Recent Volume
Vol11 , No 5
Design Optimization of Ceiling Fan Blades with Nonlinear Sweep Profile
Pages : 1153-1162
Authors : E. Adeeb,  C. H. Sohn,  A. Maqsood,  M. A. Afaq, 
This study pertains to the design optimization of a four-blade ceiling fan to enhance air circulation and energy efficiency. The sweep angle of the blade profile is nonlinear. The design of experiment (DOE) computational fluid dynamics (CFD) and response surface method (RSM) methods were used in parallel to find the optimal design solution. The design variables considered were inboard angle of attack, outboard angle of attack, blade sweep, and tip-chord length. Numerical simulations were conducted using steady state Reynolds-averaged Navier–Stokes (RANS) equations and the Spalart–Allmaras turbulence model. The baseline results were validated through experimental data. Subsequently, the DOE method was employed to generate the blade design which reduce the number of simulations without losing the influence of different geometric parameter interactions. The response variables studied were volume flow rate, mass flow rate, torque, and energy efficiency. The simulations exhibited that flow pattern has a distinct feature and is further classified into three groups. In the end, the optimal blade design was identified using response surface methodology (RSM).
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Numerical Simulation of Mucus Clearance inside Lung Airways
Pages : 1163-1171
Authors : J. Kori,  Pratibha ., 
Airway mucus is difficult to clear and to improve lung function clearance of mucus is necessary. The deep coughing, chest physiotherapy, high frequency chest wall oscillation etc. are some of the best methods to clear excessive mucus from lung airways. In this article we analysed the behavior of fluid flow between parallel walls , where both walls are porous and the flow is induced by the oscillation of these walls and pressure gradient; which is applicable for clearance of mucus from lung airways. Generalized couette flow is applicable to model the oscillation of parallel walls, however the laminar flow of viscous fluid is taken under consideration. The generalized Navier-Stokes equations are applied to make various hypotheses and finite difference scheme is used to solve the problem numerically. Effect of wall oscillation, wall porosity, pressure due to porous media on mucus clearance and particle aspect ratio on the deposition of nonspherical nanoparticles are analysed graphycally after simulating the problem on MATLAB R2013a by user defind code. Simulation show an excellent agreement of unsteady flow of viscous fluid at large values of time and significant correlation between pressure gradient and porosity of walls, frequency of wall oscillation and their imapct on mucus clearance are obtained. In addion it is observed that fluid and particle velocity are increased with the enhancement of media porosity, breathing frequency and aspect ratio. The aim of this paper is to study the influence of wall movement, wall porosity, pressure on wall, wall oscillating frequency on the clearance of mucus from lung airways.
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Effect of Viscous Gas on Stability of the Electrified Liquid Sheet
Pages : 1173-1183
Authors : R. Duan,  Y. Liu,  D. Wang,  Z. Wang,  L. Liu,  Y. Zhang, 
An electrified liquid sheet was investigated by the linear analysis method. The sheet was injected into a dielectric viscous gas bounded by two horizontal parallel flat plates with a transverse electric field. To take into account the gas boundary layer thickness, the velocity profile of the liquid sheet must be considered and derived. By analyzing the liquid and gas domain, the relation between the growth rate and the wavenumbers for electrified liquid sheets was derived, and solved using the spectral method whose accuracy is higher than those of the finite element method and the finite difference method. Two modes, namely the sinuous mode and varicose mode were also investigated. The results revealed that the maximum growth rate of the sinuous disturbance wave is greater than that of the varicose one for the electrified liquid sheet. Moreover, the effects of the electrified Euler number and other parameters on the instability of the electrified liquid sheets have been tested. It is found that the growth rate is faster for an electrified liquid sheet than a non-electrified one. The electrical Euler number, the liquid Reynolds number, the Weber number and the momentum flux ratio can promote the breakup of a liquid sheet. However, the increase in the ratio l of the distance between the liquid sheet and flat plate to the liquid sheet thickness has an opposite influence with the other parameters.
