Hi Thimal, I don't think the flux would be based on just one element of the mesh - it's probably based on one face of the part, but I'm not sure. Maybe you could run a very simple test where you have just a block that can only conduct heat from one surface by making all the other 5 faces adiabatic. Then look at the reported results and compare the heat flux to your hand calculations.
If you right click on your Resultant Heat flux plot, select probe. At the top choose "On Selected Entities". From there select the external faces you are interested in analyzing and click Update. Below, a summary will give you the average Heat Transfer coeff. in W/m^2. If you use the Measure Tool you can find the subsequent area of the same region you just probed. Multiplying the two will give you the heat transfer (Watts) through that given area.
Hope this helps.