Abstract
Absorption Refrigeration Systems (ARS) are potential alternatives to direct expansion (DX) refrigeration systems. This review focused on the incorporation of an ejector into absorption refrigeration cycles to constitute Hybrid Ejector-Absorption Refrigeration Systems (HEARS). The ejector adds several advantages to the absorption refrigeration systems depending on its location in the cycle. The two prevalent configurations of HEARS are Triple pressure level (TPL-HEARS), and Low Pressure Condenser (LPC-HEARS). Previous studies revealed the preference of the latter configuration as it allows lower circulation ratios, enhances the refrigeration effect, and could achieve a COP up to 1. Moreover, LPC configuration is suitable with single, double, and variable-effect absorption systems with a COP of above unity. In turn, the TPL-HEARS notably enhances the absorption process, particularly when a variable geometry ejector is utilized. This configuration could obtain a COP around 1.1, but only with high-density refrigerant vapor. Lately, to attain the advantages of both configurations, some studies investigated the viability of adding two ejectors to the cycle. This paper meticulously reviews investigations conducted on the emerging dual ejectors-absorption refrigeration technology. This paper reveals the general performance trend and the maximum attainable COP by each type of hybrid ejector-absorption refrigeration system. DEARS and Ejector-driven absorption refrigeration systems (ED-ARS) could achieve COP that ranges between 1.2 and 1.46. The use of a flash tank and a RHE is essential in NH3/H2O HEARS. At high generator temperatures (of 120–170 °C), DEARS was found to be the system with less complexity and best performance. Nevertheless, the performance of the DEARS might drop significantly if the heat source temperature is fluctuating. Thence, the variable-effect HEARS is considered the best alternative. The capability of HEARS to be integrated with different power generation cycles is also highlighted. Finally, the review presents possible future research opportunities to improve the absorption refrigeration technology.
Highlights
The results revealed a considerable improvement in the COPs over the single ejector cycle with flash tank
The incorporation of an ejector into the absorption refrigeration cycle constitutes a hybrid ejector absorption system (HEARS) that operates at three pressure levels instead of two levels of the basic absorption refrigeration cycle
This characteristic improved one or two of the main heat and mass transfer processes in the cycle depending on where the ejector was located
Summary
Global warming and climate change are leading a global trend for the utilization of low-grade heat and renewable energies. To a certain degree, harmful to the environment Either they have a slight ozone depletion potential (ODP) or global warming potential (GWP). Absorption chillers predominantly use ammonia or water as working refrigerants, and both are classified as environmentally friendly refrigerants with ODP and GWP equal to zero. Thence, thermally driven refrigeration systems have two distinctive features over the DX systems: the use of environmentally friendly refrigerants and the ability to utilize low-grade heat sources to drive the system [2]. Those two features make the thermally driven systems more attractive from an environmental perspective [3]
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