Discussion Forum

I have a problem to calculate the amount of power transferred from a set of hot parallel rectangular channels to a laminar air flow flowing through them.

In my understanding, it should be the product of the air mass flow by the integral of the heat capacity over the temperature; which should be evaluated between the mean temperatures of the air in the inlet and outlet surfaces of the model.

In order to simplify the 3D COMSOL model (image attached), I have simulated only a single channel with boundary conditions of Symmetry on the lateral surfaces of the channel and Periodic Flow and Heat Conditions on the lateral surfaces of the upstream and downstream air domains. In this model, the channel is heated by applying a Boundary Heat Source with Pb,tot = 21 W on the frontal surface of the channel.

Using the results of this simulation, I calculate the mass flow through the model inlet and outlet surfaces with a Surface Integration, the mean temperatures of the air in the same surfaces with a Surface Average and I evaluate the integral of the heat capacity analytically using the polynomial function of the air included in COMSOL. However, I obtain a power of 29.64 W, which is higher than the applied power (21 W).

Does anyone could explain me why my calculation is wrong? Is there a way to calculate the transmitted power to the air directly with COMSOL?

Thank you very much for the comments.