DESIGN OF A CENTRIFUGAL COMPRESSOR FAMILY FOR HIGH TEMPERATURE HEAT PUMP APPLICATIONS USING WATER (R-718) AS REFRIGERANT

Development of high-temperature heat pumps to provide heat between 100 degrees C and 200 degrees C is considered a promising avenue for the decarbonization of industry, with water identified as one of the most promising refrigerant due to high performance, safety, and environmental compatibility. In this work a family of high-speed compressors for water vapor was developed, with the aim of providing a modular system covering the temperature range between 60 degrees C and 180 degrees C using five independent stages, each driven by a high-speed electric motor. An elevated degree of part commonality was reached by constraining the design, using the same high speed electric motor, impeller diameter, and impeller back face shape for all the stages. This resulted in a range of flow coefficients between 0.010 and 0.187 at peripheral speeds up to 583 m/s. In addition to traditional configurations employing a vaneless diffuser and volute, for the lowest flow coefficient stage a "diffuserless" configuration was tested. After a preliminary design with mean line tools, an iterative design was performed using finite element modeling to evaluate the mechanical design, ensuring target stress, deformation, and first resonance mode frequency. The acceptable designs were then iteratively evaluated with computational fluid dynamics simulations, with the aim to maximize isentropic efficiency. Despite the constraints due to part commonality requirements and high peripheral speed, isentropic efficiencies up to 80 % and in line with common practice are achieved for all but the highest flow coefficient stage. The diffuserless configuration shows a promising 3.6 % pt. increase in isentropic efficiency when compared to the traditional design with vaneless diffuser.