bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of Rapid Simulation Method for Automotive Aerodynamics
Authors: Akasaka Kei , Ono Kenji
Published: March 2011

Computational fluid dynamics (CFD) is now widely used as an essential tool in the development of automotive aerodynamics. However, the time required for repairing non-watertight geometries has recently become a serious problem in current CFD processes. Therefore, we developed an efficient simulation method that allows the flow around a non-watertight geometry to be computed on a Cartesian grid. This method can substantially reduce the turnaround time and effort required for CFD processes, because the repair work can be eliminated. The proposed method adopts an embedded boundary condition technique to capture arbitrary shapes more accurately on the background Cartesian grid. In addition, a local mesh refinement technique enables higher computational efficiency to be realized, and large-eddy simulation (LES) is used to reproduce high-Reynolds-number turbulent flow. Preliminary tests were performed on an engine bay configuration that had non-watertight geometries and a 1/5-scale model of an automobile configuration. As a result, the proposed method was confirmed to enable rapid grid generation and flow simulation around non-watertight geometries. Moreover, the computed results showed good agreement with experimental data.
Optimization of Approach Flow Conditions of Vertical Pumping Systems by Computational Analysis and Physical Model Investigation
Authors: Kirst Kilian , Hellmann D.-H.
Published: March 2011

Approach flow conditions of intake structures should be in compliance with state of the art acceptance criteria for all operating conditions, to provide the required flow rates of cooling or circulating water properly. Specially for high specific speed vertical pumps the direct inflow should be vortex free, with low prerotation and symmetric velocity distribution. Flow separation in front of open and covered intake structures can lead to free surface vortices. Depending on the strength, vortices can emerge a coherent air core, starting from the surface and entering the inlet nozzle directly. High mechanical load of the pump and decreasing hydraulic performance are an immediate consequence. Energy content, stability and position of a free surface vortex are determinated by intake system geometry and operating conditions. By installing flow guiding devices, the generation of vortex formations can be prevented. Optimization steps should be accomplished with respect to installation costs and complexity on-site. Therefore the effectiveness of the improvements has to be verified. Physical model investigations are common practice and state of the art to evaluate, to optimize and to document flow conditions inside intake structures. Nowadays, computational analysis is more and more adopted in this work field. A combination of both leads to well-defined and reproducible results within a wide application range. By this means prototype intake structures can be investigated and, if necessary, optimized for their best approach flow conditions. In the report the optimization of insufficient approach flow by computational analysis and physical model tests is presented. Therefore various intake structures for cooling water systems — all having approach flow not in compliance with the acceptance criteria of common standards — were physically modeled and investigated. Simultaneously initial and optimized layouts were reviewed by numerical calculations of different kinds. Calculated results are compared with model test and prototype data for different cases and operating points. Focusing on the occurrence of free surface vortices, methods of reproducing free surface vortices with numerical approaches will be presented and evaluated.
Lattice Boltzmann Simulation of Gaseous Flow in Microchannel With Rectangular Grooves
Authors: Hashemi Zahra , Abouali Omid , Kamali Reza
Published: March 2011

This paper presents a numerical investigation based on the Lattice Boltzmann method for gaseous flow in a microchannel with rectangular grooves on the walls. Firstly, the prepared computer code is validated with comparison the obtained results with analytic solution for fully developed rarefied gas flow in a simple micro channel. The effects of the rectangular grooves on the flow characteristics and heat transfer behavior are discussed and the results are compared with a simple mircochannel. For this purpose, a two-dimensional constant wall temperature microchannel with air as the coolant is investigated. The results show that the heat removal increases for the grooved channel more than 50% compared with a simple microchannel. But the pressure drop is also increases due to the effects of grooves. The increase in friction factor is more than twice for some Knudsen numbers.
Rapid and Slow Decomposition in Large Eddy Simulation of Scalar Turbulence
Authors: Fang L. , Shao L. , Bertoglio J. P. , Lu L. P. , Zhang Z. S.
Published: March 2011

In large eddy simulation of turbulent flow, because of the spatial filter, inhomogeneity and anisotropy affect the subgrid stress via the mean flow gradient. A method of evaluating the mean effects is to split the subgrid stress tensor into “rapid” and “slow” parts. This decomposition was introduced by Shao et al. (1999) and applied to A Priori tests of existing subgrid models in the case of a turbulent mixing layer. In the present work, the decomposition is extended to the case of a passive scalar in inhomogeneous turbulence. The contributions of rapid and slow subgrid scalar flux, both in the equations of scalar variance and scalar flux, are analyzed. A Priori numerical tests are performed in a turbulent Couette flow with a mean scalar gradient. Results are then used to evaluate the performances of different popular subgrid scalar models. It is shown that existing models can not well simulate the slow part and need to be improved. In order to improve the modeling, an extension of the model proposed by Cui et al. (2004) is introduced for the slow part, whereas the Scale-Similarity model is used reproduce the rapid part. Combining both models, A Priori tests lead to a better performance. However, the remaining problem is that none eddy-diffusion model can correctly represent the strong scalar dissipation near the wall. This problem will be addressed in future work.
POD-Based Estimations of the Flowfield From PIV Wall Gradient Measurements in the Backward-Facing Step Flow
Authors: Nguyen Thien Duy , Wells John Craig , Mokhasi Paritosh , Rempfer Dietmar
Published: March 2011

