance

  17. Performance Parameter Space2” x 2” devices

  18. Other Performance Ideas • Single-fluid H.E. performance limit: cpQ • The size may be reduced by increasing: • the heat transfer surface area per volume • the heat transfer coefficient

  19. Porous Media ConceptsIncrease H.T. Surface Area

  20. Porous Exchange Matrix Layout

  21. Woven Mesh Porous Matrix 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)

  22. Serpentine Biaxial Weave Orthogonal, 3-D Mesh(copper/solder) Exchanger plate Shute Wires Exploded View Parallel Plate Heat Exchanger,(FTM)

  23. Woven Mesh FTMPerformance PredictionComparison with Offset Fin FTM

  24. CorrugatedorGrooved ChannelsIncrease U Wirtz, Huang and Greiner, ASME Journal of Heat Transfer, Vol. 121, pp. 236 - 239.

  25. Augmentation Mechanism Re < 350 Re  350 Re  800

  26. Interferograms, Re = 3200

  27. Colburn j-factor

  28. Friction Factor Grooved Smooth

  29. Serpentine ChannelConstant Cross Sectional Area CorrugationSnyder, Li and Wirtz, Int. J. Heat Mass Trans., Vol. 36, pp2965 - 2976

  30. Serpentine Channel Performance

  31. Phase Change Materials • Incorporation of a heat storage capability in the temperature control system of an electronic module having a variable heat dissipation rate will allow for a smaller, less-power-consuming module cooler and better temperature stabilization. • Materials formulated to undergo phase transition at key temperatures can provide this load-leveling capability via the latent heat effect.

  32. Heat Storage Surface qout” qin” [w/cm2] 1 cm 6% (Vol) Metalized PCM composite. qin = 6 W/cm2 qont = 3 W/cm2

  33. PCM Options • Solid - Liquid Materials • Paraffins, non-paraffin organics, salt hydrates, metallics. • Solid - Solid Materials • Materials that undergo reversible solid-state phase transitions. • Organic Compounds, Metallic Oxides, Encapsulated S-L PCM’s • Latent heat comparable to S-L PCM’s • Packaging is easier

  34. Solid-Solid PCM-based Heat Exchangers • Passive Heat Storage Mechanisms (all) • Heat exchangers that are insensitive to heat load variations • High-performance (thermally conductive solids or high-heat-flux convection and radiation surfaces) through metalization. • Near Ambient Operating Temperatures • -15oC < Ttr <150oC. • Inexpensive net-shape manufacture • Possible complex heat exchanger shapes • Operation is independent of ambient pressure or system orientation.

  35. COOLANT C B A Heat Source Design Concepts“dry” PCM Hybrid Coolers A, C = Metalized Storage Volumes B = Heat Exchange Volume Metallization = discreet or integral

  36. AIR FAN HEAT EXCHANGER METALIZED PCM q’’(t) Discreet Metallization Application

  37. Hybrid Heat Sink Thermal Response Ttr = 83oC, Ttr = 6oC, q1/qinit= 2

  38. Hybrid Sem-E FTMSteady Performance Offset strip-fin vs hybrid (porous) design. Coolant = PAO. 6% (vol) Metalized PCM heat exchanger surface.

  39. Hybrid Sem-E FTMUnsteady Load PAO flow rate = 2.5 #m/min Nominal load = 1000 watt, Load factor = 1.5, Duty cycle = 30%

  40. END

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