Heat Transfer: Free Convection

Newton's Law of Cooling
Similar to forced convection, heat transfer due to free convection is described by Newton's Law of Cooling,
The rate of heat transfered to the surrounding fluid is proportional to the object's exposed area A, and the difference between the object temperature Tw and the fluid free-stream temperature .

The constant of proportionality h is termed the convection heat-transfer coefficient. Other terms describing h include film coefficient and film conductance.

Variables needed to parameterize free convection are:

Definition of Symbols
Independent Parameters for the Fluid
Quantity Symbol Object Units
  bulk temperature   scalar K
  kinematic viscosity   n scalar m2/s
  coef. of thermal expansion   b scalar 1/K
  dynamic viscosity   m scalar kg/m-s
  density   r scalar kg/m3
  thermal diffusivity   a scalar m2/s
  specific heat   cp scalar J/kg-K
  thermal conductivity   k scalar W/m-K
Independent Parameters for the Object
Quantity Symbol Object Units
  surface reference length   L scalar m
  surface diameter (for pipes)   D scalar m
  surface (wall) temperature   Tw scalar K
Dependent Parameters
Quantity Symbol Object Units
  surface to fluid temp. difference   scalar K
  heat transfer coefficient   h scalar W/m2-K



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