In this paper, particle image velocimetry (PIV) results from a backward-facing step flow, of which Reynolds number is 2800 based on free stream velocity and step height (h = 16.5 mm), are used to demonstrate the capability of proper orthogonal decomposition (POD)-based estimation models. Three-component PIV velocity fields are decomposed into a set of spatial basis functions and a set of temporal coefficients. The estimation models are built to relate the low-order POD coefficients, determined from an ensemble of 1050 PIV fields by the “snapshot” method, and the time-resolved wall gradients, measured by a near-wall measurement technique called stereo interfacial PIV. These models are evaluated in terms of reconstruction and prediction of the low-order temporal POD coefficients of the velocity fields. In order to determine the coefficients of the estimation models, linear stochastic estimation (LSE), quadratic stochastic estimation (QSE), principal component regression (PCR) and kernel ridge regression (KRR) are applied. In addition, we introduce a possibility of multi-time POD-based estimations in which past and future information of the wall gradient events is used separately or combined. The results show that the multi-time estimation approaches can improve the prediction process. Among these approaches, the proposed multi-time KRR-POD estimation with optimized time duration of wall gradient information in the past yields the best prediction.
A LES Simulation of Atomisation
Authors: Chesnel J. , Me´nard T. , Re´veillon J. , Berlemont A. , Demoulin F. X.
Published: March 2011

Large Eddy Simulation has been used with a lot of success for single phase flows. Its extension to multiphase flows is underway. As far as liquid-gas flows are concerned, two limit cases have been addressed: In one hand, if the liquid phase corresponds to a set of droplets with diameters smaller than the LES filter size, a subgrid spray is described. In the other hand, if the characteristic sizes of the surface wrinkles are greater than the LES filters size, the surface is resolved and LES models concern the velocity field. An example of the first approach is a dilute spray and an example of the second approach is waves at ocean surface. The issue with LES simulation of atomization is that a surface resolved LES is expected close to the injector together with a subgrid sprays LES far from the injector when the spray is finally formed. If only a resolved LES is used, the drop diameter cannot be smaller than the LES filter size. It follows that smaller diameters cannot be described and the breakup process is blocked numerically at a size related to the filter size. At the contrary if a subgrid spray LES is used a model is necessarily used that is accurate only for given type of injector. The present work addresses the problem induced by this transition between resolved and unresolved spray. A first approach is proposed that is able to reach both limits. The transition is performed using a filtered surface density equation to avoid the assumption that ligaments, sheets and other surface topologies becomes spherical droplet abruptly at the subgrid level. Results will be shown to demonstrate the ability of the model to recover the essential characteristics of a spray in a Diesel like application.
Quantification of Inertial Droplet Collision Mixing Rates in Confined Microchannel Flows Using Differential Fluorescence Measurements
Authors: Carroll Brian , Hidrovo Carlos
Published: March 2011

Efficient mixing at the microscale remains a formidable engineering challenge. Recent advancement and proliferation of Lab-on-a-Chip (LOC) and Micro Total Analysis Systems (μTAS) has demanded accelerated development and demonstration of novel micromixers as successful mixing is critical to device performance. Passive techniques such as chaotic advection and shear thinning as well as active methods utilizing electric fields show great promise at meeting these requirements. A new droplet-based mixing technique currently being developed aims at improving micromixer rates passively by increasing the Reynolds number in the microchannel. High speed gaseous flows with Reynolds numbers from 1 to 300 are used to detach and transport discrete droplets to a collision zone where droplet interaction and subsequent mixing is achieved under highly inertial conditions. The design utilizes variants of the standard T-junction arrangement for both the detachment and collision process. A fluorescing and non-fluorescing droplet pair are brought into contact in a collision zone and allowed to interact with relative velocities in the 0.1 to 5m/s range. Mixing rates are quantified using an optical based measurement technique that examines temporal changes in droplet intensity as mixing progresses. Both the detachment and collision processes are captured using a high speed camera capable of frame rates in excess of 10MHz. Experimental results are obtained for different collision zone geometry arrangements and microchannel aspect ratios to assess mixing performance. A description and sufficient explanation of the optical measurement techniques used to quantify mixing rates is provided, including limitations and shortcomings of this simplified approach. Analytical models are developed to gain better understanding of the key physical mechanisms driving droplet mixing and experimental results are correlated against this order of magnitude model. Based on these results, recommendations are made for potential design improvements and issues are addressed concerning mixing using two-phase gas/liquids flows.
LES of the Flow Around a Generic Wheel in a Wheelhouse
Authors: Krajnovic´ Sinisˇa , Sarmast Sasan , Basara Branislav
Published: March 2011

