Residual-g and g-jitter effects on the measurement of thermophysical properties in microgravity

Abstract

For the evaluation of the thermo-fluid-dynamic disturbances induced by residual-g and g-jitter on the International Space Station (ISS) a numerical study is carried out for two classes of experiments that exhibit a large sensitivity to accelerations and that would benefit from conditions as close as possible to the purely diffusive fields: 1) measurement of the thermal conductivity in high Prandtl number liquids; 2) measurement of the thermodiffusion coefficient in binary mixtures. Numerical simulations are performed to compare the results of the direct integration of the full Navier-Stokes equations (that compute the instantaneous time-dependent flow) with the solutions of the equations for the time-averaged quantities (thermovibrational theory). The results show that, for the microgravity environment of the ISS, the two formulations give almost the same results. Simulations at different orientations of the residual-g and g-jitter show that, orienting the residual-g parallel to the density gradient, reduces the convective disturbances and can also help mitigating the disturbances induced by the g-jitter. Microgravity experiments will be performed during the UF#3 flight of the ISS (2003) to assess the relative importance of residual-g and g-jitter and the advantages of orienting the density gradient along the residual-g (i.e. in a stabilizing mode), to minimize the acceleration disturbances during sensitive experiments for the measurement of thermophysical properties.