15 May 2023

Presentation No 459 – Characterization of the fluid flow phenomena in an ejector for a high temperature heat pump – 14th IEA Heat Pump Conference, Chicago, USA

Decarbonization of industrial processes is one important step towards a sustainable future. The usage of hightemperature 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.