bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanical Properties of Tube-Shaped Poly (Vinyl Alcohol) Hydrogel Blood Vessel Biomodel
Authors: Kosukegawa Hiroyuki , Shida Shuya , Hashida Yoko , Ohta Makoto
Published: March 2011

Biomodels, which mimic the shape and motion of blood vessels, have been developed for clinical training in endovascular intervention and for the technical development of interventional devices such as stents. The present authors have developed a biomodel made of poly (vinyl alcohol) hydrogel (PVA-H), which has good transparency, low surface friction, and dynamic viscoelasticity similar to that of arteries. However, evaluation of its behavior as an arterial biomodel has not been carried out. In order to develop a PVA-H biomodel which can accurately mimic the motion of blood vessels, it is necessary to measure and match its mechanical properties in a tube shape mimicking blood vessels. In this study, tube-shaped PVA-H biomodels were prepared, and their mechanical properties were evaluated as to pulse wave velocity (PWV), compliance, and transfer function. PWV was calculated with Young’s modulus and dimensions of the biomodels. A tube-shaped PVA-H model and a model made of commercial silicone were set in a pulsatile flow path apparatus filled pure water (23°C). Sinusoidal pulsatile waves of various frequencies generated by a screw pump were released into flow path. The flow rate, the inner pressure, and the diameter of the biomodels were measured. The compliance of a biomodel was calculated with changing pressures and diameters. The transfer function was obtained as the ratio of the amplitude of the pressure in front of a biomodel and that behind it. The two kinds of biomodels studied showed PWV similar to that of real arteries: PVA-H shows lower PWV which younger arteries tend to show, while silicone shows higher PWV, similar to the case of aged arteries. In compliance, PVA-H shows a value similar to that of arteries in the lower pressure range, whereas silicone shows a value similar to that of arteries at higher pressure. A difference of transfer function in relation to the pulsatile frequencies was observed. This phenomenon is similar to that of real blood vessels and explainable in terms of the theory of the forced vibration in single-degree-of-freedom systems with attenuation. The transfer function is affected by mechanical properties of the wall, and the difference between biomodels is due to the viscoelasticity of the biomodels. With PVA-H, these parameters can be gradually changed by adjusting factors such as concentration. These findings indicate that PVA-H would be useful for the development of biomodels.
Numerical Modelling of Mass Transfer Through Micro and Nano Capillaries
Authors: Koupaei Ali M. , Mitra Sushanta K. , Secanell Marc
Published: March 2011

Multicomponent mass transport in the micro/nano scale is one of the most important phenomena in many engineering processes such as fuel cells. Therefore, a through understanding of the underlying physics and modeling techniques for mass transport is of crucial importance. According to Kerkhof et al. [1], due to the approximations made in the derivation of the classic transport equations for diffusion-convective dominated problems, the commonly used approach of modeling these problems by the Maxwell-Stefan and Navier-Stokes equations results in trends that are contrary to experiments even for elementary problems like gaseous counter diffusion in capillaries. A new formulation to model molecular fluid transport in multi component systems is then presented. The main aim of this study is to develop a combined experimental-numerical program to study the validity of the classical and the proposed formulations. We discuss the development of an in-house written C/C++ Object Oriented program that solves the classical and recently presented formulation numerically.
Implications of Contact Line Dynamics on Taylor Bubble Flow Morphology
Authors: Herescu Alexandru , Allen Jeffrey S.
Published: March 2011

Film deposition experiments are performed in circular glass capillaries of 500 μm diameter. Two surface wettabilities are considered, contact angle of 30° for water on glass and of 105° when a hydrophobic coating is applied. It was observed that the liquid film deposited as the meniscus translates with a velocity U presents a ridge that also moves in the direction of the flow. The ridge is bounded by a contact line moving at a velocity UCL as well as a front of velocity UF, and it translates over the deposited stagnant film. The behavior of the ridge presents striking dissimilarities when the wettability is changed. Both UCL and UF are approximately twice as large for the non-wetting case at the same capillary number Ca. The Taylor bubbles forming due to the growth of the ridge are also differentiated by wettability, being much shorter in the non-wetting case. The dynamics of the contact line is studied experimentally and a criterion is proposed to explain the occurrence of a shock at the advancing front of the ridge. The hydraulic jump cannot be explained by the Froude condition of shock formation in shallow waters, or by an inertial dewetting of the deposited film. For a dynamic contact angle of θd = 6° and according to the proposed criterion, a hydraulic jump forms at the front of the ridge when a critical velocity is reached.
Blade Curve Influences on Performance of Savonius Rotors: Experimental and Numerical
Authors: Kianifar Ali , Anbarsooz Morteza , Javadi Mohammad
Published: March 2011

