Search results for: secondary flow.

Authors: Samy M. El-Behery, Mofreh H. Hamed

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This paper presents a computational study of the separated flow in a planer asymmetric diffuser. The steady RANS equations for turbulent incompressible fluid flow and six turbulence closures are used in the present study. The commercial software code, FLUENT 6.3.26, was used for solving the set of governing equations using various turbulence models. Five of the used turbulence models are available directly in the code while the v2-f turbulence model was implemented via User Defined Scalars (UDS) and User Defined Functions (UDF). A series of computational analysis is performed to assess the performance of turbulence models at different grid density. The results show that the standard k-ω, SST k-ω and v2-f models clearly performed better than other models when an adverse pressure gradient was present. The RSM model shows an acceptable agreement with the velocity and turbulent kinetic energy profiles but it failed to predict the location of separation and attachment points. The standard k-ε and the low-Re k- ε delivered very poor results.

Keywords: Turbulence models, turbulent flow, wall functions, separation, reattachment, diffuser.

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Authors: K. Noah, F.-S. Lien

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In Computational Fluid Dynamics (CFD), there are a variety of numerical methods, of which some depend on macroscopic model representatives. These models can be solved by finite-volume, finite-element or finite-difference methods on a microscopic description. However, the lattice Boltzmann method (LBM) is considered to be a mesoscopic particle method, with its scale lying between the macroscopic and microscopic scales. The LBM works well for solving incompressible flow problems, but certain limitations arise from solving compressible flows, particularly at high Mach numbers. An improved lattice Boltzmann model for compressible flow problems is presented in this research study. A higher-order Taylor series expansion of the Maxwell equilibrium distribution function is used to overcome limitations in LBM when solving high-Mach-number flows. Large eddy simulation (LES) is implemented in LBM to simulate turbulent jet flows. The results have been validated with available experimental data for turbulent compressible free jet flow at subsonic speeds.

Keywords: Compressible lattice Boltzmann metho-, large eddy simulation, turbulent jet flows.

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Authors: Mosses E. Lufuke, Lorna M. Kamau

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This paper attempted to assess whether the size of the regional economic bloc has an impact to the flow of trade to a particular country. Two different sized blocs (COMESA and EAC) and one country (Tanzania) have been used as the point of references. Using the results from of the analyses, the paper also was anticipated to establish whether it was rational for Tanzania to withdraw its membership from COMESA (the larger bloc) to join EAC (the small one). Gravity model has been used to estimate the relationship between the variables, from which the bilateral trade flows between Tanzania and the eighteen member countries of the two blocs (COMESA and EAC) was employed for the time between 2000 and 2013. In the model, the dummy variable for regional bloc (bloc) at which the Tanzania trade partner countries belong are also added to the model to understand which trade bloc exhibit higher trade flow with Tanzania. From the findings, it was noted that over the period of study (2000-2013) Tanzania acknowledged more than 257% of trade volume in EAC than in COMESA. Conclusive, it was noted that the flow of trade is explained by many other variables apart from the size of regional bloc; and that the size by itself offer insufficient evidence in causality relationship. The paper therefore remain neutral on such staggered switching decision since more analyses are required to establish the country’s trade flow, especially when if it had been in multiple membership of COMESA and EAC.

Keywords: Economic Bloc, Flow of Trade, Size of Bloc, Switching.

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Authors: A. Abou El-Azm Aly, F. Nicolleau, T. M. Michelitsch, A. F. Nowakowski

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The dispersion of heavy particles line in an isotropic and incompressible three-dimensional turbulent flow has been studied using the Kinematic Simulation techniques to find out the evolution of the line fractal dimension. In this study, the fractal dimension of the line is found for different cases of heavy particles inertia (different Stokes numbers) in the absence of the particle gravity with a comparison with the fractal dimension obtained in the diffusion case of material line at the same Reynolds number. It can be concluded for the dispersion of heavy particles line in turbulent flow that the particle inertia affect the fractal dimension of a line released in a turbulent flow for Stokes numbers 0.02 < St < 2. At the beginning for small times, most of the different cases are not affected by the inertia until a certain time, the particle response time τa, with larger time as the particles inertia increases, the fractal dimension of the line increases owing to the particles becoming more sensitive to the small scales which cause the change in the line shape during its journey.

