A two-dimensional (2D) Keywords PCM, Natural convection, Cooling PV panel IntroductionThe photovoltaic (PV) panel absorbs only about 16 % of the incident solar energy that is converted into electricity; the remaining insolation absorbed is transformed into heat [1]. The photovoltaic cell efficiency decreases with increasing temperature [2]. This can typically result in an efficiency drop off of 0.5 % per °C increase in the cell operating temperature. Since, for example, silicon solar cells are characterized at 1000W/m 2 and 25 °C as ideal temperature for the cell, maintaining the cell temperature at 25 °C can retain the rated efficiency of the cell. Cells will also exhibit long-term degradation if the temperature exceeds a certain limit [3].This problem can be avoided by keeping a uniform temperature across the panel. The use of the extracted thermal energy from cooling can lead to a significant increase in the total conversion efficiency of the receiver. Natural or forced air circulation is a simple and low cost method to remove heat from PV modules, but it is less effective if ambient air temperature is over 20 °C, as it is usual for many months in low latitude countries.Another, more efficient way is to use a liquid as the coolant of the panel, in order to absorb more heat and to cool the panel more effectively [4]. This is the general philosophy of hybrid photovoltaic-thermal collectors. In such kind of cooling, various investigations have been made producing interesting results.In the desert, the PV temperature can exceed 40 °C inducing a power drop in crystalline silicon PV. Increased operating temperature also results in accelerated PV degradation due to cell delamination allowing moisture ingress. The air or water cooling systems are limited by very low heat transfer and large capital as well as maintenance costs [5].However, a novel method to regulate the rise in PV temperature, phase change materials (PCM), which absorb energy as latent heat at a constant phase transition temperature has been developed and employed recently. The phase change materials undergoing solid-liquid phase transition at or close to 25 °C can absorb the excess thermal energy during phase change, which otherwise would raise PV operating temperature, and can maintain the PV operating temperature at or close to 25 °C.

This paper presents a numerical investigation of a two-dimensional (2D) oscillatory flow around a cylinder of different elliptic ratios, in order to study the effect of the elliptic form of the cylinder on the vorticity field and the hydrodynamic forces that act on it. The elliptic ratio ε was varied from 1 to 0.1, where the small axis is parallel to the flow direction, simulating cases ranging from a circular cylinder to the case of a cylinder with a profiled elliptic section. The investigations presented here are for Reynolds number Re = 100 and Keulegan number KC = 5. The numerical visualization of the flow for different elliptic ratios shows five different modes of vortex shedding (symmetric and asymmetric pairing of attached vortices, single-pair, double-pair, and chaotic), which depend on the range of the elliptic ratio. The results show that the longitudinal force increases with the reduction of the elliptic ratio. The transverse force appears from the elliptic ratio ε=0.75 and increases with the reduction of this ratio in the range of 0.75≥ε≥0.4, then decreases for ε<0.4. On the other hand, concerning the Morison coefficients the results show that the drag coefficient is sensitive to the swirling layout while the coefficient of inertia does not seem to be much affected by the geometry of the cylinder.

A critical problem in the application of metal matrix composites is the presence of high residual thermal stresses induced during the development process. These thermally induced stresses are generally detrimental to the service life of this type of composite. This article discusses the influence of maximum residual stresses on the intensity factor. The results interpreted in terms of damage, allowed us to identify the risk zones; characterized by a significant level of maximum residual stresses (S11Max, S22Max, S33Max), namely the particle/Matrix interface. The results also show that the loading conditions and the inter-distance between matrix and particle with two interfacial cracks have an important effect on max residual stresses and stress intensity factors.

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Membrane distillation (MD) is a separation process used for water desalination, which operates at low pressures and feeds temperatures. Air gap membrane distillation (AGMD) is the new MD configuration for desalination where both the hot feed side and the cold permeate side are in indirect contact with the two membrane surfaces. The chapter presents a new approach for the numerical study to investigate various solar thermal systems of the MD process. The various MD solar systems are studied numerically using and including both flat plate collectors (the useful thermal energy reaches 3750 kJ/hr with a total area of 4 m2) and photovoltaic panels, each one has an area of 1.6 m2 by using an energy storage battery (12 V, 200 Ah). Therefore, the power load of solar AGMD systems is calculated and compared for the production of 100 L/day of distillate water. It was found that the developed system consumes less energy (1.2 kW) than other systems by percentage reaches 52.64% and with an average distillate water flow reaches 10 kg/h at the feed inlet temperature of AGMD module 52°C. Then, the developed system has been studied using TRNSYS and PVGIS programs on different days during the year in Ain Temouchent weather, Algeria.