Hello,

You are correct, there is a way to model the heat transfer using an effective heat transfer coefficient. Using simple one-dimensional thermal resistance analysis, you can compute the effective heat transfer coefficient. The analysis will resemble something like this:

1 / (h_cav-top, eff * A_cav-top) = ( l_top-clamp / ( k_top-clamp * A_top-clamp ) + ( 1 / ( h_top * A_top ) )

Here (knowns):

l_top-clamp = length of the top clamp

k_top-clamp = thermal conductivity of top clamp

A_top_clamp = cross sectional area of top clamp

h_top = convective heat transfer coefficient at the top surface of top-clamp

A_top = surface area at the top surface of top-clamp

A_cav-top = surface area on the cavity plate on which you want to implement this heat transfer coefficient

You can use the above equation to estimate the effective heat transfer coefficient. However, there are some big and important assumptions involved in this procedure.

- The heat transfer is only one-dimension. That is, there is no heat transfer along the top clamp surface. Heat transfer is only across it and therefore, we end up using l/(kA) type of resistance analysis.
- I am also assuming that the top clamp is not touching the machine base and am modeling it using convective heat transfer coefficient. I did this only to illustrate the method. If, in your case, the top clamp is touching the machine base, you might have to include a conductive thermal resistance (l/(kA)) type of analysis.

During numerical modeling, it is extremely important to make your problem well-posed. What this means is you want to include all the necessary aspects of your problem to make sure that the boundary conditions you plan to apply to solve the problem are physical. It is sometimes not feasible to include everything in your analysis. In such cases, you make a note of the assumptions you are using in your model.

If I were solving this problem, I would include the top clamp and use a heat transfer coefficient to model the heat loss at the top surface of this clamp. By including the top clamp in my analysis, I am ensuring a 3-dimensional heat transfer. It is likely that my solution might indicate that heat transfer is primarily across the plate, as opposed to along. This, however, becomes a conclusion rather than an assumption in my model.

To estimate the heat transfer coefficient at the top surface of the top-clamp, you have to understand the physics at this surface. Is this going to be natural or forced convection would be the first question you need to ask yourself?

I hope this helps and provides some perspective.

Best Regards,

Karthik