Performance analysis of a concentrated direct absorption solar collector (DASC) with nanofluids using computational fluid dynamics and discrete ordinates radiation modelling (CFD-DORM)

Abstract

This study utilises computational modelling to investigate the application of thermal nanofluids in direct absorption solar collectors (DASC), including the effect of optical and thermal properties on the prediction of thermal energy production. A single-phase, computational fluid dynamics (CFD) model has been used to understand the hydrothermal behaviour of nanofluids operated at high temperature. A non-gray discrete ordinate radiation model (DORM) was coupled to the CFD to capture the dependence of optical parameters on the bulk temperature variation. In order to increase the robustness of the numerical modelling approach, the extinction coefficient of the solar participating media, including the reflective and transmissive behaviour of the semitransparent wall, were taken into consideration. Results show that the exergy efficiency is lower when using fully diffusive conditions at the semitransparent wall as opposed to fully specular conditions. Overall, exergy efficiency decreases with the Nusselt number, Nu, (until Nu=10∼12), although it increases with non-dimensional irradiation. When modelling with temperature-dependent as opposed to temperature-independent properties of the working fluid, the Carnot efficiency was found to vary by 0.67% to 3.30%. Additionally, a correlation between the hydraulic entrance length and Reynolds number, Re, (in the range Re<1,000) has been established and this can be applied for the further hydrothermal analysis. This study serves as a basis for future numerical modelling of any volumetric solar receiver that takes into account the various key system performance indicators of the solar participating media.