جستجوی مقالات مرتبط با کلیدواژه « Numerical modeling » در نشریات گروه « مکانیک »

In the membrane humidifier, the characteristics of the membrane as the heart of the humidifier and the selection of Nafion as the most common membrane for use in the process of separating two wet and dry streams have a great impact on its performance. In this study, a numerical and three-dimensional investigation of a flat membrane humidifier including the dry flow channels, membrane, wet flow channels and plates on the two sides of the membrane has been investigated by Ansys Fluent software and the effect of membrane characteristics including: thickness, permeability and porosity coefficient on the mass (water) and heat transfer through the membrane and as a result the performance of the humidifier has been investigated. The results show that the use of Nafion 111 due to its lower thickness compared to Nafion 115, 117 and 211, leads to improved heat and mass transfer and therefore improves the performance of the membrane humidifier. Considering the dew point which shows the simultaneous effect of mass and heat transfer; increasing the permeability coefficient of the membrane from 10-15 to 10-21 square meters, the dew point temperature at the outlet of the dry side increases by about 3.5K. In the common limits of the porosity coefficient of common commercial membranes, the change of the porosity coefficient does not have much effect on the performance of the membrane humidifier.

Humidification of polymer membrane fuel cell (PEMFC) reactant gases is necessary for keeping the membrane humidified. Planar membrane humidifiers are widely used for reactant gas humidification due to their proper performance, simple structure, and long life span. In this study performance of a planar membrane humidifier with symmetrical L-shaped obstacles in both channels is investigated numerically by ANSYS fluent and its performance is compared with a simple planar humidifier. The Effects of geometrical parameters are studied by 3D numerical modeling. Accordingly, two parameters of water recovery ratio (WRR) and dew point temperature at the dry channel outlet are considered the main performance criteria. Results show performance decreases with the increase of the gasses mass flow rates. Dry gas outlet temperature noticeably increases by the L-shaped obstacles insertion which indicates better heat transfer. The effect of four geometrical parameters of the obstacle consisting of obstacle length, height, the distance between the obstacles and the top and bottom of the channels, and their relative distance are investigated. Three values are considered for each geometrical variable, and the distance between the obstacles and the membrane exhibits more influence on the performance of the humidifier. The geometrical study improves the performance of the obstacles and raises the WRR and the dew point temperature by about 3% and 3.5 degrees, respectively.

In this study, effects of dielectric barrier discharge (DBD) plasma on aerodynamic flow are investigated around NACA 0012 airfoil for plasma placement according to horizontal position close to leading edge based on 2%, 6% and 10% of the chord length with 20 mN/m plasma momentum and a Reynolds number of 106 using 2-D aerodynamic flow simulations. A user-defined function (UDF) source code is developed for application of plasma discharge in this work. Obtained results show that application of plasma actuator results in delay of stall from 15 degree to 18 degree angle of attack (AOA) and aerodynamic efficiency toward higher AOAs (from 8 degree to 10 degree); where plasma placement close to separation region (according to 10% of chord length) has more aerodynamic efficiency compared to smaller AOAs. However, aerodynamic efficiency of 10% placement plasma is decreasing compared to plasma placement closer to leading edge for operation of higher than 10 degrees AOAs. In addition, positive capability of plasma actuator is investigated for wide range of Reynolds number, where plasma actuator results in improvement of aerodynamic efficiency equal to 16%, 18.9% and 70.2% in optimal AOA for Reynolds number of 105, 106 and 107

Composite shells are widely used in various industries due to their low weight and high strength. Designing these structures involves various engineering analyses, and one of the most important studies is the investigation of the buckling of shells under axial load. The aim of this research is to investigate the vibrational correlation method on composite cylinders with delamination defects. Delamination defects can occur in structures under different conditions and have a significant impact on the strength of the cylinder. Therefore, in this study, different dimensions and quantities of delamination defects in various specimens were examined using the vibrational correlation method. Carbon fibers of type T300 were used as the reinforcement material, and the epoxy resin LY556 was used as the matrix. The hardener and accelerator combined with the resin in this research are HY917 and DY70, respectively. The layer stacking in the specimens was done with angles [55 90 90 55] using the filament winding method, and artificial delamination defects were created between layers 2 and 3 using Teflon sheets. The manufactured specimens were subjected to modal testing under various compressive forces, and then the critical buckling load of the specimens was obtained using the modal testing method. Using numerical modeling software, critical buckling loads and natural frequencies were calculated for various axial compressive loads through linear and nonlinear analysis. These numerical results were compared with experimental results. The vibrational correlation method accurately predicted the critical buckling load in defect-free specimens with a 3% error, but its accuracy was significantly