Keywords: Heavy particles, two-phase flow, Kinematic Simulation, Fractal dimension.

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Authors: Mehdi Kheradmand, Mehdi Azhdary Moghaddam, Abdolreza Zahiri, Khalil Ghorbani

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This research compares results of major methods of determining the flow discharge using experimental relationships with results from the M5 decision tree model in meandering compound sections in several laboratory channels. It was found that the M5 decision tree model enjoyed greater accuracy of statistical parameters compared to methods to the said methods. This suggested that the M5 decision tree model has highly improved the calculated accuracy of the flow discharge in meandering compound channels.

Keywords: Stage-discharge relationship, M5 decision tree model, compound section, meandering compound channel.

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Authors: Adriana Alexandru, Ovidiu Bica, Eleonora Tudora, Cristina Simona Alecu, Cristina-Adriana Alexandru, Ioan Covalcic

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This paper presents the results of the authors in designing, experimenting, assessing and transferring an innovative approach to energy education in secondary schools, aimed to enhance the quality of learning in terms of didactic curricula and pedagogic methods. The training is online delivered to youngsters via e-Books and portals specially designed for this purpose or by learning by doing via interactive games. An online educational methodology is available teachers.

Keywords: Education, eLearning, Energy Efficiency, InternetMethodology, Renewable Energy Sources.

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Authors: Shams-ul-Islam, Raheela Manzoor, Zhou Chao Ying

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A two-dimensional numerical study for flow past a square cylinder in presence of flat plate both at upstream and downstream position is carried out using the single-relaxation-time lattice Boltzmann method for gap spacing 0.5 and 1. We select Reynolds numbers from 80 to 200. The wake structure mechanism within gap spacing and near wake region, vortex structures around and behind the main square cylinder in presence of flat plate are studied and compared with flow pattern around a single square cylinder. The results are obtained in form of vorticity contour, streamlines, power spectra analysis, time trace analysis of drag and lift coefficients. Four different types of flow patterns were observed in both configurations, named as (i) Quasi steady flow (QSF), (ii) steady flow (SF), (iii) shear layer reattachment (SLR), (iv) single bluff body (SBB). It is observed that upstream flat plate plays a vital role in significant drag reduction. On the other hand, rate of suppression of vortex shedding is high for downstream flat plate case at low Reynolds numbers. The reduction in mean drag force and root mean square value of drag force for upstream flat plate case are89.1% and 86.3% at (Re, g) = (80, 0.5d) and (120, 1d) and reduction for downstream flat plate case for mean drag force and root mean square value of drag force are 11.10% and 97.6% obtained at (180, 1d) and (180, 0.5d).

Keywords: Detached flat plates, drag and lift coefficients, Reynolds numbers, square cylinder, Strouhal number.

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Authors: Wichai Pattanapol, Sarah J. Wakes, Michael J. Hilton, Katharine J.M. Dickinson

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Turbulence modeling of large-scale flow over a vegetated surface is complex. Such problems involve large scale computational domains, while the characteristics of flow near the surface are also involved. In modeling large scale flow, surface roughness including vegetation is generally taken into account by mean of roughness parameters in the modified law of the wall. However, the turbulence structure within the canopy region cannot be captured with this method, another method which applies source/sink terms to model plant drag can be used. These models have been developed and tested intensively but with a simple surface geometry. This paper aims to compare the use of roughness parameter, and additional source/sink terms in modeling the effect of plant drag on wind flow over a complex vegetated surface. The RNG k-ε turbulence model with the non-equilibrium wall function was tested with both cases. In addition, the k-ω turbulence model, which is claimed to be computationally stable, was also investigated with the source/sink terms. All numerical results were compared to the experimental results obtained at the study site Mason Bay, Stewart Island, New Zealand. In the near-surface region, it is found that the results obtained by using the source/sink term are more accurate than those using roughness parameters. The k-ω turbulence model with source/sink term is more appropriate as it is more accurate and more computationally stable than the RNG k-ε turbulence model. At higher region, there is no significant difference amongst the results obtained from all simulations.

