Fire Safety Science Digital Archive

Radiometers or heat flux meters used in fire testing are frequently mounted in free air in front of flames or furnaces and thus measure the total heat flux i.e. both radiation and convection. If the gages are calibrated in a pure radiative environment then corrections are needed for the convective influence. Other applications are in flammability test methods where the precise measurement of incident radiant flux is important. Again corrections for the convective influence are necessary. At low heat fluxes even the free convection induced by the sensor itself can cause substantial errors. A sensor mounted flush in an exposed specimen will be influenced by the convection induced by the hot surface of the specimen. The present paper demonstrates the feasibility of using CFD (Computational Fluid Dynamics) calculations as a tool in achieving corrections to recorded heat fluxes due to the influence of convection. The CFD code SOFIE has been used to compute the heat transfer caused by free convection for a Schmidt-Boelter gage, and the calculated corrections have been compared to experimental data Two cases have been investigated, a sensor in free air with the cooling water different from the temperature of the surrounding air, and a sensor mounted in a heated refractory board. Predicted heat transfer coefficients are in sufficient agreement with previous measurements published by Robertson and Ohlemiller [I] to confirm the utility of the approach.