A New Method to Calculate Incident Radiant Heat Flux by Using Plate Thermometer

Abstract

Plate thermometer (PT) that consists of a thin metal plate and a layer of inorganic insulation material attached to the backside of the metal plate has been used to calculate the incident radiant heat flux by other researchers. However, the incident radiant heat flux is often underestimated using PT as the heat loss from the metal plate is not appropriately reflected in the calculation. Especially when PT is placed in low ambient temperature conditions or in a heating phase, the underestimation becomes more significant. Besides the heat loss effect, some PT properties such as surface emissivity and thermo-physical properties as well as errors of temperature measurements affect the accuracy of incident radiant heat flux calculations. In the current study, a new incident radiant heat flux calculation method is proposed to overcome the aforementioned inaccuracies. The temperature that a thermally thin metal element should ideally achieve with a perfectly insulated back surface is correlated with the actually measured surface temperature under known heat fluxes for calibration. From this correlation, a set of equations to calculate the incident radiant heat flux is derived for a mixed radiation/convection environment. For validation, the incident radiant heat fluxes calculated from the proposed method and measured from a commercially available Schmidt-Boelter type total heat flux gauge were compared and a good agreement was observed.