So you're doing a surface integral of the flux? I tried this analysis on a unit cube with convection to ambient and the reaction probe correctly reported 10W. Then I applied 10W/meter^3 to a solid cylinder with radius 14.4meters and height of 17.7meters (volume = 10,898 meter^3). The reaction probe reported a heat flow of 108,910 W so pretty close. It seems a Mechanical reaction probe works correctly for an axisymmetric model. My boundary condition is convection. You might want to stay in MKS units to make the calculations easier.
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