Integrated Optical Performance Investigation and Optimization of Mixed Particle-Packed Receivers
Objective Decreasing solar radiation reflection loss and re-radiation loss is crucial for improving the thermal efficiency of solar receivers.We propose a mixed particle-packed receiver composed of a modified quartz glass Rasching ring(a short quartz glass tube with both bottom surfaces cut),quartz glass ball,and silicon nitride ball.The modified quartz glass Rasching ring reduces reflection loss by capturing incident solar radiation.In contrast,the quartz glass balls are used to mitigate re-radiation loss from the high-temperature silicon nitride balls.Thus,the values of solar radiation reflection loss and re-radiation loss can be regulated by adjusting the stacking layers of the quartz glass balls,which achieves optimized thermal efficiency for the receivers across different temperature ranges.Methods The optical performance of the mixed particle-packed receiver is analyzed using both a particle-scale optical transmission model and experimental measurements.The packing of balls inside the hollow cylinder is simulated with STAR-CCM+software,and the center coordinates of these balls are thus extracted.Next,the mixed particle-packed receiver model is reconstructed using TracePro software,integrated with a specific optical path system.This system concentrates solar radiation through a parabolic dish mirror and captures the re-radiation emitted from the silicon nitride balls.Solar radiation reflection and re-radiation losses are then simulated with this optical system.Finally,the absorptivity-emissivity ratios and thermal efficiencies are determined for various mixed particle-packed receivers.Results and Discussions The comparison between the simulation and measurement results verifies the reliability of the particle-scale optical transmission model.Results show that the reflection loss of the incident solar radiation increases with the stacking layers of the quartz glass balls.Conversely,the re-radiation loss decreases with more stacking layers.When the tube-to-particle diameter ratio(D/d)is 5,the reflection loss of the R0B5 receiver is nearly 10%higher than that of the R5B0 receiver(Fig.6),while the re-radiation emissivity of the R0B5 receiver is about 3.7%-9.7%lower than that of the R5B0 receiver across the temperature range of 800-2500 K(Fig.7).In the mid-temperature range of 500 K to 950 K,the R5B0 receiver exhibits the highest thermal efficiency.In the sub-high temperature range of 950 K to 1525 K,the R4B1 receiver shows the highest thermal efficiency.In the high-temperature range of 1525 K to 2175 K,the R1B4 receiver achieves the highest thermal efficiency.Additionally,in the ultra-high temperature range above 2175 K,the R0B5 receiver delivers the highest thermal efficiency(Fig.8).Furthermore,silicon nitride particles absorb most of the solar energy(more than 80%),while quartz glass particles absorb only 3.0%-6.5%of the solar energy(Fig.11).Conclusions Due to the adjustable optical performance of the mixed particle-packed receiver,the highest thermal efficiency across different temperature ranges can be achieved by altering the stacking layers of the quartz glass balls.The optimized design of the mixed particle-packed receiver offers a novel approach to high-temperature solar receivers,which could be implemented in advanced high-temperature power cycles.
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