The flow around generic wheels in wheel housings used in previous experimental investigations is studied using large eddy simulations. A comparison is given here of the results of the simulations with existing experimental data and previous qualitative results of RANS simulations. Both instantaneous and time averaged flows are described, showing agreement with previous knowledge and adding new insight in flow physics. Two different widths of the wheel housing are used in the simulations, and their influence on the flows is studied. The present work shows that the width of the wheel housing has an influence on flows on both the inside and the outside of the wheel.
Immersed Boundary Method for Large Eddy Simulation and Lagrangian Stochastic Modeling of Passive Scalar Dispersion Downstream of an Obstacle
Authors: Le Ribault C. , Simoe¨ns S.
Published: March 2011

A large-eddy simulation (LES) using the atmospheric code ARPS is performed to study the passive scalar dispersion downstream of an obstacle. An immersed boundary method has been introduced to take into account the obstacle. To simulate the scalar dispersion, instead of resolving the passive scalar transport equation, fluid particles containing scalar are tracked in a Lagrangian way. The results of the LES are compared with the experiments of Vinc¸ont et al. [1]. In those experiments, simultaneous measurements of the velocity and scalar concentration fields have been made in the plume emitting from a two-dimensional line source flushed with the wall. The source is one obstacle height downstream of a two-dimensional square obstacle located on the wall of a turbulent boundary layer. Our simulations predict the qualitative and quantitative features of the experimental results.
Isothermal Modeling of Meniscus Oscillation in the Continuous Strip Casting Process
Authors: Wilcox Kevin W. , Holloway A. Gordon L. , Gerber Andrew G.
Published: March 2011

In the continuous strip casting process a meniscus forms a compliant boundary between the casting nozzle and transporting conveyor. Movement of this meniscus during casting has been shown to create surface defects, which require extensive cold work to remove and limit the minimum thickness for which sections may be cast. This paper discusses experimental work conducted to test an analytical model of the meniscus oscillation. A high frame rate shadowgraph technique was used on an isothermal water model of the casting process to observe meniscus motion, and thus allowing the calculation of meniscus frequency, amplitude, contact points and contact angles. Both natural frequency and flow excited tests were conducted. Natural frequency tests were also conducted using mercury as the working fluid, having a non-wetting contact angle, typical of molten metals. The experimental results were found to be in good agreement with the predictions of theory for both wetting and non-wetting conditions. The experimentally verified analytical model for meniscus motion is valuable to the design of the continuous casting process, because it offers an opportunity to mitigate the effects of boundary motion on surface quality.
Experimental Investigation of Aerial Spray Characteristics
Authors: Bagherpour Ali , Holloway Gordon , McLeod Ian M.
Published: March 2011

An important characteristic of sprays is their statistical distribution of droplet sizes. Knowledge of the droplet distribution is particularly important for pesticide applications because droplet size affects droplet trajectory, probability of contact with foliage, and the biological dose to target pests. This work describes an experimental study of an aerial spray application in a wind tunnel environment at realistic flight speeds (67 m/s) using a full-scale rotary atomizer turning at 8600 rpm. Comparative measurements of water droplet velocity and diameter were made a 3 component Artium Phase Doppler Interferometer (PDI) and a Sympatec Helos Vario Laser Diffraction (LD) instrument. Distance from the atomizer to the measurement cross section was varied to observe the effects of the atomizer wake on the results.
Experimental and Numerical Analysis of the Flow Inside a Configuration Including an Axial Pump and a Tubular Exchanger
Authors: Solis Moise´s , Ravelet Florent , Khelladi Sofiane , Bakir Farid
Published: March 2011

In centrifugal and axial pumps, the flow is characterized by a turbulent and complex behavior and also by physical mechanisms such as cavitation and pressure fluctuations that are mainly due to the strong interactions between the fixed and mobile parts and the operating conditions. These fluctuations are more important at the tip clearance and propagate upstream and downstream of the rotor. The control of the fluctuating signal amplitudes can be achieved by incrementing the distance between the components mentioned above. This paper presents experimental and numerical results concerning the operation of a configuration that includes an axial pump and a bundle of tubes that mimics the cool source of a heat exchanger. The pump used in the tests has a low solidity and two blades designed in forced vortex, the tip clearance is approximately 3.87% of tip radius. The experimental measures were carried out using a test bench built for this purpose at the DynFluid Laboratory which was accomodated conveniently with a variety of instruments. Firstly, the characteristic curves were drawn for the pump at 1500 rpm and then a set of measurements concerning the use of pressure sensors was done in order to recover for different flow rates the static pressure signals upstream and downstream the pump and the exchanger. The pressure fluctuations and the performance curve were compared to the numerical results. The numerical simulations were carried out by using a Fluent code, the URANS (Unsteady Reynolds Averaged Navier-Stokes) approach and the k-ω SST turbulence model were applied to solve the unsteady, incompressible and turbulent flow. To record the fluctuating pressure signal, virtual sensors were necessary and placed at the same positions as in the experiments.
Effect of Wall Movement on a Jet Depositing on a Moving Wall at Moderate Reynolds Number
Authors: Hussain Md. Yahia , Khayat Roger E.
Published: March 2011

