Narrow Results

Based on the analyzing of the thermodynamic performance of the heat transfer process in the low temperature heat exchangers, the exergy efficiency of the heat transfer process is defined and a general expression for the exergy efficiency is derived, which can be used to discuss the effect of heat transfer units number and heat capacity ratio of fluids on the exergy efficiency of the low temperature heat exchanger. The variation of the exergy efficiency for several kinds of flow patterns in the low heat exchangers is compared and the calculating method of the optimal values of heat capacity ratio for the maximum exergy efficiency is given.

In this study, three novel modifications of ejector-absorption refrigeration cycles (E-ARC) are investigated to evaluate the effect of ejector location on cycle performances. In the first modification (triple pressure level absorption refrigeration cycle TPL-ARC), the ejector is located at the evaporator inlet. In the second modification (double ejector absorption refrigeration cycle DE-ARC), two ejectors are used; one is located at the evaporator inlet and the other at the absorber inlet, which are coupled to each other. In the third modification (low pressure condenser absorption refrigeration cycle LPC-ARC), the steam ejector is installed at the downstream of the vapor generator discharging line. An additional flow splitter is integrated to the steam ejector outlet and part of the vapor is extracted and returned to the absorber at a pressure equal to the diffuser pressure. Effect of ejector location on thermodynamic performances are evaluated considering three different working fluids, namely ammonia–water solution (NH₃–H₂O), lithium bromide-water solution (H₂O–LiBr), and lithium chloride–water solution (H₂O–LiCl). Even though all three configurations enhance the conventional absorption refrigeration cycle (C-ARC) performances, the LPC-ARCs work at high temperature and improve the cycle performance. The TPL-ARC proves to improve the COP and exergy efficiency up to 9.14% and 7.61%, respectively, presenting the highest thermodynamic performance enhancement and lowest operating temperature.

Water desalination unit powered by renewable energy sources is sometimes needed at places far from the energy grid lines. Consequently, even countries with rich energy resources, such as the Arabian Gulf countries, have shown strong interest in desalination processes that often use renewable energy sources. This work aims to conduct an exergy analysis of solar-powered humidification–dehumidification (HDH) unit. The exergy analysis input data are extracted from a previous work conducted in August 2020 under Baghdad conditions, 33.3^∘N latitude and 44.14^∘E longitude. The previous work’s HDH unit consisted of six parabolic trough solar collectors (PTSCs), with a total aperture area of 8.76m². Meteonorm v7.3 software was used to obtain the weather data for Baghdad City, Iraq. The HDH unit results had revealed low exergy efficiency, where the maximum overall exergy efficiency was 0.305% at 12.00noon, August 17, 2020, when the salty water flow rate was 1 L/min. The unit’s overall exergy efficiencies were 0.09%, 0.16%, 0.31%, and 0.085% when the salty water flow rates were 0.8, 0.9, 1, and 1.2 L/min, respectively. Maximum exergy destructions for the HDH unit components were 0.513, 0.156, 0.332, and 0.304kW for solar radiation, dehumidifier, humidifier, and PTSC, for a salty water flow rate of 1L/min. In contrast, the overall exergy destruction of the HDH unit was 1.3kW.