Generate Interface temps from K and cold and hot face temps

[just66horns]

Hi,

I just forget how to do this.
I am creating a spreadsheet to perform a cost tradeoff between insulation thickness, the costs of install, and the costs of energy loss. The canned programs cannot have our installation costs put into them easily, so I am working in Excel.

I know thicknesses, Thermal conductivity data, Hot and cold face temperatures and areas (both pipes and flat sided ducts). I also have the labor and material costs worked out.
I'm just not sure what formula to use to generate the interface temps. I remember I did this in college, but, don't have my notes handy...
Anyone remember?

Example, knowing 1M/S airflow, 70F ambient, 1000F duct temperature(very high flow rates), 2" of ceramic fiber, 2" in of mineral wool, what is the one interface temp and the cold face which must be held below 140F. This is just an example, I know thats not enough insulation.

Thanks in advance
Thanks in advance

Just66horns
I changed the horns and now mine goes beep beep

 

[chicopee]

Check into the critical thickness of insulation for the economics. I believe that the critical thickness of insulation is proportional to thermal conductivity of insulation and inversely proportional to the convective heat transfer coefficient around the insulation.
Look up a heat transfer book for a precise formula and explanation.