محمد سفید

The target of this research is to investigate the amount of entropy production during natural convection inside a 2D chamber containing a non-Newtonian nanofluid using the lattice Boltzmann method. The chamber is exposed to uniform heat absorption/production and uniform and non-uniform magnetic field at different angles. The feature of the present work is to evaluate the effect of thermal radiation and the shape of the cavity cold wall in three shapes: smooth, curved and diagonal on the flow characteristics. Application in the design of electronic coolers and solar collectors is one of the practical cases of this numerical research. Acceptable agreement of the obtained results with previous related studies confirmed the validity of the presented results. Based on the results, the presence of radiation parameter leads to the improvement of heat transfer, which is more evident due to the increase of fluid power-law index. In addition to reducing the Nusselt value for enhancing the fluid power-law index, the effectiveness of the presence of the magnetic field in reducing the entropy and heat transfer rate enhances as the fluid power-law index decreases. It is feasible to attain the flow strength and the Nusselt value up to 40% and 61% more, respectively, by applying a vertical and non-uniform magnetic field. Although for heat production mode, there will be the lowest value of thermal performance index and the Nusselt value, the greatest influence of the magnetic field is observed in the heat production mode. By designing the wall in a smooth shape, in addition to increase the thermal performance coefficient, it is possible to decline the Bejan value.

In this research, by using the combined lattice Boltzmann and smooth profile method, for power law non-Newtonian fluidized bed, the effect of changing the geometric and fluid on the expansion behavior of the bed has been studied. Investigations have been carried out for 7 different geometries and 4 Newtonian and non-Newtonian fluids with a power law index of 0.8 to 1. The results of the bed with Newtonian fluid show more porosity than the bed with non-Newtonian fluid. Also, increasing the index of the power law caused an increase in the porosity of the bed, and the porosity of the non-Newtonian bed decreased with an increase in the density of solid particles and the initial height of the bed. Investigating the porosity ratio in the non-Newtonian bed showed that with the increase in the diameter of the solid particles, this ratio decreases and increases with the increase in the diameter of the fluid bed. In addition, comparing the results of the bed with carboxymethyl cellulose 0.1% solution as fluid showed that the effect of reducing the particle diameter in the bed, to increase the porosity ratio is 2 times more than the effect of increasing the diameter of the bed. Finally, the output of the model showed that the porosity ratio for the bed containing solid particles with different diameters is lower than the bed containing particles with equal diameters.

Today, solar desalination is one of the promising solutions for the problem of drinking water shortage, mainly in remote and low-population areas. In the present research, a solar still with passive external condensers was designed. To store the thermal energy in the basin of this solar still, paraffin wax was used in copper tubes as phase change materials. To compare and investigate the performance of the proposed solar still, a conventional solar still with the same specifications and dimensions was built and tested. Both solar stills were investigated on the days of 28 April, 5 and 9 May. The results of the experiments showed that the performance of the proposed solar still was better than the conventional solar still; the highest produced fresh water was 3.55 and 3.04 lit/m2 day, respectively, for the proposed and conventional solar stills, which showed a 17% increase in productivity per day. It is clear from past research that the condenser increases the temperature difference between the glass covers and the saltwater of the basin, but causes the temperature of the saltwater basin to decrease. However, in this research, in addition to the increase in the temperature difference between the glass cover and salt water, the amount of salt water also increased, and this trend of increasing temperature was observed until the end of the day in all three experiments, which shows the effective performance of paraffin wax in the basin of solar still.

In this research, a novel trigeneration system driven by biomass-solar energies has been investigated from energy exergy, economic and environmental viewpoints. The solar energy is used to produce hydrogen (by a PEM electrolyzer powered by thermal photovoltaic panels). To meet the intermittent nature of solar energy, it is used for hydrogen production. The hydrogen is used as fuel in the combustion chamber. The proposed gas turbine cycle consists of two high and low-pressure turbines and two compressors with an intercooler. A combined organic Rankine-vapor compression refrigeration cycle that uses the recovered heat from the gas turbine is used to produce refrigeration and air cooling in the interstage compressor. The obtained results provide that the combination of solar-based hydrogen production and biomass-based gas turbine leads to an increase in power production capacity. The proposed combined system provides an energy and exergy efficiency of 21% and 17% and the emission of 0.00884 kg/s of CO2. The highest capital cost rate among the components is attributed to the PEM electrolyzer, amounting to 15.44 $/hr, and the total cost of the products has reached 0.5627 $/MJ. Using an intercooler, the energy and exergy efficiencies of the system have increased by 6% and 4%, respectively.

