mohammadjavad maghrebi

One of the most important sources of renewable energy is wind energy. We can harness the kinetic energy of the wind by using wind turbines. One of the fundamental problems with Savonius wind turbines is their low efficiency due to direct wind impact on the returning blade and applying negative torque to it. One new and cost-effective method to increase the efficiency of these turbines is to use a deflector upstream of the flow to prevent wind from hitting the returning blade and producing negative torque. Due to the cylindrical geometry of the deflector, it cannot guide the flow at an arbitrary angle. Additionally, a relatively large vortex region will form downstream of the deflector and near the turbine, which will have undesirable effects on turbine performance. These vortices can be controlled by installing flow splitter blades on the deflector. This study used computational fluid dynamics techniques in a two-dimensional simulation with Ansys Fluent software. Initially, a cylindrical deflector without flow splitter blades was designed and its simulation results were validated with previous experimental research. Then, as an innovation, a splitter blade was installed at a desired angle and directed flow towards the advancing blade of the turbine. The simulation results show that using a deflector with splitter blades at an angle of 5 degrees increases the turbine power coefficient by 23.4% compared to its state without a deflector at a tip speed ratio of 0.6.

In this paper, graphene nanoplate was stabilized in a water-based fluid by sodium dodecyl sulfate as a surfactant. The prepared nanofluid in weight percentages of 0.01 -0.145 was placed in a gasket plate heat exchanger in the presence of cold fluid (deionized water). All experiments were performed for laminar flow in the range of Reynolds numbers of 500-1500. The effect of flow rate and concentration of nanofluid was investigated on the overall coefficient of heat transfer and pressure drop. The concentration increase causes both to increase at the same time. As a result, heat exchange efficiency and thermal effectiveness of the nanofluid were also analyzed. The highest thermal effectiveness (89%) and efficiency (1.244) occur at a minimum flow rate (2 liters per minute) and maximum weight percentage (0.145) Taguchi method was used to find the optimal conditions and confirm the validity of the experiments. It was also found that the decrease in the flow rate (98.56%) has a greater effect on the results of thermal effectiveness than the increase in concentration (0.404%). The error rate was 0.018%, which shows the accuracy of the results.

With the advent of morphing airfoils, the aerodynamics of wind turbines and wings underwent many changes. In this study, the aerodynamic coefficients of morphing airfoil based on NACA 0015 are optimized in the range of Reynolds number 105 to 106 and the angle of attack 0 to 12 degrees using Artificial Neural Network (ANN) and Genetic Algorithm(GA). First, the airfoils were created in MATLAB software by random control points and mesh generated in Gambit software, then in two-dimensional Ansys software were simulated. The simulation results, including lift and drag coefficients, separation point and pressure center, with control points were used to train the Artificial Neural Network (ANN). The trained function is given as an input function to the Genetic Algorithm(GA) to optimize the desired coefficients.Lift coefficient, the center of pressure, separation point and lift to drag ratio were optimized as a single objective, In single-objective optimization, the lift coefficient was increased by 18% using the morphing airfoil. Also, the lift coefficient and the center of pressure, the lift coefficient and the drag coefficient were optimized as the dual-objectives optimization. In the optimization of the dual objectives, lift and drag coefficients were controlled by 0.8 and 0.03, respectively, by the morphing airfoils.

With the advent of smart materials in recent years, the aviation industry and airfoils have undergone many changes. Research into the use of smart materials in aircraft wings to increase their performance and then the use of smart materials in wind turbine airfoils has begun. In this study, computational fluid dynamics and URANS equations for a three-bladed Darrieus wind turbine equipped with a morphing airfoil was used to determine the optimum blade cross-section. 250 airfoils were generated by random control points, in Gambit software, they were unstructured and generated as a sliding mesh then they were simulated in 2D Ansys using the k-ω SST turbulence model and PISO algorithm. Control points and power coefficient were used for Artificial Neural Network (ANN)training and the Genetic Algorithm(GA) was used to optimize the power coefficient. In this study, the base airfoil is NACA0015. The results of that have been very effective. For the first case (Determine the optimal cross-section of the turbine at a full round) the power coefficient of Darrieus wind turbine with the optimal cross-section increased by 42%, and the blade section(airfoil) was also drawn. For the second case(Determine the optimal cross-section in each of the four zones of the rotor), the most efficient sections(airfoils) in four-zone were obtained, increasing the turbine power coefficient by 60% was the result of this optimization.

