Null Point Calorimeter Sweeps with Comparisons to Thermal FEA Model Predictions

Abstract

This paper presents experimental data of null point calorimeter sweeps conducted in the 60 MW Interaction Heating Facility at NASA Ames Research Center. The test setup, test conditions, and current data reduction methods are described. Finite element analysis model computations of the null point cavity temperature are also presented to demonstrate the need for application of an inverse heat conduction model to the null point calorimeter geometry. Simulations have been performed with the commercial finite element analysis software package COMSOL Multiphysics using a two-dimensional axisymmetric geometry. Two distinct IHF test conditions—one at 433 W/cm 2 and the other at 802 W/cm 2 , as measured with a 10.16 cm diameter hemispherical slug calorimeter— are considered. The heat flux distribution on the exposed surface of the null point calorimeter has been numerically computed with CFD. This heating distribution is normalized by the area- averaged heat flux over the flat face of the null point sensor. The heat flux is scaled at each time step and imposed as a boundary condition in the finite element model in order to compute the temperature at the null point cavity. The computed results differ from the measured temperature by up to 35%—a deviation sufficiently large to encourage further characterization of the methods by which heat flux is computed from the null point temperature data.