科研之友
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摘要
To optimize the performance of concentrating solar power (CSP) plants, packed bed with multiple phase change layers of spheres encapsulated by different phase change materials has been widely studied for its considerable temperature application range and heat regulation ability, but few studies indicate the effect of capsule size. In this paper, four high-temperature three-layered packed bed systems with variable capsule sizes were established using the concentric-dispersion model. It was found that changing geometric characteristics of spherical capsules inside a phase change layer affects heat transfer between layers, which has an impact on the thermal perfor-mance. The independent programming model's accuracy was validated by comparing numerical results to the experimental data. The temperature variation, charging and discharging efficiencies, and energy and exergy efficiencies were studied to investigate thermal performances, and detailed thermal energy storage and release processes were methodically evaluated. The maximum bed temperature difference of four cases increases from 32 degrees C to 39 degrees C. The exergy efficiency decreases from 0.9465 to 0.9375, but the overall energy efficiency varies significantly, with 0.8903 being the highest and 0.7854 being the lowest. For the optimal capsule size scheme, which is presented as Case 1, the air inlet temperature rises from 530 degrees C to 550 degrees C, increasing the percentage of sensible heat by 3%. Increasing the inlet temperature by another 20 degrees C raises the percentage by only 2%. Changing the tank height-to-diameter ratio has little effect on the temperature evolution of air along the tank axis but results in a slight decrease in energy and exergy efficiencies. Variable capsule sizes will increase the perturbation between layers, enhancing the effect of convective heat transfer. This novel study is conducted to improve the energy utilization of CSP plants.
