Thermodynamical analysis of two-phase water steam ejector in high-temperature heat pumps cycles

Abstract

Industrial processes often require high-temperature heat, yet conventional methods contribute significantly to carbon emissions. High-temperature heat pumps (HTHPs) using natural refrigerants like water present a sustainable alternative, capable of generating process heat up to 200°C. However, achieving these temperatures requires advanced turbomachinery systems. This study investigates the innovative application of two-phase water ejectors in HTHPs, particularly their role as first stage of compression, creating a subatmospheric pressure at the ejector inlet. This approach can enhance the cycle coefficient of performance (COP) across various Rankine cycle-based HTHPs, including single and two-stage cycles. By employing thermodynamic heat pump models and a 1D ejector model, the paper benchmarks cycle performance against a German Aerospace Centre (DLR) reference case, specifically targeting steam compression up to 200°C. Findings indicate that water ejectors can simplify HTHP systems while maintaining high efficiency. This novel use of ejectors marks an advancement in sustainable high-temperature industrial heating solutions.