Investigation of Motive Flow Expansion Inside Steam Ejectors with Fixed Compression Ratio and Expansion Ratio

Abstract

The flow behavior of motive flow plays a pivotal role in steam ejectors, yet research on its various expansion states with fixed compression ratio and expansion ratio is limited. In this paper, a novel method is proposed to obtain different expansion states, and it has been found that the proposed method can obtain different expansion states more accurately and conveniently than other methods. An investigation of the flow structure and performance of the steam ejector with fixed compression ratio and expansion ratio is conducted under different expansion states. The results illustrate that there is better entrainment performance for a steam ejector in the under-expanded state. Furthermore, the expansion wave at the nozzle exit position helps to strengthen the motive flow expansion, which will prevent the choking process of the entrained flow, thereby leading to an increase in the mass flow rate of the entrained flow (or entrainment ratio). Further, thermodynamic analysis discloses that the flow structure transitions from a strongly under-expanded flow to a strongly over-expanded flow, resulting in an increase in exergy destruction while weakening the steam ejector's entrainment performance.