مجله مهندسی مکانیک امیرکبیر
سال پنجاه و سوم شماره 5 (امرداد 1400)

Rectangular liquid jets injected into gaseous crossflow were experimentally investigated. In this study, water was used as the working fluid. Four rectangular injectors with aspect ratios of 1, 2, 3 and 4 were manufactured to study the physics of the jet flow. Diffused backlight shadowgraphy along with high speed photography was employed to capture the instantaneous physics of the liquid jet flow. Based on the flow visualizations, different breakup regimes including column breakup, arcade breakup, bag and multiple breakup were identified. Trajectory and width of the liquid jets were measured using an in-house image processing program. Effects of momentum ratio, aspect ratio and gas velocity on trajectory and width were investigated. The results showed that the momentum ratio most effective on the jet trajectory and aspect ratio was of least importance. A mathematical model was suggested to estimate the trajectory of liquid jets. In this model, jet Weber number, gas Weber number and aspect ratio were introduced as the variables. Furthermore, it was revealed that aspect ratio directly influences the jet width since it changes the axis-switching characteristics of the liquid jet.

One of the dangers that threatens spillways when excessive flooding pass is cavitation. Flow aeration using aeration systems has been used as one of the most effective methods to prevent the occurrence of this phenomenon. In this research, Flow-3D software was used to simulate flow through the spillway aerator of chute in CFD-method. To validate the results of a numerical model, Hager and Pfister (2010) laboratory data are used and the results indicate that they are in good agreement with the laboratory data. Then, the effect of geometric parameters such as height and angle of ramp, offset height and chute slope on the changes in air concentration, flow characteristics such as velocity and pressure to determine the cavitation index in order to determine distance between two aerators was explained. The average air concentration is as layer changes in the depth of flow and the reduction of air concentration is as exponential function. The value of the cavitation index is greater than the critical value during 11 meters after aerator in the chute spillway and there is no risk of cavitation occurrence. Considering the calculated concentrations, it can generally be concluded that by decreasing the air concentration in the chute bed to the values of 0.0001, 0.001, 0.01 and 0.1, chutes with slopes of 10, 12, 30 and 50 degrees do not require more aeration, respectively.

The study of cavitation inception is crucial in several hydraulic machines, e.g. pumps, nozzles and sprays. In the present study, a multiphase lattice Boltzmann method (LBM) is implemented for simulation of the cavitation bubbles dynamics and characteristics of cavitating flows. The effect of employing various equations of state (EoS) is investigated on the computing of interaction forces and the phase separation between the liquid and its vapor in the cavitating flows. Herein, the cubic EoSs of Shan-Chen (SC) and Carnahan-Starling (CS) and the non-cubic EoS of Peng-Robinson (PR) are applied. The exact difference method is imposed to improve the numerical stability for simulation of two-phase flow systems. The accuracy and efficiency of the present method are examined by comparison of the results obtained for the homogeneous and heterogeneous cavitation with those of reported in the literature. Then, the implemented multiphase LBM is used for studying the inception and growth of the cavitation bubbles in the throat of a venturi. The effect of hydrophobicity and hydrophobicity of the nozzle wall on the cavitation dynamics is investigated and a detail discussion is made for the results from the numerical and physical point of view. Evaluation of the present results shows that the multiphase LBM with incorporating an appropriate equation of state has excellent capability for prediction of the bubble dynamics and cavitating flow characteristics in applied geometries.

In this paper, we mentioned to a numerical analysis method for simulation of a micropump for microfluidic applications. Each sections of the micropump, including microvalves and pumping chamber, were studied using three-dimensional fluid-structure interaction analysis and their operational characteristic equations were extracted independently. These extracted equations were used to solve time-domain pressure equation and to obtain the flow rate of micropump. Afterwards, we were able to study different effects of actuation pressure and actuation frequency on micropump’s flow rate with and without the presence of outlet backpressure. The results show that when actuation frequency is 1 Hz and actuation pressures is equal to 1000, 1500, 2000 Pa, pumping flow rate reaches to 30, 48 and 65 mm3/min, respectively. Also, this micropump can overcome maximum backpressure of approximately 950 Pa when it was actuated using pressure of 1000 Pa, regardless of its actuation frequency. These simulated results reasonably agreed to the microfluidic and lab-on-a-chip applications. a a a a a a a a aa a a a aa a a a aa a a a a

