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: AS PER TABLE 15-1 WHERE: L IS A CHARACTERISTIC DISTANCE SUCH AS A VERTICAL RUN, DIAMETER, OR A/p L IS A CHARACTERISTIC DISTANCE SUCH AS A VERTICAL RUN, DIAMETER, OR A/p n IS 0.25 n IS 0.25 K IS DEPENDENT ON SYSTEM GEOMETRY AND INCLUDES THE EQUIVALENT Ra NUMBER AT NEAR AMBIENT CONDITIONS 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 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 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 REDUCE COOLING WHEN FORCED AIR FLOWS DOWN A HOT VERTICAL SURFACE NATURAL CONVECTION WILL INCREASE COOLING WHEN FORCE AIR FLOWS UP A HOT 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 LOCAL COOLING MAY ALSO BE REQUIRED CPU FANS CPU FANS POWER SUPPLIES POWER SUPPLIES CASE FANS CASE FANS OTHER COOLING COMPONENTS OTHER COOLING COMPONENTS HEAT SINKS HEAT SINKS LIQUID COOLING DEVICES LIQUID COOLING DEVICES CAN BE IN THE FORM OF RADIATORS TO COOL CIRCULATING AIR 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 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.co m/PDF/liquid_cold_plat es.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 TYPICAL DESIGNS ARE BASED ON THOSE USED FOR POWER TRANSFORMERS http://www.ecplaza.net/tradeleads/seller/63 19102/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/article s/1996/sep/sep96_ 02.php

18. HEAT PIPE CONFIGURATION http://media.photobucket.c om/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/cut away.jpg http://www.sure- electronics.net/DC,IC%20chips /DC-CL001-1.jpg