The steady flow of a moderately inertial jet depositing on a moving wall, is examined theoretically near channel exit. The free surface jet emerges from a channel and adheres to a wall, which may move in the same or opposite direction to the acting channel pressure gradient. The problem is solved using the method of matched asymptotic expansions. The small parameter involved in the expansions is the inverse Reynolds number. The flow field is obtained as a composite expansion by matching the flow in the boundary layer regions near the free surface, with the flow in the core region. The influence of inertia and wall velocity on the shape of the free surface, the velocity and stress is emphasized. It is found that the viscous relaxation length is essentially uninfluenced by the velocity of a forward moving wall. In contrast, it diminishes rapidly with the velocity of a backward moving wall.
Flow of Wall Jet Near Channel Exit at Moderate Reynolds Number
Authors: Azad Md. Abul Kalam , Khayat Roger E.
Published: March 2011

The wall jet flow near channel exit at moderate Reynolds Number, emerging from a two-dimensional channel, is examined theoretically in this study. Poiseuille flow conditions are assumed to prevail far upstream from the exit. The problem is solved using the method of matched asymptotic expansions. The small parameter involved in the expansions is the inverse Reynolds number. The flow and stress fields are obtained as composite expansions by matching the flow in the boundary-layer region near the free surface, flow in the outer layer region and the flow in the core region. The fluid is assumed to be Newtonian and it is found that the jet contracts downstream from the channel exit. The influence of inertia on the shape of free surface, the velocity and stress is emphasized and the higher order boundary layer is explored. To leading order, the problem is similar to the case of the free jet (Tillett) [1] with different boundary conditions. A similarity solution can be carried out using a similarity variable problem which is then solved as an initial-value problem, where the equation is integrated subject to the boundary conditions and a guessed value of the slope at the origin. The slope is adjusted until reasonable matching is achieved between the solution and the asymptotic form at large θ. The level of contraction is essentially independent of inertia, but the contraction moves further downstream with increasing Reynolds number. The present work provides the correct conditions near exit, which are required to determine the jet structure further downstream. If the jet becomes thin far downstream, a boundary layer formulation can be used with the presently predicted boundary conditions for steady and possibly transient flows.
A Hybrid Model for the Simulation of Electroosmotic Flows in Microchannels, Induced by Internal Electrodes
Authors: Stieglitz Ina , Ehrhard Peter
Published: March 2011

In general, the modeling of electroosmotic flows can be approached in two fundamentally–different ways. (i) The thickness of electrical double layer (EDL) is ignored and the effect of the electrical forces within the EDL is imaged into a modified kinematic boundary condition, the so-called Helmholtz–Smoluchowski slip condition. This approach is numerically simple and inexpensive, but implies several restrictions. (ii) The EDL is fully resolved, using a first–principle approach based on differential conservation equations for mass, momentum, and charge. This approach is enormously elaborate and numerically expensive, but appears to be applicable for a much wider range of problems. As an example, the treatment of internal electrodes, adjacent to insulating walls at defined zeta potential, appears difficult with the simple approach (i), since any non–continuous potential distribution at the wall leads to a singularity of the electrical field strength. To avoid these difficulties, we develop a hybrid model which, on the one hand, electrically resolves the EDL to reveal a perfectly-continuous potential distribution in the complete microchannel. On the other hand, the flow equations are solved in the fluid bulk only, not comprising the EDL. Hence, the effect of the EDL is still incorporated by means of modified kinematic boundary conditions. The advantage of this hybrid model is, firstly, to avoid artificial singularities of the electrical field strength, where regions of different surface charge meet. These singularities are clearly artificial, since they result from neglecting the extend of the EDL. Secondly, the hybrid model, at each time step, needs to solve only once for the potential distribution, which makes it numerically inexpensive and simple. Hence, systematic parameter studies are within reach. We apply the hybrid model to investigate the influence of internal electrodes onto the flow field, driven by electroosmosis in a modular rectangular microchannel. As internal electrodes can be positioned at lower distances (if compared to external electrodes), they can be operated at lower voltages and still ensure strong electrical field strength. Systematic studies on the effect of different electrode positions and voltages are presented, leading to optimized settings for specific tasks as pumping or mixing. Further, a comparison to first-principle simulations using the approach (ii) is presented for selected cases. This demonstrates that the hybrid model perfectly captures the dominant physics.
Heat Transfer and Evaporation of Falling Liquid Films on Surfaces With Advanced Three-Dimensional Periodic Structures: Experiments and Numerical Simulations
Authors: Lo¨ffler Karsten , Yu Hongyi , Hardt Steffen , Gambaryan-Roisman Tatiana , Stephan Peter
Published: March 2011

