Analyzing entropy and thermal behavior of nanomaterial through solar collector involving new tapes

Abstract

In the present examination, the effect of Aluminum oxide suspended in water at concentration of 0.03% as nanomaterial for turbulent flow using multiple twisted tapes (TT_n) in a solar flat plate collector was scrutinized. Properties are estimated by utilizing previous correlations. Outputs are described for a different number of turbulator and Reynolds number (Re). The increase in S_gen,f (1604.672) is more significant for higher Re = 20,000. The highest S_gen,th (15,788.13) is observed for TTn = 1 and Re = 4000. The highest number of Be is 0.9987 when the TT_n = 1 and Re = 4000. Both the Be number and the Фs shows the same trend for the reported results. The increase in the number of Re and TT_n reduces the values of Be and Фs. Output results verify that the use of turbulators enhances the nanofluid flow resulting in enhanced heat transfer, which also provides higher flow disturbance. Therefore, it can be concluded that using twisted tapes and nanofluids can result in reduces exergy losses.

Introduction

Nanotechnology has been the center of attention for several researchers due to their enhanced properties. Nanomaterials, due to their enhanced thermophysical properties, the most dominated being the higher thermal conductivity, can be employed for a vast range of engineering usages. Several studies have recently reported utilizing mono [1] or hybrid [2] nanofluids for augmenting the convective mode of conventional fluids, to be utilized as a testing fluid in several engineering applications. Several nanopowders, like metal, metal oxides, and carbon-based, are utilized for solar thermal applications. Aluminum oxide has been used most widely among the reported nanomaterials due to its availability in large amounts and cheaper costs. Mixing the nanomaterials (1–100 nm) with conventional fluids such as water or oil can result in higher convection. The term “Nanomaterial” was first coined by Choi [3]. Since several researchers have used nanofluids as a choice of heat transfer fluid because of their improved thermal conductivity in several thermal applications [4], such as SFPC [5], evacuated tube solar collectors [6], PV/PVT systems [7], concentrated solar collectors [8], heat exchangers [9] and many others [10,11]. Another way of improving the convective heat transfer in solar thermal systems is by using TT, which can create swirls and disturb the boundary layer; thus, it is the most widely used technique. Said et al. [12] carried out several empirical studies utilizing Al₂O₃/H₂O nanofluids, where the influence of volume fraction, size of nano powder, sonication time and effect of pH on stability were reported. Other experimental studies utilizing TiO₂/H₂O [12] and SWCNT/H₂O [13] were carried out for thermal efficiency enhancement for a SFPC. Improved energy efficiency was reported for all the studied nanofluids by Said et al. [13] for the solar flat plate collector (SFPC).

Sundar et al. [14] investigated Al₂O₃/H₂O nanofluids as well as twisted tapes in SFPC. Results showed higher thermal efficiency of about 76% utilizing both the nanofluids (higher volume fractions) and the twisted tape (higher inlet velocity). Tehrani et al. [15] investigated TiO₂/H₂O nanomaterial use in a solar heat exchanger using the ribbed configuration for a turbulent regime. Outputs showed improvement in convective heat transfer using ribbed plates and nanofluids. Bianco et al. [16] examined Al₂O₃/H₂O nanomaterial influence in a photovoltaic solar panel using Comsol commercial software for an asymmetrically heated channel simulating a laminar convective heat transfer. Results showed that using Al₂O₃/H₂O nanofluids reduces the wall temperature by 5 K and improved the heat transfer by up to 15%. The influence of conical wire on entropy generation of ethylene glycol within a pipe has been investigated by Keklikcioglu et al. [17]. They utilized various fractions of H₂O and ethylene glycol as the operating fluid. They found that the converging coil has the best performance. The amount of Be for ethylene glycol was lower than that of water. Jouybari et al. [18] scrutinized a solar system with inserted channels within a permeable material. The researchers reported augmentation in Nu with more significant volume fractions for the nanofluids and lower Re number. Another group scrutinized the impact of turbulator on the performance of a solar unit [19]. Improvement in heat transfer ranging from 18% to 70% compared to plain collectors was reported. An increment in pressure drop was also reported from 87% to 132%. Selmi et al. [20] numerically investigated the outlet temperature for a single glazed flat plate collector using CFD software. Low uncertainties for experimental data and numerical data were reported. Gunjo et al. [21] examined an analysis for a straight tube solar water heating system investigating the thermal performance, showing a good agreement between the two. Duct with a square cross-section with nanofluid has been investigated by Dagdevir et al. [22]. Researchers considering turbulent regimes reported the impact of chamfer length. Their outputs revealed that the length of chamfer has direct relation with Nu. Kang et al. [23] experimentally studied Al₂O₃/H₂O nanomaterial in a flat plate solar unit and reported higher enhancement. Coiled-wire device was employed inside the tube by Keklikcioglu and Ozceyhan [24]. They assumed uniform heat flux and reported that entropy ration declines with augment of pitch ratio.

As can be summarized from the literature reported above, only a few researchers have studied the 2nd law of performance in designing SFPC. Besides, recently much attention is being given to renewable energy systems that have been employed in several thermal usages. Therefore, the entropy and thermal scrutinization of an SFPC using nanofluids have been presented in the current study. Firstly, the selection of using Aluminum oxide nanomaterial suspended in the base fluid and the turbulence model has been illustrated in detail. Secondly, the verification of the code being implemented has been examined. Finally, the effect of various twisted tapes for turbulent flow in SFPC has been reported.