Estudo experimental dos métodos ativo e passivo para arrefecimento de painéis fotovoltaicos de alta concentração

Abstract

The present thesis deals with an experimental study of different cooling methods for high concentration photovoltaic (HCPV) to improve the efficiency of these systems, focusing on the analysis of a finned heatsink and a rectangular multi-microchannel heat exchanger. The working fluids used in this research were silver nanofluids with different nanoparticles sizes (with and without surfactant) dispersed in base fluids of distilled water and 50% wt diluted ethylene glycol. Tests were performed at the fin heat sink to calculate the thermal resistance under controlled conditions and under real operating conditions. For the microchannel heat exchanger, a properly instrumented experimental bench was built to conducted the stablished test conditions. The heat flux varied between 7 and 22 kW/m², the volumetric flow between 15 and 60 ml/min. The inlet temperature at the test section was maintained constant at 25 °C and 35 °C. The heat transfer and friction factor results of the base fluids in laminar flow were compared with classic and specialized models for microchannel heat exchangers obtaining a good agreement with the experimental data. The thermophysical properties of nanofluids, conductivity, viscosity and specific mass were experimentally measured and their values used for the heat transfer analysis. In general, the convective heat transfer coefficient for nanofluids based on the diluted ethylene glycol showed significant increases compared to the base fluid, however the pressure drop increased. Among the distilled water based nanofluids, only the samples with surfactant showed significant heat transfer increments relative to the base fluid. With the use of microchannel heat exchanger, the operational temperature of the photovoltaic cell can be reduced up to 22,4 °C, with an increment in the electrical efficiency of 2,75% and a global performance up to 78,8% at the tested conditions, in addition to the possibility of using residual heat in another process.