Thin liquid films are widely used in many technological applications. Heat and mass transfer in falling liquid films can be controlled and enhanced by using walls with advanced three-dimensional topographies that influence the film hydrodynamics, stability and wavy pattern or promote evaporation in a very thin film region. Furthermore, capillary suction on structured surfaces leads to a significant increase of the critical heat flux. In this work, heat transfer in laminar falling water films on heated plates with herringbone structure and with meandering grooves has been studied experimentally for different heat fluxes (up to 24 kW/m2), inclination angles and flow rates under reduced pressure, so that evaporation has a significant impact on heat transfer. The flow patterns and temperature gradients on the liquid-gas interface are visualized by high-speed infrared thermography. The wall temperature distribution is measured with thermocouples. The experimental data are compared with the results of numerical simulations. The predicted effect of micro region evaporation on heat transfer has been confirmed experimentally for the first time for partially wetting films on a plate with meandering grooves. This effect manifests itself in a significant decrease of the local wall temperature after the film rupture and consequent transition from a continuous film flow to rivulet flow regime.
Numerical Investigation of the Influence of Side Winds on a Simplified Car at Various Yaw Angles
Authors: Krajnovic´ Sinisˇa , Sarmast Sasan
Published: March 2011

The flow around a generic passenger car under the influence of crosswind was predicted using large eddy simulation (LES). The Reynolds number based on the incoming velocity the car’s length, L used was Re = 9 × 105. Yaw angles of crosswind of 10°, 20° and 30° were studied and the LES results were compared with the experimental observations and previous Reynolds averaged Naviers-Stokes (RANS) and detached eddy simulations (DES). The present LES were found to predict flows in better agreement with the experimental observations than previous RANS and DES. This shows that LES is better suited than RANS or DES for moderate Reynolds number flows around scale-model car in crosswinds which are inherently unsteady with regions of massive separations.
Numerical Analysis of the Effect of Different Channel Geometries and Electrode Materials on the Performance of Microfluidic Fuel Cells
Authors: Khabbazi Ali Ebrahimi , Richards Andrew , Hoorfar Mina
Published: March 2011

A typical microfluidic fuel cell is comprised of a Y- or T-shaped microchannel. The fuel and the oxidant streams are introduced from the two different inlets. The anodic and cathodic flows meet each other at the beginning of the main channel and start to travel together along the channel. Due to the fact that the viscous forces dominate the inertia forces in microchannels, the oxidant and the fuel streams establish a side-by-side co-laminar flow which makes the anolyte and catholyte flow together without turbulent mixing. Laminar flow in microfluidic fuel cells plays the role of the membrane in proton exchange membrane (PEM) fuel cells by maintaining the separation of the fuel and oxidant. This eliminates the need for the membrane and overcomes the membrane-related issues such as the ohmic overpotential and water management which are relevant to PEM fuel cells. In addition to the above advantage, the high surface-to-volume ratio of these micron-scale devices contributes to their high power density. This advantage is due to the fact that the electrochemical reactions in fuel cells are surface-based. The electrodes on which the electrochemical reactions are occurring are installed appropriately on the walls of the channel in a way that reacting flows are restricted to the proper electrodes. Since the flow is laminar the performance of the microfluidic fuel cell significantly depends on the device geometry. In this paper, different channel geometries and different electrode configurations are modeled and their performances are compared through the polarization curves. It has been found that the high aspect ratio provides the largest power density. In this work, the performance of the flow-through porous electrode was also modeled and compared against the conventional non-porous electrode microfluidic fuel cells. The flow-through porous electrode design is based on cross-flow of aqueous vanadium redox species through the electrodes into an exit channel, where the waste solutions meet and establish a co-laminar flow. This co-laminar flow of reacted species facilitates ionic charge transfer in a membraneless configuration. It has been found that the flow-through porous architecture provides an increased active surface area which contributes to a higher power density as opposed to the fuel cells with non-porous electrodes.
Analytical Treatment of Heat Transfer in Electrokinetic Flows
Authors: Jamaati Jafar , Niazmand Hamid , Renksizbulut Metin
Published: March 2011