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Effect of Turbulent Uniform Flow past a Two- Dimensional Square Cylinder
Pages : 1185-1192
Authors : Y. C. Li,  C. Y. Chung,  F. M. Fang, 
Turbulent uniform flows past a two-dimensional square cylinder are investigated numerically. By varying the turbulence intensity and turbulence length scale of the approaching flow, the flow effect of the cylinder are compared to that in a laminar approaching-flow case. In addition, the variations of drag and lift coefficients with respect to the changes of turbulence intensity and turbulence length scale are analyzed on a systematic basis. In the large eddy simulations, the approaching-flow turbulence is generated by a spectral method according to Kármán spectrum. Two levels of turbulence intensities (5% and 10%) and three turbulence length scales (0.25, 0.50 and 1.0 times of the cylinder width) are selected in the study to examine the effect on the cylinder. Results show that the Strouhal number remains almost unchanged when the uniform approaching-flow changes from a laminar state to a turbulent one. The approaching-flow turbulence has noticeable effect in promoting the resulting drag and lift fluctuations. However, its effect on the mean drag appears negligible. In contrast, an increase of the approaching-flow turbulence length scale leads to mild increases of the mean and root-mean-square values of drag. On the other hand, the resulting lift fluctuation is insensitive to the change of the turbulence length scale.
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Periodic Moving Track Analysis of Spiral Oil Wedge Journal Bearing under Dynamic Loading
Pages : 1193-1199
Authors : L. L. Wang,  Q. L. Zeng,  M. Wang,  Q. G. Chen, 
The moving track of journal bearing changes with the time in the condition of dynamic loading. The force balance equation of journal bearing is established, and the generalized Reynolds equation, the oil film thickness equation of spiral oil wedge journal bearing under dynamic loading are gained, which is based on axial inertia force, bearing capacity and dynamically loading. By finite difference method, Euler method and Reynolds boundary condition, the generalized Reynolds equation and force balance equations are solved simultaneously, the periodic moving track of journal bearing at different times is solved. The results show that the circumferential pressure, axis displacement, axis velocity, axis acceleration velocity of journal bearing change periodically as time goes. The influence of dynamical loading on pressure distribution of oil film and axis locus is analyzed.
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Numerical Visualization of Blast Wave Interacting with Objects
Pages : 1201-1206
Authors : S. Dey,  T. Murugan,  D. Chatterjee, 
Blast wave interaction with objects has gained attention due to military conflict and terrorist attack across the globe. Blast wave attenuating and mitigating structures are needed to be developed to protect the military vehicles and commercial buildings. In order to understand the attenuating mechanism such as the dissipation and dispersion along with the secondary effects, the blast wave interacting with three objects is examined in the present study for the diaphragm pressure ratio of 56. Here, the blast wave is generated in a short driver section open ended shock tube by solving the Euler equations using the commercial software ANSYS Fluent. It has been observed that the circular disc attenuates the blast wave more effectively compared to the cone and sphere for the same frontal area. The attenuation was lowest in the sphere and maximum in the circular disc. However, the loads acting on the sphere was more compared to the conical object. The peak load acting on the circular disc was 2.09 times more compared to the peak load acting on the conical object (cone angle 26.5°) with the same hydraulic diameter.
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Numerical Simulation of the Non-Isothermal Co-Extrusion Fiber Spinning with Flow-Induced Crystallization
Pages : 1207-1215
Authors : B. E. García,  A. Zacarías,  V. Ferrer,  R. O. Vargas, 
In this work, the numerical simulation of the non-isothermal steady co-extrusion fiber spinning with flow-induced crystallization is explored. The model is based on the formulation originally proposed by China et al. in which Newtonian and Phan-Thien-Tanner (PTT) fluids are considered the core and the skin layer, respectively. The polymeric flow rate fraction, Deborah dimensionless number and the PTTs parameters on the temperature, the velocity and the crystallization profiles are analyzed. The numerical results show: the temperature profile is sensitive to the polymeric layer flow rate and the deformation parameters (shear thinning and extensional), the tensile stress induced crystallization parameter has a strong influence at the onset of the process, increasing drastically temperature and crystallinity.
