Constructal Design of Vortex Tubes

Abstract

The vortex tube (also known as Ranque-Hilsch vortex tube) is a mechanical device which splits a compressed high-pressure gas stream into cold and hot lower pressure streams without any chemical reactions or external energy supply [1–3]. Such a separation of the flow into regions of low and high total temperature is referred to as the temperature (or energy) separation effect. The device consists of a simple circular tube, one or more tangential nozzles, and a throttle valve. Figure 15.1 depicts schematically two types of vortex tubes: Counter flow (Fig. 15.1a) and parallel flow (Fig. 15.1b). The operational principle of a counter flow vortex tube, which is the scope of the present work, Fig. 15.1a, consists of a high-pressure gas that enters the vortex tube and passes through the nozzle(s). The gas expands through the nozzle and achieves a high angular velocity, causing a vortex-type flow in the tube. There are two exits: the hot exit that is placed near the outer radius of the tube at the end away from the nozzle and the cold exit that is placed at the center of the tube at the same end as the nozzle. By adjusting a throttle valve (cone valve) downstream of the hot exit it is possible to vary the fraction of the incoming flow that leaves through the cold exit, referred as cold fraction. This adjustment affects the amount of cold and hot energy that leaves the vortex tube in the device exits.