Keywords: CFD, canopy flow, surface roughness, turbulence models.

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Authors: Rubén Bãnos, José Arcos, Oscar Bautista, Federico Méndez

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The Oscillatory electroosmotic flow (OEOF) in power law fluids through a microchannel is studied numerically. A time-dependent external electric field (AC) is suddenly imposed at the ends of the microchannel which induces the fluid motion. The continuity and momentum equations in the x and y direction for the flow field were simplified in the limit of the lubrication approximation theory (LAT), and then solved using a numerical scheme. The solution of the electric potential is based on the Debye-H¨uckel approximation which suggest that the surface potential is small,say, smaller than 0.025V and for a symmetric (z : z) electrolyte. Our results suggest that the velocity profiles across the channel-width are controlled by the following dimensionless parameters: the angular Reynolds number, Reω, the electrokinetic parameter, ¯κ, defined as the ratio of the characteristic length scale to the Debye length, the parameter λ which represents the ratio of the Helmholtz-Smoluchowski velocity to the characteristic length scale and the flow behavior index, n. Also, the results reveal that the velocity profiles become more and more non-uniform across the channel-width as the Reω and ¯κ are increased, so oscillatory OEOF can be really useful in micro-fluidic devices such as micro-mixers.

Keywords: Oscillatory electroosmotic flow, Non-Newtonian fluids, power-law model, low zeta potentials.

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Authors: Zhenquan Li, Niharika Singh

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Streamribbon is used to visualize the rotation of the fluid flow. The rotation of flow is useful in fluid mechanics, engineering and geophysics. This paper introduces the construction technique of streamribbon using the streamline which is generated based on the law of mass conservation. The accuracy of constructed streamribbons is shown through two examples.

Keywords: Mass conservation, streamline, streamtube, streamribbon.

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Authors: Danping Lin, C.K.M. Lee

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Re-entrant scheduling is an important search problem with many constraints in the flow shop. In the literature, a number of approaches have been investigated from exact methods to meta-heuristics. This paper presents a genetic algorithm that encodes the problem as multi-level chromosomes to reflect the dependent relationship of the re-entrant possibility and resource consumption. The novel encoding way conserves the intact information of the data and fastens the convergence to the near optimal solutions. To test the effectiveness of the method, it has been applied to the resource-constrained re-entrant flow shop scheduling problem. Computational results show that the proposed GA performs better than the simulated annealing algorithm in the measure of the makespan

Keywords: Resource-constrained, re-entrant, genetic algorithm (GA), multi-level encoding

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Authors: J. Sarkar, Souvik Bhattacharyya, M. Ramgopal

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This paper presents the experimental as well as the simulated performance studies on the transcritical CO2 heat pumps for simultaneous water cooling and heating; effects of water mass flow rates and water inlet temperatures of both evaporator and gas cooler on the cooling and heating capacities, system COP and water outlets temperatures are investigated. Study shows that both the water mass flow rate and inlet temperature have significant effect on system performances. Test results show that the effect of evaporator water mass flow rate on the system performances and water outlet temperatures is more pronounced (COP increases 0.6 for 1 kg/min) compared to the gas cooler water mass flow rate (COP increases 0.4 for 1 kg/min) and the effect of gas cooler water inlet temperature is more significant (COP decreases 0.48 for given ranges) compared to the evaporator water inlet temperature (COP increases 0.43 for given ranges). Comparisons of experimental values with simulated results show the maximum deviation of 5% for cooling capacity, 10% for heating capacity, 16% for system COP. This study offers useful guidelines for selecting appropriate water mass flow rate to obtain required system performance.

