International Journal of Thermofluids (Nov 2024)
Thermodynamic analysis of a solar powered ejector cooling system
Abstract
A steady-state model of an ejector cooling system activated by solar heat is presented and applied in response to the increasing demand of cooling in hot-climatic regions. The system comprises three loops connected by heat exchangers. The first loop, or collection sub-system, includes the solar collectors (both cylindrical-parabolic and flat plate collectors are modeled) and the heat transfer fluid (a thermal oil). The second loop also includes an ejector which uses polytropic efficiencies and provides the power necessary to circulate a second low-pressure stream of the refrigerant through the evaporator and an intermediate-pressure condenser. The third loop connects the load to the evaporator using ethylene glycol. In this study, the model is particularly based on the laws of classical and finite size thermodynamics and incorporates experimentally derived relations for the efficiency of the cylindrical-parabolic collectors as well as an ejector model which is based on physical laws rather than on refrigerant specific correlations used in previous studies. The results include a parametric study analysing the effect of the generator superheating and the calorific flow of the heat transfer fluid on the ejector dimensions and the overall system performance. The impact of the solar collector type on the collector surface and the system performance by a fixed incident radiation was investigated. The results illustrate that using parabolic trough collectors, the exergy efficiency of the entire system and the required collector's area are almost constant with the solar radiation intensity. They are approximately 35 % and 35 m2 respectively. It was also shown that further superheating the refrigerant by an additional 10 °C at the generator exit reduces the ejector's total length by 8.1 %, leading to positive economic impacts on raw material acquisition for the solar-powered ejector refrigeration system. Furthermore, doubling the calorific flow reduced the COP by half and increased the ejector length. The economic analysis of the system reveals two key findings: The largest portion of the initial costs is attributed to the solar collector, which is essential for providing the thermal energy required for the system's operation. The main hourly expense of the system is the electricity cost associated with powering the pumps.
