Dear all ...

I made a mistake with my posting.  The information
I posted deals with heat transferred through a solid.

What you want is heat transfer from an exposed surface
to ambient by convection.  By looking in an old 1992
iTi Ferrotech catalog, they have a great section in
the back that addresses this and many other thermal
issues.  I cannot locate this company.  Anywho, they
give the equation for Heat Conducted From Surface to
Air.  It's the following ...

Q = h * (T1 - T2) * A

h  = Heat Transfer Coefficient
T1 = temperature in degrees C
T2 = temperature in degrees C
A  = area in square meters.

h is given several values given still or turbulent air.

Still Air      h = 23 to 28
Turbulent Air, h = 85 to 113

One square inch is 0.0064 square meters.

Dissipation in Watts for 0.0064 square meters,
an ambient of 20C and a raised temp of 40C
(a temp differential of 20 degrees C), this
works out to be 2.94 Watts. Worst case it
and say 3 Watts.

For some strange reason, this sounds about right.

Thus, two square inches would be twice that
or 6 Watts.

Regards,  Doug