This paper investigates the effects of velocity slip in the presence of an electric double-layer on fluid flow and heat transfer in a parallel plate hydrophobic microchannel. The electric potential filed is determined through the Poisson-Boltzmann equation together with the Debye-Hu¨ckel (D-H) approximation, while the velocity field is obtained by solving the Navier-Stokes equations under fully developed conditions. In most previous studies, zeta-potential has been considered as an independent variable for the analysis of induced voltage. However, experimental findings show that in electrokinetic slip flows with constant wall potential, the zeta potential is related to the slip coefficient and the D-H parameter. Therefore, in the present study, the wall potential is considered as an independent variable and the zeta potential is determined from an available experimental correlation. The effects of velocity slip, the D-H parameter, the wall potential and the Brinkman number on the induced voltage and the velocity and temperature fields are examined in detail. Results indicate that the slip effects on the zeta potential dramatically affect the flow and temperature fields.
Platinum Supported Mesoporous Silica Spheres by Optimized Microfluidic Sol-Gel Synthesis Scheme
Authors: Chokkalingam Venkatachalam , Weidenhof Boris , Maier Wilhelm F. , Herminghaus Stephan , Seemann Ralf
Published: March 2011

Droplet based microfluidics is used to perform sol-gel reactions. The chemicals are dispensed, mixed, and pre-processed inside a microfluidic device allowing for long operation times without any clogging. Using this approach and optimizing all reaction and processing parameters we generate mesoporous silica particles with a very high surface area of 820 m2g−1 and a narrow pore radius distribution of around 2.4 nm. To take full advantage of the possibilities offered by this microfluidic synthesis route, we produced platinum supported silica microspheres (as high as 7 mol. %) for heterogeneous catalysis.
Sources of Experimental Errors in Specific Absorption Rate Measurement of Magnetic Nanoparticles
Authors: Huang Shujuan , Gupta Amit , Borca-Tasciuc Diana-Andra
Published: March 2011

Magnetic-nanoparticles cancer hyperthermia, a side effects-free, potential cancer therapy employing magnetic nanoparticle remotely heated by alternating magnetic field (AMF), is receiving considerable attention from researchers and physicians [1–3]. Specific absorption rate (SAR), which is used to quantify nanoparticles’ heat generation under the applied AMF, is defined as the thermal power per unit mass dissipated by the magnetic material [3]. SAR depends on field parameters (magnetic field strength and frequency) and material system (size and magnetic properties of nanoparticles). Accurate measurement of SAR is a critical step in enabling comparison with theoretical predictions for understanding other parameters that may affect the heat generation rate such as nanoparticle functionalization, clustering and immobilization in biological medium [4]. A main drawback is the fact that independent measurements on similar samples often provide significantly different SAR values. For example, the reported SAR of magnetite-based aqueous solution Endorem commercially available from Guerbet greatly differs among Ref. [3], [5] and [6], even when factors such as field intensity, H, and frequency, f, are taken into account.
The Effect of Chaotic Mixing on Heat Transfer in Continuous Thermal Processes at Low Peclet Numbers
Authors: Speetjens M. F. M.
Published: March 2011

Chaotic fluid mixing is generally considered to enhance fluid-wall heat transfer and thermal homogenisation in laminar flows. However, this essentially concerns the transient stage towards a fully-developed (thermally-homogeneous) asymptotic state and then specifically for high Pe´clet numbers numbers Pe (convective heat transfer dominates). The role of chaos at lower Pe under both transient and asymptotic conditions, relevant to continuous thermal processes as e.g. micro-electronics cooling, remains largely unexplored to date. The present study seeks to gain first insight into this matter by the analysis of a representative model problem: heat transfer in the 2D time-periodic lid-driven cavity flow induced via non-adiabatic walls. Transient and asymptotic states are investigated in terms of both the temperature field and the thermal transport routes. This combined Eulerian-Lagrangian approach enables fundamental investigation of the connection between heat transfer and chaotic mixing and its ramifications for temperature distributions and heat-transfer rates. The analysis exposes a very different role of chaos in that its effectiveness for thermal homogenisation and heat-transfer enhancement is in low-Pe transient and asymptotic states marginal at best. Here chaos may in fact locally amplify temperature fluctuations and thus hamper instead of promote thermal homogeneity. These findings reveal that optimal thermal conditions are at lower Pe not automatic with chaotic mixing and may depend on a delicate interplay between flow and heat-transfer mechanisms.
Integration of a PDMS/SU-8/Quartz Microfluidic Chip With a Novel Macroporous Poly Dimethylsiloxane (PDMS) Membrane for Isoelectric Focusing of Proteins Using Whole-Channel Imaging Detection
Authors: Shameli Seyed Mostafa , Elbuken Caglar , Ren Carolyn L. , Pawliszyn Janusz
Published: March 2011

Capillary isoelectric focusing (CIEF) is a high-resolution capillary electrophoresis (CE) technique for separating zwitterionic biomolecules, such as proteins and peptides. In this method, by generating a stable pH gradient along the length of the capillary and under the influence of a constant electric field, samples can be separated according to their different isoelectric points (pI). For identifying the focused zones in CIEF, the whole column imaging detection (WCID) is more reliable than any other single point detection methods since it avoids the need of focused peak mobilization, presenting several advantages such as lower detection time, minimized peak dispersion and consequently higher resolution. Capillary-based IEF-WCID has been invented by Convergent Bioscience Inc. (iCE280 analyzer) for separation of proteins and biomarkers [1–2]. In the iCE280 analyzer, hollow fibers are glued to the capillary to separate electrolytes from the samples and a metal slit with a 65 μm opening is glued to the top of the capillary to improve detection sensitivity by blocking stray light. However, this method has several limitations because of the use of capillary such as low throughput, difficulty to be integrated with other separation modes and low detection sensitivity.
Turbulent Two-Phase Flows and Particle Deposition in a Duct at High Concentrations
Authors: Ahmadi Goodarz , Nasr Hojjat , McLaughlin John B.
Published: March 2011