Keywords: CO2 heat pump, experiment, simulation, performance characteristics.

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Authors: Bülent Dilmaç, Didem Aydoğan

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The use of new technologies such internet (e-mail, chat rooms) and cell phones has steeply increased in recent years. Especially among children and young people, use of technological tools and equipments is widespread. Although many teachers and administrators now recognize the problem of school bullying, few are aware that students are being harassed through electronic communication. Referred to as electronic bullying, cyber bullying, or online social cruelty, this phenomenon includes bullying through email, instant messaging, in a chat room, on a website, or through digital messages or images sent to a cell phone. Cyber bullying is defined as causing deliberate/intentional harm to others using internet or other digital technologies. It has a quantitative research design nd uses relational survey as its method. The participants consisted of 300 secondary school students in the city of Konya, Turkey. 195 (64.8%) participants were female and 105 (35.2%) were male. 39 (13%) students were at grade 1, 187 (62.1%) were at grade 2 and 74 (24.6%) were at grade 3. The “Cyber Bullying Question List" developed by Ar─▒cak (2009) was given to students. Following questions about demographics, a functional definition of cyber bullying was provided. In order to specify students- human values, “Human Values Scale (HVS)" developed by Dilmaç (2007) for secondary school students was administered. The scale consists of 42 items in six dimensions. Data analysis was conducted by the primary investigator of the study using SPSS 14.00 statistical analysis software. Descriptive statistics were calculated for the analysis of students- cyber bullying behaviour and simple regression analysis was conducted in order to test whether each value in the scale could explain cyber bullying behaviour.

Keywords: Cyber bullying, Values, Secondary SchoolStudents

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Authors: A. Ursoiu, C. Paul, C. Marcu, M. Ungurean, F. Péter

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Sol-gel immobilization of enzymes, which can improve considerably their properties, is now one of the most used techniques. By deposition of the entrapped lipase on a solid support, a new and improved biocatalyst was obtained, which can be used with excellent results in acylation reactions. In this paper, lipase B from Candida antarctica was double immobilized on different adsorbents. These biocatalysts were employed in the kinetic resolution of several aliphatic secondary alcohols in organic medium. High total recovery yields of enzymatic activity, up to 560%, were obtained. For all the studied alcohols the enantiomeric ratios E were over 200. The influence of the reaction medium was studied for the kinetic resolution of 2-pentanol.

Keywords: Double immobilization, enantioselectivity, kineticresolution, lipase, racemates, sol-gel entrapment.

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Authors: Morten Willatzen, Mikhail Vladimirovich Deryabin

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The governing two-dimensional equations of a heterogeneous material composed of a fluid (allowed to flow in the absence of acoustic excitations) and a crystalline piezoelectric cubic solid stacked one-dimensionally (along the z direction) are derived and special emphasis is given to the discussion of acoustic group velocity for the structure as a function of the wavenumber component perpendicular to the stacking direction (being the x axis). Variations in physical parameters with y are neglected assuming infinite material homogeneity along the y direction and the flow velocity is assumed to be directed along the x direction. In the first part of the paper, the governing set of differential equations are derived as well as the imposed boundary conditions. Solutions are provided using Hamilton-s equations for the wavenumber vs. frequency as a function of the number and thickness of solid layers and fluid layers in cases with and without flow (also the case of a position-dependent flow in the fluid layer is considered). In the first part of the paper, emphasis is given to the small-frequency case. Boundary conditions at the bottom and top parts of the full structure are left unspecified in the general solution but examples are provided for the case where these are subject to rigid-wall conditions (Neumann boundary conditions in the acoustic pressure). In the second part of the paper, emphasis is given to the general case of larger frequencies and wavenumber-frequency bandstructure formation. A wavenumber condition for an arbitrary set of consecutive solid and fluid layers, involving four propagating waves in each solid region, is obtained again using the monodromy matrix method. Case examples are finally discussed.