The purpose of this analysis using lattice Boltzmann method (LBM) is to investigate the matter with which strategies can be used to control the amount of heat transfer and entropy formation. For this goal, the mixed convection heat transfer of non-Newtonian nanofluid under the impact of the magnetic field inside the square chamber containing the conductor wall has been analyzed. The results depicted that the flow characteristics and heat transfer are strongly affected by changing the position in these places. If the magnetic field is applied at the same location as the speed application position, the effect of increasing the Hartmann number in reducing the average Nusselt number becomes more evident. In order to have the highest value of Nusselt number, CASE3 should be considered, however, the greatest impact of magnetic field on fluid flow was observed for CASE2. By increasing the distance between the conductive wall and the moving wall, the average Nusselt number increases up to 1.5 times. By decreasing the thermal conductivity ratio from 10 to 0.5, the average Nusselt number decreases to about 55%. The entropy value has a direct/inverse relationship with the Richardson number/power-law index.

This study provides the energy, exergy, economic and environmental (4E) analysis of an organic Rankine cycle with the aim of producing power, hydrogen, and desalinated water with combined geothermal and biomass energy sources. In the proposed system, different heat exchangers have been used to increase the exergy efficiency of the system. Also, the cycle performance in both modes of with and without geothermal energy is compared. The results provide that the highest rate of exergy destruction is equal to 119.4 kW which is related to the boiler. Also, the lowest amount of exergoeconomic factor for the boiler is equal to 12.31%. The amount of produced hydrogen and desalinated water is equal to 1.58 lit/s and 15.15 kg/s, respectively. Moreover, with an increment in the temperature of the geothermal source from 125 to 160 C, the production rate of hydrogen and desalinated water are increased 30 and 18 %, respectively. In the case that geothermal energy is not used and all energy is supplied from biomass, the amount of carbon dioxide emission will increase by 68%.

The usage of multi-generation systems is quickly developing in recent years. The present study analyzes the energy, exergy, economic and environmental (4E) of a novel Rankine organic cycle to produce power, hydrogen and fresh water with a combined energy source of geothermal and heat recovery. Also, the cycle performance in both modes with and without geothermal energy is compared. Calculations show that the highest percent of exergy destruction is equal to 35% and is related to the PEM Also, the lowest amount of exergoeconomic factor is calculated for the PEM is equal to 8.39 The amount of hydrogen and desalinated water produced is 1.64 lit/s and 4.36 kg/s, respectively. With increasing the temperature of the geothermal source from 125 to 155°C, the amount of hydrogen and desalinated water produced are 29 and 17 percentage increases, respectively. If geothermal energy is not used and all energy is supplied by heat recovery, the amount of carbon dioxide emitted will increase to 69%.

Numerical simulation of multiphase problems with complex interface as well as high density ratios is one of the numerical challenges associated with particle scattering and divergence. Fewer problems have been performed with density-based smooth particle hydrodynamics (WCSPH) to solve complex joint surface currents, and most simulations have been performed using Incompressible Smooth Particle Hydrodynamics (ISPH). Solution of high density flows by the smooth particle hydrodynamics is associated with particle dispersion and divergence. Various methods have been used to eliminate the scattering of particles, such as a repulsive force at the interface or the corrected density re-value, but there is a problem of particle disintegration at the interface at higher times. In the present simulation, to simulate multiphase flows with complex surfaces and high density ratios, a new density-based smooth particle hydrodynamics approach has been utilized. To prevent the scattering of particles, especially at the interface at the end times, a simple method with the removal of incompatible particles is used. In the present study, the particle displacement optimization scheme for regularization at the interface of the phase is created by precisely implementing a two-stage change algorithm, so as to maintain the regular particle distribution continuously and conservatively. To examine the accuracy of the present simulation method, it is firstly compared with two-phase Poiseuille flow with three fluids having different values of viscosity, Reynolds-Taylor instability and single bubble rising in a fully filled container., Then it is compared with analytical and numerical solutions. The accuracy and consistency of the current simulation is higher or equal to other simulations.

