Abstract Heat pumps are playing a key role in reducing carbon footprint of heating and cooling systems. In large-scale industrial applications, centrifugal compressors are often used under variable conditions and at low mass flow rate, where instabilities may occur. To investigate compressor response in refrigerant closed-loop systems, Carrier supplied the University of Genoa with a small-size chiller test rig, equipped with a vaned diffuser high-speed centrifugal compressor driven by a variable-speed motor, enabling experimental investigation in a wide operating range. This experimental activity investigates surge transients in centrifugal compressors by employing both pressure measurements using high-frequency piezoresistive pressure transducers and dynamic vibro-acoustic response data. Different signal processing techniques in time and frequency domain were applied to investigate system response , and to separate the overall signal into individual components to better identify the rise of anomalous fluid-dynamic conditions. A coherence analysis was also applied where different responses signals were considered, including the function computation between physically non-homogeneous system responses such as inflow pressure and vibrational signals. Additionally, the acquired uniform-time-increment signals were resampled at constant increments of compressor shaft angle to obtain angle-domain sampled data. This allowed to compute synchronously averaged response spectra. Statistical techniques were also utilized for the detection of signals with strong additional noise, where transient and non-deterministic contents may arise as the compressor approaches unstable conditions. The obtained results provide promising diagnostic and predictive paths to detect compressor instabilities in closed-loop heat pump systems.
Silvestri et al. (Thu,) studied this question.
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