``End effects'' in thermogravitational thermal diffusion. Thermal diffusion factors for the carbon tetrachloride-cyclohexane system

Thermogravitational thermal diffusion separations are studied for carbon tetrachloride-cyclohexane mixtures as a function of temperature difference using an apparatus without reservoirs. There is a very small negative temperature difference dependence of 0.25% per °C which is in excellent agreement with Horne and Bearman's phenomenological theory of thermogravitational thermal diffusion [J. Chem. Phys. 46, 4128 (1967); 49, 2457 (1968)]. This is in contrast to the large positive temperature difference dependence of 1% per °C observed for an apparatus with reservoirs. These contrasting results substantiate the earlier conjecture of Beyerlein and Bearman that temperature difference effects are the result of ``end effects.'' Thermal diffusion factors, α1, at 25°C calculated as a function of carbon tetrachloride mole fraction using the experimental separations and Horne and Bearman's theory are α1 = − 1.837 + 0.181 X1 with a standard error of 1.7%. This is within 1% of Anderson and Horne's pure method results [J. Chem. Phys. 55, 2831 (1971)]. Agreement with other independent work ranges from 1% to 5%. It is concluded Horne and Bearman's theory provides an accurate description of thermogravitational thermal diffusion.