Two-phase flows including particle-particle collisions and two-way coupling in a turbulent duct flow were simulated using a direct simulation approach. The direct numerical simulation (DNS) of the Navier-Stokes equation was performed via a pseudospectral method was extended to cover two-way coupling effects. The effect of particles on the flow was included in the analysis via a feedback force that acted on the fluid on the computational grid points. The point particle equation of motion included the Stokes drag, the Saffman lift, and the gravitational forces. Several simulations for different particle relaxation times and particle mass loading were performed, and the effects of the inter-particle collisions and two-way coupling on the particle deposition velocity, fluid and particle fluctuating velocities, particle normal mean velocity, and particle concentration were determined. It was found that when particle-particle collisions were included in the computation, the particle deposition velocity increased. When the particle collision was neglected but the particle-fluid two-way coupling was accounted for, the particle deposition velocity decreased slightly. When both inter-particle collisions and two-way coupling effects were taken into account in the simulations, the particle deposition velocity increased. Comparisons of the present simulation results with the available experimental data and earlier numerical results are also presented.
Local Thermal Equilibrium in Forced Convection Through Porous Media
Authors: Nouri-Borujerdi A.
Published: March 2011

Forced convection heat transfer through a channel filled with a porous medium is investigated using perturbation method. Two-energy equation model is utilized to represent the assumption of local thermal non-equilibrium which exists between the solid and fluid phases. The Brinkman-Forchheimer extension of the Darcy model is used to represent the fluid transport within the porous medium. Analytical solution is obtained for both fluid and solid temperature fields incorporating the effects of various pertinent parameters such as the Darcy number, the Biot number, the thermal conductivity and the pressure gradient. It is found that the Darcy number and the pressure gradient have significant effects on the local thermal equilibrium assumption.
Transport Across Sub-Nanometer Zeolite Pores for Water Desalination
Authors: Humplik Thomas , Laoui Tahar , Wang Evelyn N.
Published: March 2011

The molecular sieving capability of zeolites, alumino-silicate minerals with 3–8 Å diameter pores, promises an efficient method to remove salt from seawater. In this work, we synthesized and characterized MFI zeolites with a nominal pore diameter of 5.6 Å with varying Si/Al ratio from 23 to infinity to alter the wetting properties. We subsequently performed pressure infiltration tests with the synthesized zeolites suspended in water to investigate the effect of wetting properties on water transport in the pores. Water sorption isotherms were obtained that show distinct infiltration stages of water transport. For MFI zeolites, pressures of over 100 MPa were needed to fill the pore volume. The insight gained from this work is a first step towards designing zeolite-based membranes for the active layer of a reverse osmosis membranes. This work will be further developed in future work to understand ion transport through zeolites.
Unsteady Aerodynamics on a Low Aspect Ratio Flat Plate
Authors: Hart Adam , Ukeiley Lawrence
Published: March 2011

The study of biological flight has shown the potential of using unsteady fluid mechanism to enhance lift and drag capabilities in low Reynolds number flight regimes. To help further the knowledge of unsteady aerodynamic fluid phenomena, a low aspect ratio flat plate is subjected to a pitching motion superimposed on a plunging motion. Variations in this motion are introduced by adding a phase lag to the pitching cycle relative to the plunge cycle. Particle Image Velocimetery (PIV) is used to measure the instantaneous velocity fields over the upper surface of the flat plate at several points in the motion cycle. These vector fields are then averaged over approximately 420 ensembles to obtain the mean velocity field at the points in the cycle. Three vortex detection algorithms are implemented to identify the center of the vortex structures created off the leading edge and track their convection downstream. Experiments show that phase lags between 75° and 90° are more prone to create organized vortex structures and convect them in close proximity to the upper surface of this low aspect ratio flat plate.
Validated Reduced Order Models for Simulating Trajectories of Bio-Inspired Artificial Micro-Swimmers
Authors: Tabak Ahmet Fatih , Yesilyurt Serhat
Published: March 2011

