Characterization of the fluid flow phenomena in an ejector for a high temperature heat pump

Decarbonization of industrial processes is one important step towards a sustainable future. The usage of high-temperature heat pumps to provide heat for industrial processes is a promising way towards that goal. Heat pumps used for such high temperature applications have a large difference between condenser and evaporator pressure and therefore the losses due to irreversible dissipation within the expansion process are high. To make high-temperature heat pumps more efficient and therefore interesting for industrial applications, the ejector, which is an alternative expansion device to replace the conventional throttle valve, is investigated. The flow inside an ejector of a high temperature heat pump is simulated numerically to gain better understanding of the underlying fluid flow phenomena, its applicability to heat pump cycles and to give an outlook on possible cycle efficiency improvements. To reduce the computational demand of simulating the two-phase flow inside the ejector and to avoid the need for experimental-based fine-tuning as opposed to a full multiphase model, the Homogeneous Equilibrium Model (HEM), which assumes thermal and mechanical equilibrium between both phases, is applied. This model was implemented into the commercial Computational Fluid Dynamics (CFD) software Ansys Fluent. The main flow features are analyzed, and phenomena occurring at unfavorable operating points, obtained through an unsuitable geometry, are identified.