Due to the high mortality rates associated with cancerous tumors, many researchers are focused on finding methods and tools for early detection and effective treatment. Among these, mathematical models and numerical simulations along with clinical studies can help provide better understanding of drug delivery mechanisms, enhance the efficacy of therapy, and demonstrate the effect of various physiological parameters on tumor behavior. The main objective of this study is to use a multiscale model based on mathematical modeling and computational fluid dynamics to evaluate drug delivery to a solid tumor and to predict treatment efficacy. A more-realistic physiological model of the tumor compared to the previous models is examined by obtaining the capillary-network’s geometry from an image, as well as by considering the necrotic area and cellular uptake. Fluid flow modeling and drug delivery simulation are then performed for the interstitium. The fraction of killed cells is obtained approximately 69.03% after the cancerous tissue is treated with doxorubicin. Results also demonstrate that the drug concentration in the necrotic area is very low; only a small amount of the drug penetrates into the necrotic area by diffusion. The findings of this study may help researchers better understand the mechanism of drug delivery to solid tumors, —a necessary step in overcoming the micro-environmental barriers of tumors that impede treatment efficacy.

The phenomenon of abrasion and friction in mechanical mechanism and the ways to reduce them have been highly regarded. One of these methods is surface texturing, which can be accomplished using a laser with high speed and accuracy. In this study, a precise numerical model is developed to investigate the frictional behavior of the dimple transient film formation effect. Then the effect of laser made textures on a ST37 steel disc is studied experimentally in linear contact situation in the mixed lubrication regime. In this study, the friction coefficient is measured after 100m distance for different input important parameters of velocity and vertical load. Results have shown that friction coefficient decreases with increasing speed and decreasing applied force. Comparison of the results between the textured and smooth discs showed that the friction coefficient decreased by 12 to 23% in the experimental study, while numerical estimates of the possibility of a decrease of between 25 and 40% were also predicted. At high velocities, the numerical model estimates and the results of the experiment are very close.

In this paper, the effect of evaporating sprays of Ethanol and Acetone injected into a cylindrical gaseous environment is numerically investigated. To make this investigation the Eulerian gas phase equations together with the Lagrangian liquid phase equations are solved assuming a two-way coupling between the two phases. According to the results, after a certain time from the start of injection, the overall percentage of total evaporation of acetone becomes significantly higher than ethanol, but at the early spraying time, both alcohols had similar overall evaporation rates. Also, in terms of spray tip penetration, they have almost the same amount of progress and more or less the same behaviour. Also due to the almost identical injection flow rate of the droplets, the effects on the velocity fields in the gas phase have been almost similar. The important point to compare is the gas phase temperature field for both sprays after 1.5 ms of injection. Due to the fact that most of the evaporation occurs when the particles reach boiling temperature and the fact that all the heat required for evaporation is taken from the gas phase, the ambient temperature becomes much lower in ethanol spray because ethanol’s boiling temperature and latent heat are both much higher than acetone.

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.

In the present study, a laminar pressure-driven flow within a microchannel consisting of two parallel flat plates with rugged walls has been simulated. Walls ruggednesses have sinusoidal profiles with relative heights of 0≤h/H≤0.15. The main purpose is the determination of differentiation boundary of surface roughness and wall blocks. The flow governing equations in a system of two-dimensional general coordinates are solved using finite-volume numerical method in a non-uniform grid with maximum orthogonality of grid lines adjacent to rugged boundaries. In the first step, the surface ruggednesses of wall are divided into two categories: “surface roughness” and “wall blocks”. Then, the differentiation boundary of surface roughness from wall blocks is determined by applying two qualitative and quantitative criteria. According to the qualitative criterion, when the surface ruggedness is surface roughness, the pressure distribution at the centerline remains as linear as a perfectly smooth microchannel. But when the surface ruggednesses are wall blocks, however, the pressure distribution at the centerline is oscillating. Also, on the quantitative criterion, the average shear and normal forces just adjacent to the rugged surfaces are calculated and compared for different relative ruggednesses. According to the results, in the laminar flow within the rugged planar microchannels, firstly, ├ h/H┤|_cr is 0.042 which is independent of Δp. Secondly, the surface roughness affect the flow dynamics and increase the friction factor and decrease the flow.

