Centrifugal compressor surge in closed loop systems: modeling and comparison with experiments

Electrically driven heat pumps are expected to have a growing market for efficient and sustainable thermal supply in compliance with global decarbonization goals and renewable power penetration. Vapor compression heat pumps feature compact size, straightforward scaling-up, affordable costs, and good performance in terms of efficiency and low acoustic emissions. Large industrial applications usually implement dynamic compressors in particular, in either single or multi-stage configuration, requiring detailed on-design and off-design analysis, including reliable prediction of fluid dynamic instabilities such as surge & stall. This work presents a quasi-1D lumped-volume model focused on the post-stall (surge) dynamics of a radial compressor operating in a heat pump loop employing low-pressure refrigerant, validated through a dedicated experimental campaign, encompassing two different geometrical layouts of the test rig. The quasi 1-D model approach, represents an evolution of a preliminary 0-D simplified model, showing improved accuracy and retaining a physics-based formulation of the fundamental equations. Simulation and experimental results are compared in terms of surge frequency (0.6–1.2 Hz) and amplitude of compressor exit pressure fluctuations at different compressor speeds and with two test rig geometrical configurations, supporting its general validity. The expansion valve is not modeled and the heat exchanger liquid levels are held constant within the simulated surge cycles, consistently with the separation between the surge time scale (∼1 s) and the liquid level dynamics (tens of surge cycles). Finally, comparison with high-frequency experimental pressure data shows that the detailed model, despite its quasi 1-D representation of the physical rig, is also capable of predicting intermediate frequency (∼ 10 Hz) low-energy oscillations, consistent with the intermediate-frequency content found in the measured pressure spectra; their possible role as surge precursors remains to be verified experimentally.