Application of a Similarity Criteria approach for centrifugal compressor design in high temperature heat pumps with overheated water vapor.

Authors

Clément Moller - German Aerospace Center, Institute for Low-Carbon Industrial Processes
Bojan Kajasa - German Aerospace Center, Institute for Low-Carbon Industrial Processes
Maximilian Kriese - German Aerospace Center, Institute for Low-Carbon Industrial Processes
Robert Schaffrath - German Aerospace Center, Institute for Low-Carbon Industrial Processes
Martino Köhler - German Aerospace Center, Institute for Low-Carbon Industrial Processes
Eberhard Nicke - German Aerospace Center, Institute for Low-Carbon Industrial Processes

Abstract

One way of decarbonizing industrial processes is to provide process heat using a high-temperature heat pump (HTHP) based on the Rankine cycle. In the here presented project centrifugal compressors will be used to meet the power requirement of industry processes. The performance of the HTHP correlates directly with the efficiency of the compressor. The aim of this work is the application of similarity criteria between two working fluids used for centrifugal compressor. This approach allows the utilization of Compressor Maps for different working fluids. The investigation of this similarity criteria approach will be performed by CFD calculations based on a 3D-RANS solver. Based on proven similarity criteria a developed script recalculates the performance data from air to the water vapor condition assuming in this moment constant gas parameters (ideal gas assumption). This script not only helps to make the work efficient, but is also helps to use the compressor design know-how form aviation engines and other applications using air. An automated aero-mechanical optimization was performed to maximize the impeller efficiency and pressure ratio. To decrease the computational costs, restrictions and modifications of the impeller are considered before the optimization, like tip clearance height, flow path outline and blade thickness. The second aim of this work is to setup this optimization process chain, which include the performance parameter calculation, the generation of the impeller geometry, the meshing for the CFD and CSM simulations including pre- and post-processing. Regarding the validation of the similarity criteria, the numerical results show that the performance parameters, like efficiency and pressure ratio, match very precisely between reference gas and recalculated gas. In fact, the comparison show a difference between air and water vapor of 2% for the pressure ratio and 1%-points for the efficiency. Concerning the second aim of this work, the proposed optimization process leads to a significant increase of the impeller efficiency, where at the same time the pressure ration increases from 2.5 to 3.0. The improve of design process chain has shown that the usage of similarity criteria, with the CFD calculation can establish an optimized geometry in perspective for an integration of the centrifugal compressor into a high temperature heat pump with different working fluids.