In targeted drug delivery, the use of temperature-sensitive microparticles as drug carriers has been the subject of many researchers recently. In one approach, the use of NIPAM microparticles as temperature-sensitive drug carriers can be effective in the topical treatment of chronic, diabetic or burned wounds. In this study, we first fabricated a flow focusing microchannel by photolithography. Then NIPAM solution was made with different percentages and used as the drop phase in the microchannel. The results showed that the use of 10% of NIPAM was successful in the polymerization reaction and the use of NIPAM with a lower percentage didn't show any result in the production of high quality and usable polymers. Thus the NIPAM solutions and silicone oil were used as discrete and continuous phases, respectively, and the NIPAM microparticles were produced through the two-phase flow generated in the microchannel. The effect of flow ratio on the diameter of droplets produced was evaluated using a digital microscope. The results of the study showed that by changing the ratio of discrete phase to continuous phase from 0.14 to 0.84, the droplet diameter increased from 360 to 515 microns. Thus, the microparticles produced in this method can be used as temperature-sensitive drug carriers in the treatment of chronic wounds.

In the first part of this research, non-catalytic natural gas converter is analyzed numerically. The GRI-1.2 mechanism, which includes 177 basic chemical reactions, is used to calculate the reaction rate in natural gas oxidation processes. The EDC waste loss model is used to model combustion. Due to the fact that the calculations have been done for a very large natural gas converter, a symmetric axial model is used to reduce the computational costs. The results of the first phase of the study show that increasing the pressure increases the conversion of CH4 to hydrogen, but from a pressure of 3 MPa and above, the amount of hydrogen production remains almost constant. In addition, with increasing the ratio of water vapor to natural gas, the maximum flame temperature in the converter decreases and the molar fraction of H2 / CO in the output increases. In the second part of the research, a stable three-dimensional heterogeneous numerical model for studying the methane vapor vapor reforming process is investigated. The results show that by increasing the inlet temperature of heating pipes, the CH4 / H2O ratio increases to about 0.25 and the number of methane heat supply pipes increases. Also, by comparing the results of this simulation and the existing experimental research in this field, the results of this study can be used for the development of industrial.

Primary Cilia is appendage that extrudes from cell surface into the extracellular matrix .These organelles play a sensor role for mechanical stimulation in the cell and due to stretch ion channels in its base, play critical role in induce osteogenic differentiation of stem cells. Primary cilia deflected under fluid flow passing through the surface of the cell, which deflection causes tensile ion channels to be opened. In this study, cilia is assumed as linear elastic. The innovative aspect of this research is exerting of oscillatory fluid flow to the primary cilia and evaluating the response of cilia to the fluid flow. The results show that under conditions of exerting the oscillatory fluid flow, maximum strain occur in the base of the cilia which is experienced by tensile ion channels, is 0.5 and in the condition of steady flow is 0.3, Accordingly, mechanical stimuli are sensed by the tensile ionic channels during oscillatory flow higher than steady flow. osteogenic differentiation of stem cells, in addition, the result showed that by using the oscillatory fluid flow the mechanical stimulation better senses by cilia and It is anticipated that exerting oscillatory fluid flow facilitate osteogenic differentiation of stem cell.