In this study, the effect of blade curve on the power coefficient of a Savonius rotor is investigated by means of numerical simulation and wind tunnel tests. The tests were conducted on six rotors with identical dimensions but different blade curves, and the influences of blade curve and Reynolds number were studied. Followed by a simulation of the flow field around rotors with identical semi-circular curves and different overlaps, torque was calculated using pressure distribution on the blade surface, and the effect of Reynolds number and blade curve were studied on torque as well. Results indicate that changing the blade curve affects the power coefficient and torque by causing different drag coefficients. Also the rotor that yields the highest power coefficient and torque in one revolution compared with other rotors is highlighted.
A Numerical Method for Uncertain Compressible Flows
Authors: Poe¨tte G. , Lucor D. , Despre´s B.
Published: March 2011

The treatment of uncertain interface positions in complex simulations and the propagation of the latter uncertainty through complex systems is an important issue. In this paper, we tackle the characterization of perturbed interfaces between fluids thanks to stochastic modelization and the propagation of the initial uncertainty through the Euler system. The stochastic Euler system is solved applying Polynomial Chaos theory through the Intrusive Polynomial Moment Method (IPMM), see [23]. Numerical results are presented for several configurations of the uncertain interface. The system presents an important sensitivity with respect to the stochastic initially leading modes of the uncertain interface.
Measurement of Burst Pressure of Capillary Burst Valve
Authors: Chen Hong , Yamada Toru , Faghri Mohammad
Published: March 2011

Capillary burst valve (CBV), a counterpart to an elastomeric diaphragm microvalve, handles fluid in microchannels by capillarity. Thus, it avoids integration of mechanical components. We experimentally estimated the burst pressure, beyond which CBV cannot hold fluid, using fluids with distinct surface tensions in CBVs grafted with distinct surface constitutions in microchannels. We found that both the fluid surface tension and the solid surface constitution influence the burst pressure. The burst pressure reduces more significantly under the influence of the fluid surface tension.
Nonlinear Finite Element Approach to Simulate Wake-Induced Oscillation in Transmission Line Span
Authors: Snegovskiy Dmitry , Lilien Jean-Louis
Published: March 2011

Wake-induced oscillations (WIO) in transmission line bundle conductors are simulated using finite-element nonlinear formulation. This allows obtaining the conductor oscillations in the line spans equipped either with spacers or with spacer dampers. Within this approach, the interaction of subconductors due to the wake is represented using Simpson’s aeroelastic model. A special force element is created to introduce the aerodynamic loads due to the wake. The aeroelastic properties of the wake force field are tuned to meet the wake-induced instability properties as measured by Price. Extension of the wake interaction sample onto the full line span is done taking into account the inertia-stiffness properties of the line fittings (spacer dampers). It is emphasized that in WIO the ability of spacer (spacer damper) to transfer the loads and motions plays essential role. Thus, the transfer matrix logic to simulate the spacer, established by Diana, Rawlins and other researchers, is now transferred into the finite element model of WIO. Some important structural specifics of transmission line fittings are thus highlighted by the performed simulations. All these developments are introduced into the FE package SAMCEF Mecano. Results of a series of calculations are presented to illustrate the feasibility of the established model. Comparison of FEM simulations to the benchmarking field test data is presented.
Stokes Flow Around a Rolling Cylinder
Authors: Merlen A. , Frankiewicz C.
Published: March 2011

Micropumps are a necessary device for microfluidics. Many solutions are possible and technical devices are numerous. In this paper, we have developed an analytical solution for the peristaltic technique in microchannels that enlighten some physical limitations. We have then compared this solution to a numerical one that also provides results when no theoretical results were found. The squeezing of the wall, in the peristaltic technique, is represented by the corner formed by a rolling cylinder on a wall (cf. fig.1).
Investigation of the Behavior of Ventilated Supercavities
Authors: Kawakami Ellison , Arndt Roger E. A.
Published: March 2011

A study has been carried out at the Saint Anthony Falls Laboratory (SAFL) to investigate various aspects of the flow physics of a supercavitating vehicle. For the experimental work presented here, artificial supercavitation behind a sharp-edged disk was investigated for various model configurations. Results regarding supercavity shape, closure, and ventilation requirements versus Froude number are presented. Conducting experiments in water tunnels introduces blockage effects that are not present in nature. As a result, effects related to flow choking are also discussed. Various methods for computing ventilated cavitation number, including direct measurement of pressure, Laser Doppler Velocimetry, and use of previous numerical results, were compared. Results obtained are similar in character to previous results from various authors, but differ significantly in measured values. Supercavitation parameters, especially the minimum obtainable cavitation number are strongly affected by tunnel blockage.
Study on Installation Position of Sewage Treatment Mixer
Authors: Tian Fei , Shi Wei-dong , Chen Bin , Cao Wei-dong
Published: March 2011

