آرش میرعبدالله لواسانی

Scientists have always emphasized on reducing the temperature of solar cells and have used various methods with the aim of reducing the temperature of solar panels, because high temperature causes damage and various defects in the structure of photovoltaic panels. Among the effective and important researches that have been carried out on solar cells with the aim of reducing their temperature and increasing their efficiency, we can mention the radiation cooling method, which shows that the photovoltaic cell coated with a transparent layer is better than the bare solar cell. It is more efficient than any additional layer. In this study, the conventional (commercial) structure of the solar cell was compared with the coated structures in terms of optics and temperature. This comparison showed that the coated structures have higher efficiency than the commercial structure. In this research, three solar photovoltaic structures have been put together, which include 1- commercial (simple) structure, 2- solar panel with a PDMS layer, 3- solar panel with a PVB layer. Then to software research and simulation. The radiation and temperature properties of these three structures were discussed and by comparing them, it was shown that in the structures with PDMS and PVB, the layering temperature in terms of radiation intensity is reduced by about 5 and 9 K, respectively, compared to the commercial structure, which is an indication of the effect of cooling. The radiation of transparent polymer materials has on these two structures.

This numerical study examines the influence of a magnetic field and hybrid nanofluid on heat transfer in a microchannel. The microchannel with a square cross-section and dimensions of 0.5 × 0.5 mm, is situated within a cube-shaped piece. A heat flux of 3750 W/m2 and a constant magnetic field of 1 tesla, perpendicular to the flow, are applied. The research employs a hybrid nanofluid, with soybean oil as the base fluid and hybrid nanoparticles comprising 75% magnesium oxide and 25% aluminum dioxide, at a volume fraction of 1 to 4%. The laminar fluid flow is used, and the volume flow inside the microchannel is 0.01, 0.025, 0.05, 0.075, and 0.1 ml/s, respectively. The numerical analysis utilizes a single-phase model, and the finite volume method is employed to solve the equations. The results indicate that applying boundary conditions of forced convection with ambient air on the five sides of the cube-shaped piece can enhance the convective heat transfer coefficient by 8.3% to 50%, compared to the absence of force convection in the faces under certain conditions.

In this study, the cooling of a photovoltaic system with a concentrator is done with the help of a heat sink containing phase change materials and copper oxide nanoparticles using a numerical method. The photovoltaic module has a two-dimensional concentrator, and n-octadecane is chosen as the phase change material, and the mass fraction of copper oxide nanoparticles is 3 and 5%. The results of this research show that adding copper oxide nanoparticles with a mass fraction of 3% and 5% to the basic phase change material reduces the temperature of the solar cell from 191 o C to 185 o C and 180 o C, respectively.

In this study, the hydraulic-thermal performance of a semi-porous wave channel with nanofluid flow and applied magnetic field has been evaluated. The magnetic field is perpendicular to the channel. In this design, single-phase, incompressible and permanent nanofluid flow is considered. The ranges of Hartmann number and Darcy number are 0 ≤ Ha ≤ 10 and 10-5 ≤ Da ≤ 10-2, respectively. Magnesium oxide nanoparticles have been investigated in four different volume fractions (0, 2, 4 and 5%). The governing equations are solved by the finite volume method. Based on the obtained results, increasing the volume fraction of nanoparticles and channel wave improves heat transfer. At constant Reynolds number, increasing the number of wave channels from 4 to 6 resulted in a 7.8% decrease in thermal hydraulics. The increase in permeability in the porous medium has increased the Nusselt number and reduced friction. The best thermal hydraulic performance is 10.08 at Darcy number 0.01 and the lowest is 0.52 at Darcy number 0.0001. Also, the presence of magnetic field has a positive effect on thermal performance. The results of this study can be useful in the design of heat exchangers.

