Experimental In-Cavity Radiative Calibration of High Heat-Flux Meters

The accuracy of the calibration of heat-flux meters up to 500 kW · m -2 irradiance levels by insertion into the cavity of a high-temperature blackbody is examined. The experimental study consists of measurements on two thermopile heat-flux meters using two graphite-tube variable-temperature blackbodies. To provide a baseline comparison, the meters were first calibrated up to 50 kW · m -2 outside the blackbody cavity with the irradiance level determined using a well-characterized electrical substitution radiometer. In contrast to the outside calibration method, in-cavity calibration covers the full heat-flux range of the meters. The measured radiance distribution along the cavity axis, corroborated by Monte Carlo simulations, shows that the optimum location for the meter is approximately one cavity radius from the closed end of the cavity. The in-cavity measured responsivity values corrected for the effective emissivity agree with the outside-cavity values within the measurement uncertainty. The results demonstrate the feasibility of using in-cavity techniques to calibrate heat-flux meters at high irradiance levels, limited primarily by the blackbody operating temperature.