bluuebunny/crossref_metadata_2025 huggingface dataset:
Convergence of a Greedy Algorithm on Nonlinear Convex Problems and Application to Uncertainty Quantification on Obstacle Problems
Authors: Ehrlacher Virginie
Published: March 2011

In this article, a method is proposed to study uncertainty propagation on high-dimensional obstacle problems. A greedy algorithm, based on variable decomposition, is used to approximate the solution of regularized problems obtained by penalization of the initial problem. The convergence of this algorithm is a consequence of a more general theorem. Indeed, the algorithm converges for the minimization of a strongly convex functional whose derivative is Lipschitz on bounded sets. We describe how this algorithm was numerically implemented and present the results which were obtained with a one-dimensional membrane problem.
Droplet Formation by Dripping at Micro T-Junction in Liquid-Liquid Mixing
Authors: Yeom Sujin , Lee Sang Yong
Published: March 2011

In the present work, the phenomenon of droplet formation by dripping at a micro T-junction in liquid-liquid mixing was studied experimentally. The drop formation process consisted of three stages: the X-Y growth, X growth, and the detachment stages. In the X-Y growth stage, the bulged part of the disperse phase grows both in X (parallel to the main channel) and Y (lateral to the main channel) directions. The X-Y growth stage is followed by the X growth stage where the bulged part grows only in the main channel direction. Subsequently, in the detachment stage, the drag force exerted by the continuous phase becomes larger than the surface tension force between the two phases and the bulged part is finally separated into a droplet with regular intervals through a rapid necking process. Droplet sizes were estimated from the drop generation frequency and the flow rate of the disperse phase, and were also confirmed by direct measurements through photography. The sizes of the micro droplets generally decrease with the larger flow rate of the continuous phase or with a smaller flow rate of the disperse phase. This is due to the increase of the interfacial shear force between the two phases through the increase in the relative velocity. The droplet size also decreases with increase of the viscosity of the either phase. This again is due to the increase of the interfacial shear force (and hence the drag force) between the phases when the viscosity of either phase becomes large. The measured drop sizes will serve as a set of the benchmarking data for the development of a droplet detachment model in the dripping mode at micro T-junctions.
Compressible Microchannel Flow
Authors: Mirshekari Gholamreza , Brouillette Martin
Published: March 2011

We present experiments on the isothermal gas flow at relatively high Mach numbers in microfabricated channels of small aspect ratios. The microchannels were fabricated by deep etching on silicon wafers, bonded to a Pyrex wafer to cover and seal them; the microchannels were 10 microns deep with a variety of widths. The accurate determination of the small flow rates was performed by measuring the displacement of a bead of mercury in a precision bore glass tube in a controlled environment. The experiment setup has been specially designed to account for inlet and outlet loss. The inferred friction coefficient at different values of Knudsen, Reynolds and Mach numbers shows that the flow inside the microchannel follows the classical laminar behavior over the range of experiments.
Preparation of Stable Silicon Oil Based Nanofluid Containing Multi-Walled Carbon Nanotube by Using Hexamethyldisiloxane as Dispersant
Authors: Chen Lifei , Xie Huaqing , Li Yang , Yu Wei
Published: March 2011

Stable and homogeneous silicone oil based nanofluids of multi-walled carbon nanotubes (MWNTs) were prepared by using hexamethyldisiloxane as surfactant. The used MWNTs were cut by mechanical ball-milling approach following strong acid treatment. Scanning electronic microscopy results show that the MWNTs disperse well in the silicone oil. The addition of hexamethyldisiloxane reduces the viscosity of silicone oil greatly in all the studied temperatures. It is different from some water based nanofluids with surfactant. The minor viscosity augmentation of silicone oil based MWNT nanofluid with high thermal conductivity make it the ideal media in high burden of heat transfer and heat transfer enhancement in special condition. As expected, the viscosity of the nanofluid increases with MWNT volume fraction, but decreases with temperature. The 0.54 vol% MWNT dispersions with the addition of 0.6 wt % hexamethyldisiloxane show no MWNT precipitation for a couple of weeks.
Flow Characteristics of Electronic Expansion Valves for Heat Pump System Using Carbon Dioxide as a Refrigerant
Authors: Kim Ook Joong , Choi Young-Ho , Yoon Seok Ho
Published: March 2011