In the present work the amount of entropy produced due to the conjugate heat transfer of power-law fluids during natural convection within the inclined chamber under magnetic field and heat absorption/production is investigated. Outcomes:1-The flow power,the amount of heat transfer and the entropy produced decrease with increasing Hartmann number, decreasing Rayleigh number and increasing the fluid power-law index.2-As the power-law index decreases,the influence of the magnetic field becomes more pronounced.The mean Nusselt number decreases by about 52% for shear thinning fluid and by about 18% for dilatant fluid by increasing the Hartmann number to the highest value.3-To achieve a current with higher power and higher average Nusselt number,the magnetic field can be used non-uniformly,especially TMF1. The larger the Hartmann number, the more pronounced the change in the type of magnetic field applied.The influence of the change in the type of magnetic field applied to the shear thickening fluid is minimal.4-As the thermal conductivity ratio increases, the maximum mean Nusselt number is obtained, in which case the impact of increasing the Hartmann number and the Rayleigh number becomes more pronounced.5-The minimum amount of heat transfer, current strength and magnetic field influence is obtained when the chamber is at an angle of +90 degrees,in which case the average Nusselt number is up to about 82% less than the zero angle.6-The Bejan number increases with increment of heat absorption/production coefficient,increasing Hartmann number, decreasing Rayleigh number and decrement of thermal conductivity ratio,and maximum the Bejan number is obtained at an angle of +90 degrees.

The purpose of this paper is to investigate the heat transfer and entropy generated due to mixed convection of hybrid nanofluid inside the lid-driven semi-oval chamber. The magnetic field is applied uniformly and non-uniformly. The simulation is performed by MRT-LBM and by writing computer code in Fortran language. Effect of Richardson number (0.1, 1 and 10), nanoparticles volume fraction (0-0.06), Hartmann number (0-60), inclination angle of the chamber (-90, 0 and +90 degrees) and type of magnetic field applied (uniform and non-uniform) on the flow formed in the chamber is evaluated. The results show that increasing the volume fraction of nanoparticles increases the flow strength, average Nusselt number, total volumetric entropy and Bejan number and most of the effect is observed for Richardson number 10 and inclination angle +90°. In all cases, increasing the Hartmann number decreases maximum values of streamlines and heat transfer, and this effect decreases with increasing Richardson number. By applying a magnetic field non-uniformly, it can change the flow strength by more than 80% and increase the heat transfer to 35%. Increasing the Hartmann number makes the effect of the non-uniform magnetic field more obvious, and the heat transfer has the largest share in the total volumetric entropy.

the flat solar heating transpired collector can be used for heat buildings and large spaces, industrial applications, and drying of agricultural products. The flow structure and convection heat transfer mechanisms are very important to the air performance of uncovered flat solar heating transpired collector. In these solar air heaters, the air is usually heated by a perforated absorber plate (metal). In this research, copper adsorbent plate has been used and numerical simulation has been performed for mass flow rate (0.007, 0.01, 0.0125, 0.015) kg/s. In order for the simulation to be consistent with the physical reality of the problem, the simulation is three-dimensional, non-continuous with a large computational range and continuous suction. Thermal efficiency, mass flow rate, and outlet temperature parameters were investigated. According to the obtained results, with decreasing mass flow rate, the temperature of the absorber plate and consequently the temperature of the outlet air increases; But increasing the temperature of the absorber plate is more than increasing the temperature of the outlet air. As the mass flow rate increases, the thermal efficiency of the flat solar heating transpired collector increases. The lowest efficiency in mass flow rate is 0.007 kg / s with 66.51 % and the highest efficiency in mass flow rate is 0.015 kg / s with 78.02 %.

In this study, energy and exergy for different parts of a 5 MWe direct steam generation (DSG) solar power plant was analyzed for Yazd city climate. It was observed that the most energy in the condenser and the most exergy losses occurred in the parabolic solar concentrator. To improve the efficiency of the concentrator, this study recommends to preheat the water entering the concentrator with one or more open preheaters in which the extractions of steam from turbine should be optimized by their pressures and mass flow rates. For different cases in which the cycle has up to 4 preheaters, the efficiency of the first and second laws of thermodynamics was investigated. In the case of 4 preheaters, based on obtained results, it was revealed that the efficiency of the first and second laws were 17.2% and 16%, respectively which was a significant increase compared to the case where the cycle had one, two or three preheaters. Therefore, according to the obtained results from the efficiency of the first and second laws as well as the irreversibility of power plant components, the cycle of the present article can be recommended for the city of Yazd.

