Abstract Solar thermal receivers collect and can store concentrated solar radiation using solid particles. Solid ceramic particles have shown to be a practical and efficient heat transfer media in solar-particle receivers, however, their emissivity and absorptivity at high temperatures are scarcely reported. This gap has led to large uncertainties in the assessment of solar thermal receivers’ efficiency. In this work, an experimental method was developed to measure the emissivity and absorption function of solar particles at elevated temperatures up to 1200 K. Two types of solar particles, aluminum oxide (Al2O3, ∼95% purity) and silica carbide (SiC, ∼99% purity), were studied, particularly aiming to understand the dependence of emissivity and absorption function on temperature. Using a heat transfer model, the emissivity of particles was evaluated based on the fitting of the cooling rate, while the particle absorption function was obtained by fitting of the heating rate, following a well-controlled heating radiation at 910 nm. It was found that the emissivity values of the two particles are independent of temperature, showing constant values of 0.75 ± 0.015 and 0.92 ± 0.012 for Al2O3 and SiC respectively, in the temperature from 300 to 1200 K. The absorption function was found to be increased nonlinearly with temperature for Al2O3, while that of SiC dropped slightly. These absorption functions are specified for 910 nm. Using the evaluated experimental values of emissivity and absorption function, the maximum temperature and the temperature rise time of micro-sized particles (hundreds of micrometers) under different radiation fluxes were simulated taking into account the effect of particle diameter.

中文翻译：

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用于聚光太阳能接收器的高温下 Al2O3 和 SiC 颗粒的发射率和吸收函数测量

摘要 太阳能热接收器使用固体粒子收集并储存集中的太阳辐射。固体陶瓷颗粒已被证明是太阳能颗粒接收器中一种实用且有效的传热介质，然而，它们在高温下的发射率和吸收率鲜有报道。这种差距导致太阳能热接收器效率评估中存在很大的不确定性。在这项工作中，开发了一种实验方法来测量太阳能粒子在高达 1200 K 的高温下的发射率和吸收函数。两种类型的太阳能粒子，氧化铝（Al2O3，纯度约 95%）和碳化硅（SiC，约99% 纯度）进行了研究，特别是旨在了解发射率和吸收函数对温度的依赖性。使用传热模型，粒子的发射率是基于冷却速率的拟合来评估的，而粒子吸收函数是通过在 910 nm 处良好控制的热辐射后的加热速率拟合来获得的。发现这两种粒子的发射率值与温度无关，在 300 至 1200 K 的温度下，Al2O3 和 SiC 的常数值分别为 0.75±0.015 和 0.92±0.012。发现吸收函数增加Al2O3 与温度呈非线性关系，而 SiC 则略有下降。这些吸收函数是针对 910 nm 指定的。使用辐射率和吸收函数的评估实验值，