Differential thermo-osmotic permeability in water–cellophane systems

Abstract

The thermo-osmosis of pure water through two different cellophane membranes at temperatures ranging between 33 and 47 °C has been studied. Two types of experiments have been carried out: one to determine the dependence of the phenomena on stirring rate, with the average temperature and the temperature difference between the two bulk phases being kept constant while varying the stirring rate; the other varying the temperature difference between the two bulk phases, with the temperature of the cold bulk phase being kept as close to a fixed value as possible and employing a constant stirring rate. In all experiments the thermo-osmotic flow was from the hot to the cold side, and thermo-osmotic permeability was found to decrease with the mean temperature. The experimental values of the global thermo-osmotic permeability were corrected by taking into account the temperature polarization, and from these corrected values the differential thermo-osmotic permeabilities were calculated for the two membranes employed. The relationship between the differential thermo-osmotic permeability and the temperature was found to be different for the two membranes, being linear for the 600P membrane and quadratic for the 500P membrane. However, within the range of temperatures used in the present study, in each case, the differential thermo-osmotic permeability decreased with temperature. For comparison, the differential thermo-osmotic permeabilities of two analogous membranes mentioned in the literature were calculated, and their behaviour was shown to be very similar to those of the membranes used in the present study within the same temperature range.