According to the problem that how to choose the installation position for sewage treatment mixer was uncertain, the flow field in the sewage treatment pool was simulated by the software FLUENT 6.3, using unstructured tetrahedral grid, moving coordinate system technology, k ∼ ε turbulence model and the SIMPLE algorithm. The distribution of velocity gradient in the whole pool was analyzed, and the flow field was compared at the different installation angles of sewage treatment mixer. The results show that the fluid flows along the axial direction of sewage treatment mixer, and diffuses along the radial direction. The stirring circulation is evident when the installation deviates from the narrow side, and the flow velocity of the whole pool is relatively uniform and greater than 0.3m/s. It is consistent with their work requirements, which not only improves the efficiency, but also saves costs.
An Experimental Study on Convective Boiling Heat Transfer in Micro Heat Exchangers
Authors: Yang Chien-Yuh , Liu Wei-Chi
Published: March 2011

Attributed to its high heat transfer coefficient, evaporating cooling involving the use of micro heat exchangers is considered a possible thermal management solution for cooling of high heat flux electronic devices. The desire to develop high-performance micro heat exchangers operating in the evaporation regime provides a major motivation for the present work. Methanol evaporated in two micro heat exchangers with chevron flow passages and straight flow passages respectively were tested in the present study. The test results show that the heat transfer coefficient increased with increasing flow rate in both chevron and straight flow passages micro heat exchangers. However, the effect of vapor quality on the heat transfer coefficient in the straight passages heat exchanger is in adverse to that in the chevron passages heat exchanger. The heat transfer coefficient increased with increasing vapor quality in the chevron passages heat exchanger but decreased in the straight passages heat exchanger. The flow visualization through transparent cover heat exchangers showed that the liquid film inside channel is partially dry out in the straight passages heat exchanger. The dryout portion area increased with increasing heating rate and exit vapor quality. This degraded the average heat transfer performance for evaporation in the straight passages heat exchanger. Because of the surface tension effect, the liquid film was dragged at the intersection corner of the upper and lower plate chevron passages. There is no significant dryout portion in the chevron passages heat exchanger. The relation of vapor quality with heat transfer performance in chevron passages heat exchanger is therefore similar to the boiling in a single channel prior to critical heat flux condition.
Numerical Study of Disperse, Multiphase Microslug Formation at a Microchannel Junction
Authors: McDevitt M. Ryan , Hitt Darren L. , McCabe Justin W.
Published: March 2011

In this study, we use numerical methods to examine microslug formation via converging flows of a liquid propellant and inert gas at a 4-way 90° microchannel junction. The primary goal of this study is to characterize microslug formation in a microchannel using the level set method to model the multiphase flow. The significance of this work lies in the utilization of the microslug formation phenomena as the basis for a fuel injection system in a novel, discrete monopropellant microthruster design for use in next-generation nano-satellites.
Design of Volumetric Solar Flow Receivers
Authors: Veeraragavan Ananthanarayanan , Lenert Andrej , Al-Dini Salem , Wang Evelyn N.
Published: March 2011

The development of efficient solar thermal receivers has received significant interest for thermal energy to electrical power conversion and heating applications. Volumetric receivers, where the incoming solar radiation is absorbed in a fluid volume, have advantages over state-of-the-art surface absorbers owing to the reduced heat losses at the surface. To efficiently distribute and store the thermal energy in the volume, nanoparticles can be suspended in the liquid medium to scatter and absorb the incoming radiation. In such systems, however, compact models are needed to design and optimize the performance. In this paper, we present an analytical model that can be used to perform parametric studies to investigate the effect of heat loss, particle distribution, and flow rate on receiver efficiency. The analytical model was formulated by modeling the suspended nanoparticles as embedded heat sources. The heat equation was solved with the surface heat losses modeled using convective losses based on Newton’s law of cooling. The analytical solution provides a convenient tool to predict two-dimensional temperature profiles for a variety of heat loss and inlet fluid temperature conditions. The efficiency of the receiver is defined as the ratio of the amount of thermal energy transported by the fluid to the total incident solar energy. For very large lengths the thermal energy carried by the fluid reaches a maximum steady value as the amount of heat loss equals the incident solar energy. The model can be used to estimate the approximate receiver lengths required to achieve near peak bulk fluid temperature. The results from this study will help guide experimental design, as well as practical flow receivers for solar thermal systems. Predictions made on a channel of 1mm depth with a solar concentration of 1 show that there exists a maximum system efficiency of 0.3373 for a dimensionless receiver length of 1.66.
Characterization of Oil-Water Dispersions/Emulsions Flowing Through Restrictions
Authors: Parra Mari´a V. , Go´mez Luis , Mohan Ram S. , Shoham Ovadia , Kouba Gene , Avila Carlos
Published: March 2011

An experimental study of the characterization of oil-water dispersions/emulsions flowing through an orifice plate was carried out in the Dispersion Characterization Rig® (DCR), a state-of-the-art facility for studying the separation process of dispersions/emulsions. In this study, experiments with distilled water and mineral oil at different choke pressures, velocities, and different orifice sizes were conducted in order to find the phase-inversion zone and observe how the separation profile is affected by these variables. Bulk flow kinetic energy and water cut, are plotted against the pressure drop in the orifice plate to find the inversion point. Image processing technique is used to measure the coalescing and sedimenting profiles with respect to time. Results indicate a good agreement between the two methods used to find where phase inversion occurs and that this is affected by velocities, choke pressure and orifice plate size; also that emulsions become more stable when smaller size of orifice plates are used, as expected.
A Comparison on the Heat Transfer and Flow Characteristics of TiO2-Water Nanofluids Having Two Different Chemical Agents
Authors: Duangthongsuk Weerapun , Wongwises Somchai
Published: March 2011

