An Introduction to the Dynamic Pressure Exchanger

Abstract

The historical background and operational principle of the Dynamic Pressure Exchanger (DPE) are outlined. The basic aerodynamic processes of cell-emptying and cell-filling are analysed by the ‘method of characteristics’ for air and for no temperature discontinuities in the unsteady flow pattern. The results of the analysis are then used to generalize performance qualitatively for overall pressure ratios up to the sonic threshold. It is shown that, for pressure wave effects to be fully utilized, a DPE rotor should run such that 8 is of the order of or less than 0.5, where δ is the ratio of the time taken to open or close a cell to the time taken for a sound wave to travel a cell length at the thermodynamic stagnation state of the primary or secondary fluid. In the case where the thermodynamic properties of the fluids vary considerably, it is suggested that 8 be referred to the gas which yields the highest sonic speed. In general, the extent to which the performance is affected by a change in δ, within the range 0 < δ < 0.5, is inappreciable. It is also shown that the use of a transfer passage may be expected to yield a significant improvement in performance and an increased range in overall pressure ratio. A number of applications are described and some recent developments are reviewed. It is also indicated that the main sources of loss can be incorporated within the method of characteristics used in the prediction of performance.