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Study of Heat and Mass Transport in Bénard-Darcy Convection with G-Jitter and Variable Viscosity Liquids in a Porous Layer with Internal Heat Source
Pages : 1217-1229
Authors : A. Srivastava,  B. S. Bhadauria,  A. K. Singh, 
In this research article, we investigated the weakly non-linear effect of gravity modulation for the temperature dependent viscous fluid in a horizontal porous layer in the presence of internal heat source. We use power series expansion in terms of the amplitude of gravity modulation, which is considered to be small for double-diffusive convection in porous media. We graphically show the effect of internal heat source, solute Rayleigh number, Lewis number, Vadász number, thermo-rheological parameter, the amplitude of gravity modulation, the frequency of modulation on the heat and mass transfer using Ginzburg-Landau equation. The effect of gravity modulation is found significant and is more effective for the low values of frequency of modulation.
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CFD-Based Optimization of Micro Vortex Diodes
Pages : 1231-1237
Authors : K. Fouladi,  J. Czupryna, 
Microvalves can play an essential role in transport and control of fluids for biomedical applications. These valves may face reliability issues as they can fail due to deterioration of the moving parts exposed to prolonged and repeated movements or handling fluids that contain particles of several microns in diameter. An alternative to valves with moving parts are microdiodes such as micro vortex diode, which offers high resistance to flow in one direction and much smaller resistance in the opposite direction. The present study is focused on developing a two-step computationally-based approach for design and optimization of micro vortex diodes. A numerical design optimization based on the Design of Experiment and Response Surface Method is employed to improve the efficiency of a micro vortex diode using geometrical parameters. The results of the optimization study suggest an optimal design with about 69% improvement in efficiency compared to the reference design.
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Development of the Couple Stress Relationships for the Power Law Fluid and the Solution of Flow in Ceramic Tape Casting Process
Pages : 1239-1246
Authors : F. Karami,  A. Ahmadi Nadooshan,  Y. Tadi Beni, 
The absence of characteristic material length in the Navier-Stokes equations has led to the development of different couple stress theories. In the present study, for the first time, the relations of a couple stress theory are extended to power-law fluids. Moreover, considering the significance of the length scale in nano- and micromechanics, the relations of the extended theory were applied to Newtonian and power-law fluids in tape casting of ceramics. The obtained velocity was used to calculate the volumetric flow rate as well as the thickness of the ceramic tape. A comparison between the results of the Newtonian fluid and the analytical and experimental results indicated a close agreement between the present results and the results of other studies. Moreover, the tape thickness was obtained for different length scales (L) by numerically solving the velocity relations obtained for the non-Newtonian fluid. Also, the impact of casting speed on the tape thickness was shown for four power-law fluids assuming L=0.35.
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Experimental and CFD Study of Internal Flow inside a Sessile Microdroplet undergoing Lateral Vibration
Pages : 1247-1253
Authors : T. Zhu,  Z. Zhao,  L. Lv,  W. Chen,  L. Dong, 
In this study, the internal flow pattern of a sessile microdroplet undergoing a lateral vibration was analyzed by using both the experimental and CFD simulation methods. By initially staining the droplet partially with fluorescent dye, the main flow inside the laterally vibrating microdrop was experimentally demonstrated to be that the main fluid flows downward along the central axis and ascends upward along the surface to form two counterflow circuits. Experimental evaluation of fluid mixing inside the droplets verified that the internal flowing velocity is dependent on the vibrating frequency, the main fluid flows faster at the resonant modes. CFD simulation using the VOF-CSF model showed that extra flow circuits exit inside the oscillating droplet besides the main flow. The diffusion of substrate momentum within the Stokes layer results in the two flow circuits near the bottom substrate, and the Laplace force due to the droplet deformation induces the two counter-current flow circuits near the surfaces of the microdroplet.
