Measurements on thermodiffusion in ternary hydrocarbon mixtures at high pressure

Experimental investigations on thermodiffusion have been conducted for five different ternary mixtures of methane, n-butane, and n-dodecane at a high temperature and pressure. While the mole fraction of methane was fixed at 0.2 the mole fraction of n-dodecane was varied from 0.7 to 0.2. The experiments were performed in a microgravity environment on board the satellite FOTON-M3. It was found that in all mixtures, n-dodecane separated to the cold side whereas methane segregated to the hot side. n-butane, the species with an intermediate density, showed a change in sign as its mole fraction was increased. At low concentrations it collected on the cold side but moved in the opposite direction with an increase in its mole fraction. The role of the relative density coupled with the species concentrations has been used to explain the thermodiffusion factor in each mixture. Computational investigations showed a similar behavior. However, the theoretical model was not able to capture the sign change of n-butane accurately. The inadequate representation of the significance of the relative densities and the mole fraction of the species has been found as the reason for this. (C) 2009 American Institute of Physics. [doi:10.1063/1.3236745]