In the present study, the entropy generated due to the conjugate heat transfer of the hybrid nanofluid inside the K-shaped chamber under magnetic field and uniform heat absorption/generation is investigated. The simulation was performed by writing computer code in Fortran language using the lattice Boltzmann method. Variations in Rayleigh number, volumetric fraction of nanoparticles, Hartmann number, heat absorption/generation coefficient, thermal conductivity ratio, chamber aspect ratio and type of magnetic field applied have been evaluated as the main variables of this study. The findings showed that the flow strength, heat transfer rate and entropy produced could be reduced by applying a magnetic field. A lower reduction of the average Nusselt number is achieved by non-uniform application of a magnetic field. Increasing the heat absorption/generation coefficient due to increasing the set temperature leads to decreasing the mean Nusselt number, which this influence increases with increasing the Hartmann number. Addition of nanoparticles to the base fluid in which the conduction of the phenomenon is predominant, increases the rate of heat transfer. Heat transfer is a function of the ratio of thermal conductivity and Rayleigh number that increasing these two parameters increases the convection effects, and in this case, the effect of increasing the Hartmann number is more pronounced. Increasing the chamber aspect ratio leads to a decline in the mean Nusselt number and entropy production, but the effect of adding nanoparticles is greater in this case. Entropy production decreases with increasing Hartmann number and increases with Rayleigh number and heat absorption/generation coefficient.

The purpose of this work is to investigate the effect of magnetic field direction on heat transfer of Newtonian and non-Newtonian fluids in both uniform and non-uniform forms, with the power-law model by using the multiple relaxation time lattice Boltzmann method (MRT-LBM) with written computer code by Fortran language. The natural convection is created in the two-dimensional cavity with lozenge barrier and is examined in three different temperature boundary conditions. The cold wall of the cavity is investigated in three modes: smooth, curved and diagonal. The results show that increasing the Rayleigh number and decreasing the power-law index and the Hatmann number increase the strength of fluid flow and heat transfer. The smooth design of the wall increases the average Nusselt number by about 30%. Placing the barrier at a constant cold temperature increases the average Nusselt number by 20% on average. The effect of the magnetic field is highest for the smooth wall and lowest for the diagonal wall and this effect decreases with increasing the power-law index. In general, an applied non-uniform magnetic field increases the average Nusselt number by about 10% and increases the flow strength. The effect of wall shape and type of magnetic field applied on shear thickening fluid is negligible. Further reduction of flow strength and average Nusselt number is observed by applying a magnetic field horizontally.

In the present study, a combined Lattice Boltzmann method-smoothed profile method is used for simulation of a liquid-solid fluidized bed with non-Newtonian Power-law fluids. The geometry is contained circular monodisperse particles in a cylindrical channel. The hydrodynamic model of the flow is based on the Bhatnagar–Gross–Krook Lattice Boltzmann method and the smoothed profile method is adopted to enforce the no-slip boundary condition at the liquid-solid interface. A numerical instance of a fluidized bed involving 416 particles is presented to demonstrate the capability of the combined scheme. The results for both Newtonian and non-Newtonian liquids have compared with the experimental results of other researchers. Porosity and bed height results of Newtonian fluid (water) compared with the Richardson-Zaki equation which was showed good correspondence. Non-Newtonian fluid results compared with the Yu equation for estimating minimum fluidization velocity and the Machač-Ulbrichová equation for porosity and bed height, yet by considering uncertainty in non-Newtonian equations results of comparisons are acceptable.