This article reports an experimental study of heat transfer characteristics of multi-walled carbon nanotubes (MWCNTs). These nanofluids, consisting of water with different weight concentrations of nanofluid (0.0.1–0.145% wt.), have flown in counter flow plate heat exchanger under turbulent conditions (the range of Reynolds numbers 2500-6500) for cooling applications. The nanofluid was prepared by dispersing MWCNT nanoparticles in the presence of sodium dodecyl sulfate (SDS) and water as base fluid. The results showed that the convective heat transfer coefficient (HTC) of nanofluid was higher than that of the base fluid at an equal mass flow rate and inlet temperature. The heat transfer coefficient of nanofluid increased by mass flow rate and temperature rising. Also, the heat transfer coefficient and the concentration of MWCNTs nanofluid showed a positive association at the same temperature.  At a constant weight concentration, the heat transfer coefficient increased when the Reynolds number increased. The slope weight concentration tended to rise as the heat transfer coefficient growing. The increase in Reynolds numbers (or mass flow) was less than the increase in the concentration of carbon nanotubes. According to the performed experiments and software analysis (QUALITEK 4), the heat transfer coefficient and concentration both multiplied at the same time. But there was an inverse relationship between the heat transfer coefficient and flow rate.

Heat transfer enhancement is widely applicable in various industries, specifically in heat exchangers. Optimizing of heat transfer in the absence of increased pumping energy will result in increased of total efficiency in different systems. In this paper, forced convection heat transfer and fluid flow of fully developed laminar regime in a horizontal tube under uniform and non-uniform step heat fluxes is investigated experimentally. The effect of uniform, non-uniform increasing and decreasing applied heat fluxes on heat transfer and fluid flow are investigated. The effect of various parameters on heat transfer and fluid flow characteristics in these models are reported. Uncertainty analysis is performed and acceptable maximum of 1.8 percent is acquired. The primary results compared to well-known Shah and London equation for validation and maximum error of 8.5 percent is reported. In the present paper, Energy and exergy are two approach of analyzing. Convection heat transfer coefficient enhancement of 19.3 and 22.3 percent compared with model 1 are reported for model 2 and 3 respectively, in energy analysis. Furthermore, in this paper, exergy analysis is done and irreversibility values of 0.0887, 0.0803 and 0.1037 are reported for model 1, model 2 and model 3 respectively. Finally, it is concluded that the model number 3 is the best way to enhance heat transfer because of the maximum averaged Nusselt number and the minimum entropy generation values

In this paper, multi-wall carbon nanotubes (MWCNTs), gold nanoparticles (GNp) and glucose oxidase (GOD) was developed for the specific detection of glucose. MWCNTs were chemically modified with the H2SO4–HNO3 pretreatment to introduce carboxyl groups which were used to interact with the amino groups of poly(allylamine) (PAA) and cysteamine via 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide/N-hydroxysuccinimide cross-linking reaction, respectively. A cleaned Pt electrode was immersed in PAA, MWCNTs, cysteamine and GNp, respectively, followed by the adsorption of GOD, assembling the one layer of films on the surface of Pt electrode (GOD/GNp/MWCNTs/Pt electrode) and was used as working electrodes (anode) along with a platinum auxiliary electrode and the reference electrode Ag/AgCl (cathode). Working electrode was containing the Phosphate-buffered saline (PBS) with PH = 4, 6 and 8 enzyme. Glucose concentration and PBS pH design has been tested and analyzed by QUALTEK-4 software measure. According to the performed experiments and software analysis, with increasing concentration, the flow rate of current production is increased and pH deviance from neutral range reduces the flow. Optimal conditions was obtained in concentrations 1 mmol/lit and pH =6, respectively. After confirmation tests in optimum conditions, the rate of production was obtained, 21.67 mA, which with respect to the expected error rate of application, it was calculated to be 8.1% . This error rate demonstrates that the accuracy of tests is with high sensitivity and accuracy.

In this study, the self-starting of a Darrieus vertical axis wind turbines (VAWT) is enhanced using a J-Shaped airfoil profile. The paper investigated the performance of VAWT with the J-shaped blades. Since the J-shaped blades utilize the lift and drag forces simultaneously, the turbine performance at low tip speed ratios (TSRs) enhances. Thus, it is expected that using these blades improves the starting torque and output power. The main goal in this study is to find an optimum J-shaped profile acquiring the best performance of wind turbine. For this purpose, a 3kW J-Shaped straight-bladed Darrieus type VAWT is investigated numerically using OpenFOAM computational fluid dynamic package. It employs the finite volume method to solve the Navier-Stokes equations. The J-Shaped profile is designed by means of eliminating a fraction of pressure side of Du 06-W-200 airfoil. The results indicate that the performance of turbine is optimized for J-shaped profile which eliminates the pressure side of airfoil from the maximum thickness toward the trailing edge. Moreover, employing this J-Shaped profile, the wind turbine performance is intensified TSRs and self-starting of turbine is improved.

