نشریه علوم کاربردی و محاسباتی در مکانیک
سال سی و سوم شماره 2 (پاییز و زمستان 1400)

So far, many experimental researches have been done in the field of placing various inserts in the solar collector, but the effect of using the twisted tape insert inside the collector of a thermal photovoltaic unit (PV/T) isn’t done and for the first time in this research it is accomplished experimentally. Last researches were investigated to determine which type of twisted tapes had the highest efficiency. Meanwhile, ten types of twisted tape inserts were selected to evaluate. Due to the high cost of materials needed to fabricate twisted tapes, the evaluation of the ten twisted tapes was performed numerically. Therefore, in order to validate numerical modeling, an experimental apparatus was prepared to perform smooth tube experiments without / with a simple twisted tape. After validating the numerical model, numerical examination of ten selected twisted tapes (with different shapes) was carried out in the same conditions and the best one (with the highest efficiency) was selected. Finally, the best twisted tape insert was placed in the collector tubes (header-raiser model) of the PV/T system and its effect was evaluated using indoor experimental tests.

The nonlinear bending analysis of a composite beam reinforced by graphene platelets (GPL) nanofillers having nonuniform distribution through the thickness, is presented. Governing nonlinear differential equations are derived based on the first order shear deformation theory with the aid of minimum potential energy principle. The nonlinear differential equations are solved using harmonic differential quadrature method (HDQM). The modified Halpin-Tsai model is implemented to determine the effective Young’s modulus of graphene platelet reinforced composite (GPLRC) beams. Moreover, the rule of mixture is used for definition of the effective Poisson’s ratio. At first, conventional nanocomposite beams are studied for evaluation of the applicability of the proposed method for nonlinear bending analyses. Then for the beams reinforced by graphene platelets, the effects of some parameters including boundary conditions, number of layers, weight fraction and distribution pattern of graphene platelet on the nonlinear bending characteristics of the GPLRC beams, are investigated. This study shows the capability of the proposed method to solve the nonlinear problems and to get the beams behavior under bending loading. In addition, by increasing the weight fraction of graphene platelets in the beam, the bending strength of the beam improves and the beam deflection decreases. Moreover, increasing the number of layers for GPLRC tends to smoother variation of stress through the beam thickness.

In the present study, the effect of different projectiles on the carbon and glass fiber reinforced laminated composites is investigated experimentally and numerically. 8 samples of six-layers composite sheets with dimensions of 25×25 cm reinforced with glass and carbon fibers and epoxy resin3001 are subjected to low velocity impact. Also, spherical and semi-spherical steel projectiles of 680 grs weight and 55 mm diameters are used. Drop weight height of projectiles are supposed to be 1 and 1.5 m which leads to equivalent 6.7 and 10 J of impact energy. ANSYS and LSDYNA packages are used for numerical study. Results show that maximum deflection is occurred at the center of laminates for carbon and glass reinforced samples by the spherical projectiles. In addition, it is seen that deflection of carbon and glass laminated composites due to the impact of semi-spherical projectile reduces 18.7% and 34.3% respectively in comparison with the spherical projectile.

Due to the increasing importance of using clean and renewable energies, one of the simplest mechanisms for converting solar radiant energy into thermal energy, on non-industrial applications, is the use of solar air heaters, which has always been an attractive idea for researchers. Therefore, the present study investigates the effect of air gap on the performance of plane solar air heaters with two glass covers by means of numerical simulations. A similar study has not been yet reported in various research resources. For this purpose, the equations governing the forced convection flow of air passing through the heater duct and also the natural convection flow caused by the buoyancy force in the air gap between two glass covers are numerically solved by applying the finite element method and using COMSOL Multiphysics software. In addition, in order to determine the temperature field in the solid elements of the air heater (including glass cover, absorber plate and insulation layer), conduction heat transfer equations are simultaneously solved with the flow equations. The accuracy of the numerical simulations performed in this research has been evaluated by comparing those with the theoretical and experimental findings of previous researches, and an acceptable consistency and agreement has been obtained in this regard. The results demonstrate the desired effect of the presence of air gap between the two covers on the performance of plane solar air heaters, such that changing the air flow rate from 2 to 14 g/s, the performance of this type of air heaters at a radiant heat flux of 1000 W/m2 compared to the simple model (without air gap) has shown an increase in efficiency about 4 to 6 percent. Also, in the conditions of inlet flow rate of 9.6 g/s and radiant heat flux varying between 400 to 1200 W/m2, the use of two glass covers has increased the outlet air temperature about 2 to 6 °C, compared to the simple model.

In the present study, with the aid of computational fluid dynamics tools three different radiant tubes including straight, u-shape and w-shape were compared. After designing the geometry, the grids generated for geometries in Gambit software. Grid independence was also performed for the W-shaped geometry, which was the most complex geometry. Firstly, the results showed that the amount of nitrogen oxide emission in the U-shaped radiant tube is the highest compared to direct and W-shaped radiant tubes and the lowest was in the W-shaped type. W-shaped radiant tube had the highest efficiency (55.3%) among all radiant tubes. Besides, the ratio of radiant heat transfer from the tube wall surface to the total heat transfer from it in all three types of radiant tubes was high and more than 90%. By moving away from the wall of the radiant tube in all tubes, the amount of radiation per unit area decreases. Furthermore, the highest amount of radiation intensity was devoted to the W-shaped tube, then the U-shaped tube, and finally the lowest amount was related to the direct tube.

Space solar cells are usually made of gallium-arsenide and have many applications. Photovoltaic arrays generate stable and renewable electricity, which are mainly used in the absence of electrical transmission and distribution network. Similar to a layered composite, solar cells consist several layers such as glass layer, transparent layer, negative silicon layer, and positive silicon layer. The glass layer is one of the most important components of the solar cell, which is directly exposed to solar energy radiation and experiences many temperature changes during the day and night. Due to the different coefficients of thermal expansion of different layers, cracking of the glass layer is possible. The presence of one or more primary microscopic cracks in this layer and the extreme ambient temperature gradient will lead to the crack growth, resulting the failure or destruction of the glass layer, as well as improper functioning of the solar cell. In this research, crack growth in the glass layer is simulated by the extended finite element method and the effect of the length, location and angle of the initial crack as well as the thickness and dimensions of the layer are investigated. The results of numerical simulations reveal that among the above parameters, the dimensions of the protective glass layer have the greatest impact on the crack growth.