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A Novel Method (T-Junction with a Tilted Slat) for Controlling Breakup Volume Ratio of Droplets in Micro and Nanofluidic T-Junctions
Pages : 1255-1265
Authors : A. Kiani Moqadam,  A. Bedram,  M. H. Hamedi, 
We propose a novel method for producing unequal sized droplets using a titled slat in the center of a T-junctions. In the available methods for generating unequal-sized droplets such as T-junction with valve and T-junction with a heater, the minimum breakup volume ratio that is accessible is approximately 0.3 while the system of this paper can generate droplets with the volume ratio 0.05. Therefore, the manufacturing cost of the system decreases considerably because it does not need to the consecutive breakup systems for generation of small droplets. The employed method was investigated through a numerical simulation using the volume of fluid (VOF) algorithm. The simulation results are reported for micro and nano-scaled T-junctions in various tilted slat sizes, capillary numbers (a dimensionless group describes the ratio of the inertial forces to the surface tension forces) and slat angles. Our method decreases (increases) considerably the breakup time (speed of the breakup process). For example in the case Ca=0.1 and volume ratio 0.4, dimensionless breakup time of our method and the method of T-junction with valve are 0.25 and 3.6, respectively. The results revealed that the breakup length of the nanoscale T-junction is smaller than microscale and increases by increasing the slat angle in both scales. The results demonstrated the breakup volume ratio decreases by increasing the tilted slat length. Also the breakup volume ratio minimizes in a specific slat angle. The results showed the breakup time is reduced by decreasing the slat angle. We also found that the pressure drop of the system is almost independent of the system geometry.
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Experimental Investigation of Flow Control over an Ahmed Body using DBD Plasma Actuator
Pages : 1267-1276
Authors : S. Shadmani,  S. M. Mousavi Nainiyan,  M. Mirzaei,  R. Ghasemiasl,  S. G. Pouryoussefi, 
Ahmed body is a standard configuration of road vehicles and most of the studies of automobile aerodynamics are performed based on it. In this paper, the plasma actuator was used as an active flow control method to control the flow around the rear part of the Ahmed body with the rear slant angle of 25°. Experiments were carried out in a wind tunnel at two different velocities of U=10m/s and U=20m/s using steady and unsteady excitations. The hot-wire anemometer was used to measure the vortex shedding frequency at the downstream of the body. Pressure distribution was measured using 52 sensors and total drag force was extracted with a load cell. Furthermore, smoke flow visualization was employed to investigate the flow pattern around the body. The results showed that the plasma actuator was more effective on the pressure distribution and total drag force at the velocity of U=10m/s. In fact, by applying steady and unsteady excitations there was 7.3% and 5% drag reduction; respectively. While at the velocity of U=20m/s; the actuator had no significant effect on pressure distribution and total drag. As a remarkable result, the plasma actuator, especially in the steady actuation, has demonstrated its effectiveness on dispersing the longitudinal vortices and suppressing the separated flow on the rear slant at low velocities.
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Optimization of Convective Heat Transfer from Two Heating Generators into Horizontal Enclosure Including A Discrete Obstacle: A Lattice Boltzmann Comprehensive Investigation
Pages : 1277-1286
Authors : T. Naffouti,  L. Thamri,  A. Naffouti,  J. Zinoubi, 
This paper is intended to address the effect of a discrete obstacle on the behavior of flow and heat transfer of laminar natural convection in horizontal enclosure heated from below and symmetrical cooled from sides. Horizontal walls of the enclosure are considered adiabatic except the obstacle. Heating generators of a rectangular form and localized symmetrically are heated at a same uniform temperature. The cold obstacle is placed between active generators that create two thermal plumes. The double population lattice Boltzmann with standard models D2Q9 and D2Q4 for flow and temperature is used to simulate the problem. Prandtl number (Pr), Grashoff number (Gr) and aspect ratio of the enclosure (A) are fixed to 0.71, 105 and 2, respectively. Computational results are performed for pertinent geometric parameters of the obstacle in the following ranges: height 0 ≤ HO ≤ 0.75, position 0 ≤ XCO ≤ 0.5 and length 0.1 ≤ LO ≤ 0.6. It is found that predicted results with LBM are in line with previous investigations. Simulations show that adding the obstacle inside an enclosure conduct to change considerably the thermo-fluid characteristics. Hence, increasing the obstacle height causes a destruction of the interference between thermal plumes. On the other hand, optimum of heat transfer is discovered for a centred obstacle (XCO = 0) and for smaller length and greatest height of this one.
