ABSTRACT

Bauxite and silica particles are candidate materials for solar thermal energy storage at high temperatures. The temperature-dependent emittance of packed beds with bauxite and silica particles was measured using a newly upgraded emissometer at wavelengths 2 μm ≤ λ ≤ 16 μm and temperatures up to ~730 K. The room-temperature emittance was obtained from the measured directional-hemispherical reflectance. A fused silica disc was used to test the emissometer by comparing the measured spectral emittance with the calculated emittance from a fitted Lorentz oscillator model. For the polycrystalline silica particles and the fused silica disc, the measured emittance increases with temperature in the mid-infrared region. The underlying mechanism is interpreted as the temperature-dependent damping coefficient in the Lorentz oscillator model. Two types of bauxite particles with different compositions and sizes were investigated. For λ > 10 μm, the measured emittance at elevated temperatures is higher than that at room temperature. In the region 2 μm < λ < 6 μm, the temperature dependence varies for different types of particles. The total emittance of bauxite particle beds was calculated by spectral integration using Planck’s distribution at the prescribed temperature. The calculated total emittance is between 0.89 and 0.96, but it does not change monotonically with temperature.

摘要

铝土矿和二氧化硅颗粒是高温下太阳能热能储存的候选材料。使用新升级的发射计在波长 2 μm ≤ λ下测量铝土矿和二氧化硅颗粒填充床的温度依赖性发射率 ≤ 16 μm，温度高达 ~730 K。室温发射率是从测量的定向半球反射率获得的。通过将测量的光谱发射率与拟合洛伦兹振荡器模型计算的发射率进行比较，使用熔融石英盘来测试发射计。对于多晶二氧化硅颗粒和熔融二氧化硅圆盘，测得的发射率随着中红外区域的温度而增加。基本机制被解释为洛伦兹振荡器模型中与温度相关的阻尼系数。研究了两种不同成分和尺寸的铝土矿颗粒。当λ  > 10 μm 时，高温下测得的发射率高于室温下的发射率。在 2 μm < λ区域 < 6 μm，不同类型的颗粒的温度依赖性有所不同。铝土矿颗粒床的总发射率是通过在规定温度下使用普朗克分布的光谱积分来计算的。计算出的总发射度在0.89~0.96之间，但不随温度单调变化。