Significant photothermal conversion enhancement of nanofluids induced by Rayleigh-Bénard convection for direct absorption solar collectors
The reverse illumination nanofluids-based direct absorption solar collectors can effectively increase the collector photothermal efficiency and decrease the agglomeration rates of nanofluids. [Display omitted] •Reverse illumination is proposed for nanofluids-based direct absorption solar collectors....
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| Published in: | Applied energy Vol. 254; p. 113706 |
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| Main Authors: | , , , , , , , , |
| Format: | Journal Article |
| Language: | English |
| Published: |
Elsevier Ltd
15-11-2019
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| Subjects: | |
| Online Access: | Get full text |
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| Summary: | The reverse illumination nanofluids-based direct absorption solar collectors can effectively increase the collector photothermal efficiency and decrease the agglomeration rates of nanofluids.
[Display omitted]
•Reverse illumination is proposed for nanofluids-based direct absorption solar collectors.•Heat transfer is significantly enhanced by Rayleigh-Bénard convection.•Uniform temperature distribution is achieved in nanofluids due to efficient heat transfer.•The photothermal conversion efficiency is improved from ~26% to ~51.9%.•7 days test shows sedimentation and agglomeration of nanoparticles in nanofluids are alleviated.
Large temperature gradients and serious nanoparticles aggregation are the two vital issues, which lead to a low photothermal conversion efficiency of Nanofluids-Based Direct Absorption Solar Collectors (NB-DASCs) in the solar thermal utilization. It is reported that reverse illumination is a good way to address the above issues of the NB-DASCs, which can change the way of energy transport by Rayleigh-Bénard convection. However, the previous studies are based on simulation and few experiments are found. In this paper, a novel test rig is designed for the first time to experimentally study the reverse illumination NB-DASCs. Uniform temperature distribution inside nanofluids is obtained. It is found that the photothermal conversion efficiency of the reverse illumination NB-DASCs is up to 51.9% in a continuous test of 10,000 s, which is 99.6% higher than that of the conventional NB-DASCs. Furthermore, the spontaneous convection, resulted from reverse illumination, can effectively alleviate the sedimentation and agglomeration of nanoparticles, which enhances the stability of nanofluids. In addition, the mechanism is also studied in detail. This paper provides a practical avenue for improving the solar thermal conversion efficiency of the direct absorption solar collectors. |
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| ISSN: | 0306-2619 1872-9118 |
| DOI: | 10.1016/j.apenergy.2019.113706 |