Abstract
Application of solar collectors for hot water supply, space heating, and cooling plays a significant role in reducing building energy consumption. For conventional solar collectors, solar radiation is absorbed by spectral selective coating on the collectors’ tube/plate wall. The poor durability of the coating can lead to an increased manufacturing cost and unreliability for a solar collector operated at a higher temperature. Therefore, a novel nanofluid-based direct absorption solar collector (NDASC) employing uncoated collector tubes has been proposed, and its operating characteristics for medium-temperature solar collection were theoretically and experimentally studied in this paper. CuO/oil nanofluid was prepared and used as working fluid of the NDASC. The heat-transfer mechanism of the NDASC with parabolic trough concentrator was theoretically evaluated and compared with a conventional indirect absorption solar collector (IASC). The theoretical analysis results suggested that the fluid’s temperature distribution in the NDASC was much more uniform than that in the IASC, and an enhanced collection efficiency could be achieved for the NDASC operated within a preferred working temperature range. To demonstrate the feasibility of the proposed NDASC, experimental performances of an NDASC and an IASC with the same parabolic trough concentrator were furthermore evaluated and comparatively discussed.
Highlights
Solar energy utilization is one of the effective ways to relieve the pressures on energy shortage and environmental conservation
Otanicar et al [9] experimentally investigated a flat-plate solar collector using nanofluid made from water added with a variety of nanoparticles including carbon nanotubes, graphite, and silver, and the study results suggested that the efficiency could be improved by up to 5%
In a concentrating medium-temperature solar collector, its concentrator reflects the solar radiation to its collector tube, so that the received solar radiation can be improved by several folds
Summary
Solar energy utilization is one of the effective ways to relieve the pressures on energy shortage and environmental conservation. For commonly used solar collectors, solar radiation is firstly captured and absorbed by spectral selective coating on the collectors’ tube/plate wall, converted into heat, and indirectly transferred to the heat-transfer fluid (HTF) inside the tubes Unlike these commonly used indirect absorption solar collectors (IASC), novel nanofluid-based direct absorption solar collectors (NDASC) have been recently proposed [2,3,4,5,6,7,8,9,10,11,12,13,14,15]. Previous studies demonstrated that the use of NDASCs could lead to an acceptable efficiency with a reduced manufacturing cost for low-temperature solar collectors Such an advantage may make much sense to a medium-temperature solar collector. The performances of an NDASC and an IASC with the same parabolic trough concentrator are experimentally evaluated, to demonstrate the feasibility of the proposed NDASC
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