On the impact of the ISS reboosting maneuvers during thermodiffusion experiments of ternary liquid systems: Pure diffusion

Abstract

In the present study, the effects of reboosting maneuvers on the diffusion process during the thermodiffusion experiments known as Diffusion and thermodiffusion Coefficients Measurements in ternary liquid mIXtures (DCMIX) are analyzed. These experiments have systematically conducted in the International Space Station (ISS). Six different compositions of a 1,2,3,4-TetraHydroNaphtalene (THN), IsoButylBenzene (IBB) and n-Dodecane (nC12) mixture have been studied by means of numerical simulations. Real acceleration levels have been used to compute the unsteady buoyancy term in the momentum equation. Different gravity scenarios have been considered by changing both the intensity and the duration of the reboosting as well as its orientation, parallel or perpendicular to the concentration gradients. In these thermodiffusion experiments, the different components of the mixture separate in a parallelepipedic Soret cell, with a constant externally imposed temperature gradient between two opposite walls. When the temperature and concentration distributions reach the steady state, and consequently linear concentration profiles between hot and cold walls are achieved, the temperature difference is switched off and the components of the mixture diffuse until uniform concentration distributions are obtained. The present simulations only reproduce this last pure diffusive part of the thermodiffusion experiment. Results show that when a reboosting occurs, errors in the obtaining of the diffusion coefficients arise because of the convection generated. The lower values of the diffusion coefficient show a larger error since they are more sensitive to disturbances. The maximum error is obtained when the acceleration is acting perpendicular to the concentration gradient, which is the most harmful orientation.