A method for time and spatially resolved measurement of convective heat transfer coefficient (h) in complex flows

A miniaturized plane probe (5×5×1.1mm3) was developed to measure on-line local and unsteady convective heat transfer coefficients (h) in complex flows. The proposed method is in particular dedicated to assess h at the surface of porous media subjected to mass transport that interacts with the surrounding flow such as those that occur between a partially saturated porous medium and hot fluid phase (superheated steam, oil, etc.). The active h-probe consisted of a combination of a film heater sandwiched between two heat flux sensors, and h was obtained on each side from temperature and flux outputs of flux sensors in response to a periodic input of heating (maximum increase in probe surface temperature <2.5∘C). In controlled hydrodynamic conditions, it was found that 3 cycles of 1 Hz measurements ensured h relative errors ranged between −3% and −0.5% with 98% confidence for h values ranged between 200 and 500Wm-2K-1.