Experimental investigation on a two-stage vapor compression industrial heat pump incorporating liquid separation condensation

Industrial heat pumps are poised to play a critical role in the decarbonization of industrial thermal energy, supporting the broader transition to sustainable energy systems. Owing to their superior energy efficiency, heat pumps offer the potential to expand across various heating applications, thereby accelerating the shift toward low-carbon energy solutions.

This study presents a novel two-stage compression cycle incorporating liquid separation condensation (LSC), designed to substantially minimize thermodynamic losses associated with compression, heat exchange, and throttling processes. The proposed system integrates several advanced features, including two-stage compression, the use of zeotropic refrigerants, liquid separation condensation, and a recuperator. A prototype of the system was developed and experimentally tested. The key findings from the experimental analysis are as follows:

(1) An optimal liquid separation point was identified under the testing conditions. The most effective separation position was located at approximately one-third the length of the condenser tube from the inlet, designated as Point 2. (2) In comparison to a system employing an internal heat exchanger with a recuperator, the LSC system demonstrated a 64 kPa reduction in condensation pressure and a 148 kPa increase in evaporation pressure. (3) When the condenser-side outlet water temperature was raised from 70 °C to 90 °C, the system exhibited performance improvements, with heating capacity increasing by up to 14.3 % and the coefficient of performance (COP) rising by as much as 12.6 %.