Thermal Stability and Performance Testing of Oil based CuO Nanofluids for Solar Thermal Applications

For solar thermal systems, nanofluids have been proposed as working fluids due to their enhanced optical and thermal properties. However, nanoparticles may agglomerate over time, heating and thermal cycles. Even though pristine nanofluids have be proven to enhance performance in low temperature application, it is still unclear if nanofluids can meet the reliability requirements of solar thermal applications. To investigate this, the present study conducted experiments with several formulations of oil‐based CuO nanofluids in terms of their maximum operational temperature and their stability upon cyclic heating. In the samples tested, the maximum temperature ranged from 80oC to 150 22 oC and the number of heating cycles of ranged from 5 to 45, with heating times of between 5 to 60 minutes. The results showed that heating temperature, heating cycles, and heating time all exacerbated agglomeration of the samples. Following these experiments, orthogonal experiments were designed to improve the preparation process and the resultant thermal‐impulse stability. Thermal properties of these samples were characterized and thermal performance in an ‘on‐sun’ linear Fresnel solar collector was measured. All tests revealed that thermal performance of solar collecting system could be enhanced with nanofluids, but that thermal stability still needs to be further improved for industrial applications.