An experimental study on the flow characteristics of electronic expansion valves (EEVs) for heat pump system using carbon dioxide as a refrigerant have been carried out in this study. Many researches and efforts have been made to replace chemical refrigerants like Chloro-Fluoro-Carbon (CFC) and Hydro-Chloro-Fluoro-Carbon (HCFC) with natural refrigerants such as carbon dioxide and apply natural refrigerants to chillers or heat pump systems. In this study, we focused on the development of EEV and 4-way valve among the important components of heat pump system using natural refrigerant. The mass flow rate was measured at various EEV inlet temperature and pressure conditions with respect to several EEV openings operated at a heat pump system which has about 10 kW of cooling capacity. The heat pump system consists of a reciprocating compressor, a gas cooler, an evaporator, an EEV, and a 4-way valve which was developed for this study. The inlet temperature and pressure of an EEV was varied from 5°C to 40°C and from 7 MPa to 10 MPa, respectively. The mass flow rate of carbon dioxide through the EEV ranged from 50 g/s to 120 g/s. The mass flow rate of carbon dioxide around the critical point was affected by the inlet temperature and pressure of EEV, valve opening, and density variation. An empirical mass flow rate correlation of carbon dioxide based on the Buckingham π-theorem was developed in this study, and this correlation predicted experimental data within an average absolute deviation of 4.2%. The correlation can be applied to predict the mass flow rate through EEV used in the heat pump system using carbon dioxide as a refrigerant. And the reliability test of developed 4-way valve was conducted. This 4-way valve showed stable operation in the high pressure condition.
Two Algorithms for Solving Coupled Particle Dynamics and Flow Field Equations in Two-Phase Flows
Authors: Kamali R. , Shekoohi S. A.
Published: March 2011

Two methods for solving coupled particle dynamics and flow field equations simultaneously by considering fluid-particle interactions to simulate two-phase flow are presented and compared. In many conditions, such as magnetic micro mixers and shooting high velocity particles in fluid, the fluid-particle interactions can not be neglected. In these cases it is necessary to consider fluid-particle interactions and solve the related coupled equations simultaneously. To solve these equations, suitable algorithms should be used to improve convergence speed and solution accuracy. In this paper two algorithms for solving coupled incompressible Navier-Stokes and particle dynamics equations are proposed and their efficiencies are compared by using them in a computer program. The main criterion that is used for comparison is the time they need to converge for a specific accuracy. In the first algorithm the particle dynamics and flow field equations are solved simultaneously but separately. In the second algorithm in each iteration for solving flow field equations, the particle dynamics equation is also solved. Results for some test cases are presented and compared. According to the results the second algorithm is faster than the first one especially when there is a strong coupling between phases.
Effects of Real Surface Roughness on Fluid Flow in Nanochannels
Authors: Kharazmi Ali , Kamali Reza
Published: March 2011

In the present study, a computer program based on a molecular dynamics scheme has been developed for simulating fluid flow in nano- and micro-channels with roughness. According to the previous studies of nanochannels flows, surface roughness has a great effect on the rheology of the flow. Therefore a more realistic surface roughness has been developed and its influence on the fluid flow has been investigated using Molecular Dynamics (MD) Simulation.
A Continuum - Molecular Dynamics Hybrid Method for Micro- and Nano-Fluid Flow
Authors: Kharazmi Ali , Kamali Reza
Published: March 2011

A computer program based on a Molecular Dynamics-Continuum hybrid numerical method has been developed in which the Navier-Stokes equations are solved in the continuum region and the atomistic molecular dynamics in molecular region. The prepared algorithm and the computer code are capable of computing flows in micro and nano-scale geometries. The coupling between the continuum equations and the molecular dynamics is constructed through constrained dynamics within an overlap region where both molecular and continuum equations are solved simultaneously. An Overlap region is introduced in two directions to improve the choice of using molecular region in smaller areas. The proposed method is used to simulate steady and start-up Couette flow showing quantitative agreement with results from analytical solutions and full molecular dynamics simulations.
A High-Order LES Turbulent Model to Study Unsteady Flow Characteristics in a Low Pressure Turbine Cascade
Authors: Jimbo Tomohiko , Biswas Debasish
Published: March 2011