The prediction of distillation zone is very important in steam turbine blades and steam nozzles. In identification of distillery with equilibrium method, as the steam flow contacts the two-phase dome, the second phase formes and flow properties will pass the distillery without any jumping, therefor after crossing the saturation curve, the droplet formation transpires, but in non-equilibrium method by a sudden increase in pressure, called “condensation shock” a discontinuity in the flow characteristics is seen and after crossing the saturation curve, the formation of droplets starts. In this paper, numerical analysis of a vapor-liquid two-phase transonic flow in a convergent-divergent nozzle with and without shock is investigated. Effects of stagnation temperature at nozzle inlet, viscosity and geometry is studied using thermodynamic equilibrium and non-equilibrium methods and results compared with experimental datas. Roe numerical method is used for vapor-liquid two-phase flow numerical solution. The main properties of the flow at the boundary of elements is extrapolated by MUSCL third order acuracy and time discretization is performed using Lax-Wendroff explicit two-step method of second order accuracy. It is observed that the results of non-equilibrium solution, has more correspondence to experimental results and Condensation starts earlier in the nozzle with further expansion rate. By increasing the temperature at nozzle inlet, the place at which condensation starts goes forward. Also in comparision with non-viscous flow, the shock location in viscous flow comes closed to the throat.

A steady two-dimensional laminar free convection heat transfer from a cold horizontal isothermal cylinder located above an adiabatic floor is studied both experimentally and numerically. In the experimental measurements the effects of cylinder distance from horizontal floor to its diameter (L/D) on heat transfer coefficient is studied for Rayleigh numbers of 3×105 and 6×105. Computations are made using OpenFOAM (an open source) code for wide range of Rayleigh numbers from 104 to 106 and comparisons are made with the corresponding experimental measurements. Flow stream lines and isothermal lines are plotted for different cylinder relative positions. Results indicate that cold plume flows downstream and strikes to the horizontal floor and moves horizontally away from cylinder over the horizontal floor. The finite space between cylinder and floor makes the flow different from those cylinders surrounded by an infinite medium. Results also indicate that variation of average heat transfer coefficient of the cold cylinder is highly affected by L/D. A new correlation for estimation of convection heat transfer for a single horizontal cylinder placed over an adiabatic floor is also developed.

In this paper, the thermo-hydrodynamic analysis of incompressible fluid flow in conjunction with cell-centered finite volume-lattice Boltzmann method is developed. To demonstrate the temperature field, the double distribution function model was used. Since, instability is the most severe problem of the thermal lattice Boltzmann methods to handle flows; a stable and accurate cell-centered scheme is presented. For this purpose, the pressure and temperature based upwind biasing factors are used as flux correctors. Also, additional lattices at the edge of each boundary cell are introduced, which allow a much better description of the actual geometrical shape. The unknown energy distribution at the boundary cells were decomposed into its equilibrium and non-equilibrium parts. This treatment enlarges the domain stability and leads to faster convergence. In addition of calculating numerical viscosity, The method is applied to two dimensional incompressible thermal plane duct flow. The results show a very good accuracy and agreement with the exact solution and previous numerical results.

In this paper, a viscous flow simulation is presented using the Lattice Boltzmann Equation (LBE). A finite volume approach is adapted to discretize the LBE on a cell-centered, arbitrary shaped, rectangular tessellation. The formulation includes upwind scheme and high order descretization schemes for the flux term and collision operator respectively. A consistent open and solid boundary treatment according to cell-centered scheme also addressed, which resulted in a wider domain of stability and faster convergence. Validation of the results is conducted by symmetric sudden expansion. The results are compared with reliable analytical or experimental results, indicating the accuracy and robustnes's of the proposed method for analyzing different flows of the interest.

Linear stability analysis of the three dimensional plane wake flow is performed using a mapped finite di?erence scheme in a domain which is doubly infinite in the cross–stream direction of wake flow. The physical domain in cross–stream direction is mapped to the computational domain using a cotangent mapping of the form y =? cot(??). The Squire transformation [2], proposed by Squire, is also used to relate the three–dimensional disturbances to the equivalent two– dimensional disturbances. The compact finite di?erence scheme of Lele [3] and the chain rule of di?erentiation are used to solve the Orr Sommerfeld equation. The results of linear stability analysis indicates that streamwise and the span- wise component of velocity eigenmodes are antisymmetric and the cross stream velocity eigenmode is symmetric. This is consistent with the DNS requirement of plane wake flow pertaining to solvability conditions[5]