Steady-state heat flux measurements in radiative and mixed radiative-convective environments

The steady-state responses of four heat flux gauges (Schmidt-Boetter, Gardon, directional flame thermometer (DFT) and hemispherical heat flux gauge (HFG)) were examined under various radiative and convective heating conditions. In radiative environments, Gardon measurements were up to 8% higher than Schmidt-Boelter measurements, but in mixed radiative-convective environments, Gardon measurements were 8-18% below those of the Schmidt-Boelter gauge. This difference increased as the convective portion of the total heat transfer increased, due to discrepancies between the radiation-based calibration environment and the application environment. The DFT data in radiative environments were comparable with the Schmidt-Boelter and Gardon values (within 12%), with the difference largely attributed to natural convection losses from the DFT. In mixed environments, the DFT values were significantly lower than those of the Schmidt-Boelter gauge due to differences in the surface temperatures of the gauges, resulting in the convective flow cooling, rather than heating, the DFT. The HFG heat flux estimates were 35-48% lower than the Schmidt-Boelter measurements under radiative conditions, influenced by large conduction losses from the sensor plate to the gauge housing. Lateral conduction due to a mismatch between the experimental convective flow outlet diameter and the gauge width also affected results from the DFT and HFG. Copyright (C) 2009 John Wiley & Sons, Ltd.