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

Quantity

Symbol

Units

  bulk temperature  

K

  kinematic viscosity  



m²/s

  coef. of thermal expansion  



1/K

  dynamic viscosity  



kg/m-s

  density  

ρ

kg/m³

  thermal diffusivity  



m²/s

  specific heat  

c_p

J/kg-K

  thermal conductivity  

k

W/m-K

Independent Parameters for the Fluid

Quantity

Symbol

Units

  surface reference length  

L

m

  surface diameter (for pipes)  

D

m

  surface (wall) temperature  

T_w

K

Independent Parameters for the Object

Quantity

Symbol

Units

  surface to fluid temp. difference  

K

  heat transfer coefficient  

h

W/m²-K

Dependent Parameters

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