Keywords: Flow, acoustics, solid-fluid structures, periodicity.

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Authors: Babajide S. Adeokin, Oguntoyinbo O. Kazeem

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The not so pleasing state of the nation's quality of education has been a major area of research. Many researchers have looked into various aspects of the educational system and organizational structure in relation to the quality of service delivery of the staff members. However, there is paucity of research in areas relating to the sense of competence and commitment in relation to leadership styles. Against this backdrop, this study investigated the impact of leadership style and sense of competence on the performance of post-primary school teachers in Oyo state Nigeria. Data were generated across public secondary schools in the city using survey design method. Ibadan as a metropolis has eleven local government areas contained in it. A systematic random sampling technique of the eleven local government areas in Ibadan was done and five local government areas were selected. The selected local government areas are Akinyele, Ibadan North, Ibadan North-East, Ibadan South and Ibadan South-West. Data were obtained from a range of two – three public secondary schools selected in each of the local government areas mentioned above. Also, these secondary schools are a representation of the variations in the constructs under consideration across the Ibadan metropolis. Categorically, all secondary school teachers in Ibadan were clustered into selected schools in those found across the five local government areas. In all, a total of 272 questionnaires were administered to public secondary school teachers, while 241 were returned. Findings revealed that transformational leadership style makes room for job commitment when compared with transactional and laissez-faire leadership styles. Teachers with a high sense of competence are more likely to demonstrate more commitment to their job than others with low sense of competence. We recommend that, it is important an assessment is made of the leadership styles employed by principals and school administrators. This guides administrators and principals in to having a clear, comprehensive knowledge of the style they currently adopt in the management of the staff and the school as a whole; and know where to begin the adjustment process from. Also to make an impact on student achievement, being attentive to teachers’ levels of commitment may be an important aspect of leadership for school principals.

Keywords: Leadership style, sense of competence, teachers, public secondary schools, Ibadan.

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Authors: A. M. Tahsini

Abstract:

Solid fuel transient burning behavior under oxidizer gas flow is numerically investigated. It is done using analysis of the regression rate responses to the imposed sudden and oscillatory variation at inflow properties. The conjugate problem is considered by simultaneous solution of flow and solid phase governing equations to compute the fuel regression rate. The advection upstream splitting method is used as flow computational scheme in finite volume method. The ignition phase is completely simulated to obtain the exact initial condition for response analysis. The results show that the transient burning effects which lead to the combustion instabilities and intermittent extinctions could be observed in solid fuels as the solid propellants.

Keywords: Extinction, Oscillation, Regression rate, Response, Transient burning.

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Authors: Asep Saepuloh, Katsuaki Koike

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Field mapping activity for an active volcano mainly in the Torrid Zone is usually hampered by several problems such as steep terrain and bad atmosphere conditions. In this paper we present a simple solution for such problem by a combination Synthetic Aperture Radar (SAR) and geostatistical methods. By this combination, we could reduce the speckle effect from the SAR data and then estimate roughness distribution of the pyroclastic flow deposits. The main purpose of this study is to detect spatial distribution of new pyroclastic flow deposits termed as P-zone accurately using the β°data from two RADARSAT-1 SAR level-0 data. Single scene of Hyperion data and field observation were used for cross-validation of the SAR results. Mt. Merapi in central Java, Indonesia, was chosen as a study site and the eruptions in May-June 2006 were examined. The P-zones were found in the western and southern flanks. The area size and the longest flow distance were calculated as 2.3 km2 and 6.8 km, respectively. The grain size variation of the P-zone was mapped in detail from fine to coarse deposits regarding the C-band wavelength of 5.6 cm.

Keywords: Geostatistical Method, Mt. Merapi, Pyroclastic, RADARSAT-1.

