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Showing 2 results for Second Law Efficiency
Damoon Aghazadeh Dokandari, Seyyed Mohammad Seyyed Mahmoudi, Alireza Setayesh Hagh,
Volume 14, Issue 7 (10-2014)
Abstract
Throttling process through expansion valves causes a considerable amount of exergy loss so that reducing this loss improves the performance of compressed refrigeration cycle considerably. In the present work, the effect of using an ejector on the performance of a cascade refrigeration cycle is evaluated. It is concluded that the using ejector and selecting R134a as the high temperature circuit refrigerant cause the COP and second law efficiency to increase by approximately 6.5 percent as compared to the conventional cascade cycle with the same cooling capacity. In addition, several refrigerants including R717, R290, R134a, and R123 are examined to reveal the effect of refrigerant type in the high temperature circuit on the cycle performance. It is also found that, at a temperature of more than 255.4 K, for the evaporator of high temperature circuit, the refrigerant combination of R744-R123 results in a better performance as compared to the other combinations. Finally, the cycle performance is optimized with respect to the temperatures of low temperature evaporator, high temperature evaporator, and the ambient from the view points of both the first and second laws of thermodynamics. It is concluded that the COP and the second law efficiency are the highest when R123 is used as the refrigerant at the high temperature circuit.
A. Gharehghani,
Volume 20, Issue 8 (8-2020)
Abstract
Reducing fossil fuel sources together with tighter environmental laws to control the engine exhaust emissions makes the use of cleaner and renewable fuels inevitable. Therefore, the use of biodiesel fuel as a strategy to conserve energy and reduce emissions is becoming increasingly important in engines. On the other hand, biodiesel fuels increase NOx emissions in the engines, which necessitate the use of water additives to reduce the combustion temperature. To compensate for the negative effect of water addition by reducing combustion quality and thus reducing thermal and exergy efficiency, the use of metal-based nano-particles additive can be a reliable solution. In this study, the effect of adding different concentrations of nano-particles on improving efficiency of the first and second laws as well as fuel consumption of a single-cylinder engine with different fuel combinations with BXWYNZ formula (diesel fuel with X% biodiesel mass, Y% water mass%, and Zppm nano-particles), has been studied experimentally. The results of this study show that adding 60ppm nano-particles to B0W5 will improve about 3% efficiency in the first law and 2.5% efficiency in the second law compared to pure diesel fuel. These values were about 4 and 3.8% for 90ppm nano-particles, and 5 and 4.7% for 120ppm nano-particles, respectively. In addition, based on the experimental results, the B15W5N120 has 7.5% higher first-law efficiency and 7% higher second-law efficiency than pure diesel fuel.
