This study investigates the influence of Ni–Al coating thickness on the spectral selectivity and thermal performance of a parabolic trough collector (PTC). Three thicknesses of Ni–Al coating for use as solar absorber material were successfully prepared on the outer surface of a stainless steel 316L (SS) tube by flame spray. The phase, morphology, and reflectance (R) of the Ni–Al coatings were characterized using several techniques. The PTC and solar receiver tube were specially designed and constructed for observing the collector thermal performance by following ASHRAE 93-1986. Looking at the results, the actual average thicknesses of the three Ni–Al coatings turn out to be 195, 215, and 299 μm. The morphology and chemical composition of all three thicknesses are similar. The chemical composition in the cross-sectional view exhibits non-uniform distribution. The three thicknesses of the coating are composed of NiO and Al₂O₃ phases, which also corresponded to the results of SEM–EDX mapping. The differences in a solar absorptance (α) of the three thicknesses of Ni–Al coating are not statistically significant, with an average α value of 0.74–0.75. However, there are differences in thermal efficiency of the PTC depending on the thickness of the Ni–Al coating. Of the three samples, the thickest one (299 µm) demonstrates the highest ability to convert solar radiation into thermal energy.

中文翻译：

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Ni-Al镀层厚度对抛物槽收集器光谱选择性和热性能的影响

这项研究调查了Ni-Al涂层厚度对抛物槽式集热器（PTC）的光谱选择性和热性能的影响。通过火焰喷涂在不锈钢316L（SS）管的外表面成功制备了三种厚度的Ni-Al涂层用作太阳能吸收材料。相，形态和反射率（RNi-Al镀层使用多种技术进行了表征。PTC和太阳能接收管经过特别设计和制造，以遵循ASHRAE 93-1986的规定观察集热器的热性能。从结果看，这三个镍铝涂层的实际平均厚度为195、215和299μm。这三种厚度的形态和化学组成都相似。截面图中的化学组成显示出不均匀的分布。涂层的三个厚度由NiO和Al ₂ O ₃相组成，这也与SEM-EDX映射的结果相对应。日吸收率的差异（α）Ni-Al镀层的三种厚度均无统计学意义，平均α值为0.74-0.75。但是，PTC的热效率会有所不同，具体取决于Ni-Al涂层的厚度。在这三个样本中，最厚的样本（299 µm）显示出将太阳辐射转换为热能的最高能力。