Heat transfer performance and flow characteristics of aqueous TiO2 nanofluids with particle volume fraction of 0.2% flowing under turbulent flow regime are investigated. The test section is a 1.5 m long counter-flow double tube heat exchanger. Two different nanofluids are used as working fluids at the same concentration. Firstly, TiO2 nanoparticles with mean diameters of 21 nm mixed with small amount of CTAB (about 0.01%) named “SAM 1”. Secondly, VP Disp. W740x provided by DEGUSSA AG Company is used and called “SAM 2”. The latter mixture is composed of TiO2 nanoparticle with average diameter of 21 nm dispersed in water. The pH values of nanofluid SAM 1 and SAM 2 are 7.6 and 7.5, respectively. The heat transfer performance and friction characteristics of two samples of nanofluid were presented. In addition, the Nusselt numbers predicted from the published correlation for nanofluids are compared with the present experimental data.
Two-Phase Pressure Drop of Ammonia in a Mini/Micro-Channel
Authors: Maqbool M. Hamayun , Palm Bjo¨rn , Khodabandeh R. , Ali Rashid
Published: March 2011

Experiments have been performed to investigate two-phase pressure drop in a circular vertical mini-channel made of stainless steel (AISI 316) with internal diameter of 1.70 mm and a uniformly heated length of 245 mm using ammonia as working fluid. The experiments are conducted for heat flux range of 15 to 350 kW/m2 and mass flux range of 100 to 500 kg/m2s. A uniform heat flux is applied to the test section by DC power supply. Two phase frictional pressure drop variation with mass flux, vapour quality and heat flux was determined. The experimental results are compared to predictive methods available in literature for frictional pressure drop. The Homogeneous model and the correlation of Mu¨ller Steinhagen et al. [14] are in good agreement with our experimental data with MAD of 27% and 26% respectively.
Gas Properties Effects in Microchannel Studies Using Direct Simulation Monte Carlo
Authors: Darbandi Masoud , Karchani Abolfazl , Akhlaghi Hassan , Schneider Gerry
Published: March 2011

This paper concern is to study the gas properties effect in flow and heat transfer behaviors through microchannels using the direct simulation Monte Carlo method. The flow is rarefied and supersonic. The channels are investigated at two different inlet boundary conditions. The collision process is modeled using the NTC (no-time-counter) scheme. The VHS model is chosen to simulate collision between particle pairs. The study is provided for many different gases including nitrogen, helium, and oxygen. The Knudsen number is chosen in a manner to provide slip flow through the channel. The results show that the heat transfer from the wall is lower for heavier gases. A comparative study among the monatomic, diatomic, polyatomic gases shows that the heat transfer rate is lower for the polyatomic gases. The result shows that, the heat transfer from the wall is lower for the heavier gases than that for the lighter gas. For a fixed Mach number, the heat transfer from the wall decreases as the molecular diameter increases.
Reynolds Number Dependence for Laminar Flow Loss Coefficients in Tee and Wye Junctions
Authors: Kiser Chris C. , Handy Tim A. , Lemley Evan C. , Papavassiliou Dimitrios V. , Neeman Henry J.
Published: March 2011

In fluid flow piping systems, tee and wye junctions are commonly encountered and the study of flow through them has been well documented. Most of these studies have focused on flow characterized as turbulent for which there are nearly constant losses in pressure and kinetic energy in the junctions. Laminar flow has received much less attention since it is not frequently observed in macro scale piping systems where pipe diameters are measured in centimeters. The recent increase in use of micro scale flow devices calls for more research into laminar flow behavior that dictates the design and operation of these devices. This paper documents results from computational fluid dynamics (CFD) simulations of flow in planar tee and wye junctions. The junctions studied consisted of circular pipes with two outlets and one inlet. The angles between the tee and wye junctions were fixed to 180 and 60 degrees, respectively. The inlet pipe diameter was fixed at 50 microns and the outlet pipe diameters were chosen to satisfy the continuity equation constrained to have equal velocities in all pipes. The lengths of the inlet and outlet pipes were varied to achieve fully developed flow within the junction. Following a grid resolution study performed on a sample tee junction, a generalized algorithm was designed and implemented to create three-dimensional models of these junctions subject to the former conditions. In the CFD simulations, Reynolds number was varied in the laminar characterized region between 1 and 2000. The simulations calculated static pressure and velocity magnitude values for a number of planes intersecting the junctions along the inlet and outlet pipes. From these values, pressure and kinetic energy gradients were calculated to estimate the static pressure and kinetic energy at the inlet and outlet pipes of each junction. Finally, these inlet and outlet values were used to calculate the stagnation pressure loss coefficient, which reflects dimensionless losses of pressure and kinetic energy for the junction. These coefficients ranged from 1 to 300 for the tee junction and 1 to 400 for the wye junction over the specified range of Reynolds number. The values were inversely proportional to Reynolds number and curve fits were provided for valid ranges.
Organization of Cylinder Wake Using a Splitter-Plate Active Flow Control
Authors: Weiland Chris , Vlachos Pavlos
Published: March 2011

