Heat Transfer In Solar Collectors Research Articles

Enhancement of heat transfer from solar thermal collector using nanofluid

Abstract Global energy consumption is increasing due to population growth and with it the adverse impact of fossil fuels on the environment, making it necessary to use renewable energy sources and convert them to electrical energy using different technologies. However, the solar energy potential remains unused, while it has numerous advantages, including as a source of clean electricity and heat. One of the main difficulties in energy-saving and compacted design is how to increase the heat transfer of solar equipment. As an innovative approach to enhancing fluids’ heat transfer performance, some of the most active techniques are to exchange the working fluid with nanofluids. This work attempted to demonstrate heat transfer behavior changes when using nickel oxide (NiO), aluminum oxide (Al2O3), and copper oxide (CuO) as nanofluids at concentration volumes of 0.05, 0.075, and 0.1%. For this goal, a conical solar collector was built using local public steel sheets. Insulating polyurethane foam padding is used inside the cone. The sun’s energy is focused on the absorbing surface using thin reflective aluminum foil. The study also includes a literature review showing how nanofluids can improve heat transfer in solar collectors. The results showed that adding nanoparticles can increase the rate of heat transfer and CuO nanofluids have better augmentation in heat transfer than Al2O3 or NiO-water nanofluids where 1% CuO nanofluids increases the efficiency by up to 7% compared to water.

Forced-Convection Heat Transfer in Solar Collectors and Heat Exchangers: A Review

Solar thermal collectors, as well as heat exchangers, are energy systems that have become very popular recently in various research centers around the world. Clean systems used to generate thermal energy for its importance in human life. Most of the studies focused on the impact of various physical factors on the efficiency and performance of these systems in the presence of different structures and problems. The current research is mostly focused on evaluating thermal performance in solar receivers and heat exchangers using forced thermal transfer. Due to its importance in numerous industrial domains, the current study is primarily focused on evaluating thermal performance based on forced thermal transfer in solar receivers and heat exchangers.

Enhancement of heat transfer in solar collectors by vortex generation

ABSTRACT The importance of solar energy is evident by considering running out of fossil fuel resources and the growing energy demand. The clean and worldwide source of the sun can be a crucial remedy for the energy crisis throughout the world by extracting renewable and CO2-free solar energy. Solar air heaters are the most common type of heat exchanger for various aspects of solar energy. The conventional type of solar air heaters suffers from low thermal performance. In the current numerical study, some novel geometries are introduced for improving the thermal performance of the air heaters with a highly turbulent flow by borrowing the vortex cooling concept in gas turbine blades. The parameters of Nusselt number, friction factor, and effective efficiency are investigated. The results show a higher heat transfer for the current configurations in comparison to those examined and simulated in the literature. It is such that a minimum 400% increment in the Nusselt number can be obtained compared to that of the simple channel of absorber plate. The efficiency values reveal that the proposed configurations are more economically efficient compared to traditional solar air heaters, especially in the lower Reynolds number, by an increment of about 25%.

Computational study of heat transfer in solar collectors with different radiative flux models

AbstractTwo‐dimensional steady incompressible laminar Newtonian viscous convection‐radiative heat transfer in a rectangular solar collector geometry is considered. The ANSYS FLUENT finite volume code (version 17.2) is used to simulate the thermo‐fluid characteristics. Extensive details of computational methodology are given to provide engineers with a framework for simulating radiative‐convection in enclosures. Mesh‐independence tests and validation are conducted. The influence of aspect ratio, Prandtl number ( Pr), Rayleigh number ( Ra) and radiative flux model on temperature, isotherms, velocity, and pressure is evaluated and visualized in colour plots. In addition, local convective heat flux is computed, and solutions are compared with the MAC solver for various buoyancy effects achieving excellent agreement. The P1 model is shown to better predict the actual influence of solar radiative flux on thermal fluid behaviour compared with the limited Rosseland model. With increasing Ra, the hot zone emanating from the base of the collector is found to penetrate deeper into the collector and rises symmetrically dividing into two vortex regions with very high buoyancy effect. With increasing Pr there is a progressive incursion of the hot zone at the solar collector base higher into the solar collector space and simultaneously a greater asymmetric behaviour of the dual isothermal zones.

Natural Convection in a Square Cavity Using Lattice Boltzmann Method for numbers Riley less than 10^6

Abstract. Since the phenomenon of free convection in a closed container, have a lot of engineering applications.The heat transfer in solar collectors, Equipment designed for cooling, heat transfer in double-glazed windows and applications of this branch of engineering optimization problems.therefore for The analysis easier and more practical for such applications in this paper, the cavity is filled up with air and water would have to rely on Lattice Boltzmann Method simulation. Results for the basis fluid, air and water are provided. In this paper, the Pacific and the four Rayleigh number (Ra =10^3, 10^4,10^ 5, 10 ^ 6) is presented.Single-phase method was used to solve this fluid flow.The main objective of the present study is demonstrate the ability of Lattice Boltzmann Method for solving fluid flow in the long cavity.Lattice Boltzmann results with previous work has been validated.This results have a good agreement with the results of earlier studies.Boundary conditions in the shield to wall upper and lower is adiabatic,and wall of the left and right is temperature constant.

Non-equilibrium heat transfer in metal-foam solar collector with no-slip boundary condition

Convective heat transfer in solar collectors filled with metal foams is analytically investigated with different methods, including numerical, analytical and fin-analysis methods. The Forchheimer/Brinkman/Darcy models are used to establish momentum equations for metal foams while the local thermal non-equilibrium (LTNE)/local thermal equilibrium (LTE) models are employed for energy equations. Some analytical solutions for velocity and temperature are obtained based on Darcy/Brinkman models with thermal dispersion effect considered. Numerical solution and fin solution are also obtained and compared with the analytical solutions with the pros and cons of different models discussed. Effects of some key parameters on flow and heat transfer are discussed. Present fin solution can provide more accurate estimation compared with the fin solution in the literature. The heat transfer difference between Brinkman model and Darcy model is obvious when the duct scale is small. In addition, the combined fin-LTE model is proposed for effectively evaluating thermal performance of metal foams.

Comparison of Heat Transfer in Solar Collectors With Heat-Pipe Versus Flow-Through Absorbers

Analysis of heat transfer in solar collectors with heat-pipe absorbers is compared to that for collectors with flow-through absorbers for systems that produce hot water or other heated fluids. In these applications the heat-pipe absorber suffers a heat transfer penalty compared with the flow-through absorber, but in many cases the penalty can be minimized by proper design at the heat-pipe condenser and system manifold. When the solar collector is used to drive an absorption chiller, the heat-pipe absorber has better heat transfer characteristics than the flow-through absorber.