Energy separation in a channel with permeable wall

Abstract

The present paper is an experimental and numerical analysis of a new method of energy separation. By energy separation, we mean the spontaneous separation of the gas flow into two flows with stagnation temperatures above and below the initial (“hot” and “cold”). One of the most famous devices using the phenomenon of energy separation is the Rank-Hilsch vortex tube. The considered method is based on the well-known effect of the stagnation temperature profile curvature over the boundary layer thickness, which occurs when a high-speed gas flows around an adiabatic surface. It is known that the higher the flow velocity and the more the Prandtl number differs from unity, the higher the energy separation within the boundary layer. In a channel with a permeable wall, part of the high-speed flow can be sucked out through the wall due to the natural pressure drop. As a result, the flow's stagnation temperatures at the outlet of the channel and the flow sucked out through the wall are different: one is hotter, the other is colder compared to the initial stagnation temperature. Based on the obtained experimental data, validation of one- and two-dimensional mathematical models was carried out. The influences of the initial Mach number, the initial stagnation pressure, the relative channel length, and the Prandtl number on the energy separation were investigated. It was found that as the initial Mach number changes from Mis = 1 to Mis = 3, the air flow's cooling increases from −5 to −15 K. When the Prandtl number changes from Pr = 0.7 to Pr = 0.2, the flow's cooling is increased by factor of 2.25 from −20 to −45 K. It is shown that at a certain ratio of parameters, the heating and the cooling of flows pass through an extremum.The obtained temperature difference due to the suction of a part of the flow can find application in the analysis of flows with variable mass flow rates in power systems, such as heat pipes, boundary layer control devices, etc.