Analysis of Mixed Convection and Free Convection in a Reduced Solar Collector Using a Nanofluid as Heat Transfer Fluid

A three-dimensional investigation of mixed convection which occurs from Al2O3-water nanofluid flow in tube of a reduced solar collector and free convection in air gap situated between cover of solar collector and its absorber was investigated. Heat transmission by conduction in absorber and cover as well as thermal losses to exterior expressed in form of a convective flux have also been taken into account. The different transport equations were solved using CFD-Fluent software which is founded on finite volume method and Boussinesq’s law was introduced to take into account of buoyancy effects. In this investigation, thermal efficiency of solar collector was evaluated and use of nanofluids allows to increase this parameter which is generally low for this kind of thermal systems. Length of thermal regime established in the tube is proposed and this investigation is extended relative to other works developed in this research field. Results obtained gave an idea about the flow structure of the fluid under consideration in a tube of a solar collector and heat transmission mechanisms in air gap and in other elements of the solar collector. These results can facilitate design of this thermal system.