A 0D approach fot extended operational modeling of air ejectors in thermal systems

Abstract

Classic ejector models work accurately only in normal operating conditions, i.e. when the primary flow is in supercritical conditions. Moreover, they do not take into account abnormal situations, such as when the primary flow is subsonic or if primary or secondary flows are reversed or null (closed ports). Hence, the development of a robust and accurate ejector model capable of handling abnormal modes and transitions is necessary to build the control system of thermal applications that rely on the multi-mode operation of ejectors, e.g. bleeding system in aircrafts. In this paper, a 0D model is presented, capable of working in multiple normal and abnormal modes. An experimental set-up was built to test real ejectors under different thermal conditions and to provide validation material for the simulation models. In parallel, CFD simulations were performed to provide reference solution for a more extended operational range. The 0D model was compared against experiments first, and then against CFD results, to provide a high range of reference results with variable boundary conditions in terms of pressure and temperature. Special attention is given to the temperature effect on primary and secondary inlet flows, showing the capability of the 0D model to reproduce the characteristic curves obtained from experimental and numerical tests. The validated model was then introduced within a dynamic thermal system which includes control valves and a heat-exchanger, to mimic the behaviour of bleeding systems under variable conditions of the inlet ports, demonstrating its capability of providing an efficient tool for the assessment of the system behaviour.