الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
The cooling fluid is a key factor in cooling of photovoltaic (PV) panels especially in the case of concentrated irradiance or when operates in hot climates such as that prevail in the Middle East region. Maintaining the panel at low temperature increases its efficiency. The present study investigates the implementation of novel cooling fluids such as nanofluids and phase change slurries for achieving the required cooling demand. The current research was performed using ANSYS CFD software with two different approaches: the single-phase with average properties and the discrete multi-phase model with the Eulerian-Lagrangian frame work. Both approaches are compared to experimental results found in the literature. Both approaches show good agreement with the experimental results, with some advantage for the single-phase model in computational time. The resulting error in predicting heat transfer coefficient was less than 5% using single phase model and less than 10% for discrete phase model.
Firstly, the usage of water/Al2O3 as a nanofluid was investigated for achieving the required cooling process. The particle concentrations and sizes were investigated to record their subsequent effects on heat transfer coefficient and pressure DROP in the developing and developed flow regions. It was shown that, the heat transfer coefficient was greatly enhanced by increasing the particle concentration and/or decreasing the particle size. On the other hand, the usage of nanofluid causes a severe increase in the pumping power, especially with the increase in nano-particles concentration and the reduction in particle size. Thus, a system optimization was suggested in order to raise the overall system efficiency for photovoltaic applications. . It was concluded that the PV panel efficiency could be increased by 1.5-2% in the concentration range of 2-4% for particle sizes in the range of 20-60 nm.
Secondly, the impact of using microencapsulated phase change material (MPCM) particles suspended in water as a base fluid on the cooling performance of PV panel was investigated numerically. Using MPCM slurry has shown enhanced heat transfer characteristics due to their higher apparent specific heat values when subjected to heating within their phase change temperature range. The performance was further improved to suit operation under concentrated irradiance by implementing staggered circular pins attached to the back side of the Photovoltaic panel (PV). The simulation was done by using FLUENT solver by the incorporation of several user-defined functions (UDF) to define the thermophysical properties of the microencapsulated phase change slurry. The effect of adding staggered circular pins inside the flow channel was also investigated at various mass fractions for the microencapsulated phase change slurry.
It was shown that, the heat transfer coefficient is greatly enhanced due to introducing MPCM particles inside the base fluid especially at higher mass fractions with and without pins. Also, a large DROP in the panel temperature was noticed using slurry flow when compared to single phase flow of water. It was also shown that the presence of pins substantially contributed in decreasing the panel temperature especially at concentrated irradiance; however, this comes on the expense of the severe increasing in the pumping power. Also, there was a remarkable increase in panel efficiency at normal and concentrated irradiance as a result of introducing the phase change particles inside the base fluid. It was shown that the PV panel efficiency could be improved using MPCM slurry with 3% relative to base water at normal irradiance conditions, and with about 5.5 % at concentrated radiance condition.
Finally, the effect of deposition of nano-particles inside the cooling passage of Photovoltaic (PV) panel was also investigated to record the subsequent effect on the cooling process performance. The particles transport is modeled through Eulerian-Lagrangian frame work using two-way coupling method to perform the particles trajectories. In the absence of turbulence, Brownian diffusion force was the main force that contributed to particles deposition due to small size of particles used in the current study (below 100 nm). Several parameters were investigated such as particle size, concentration, inlet temperature, and Reynolds number so as to record the subsequent effects on the heat transfer coefficient, deposition efficiency, and the pressure drop.
It was shown that, the deposition efficiency is higher for smaller particles at lower Reynolds number flows which resulted in more concentration loss, and hence lower heat transfer rates and lower pressure DROP across the channel. It was also shown that the deposition efficiency could reach more than 3% for 10% volumetric concentration. Additionally, a reduction in the average value of Nusselt number of more than 12% was noticed for the same volumetric concentration of particles as a result of particles deposition inside the flow channel.