Ceramic Insulated Slug Calorimeter for High- Enthalpy Flows

This work presents an approach to the design, and successful experimental validation, of a slug-type calorimeter for long-duration high-enthalpy flows. Specifically, a ceramic shell is used to insulate the slug. Although slug calorimeters have been widely used in arcjets for decades, significant uncertainties are known to be associated with these instruments, which directly affect the uncertainty of critical derived flow quantities such as specific enthalpy. A detailed analysis of the newly proposed design approach is presented. Particular attention has been devoted to the minimization of heat losses from the slug to the shroud, one of the major contributors to the instrument’s uncertainty. The effect of the shroud geometry, insulation thickness, and slug dimensions have been investigated numerically; variable thermophysical properties, nonuniform heat fluxes, and radiation were considered. The analysis showed that the shroud geometry plays a significant role in the heat losses. Based on this design approach, a calorimeter was manufactured to be used in the Office of Naval Research (ONR)–University of Texas at Arlington (UTA) arc-heated wind tunnel “Leste” facility. Experimental measurements in flows with bulk enthalpies up to 4 MJ/kg showed good agreement with the numerical simulations, and measured heat losses were well below the American Society for Testing and Materials standard recommendation.