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Accuracy of Dynamic Stall Response for Wind Turbine Airfoils Based On Semi-Empirical and Numerical Methods
Pages : 1287-1296
Authors : S. Rasekh,  M. Hosseini Doust,  S. Karimian Aliabadi, 
The aim of the present study is to investigate the accuracy of two different dynamic stall approaches for wind-turbine airfoils. The first approach is the semi-empirical Leishman-Beddoes model (L-B), and the second is the computational fluid dynamic (CFD) results. National Renewable-Energy Laboratory (NREL) S series airfoils are used, and the simulations are performed in Re=106. For both approaches, aerodynamic coefficients are represented and compared to experimental data. Validation data refer to Ohio State University (OSU) experiments, which are for pitch oscillation. Results show that the accuracy of the L-B and CFD methods is dependent on mean angle of attack, reduced frequency and the phase of motion. The semi-empirical model has appropriate accuracy as well as low computational cost while the CFD unsteady simulation could be properly used to predict the drag coefficient.
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Experimental and Numerical Study of a Submarine and Propeller Behaviors in Submergence and Surface Conditions
Pages : 1297-1308
Authors : A. Vali,  B. Saranjam,  R. Kamali, 
In this paper, hull/propeller interaction of a submarine model which has a realistic geometry, in submergence and surface conditions has been studied. For this purpose, the computational fluid dynamics (CFD) method has been used to solve the viscous, incompressible, two phase flow field (in surface condition) around a model of the propeller and submarine hull with and without propeller. The rotation of the propeller has been modeled using the sliding mesh technique. For turbulent flow modeling and free surface simulation, the k-ω SST model and the volume of fluid method (VOF) have been used, respectively. Experimental data obtained from test conducted by the authors in M.U.T. towing tank have been used to validate the numerical scheme. Comparing numerical and experimental results shows good agreement. The experimental and numerical results show that operation of the propeller near water surface reduces the thrust coefficient of the propeller comparing to open water condition, so that according to experimental results the maximum relative reduction of the thrust coefficient is 8.95%. In addition, the results indicated the amount of hull resistance coefficient in surface condition is more than submergence condition. According to the thrust reduction and wake factors obtained from the numerical results, it is known that their values in surface condition are less than submergence condition. This research can be used for more realistic investigation of hull/propeller interaction and thus, more accurate powering performance prediction of submarines.
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Experimental Study on the Effects of Water-in-oil Emulsions to Wall Shear Stress in the Pipeline Flow
Pages : 1309-1319
Authors : S. S. Dol,  S. F. Wong,  S. K. Wee,  J. S. Lim, 
Study on the emulsion formation mechanically and relate the effect of emulsions to the friction or wall shear stress ( ) in the pipeline flow has not yet been explored. So, this study aims to understand the emulsions formation mechanically and to discover the effects of water-in-oil emulsions to the pipeline flow transport by relating the effect of emulsions to the wall shear stress or friction of the pipe. In this study, wall shear stress is compared at water cuts from 0% to 40%, Reynolds number that covers laminar (1100 < Re < 1800) and transitional (2400 < Re < 2800) flow regime, pipeline constrictions that consists of gradual and sudden contraction with a contraction ratio of 0.50 and 0.75, respectively as well as along the pipelines. To carry out the experiments, the Ultrasonic Velocity Profiler and a lab-scale flow rig were used. The results show that the maximum wall shear stress happens at 10% water cuts, higher Reynolds number results in lower wall shear stress, pipeline constriction with contraction ratio of 0.75 results in higher wall shear stress than the contraction ratio of 0.50 and sudden constriction results in higher wall shear stress than the gradual constriction, and wall shear stress increases with the increase in the length of the pipeline downstream the pipeline constriction. In conclusion, pipeline flow with higher Reynolds number and pipeline constriction (which represents the usage of choke valve in the industries) type gradual constriction ratio 0.50 are recommended to be used in the oil and gas industries because this combination results in the lowest wall shear stress
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A Study on the Effect of Peristalsis and Cilia of MHD Micropolar Fluid Flow through an Inclined Porous Channel
Pages : 1321-1331
Authors : S. V. H. N. Krishna Kumari. P,  D. Saroj Vernekar,  Y. V. K. Ravi Kumar, 
The study of the influence of magnetic field, channel inclination, porous medium and cilia on the Micropolar fluid under different boundary conditions is carried out. The methods of solving Navier Stokes equation specific to Micropolar fluid under the joint influence of these effects are presented. The profiles of velocity (along the flow direction), the micro rotation vector and the variation of pressure rise with time average flow rate for fixed values of other parameters were carried out and the results are discussed.
