A new variable mixing chamber ejector: CFD assessment

Abstract

• A new variable mixing chamber ejector is proposed for waste-heat driven chillers. • The mixing chamber cross-sectional area can be increased or reduced. • The cooling capacity increased by up to 120%. • The backflow condensing temperature increased by almost 8 °C. Research on the reduction of refrigeration systems energy consumption is a topic in which popularity benefits from the contextual growth of the refrigeration market. Solar or waste heat-driven ejector refrigeration systems are very promising in this context. However, the lack of operational flexibility of ejectors penalizes the performance of such systems. Since the mixing chamber has a fixed cross-section, for condensation temperatures above critical, the cooling capacity vanishes and, for temperatures lower than critical, the cooling capacity stagnates. The paper proposes a new variable mixing chamber solution that overcomes these limitations. It is a range extender that allows ejectors to operate at high cooling capacity all over the operation range of the system. This range extender is based on the concept of lateral cylindrical moving slots. The paper compares the new ejector to a reference ejector from the literature. First, the Computational Fluid Mechanics (CFD) model viability is evaluated thanks to the experimental measurements on the reference ejector. Then, the new system’s performance is evaluated. The results show that the adaptation of the mixing chamber section to the condensation temperature allows increasing the cooling capacity without supplementary motive energy. That leads to an increase of up to 120% of the cooling capacity at low condensation temperatures and a shifting of 8 °C of the critical temperature. Such extension of the operational range was never obtained before. That means that an ejector stalling at 33 °C could operate at 41 °C using the proposed range extender.