A review of solar collectors using carbon-based nanofluids

The quest to enhance the thermal efficiency of solar collectors by improving the working or absorbing fluid led to the synthesis of nanofluids. Numerous studies have highlighted different nanomaterials such as copper oxide, alumina, silica and so on for dispersion in working fluid and subsequent application in solar collectors. However, carbon nanomaterials have been adjudged as the most promising for preparing nanofluids and heat transfer application. This is because carbon nanomaterials possess remarkable thermophysical properties. These properties contribute a notable enhancement in the thermophysical properties of the working fluid and consequently improve the performance of solar collectors. This study succinctly presents an overview of the performance of various solar collectors utilizing carbon-based nanofluids. The influence of nanofluid concentration, temperature and flow rate on the collector efficiency of the solar collectors were highlighted. This research outcome showed that carbon-based nanofluids with a low concentration of about 0.3 vol% improved the collector efficiency of flat-plate, evacuated-tube, parabolic trough and hybrid photovoltaic thermal solar collector up to 95.12%, 93.43%, 74.7% and 97.3% respectively. Also, direct absorption solar collector using carbon-based nanofluid with a low concentration of at least 0.01 vol% achieved a photothermal efficiency of up to 122.7%. The study further revealed that there is a huge potential to achieve the application of carbon-based nanofluid on a commercial scale. The challenges and prospects for further research were identified. (C) 2019 Elsevier Ltd. All rights reserved.