Today,the study of combustion of metal particles is considered due to applications such as particle oxide production, high energy density and thus increasing the temperature resulting from combustion, medical applications,etc.In this study,the analytical model of titanium dust cloud combustion in counter-flow geometry with a multi-zone approach is examined and presented.Fuel flows on the one hand and oxidizing currents on the other flowed as counter-flow,and in order to analytical modeling,three distinct areas were considered.The equations governing,including the mass fractional survival of the components and the survival of the energy, were expressed and,using appropriate boundary and adaptive conditions,the solution of the equations in each zone was presented using Matlab and Mathematica softwares.Then the temperature distribution and mass fraction of fuel, oxidizer and fuel products in the liquid phase were plotted according to location and the effect of some variables such as Lewis number,particle diameter and mass particle concentration on the flame was investigated. It was observed that with increasing Lewis fuel number from 0.6 to 1.4 at 300 g/m3, the flame temperature decreased from 3600 Kelvin to 3050 Kelvin and also the flame location was transferred to the oxidizer nozzle and the reason for this was the reduction of mass penetration. Also with increasing particle diameter of fuel from 2μm to 200μm, temperature of the flame was shifted from 3600 K to 3400 K.

Ground source heat pumps (GSHPs) have received much attention due to their high coefficient of performance (COP). In these systems, the ground is used as a sink/source for heat pumps and the heat transfers between the ground and the heat pump is performed by the ground heat exchanger (GHE). In this study, the long-term performance and initial cost of these systems have been compared with conventional air-source systems in a hot region. To evaluate the performance of the GSHP, using fluent software, numerical modeling of a linear horizontal GHE was carried out in Bandar-Abbas. Also, the effect of various system operating parameters, i.e., length, distance, buried depth, and diameter of GHE pipes have been studied. According to results, the five-year COP and exergy efficiency of GSHP systems is 19.9% to 24.30% and 5.95% to 6.55%, respectively, more than that of the air-source system. However, 1.2 to 2.5 million Tomans is needed as the installation cost for each kW of maximum building load per year. Also, it is demonstrated that by reducing the length of the GHE, the initial cost is reduced, and the performance increases, the pipe spacing is the most important factor in the required ground surface, the depth has the most impact on the initial cost and the performance, and the pipe diameter does not affect the system performance.

When the fire in the room reaches a critical state, the leaving hot gases can create hazards for the upper floors. In this paper, different fire cases with more and less natural ventilation than the critical state are discussed, and the temperature, velocity, and toxic species are discussed. A two-floor building is simulated using a large eddy simulation and PIMPLE algorithm at different fuel flow rates and how the fire spreads upstairs is examined. Fuel flow rates are considered at three heat release rates of 500, 1000 and 5000 kW. In order to accurately analyze toxic species, the FGM combustion model is used and the results are compared with the experimental results. The relative error are less than 15%. With increasing fuel heat release rates, the upper floor is more exposed to fire hazards such that if the heat release rates is 500 kW, the temperature in the second floor reaches 390 Kelvin and the carbon monoxide species reaches 25 ppm. But if the heat release rates is below 1000 kW, the upper floor will not be at particular risk. Generally, the level of diffusion of carbon monoxide into the second floor is lower than the toxicity level for humans (25-50 ppm) and the second floor is not particularly endangered for carbon monoxide gases.

The world is currently facing the prospect of a severe global shortage of fresh water. Desalination of seawater can provide an almost inexhaustible source of freshwater if it can be made affordable. Freezing is a well-known technique for water desalination. The carbon dioxide refrigeration system is used for cooling required in the freezing desalination system and the evaporator and condenser of the refrigeration system are respectively crystallized and melted in the freezing desalination system. In this paper the basic principles of freeze concentration processes are presented and a model of a freeze desalination that coupled with CO2 refrigeration has been developed based on the theories of heat and mass transfer. To examine the performance of the system, a parametric study is performed to investigate the effect of different parameters such as FD feed temperature, feed concentration, distillate temperature, distillate concentration and FD recovery ratio on COP and energy consumption have been explored. It can be concluded that increasing the feed concentration and feed temperature is accompanied with the reduction of COP and a raise in SEC. Increasing the ice fraction also increases the SEC system. Freezing desalination System in the present study is comparable in energy consumption to reverse osmosis desalination system.

