LECTURE 22 - ELECTRONICS COOLING MECHANISMS

							       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
   BASIC EQUATION IS
         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
    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
         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
         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
      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
     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
    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
   LIQUID COOLING EXAMPLE




http://www.tweaknews.net/reviews/bigwater735/img/2.jpg
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
              COOLING PLATE SPECS



http://www.wakefield.co
m/PDF/liquid_cold_plat
es.pdf
             COOLING PLATE SPECS




http://www.wakefield.com/
PDF/liquid_cold_plates.pdf
         IMMERSION COOLING

   IS OBTAINED BY
    PUTTING THE
    COMPONENTS IN A
    CONTAINER
    CONTAINING A
    DIELECTRIC FLUID
   TYPICAL DESIGNS
    ARE BASED ON
    THOSE USED FOR
    POWER              http://www.ecplaza.net/tradeleads/seller/63
                       19102/supply_transformers.html#none
    TRANSFORMERS
IMMERSION COOLING CONFIGURATION
      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
                      HEAT PIPE DESIGN



http://electronics-
cooling.com/article
s/1996/sep/sep96_
02.php
         HEAT PIPE CONFIGURATION




http://media.photobucket.c
om/image/heat%20pipes%
20for%20electronics/tiesum
/vinnen.jpg
    THERMOELECTRIC COOLERS                            H


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




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                                   http://www.sure-
away.jpg
                                   electronics.net/DC,IC%20chips
                                   /DC-CL001-1.jpg