# Film Coefficient Dependency in Thermal Analysis

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• Last Post 23 February 2020
lordofthethings posted this 21 February 2020

Hello,

I am modelling the temperature distribution over the wall-thickness of a rubber pipe based on the temperature of a fluid flowing inside the pipe. The conditions are as follows:

T_fluid = 100°C, T_environment = 22 °C

Based on tests, it was estimated that the temperature at the inner wall which is in contact with the fluid, is 108  72 °C after steady-state was reached. So :

T_inner wall = 72°C, T_outer wall = 62°C

My approach was to play around with the "Film Coefficients" in the convection boundary condition until I got the above mentioned inner and outer wall temperatures.

I was quite surprised to see that multiple combinations of film coefficients can produce the same temperature distribution within the solid:

My question : what role (if any) does the film coefficient play in a thermal analysis? And what does it mean practically, when different sets of film coefficients produce the same results?

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peteroznewman posted this 21 February 2020

How can the temperature of the inner wall be 108 C if the fluid is 100 C and everything else is cooler than that?

lordofthethings posted this 21 February 2020

Hi Peter,

That was a typo from my side. I edited the post a number of times and missed out on correcting the temperature. I have edited it now.

For others: Initially I had mentioned wrongly that the inner wall temperature was 108 °C. It has been now corrected to 72 °C

peteroznewman posted this 23 February 2020

Do a Mesh Refinement Study to find the element size required so that the temperature has converged and you have a mesh independent solution.

Wikipedia has a decent page on Convective Heat Transfer Coefficient.

With the mesh that has elements small enough to deliver a converged temperature, you can perform a two-factor parameter sweep to map out the relationship between heat transfer coefficient and temperature on the inner and outer walls of the tube.