Thermal Transpiration in a Dissociating Gas

Abstract

By use of the dusty‐gas model, an analysis is given of the gradient of pressure set up in the steady state in a dissociating gas in local chemical equilibrium in a gradient of temperature in a porous medium (or in a capillary tube). For a dissociating gas, though not for an isomerising gas, the gradient of pressure thereby induced can be appreciably greater than for a non‐reacting gas (though the enhancement is less marked than the corresponding enhancement of the thermal conductivity). The enhancement remains appreciable even for a gas in which there is only a small proportion of the associated species; and for a porous medium with very small pores the steady state could in consequence be one with (p−1 δp/δz)/(T−1 δT/δz) detectably greater than the conventional 0.5000. It is shown in passing that a result previously established for a dusty gas at uniform temperature, that the Stefan‐Maxwell equations for diffusion can be compounded with relevant equations for viscous contributions to the resultant fluxes, to give a set of equations of the unaugmented Stefan‐Maxwell form but with modified values for coefficients appearing in them, also holds for a dusty gas in a gradient of temperature.