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Foreword

Foreword. 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.

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Foreword

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  1. Foreword • 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.

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

  3. Objective Develop tools to evaluate the thermal response characteristics of hybrid coolers charged with phase change materials (PCM)

  4. Overview • Examples • PCM Options  “dry” PCM • Hybrid Cooler Design Concepts • Heat Transfer Performance Model • Model Calibration Experiments • Parametric Study of Cooler Response • Cooler Figure of Merit

  5. ExamplesofCurrentTechnology

  6. Wearable and Handheld Electronics

  7. PCM Options • Non-metallics have low thermal conductivity (thermal diffusivity). • S-L PCM’s  liquid containment problems (provision for volume expansion) • Salt Hydrates absorb water (they are also corrosive) • Metallics  mass penalty

  8. PCM Options • Solid - Solid Materials • Organic Compounds, Metallic Oxides, Encapsulated S-L PCM’s • Latent heat comparable to S-L PCM’s • Packaging is easier • Performance insensitive to cooler orientation or g-loading

  9. Solid - Solid PCM-based Heat Exchangers • Passive Heat Storage Mechanisms (all) • High-Performance (thermally conductive solids or high-heat-flux convection and radiation surfaces) through metalization. • Near Ambient Operating Temperatures, -30oC - +188oC (0oC - 100 oC). • Inexpensive Net-Shape Manufacture Resulting in Complex Heat Exchanger Shapes • Aerospace environment (operation is independent of ambient pressure or system orientation). • Heat exchangers that are Insensitive to Load Variations

  10. COOLANT C B A Heat Source Design Concepts“dry” PCM Hybrid Coolers A, C = Metalized Storage Volumes B = Heat Exchange Volume

  11. AIR FAN HEAT EXCHANGER METALIZED PCM q’’(t) Digital Electronics Application

  12. Electronics LRU

  13. SEM-E Module

  14. SEM-E FTM

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

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

  17. Figure of Merit

  18. s H Hpcm D b W Prototype Hybrid Cooler 15 fins H = W = D  50 mm, Hpcm  25 mm ( 40 gm PCM) PCM: sp. gr.  1, htr  200 j/cc, Ttr  80- 90oC, Ttr  1- 8oC

  19. (UAs)n [T – Tamb] qn(t) s/2 t/2 Dx b Hpcm H 0 x m4 m5 m6 qn(t) Tamb m0 m1 m2 m3 Heat Transfer Model(half-fin model)

  20. DSC - Latent Heat

  21. Heat Transfer ModelPCM Heat Capacity

  22. Heat Transfer ModelCalibration • Hybrid Cooler • Base heater • Base Temperature measurement • Insulation (~ 3% loss) • Procedure • Steady State @ To Ttr • Establishes (UAs) • Record transient with q  qinit

  23. Digital Electronics Application Cont.

  24. Heat Transfer ModelCalibration Ttr = 83oC, Ttr = 6oC, q1/qinit= 2 C” = 45 watt/m2oC gives “best fit” of base temp. response.

  25. Parametric StudyStabilization/Recovery Times C” = 45 watt/m2oC, Ttr = 83oC, Ttr = 6oC q1/qinit = 1.5 q2/qinit = 0.5

  26. Parametric StudyHeating Rate C” = 45 watt/m2oC, Ttr = 83oC, Ttr = 6oC • Increase in q1/qinit results in: • increased operating temperature • decreased ts • little impact on tr

  27. Parametric StudyPCM Conductance Ttr = 83oC, Ttr = 6oC Increase in C” results in: reduced operating temperature relative to Ttr reduction in ts and tr

  28. Parametric StudyTransition Temp Interval C” = 45 watt/m2oC, Ttr = 83oC Increase in the transition temperature interval, Ttr results in poor temperature control.

  29. Dimensional AnalysisHeating “The temperature stabilization time (ts) is inversely proportional to the incremental change in input power: (q1-qinit) Dimensional Analysis: Where s is a characteristic of the system

  30. Dimensional AnalysisCooling “The temperature recovery time (tr) is inversely proportional to the decrement in input power below qinit, (q2-qinit) Dimensional Analysis: Where r is a characteristic of the system

  31. Hybrid Figure of Merit C” = 20 watt/m2oC, Ttr = 81oC, Ttr = 1oC s = r = 17 min The hybrid cooler’s figure of merit,  can (in principal) be measured with a single experiment.

  32. Conclusions • Incorporation of a “dry” PCM allows for a simple, rugged design. • A simple performance model based on lumped-mass elements contains essential system characteristics. • Semi-empirical • The transient response of the hybrid cooler can be characterized by 

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