Abstract
In the current investigation, the thermal and thermodynamic behavior of a buoyancy-driven evacuated tube solar collector (ETSC) has undergone precise evaluation, and the efficacy of nanoparticle dispersion in the testing fluid was scrutinized. The natural convection process was analyzed in different vertical sections of the absorber tube. The outputs for water and the utilized nanofluid were compared at various cutting planes along the tube during the simulation time. In this problem, CuO nanoparticles with optimum thermal properties were distributed in the base fluid. According to the surveyed results, the temperature distribution analysis illustrates that the mean wall temperature experiences more enhancement when the nanofluid is used. The comparison of the heat transfer coefficient between the two simulated cases show the competency of utilizing CuO-{mathrm{H}}_{2}mathrm{O} nanofluid and highlight its crucial character in improving the thermal treatment of the operate fluid through the collector pipe. Based on irreversibility assessment, the irreversibility due to fluid friction rises when the nanofluid is applied during the flow time. In contrast, the entropy generation of pure water owing to heat transfer surpasses the case with nanofluid. More specifically, the heat transfer entropy generation experience a reduction of about 6.3% (0.143–0.134 W/K) by utilization of CuO with a volume fraction of 5% after 1 h of flow time, whereas the entropy generation by fluid viscosity enhances up to 23% when the nanofluid is applied in the system. The irreversibility originated from heating and fluid viscosity has significant difference in value, owing to the fluid’s low-velocity range in the natural convection process.
Highlights
In the current investigation, the thermal and thermodynamic behavior of a buoyancy-driven evacuated tube solar collector (ETSC) has undergone precise evaluation, and the efficacy of nanoparticle dispersion in the testing fluid was scrutinized
ETSCs are composed of an absorber tube surrounded by two concentric glass tubes that are directly exposed to solar radiation
The thermal functionality of the ETSC has been analyzed in multifarious volume concentration (0.015%, 0.025% and 0.035%) of CeO2/water nanofluid by authors of Ref.[16] who found that, using CeO2/water nanofluid with 0.035% volume fraction has shown the greatest influence on the collector efficiency enhancement up to 34%
Summary
The last decades have witnessed a burgeoning demand for energy consumption produced by fossil fuels, which in turn has led to growing concerns about environmental issues such as air pollution and other serious problems. Dehaj and M ohiabadi[19] conducted an experimental study to evaluate the efficiency of HPETC by using MgO nanofluid at different volume fractions They found that MgO/water nanofluid can enhance the productivity of the collector more than case with water. The obtained results revealed that ETSC has higher thermal entropy generation than FPC by virtue of more heat transmission, which takes place in a vacuum tube collector. According to the lack of numerical researches concentrating on the appraisal of irreversibility in ETSCs, this study is fixated on analyzing the irreversibly inside an open thermosyphon solar collector aim to extract the efficacy of entropy generation on the productivity of suggested unit. For thermal evaluation of the proposed system, temperature and velocity distributions and contours inside the three cutting sections of collector along with the heat transfer coefficient were analyzed for water and nanofluid, by which the merits of using the CuO nanofluid are demonstrated
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