Precise measurement of the thermal conductivity of gases by transient hot-wire method

A high-precision instrument to measure the thermal conductivity of gases up to 800 C and 400 atm in an absolute way is described. The instrument works on the hotwire principle with a five micron platinum wire, and operates in the transient regime thus eliminating completely the effects of natural convection. The design parameters combined with an end-effects compensator ensure that the instrument performs almost exactly like a line source in an infinite fluid, thus permitting us to calculate the thermal conductivity from the slope of a Delta T log t diagram on which 36-42 conjugate pairs of these quantities have been determined with great precision. Measurements on the noble gases He, Ne, Ar, Kr and Xe combined with our best measurements of viscosity, all extrapolated to rho = 0, yield Eucken factors at 300 K which do not differ from the theoretical value by more than 0.4%.