Molecular Relaxation Times from Thermal Transpiration Measurements

Abstract

It is suggested that measurements of the maximum pressure difference across a capillary due to thermal transpiration can be used for the determination of the molecular relaxation time of the gas (usually rotational relaxation). This pressure difference is related to the translational thermal conductivity of the gas, which in turn is affected by the relaxation times. Available experimental data on thermal transpiration are analyzed in this way, and the results compared with other determinations of relaxation times. The results, although scanty, indicate that the method has promise. The greatest asset of the method is its extreme experimental simplicity; the greatest liability is that two approximate theories intervene between the experimental measurements and the calculated relaxation times.