Thermal equiblium between conduction and convetion

Hi every one,

 

I am trying to simulate a convection and conduction model and compare it with analytic results. I have a cube with K value of 100 as it can be seen in the attachment, with upper surface temperature of 40. The lower surface is exposed to free convection with amb. temp of 20 and H value of 40. The thinkness if cube is 0.35m.

 

Analytical calculation of problem would yield lower surface temp. of 37.3 while simulation results always gets very close to ambient temperature. can anyone explain why there is a difference ?

 

T1 = 40

K = 100

H = 40

Tamb = 20

L = 0.35

T2 = ?

 

k.(T1-T2)/L = H(T2 - Tamb)

T2 = 37.3

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