The polymer membrane fuel cell, which works with hydrogen and air and has high efficiency and power density, low-temperature operation, and the ability to start quickly and without pollution, can be a good alternative to fossil fuels. The performance of a proton exchange membrane fuel cell is highly dependent on the geometry, flow channel configuration, and size. In the current research, which is a numerical study, the performance of the polymer membrane fuel cell has been investigated by relying on the design of gas injection channels with different geometries in an unsteady state. The computational fluid dynamics method has been used to solve the governing equations. In this method, the finite volume method is used to discretize and solve the equations. Different geometries have been used for this research, including pseudo-spiral (model A), parallel (model B), and pin (model C), whose dimensions are the same as the spiral base model. Using dynamic simulation, it was observed that after about 70 seconds, the flow reached a stable state, and water production gradually increased. The results show that model C performs better than other models, and model B shows the worst performance.

In this study, the effects of a cavity on the pitching characteristics of NACA0012 airfoil under dynamic stall conditions were examined numerically and the transient incompressible turbulent flow was simulated in two dimensions. Two different sets of circular cavities with R=0.05c were set at two different positions of x=0.13c and x=0.6c from the leading edge (LE) to investigate the effect of cavity position on the aerodynamic parameters of the airfoil such as lift, drag, and pitching moment coefficients as well as aerodynamic efficiency (lift to drag ratio), using Re=106 and reduced frequency of kf=0.15. Results indicated that the cavity at distant location from the airfoil LE showed a better performance in improving the lift coefficient along with aerodynamic efficiency of the pitching airfoil and the averaged values of the lift coefficient for cavities at x=0.13c and x=0.6c locations increased by 3.57% and 0.18%, respectively compared to the baseline. The averaged value of the drag coefficient for the cavity located at x=0.6c decreased by 3.25% and for the cavity at x=0.13c went up by 3.97% in comparison to the clean airfoil.

In this study, we combined the experimental work performed using a one-dimensional simulation program to simulate the capacity of a solar cell. Simulation can be used to show the real effects of a phenomenon on the target subject, under controlled and regulated conditions.In this here, CdTe based thin film solar cell has been investigated under AM 1.5 ghobal spectrum with using Solar Cell Capacitance Simulator-1D (SCAPS-1D) software. Initially, solar cells with nanostructured FTO/TiO2/n-CdSe/p-CdTe were considered as the elementary cells and FTO/ TiO2/n-CdSe/p- CdSe1_xTex/p-CdTe as the upgraded cells. The purpose of this study was to investigate the key role of layer CdSe xTe 1-x. The results of the analyzes showed that the presence of CdSe xTe1- x nanostructured layer, between p- type CdTe absorber layer and n- type CdSe layer increased PCE from 14.05% to 21.98%, JSC from 20.42. mA/ cm2 to 26.06 mA/cm2, FF from 54.73% to 57.69% and VOC from 1.25 V to 1.46 V compared to the elementary cell.

With the help of mathematical models, complex hydraulic conditions and especially the presence of two-phase flows over spillway chutes can be simulated in three dimensions with acceptable accuracy. By establishing different flow flows, the possibility of vacuum generation in this structure can be examined. In the present study, the possibility of cavitation and cure on the service spillway of Aghchai dam using numerical methods in Flow-3D software is evaluated. The flood flow regime has 4400 and 1065 cubic meters per second rate, which is provided by the project consultant. The free flow level in this model is calculated by volume of fluid (VOF) method. The results of flow simulation at a flow rate of 4400 cubic meters per second show that cavitation is very likely to occur at the ogee and the angle change of the chute channel where should be prevented by taking some actions. However, in lower flows, such as 1065 cubic meters per second, due to lower speed and lack of separation of flow from the bed, the occurrence probability of vacuum generation is low and not very significant. The results obtained are in good agreement with the results of the project consultant.