The purpose of this work is to investigate a different geometry in the parabolic collector in order to increase the thermal efficiency through simultaneous surface and volume absorption in a combined condition. Recently, it has been observed that if the inlet temperature is above 250 °C, Direct absorption collectors can increase efficiency up to 10% Considering that there is a direct relationship between the concentration of nanofluid and the diameter of the transparent tube carrying the fluid with the absorption coefficient, On the other hand, as the concentration of nanofluid increases, fluid sedimentation and system maintenance problems occur. In this research, the amount of nanocarbon used as a suspension of 0.02 gr/l in oil base fluid is considered. According to experimental data, this amount of nano carbon concentration completely absorbs light rays at a depth of 24 (mm) and this absorption coefficient has been used for this specific geometry of the collector. The results show that the rest of the radiation is absorbed on the surface using the central tube, so that the thermal efficiency is up to 6% compared to the usual copper absorption collector, which is about 19 degrees Kelvin.

In this present, two pairs of cable models were designed and tested to reproduce the induced vibration of stay cables in a wind tunnel. Cable of cable-stat stayed bridges are flexible structural members that have very low natural frequency and low intrinsic attenuation, Therefore, they are able to various vibrations such as wind vibration, wind-rain-induced vibration (RWIV), and earthquakes. Wind-rain-induced vibration has become one of the major concerns of bridge engineering. One of the ways to reduce the effects of wind and rain on cable bridges has been examined is cable aerodynamic specification and also one of the factors affecting the aerodynamics of the cable is the formation of rainwater flow on the surface of the cable. Therefore, spiral grooves were installed on the surface of the cable to direct this flow of water to the bottom of the cable. By testing two cable models (without grooves and with grooves) in the wind tunnel with artificial rain flow, the effect of different wind speeds, and also different yaw angles, it was concluded that by creating spiral grooves to The cable circumference can reduce the induced vibration caused by wind and rain, and the presence of these spiral grooves around the cable eliminates low-frequency currents and thus reduces the amplitude of the induced vibration.

Heat sinks have always played a crucial role in cooling electrical equipment. In this research, in a new approach, paraffin is used as a phase change material according to the suitable phase change temperature range with multi-wall carbon tube nanoparticles homogeneously in a heat sink. AnasysFluent software with finite volume method and PISO algorithm was used to model and solve the governing equations. The melting process of the PCM is numerically investigated in a three-dimensional space by applying three heat fluxes of 10,000, 20,000, and 30,000 watts per square meter, using the enthalpy-porosity method. According to the obtained results during the phase-change process, the addition of nanoparticles with volumetric percentages of 4, 6, and 8% leads to better performance in reducing the phase-change temperature. After the completion of the phase change process, increasing the volume percentage of nanoparticles does not always have a positive effect, and among the proposed options, nanoparticles with a volume fraction of 4% showed the best performance.This improvement is due to the increased conductive heat transfer in the PCM, resulting from reduced viscosity. Overall, adding 8% nanoparticles increases the total melting time by 15% compared to the pure PCM.

In this study, the heat transfer of nanofluids as single-phase, incompressible, laminar, permanent in a two-dimensional sinusoidal channel under the influence of a magnetic field with a porous medium is investigated. Alternating heat flux is applied to the channel walls. The governing equations are discretized using Fluent software with finite volume method (FVM) and velocity and pressure coupling is performed using SIMPLE algorithm. The Reynolds number range is 500 ≤ Re ≤ 200. Water is considered as the base fluid and magnesium oxide nanoparticles have been added to it. The volume percentage of nanofluid is 0.04. Nanofluid flow in 4 different Darcys (0.00001, 0.0001, 0.001, and 0.01) and magnetic field application in 4 Hartmann numbers (0, 4, 7 and 10) have been investigated. The results show that in all cases, with increasing Hartmann number, the heat transferred improves and the pressure drop increases. By increasing the Darcy number from 0.00001 to 0.01 under the same conditions (Reynolds 500 and Hartmann 10), the Nusselt number equals 4.392. Also, with increasing the Darcy number, the viscous resistance decreased and the pressure drop was always lower, so that the numerical pressure drop ratio was less than 1.

