Abstract
A parabolic trough is defined as a type of solar thermal collector that is straight in one dimension and curved as a parabola in the other two, lined with a polished metal mirror. Enhancing the thermal efficiency of this collectors is one of the major challenges of developing and growing of parabolic trough solar thermal power plants. Ferrofluids were proposed as a novel working fluid for industrial applications, due to their thermal performances. In this study, the convective heat transfer of Fe3O4-Therminol 66 ferrofluid under magnetic field (0–500 G) is evaluated using computational fluid dynamics. The ferrofluid with different volume fraction (1–4%) and the Therminol 66 (as the base fluid) are considered as the working fluids for a parabolic trough solar collector. Numerical analysis first validated using theoretical results, and then a detailed study is conducted in order to analyze the effect of the magnetic field on different parameters. The result demonstrated that using magnetic field can increase the local heat transfer coefficient of the collector tube, thermal efficiency as well as output temperature of the collector. In addition, increasing the volume fraction of nanoparticle in the base fluid and intensity of magnetic field increased the collector performance.
1. Introduction
Renewable energy, for instance solar and wind energy, is one of the most promising solutions to produce clean energy for the future since the conventional energy sources (such as oil, coal and natural gas) will be finished in a few decades [1,2]. World energy consumption is increasing continually and this is worrisome for all researchers and scientists [3]. Solar energy, as an abundant energy source, can either be converted into heat or electricity. It is a useful source of energy for various applications: solar dryers, local hot water production, and electricity production in concentrating solar power plants [4]. Global solar energy production was predicted to reach a rate of 8.9% annually between 2012 and 2040, making it the fastest developing type of energy generation in the forthcoming decades [5].
4. Conclusion
Current study presented a numerical study based on computational fluid dynamics incorporated within ANSYS® FLUENT®, in order to study the effects of ferrofluid and magnetic field on the performance of a parabolic trough solar collector. Fe3O4-Therminol 66 ferrofluid with different volume fraction was considered as the working fluid, having the Therminol 66 as the base fluid. In addition, analyses were done with and without presence of a magnetic field which was provided by a current-carrying wire located close to the collector tube. Effect of the magnetic field on the convective heat transfer coefficient, thermal efficiency, and collector performance was investigated in detail. The results have shown that the HTC of solar collector increases by using submerged nanoparticles in the base fluid. Increasing in volume fraction of nanoparticles can increase the HTC as well. Also, current investigations have shown that using magnetic field helps to increase local HTC of the collector tube, output temperature, and thermal efficiency of the collector. The best performance was obtained for ferrofluid with 4 vol% under a magnetic field of 500 G, which proves effectiveness of both ferrofluid and magnetic field on the collector performance. Finally, the best thermo-hydraulic performance occurs for ferrofluid with 1 vol % in the case of magnetic field absence for which the flow pressure drop and friction factor have the smallest values, similar to the results obtained in the literature.
