Development and Experimental Assessment of Oil Free Combine Absorption-Compression Heat Pump for High Temperature Applications

Abstract

This experimental study evaluates the performance of a combined absorption-compression heat pump system utilizing an oil-free standard twin screw compressor under various operational conditions. The primary objective is to assess the system's performance characteristics using standard components and natural working fluid ammonia-water mixture in the system. Specific performance parameters, such as heat sink and source loads, temperature glides, and overall heat transfer coefficients in absorbers, are thoroughly evaluated during the experimental operation. Experiments were conducted at a constant 60°C inlet temperature for the heat sink and heat source, with heat loads reaching 60 kW on the sink side and 30 kW on the source side was achieved during the preliminary results. The effects of increasing ammonia concentration from 0.44 to 0.56 and pressure from 13 to 15.5 bar on heat loads were analyzed, revealing that higher concentrations and pressures increases the thermal load in heat sink and source sink.  Increasing the pressure ratio from 2.2 to 3.5 increases temperature lift from 15 to 35 K . Additionally, altering the mass flow rate of the strong solution significantly influence thermal load on the secondary sides, while increasing the weak solution injection mass rate from 0.0 kg/s to 0.03 kg/s reduces the compressor discharge temperature from 140 °C to 126 °C. The results identify differences in the overall heat transfer coefficients and heat flux between absorber 1 and absorber 2. The system's performance and behavior are comprehensively evaluated, laying the groundwork for future improvements and the advancement of absorption-compression heat pump oil free technology. Future research will focus on refining system components and operational parameters to further enhance efficiency and performance, aiming to establish this technology as a competitive and sustainable option for clean heat in different industrial applications.

Keywords: High temperature heat pump, Absorption-compression, Oil free twin-screw compressor, Ammonia-water mixture, Osenbrück cycle