Experimental investigation of energy (temperature) separation of a high-velocity air flow in a cylindrical channel with a permeable wall

Abstract

Energy (temperature) separation is the redistribution of the total enthalpy (stagnation temperature) in a gas flow without external work and heat exchange with the ambient medium. Some simple devices for obtaining “hot” and cold” flows of compressed gas can be developed on the basis of the temperature separation effect. The best known of these devices is, apparently, the Ranque-Hilsch vortex tube. In this study, a new method of the temperature separation of gas flows is described and the first systematic experimental data are obtained. The method is based on the well-known effect of energy (temperature) separation in the boundary layer of a compressible gas flow. The “cold” regions layers are separated from the “hot” ones in a device consisting of a nozzle and a cylindrical tube with a permeable wall. When compressed air flows out into the atmosphere through this device, a part of the flow seeps through the permeable wall due to a steady pressure gradient. Its stagnation temperature turns out to be smaller than the initial temperature, whereas the stagnation temperature of the other part of the flow is greater than the initial temperature. In the pressure and temperature ranges considered the cooling effect is by a factor of about five greater than that of Joule—Thomson. The initial pressure of the compressed air varied in the range from 1.2 to 8.0 bar, while the initial temperature was 295.6 K. Both convergent and convergent-divergent (supersonic) nozzles were used. The temperature separation increases with increase in the initial pressure up to a certain value but it remains almost constant after this value has been attained. The greatest temperature difference between the “hot” and “cold” flows is about 11 K.