Experimental Study on the Thermal Performance and Heat Transfer Characteristics of Solar Parabolic Trough Collector Using Al2O3 Nanofluids J. Subramani,a P.K. Nagarajan ,a Somchai Wongwises,b S.A. El-Agouz,c and Ravishankar Sathyamurthya a Department of Mechanical Engineering, S.A. Engineering College, Affiliated to Anna University, Chennai, Tamil Nadu, India;
[email protected] (for correspondence) b Fluid Mechanics, Thermal Engineering and Multiphase Flow Research Laboratory (FUTURE), Department of Mechanical Engineering, King Mongkut’s University of Technology, Thonburi, Thailand c Mechanical Power Engineering Department, Faculty of Engineering, Tanta University, Egypt Published online 00 Month 2017 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ep.12767 The present work investigated thermal performance and heat transfer characteristics of a solar parabolic trough collector using Al2O3/DI-H2O nanofluids. Nanofluids of varying concentrations (0.05% / 0.5%) with mass flows (0.0083–0.05 kg/s) were considered for turbulent regime (2401 Re 7202) analysis. Experiments were carried out as per ASHRAE 93(2010) standards. By thermal performance analysis using Al2O3 nanofluid, it was understood that the collector efficiency improved up to 56% at a maximum volume concentration of / 5 0.5% and flow rate of 0.05 kg/s. The heat transfer study comparing Al2O3 nanofluid with pure water showed appreciable reduction in temperature gradient and surface temperature of the absorber. The heat transfer characteristics such as Nusselt number and friction factor relating to Reynolds number fits the experimental and predicted data and found within the limits of 65.35% and 69.61% for Nusselt number and friction factor respectively. Moreover, a similar empirical correlation was developed for collector efficiency, C 2017 which was identified to be within the limit of 61.02%. V American Institute of Chemical Engineers Environ Prog, 00: 000–000, 2017
Keywords: solar parabolic trough collector, nanofluid, aluminum oxide, collector efficiency INTRODUCTION
Depleting fossil fuel reserves coupled with the irreversible impact they have on the environment have pushed the thrust toward solar energy. One of the major challenges in solar energy is that it can be harnessed only during day time. To extend the utilization of solar PTCs, the introduction of heat storage techniques (PCM, brine water, and chemical storage systems) has made it possible to store the energy in day time and radiate the stored energy at night and when cloudy. With the aim of identifying an ideal energy storage material in solar heat collectors, Koli [1] studied the heat storage capacity of rhodamine B-fructose with Pt electrode and sodium lauryl sulfate as surfactant, with a resulting Additional Supporting Information may be found in the online version of this article. C 2017 American Institute of Chemical Engineers V
enhancement in system performance of the PG cell by 11.28%. The use of FCF and fructose as surfactants in a Pt electrode photo galvanic (PG) cell increased performance by 6.59% [2]. Similarly, Gangothri and Koil [3] designed a PG panel consisting of an EDTA-safranine-O-NaLS system, which reported an increase in energy storing efficiency of 8.93%. One of the widely used devices for harnessing solar energy is a parabolic trough collector (PTC). The most prominent work in this regard was by Clark [4] who configured the various components of a solar PTC based on parameters like reflectivity, incident angle, and tube intercept factor. As a further enhancement, Thomas and Guven [5] improved the system design, construction, and evaluation of reflectors/support structure. When experimentally evaluating the performance characteristics of a solar PTC, Kalogirou [6] and Price et al. [7] identified that maximum collector efficiency depends on the intercept factor and the tracking mechanism. Several researchers have stated the importance of working fluid and temperature range on the efficiency of a solar collector. The advent of nanotechnology motivated many new researches to exploit nanofluids in heat transfer applications. A primary heat transfer augmentation technique was proposed by Choi [8] using nanofluids as a working fluid. Notable researchers have designed solar collectors using different nanofluids. In an earlier significant work, Tyagi et al. [9] showed that the presence of Al2O3 nanoparticles improves the absorption rate by nine times compared to pure water. Moreover, efficiency improved by 10% when using Al2O3 nanofluids as a working fluid. Taylor et al. [10] studied the impact of graphite nanoparticles on high flux concentrators, reporting an improvement in the thermal performance of the collector by 10%.Yousuf et al. [11] studied the effects of Al2O3/water nanofluids on the performance of a solar flat plate collector, concluding that a 0.2% concentration of nanofluid augmented the collector e fficiency by 28%. Khullar et al. [12] numerically studied the performance of a solar PTC and compared the experimental results with those of a solar collector. They showed that a 0.05% concentration of aluminum nanoparticles/therminal oil as a working fluid
Environmental Progress & Sustainable Energy (Vol.00, No.00) DOI 10.1002/ep
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improved the productivity of the solar collector by 5–10%. Saidur et al. [13] studied the thermal performance of Al2O3/ water as a working fluid on a direct solar absorption system, whereby an addition of nanoparticles up to 1% volume fraction improved the collector absorption performance. Mahian et al. [14] investigated the effects of Nusselt number and thermal performance of different combinations of nanofluids, CuO/water, TiO2/water, Al2O3/water, and SiO2/water, in a solar collector. Javidi et al. [15] reviewed the performance improvement in solar collectors using nanofluids as a working fluid. A review by Nagarajan et al. [16] discussed the thermophysical properties of nanofluids and their applications in solar collectors. Chandra Prakash et al. [17] reviewed the uses and behaviors of nanofluids in solar thermal applications. Among the recent works on the performance of a solar PTC is one by Kaisaian et al. [18] who investigated the thermal performance of MWCNT/mineral oil in the concentration of 0.2% and 0.3% on solar PTC, with an enhancement in efficiency by 4–7%. Sokhansefat et al. [19] investigated the effects of Al2O3/synthetic nanofluid oil on the thermal performance of a solar PTC, with a presence of
