Experimental Results of a Novel Two-Phase Water Ejector Design for High-Temperature Heat Pump Applications

Abstract

High-temperature heat pumps (HTHPs) are a key technology for decarbonizing industrial process heat. Within such systems, two-phase water ejectors offer a promising opportunity to function as secondary steam compressors. By entraining hot steam with high-pressure water, they enable simultaneous cooling and pressure increase, thereby reducing both the power consumption and the number of mechanical compressor stages required. This integration has the potential to significantly enhance the energy efficiency and economic viability of HTHPs. However, the internal flow dynamics of two-phase ejectors remain insufficiently understood, particularly under the demanding high-pressure and high-temperature operating conditions relevant for heat pump applications. In the mixing region of the ejector, where the twophase flow approaches critical design conditions, the speed of sound is strongly affected, potentially giving rise to shock structures and strong variations in thermophysical properties. The lack of experimental insights into these phenomena limits the reliable design and optimization of ejectors for industrial applications. This paper investigates how two-phase water ejectors can be experimentally characterized to advance their efficient integration into HTHP systems. To address this, a novel closedloop experimental facility has been developed, enabling continuous operation with a flexible operating range of water and steam conditions representative of different potential heat pump architectures. The facility integrates novel designs for the nozzle and mixing chamber, a water separation and condensation system, and advanced sensors and control strategies to precisely regulate inlet and outlet conditions. The ejector has been designed based on prior CFD simulations by the authors, allowing comparison of numerical and experimental results. Preliminary tests provide performance indicators such as pressure ratio and entrainment ratio. This work delivers new ejector components designs, with a custom experimental methodology and initial results that deepen the fundamental understanding of two-phase ejector behavior. It thereby contributes to the optimized application of ejectors as efficient compression components in next-generation high-temperature heat pump systems.