Session: 37-05 Radial Turbomachinery Design

Paper Number: 123835

123835 - Design of a Centrifugal Compressor Family for High Temperature Heat Pump Applications Using Water (R-718) As Refrigerant 

A considerable share of the world’s energy consumption and greenhouse gas emissions are related to industrial heat production at temperatures below 200°C. High-temperature heat pumps can effectively be used to decarbonize this sector, however for a widespread adoption, reduction in both capital and running costs are required.

Water (R-718) has drawn attention as a refrigerant due to its low cost, low environmental impact, and potential for high coefficients of performance. In addition, steam is often either an available heat source or the required product, making open or semi-open cycles an attractive choice. However, a disadvantage of using water compared to other refrigerants is that its saturation pressure and density are low in the temperature range of interest, which leads to large flow rates.

Centrifugal compressors are considered an ideal match for water based high-temperature heat pump, due to the compactness and high efficiency at high volume flow rates. The elevated speed of sound presents a challenge in the design of centrifugal compressors for such applications, with stress considerations limiting the maximum compression ratio that can be achieved in a single stage.

This paper presents the aerodynamic and mechanical design of a cohesive centrifugal compressor family specifically tailored for such applications using mean line and 3D numerical tools. The compressor family comprises five distinct units, each with a single unshrouded impeller, catering to a pressure range of 0.02 MPa to 1 MPa, corresponding to saturation temperatures from 60 °C to 180 °C. ANSYS CFX was used to simulate the aerodynamic performance of each stage including rotor, either a vaneless or vaned diffusers, volute, and secondary flow path on the back face of the rotor. ANSYS Mechanical was used to verify both the static stress and first natural frequency in the rotor.

In order to optimize production and maintenance costs, all units of this compressor family utilize the same model of directly coupled high-speed electric motor and have the same rotor diameter, allowing extensive part commonality among the stages. This results in flow coefficients ranging from 0.01 to 0.185 at a peripheral speed of 580 m/s.

For the lowest flow coefficient stage, the mean-line model suggests that the most efficient configuration should include a very short vaneless diffuser section, with a flow angle close to tangential, allowing increased blade height and reduced clearance losses, at the expense of higher losses in the volute. This “diffuserless” configuration presents the possibility of increased efficiency under some circumstances compared with the conventional configuration. Moreover, the numerical results from the developed models indicate promising efficiency levels and operational stability across the pressure spectrum.  

Presenting Author: Simone Parisi Technical University of Denmark

Presenting Author Biography: Simone Parisi is currently pursuing his Ph.D. at the Technical University of Denmark. He holds a bachelor’s degree in aerospace engineering and a master’s degree in mechanical engineering, both from Politecnico di Milano. His research is centered around the design and analysis of radial flow turbomachinery, including reversible turbomachinery, with applications in energy storage, power cycles, and heat pumps.

Authors:

Simone Parisi Technical University of Denmark
Mogens Weel Weel & Sandvig Energi og Procesinnovation ApS
Fredrik Haglind Technical University of Denmark
Brian Elmegaard Technical University of Denmark