In this work, unsteady viscous flow analysis around Low Pressure Turbine (LPT) cascade using a High-Order LES (Large Eddy Simulation) turbulence model is carried out to investigate basic physical process. In the aerospace industry, input shaft power for fan and compressor components of turbine engines is most commonly supplied by the LPT. Considering this fact, in the endeavor of developing engines of increased efficiency and decreased weight LPT is an important component worth paying attention. Therefore, a better understanding of low-Reynolds number flow transition and separation behavior is very much essential to such improvements. Blades in the LPT environment may be designed for higher loading if the effects of passing wakes on bypass transition are properly included in the design. Also, under the LPT working conditions, boundary layers along a large extent of blade surface can remain laminar, even in the presence of elevated free-stream turbulence levels. The laminar boundary layers are then particularly susceptible to flow separation over the aft portion of blade suction surfaces, causing blockage in flow passages and a significant reduction in turbine efficiency. Related to weight reduction, the blade spacing in LPT can be increased with a rise in per blade loading. Increased blade spacing however, is accompanied by more extensive boundary layer separation on the suction surface of each blade due to uncovered turning, resulting in a further reduction of efficiency and additional wake losses. In the present work, experimental work is numerically simulated. Features of the flow-fields are described and compared with the experimental data on baseline case and active flow separation control using Vortex Generator Jet (VGJ).
Study on Performance of Canned Motor Pump Based on Numerical Simulation
Authors: Zhou Shuiqing , Kong Fanyu , Wang Ting , Wang Wenting
Published: March 2011

The pressure fluctuations in a centrifugal pump at both design and off-design points and the internal electromagnetic field of canned motor are presented in this paper. The 3D unsteady flow numerical simulation is completed at different operating points by using the FLUENT. A sliding mesh technique is applied to take into account the impeller-volute interaction. The FFT technology is adopted to process those dynamic pressure data to reveal the frequency features. All the power spectrum results present that the pressure fluctuation amplitude of blade suction side is greater than the one of blade pressure side. Some unknown high-frequency contents are discovered in the flow field. Meanwhile, the canned motor designed are applied by the design method of permanent magnet synchronous motor. The internal electromagnetic field of the motor is simulated with the ANSOFT software. Magnetic field analysis is carried out between two different magnetic circuit structure: U-type and inverted U-type. Comparing to U-type magnetic circuit structure, the latter is more conducive to reduce the magnetic flux leakage in the iron core tooth.
The Influence of Polymers on Coherent Structures in Decaying Homogeneous Isotropic Turbulence
Authors: Cai Wei-Hua , Zhang Hong-Na , Li Feng-Chen
Published: March 2011

Drag reduction in decaying homogeneous isotropic turbulence (DHIT) with polymer additives has been observed, which leads to weaker turbulent characteristic quantities. Coherent structures play an important role in the understanding of turbulent dynamics, and the introduction of polymer additives can significantly modify their behavior. It is believed the modifications are closely related to drag reduction mechanism. In the present study, we mainly focus on investigating the influence of polymers on coherent structures from phenomenological and energetic viewpoint for DHIT with polymers based on direct numerical simulation (DNS). The results show that polymers can not only suppress the increase rate of the enstrophy and strain but also their productions, leading to a remarkable inhibition of coherent structures especially at fine scale.
Numerical Study on Liquid Droplet Formation in T-Junction Microchannel
Authors: Li Xiao-Bin , Yang Juan-Cheng , Li Feng-Chen
Published: March 2011

