In the paper, it has been proposed to unite the heat flux measurements with thermal imaging and the PIV diagnostics for studies in aerodynamics and heat transfer at the surface of a circular fin. The hollow fin under consideration was heated by saturated steam from within; meanwhile the isothermal external surface simulated an ideal fin. The surface flow and heat transfer of the solid fin sized and shaped identically, and made of titanium alloy, was investigated in the same regimes. Gradient heat flux sensors were placed on the fin surface. The velocity field near the fin, the temperature field and the heat flux per unit area at its surface were obtained. The data analysis gave an impartial piece of information. The proposed method allows examination of a flow and a heat transfer on the fin surface in the real-time processing.