Time Resolved Digital Particle Image Velocimetry (TRDPIV) was used in conjunction with spectral analysis to study the effects of Leading Edge Blowing (LEB) flow control on the near-wake of a circular cylinder. The airfoil was placed 1.9 circular cylinder diameters downstream, effectively acting as a splitter plate. Spectral measurements of the TRDPIV results indicated that the presence of the airfoil decreased the Strouhal number from 0.19 to 0.12 as anticipated. When activated the LEB jet organized the circular cylinder wake, effectively neutralizing the effect of the splitter plate and modifying the wake so as to return the Strouhal number to 0.19. Thus the circular cylinder wake returned to its normal shedding frequency, even in the presence of the airfoil. Evidence presented in this study supports the notion that the LEB jet directly excites the circular cylinder shear layers causing instability, roll up, and subsequent vortex shedding.
The Balanced-Force Volume Tracking Algorithm and Global Embedded Interface Formulation for Droplet Dynamics With Mass Transfer
Authors: Francois Marianne M. , Carlson Neil N.
Published: March 2011

Understanding the complex interaction of droplet dynamics with mass transfer and chemical reactions is of fundamental importance in liquid-liquid extraction. High-fidelity numerical simulation of droplet dynamics with interfacial mass transfer is particularly challenging because the position of the interface between the fluids and the interface physics need to be predicted as part of the solution of the flow equations. In addition, the discontinuity in fluid density, viscosity and species concentration at the interface present additional numerical challenges. In this work, we extend our balanced-force volume-tracking algorithm for modeling surface tension force (Francois et al., 2006) and we propose a global embedded interface formulation to model the interfacial conditions of an interface in thermodynamic equilibrium. To validate our formulation, we perform simulations of pure diffusion problems in one- and two-dimensions. Then we present two and three-dimensional simulations of a single droplet dynamics rising by buoyancy with mass transfer.
Testing Device for Hydrodynamic Characteristic on Conversion Devices of Tidal Stream Energy
Authors: Long Li , Ze Wang , Kaining Zhou , Bo Li
Published: March 2011

The feasibility of tidal in stream energy conversion technology, especially the demonstration of the efficiency in energy conversion, is of consequence to provide efficient devices and cost-effective electrical energy. The excellent hydrodynamic model of the conversion devices is an essential condition of a successful tidal flowing power. The experimentation of the hydrodynamic model in laboratory should be first selecting by reason of the reliability and immediate data to assess the hydrodynamic characteristic. But, the simulation of a flowing condition in laboratory is not easily accomplished, as a result of need of bigger flowing speed and greater bigger flume. Based on the relativity principle, the relative testing method of the energy conversion technology in tidal stream was provided. The peculiarity, the structure of the testing device was indicated. The function of every composing proportion on the testing device was explained. The process of experimentation was introduced.
Scouring Below Pipelines: The Role of Vorticity and Turbulence
Authors: Mattioli Matteo , Mancinelli Alessandro , Colicchio Giuseppina , Brocchini Maurizio
Published: March 2011

A numerical study on the turbulence and vorticity of local scour underneath an offshore pipeline placed on a non-cohesive sandy seabed and forced by a steady flow current is presented. The numerical model solves the Navier-Stokes equations using an innovative Level Set technique. The model predicts the behavior of the movable sediments through both drift and lift force components. Mean and turbulent flow quantities were extracted by temporal averaging. Results on the distribution and evolution of turbulent kinetic energy and vorticity will be illustrated at the conference.
Modeling the Forces Exerted on the Tool-Electrode During Spark Assisted Chemical Engraving Constant Velocity Feed-Drilling
Authors: Ziki Jana Abou , Dhawale Nand Kishor M. , Wu¨thrich Rolf
Published: March 2011

Spark Assisted Chemical Engraving (SACE) is an interesting technology for micro-machining several types of non-conductive materials like glass, quartz, polymers and some ceramics. The process takes place in an electrochemical cell with two electrodes immersed in an electrolyte. The electrolytic solution is typically sodium hydroxide (30%wt NaOH) or potassium hydroxide (KOH). The cathode is used as tool and the anode as counter-electrode. When the applied voltage is higher than a critical value (typically around 30V, depending on the electrolyte and tool-electrode geometry) bubbles grow so dense on the electrode surface that they coalesce into a gas film. Electrical discharges occur between the electrode and the electrolyte. Machining begins consequently if the electrode is placed close enough to the surface to be machined (typically 25μm for glass). In the present paper, the forces exerted on the tool-electrode during constant velocity feed drilling is investigated experimentally and a model is proposed. The setup is composed of a machine head mounted on XYZ precision linear stage holding the tool-electrode. The machining head further incorporates a force sensor which is able to monitor, during drilling operation, the force exerted on the tool-electrode based on the zero displacement measurement principle.
Vortex Ring Formation in Wall-Bounded Domains
Authors: Stewart Kelley C. , Vlachos Pavlos P.
Published: March 2011

