Heat Flux Measurements and Their Uncertainty in a Large-Scale Fire Test

Abstract

Heat flux data from a series of controlled experiments involving a 2 m diameter, wind-blown pool fire are examined to highlight the difficulties involved in conducting heat flux measurements in a realistic, large-scale, hydrocarbon-fueled fire. Data were taken at several locations along the ground near the fire. At each location, three different heat flux sensors were positioned together: a Gardon gage, a directional flame thermometer (DFT) and a Sandia heat flux gage (HFG). Methods were first developed to correct measured values of heat flux for the slight differences in gage location relative to the fire. The remaining discrepancies between the values of heat flux measured by the different gages were then used to highlight uncertainties in heat flux measurements due to differences in gage surface temperature, in gage thermal response to the inherent modes of heating involved in the large hydrocarbon fire environment, and in conduction losses from the gage sensor plates. The importance of these sources of discrepancy varied depending on the magnitude of the measured heat flux and on whether the gages were located in a radiation-dominated or mixed radiative-convective environment within the fire.