Investigation of heat transfer in rarefied gases over a wide range of Knudsen numbers

Abstract

The paper presents experimental results on heat exchange of fine metallic filaments with a rarefied gas at different pressures. The investigations were carried out using the transient hot-wire technique in the case of small temperature perturbations. The heat fluxes for a number of inert and some polyatomic gases have been measured under different heat transfer conditions ranging from a molecular to a continuum regime. The experimental results showing the dependence of heat fluxes on the gas rarefaction degree have been compared with the theoretical ones obtained from the solution of the BGK model by the variational method. Under the conditions of molecular heat transfer, the dependence of the energy accommodation coefficients on the kind of material and the state of the filament surface, kind of gas and mean temperature of the system is found. The filaments were made of platinum, nickel, tungsten and tantalum. The surface was cleaned by annealing in high vacuum and in a weak hydrogen atmosphere. Control of the surface state was accomplished by the thermal flash method and by checking a change in the surface emissivity. The degree of filament recrystallization in the process of thermal refining was determined by X-ray structural analysis.