In this research, the thermal-hydraulic performance for non circular tube with louvered and flat fin in cross flow of the air at 70 ≤ ReH ≤ 350 were numerically investigated. The comparison of the thermal-hydraulic performance between louver fin and flat fin having cam-shaped tube has been carried out. Geometrical parameters of louvered fin such as louver length and louver angle and louver pitch are investigated. The results indicate that in the range of Reynolds testing, the thermal-hydraulic performance of cam-shaped tube with louvered fin 18.99 to 26% is more than circular tube with louvered fin. Investigation the geometrical parameters of louver fin reveal that by increasing the louver angle (15 to 25o) or louver length (6 to 12 mm), the thermal-hydraulic performance increases by about 1 to 8 percent. However, increasing the number of congresses (4 to 5) has a small effect on the thermal-hydraulic performance of the cam-shaped.

In this study, the aerodynamic performance of a high-speed train against a turbulent air flow is examined numerically from two approaches. First, using computational fluid dynamics, the parameters of aerodynamics and fluid flow are analyzed and then, using Multi-Layer Feed-Forward Neural Network (MLFFNN) Algorithm, a prediction and comparison with the obtained values from the CFD analysis are presented. To achieve this, using Reynolds-Averaged Navier-Stokes (RANS) method with 𝑘-𝜔 (SST) turbulence model, an incompressible turbulent air flow around a high-speed train model by OpenFOAM CFD Software is simulated. In this research, some of the significant and key parameters of fluid flow and aerodynamics as velocity, pressure, streamlines, flow structure, pressure coefficients, drag, lift and side forces for some yaw angles of wind movement and velocity changes are analyzed and compared. In the following, the Multi-Layer Feed-Forward Neural Network which is modified with various data is applied for prediction of the output of the problem. Accordingly, the aerodynamic drag, lift and side forces for the yaw angles of wind movement and velocity changes by this algorithm method are obtained and compared with the obtained results from CFD analysis. The comparisons indicate an appropriate similarity between the CFD data and the used MLFFNN one.

The purpose of this study was to investigate the effect of distance between glass cover and absorber plate, the height of the V grove in the absorber plate, The mass flow rate of the air inlet to the collector, on the energy and exergy efficiencies of a solar air collector with V grove absorber plate, by mathematical modeling. The heater is of dual pass type and its length, width and height are 2, 1 and 0.2 meters, respectively. The distance between the glass and the absorber plate is 12.5, 25, 50, 75, 100 millimeter, , respectively. The results show that by increasing the distance between the glass and the absorber, the thermal efficiency increases by 9 percent and the exergy efficiency by 30 percent. Also increasing the height of the V grove more than 10 cm will not cause significant changes in the efficiency of the first and second laws.

Today, electricity generation from photovoltaic panels is on the rise due to the reduction of fossil fuel resources and the problem of global warming. Because these modules are exposed to the outdoors, they are greatly affected by weather conditions. This study was conducted to investigate the effect of radiation intensity on the performance of photovoltaic panels in Tehran with different climates. The results show that the amount of radiation is linearly dependent on the panel output power and the panel surface temperature. The radiation in summer is 70% more than winter and the panel output power is 50% more in winter. The results show that solar air temperature can be used as a heating source from 8 am to 4 pm in winter and 7 pm in summer and can be used as a cooling source after such times. The measurement uncertainty and equipment measurement uncertainty were also found to be in the range (7.91% - 7.69%).

