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This study examines the performance of a novel recompression supercritical CO2 (S-CO2) Brayton cycle of nuclear power plant with pre-cooler exergy utilization, which uses a transcritical CO2 cycle to enhance the performance of this new cycle. More attention was paid to irreversibilities generated in the combined cycle. Individual models were developed for each component through the application of the first and second laws of thermodynamics. The effects of the turbine inlet temperature, compressor pressure ratio, maximum cycle pressure, main compressor inlet temperature, and also environment temperature on the first- and second-law efficiencies and also on the exergy destruction of the S-CO2 and the presented new S-CO2 recompression cycles were studied. Finally, the recompression S-CO2 cycles were thermodynamically optimized using the Engineering Equation Solver software. Based on identical operating conditions, a comparison between the new S-CO2 and a simple S-CO2 cycle was also performed. It was found that both the first- and second-law efficiencies of the new S-CO2 cycle are about 5.5 per cent to 26 per cent higher than that of the simple S-CO2 cycle. The exergy destruction of the new S-CO2 cycle is also about 6.7 per cent to 28.8 per cent lower than that of the simple S-CO2 cycle.

Abstract In the current paper, a new configuration of the ejector-vapour compression refrigeration cycle was presented, which uses an internal heat exchanger and intercooler to enhance the performance of the cycle. The theoretical analysis on the performance characteristics was carried out for this new cycle based on the first and second laws of thermodynamics. The effects of the evaporative and condenser temperatures on the coefficient of performance (COP), second law efficiency, exergy destruction rate and entrainment ratio were investigated. The exergy analysis is employed in order to identify the amounts and locations of the irreversibility within the cycles. It was found that the COP and second law efficiency values of the new ejector-vapour compression refrigeration cycle are on average 8.6 and 8.15 per cent higher than that of the conventional ejector-vapour compression refrigeration cycle with R125. It was also shown that the COP of the new ejector-vapour compression cycle is 21 per cent higher than that of the conventional vapour compression.

The dehydration kinetics of the fruits with special geometries, i.e. spherical and cylindrical (apple, peach, banana, pineapple, etc.), were studied based on mathematical methods. The influence of the size reduction (slicing) of these fruits into smaller rings was also investigated. The mathematical modelling was performed based on the Fick's second law. The results showed that increasing the value of the water diffusion coefficient in fruit (for instance via increasing the process temperature) promotes faster water migration from the fruit. Mathematical modelling also showed that the characteristic length of fruits (radius) is in an inverse relation to the dehydration kinetics. Comparing the results obtained with both the sphere- and cylinder-shaped fruits revealed that slicing the fruit into more thin rings makes a better condition for operating the osmotic dehydration process with a higher efficiency and a shorter duration.

This study examines the performance of a novel recompression supercritical CO 2 (S-CO 2 ) Brayton cycle of nuclear power plant with pre-cooler exergy utilization, which uses a transcritical CO 2 cycle to enhance the performance of this new cycle. More attention was paid to irreversibilities generated in the combined cycle. Individual models were developed for each component through the application of the first and second laws of thermodynamics. The effects of the turbine inlet temperature, compressor pressure ratio, maximum cycle pressure, main compressor inlet temperature, and also environment temperature on the first- and second-law efficiencies and also on the exergy destruction of the S-CO 2 and the presented new S-CO 2 recompression cycles were studied. Finally, the recompression S-CO 2 cycles were thermodynamically optimized using the Engineering Equation Solver software. Based on identical operating conditions, a comparison between the new S-CO 2 and a simple S-CO 2 cycle was also performed. It was found that both the first- and second-law efficiencies of the new S-CO 2 cycle are about 5.5 per cent to 26 per cent higher than that of the simple S-CO 2 cycle. The exergy destruction of the new S-CO 2 cycle is also about 6.7 per cent to 28.8 per cent lower than that of the simple S-CO 2 cycle.

A series of freeze-thawed, polyvinyl alcohol nanocomposite hydrogels were prepared using various loading levels (0-15 wt%) of hydrophilic natural Na-montmorillonite nanoclay. The morphology of nanocomposite hydrogels, their dehydration kinetics at different temperatures and the effect of Na-montmorillonite on the gelation process were investigated. The results showed a partially exfoliated morphology for the prepared nanocomposite hydrogels. Also by increasing the amount of nanoclay incorporated into the specimens, the gel fraction values of nanocomposite hydrogels were increased. According to the dehydration tests, the dehydration rates of nanocomposite hydrogels exhibited an inverse dependency on the nanoclay loading level and a direct dependency on the dehydration temperature. Finally, it was concluded that the dehydration mechanism of all specimens prepared is non-Fickian at 20 °C, while it is Fickian at 37 °C and 55 °C. [PUBLICATION ABSTRACT]