Adsorption desalination system employs low temperature waste heat, which is available in renewable energy sources. A three-dimensional transient model has been developed for modeling heat and mass transfer in adsorbent bed silicagel/water pair and validated by the experimental results. Evaporator is one of the main adsorption desalination parts and in this study, the effects of shell and tube evaporator pipe lenght on the performance ratio (PR) and specific daily water production (SDWP) are numerically investigated. According to modeling results, it was found that the performance ratio increases by increasing the evaporator pipe length, while aproaching 0.66. SDWP has an optimum cycle time for each evaporator pipe length, which increases with increasing the evaporator size. However, it was also found that the SDWP remains almost constant for evaporator pipe length larger than 4m. Specific daily water production increases by 11% for the pipe length increase from 2m to 4m, while it only increases by 6% when the pipe lenght increases from 4m to 8m.

In this paper, the performance of a diaphragm dosing pump of the injection odorizers is simulated with the fluid-structure interaction analysis. The simulation results are validated with experimental data and the largest relative error is 16% for the average flow rate. Performance simulation of the diaphragm pump for the diaphragm oscillation period of 1 second and three different diaphragm displacement amplitudes of 0.8, 0.5, and 0.2 mm, shows that as the amplitude increases, the fluid velocity and consequently the flow rate of the pump increases. The average flow rate of the pump in the mentioned amplitudes is equal to 0.002, 0.0013, and 0.0005 kg/s, respectively. As the amplitude increases from 0.2 to 0.8 mm, the maximum stress applied to the diaphragm increases from 32.2 to 99.2 MPa (equivalent to 208%). Also, the effect of diaphragm oscillation frequency on pump performance is investigated. The results show that the pump's flow rate directly and linearly relates to the diaphragm oscillation frequency. In contrast, the applied stress on the diaphragm is not frequency-dependent and in the same ratios of the period, the applied stress is almost constant. According to the results, if the pump amplitude is set to 0.5 mm and the frequency is 1.6 Hz, instead of operating at a diaphragm amplitude of 0.8 mm and a frequency of 1 Hz, the pump's flow rate will be the same. While the maximum amount of stress in the diaphragm will be reduced by about 30% and the probability of damage will be reduced.

In this research, firstly, a conceptual model designed of ten deep exploratoration wells has been developed, and based on this, a three-dimensional numerical model of the North-West Sablan geothermal system has been presented. For this purpose, the EOS3 module (water-air equation) of the Tough2 simulator code was used to simulate the model. The numerical model of the reservoir is expressed by a rectangular prism with a length of 11.5 km, a width of 8 km (92 km2) and a depth of 5.11 km, and it was expanded with 21 horizontal layers with a thickness range of 100 to 1000 meters from the maximum altitude of 4110 to -1000 masl. The number of 22 rock-types, whose distribution is based on the distribution of rock units and geological structures in 10 deep exploratory wells, was assigned to the model. The permeability of the rock types varies from 1*10E-17 to 9*10E-13 square meters. Modeling was done for the natural state of the reservoir and the validation results showed a good match between the data measured in the well and modeled for temperature and pressure. In the best fit, the simulation provided a zone of high temperature upward flow in the southeastern part of the range (sites D and E). This flow is transferred through permeable, faulted and fractured zones and is finally discharged through surface features (hot water springs) in the northwestern part of the area.

Intraperitoneal injection of chemotherapy has been proposed as a promising method for the treatment of peritoneal metastasis, and its use in conjunction with cytoreductive surgery has shown interesting results in the treatment of patients. However, drug penetration into the tumor is limited in this method, and a better understanding of the factors influencing this low penetration depth is necessary. For this purpose, in the present study, a numerical model has been developed to investigate drug transport during intraperitoneal chemotherapy. Using this model, first, the Spatio-temporal distribution of free, bound and internalized drug concentrations are calculated. Then, by calculating the drug penetration depth and the fraction of killed cells, the effectiveness of the treatment is evaluated. Results of a 10mm tumor after 60 minutes of treatment showed that the drug is available only in a limited area of the outer region of the tumor. The values of fraction of killed cells and drug penetration depth were 1.2% and 11.4%, respectively, which indicates a poor treatment efficiency. The findings of this paper can be used in future numerical and experimental studies to gain a deeper insight into the mechanisms of drug delivery to the tumor by intraperitoneal injection.