An experimental study was made to determine the effect of angle of attack on Hydraulic- Thermal Performance from a cam-shaped tube with constant heat flux in cross flow. Reynolds numbers based on an equivalent diameter are within 15500 < Re_(D_eq ) < 42000. Angle of attack is between 0 < α < 180 using air as fluid for cross flow. Results indicate that with increasing the angle of attack from 0˚ to 90˚ the mean nusselt number and drag coefficient increases about 7-13 and 114-122%, respectively. Drag coefficient and mean Nusselt number have been studied and the results demonstrate that in all Reynolds numbers the angles of 0˚ and 150˚ results in lowest and 90˚ results in the highest amount. A Hydraulic-Thermal comparison of the tube was made and the results show that the angles of 0˚ and 150˚ have the best performance comparing to other angles and the difference is about 31-125 %. Also angles of 0˚ and 150˚ are about 36-82 % better than a circular tube with equivalent diameter.

In this paper, the heat transfer characteristics of a cam-shaped tube with aspect ratios from L/D=1.35 to 3.74 in the crossflow of air have been experimentally investigated for two angles of attack, 0o and 180o. The Reynolds number varies in the range of 20000 to 46000 based on the equivalent diameter of a circular tube. One can conclude from the results that the best thermal performance was for L/D=1.35 at 180 degrees. The mean Nusselt number for this tube is 11% higher than that of a circular tube with equivalent diameter. For this tube, when the Reynolds number is 20695, the mean Nusselt number is 19.4% higher than that of a circular tube with equivalent diameter. And the lowest mean Nusselt number was recorded for the tube with L/D=3.74 at zero angle of attack. The mean Nusselt number for this tube is 21% lower than that of a circular tube with equivalent diameter.

An experimental study has been conducted to show the effect of aspect ratio on pressure drag of a cam-shaped tube in cross-flow of air. The aspect ratio varies between 1.35 ≤ L/D ≤ 3.13 and Reynolds number based on equivalent diameter changes in the range of 2.5×103 to 5.5×103. Studies were carried out at the angles of attack of 0 and 180 degrees. Results show that by increasing the aspect ratio, the drag coefficient decreases. The drag coefficient at the angle of attack zero degrees is about 54 to 82 percent lower than the circular tube with the same equivalent diameter. Also, the drag coefficient at the angle of attack 180 was about 42 to 82 percent lower than the circular tube with the same equivalent diameter. It was found that the cam-shaped tube with L/D=3.13 has a minimum drag coefficient which is about 82% lower than a circular tube with equivalent diameter.

This numerical study carried out to find the effects of wall geometry and fluid content of a sinusoidal corrugated channel of turbulent fluid flow on increasing thermal- hydraulic performance factor. The channel consisted of two zones namely, zone1 where the fluid pass through it, and zone2 where the fluid was trapped in the channel walls. . Air and TiO2-water Nano fluid were used as fluid in 1st and 2nd zones. Nano fluid was homogeneous, single-phase, with volumetric concentration of 1%. The upper and lower plates of the channel were heated with a constant heat flux of 616 W/m2. The Reynolds numbers of fluid flow of channel were 3700 to 40,000. The turbulent fluid flow in the 1st zone was simulated using the standard k-ε model. The effects of fluid type used inside the channel wall and wave angle and wave height were investigated. The results showed that when the TiO2-water nanofluid was in the 2nd zone and air passed through 1st zone, the channel performance was the best. The optimum wave angle is 35 degrees and produced the most thermal-hydraulic performance factor in 12000 to 40000 Reynolds numbers. With increasing wave height from 4 to 6 mm, the thermal-hydraulic performance coefficient increases from 65 to 110%. The effect of wave height on the increase of the thermal-hydraulic performance coefficient was more significant than the wave angle change.

The purpose of this study was to investigate the effect of surface changes to reduce the drag coefficient in a triangular array heat exchanger. Experiments were carried out in an open-circuit wind tunnel. The range of distance to diameter is between 2 to 4 and the Reynolds number is between 5.2×104 to 6.9×104. The diameter and length of the tubes are 41.5 mm and 42 cm, respectively. Tubes are made of copper. On each tube, 10 holes were created from zero to 180 degrees. The outer diameter of each hole is 3 millimeters.Shark skin is used as a surface accelerator. In these experiments, the effect of increasing the space ratio is studied. The results show that the coefficient of drag force decreases 14.5 to 25.4 percent for tube with shark skin. The greatest reduction in the drag coefficient is in Reynolds number 69920 and in the ratio of distance to diameter 2.

