Calibration and Application of Gardon Gages for use in High Heat Flux Environments

Abstract

Gardon gages were calibrated at heat flux levels representative of those experienced in arc jet facilities for Thermal Projection System (TPS) material evaluations. This is the first known calibration of Gardon gages at high heat fluxes, which included values as high as 2,000 BTU/ft 2 -sec. The high heat flux calibration was accomplished using the Laser Hardened Materials Evaluation Laboratory (LHMEL) at Wright Patterson Air Force Base (WPAFB). The results demonstrate a linear response is maintained between the incident heating and voltage output of each Gardon gage at high heat fluxes with a correlation coefficient for the linear least squares regression for each gage exceeding 0.999. Agreement within 4% was obtained when comparing LHMEL calibration constants to manufacturer calibration constants, which were determined at heating levels approximately one order of magnitude lower than those experienced in an arc jet heating environment. The LHMEL calibrated Gardon gages were then tested in the Arnold Engineering Development Complex (AEDC) H1 arc jet, and the results were compared to heating results obtained from coaxial thermocouples and inferred heating using Teflon. Advantages and disadvantages of these different methods of heat flux measurement techniques are discussed relative to their application in arc jets, and recommendations are presented to further improve the understanding and characterization of incident heating on TPS sample surfaces in arc jet evaluations. NomenclatureB = thermochemical ablation potential δ = thickness Ch = Stanton number ε = emissivity E = emf output η = blowing correction H = enthalpy ρ = density ṁ = mass flux rate σ = Stefan-Boltzmann constant q = heat flux rate R = correlation coefficient Subscripts R 2 = coefficient of determination b = blowing s = ablation depth cw = cold wall T = temperature e = boundary layer edge u = velocity gw = gas wall α = absorptance o = no blowing Δt = arc jet dwell time Tef,o = Teflon at initial conditions