Vortex ring formation and propagation have been studied extensively in quiescent semi-infinite volumes. However, very little is known about the dynamics of vortex-ring formation in wall-bounded domains where vortex wall interaction will affect both the vortex ring pinch-off and propagation velocity. This study addresses this limitation and studies vortex formation in radially confined domains to analyze the effect of vortex-ring wall interaction on the formation and propagation of the vortex ring. Vortex rings were produced using a pneumatically driven piston cylinder arrangement and were ejected into a long cylindrical tube parallel to the piston cylinder arrangement which defined the confined downstream domain. Two different domains were studied with diameters twice and four times the size of the piston cylinder. A semi-infinite unbounded volume with no downstream cylinder was also investigated for comparison. The piston stroke-to-diameter ratio (L/D0) for the studied vortex rings was varied between 0.75 and 3 with corresponding Reynolds numbers, based on circulation, of approximately 500 to 8,000. Velocity field measurements were performed using planar Time Resolved Digital Particle Image Velocimetry (TRDPIV). The TRDPIV data were processed using an in-house developed cross-correlation PIV algorithm and post processed using Proper Orthogonal Decomposition to remove high frequency noise. The propagation velocity and vorticity were investigated and vortex identification was used to track the changing size, location, and circulation of the vortices. The combination of these parameters was used to investigate the effects of wall interaction on vortex ring formation and propagation.
Second Law Analysis for Extended Graetz Problem Including Viscous Dissipation in Microtubes
Authors: Sadeghi Arman , Baghani Mostafa , Saidi Mohammad Hassan
Published: March 2011

The entropy generation rate has become a useful tool for evaluating the intrinsic irreversibilities associated with a given process or device. This work presents an analytical solution for entropy generation in hydrodynamically fully developed thermally developing laminar flow in a microtube. The rarefaction effects as well as viscous heating effects are taken into consideration, but axial conduction is neglected. Using fully developed velocity profile, the energy equation is solved by means of integral transform. The solution is validated by comparing the local Nusselt numbers against existing literature data. From the results it is realized that the entropy generation decreases as Knudsen number increases, while the effect of increasing values of Brinkman number and the ratio of Brinkman number to dimensionless temperature difference is to increase entropy generation. The average entropy generation number over the cross section of channel increases with increasing values of axial coordinate, until it reaches a constant value at fully developed conditions.
Investigation of POD Bases for Flow Control on Disk Wakes
Authors: Berger Zachary , Bigger Rory , Fardad Makan , Higuchi Hiroshi , Glauser Mark N. , Orbaker Aaron J.
Published: March 2011

This work investigates the effects of flow control on the near wake region of a disk in a water flow, utilizing the POD reconstructed time dependent velocity fields. Velocity measurements were collected using time resolved particle image velocimetry (TRPIV) at a Reynolds number of 20,000 based on the disk diameter, both with and without control. An open-loop control was applied via periodic synthetic jet excitation from the disk edge. With the advantage of a time resolved velocity database, we have the ability to reconstruct the time dependent velocity field in the wake of the disk. This reconstruction is done for the baseline and controlled cases using various POD truncations to observe velocity reconstructions, based on the overall energy of the system. In doing so, we will consider the convergence rate of the spatial eigenvalues when conducting our POD reconstruction of the fluctuating velocity field, for both the baseline and controlled cases. Since a complex flow exists in the wake of the disk, the goal will be to form a state space representation of the flow in the form of a linear time invariant (LTI) system. This model is simply a linearization of the flow around the baseline. Furthermore, our knowledge of the input control signal will allow us to predict the flow at a later instant in time. We would like to extract the most energetic modes of the system and thereby form our observer-based controller to close the loop. In order to accomplish this, and with a rich open-loop dataset at our disposal, we will first form the POD reconstruction of the baseline. We then form a new basis, obtained by taking the actuated (controlled) data and subtracting from it the components of the flow that fall in the subspace spanned by the baseline flow. This will characterize the flow field by capturing the effect of the control input (actuation), from which the parameters of the LTI system can be identified. Preliminary POD reconstruction shows that 60% of the energy is recovered from 20 POD modes of the total 511 modes for the baseline case; similarly 60% of the energy is also recovered from 100 POD modes of the total 1,024 modes for the actuated case.
Multi-Scale Particle Simulation of Red Blood Cell in Microcirculation
Authors: Kumar Anurag , Yamada Toru , Faghri Mohammad
Published: March 2011

