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CHE/ME 109 Heat Transfer in Electronics

CHE/ME 109 Heat Transfer in Electronics. LECTURE 22 – ELECTRONICS COOLING MECHANISMS. COOLING MECHANISMS FOR ELECTRONIC COMPONENTS AND DEVICES. NATURAL CONVECTION COOLING RELIABLE NATURAL CONVECTION EMPLOYS NO MOVING PARTS COOLING MEDIA IS READILY AVAILABLE MODELS FOR CONVECTION

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CHE/ME 109 Heat Transfer in Electronics

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  1. CHE/ME 109 Heat Transfer in Electronics LECTURE 22 – ELECTRONICS COOLING MECHANISMS

  2. COOLING MECHANISMS FOR ELECTRONIC COMPONENTS AND DEVICES • NATURAL CONVECTION COOLING • RELIABLE • NATURAL CONVECTION EMPLOYS NO MOVING PARTS • COOLING MEDIA IS READILY AVAILABLE • MODELS FOR CONVECTION • BASIC EQUATION IS

  3. MODELS FOR CONVECTION • FOR AIR AT AMBIENT CONDITIONS, THERE ARE SIMPLIFIED CORRELATIONS AVAILABLE FOR LAMINAR FLOW CONDITIONS OF THE FORM: • AS PER TABLE 15-1 WHERE: • L IS A CHARACTERISTIC DISTANCE SUCH AS A VERTICAL RUN, DIAMETER, OR A/p • n IS 0.25 • K IS DEPENDENT ON SYSTEM GEOMETRY AND INCLUDES THE EQUIVALENT Ra NUMBER AT NEAR AMBIENT CONDITIONS

  4. MODELS FOR NATURAL CONVECTION • FOR A SUMMARY OF THIS METHOD, GO TO: http://electronics-cooling.com/articles/2001/2001_aug_calccorner.php • Simons, R.E., Simplified Formula for Estimating Natural Convection Heat Transfer Coefficient on a Flat Plate, ElectronicsCooling, Vol. 7, No. 3, August 2001, pp 12-13. • CORRELATIONS CAN BE ADJUSTED FOR PRESSURE USING • CORRELATIONS ASSUME UNRESTRICTED FREE FLOW PASSED THE SURFACE • RADIATION COOLING IS ALSO PRESENT FOR THESE SYSTEMS AND SHOULD BE INCLUDED FOR THE OVERALL HEAT BALANCE

  5. FORCED CONVECTION • BASED ON THE HEAT BALANCE: • USE HYDRAULIC DIAMETER FOR THE MORE COMPLEX SHAPES (NOT PLATES, CYLINDERS OR SPHERES) • HEAT TRANSFER CORRELATIONS • SEE TABLE 15-2 FOR EXTERNAL FLOWS • SEE TABLE 15-3 FOR INTERNAL FLOWS

  6. PARALLEL MECHANISMS • NATURAL CONVECTION IS NORMALLY PRESENT • SIGNIFICANT IF • CAN INCREASE OR DECREASE FORCED CONVECTION, DEPENDING UPON THE FLOW DIRECTION AND SURFACE CONFIGURATION • NATURAL CONVECTION WILL REDUCE COOLING WHEN FORCED AIR FLOWS DOWN A HOT VERTICAL SURFACE • NATURAL CONVECTION WILL INCREASE COOLING WHEN FORCE AIR FLOWS UP A HOT SURFACE

  7. AIR CIRCULATION PATTERNS • AN EFFECTIVE SYSTEM NEEDS A CLEAR OPENING FOR AIR FLOW TO AND FROM THE OUTSIDE OF THE CASE • THIS CAN BE FROM THE SIDES IF THE BOTTOM OF THE CASE IS NOT CLEAR • THE EXHAUST IS TYPICALLY AT THE TOP OF THE CASE

  8. AIR CIRCULATION PATTERNS • ASSURANCE OF ADEQUATE HEAT TRANSFER COEFFICIENTS AT THE SURFACE OF EACH DEVICE • FLOW DIVERSION CAN SEND A BALANCED FLOW TO ALL MAJOR HEAT GENERATING COMPONENTS

  9. FORCED AIR CONVECTION WITH FANS • CAN BE SINGLE FANS • CAN BE DUAL FANS (PUSH - PULL) METHOD TO MAINTAIN VELOCITIES AND OVERCOME PRESSURE DROP • LOCAL COOLING MAY ALSO BE REQUIRED • CPU FANS • POWER SUPPLIES • CASE FANS • OTHER COOLING COMPONENTS • HEAT SINKS • LIQUID COOLING DEVICES • CAN BE IN THE FORM OF RADIATORS TO COOL CIRCULATING AIR • COOLANT FLOW CAN ALSO BE DIRECTED TO MODIFIED HEAT SINKS TO INCREASE LOCAL CONDUCTION COOLING http://www.binbin.net/compare/Akasa-Integral-P2-AK-ENP2USB-BK.htm

  10. LIQUID COOLING EXAMPLE http://www.tweaknews.net/reviews/bigwater735/img/2.jpg

  11. LIQUID COOLING DESIGN SPECIFICS • ADVANTAGES OF LIQUID COOLING INCLUDE REDUCED NOISE IF THE FAN IS REDUCED IN POWER OR SIZE • COOLANT CAN BE REFRIGERANT OR CIRCULATING WATER SYSTEM • HIGHEST EFFICIENCY WHEN PHASE CHANGE HEAT TRANSFER IS USED

  12. COOLING PLATE SPECS http://www.wakefield.com/PDF/liquid_cold_plates.pdf

  13. COOLING PLATE SPECS http://www.wakefield.com/PDF/liquid_cold_plates.pdf

  14. IMMERSION COOLING • IS OBTAINED BY PUTTING THE COMPONENTS IN A CONTAINER CONTAINING A DIELECTRIC FLUID • TYPICAL DESIGNS ARE BASED ON THOSE USED FOR POWER TRANSFORMERS http://www.ecplaza.net/tradeleads/seller/6319102/supply_transformers.html#none

  15. IMMERSION COOLING CONFIGURATION

  16. OTHER COOLING DEVICES • HEAT PIPES • HEAT PIPES ARE FILLED SYSTEMS THAT USE CHANGE OF PHASE HEAT TRANSFER • THE HEAT VAPORIZES THE CHEMICAL IN THE SYSTEM AT THE HEATING END OF THE PIPE • THE VAPOR IS CONDENSED AT THE COOLING END OF THE PIPE

  17. HEAT PIPE DESIGN http://electronics-cooling.com/articles/1996/sep/sep96_02.php

  18. HEAT PIPE CONFIGURATION http://media.photobucket.com/image/heat%20pipes%20for%20electronics/tiesum/vinnen.jpg

  19. THERMOELECTRIC COOLERS H • TAKE ADVANTAGE OF THE PELTIER EFFECT TO COOL IN WHICH CONDUCTING A DC CURRENT ACROSS TWO DISSIMILAR MATERIALS CAUSES A TEMPERATURE CHANGE http://www.peltier-info.com/info.html

  20. THERMOELECTRIC COOLING http://www.melcor.com/images/cutaway.jpg http://www.sure-electronics.net/DC,IC%20chips/DC-CL001-1.jpg

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