In this paper, the performance of a piezoelectric pump is numerically simulated by considering the main equations of fluid flow, elastic diaphragm and electric field. The simulation is conducted using the two-way fluid-structure interaction approach, as the fluid and structure affect each other in performance of piezoelectric pumps. The simulation results are compared with experimental results and the maximum error in steady analysis is obtained 9.66% and in un steady analysis is 8.95%. Due to the good time response and the possibility of flow control by piezoelectric pumps, the feasibility of using piezoelectric pumps as dosing pumps is investigated. The simulation results showed that the designed piezoelectric pump could be used as a dosing pump; so that if the pilot gas pressure reducing station operates at its maximum capacity (10,000 cubic meters per hour), the proposed pump will inject the required odorant at a voltage of 200 volts and a frequency of 0.167 Hz. The proposed odorizer system, in addition to the possibility of precise control of the amount of injected odor, has a lower initial cost and operation cost than the present bypass system at the station.

The numerical modeling of particle deposition in industrial problems is essential due to domination on intricate details of this phenomenon. In the present study, suggestions for properly using the governing equations and conditions have been presented. Modeling particle deposition phenomenon is generally divided into the Lagrangian and Eulerian approaches. Eulerian approaches are used to model particles deposition when the volumetric ratio is higher than 10−3 and The Lagrangian approaches are used for the volumetric ratio of particles less than 10−3 . The Drift Flux method is more common among the Eulerian approaches than others. In Lagrangian approaches, if the particles are small (in Nano size), and the volumetric ratio of particles is less than 10−6 due to the greater Van der Waals force between the particles and deposition place, the condition of the sticky wall is invoked. Furthermore, with increasing the size of the particles, the possibility of rebounding after their collision should be investigated. Moreover, if the flow rate is high, the possibility of particles detachment from the deposited layer should be considered. Also, the temperature affects particles deposition. Increasing temperature changes the phase of the particles, and as a result, they settle when they hit the surface.

In the present study, in order to fabricate AC electroosmotic micropumps, the improvement of geometrical parameters of the 3D electrode, such as width, height, and location of 3D steps on the base electrodes in one pair, the base electrodes size (symmetric or asymmetric), electrodes gap, and also electrical characteristics including voltage and frequency have been investigated. Also, the fluid flow (KCl) in the channel was analyzed. The governing equations of fluid flow and electrical domain have been solved using the finite element method to investigate the effect of electrode geometry on slip velocity, which affects the fluid flow. In order to validate our numerical simulation, this chip is fabricated by photolithography method such as deposition of platinum electrodes, creating 3D steps on the base electrodes using a polymer, and fabrication of a microchannel. Finally, Our results indicate that an optimal design results in a pump with the width (50 µm) and steps height (5 µm) of each electrode and their displacement (30 µm) are capable of generating a high velocity, flow rate, and pressure around 1.77 mm/s, 14.9 ml/min and 74.6 Pa, respectively at a given voltage (2.5 V) and frequency (1 kHz), which qualitatively matches the trend observed in the experiment. This design provides an improvement in electroosmotic pumping.

Not only are Fuel cell vehicles one of the significant options to replace gasoline engines, but they also come with a multitude number of benefits; For instance, fuel cell efficiency is more than about three times the efficiency of engines with internal combustion. According to the specific complexities of modeling the behavior of PEMFC, determining the performance of this system in case of its structural characteristics is considered as one of the parameters needed to better know of behavior the PEMFC. The present study attempts to find and examine a polymer membrane fuel cell for utilizing in a vehicle. To examine the performance of fuel cells, the modeling process was done by addressing diverse production-consumption heat in the anode and cathode positions and waterflood conditions. Using quadratic method, the flow channels were meshed and based on the finite difference method the mathematical equations were numerically discretized in the steady-state. Based on the simulation results, all heat values decrease over the channel of flow. By evaluating the relative humidity effect, it was obvious that the cathode relative humidity didn’t change considerably along the channel of flow and at the same time, the relative humidity of the anode decreased along the channel of flow. There was a significantly low membrane layer velocity given the fact that this layer had a lower permeability coefficient in comparison with reactant layers and gas diffusion (Average Reynolds number: 612).