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Evaluation of Partially Averaged Navier-Stokes Method in Simulating Flow Past a Sphere
Pages : 1333-1348
Authors : S. Saroha,  S. S. Sinha,  S. Lakshmipathy, 
In recent past partially averaged Navier-Stokes equation (PANS) has been proposed as a scale-resolving bridging method for turbulence computations. Despite the geometric simplicity of the involved boundary conditions, the flow past a sphere is ripe with various complex flow phenomena, which make it an excellent test bed to evaluate various computational fluid dynamics modelling methodologies − both in terms of numerical schemes as well as turbulence models. Specifically, in this work we evaluate PANS in conjugation with the standard k-ε model in terms of (i) influence of filter parameters, (ii) sensitivity to free stream viscosity ratio and (iii) choice of numerical schemes at supercritical Reynolds number of 1.14x106. Careful evaluations are made by comparing PANS results against available experimental data as well available detached eddy simulation (DES) and large eddy simulation (LES) results. Our study finds that indeed − as purported by the PANS theory − a reduction in the value of the first filter parameter (fk) successfully captures the complex vortical structures that exist past a sphere, shows far superior performance than unsteady Reynolds-averaged Navier-Stokes (URANS) simulations and somewhat improved performance even over some of the LES studies reported in literature. Our study shows that in terms of most of the quantities of interest, PANS performance is almost at par with that of DES.
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Application of Electric Field to Developing Falling Films using Wire-Plate Electrode Configuration- An Experimental Study
Pages : 1349-1363
Authors : R. Rouhollahi,  S. Baheri Islami,  R. Gharraei,  M. R. Heirani Nobari, 
Experimental investigation of Electrohydrodynamic developing falling film flow of transformer oil has been conducted within an inclined rectangular channel and hydrodynamic characteristics of the flow have been revealed. The electric field has been generated by five overhead thin wire electrodes connected to the positive high DC voltage on the air and the grounded plate electrodes which are placed upon the floor of the channel. It is the first time that the wavy behavior on a liquid falling film's interface has been created by this electrode configuration. A non-intrusive method has been used to measure the local flow structure by a high-speed camera, then statistical characteristics of the wavy falling film have been computed by image processing of the captured video frames. By applying 13-16 kV to the wire electrodes, the influence of EHD force on the wavy behavior of falling film has been conducted for Reynolds number 10-120 in the laminar-wavy regime at three different inclination angles 15◦, 30◦ and 45°. The vertical distance of the high-voltage wire electrodes to ground electrodes has been set to 14 mm. The liquid velocity, film thickness, and wave frequency have been measured for non-electrified and electrified falling film, and their results have been evaluated with other experimental studies and an acceptable agreement has been obtained. The results indicate that the proposed HV wire-grounded plate electrode configuration in this study does not disturb the original structure of the falling film and by intensifying the wavy behavior of laminar falling film can either suppress or enhance heat/mass transfer rate. The effects of the applied voltage on the frequency, velocity and film thickness of the falling liquid film have been also discussed in detail.
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Particle Image Velocimetry and Finite Volume Method Study of Bi-leaflet Artificial Heart Valve
Pages : 1365-1375
Authors : H. Abu Bakar,  A. Abas,  N. Hafizah Mokhtar,  N. Razak,  M. Najib Bin Abdul Hamid, 
The key feature of the bi-leaflet valve is the geometry of the two leaflets, which can be crucial in determining the flow field. In this paper, observations were made on the flow pattern of the blood through the use of bi-leaflet type mechanical prosthetic valve (MHV). Finite volume method (FVM) analysis was conducted using fluid-structure interaction (FSI) method that solved on a dynamic mesh. In terms of the validation, particle image velocimetry (PIV) was used to verify the findings obtained from FVM analysis. The results of velocity and vorticity were the main parameters to be compared. Based on the findings, the results computed for the leaflets motion and the flow field using FVM was found to be in agreement with PIV experimental data. The pressure obtained for the simulation is in the range of 10,666 – 16,000 Pa, which is an ideal and healthy blood pressure level of human. The vorticity was observed to be formed behind the valve with DVI value of 1.275 (simulation) and 1.457 (experiment), lower than the expected range for a normal DVI in mitral valve. The maximum shear stress achieved (22.5481 Pa) is in the range of platelets activation, which could lead to thrombus formation. The maximum Von Mises stress was found to be at the hinge region of the bi-leaflet valve. These results will serve as a basis for valve design to improve the hemodynamic properties of the heart valve.