The complex rheology of red blood cell (RBC) in microcirculation has been a topic of interest for many decades. As RBC is highly deformable, shape change affects the microcirculation and such effect should be accounted accurately to understand the rheology of blood flow. A particle based model is developed to construct the red blood cell (RBC) based on the minimum energy principle. A bead-spring network is utilized to represent the cross-sectional plane of RBC membrane. The total energy of the RBC is associated with spring stretch/compression, bending and constraint of fixed area. Shape optimization of swollen RBC due to continuous deflation is performed. A bi-concave RBC shape is accurately achieved when the circular shape is deflated to 65%. Dissipative particle dynamics (DPD), a coarse-grained Mesoscopic particle simulation is used to simulate the flow. RBC in its equilibrium shape is placed inside a microchannel of height 10 μm to study the deformation of the cell under shear. Force exerted on RBC particles by plasma particles were determined and solved as the external force in the DPD equation to calculate the position and velocity of each particle. As the simulation started, the RBC experienced the shear and drag force by surrounding plasma and evolved to the characteristic parachute type shape as observed in experiments. Once the RBC reached the steady deformation, it continued with the same shape and stayed in the center of the channel. It is observed that the parachute shape and its motion along the centerline of the flow help reducing the drag and subsequently achieving the state of minimum energy. Formulation and results were validated against the experimental and computational results reported in the literature.
Numerical Simulation of Confined Nano-Impinging Jet in Microscale Cooling Application Using DSMC Method
Authors: Darbandi M. , Akhlaghi H. , Karchani A. , Schneider G. E.
Published: March 2011

In this study, we simulate rarefied gas flow through a confined nano-impinging jet using direct simulation Monte Carlo (DSMC) method. The effects of geometrical parameters, pressure ratio, and wall conditions on the heat transfer from a hot surface are examined. Hot surface modeled via diffusive constant wall temperature. Various inlet/confining surface conditions such as specular, adiabatic, and constant temperature are implemented and the effects of them on the wall heat flux rates are studied. The results show that Knudsen number, velocity slip, and temperature jump are main reasons which specify magnitudes of wall heat flux rates. Among all geometrical parameters, H/W ratio has the greatest effect on heat transfer, where H is jet distance from the hot surface and W is the jet width. For different values of pressure ratio, the biggest quantity of wall heat flux rate relates to the lowest velocity slip case. Also for inlet/confining walls with constant temperature condition equal to coolant flow temperature, heat transfer from the hot surface was the maximum.
Experimental and Numerical Study of a Pitching Blade
Authors: Amiralaei M. R. , Alighanbari H.
Published: March 2011

The objective of the present study is to investigate the effects of the reduced frequency on the aerodynamic characteristics of a three dimensional pitching blade. Experimental data are recorded at three sections of the blade model; tip, middle, and root sections at low and high turbulence intensities. A 2D numerical simulation is also conducted based on the Unsteady Reynolds Averaged Navier-Stokes (URANS) equations and Finite Volume Method (FVM) and the results are compared with those of the experimental observations. The results show that 2D numerical simulations are useful in obtaining the qualitative behavior of the flow field. Moreover, it is shown experimentally that the reduced frequency is of great importance to the flow physics. It affects the maximum lift coefficients, hysteresis loops, lift curve slopes, and angles at which stall occurs.
Effects of Increasing Inlet Velocities and Side Port Air Injection on a Biomass Fluidizing Bed
Authors: Deza Mirka , Battaglia Francine
Published: March 2011

Fluidized beds are being used in practice to gasify biomass to create producer gas, a flammable gas that can be used for process heating. However, recent literature has identified the need to better understand and characterize biomass fluidization hydrodynamics, and computational fluid dynamics (CFD) is one approach in this effort. Previous work by the authors considered the validity of using two-dimensional versus three-dimensional simulations to model a cold-flow fluidizing biomass bed configured with a single side port air injection. The side port is introduced to inject air and promote mixing within the bed. Comparisons with experiments indicated that three-dimensional simulations were necessary to capture the fluidization behavior for the more complex geometry. This paper considers the effects of increasing fluidization air flow and side port air flow on the homogeneity of the bed material in a 10.2 cm diameter fluidized bed. Two air injection ports diametrically opposed to each other are also considered to determine their effects on fluidization hydrodynamics. Whenever possible, the simulations are compared to experimental data of time-averaged local gas holdup obtained using X-ray computed tomography. This study will show that increasing the fluidization and side port air flows contribute to a more homogeneous bed. Furthermore, the introduction of two side ports results in a more symmetric gas-solid distribution.
Fuzzy Clustering of Vertical Two Phase Flow Regimes Based on Image Processing Technique
Authors: Ghanbarzadeh Soheil , Hanafizadeh Pedram , Saidi Mohammad Hassan , Bozorgmehry B. Ramin
Published: March 2011

