The present experimental study focuses on the energy storage performance of Therminol 55-TiO2 nanofluids for the absorption of solar energy. Photothermal conversion efficiency is enhanced using Fresnel lens and secondary reflectors with a glass-type evacuated absorber tube. The focal length of the Fresnel lens is 150 mm, and that of the secondary reflector is 70 mm. The optical absorbance, extinction coefficient, and thermal conductivity of nanofluids at 100, 250, 350, and 500 ppm are reported. The optical path length of the energy storage medium is 1 cm. The optical performance of the nanofluids is analyzed in the range of 400 to 800 nm. Compared to base fluid, the prepared concentrations show higher absorbance in the measured range of wavelength. The optimum concentration is found to be 250 ppm, and its specific heat is measured in the temperature range of 27 to 117°C and is found to vary from 1.85 to 2.19 J/g °C. The thermal conductivity of the maximum concentration of nanofluid is 0.134 W/mK. The optical absorbance test confirms the stability of nanofluids. Maximum temperature and photothermal conversion efficiency are obtained.

中文翻译：

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用于太阳能存储的 Therminol 55-TiO2 纳米流体的光学和热学特性

目前的实验研究侧重于 Therminol 55-TiO2 纳米流体吸收太阳能的储能性能。使用菲涅耳透镜和带有玻璃型真空吸收管的二次反射器提高了光热转换效率。菲涅耳透镜的焦距为 150 mm，副反射镜的焦距为 70 mm。报告了纳米流体在 100、250、350 和 500 ppm 下的吸光度、消光系数和热导率。储能介质的光路长度为 1 cm。在 400 至 800 nm 范围内分析纳米流体的光学性能。与基液相比，制备的浓度在测量的波长范围内显示出更高的吸光度。发现最佳浓度为 250 ppm，其比热在 27 至 117°C 的温度范围内测量，发现其变化范围为 1.85 至 2.19 J/g °C。纳米流体最大浓度的热导率为0.134 W/mK。吸光度测试证实了纳米流体的稳定性。获得最高温度和光热转换效率。