Thermo-osmosis of gases and gaseous mixtures

Number of experimental smdies on thermo-osmosis of gases have been reported in literature [32], The steady-state relation is found to be satisfied in all cases studied within a limited range of non-equilibrium. A typical experimental set-up used for studying thermo-osmosis is shown in Fig. 3.9 [33]. 

For isothermal permeability measurements, differential manometer Mj was replaced by an ordinary manometer, which was in communication with both the compartments A and B. After evacuation, the gas was introduced into one compartment. This created a difference of pressure on the two sides of the membrane, which decreased with time. 

AP was noted at different time intervals. The decay of pressure as a function of time is shown in Fig. 3.11. If h is the distance traversed at time t and A is the cross-sectional area of the membrane, the rate of flow J, is given by 7 = A(d/i/dr) 

The isothermal permeability of a gas may be estimated by plotting J against AP. A typical plot is shown in Fig. 3.12 for COj from which isothermal permeability of CO2 was found to be 7.4 x 10 cm (aims) at 33°C. 

Typical thermo-osmotic pressure data for COj using unglazed porcelain membrane at various AT/T1T2 are presented in Fig. 3.13. The result are in conformity with the steady-state relation. This also implies that heat of transport Q is independent of mean temperature within the range of investigation. Heat of transport was also found to be independent of difference of temperature up to AT = 130°C. It shows that, so far as thermo-osmosis of gases is concerned, thermodynamic predictions have a wide range of validity. 

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