Autonomous micro-swimming robots can be utilized to perform specialized procedures such as in vitro or in vivo medical tasks as well as chemical surveillance or micro manipulation. Maneuverability of the robot is one of the requirements that ensure successful completion of its task. In micro fluidic environments, dynamic trajectories of active micro-swimming robots must be predicted reliably and the response of control inputs must be well-understood. In this work, a reduced-order model, which is based on the resistive force theory, is used to predict the transient, coupled rigid body dynamics and hydrodynamic behavior of bio-inspired artificial micro-swimmers. Conceptual design of the micro-swimmer is biologically inspired: it is composed of a body that carries a payload, control and actuation mechanisms, and a long flagellum either such as an inextensible whip like tail-actuator that deforms and propagates sinusoidal planar waves similar to spermatozoa, or of a rotating rigid helix similar to many bacteria, such as E. Coli. In the reduced-order model of the micro-swimmer, fluid’s resistance to the motion of the body and the tail are computed from resistive force theory, which breaks up the resistance coefficients to local normal and tangential components. Using rotational transformations between a fixed world frame, body frame and the local Frenet-Serret coordinates on the helical tail we obtain the full 6 degrees-of-freedom relationship between the resistive forces and torques and the linear and rotational motions of the swimmer. In the model, only the tail’s frequency (angular velocity for helical tail) is used as a control input in the dynamic equations of the micro-swimming robot. The reduced-order model is validated by means of direct observations of natural micro swimmers presented earlier in the literature and against; results show very good agreement. Three-dimensional, transient CFD simulations of a single degree of freedom swimmer is used to predict resistive force coefficients of a micro-swimmer with a spherical body and flexible tail actuator that uses traveling plane wave deformations for propulsion. Modified coefficients show a very good agreement between the predicted and actual time-dependent swimming speeds, as well as forces and torques along all axes.
Optimization and Active Control of the Underhood Cooling System: A Numerical Analysis
Authors: Khaled Mahmoud , Harambat Fabien , Yammine Anthony , Peerhossaini Hassan
Published: March 2011

Here numerical analysis is focused on optimizing the vehicle heat exchanger by varying the geometry in which it is integrated in the vehicle’s cooling system. This analysis also elucidates how one can affect the different parameters that influence heat exchanger performance in order to optimize their functioning, in relation to the geometry in which they are integrated. The two-dimensional computational code developed permits optimizing the performance of the cooling module by positioning different heat exchangers, in both driving and stop phases of the vehicle. The ultimate aim is to develop new approaches to controlling heat exchanger positions in a real vehicle cooling system.
Numerical Simulation of Thermomagnetic Convection in an Enclosure Using the Lattice Boltzmann Method
Authors: Hadavand Mahshid , Nabovati Aydin , Sousa Antonio C. M.
Published: March 2011

The application of the single relaxation time lattice Boltzmann method (LBM) is extended to the study of thermomagnetic convection in a differentially heated square cavity with an infinitely long third dimension. The magnetic field is created and controlled by placing a dipole at the bottom of the enclosure. The magnitude of the magnetic force acting on the ferrofluid is controlled by changing the electrical current through the dipole. In this study, the effects of combined natural convection and magnetic convection, which is commonly known as “thermomagnetic convection”, are analysed in what concerns the flow modes and heat transfer characteristics of a magnetic fluid (ferrofluid). This is a situation of considerable interest for cooling micro-electronic devices, when natural convection does not meet the cooling requirements, and forced convection is not viable due to the difficulties associated with pumping a ferrofluid.
Experimental Investigation of the Mean Concentration Fields in a Counterflowing Jet
Authors: Torres Luis A. , Fleck Brian A. , Wilson David J. , Nobes David , Mahmoudi Mohammad
Published: March 2011

The geometrically similar region of the centerline concentration decay of a counter-flowing jet was investigated using planar laser induced fluorescence. The jet is investigated for jet to counterflowing velocity ratios (Ur) in the range 4<Ur<19. New length scales for this flow were studied and used to generate empirical expressions to predict the concentration decay in the established flow zone. These length scales were defined using the 5% contour of the mean concentration field of the counterflowing jet. Additional experiments for two jet to counterflow velocity ratios were used to validate these empirical expressions. The new empirical expressions correlate well with the concentration decay in the centerline of the counterflowing jet within the free jet-like region. It was found that for some cases, the centerline concentration decay of the counterflowing jet was better predicted considering decay proportional to x−6/5, even though it can also be predicted by assuming decay with x−1.
Direct Numerical Simulation of Turbulent Flows in Rough Pipes Using an Immersed Boundary Method With a Spectral Representation of the Roughness Topography
Authors: van Nimwegen A. T. , Portela L. M.
Published: March 2011

An immersed boundary method, similar to the one used by Kim et al. [1] was developed to implement a varying wall topography into an existing DNS code for pipe flow. Validation using a semi-analytical solution and numerical results showed that the method yields accurate results for laminar flow. Four simulations for turbulent flow where performed, each with a different wall geometry. Wall topographies varying in the axial direction and topographies varying in the azimuthal direction have been considered. Time-averaged as well as instantaneous results are presented for the different geometries. The results for turbulent flow are consistent with the expected physical behaviour. They confirm the hypothesis that flow in the outer layer is largely unaffected by the wall topography.