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Authors: J. B. V. Subrahmanyam, C. Radhakrishna

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This paper presents a simple three phase power flow method for solution of three-phase unbalanced radial distribution system (RDN) with voltage dependent loads. It solves a simple algebraic recursive expression of voltage magnitude, and all the data are stored in vector form. The algorithm uses basic principles of circuit theory and can be easily understood. Mutual coupling between the phases has been included in the mathematical model. The proposed algorithm has been tested with several unbalanced radial distribution networks and the results are presented in the article. 8- bus and IEEE 13 bus unbalanced radial distribution system results are in agreements with the literature and show that the proposed model is valid and reliable.

Keywords: radial distribution networks, load flow, circuitmodel, three-phase four-wire, unbalance.

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Authors: Shanthi Thomas

Abstract:

This research paper presents the current practices of teacher professional development, perceived as beneficial by teachers themselves, in a private secondary school in Brunei Darussalam. This is part of the findings of a larger qualitative study on teacher empowerment, using ethnographic methods for data collection, i.e. participant observation, interviews and document analysis. The field work was carried out over a period of six months in 2013. An analysis of the field data revealed multiple pathways of teacher professional development existing in the school. The results indicate that school leaders, the teacher community in the school, students, and the teachers themselves were the agents in a school that facilitated teacher empowerment. Besides contributing to the knowledge base on teacher professional development, the results of this study provide directions for educational policy makers in their efforts to enhance professional development in secondary schools of similar characteristics. For school leaders and the teacher community, these findings offer guidelines for maximizing the opportunities for these professional development practices, by strengthening collegiality and by using the existing structures optimally for the benefit of all concerned.

Keywords: Colleagues and the wider teacher community, school leaders, self-driven professional development, teacher professional development.

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Authors: Motahar Reza, Anadi Sankar Gupta

Abstract:

An analysis is made of the flow of an incompressible viscoelastic fluid (of small memory) over a porous plate subject to suction or blowing. It is found that velocity at a point increases with increase in the elasticity in the fluid. It is also shown that wall shear stress depends only on suction and is also independent of the material of fluids. No steady solution for velocity distribution exists when there is blowing at the plate. Temperature distribution in the boundary layer is determined and it is found that temperature at a point decreases with increase in the elasticity in the fluid.

Keywords: Viscoelastic fluid, Flow past a porous plate, Heat transfer

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Authors: M. Salmanpour, O. Nourani Zonouz

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In this research, a numerical simulation of an Electrohydrodynamic (EHD) actuator’s effects on the flow around a square cylinder by using a finite volume method has been investigated. This is one of the newest ways for controlling the fluid flows. Two plate electrodes are flush-mounted on the surface of the cylinder and one wire electrode is placed on the line with zero angle of attack relative to the stagnation point and excited with DC power supply. The discharge produces an electric force and changes the local momentum behaviors in the fluid layers. For this purpose, after selecting proper domain and boundary conditions, the electric field relating to the problem has been analyzed and then the results in the form of electrical body force have been entered in the governing equations of fluid field (Navier-Stokes equations). The effect of ionic wind resulted from the Electrohydrodynamic actuator, on the velocity, pressure and the wake behind cylinder has been considered. According to the results, it is observed that the fluid flow accelerates in the nearest wall of the frontal half of the cylinder and the pressure difference between frontal and hinder cylinder is increased.

Keywords: CFD, corona discharge, electro hydrodynamics, flow around square cylinders.

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Authors: Nouri Sabrina, Benzeghiba Mohamed, Ghezal Abderrahmane

Abstract:

Numerical parametric study is conducted to study the effects of ampoule rotation on the flows and the dopant segregation in vertical bridgman (vb) crystal growth. Calculations were performed in unsteady state. The extended darcy model, which includes the time derivative and coriolis terms, has been employed in the momentum equation. It’s found that the convection, and dopant segregation can be affected significantly by ampoule rotation, and the effect is similar to that by an axial magnetic field. Ampoule rotation decreases the intensity of convection and stretches the flow cell axially. When the convection is weak, the flow can be suppressed almost completely by moderate ampoule rotation and the dopant segregation becomes diffusion-controlled. For stronger convection, the elongated flow cell by ampoule rotation may bring dopant mixing into the bulk melt reducing axial segregation at the early stage of the growth. However, if the cellular flow cannot be suppressed completely, ampoule rotation may induce larger radial segregation due to poor mixing.