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Experimental and Theoretical Study on Spray Angles of Bi-Swirl Coaxial Injectors
Pages : 1377-1386
Authors : W. Yoon,  K. Ahn, 
An experimental and theoretical study was undertaken to investigate the effects of the recess length, swirl direction, and mixture ratio on the spray angles of the bi-swirl coaxial injectors with the inner, closed-type and outer, open-type swirl injectors. Eight bi-swirl coaxial injectors with a range of recess lengths and different swirl directions between the inner and outer swirl injectors were used. As the recess length was increased, each bi-swirl coaxial injector exhibited external-mixing, tip-mixing, or internal-mixing spray characteristics. To measure the spray angles, cold-flow tests for which the mass flow rates of the two injectors were varied were performed to capture the spray images. The single-injection results indicated that the spray cone angles of both the inner and outer swirl injectors were relatively unaffected by the mass flow rate and the swirl direction, with the recess length influencing the spray cone angles of the inner swirl injectors. The bi-injection tests show that the spray angles are significantly dependent on the recess length and the mixture ratio, while also being affected by the swirl direction, especially regarding the internal-mixing bi-swirl coaxial injectors. Theoretical models that can predict the spray angles were developed and compared using the experimental data. The theoretical models could approximate the combined spray angles of the internal-mixing bi-swirl coaxial injectors.
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Determination of Pressure Drop Characteristics of Fly Ash Suspension with Additive for Hydraulic Transportation
Pages : 1387-1393
Authors : S. Kumar, 
Present study was conducted with objective of investigating the fly ash slurry transportation at higher solid concentration. The rheological behaviour of fine-particulate fly ash slurry suspension was studied with the additive. Pressure drop was measured in 50 mm diameter pipe with fly ash slurry at solid concentration (Cw) of 30, 40, 50 and 60% (by weight). Measurements were made for flow velocities in the range of 1 to 3 ms-1. Sodium sulfate was used as an additive in range of 0.2-0.6% (by weight). Addition of sodium sulfate in fly ash slurry suspension tends to improve the pressure drop characteristics. Reduction rate in pressure drop was pronounced more with 0.4% sodium sulfate in fly ash slurry and marginal with 0.2 and 0.6%. Therefore, results revealed that fly ash-water slurry can be transported at high concentration thorough pipelines with lower power consumption.
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Improvement of Compressible Vorticity Confinement Method by Combining It with Vortex Feature Detection Methods
Pages : 1395-1406
Authors : M. Mohseni,  M. Malek Jafarian, 
In the present study, the performance of the vorticity confinement method has been improved by combining it with the vortex feature detection methods. In the conventional vorticity confinement method, the only parameter to apply or not to apply vorticity confinement is the non-zero value of vorticity. On the other hand, the presence of vorticity in some cases, like the boundary layer and the shear layer flows, does not imply the presence of vortices. Applying the vorticity confinement at these points can lead to errors, in addition to loss of solution time. In order to solve this problem, using the combination of vorticity confinement method and four methods of vortex feature detection (nondimensional Q, nondimensional λ_2, nondimensional modified ∆, and the S-Ω correlation) the vorticity confinement term is applied only in vortex regions. In order to investigate the effects of this combination, the compressible Euler equation has been investigated for the problem of two-dimensional stationary single vortex at Mach number 0.5. The results indicate significant positive effects in reducing the solving time, decreasing the sensitivity of the solution to the amount of confinement parameter and significant elimination of the oscillation.
