Thermal Resistance of a Surface Area

[Jakwani]

I have a piece of metal (2"x4&quot that I am using as a heat sink (amplifier is mounted on heat sink). I would like to calculate Thermal resistance (C/W ) from sink to ambient. Can someone help me with this?
Thanks a lot.

 

[22672]

Heat transfer to the ambient air is through natural convection. You could read the articles and the procedure to calculate natural convection coefficient for your application.

You could refer to any heat transfer calculation book or Perry's handbook.

 

[20342170]

There are two modes of heat transfer involved.1)thermal radiation, 2)convection. One dimensional analysis would yield:

q_total = (T_sink - T_air)/R_total

where R_total= 1/(hA) + 1/(h_rad *A)

where h = convective heat transfer coefficient and is a function of the fluid properties, temperature difference and the orientation of your sink. Must be determined using correlations from any heat transfer book
A: is the heat transfer area

h_rad: normalized radiant heat transfer coefficient
h_rad = (surface emmisivity * Stefan Boltzman constant)*(T_sink^2 + T_air^2)*(T_sink + T_air)