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Waste heat recovery plays an important role in energy resource management. Low grade waste heat could be recovered by Organic Rankine Cycle (ORC). This is the same as the Rankine cycle and an organic fluid is used as working fluid. In this work the effects of using two-component mixtures with different temperature glides during phase change, on performance of Organic Rankine Cycle are studied. Four two-component mixtures are selected: n-pentane/n-butane, isopentane/isobutene, n-pentane/isobutene and isopentane/n-butane. In this study for more reasonable comparison of thermal recovery the inlet and outlet temperatures of heat source heat carrier fluid and its mass flow rate are considered to be constant. Results show that in the use of two-component mixtures in comparison with pure fluids, approximately 9% increase in energetic and exergetic efficiencies for simple configuration and 14% in configuration with the internal heat exchanger can be achieved with respect to the temperature glide match in the condenser and evaporator.

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In this paper, the effect of expander and the internal heat exchanger is investigated in transcritical carbon dioxide direct-expansion geothermal heat pump. In this regard, a comparison is performed between four cycles. The four cycles are: (1) the cycle with expansion valve, (2) the cycle with expander, (3) the cycle with expansion valve and internal heat exchanger, (4) the cycle with expander and internal heat exchanger. The present numerical model has been investigated performance analysis of the four cycles under study in different operating conditions in two district cases. The first study includes a specific heating load, and the second study is a constant evaporator loop length (ELL). Then model evaluates characteristics including coefficient of performance (COP), evaporator loop length and heating capacity of the four cycles under study. To examine the performance of the four cycles, a parametric study is performed to investigate the effect of different parameters such as difference between soil temperature and evaporator outlet temperature, water inlet temperature, water mass flow rate, gas cooler length. The results indicate that COP associated with the expander cycle is always higher than the values related to the expansion valve cycle. The use of internal heat exchanger in a cycle including an expansion valve always leads to a slight increase in COP. An internal heat exchanger has negligible effect on COP in the cycle with an expander but reduces the evaporator loop length.