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One-Dimensional Mathematical Model for Solar Drying of Beds of Sludge
Pages : 1407-1419
Authors : A. M. O. Siqueira,  N. Krink,  F. P. S. Pereira,  F. G. Villela,  G. S. Silva,  A. F. Moura, 
A one-dimensional mathematical model for the description of solar drying of beds of sewage sludge is developed and implemented with the software Engineering-Equation-Solver. After the discussion of relevant literature, the assumptions and general conditions of the model are explained. Governing differential equations for heat and mass transport inside the sludge are derived, followed by a discussion about correlations used for the determination of surface transport phenomena and for the description of thermophysical properties. Numerical discretization is achieved locally through the Finite Difference Method and temporary through the Runge-Kutta-Method. Finally, a parametric analysis on the sludge drying process is carried out. The obtained results demonstrate the effect of ambient parameters such as solar radiation, airflow rate, gas temperature, geometric aspects etc. on the drying process. The developed model may be used for further prediction and estimation of drying characteristics under several conditions.
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Comparative Study of Reversal Flow during the Evaporation or Condensation of Water and Ethanol Film in a Vertical Channel
Pages : 1421-1426
Authors : K. Sellami,  N. Labsi,  M. Feddaoui,  M. Oubella,  Y. K. Benkahla,  M. Najim, 
A comparative study of reversal flow is carried out to investigate the effect of thermal and mass buoyancy forces with evaporation or condensation along a vertical channel. The highlight is focused on the effects of phase change of two different liquid films having widely different properties, on heat and mass transfer rates in the channel. The evaporation occurs along isothermal and wetted walls. The induced laminar upward flow consists of a mixture of blowing air and vapour of water or ethanol. Various combinations of thermal and solutal boundary conditions (cooling and heating modes) are considered to investigate extensively their influence on the flow development. A two-dimensional steady state and elliptical flow model is used and the liquid film is assumed extremely thin. The governing equations of the model are solved by FVM and the velocity-pressure fields are treated with the SIMPLER algorithm. The results show that the buoyancy forces have a significant effect on the hydrodynamic, thermal and mass fields of both gas mixtures. In addition, the flow reversal is predicted with a relatively high temperature difference between the air-mixture and the wetted walls.
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Two Semi-Analytical Methods Applied to Hydrodynamic Stability of Dean Flow
Pages : 1427-1435
Authors : H. Nowruzi,  S. Salman Nourazar,  H. Ghassemi, 
Hydrodynamic stability of Dean flow is studied using two semi-analytical methods of differential transform method (DTM) and Homotopy perturbation method (HPM). These two methods are evaluated to examine the effectiveness and accuracy of the solution of considered eigenvalue problem. Very good accordance is achieved between our semi-analytical results compared to existing numerical data. Based on our analysis, in the similar number of truncated terms, HPM is more accurate in comparison with DTM. We also concluded that for the higher wave numbers, HPM provide more accurate results with less truncated terms compared to the DTM. Finally, we found the critical Dean number 35.927 corresponding to wave number of 3.952 for onset of instability of Dean flow.
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Design of a Mini Double-Discharge Centrifugal Pump under Multiphase Flow by CFD and Experimental Verification
Pages : 1437-1448
Authors : Z. Parlak,  M. Kemerli,  T. Engin,  Y. Koç, 
Pumps are irreplaceable products in various systems and processes. Pumps can be manufactured in various size in industry. The mini pumps are commonly used in some household electrical appliances, automobile etc. Some pumping applications is required two outlet ports. The use of two pumps in such a case brings high costs. Instead, pumping on two different lines with a single pump provides both a more compact design and lower cost, if the system is available. In this study, it is aimed to design a single-suction and double-outlet pump by using a single electric motor. For this purpose, a conceptual design for the pump has been proposed and design parameters which have an effect on the pump performance have been determined. Pump performance have been calculated by using the ANSYS Fluent, Computational Fluid Dynamics (CFD) code considering to multiphase flow, and optimization studies have been performed with the determined parameters. The pumps have been obtained by the optimization works have been manufactured and tested to investigate whether the pumps provide the expected operating conditions and performances. Finally, the CFD results have been verified by the tests and the pump provided the expected operating conditions and performances.
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