In the present work, the effect of magnetic field, changes in the angle of inclination of the cavity and the shape of nanoparticles on the flow field and heat transfer of water-alumina with uniform heat generation/absorption is investigated by Lattice Boltzmann method (LBM). The curved wall and the diagonal walls of the cavity are at a constant temperature of hot and cold, respectively. Nanoparticle volume fraction  of 0, 0.02 and 0.04, Hartmann number of 0, 15, 30, 45 and 60, heat generation/absorption coefficient of -5, 0 and +5 and inclination angle of 45, 135 and 225 degrees are studied. The high accuracy of the results compared to previous studies confirmed the correctness of the code written in Fortran language. The results shows that in all cases, increasing the Hartmann number leads to a decrease in the maximum value of the streamlines and the average Nusselt number, with the lowest effect at 225 degrees. Also increasing the strength of the magnetic field leads to an average decrease of 28, 23 and 7% of the average Nusselt number for angles of 45, 135 and 225 degrees, respectively. Increasing the heat generation/absorption coefficient is a determining factor in the effectiveness of the magnetic field and adding nanoparticles, and increasing it reduces the amount of heat transfer. On average, heat generation reduces the average Nusselt number by 71, 98, and 145 percent for the angles of 45, 135, and 225 degrees, respectively. In general, the lowest value of the average Nusselt number is related to the angle of 225 degrees, but the effect of adding nanoparticles in increasing the average Nusselt number is the highest at this angle. Generally, an increase in the percentage of nanoparticles leads to an average increase of 12% in the average Nusselt number. The effect of nanoparticle shape is more apparent with increasing their volume fraction. The highest amount of heat transfer is related to the cylindrical nanoparticles, in which the average Nusselt number is on average about 6% higher than the spherical state.

This study investigates a numerical analysis of the electroosmotic / pressure driven flow in Newtonian fluids. Laplace, Poisson-Boltzmann and Momentum two-dimensional equations are solved numerically in a rectangular microchannel using the smooth particle hydrodynamics method. In order to improve the smooth particle hydrodynamics method, an improved and well-behaved algorithm has been used to solve problems in microchannels. To validating the algorithm, the effect of the zeta potential and the applied pressure gradient parameters on the flow has also been researched and compared with analytical and numerical results. In the middle patch of the microchannel where there is an electric potential, the volumetric force caused by the electroosmotic flow affects the parabolic velocity distribution and this impact is discussed in this article. The effect of changing the zeta potential and pressure gradient on the flow has been shown as well. The results show increasing in the applied pressure gradient increases the share of the parabolic of velocity distribution in the velocity profile in the mixed region and the velocity distribution becomes flat parabolic, while increasing the zeta potential increases the velocity in the electric double layer and the velocity distribution takes the form of a horse saddle.

In this paper, the effect of shape and aspect ratio of wall on natural convection heat transfer of non-Newtonian fluid with power law model within two-dimensional enclosure in the presence of a uniform magnetic field by lattice Boltzmann method (LBM) is investigated. The left wall is at a constant hot temperature, while the right wall is kept on cold constant temperature and other walls are considered adiabatic. In this simulation, the flow field and temperature are calculated by simultaneously solving the flow and temperature distribution functions. The effect of various parameters such as Hartmann number, aspect ratio, different shape of the wall and power index of non-Newtonian fluid is investigated. The results show that increasing power index, aspect ratio and Hartmann number decrease the average Nusselt number. Also, the highest amount of heat transfer is generally associated with the case of a triangular wall. In addition, increasing the power index reduces the effect of the magnetic field.

The present study numerically investigates the feasibility of using multiple dielectric barrier discharge multi-DBD plasma actuators inside the surface of geometry as a novel approach for active flow control over a large vertical axis wind turbine. For this reason, the plasma actuator is modeled based on Suzen Model and the results are validated. Then, a computational study is carried out on a commercial large scale vertical -axis wind turbine to examine the effect of the presence of the plasma actuator. The 530G vertical-Axis wind turbine is used as the baseline case. The plasma actuator was applied inside the surface of the blades of turbine and on all their surfaces in a sequential and simultaneous way. Plasma actuator is one of the newest devices in flow control techniques which can delay separation by inducing external momentum to the boundary layer of the flow. It is revealed that the use of multi-DBD actuators could enhance the induced velocity; this affects the pressure distribution and increases the aerodynamic torque. Consequently, an averaged power increase of 3 % was achieved. Possibility of increase in wind turbine power even in a commercial scale large turbine has been proved by flow separation control using the plasma actuation technology. In addition, the application of the plasma inside the surface of the blades will not effect on its performance.

