HEAT CONDUCTION IN AN ANNULAR GAP FILLED WITH A RAREFIED GAS

In this paper a first experimental attempt is described in which heat conduction through rarefied air contained between two concentric cylinders is analysed. The heat transfer between a heated platinum wire having a diameter (d) of 0.15 mm, disposed along the axis of a cylindrical shell in stainless steel having an inner diameter (D) of 100 mm, and a surrounded rarefied gas has been studied experimentally. The ratio between the outer and inner diameter of the annular region filled by the gas is large (D/d=667). In the annular region filled with air the pressure was varied by using a vacuum pump from atmospheric value down to 10-3 mbar. Temperature differences between the wire and the external stainless steel wall in the range 50-125 K were imposed and the heat power transferred from the wire to the surround was measured as a function of the gas pressure starting from air at atmospheric conditions down to 10-3 mbar. The experimental results were compared with the numerical results obtained using a linear Shakhov kinetic model. A good agreement between the numerical results and the experimental results were observed for DT=50 and 75 K; on the contrary, for DT>75 K the experimental heat flux was larger than the numerical values. The results suggest the need of an improved accuracy in the experimental tests.