Measurement of the thermal conductivity of gases and - liquids

摘要

Measurement of the thermal conductivity of gases and liquids.. Is independent of the ambient temperature and of the speed of flow of the gases or liquids. A wire is stretched in a chamber, through which the fluids flow, and is heated by electric current pulses applied to the ends of the wire; during each interval between two current pulses, during which the wire is not heated, the cooling of the wire, produced by the surrounding thermal conductors, is measured and recorded. The wire is fed with square-wave voltage pulsed by the intermediary of a pair of rectifiers of staggered polarity which are mounted in series with resistances determining two different current densities. A constant resistance is mounted in series with the wire to eliminate residual temperature errors. The measurement is made without waiting for the wire to attain its equillibrium temperature but the process is operated with frequencies of up to several hundred Hz. A commutator is included which is controlled by the frequency of the repitition of the current pulses through the wire, so as to be closed during each measuring period and open during each heating period.