In this paper for the first time, the effect of direction of wall movement on mixed convection in circle quarter porous enclosure with heat absorption/generation is investigated by LBM. The magnetic field is applied to the enclosure in uniform and periodic forms. Mixed convection is caused by the movement of walls at different angles. The results show that increasing the Richardson number, Hartmann number, heat absorption/generation coefficient and decrease the porosity coefficient reduce the average Nusselt number. With fixed all parameters the maximum value of the average Nusselt number is related to the 90 ° velocity angle, in which case the average Nusselt number is about 25% higher.  Increasing the Richardson number reduces the effect of the magnetic field. Periodic applied of a magnetic field results in about 30% more than uniform applied. Increasing the porosity coefficient also increases the effect of the Hartmann number and the angle of wall movement. It is observed that the simultaneous increase of the heat absorption/generation coefficient and the Hartmann number lead to a further decrease of the average Nusselt number.

In this study the strongly coupled method (two-way fluid structural interaction (FSI)) is presented to simulate the membrane wings used in ultralight aircraft. In the present study, numerical modeling is performed by commercial software ANSYS using two separate solvers one for fluid and one for structure. Unlike the one-way method, the two-way coupled method, membrane wing deformation is considered at each time step, which increases the accuracy of the simulation. The membrane wings are made of fabric covering on the naca 2418 plan. fabric is considered to be orthotropic and non-porous. Influence of angle of attack, Young's modulus and thickness of fabric on the aerodynamic coefficients and membrane wing deformation were investigated. All simulations were performed at Re=100000. The results show that increasing the Young’s modulus from 180.25 to 270 MPa reduces the maximum membrane displacement in X and Y direction by 81% and 78%, respectively. Increasing the fabric thickness from 0.4 to 0.6 mm also reduced the maximum displacement of the membrane wings in the X and Y directions by 85 and 80%, respectively.

In the present study, mixing of two fluids of different viscosities in a micro channel with an oscillating curved stirrer was simulated by MRT-LBM and the effect of geometric shape, oscillating speed and amplitude and viscosity logarithmic ratio on mixing efficiency was analyzed. Most researches in this field have studied the mixing of two same fluids but the mixing makes sense when two miscible fluids have different properties. Also in these researches, stirrers in micro channel are considered cylinder or rectangle shape. In this study, a curved stirrer was used for mixing two fluids of different viscosities in micro channel for the first time. The simulation was performed at Re=80 and Sc=10 and NASA/LANGLEY LS(1)-0417 (GA(W)-1) airfoil shape was used for curved stirrer. At the study of geometric shape, results showed that mixing efficiency of two fluids of same and different viscosities in micro channel with oscillating curved stirrer was higher than micro channel with oscillating rectangle stirrer. The results of stirrer oscillating amplitude and velocity survey revealed that increase in Strouhal number causes increase in mixing efficiency on studied oscillating amplitude and Optimum efficiency is on oscillating amplitude 0.5 on all studied Strouhal numbers. Also mixing efficiency decreases with increase of viscosity logarithmic ratio on studied Strouhal numbers and this decrease is noticeable in high Strouhal numbers.

The aim of this research is the simulation of multi-layer flows of the core-annular type in a 2-dimensional channels, in which the Newtonian fluid in the core is surrounded by a viscoplastic fluid of the regularized Bingham type as a lubricant. This simulation is based on the volume of fluid technique and in the mixing regions of the two fluids, the stress is achieved by harmonic interpolation. Flow and concentration equations are discretized spatially by spectral element method. The velocity correction scheme, as a high order algorithm, is developed for splitting the velocity and pressure variables for the viscoplastically lubricated two phase flow. Applying the developed flow considerations leads to a nonlinear equation in the plastic region of the flow, which is solved numerically and is called semi-analytic solution. This solution, along with previously published works, is used to validate the spectral element results. The effect of the main parameters of the flow, i.e. Bingham number, viscosity ratio and core thickness on the pressure drop and un-yielded region thickness is evaluated. The results show that, for constant Reynolds number, the Bingham number is the most effective parameter on the pressure drop and un-yielded region thickness, respect to the core flow thickness and viscosity ratio. Also the profiles of secondary variables, including apparent viscosity and shear stress, across the channel section is presented and show that in the interface of the fluids, there is a difference between numerical and semi-analytic solutions due to the mixing of the two fluids.