Theoretical and experimental behaviour of a thermal conductivity detecter for the determination of the ortho/para hydrogen composition of gas mixtures in the temperature-jump region

The theoretical characteristics of a thermistor type thermal conductivity detector were determined for gases in the range 1 to 30 Torr, and were tested experimentally for mixtures of ortho- and para-hydrogen in pure hydrogen and in dilute mixtures of hydrogen in helium. It was found that the detector could be treated as being spherically symmetric. For temperature-jumps of up to 100 K, the total heat transfer could be adequately explained by a simplified form of the Kennard temperature-jump theory, only two parameters being required, the radius of the thermistor and its accommodation coefficient. The differential behaviour, the sensitivity to changes in ortho/para composition, required an additional parameter, the apparent gas phase relaxation rate for rotational energy.