In order to safe design and optimize performance of industrial systems which work under two phase flow conditions, it’s often needed to categorize flow into different regimes. In present work the experiments of two phase flow were done in a large scale test facility with length of 6m and 5cm diameter. Four main flow regimes were observed in vertical air-water two phase flows at moderate superficial velocities of gas and water: Bubbly, Slug, Churn and Annular. Some image processing techniques were used to extract information from each picture. This information include number of bubbles or objects, area, perimeter, height and width of objects (second phase). Also a texture feature extraction procedure was applied to images of different regimes. Some features which were adequate for regime identification were extracted such as Contrast, Energy, Entropy and etc. To identify flow regimes a fuzzy interface was introduced using characteristic of second phase in picture. Also an Adaptive Neuro Fuzzy (ANFIS) was used to identify flow patterns using textural features of images. The experimental results show that these methods can accurately identify the flow patterns in a vertical pipe.
Validation of a Smoothed Particle Hydrodynamics Code for Internal Flow Simulations: Application to Hemodynamics in a Realistic Left Heart Cavity Model
Authors: Shahriari Shahrokh , Hassan Ibrahim , Kadem Lyes
Published: March 2011

A numerical simulation of flow in the left heart cavity, left ventricle, based on Smoothed Particle Hydrodynamics, a meshfree particle method is presented. Most of the works using this numerical method have been dedicated to simulation of free surface flows or internal flows with low Reynolds number. The present study is the first work dedicated to simulate the complex flow in a realistic rigid model of left ventricle applying the realistic pulsatile inlet velocity (having moderate Reynolds number) using a meshfree particle method. The numerical validation of our code is performed through the simulation of flow in a cavity at a Reynolds number equal to 1000. Also, the comparison of the results of flow simulation in a simplified geometry of left ventricle with the finite volume results is presented. The smoothed particle hydrodynamics method was able to resolve the flow patterns showing its potential to be applied in complex cardiovascular flow simulations.
Diffusion Analysis of Chloride in Concrete Following Electrokinetic Nanoparticle Treatment
Authors: Kupwade-Patil K. , John T. J. , Mathew B. , Cardenas H. , Hegab H.
Published: March 2011

Concrete is a highly porous material which is susceptible to the migration of highly deleterious species such as chlorides and sulfates. Various external sources including sea salt spray, direct sea water wetting, deicing salts and brine tanks harbor chlorides that can enter reinforced concrete. Chlorides diffuse into the capillary pores of concrete and come into contact with the rebar. When chloride concentration at the rebar exceeds a threshold level it breaks down the passive layer of oxide, leading to chloride induced corrosion. Application of electrokinetics using positively charged nanoparticles for corrosion protection in reinforced concrete structures is an emerging technology. This technique involves the principle of electrophoretic migration of nanoparticles to hinder chloride diffusion in the concrete. The re-entry of the chlorides is inhibited by the electrodeposited assembly of the nanoparticles at the rebar interface. In this work electrochemical impedance spectroscopy (EIS) combined with equivalent circuit analysis was used to predict chloride diffusion coefficients as influenced by nanoparticle treatments. Untreated controls exhibited a diffusion coefficient of 3.59 × 10−12 m2/s which is slightly higher than the corrosion initiation benchmark value of 1.63 × 10−12 m2/s that is noted in the literature for mature concrete with a 0.5 water/cement mass ratio. The electrokinetic nanoparticle (EN) treated specimens exhibited a diffusion coefficient of 1.41 × 10−13m2/s which was 25 times lower than the untreated controls. Following an exposure period of three years the mature EN treated specimens exhibited lower chloride content by a factor of 27. These findings indicate that the EN treatment can significantly lower diffusion coefficients thereby delaying the initiation of corrosion.
Performance of Cross Flow Microchannel Heat Exchangers Subjected to Viscous Dissipation
Authors: Mathew B. , John T. J. , Dai W. , Hegab H.
Published: March 2011

This paper analyzes the effect of viscous dissipation on the thermal performance of balanced flow cross flow microchannel heat exchangers. The cross flow microchannel heat exchanger analyzed in this paper is one that is subjected to axial heat conduction. Governing equations are developed for each of the fluids and the wall separating the fluids. The equations are solved simultaneously using the numerical technique of finite difference method to obtain the temperature profile. The effectiveness of each fluid is determined using the temperature profile thus obtained. The effectiveness and the temperature of the fluids are found to depend on NTU, axial heat conduction parameters and the viscous dissipation parameter. In the presence of axial heat conduction the effectiveness of the fluid decreases for a specific NTU. In addition, the effectiveness of the fluids decreases with increase in axial heat conduction parameters at a particular NTU. The effectiveness of the hot fluid in the presence of viscous heat dissipation alone decreased at a particular NTU. On the other hand the effectiveness of the cold fluid for the same amount of viscous heating improved at a specific NTU. The combined effect of axial heat conduction and viscous dissipation on the hot fluid is to decrease its effectiveness. With regard to the cold fluid effectiveness it can either increase or decrease due to the combined effect of axial heat conduction parameter and viscous dissipation.