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Nanofluids have been used in direct absorption solar collectors (DASC) to enhance their performance, wherein contribution of entropy generation plays a decisive role. Among other factors, entropy generation is influenced including physical structure of the system and operation conditions. In this article, heat transfer and efficiency of a nanofluid based DASC considering the entropy generation has been performed for various physical alterations and operating conditions. Working nanofluids are chosen to Cu-water nanofluid, Al2O3-waternanofluid, TiO2-waternanofluid and water is chosen as base fluid. Solar irradiation value for the current analysis is considered 225W/m2 from the annual average solar irradiance range (215 W/m² in the north-west to 235 W/m² in the south-west per day) in Bangladesh according to UNDP report. Governing equations consisting of Navier-Stokes and energy equations are solved by Penalty finite element method with Galerkins weighted residual approach. Impact of parameters nanoparticle concentration and thickness of flow on isotherms, average output temperature, the average Nusselt number, collector efficiency, average entropy generation and Bejan number are discussed for all considered fluids. Results reveal that DASC system exhibits efficacy in heat transfer using 2% Cu nanoparticles under 225W/m2 irradiance, 0.015 kg/s mass flow rate and 0.015 m flow thickness. The outcomes will be supportive in designing DASC to attain improved heat transfer performance considering entropy generation. [ABSTRACT FROM AUTHOR]

A numerical attempt of the two-phase (non-homogeneous) nanofluid approach towards the convection heat transfer within a 3D wavy direct absorber solar collector is reported. The solar collector is permeated by a water- Al 2 O 3 nanofluid and contains a wavy glass top surface that is exposed to the ambient atmosphere and a flat steel bottom surface. The left and right surfaces are maintained adiabatic. The governing equations of the Navier–Stokes and energy equations for the nanofluid are transformed into a dimensionless pattern and then solved numerically using the Galerkin weighted residual finite-element technique. Validations with experimental and numerical data are performed to check the validity of the current code. Impacts of various parameters such as the number of oscillations, wave amplitude, Rayleigh number and the nanoparticles volume fraction on the streamlines, isotherms, nanoparticle distribution, and heat transfer are described. It is found that an augmentation of the wave amplitude enhances the thermophoresis and Brownian influences which force the nanoparticles concentration to display a nonuniform trend within the examined region. Furthermore, the heat transfer rate rises midst the growing wave amplitude and number of oscillations. More importantly, such enhancement is observed more significantly with the variation of the wave amplitude. [ABSTRACT FROM AUTHOR]

This article presents a numerical visualization of heat transport for forced convective heat transfer by a two-dimensional heat function formulation through a direct absorption solar collector (DASC) filled with water-copper nanofluid. The penalty finite element method is used to solve nonlinear partial differential equations, and the numerical results are presented for variations in the radiative heat flux, Prandtl number, particle diameter, and solid volume fraction of the nanoparticle. The rate of heat transfer, thermal efficiency, mean entropy generation, and Bejan number are strongly dependent on certain parameters. It is observed that the radiative heat flux variation decreases the mean heat transfer, but increases the collector efficiency and entropy generation for nanofluids more than that for pure water. According to the results obtained from this study, under similar operating conditions, DASC is found to have higher efficiency than a flat-plate solar collector (FPSC). Generally, a DASC performs better than a flat-plate collector; however, much better designed flat-plate collectors might be able to match or outperform the efficiency of a nanofluid-based DASC under certain conditions. [ABSTRACT FROM AUTHOR]

Forced convective flow and heat transfer by different nanofluids through a flat plate solar collector is analyzed numerically by this article. The solar collector has the flat-plate cover and sinusoidal wavy absorber. Four different nanofluids like water-Ag nanofluid, water based Cu nanofluid, water-Al 2 O 3 nanofluid and water-CuO nanofluid are used as the operational fluids inside the solar collector. The governing partial differential equations with proper boundary conditions are solved by Finite Element Method using Galerkin's weighted residual scheme. The behavior of different nanofluids related to performance such as temperature and velocity distributions, radiative and convective heat transfers, mean temperature and velocity of the nanofluid is investigated systematically. This performance includes the solid volume fraction namely ϕ with respect to above mentioned nanofluids. The results show that the better performance of heat transfer inside the collector is found by using the highest ϕ of water based Ag nanofluid. [ABSTRACT FROM AUTHOR]

Abstract: Sustainable energy generation is one of the most important challenges facing society today. Solar energy is one of the best sources of renewable energy with minimal environmental impact which offers a solution. The present work investigates the heat transfer performance and entropy generation of forced convection through a direct absorption solar collector. The working fluid is Cu–water nanofluid. The simulations focus specifically on the effect of solid volume fraction of nanoparticle and Reynolds number on the mean Nusselt number, mean entropy generation, Bejan number and collector efficiency. Also Isotherms and heatfunction are presented for various solid volume fraction and inertia force. The governing partial differential equations are solved using penalty finite element method with Galerkins weighted residual technique. The results show that both the mean Nusselt number and entropy generation increase as the volume fraction of Cu nanoparticles and Reynolds number increase. The results presented in this study provide a useful source of reference for enhancing the forced convection heat transfer performance while simultaneously reducing the entropy generation. [Copyright &y& Elsevier]