1D transient heat conduction problem not matching with CFD results

[paul.bunuan]

I’m trying to match a very simple 1-dimensional transient heat conduction hand calc to a CFD result and have an accuracy error of about 7%. The case I’m trying to match is a 1” thick wall x 12" x 12" of stainless steel at an initial temp of 72 degF that is exposed on one side to a prescribed temp of 350 degF. What I’m trying to solve for is the temperature on the opposite side of the wall after 60 seconds. All of the side walls are insulated (i.e., I did not apply any BCs to the side walls).

The hand calc gives me a result of 195 degF while the CFD results give me around 208 degF.

For the hand calcs, I assumed an infinite plate with a characteristic length of 1" thick. To apply a prescribed temperature at the wall, I used a convection coefficient of ~11,000 W/m-K.

Is there an inherent limitation to the use of the infinite plate analytical approach that I'm seeing in this comparison or did i setup the CFD incorrectly? Any suggestions would be appreciated as this will help me determine how much confidence I have in using this COTS code for my more complex problem.

-Paul