The purpose of the present study is to investigate the performance evaluation of a greenhouse solar dryer equipped with photovoltaic cells and phase change material. The governing equations of problem is obtaind by writing the energy balance for the various component of the system including photovoltaic module, greenhouse chamber air, crop, absorber plate and phase change material. An empirical model is used to calculate the electrical power of photovoltaic module. In order to calculate the thermal and electrical parameters of the system including photovoltaic cells temperature, the temperature of greenhouse chamber air, crop temperature, phase change material temperature, absorber plate temperature and electrical power, the governing equations on the system performance is solved by numerical methods. Also, a relation for the overall energy efficiency of the system is introduced. The modeling results of the present study is in good agreement with the experimental data of the previous literature. The results obtained for the sample day of Zahedan show that the phase change material by storing the system loss heat during the day and releasing it at night enables the crop drying process to continue well into the night, so that the overall evaporation rate increases by about 38.76%. The maximum energy efficiency of the system is about 15%.

This paper introduces solar radiation estimation function based on air mass and the statistics information about sunny and cloudy days for use in numerical modeling of solar ponds. Solar ponds are one of the methods of absorbing solar radiation and storage it with long storage periods. By using one-dimensional simulation, the performance of salt gradient solar pond is investigated. By removing the usual assumptions, it is attempted to take into account the effects of environmental conditions more realistically. These conditions included the variability of ambient temperature by day and hour, the solubility of salt depend on temperature and concentration, the variability of radiation intensity with respect to the angle of elevation of the sun, and the effect of wall shading on the pond. The analysis is transient and the day and night conditions are included. The innovation was to estimate the intensity of solar radiation using the concept of air mass and the amount of cloudy sky. A relation for the calculation of cloud cover factor, which was extracted using the statistics of cloudy and semi-cloudy days and was compared with empirically amount. The ability of this relationship is to estimate the radiation intensity for locations where statistics or tools and equipment for recording radiation intensity are missing. Presented results show that the radiation intensity is in good agreement with the existing experimental data.

The oscillating heat pipe is a new technology that, despite its simple structure, has a very high heat transfer rate. Due to boiling and condensation during operation, the oscillating heat pipe is capable of transferring heat at low temperature without the need for external power, high heat transfer and small volume. The thermal conductivity equivalent to an oscillating heat pipe can reach several hundred times the best conductors such as copper. The present study investigated thermal performance of Nano fluid carboxylic multi walled carbon nano tubes (MWCNTs-COOH) with 0.1 wt% based on water with corrugated evaporator in newly designed three dimensional oscillating heat pipe. The results show that using this Nano fluid, the thermal resistance has been reduced up to 13%. Also, in filling ratio of 60% compared to 50% , temperature difference between evaporator and condenser has been reduced 8 degree centigrade and the thermal resistance has been reduced up to 6.4%. Corrugating the evaporator leads to mixing and turbulence in the pipe and increases heat transfer. The results showed that thermal resistance decreased with increasing thermal load. It also reduces thermal resistance by reducing the temperature difference between the evaporator and the condenser.

In this paper, mixed convection of Bingham fluid between two coaxial cylinders has been studied numerically without using any regularization method. The temperature of the inner rotating circle is higher than the temperature of the outer stationary circle. The finite volume method and non-iterative PISO algorithm have been employed to solve the problem. One of OpenFOAM solver, icoFoam, has been modified for solving the exact Bingham model. After validating the modified solver, it has been used to solve the problem for the following ranges of conditions: Reynolds number, Re=10, Prandtl number, Pr=10, Grashof number, Gr=500, Bingham number, 0≤Bn≤1000, and aspect ratio (AR) of 0.1. The effects of the Bingham number on flow and heat transfer characteristics such as the shape and size of the unyielded regions, streamline contours, the local and mean Nusselt number, and the torque coefficient have been investigated. The mean Nusselt number and the torque coefficient decreases and increases, respectively, when the Bingham number increases. The variation range of the local Nusselt number and dimensionless tangential stress on the inner wall decrease with Bn.