Assessing Calorimeter Evaluation Methods in Convective Heat Flux Environments

Slug calorimeters are routinely used for characterization of arc-jet plasma conditions at NASA Ames Research Center facilities. The current model for evaluation of the temperature data from these measurements assumes no thermal losses when calculating incident heat flux. In order to investigate the importance of the losses, three different methods of evaluating slug calorimeter measurements are compared. The three methods were ASTM standard E 457-96, a finite element model and an analytical model. The latter two account for thermal losses, whereas the ASTM standard does not. In this study, data from arc jet tests, and, from a radiant heat source in a laboratory setting are evaluated. For the radiant heat source, the heat flux reaching the slug calorimeter was measured with a Kendall electric substitution radiometer with calibration traceable to National Institute of Standards and Technology (NIST). The results from all three methods of data analysis were compared to the value recorded by the electric substitution radiometer, which provides an absolute measurement of incident radiative heat flux.