Experimental and Computational Characterization of High Heat Fluxes During Transient Blackbody Calibrations

Abstract

High heat fluxes are encountered in numerous applications, such as on the surfaces of hypersonic vehicles in flight, in fires, and within engines. The calibration of heat flux gauges may be performed in a dual cavity cylindrical blackbody. Insertion of instruments into the cavity disturbs the thermal equilibrium resulting in a transient calibration environment. To characterize the transient heat fluxes, experiments were performed on a dual cavity cylindrical blackbody at nominal temperatures varying from 800°C to 1900°C in increments of 100°C. The pre-insertion, steady state, axial temperature profile is compared experimentally and numerically. Detailed transient thermal models have been developed to simulate the heat flux calibration process at two extreme fluxes: the high flux is 1 MW/m2 and the relatively low is 70 kW/m2. Based on experiments and numerical analysis, the optimum heat flux sensor insertion location as measured from the center partition was determined. The effect of convection (natural and forced) in the blackbody cavity during the insertion is calculated and found to be less than 2% at high temperatures but reaches much higher values at relatively lower temperatures. The transient models show the effect of inserting a heat flux gauge at room temperature on the thermal equilibrium of the blackbody at 1800°C and 800°C nominal temperatures. Also, heat flux sensor outputs are derived from computed sensor temperature distributions and compared with experimental results. The numerical heat flux agreed with the experimental results to within 5%, which indicates that the numerical models captured the transient thermal physics during the calibration. Based on numerical models and all experimental runs the heat transfer mechanisms are explained.

Development of integrated high temperature sensor for simultaneous measurement of wall heat flux and temperature

“…These gaps are considered ideally to be a ring column model and heat flows from the outside into inside. Air's conductivity λ 23 …”

“…[13][14][15][16][17][18][19][20] Calibrations of water-cooled sensors placed inside blackbody cavity have been tested recently and maximum heat flux up to 0.5 MW/m 2 and 1.0 MW/m 2 were obtained by Murthy at NIST (Refs. 21 and 22) and Abdelmessih at Saint Martin's University, 23 respectively. This paper is aimed to develop a high temperature sensor used to simultaneously measure the wall heat flux and temperature in supersonic combustors.…”