In this study, the variation of aspect ratio (height to width) and nanoparticles volume fractions of on natural convection heat transfer of Alumina-water nanofluid in enclosures was investigated. It is supposed that the nanofluid are applied as incompressible fluid and single phase base on water (as basefluid) include Alumina (Al2O3), with volume fraction (concentration) 0 - 4%, under laminar flow. Governing equations were solved numerically by finite volume method (Fluent). Rayleigh number is in the range of 4×105-108 in 2D enclosures with specific aspect ratios (0.6-3.2) and temperature difference. In the present work with due attention to the used models for the viscosity and the nanofluid coefficientof thermal conduction was showed that the Nusselt number of the nanofluid with more concentration, is increasing due to more viscosity and coefficient of thermal conduction rather than pure water. In other words the Nusselt number in every specific aspect ratio, in minimum of concentration equals 0.3% and in maximum of concentration equals 14% would be decreased. In a specific concentration, The Nusselt number was more related with aspect ratio rather than the coefficientof natural convection heat transfer and thermal conduction.

Since solar energy is known as one of the most important and renewable energy resources, increasing the absorption of solar energy plays significant roles in the effectiveness of thermal collector systems. This research aims to analyze empirically the function of direct absorption solar collectors with the use of graphene oxide nanoplatelets /deionized water. Weight percent’s of the graphene oxide in the deionized water are selected 0.005, 0.015 and 0.045. Collectors have been examined according to EN 12975-2 standard in various intern fluid temperature and with flow rates of 0.0075, 0.015 and 0.0225. Results show by increasing the weight percent of Nanofluid, collector’s performance is increased. Moreover, the maximum efficiencies of collector with the flow rate of 0.045 are determined 63.28%, 72.59% and 75.07%. This amount for the normal fluid is 58.25%.

Removal of fluid in solar energy for maintenance and environmental problems is an important issue in recent years studied and tested operation. This technology is known as direct steam generation technology (DSG). The boiling liquid absorbing power plants is problematic in this article to help nanofluid trying to be that the problem is less absorbent and improve performance. In this study, based on numerical calculations of heat transfer and thermodynamics that govern the major parameters affecting the efficiency of the power plant is built in two pure fluid and nanofluid is investigated. Using equations related to it (single-phase or two-phase fluid), temperature, quality of steam and heat transfer coefficient of fluid throughout the pipes have been investigated and the positive impact of added nanoparticles was concluded. By adding 0.05% nanoparticles of copper, copper oxide, silver oxide, titanium was found to boil water faster and heat transfer coefficient of around 12.5 percent.

Nowadays, the ever increasing demand to provide energy and the constant decrease of fossil fuels resources has made the usage of renewable energy resources vital. Solar chimneys are considered a significant approach to supply electricity. They are of particular interest due to the high absorption level of solar energy and also because of the advantages of using air as an absorber. However, these systems do not provide enough economic efficiency. Plant breeding in the collector’s section of a solar chimney was presented in this study as a mean to overcome the economical obstacles. Also possible geometrical and physical effects on air flow parameters were investigated by means of numerical simulation. Our simulation results were validated with comparison to the experimental model in Manzanares, Spain. Velocity as well as the temperature gradient at collector’s outlet was calculated. Our results showed excellent affinity to those of Spanish prototype as the error percentage was lesser than 5%. Vegetation layer was modeled as a porous media at the bottom of the collector and its possible effects was investigated on the air flow parameters at Ra = 1010. It was observed that due to the vegetation layer the velocity and temperature gradient at collector’s outlet were decreased 2.5% and 2%, respectively. These slight reductions show that plant breeding in large areas of collector’s bottom could be served as an outstanding idea to enhance the costefficiency challenges of solar chimneys while producing only negligible negative effects on air flow parameters.