An Improved Hot Wire Cell for Accurate Measurements of Thermal Conductivities of Gases over a Wide Temperature Range Results with Air between 87° and 375°K

An improved hot wire cell of the potential lead type is described, and theoretical treatments given for radiation, end conduction, potential lead conduction, and the ``temperature jump'' effect. The latter is found to be satisfactorily eliminated by linear extrapolation of reciprocal plots of ``apparent conductivities'' as a function of pressure. Convection effects are absent at pressures below about 20 cm of mercury. The emissivity from bright platinum was measured. The results confirm the measurements by Milverton. The thermal conductivity of air was measured at seventeen temperatures between 87° and 375°K. Our results, which are believed accurate to within ±0.5 percent, are generally lower than other results which have been reported in recent years, for air. Tabulation of our results is given, together with a critical analysis of possible sources of error. The advantage of our method over either the ``thick wire'' or ``compensating lead'' type of cells is pointed out.