Keywords: Numerical Simulation, Heat and mass transfer, vertical solidification, chemical segregation.

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Authors: A. M. Tahsini, S. Tadayon Mousavi

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In the present paper, a numerical investigation has been carried out to classify and clarify the effects of paramount parameters on turbulent impinging slot jets. The effects of nozzle-s exit turbulent intensity, distance between nozzle and impinging plate are studied at Reynolds number 5000 and 20000. In addition, the effect of Mach number that is varied between 0.3-0.8 at a constant Reynolds number 133000 is investigated to elucidate the effect of compressibility in impinging jet upon a flat plate. The wall that is located at the same level with nozzle-s exit confines the flow. A compressible finite volume solver is implemented for simulation the flow behavior. One equation Spalart-Allmaras turbulent model is used to simulate turbulent flow at this study. Assessment of the Spalart-Allmaras turbulent model at high nozzle to plate distance, and giving enough insights to characterize the effect of Mach number at high Reynolds number for the complex impinging jet flow are the remarkable results of this study.

Keywords: Impinging jet, Numerical simulation, Turbulence.

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Authors: D. K. Tiwari, Mukesh Kumar Awasthi, G. S. Agrawal

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The effect of an axial electric field on the capillary instability of a cylindrical interface in the presence of heat and mass transfer has been investigated using viscous potential flow theory. In viscous potential flow, the viscous term in Navier-Stokes equation vanishes as vorticity is zero but viscosity is not zero. Viscosity enters through normal stress balance in the viscous potential flow theory and tangential stresses are not considered. A dispersion relation that accounts for the growth of axisymmetric waves is derived and stability is discussed theoretically as well as numerically. Stability criterion is given by critical value of applied electric field as well as critical wave number. Various graphs have been drawn to show the effect of various physical parameters such as electric field, heat transfer capillary number, conductivity ratio, permittivity ratio on the stability of the system. It has been observed that the axial electric field and heat and mass transfer both have stabilizing effect on the stability of the system.

Keywords: Capillary instability, Viscous potential flow, Heat and mass transfer, Axial electric field.

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Authors: Cha’o-Kuang Chen, Ching-Chang Cho

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The study investigates the mixing performance of electrokinetically-driven power-law fluids in a microchannel containing patterned trapezoid blocks. The effects of the geometry parameters of the patterned trapezoid blocks and the flow behavior index in the power-law model on the mixing efficiency within the microchannel are explored. The results show that the mixing efficiency can be improved by increasing the width of the blocks and extending the length of upper surface of the blocks. In addition, the results show that the mixing efficiency increases with an increasing flow behavior index. Furthermore, it is shown that a heterogeneous patterning of the zeta potential on the upper surfaces of the trapezoid blocks prompts the formation of local flow recirculations, and therefore improves the mixing efficiency. Consequently, it is shown that the mixing performance improves with an increasing magnitude of the heterogeneous surface zeta potential.

Keywords: Non-Newtonian fluid, Power-law fluid, Electroosmotic flow, Passive mixer, Mixing, Micromixer.

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Authors: G.Ashwini, A.T.Eswara

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This paper examines the forced convection flow of incompressible, electrically conducting viscous fluid past a sharp wedge in the presence of heat generation or absorption with an applied magnetic field. The system of partial differential equations governing Falkner - Skan wedge flow and heat transfer is first transformed into a system of ordinary differential equations using similarity transformations which is later solved using an implicit finite - difference scheme, along with quasilinearization technique. Numerical computations are performed for air (Pr = 0.7) and displayed graphically to illustrate the influence of pertinent physical parameters on local skin friction and heat transfer coefficients and, also on, velocity and temperature fields. It is observed that the magnetic field increases both the coefficients of skin friction and heat transfer. The effect of heat generation or absorption is found to be very significant on heat transfer, but its effect on the skin friction is negligible. Indeed, the occurrence of overshoot is noticed in the temperature profiles during heat generation process, causing the reversal in the direction of heat transfer.

