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Heat Flux
Heat Transfer Terminology Summary

Thermodynamics Heat Transfer and Fluid Flow Volume 2 of 3
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HEAT TRANSFER TERMINOLOGY Heat Transfer Convective Heat Transfer Coefficient The convective heat transfer coefficient (h), defines, in part, the heat transfer due to convection. The  convective  heat  transfer  coefficient  is  sometimes  referred  to  as  a  film  coefficient  and represents the thermal resistance of a relatively stagnant layer of fluid between a heat transfer surface  and  the  fluid  medium.    Common  units  used  to  measure  the  convective  heat  transfer coefficient are Btu/hr - ft2 -oF. Overall Heat Transfer Coefficient In  the  case  of  combined  heat  transfer,  it  is  common  practice  to  relate  the  total  rate  of  heat transfer (    ), the overall cross-sectional area for heat transfer (Ao), and the overall temperature Q difference  (DTo)  using  the  overall  heat  transfer  coefficient  (Uo).    The  overall  heat  transfer coefficient combines the heat transfer coefficient of the two heat exchanger fluids and the thermal conductivity of the heat exchanger tubes.  Uo is specific to the heat exchanger and the fluids that are used in the heat exchanger. (2-3) Q UoAoDT0 where: = the rate heat of transfer (Btu/hr) Q Uo = the overall heat transfer coefficient (Btu/hr - ft2 -oF) Ao = the overall cross-sectional area for heat transfer   (ft2) DTo = the overall temperature difference   (oF) Bulk Temperature The fluid temperature (Tb), referred to as the bulk temperature, varies according to the details of the situation.   For flow adjacent to a hot or cold surface, Tb is the temperature of the fluid that is  "far"  from  the  surface,  for  instance,  the  center  of  the  flow  channel. For  boiling  or condensation, Tb is equal to the saturation temperature. HT-02 Page 4 Rev. 0







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