Keywords: Heat generation / absorption, MHD Falkner- Skan flow, skin friction and heat transfer

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Authors: Nor Hayati Ibrahim, Yaakob B. Che Man, Chin Ping Tan, Nor Aini Idris

Abstract:

Interaction effects of xanthan gum (XG), carboxymethyl cellulose (CMC), and locust bean gum (LBG) on the flow properties of oil-in-water emulsions were investigated by a mixture design experiment. Blends of XG, CMC and LBG were prepared according to an augmented simplex-centroid mixture design (10 points) and used at 0.5% (wt/wt) in the emulsion formulations. An appropriate mathematical model was fitted to express each response as a function of the proportions of the blend components that are able to empirically predict the response to any blend of combination of the components. The synergistic interaction effect of the ternary XG:CMC:LBG blends at approximately 33-67% XG levels was shown to be much stronger than that of the binary XG:LBG blend at 50% XG level (p < 0.05). Nevertheless, an antagonistic interaction effect became significant as CMC level in blends was more than 33% (p < 0.05). Yield stress and apparent viscosity (at 10 s-1) responses were successfully fitted with a special quartic model while flow behaviour index and consistency coefficient were fitted with a full quartic model (R2 adjusted ≥ 0.90). This study found that a mixture design approach could serve as a valuable tool in better elucidating and predicting the interaction effects beyond the conventional twocomponent blends.

Keywords: O/W emulsions, flow behavior, polysaccharideinteraction, mixture design.

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Authors: Ayman A. El-Saleh, Mahamod Ismail, Mohd. A. M. Ali, Ahmed N. H. Alnuaimy

Abstract:

The dynamic spectrum allocation solutions such as cognitive radio networks have been proposed as a key technology to exploit the frequency segments that are spectrally underutilized. Cognitive radio users work as secondary users who need to constantly and rapidly sense the presence of primary users or licensees to utilize their frequency bands if they are inactive. Short sensing cycles should be run by the secondary users to achieve higher throughput rates as well as to provide low level of interference to the primary users by immediately vacating their channels once they have been detected. In this paper, the throughput-sensing time relationship in local and cooperative spectrum sensing has been investigated under two distinct scenarios, namely, constant primary user protection (CPUP) and constant secondary user spectrum usability (CSUSU) scenarios. The simulation results show that the design of sensing slot duration is very critical and depends on the number of cooperating users under CPUP scenario whereas under CSUSU, cooperating more users has no effect if the sensing time used exceeds 5% of the total frame duration.

Keywords: Capacity, cognitive radio, optimization, spectrumsensing.

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Authors: Arunrungrusmi S, Chaokamnerd W , Tanitteerapan T , Mungkung N., Yuji T.

Abstract:

This research aimed to develop plasma system used in air conditioners. This developed plasma system could be installed in the air conditioners - all split type. The quality of air could be improved to be equal to present plasma system. Development processes were as follows: 1) to study the plasma system used in the air conditioners, 2) to design a plasma generator, 3) to develop the plasma generator, and 4) to test its performance in many types of the air conditioners. This plasma system was developed by AC high voltage – 14 kv with a frequency of 50 kHz. Carbon was a conductor to generate arc in air purifier system. The research was tested by installing the plasma generator in the air conditioners - wall type. Whereas, there were 3 types of installations: air flow out, air flow in, and room center. The result of the plasma generator installed in the air conditioners, split type, revealed that the air flow out installation provided the highest average of o-zone at 223 mg/h. This type of installation provided the highest efficiency of air quality improvement. Moreover, the air flow in installation and the room center installation provided the average of the o-zone at 163 mg/h and 64 mg/h, respectively.

Keywords: Air Conditioner, Plasma generator, High voltage, Optimization, Installation position.

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