The formation of micro droplets involved a complex mechanism deriving from the competition between the interfacial tension, viscous shearing and other counterparts. In the present study, a volume-of-fluid (VOF) method within FLUENT software was used to study the droplet formation in a T-junction microchannel. By varying the velocity of continuous phase, we got droplet formation in “squeezing” process, and the shifting to “dripping” regime at a critical Capillary number. The pressure and velocity changing in both regimes were investigated in detail, supporting the result that the squeezing was dominated by the upstream pressure rising and the dripping was driven by shearing force. The numerical results hold a good agreement with the previously experimental measurements using confocal micro-PIV system. Furthermore, the motion inside an emerging droplet was also studied, showing intricate circulation flow.
LES of Active Separation Control on Bluff Bodies by Steady Blowing
Authors: Eichinger Sa´ndor , Thiele Frank , Wassen Erik
Published: March 2011

An active flow control approach was investigated in order to reduce the aerodynamic drag of a generic square-backed vehicle. The investigations were carried out at a Reynolds number of ReL = 500,000. Large Eddy Simulations were performed which are suitable for time dependent flows around vehicles with large coherent structures. After the base flow simulations active flow control was applied in order to achieve drag reduction using steady blowing through small slits near the edges of the rear surface. The blowing velocity was equal to the inflow velocity (vblow = U0), and the blowing angle was changed from θ = 0° to θ = 60°. It is shown that these control techniques can achieve a maximum drag decrease for the θ = 45° control version of around 12%. Additionally the effect of moving floor was studied and comparison was made for the baseline and for the 45° flow control variant. It was found that the stagnation point on the rear surface moves upwards, and the vertical extension of the wake section reduces, so the evolving pressure level on the back surface increases. Finally a study of the blowing velocity was performed, changing vblow = 0.25U0 until vblow = 2.25U0 at θ = 45° blowing angle. An efficiency optimum was found around vblow = 1.25U0.
Optically Induced Electrokinetic Trapping and Sorting of Colloids
Authors: Williams Stuart J. , Kumar Aloke , Wereley Steven T.
Published: March 2011

Recently, we have demonstrated electrothermal hydrodynamics with an external heating source of a highly focused 1,064 nm laser beam [1]. This phenomenon, when coupled with particle-electrode electrokinetic interactions, has led to the rapid and selective concentration of suspended colloids [2–6]. This technique, termed Rapid Electrokinetic Patterning (REP) was demonstrated without any additional surface modification or patterning of the electrodes. This dynamic, optically induced fluid and particle manipulation technique could be used for a variety of lab-on-a-chip applications. However, there are additional effects that have yet to be investigated that are important for a complete understanding of REP. This paper showcases experimental particle-particle behavior observations by varying particle diameter, electrode material, and preliminary results of varying fluid electrical conductivity.
Flow Boiling of Water on Nanocoated Surfaces in a Microchannel
Authors: Phan Hai Trieu , Caney Nadia , Marty Philippe , Colasson Ste´phane , Gavillet Je´roˆme
Published: March 2011

Experiments were performed to study the effects of surface wettability on flow boiling of water at atmospheric pressure. The test channel is a single rectangular channel 0.5 mm high, 5 mm wide and 180 mm long. The mass flux was set at 100 kg/m2 s and the base heat flux varied from 30 to 80 kW/m2. Water enters the test channel under subcooled conditions. The samples are silicone oxide (SiOx), titanium (Ti), diamond-like carbon (DLC) and carbon-doped silicon oxide (SiOC) surfaces with static contact angles of 26°, 49°, 63° and 103°, respectively. The results show significant impacts of surface wettability on heat transfer coefficient.
Unsteady Flow Numerical Analysis of New-Type Deep Well Pump Under Multi-Conditions
Authors: Lu Wei-gang , Zhou Ling , Zhang De-sheng , Zou Ping-ping , Wang Chuan
Published: March 2011

The interaction between impeller and guide vane of the deep well pump is one of the most important factors which cause the pressure fluctuation in the channels. However, even nowadays some flow events in the deep well pump are still under study and far from fully understood. So the unsteady flow field of a two-stage deep well pump was simulated with FLUENT code based on sliding mesh and the RNG k-ε turbulence model, to investigate the pressure fluctuation by interactions between the impeller and guide vane. The computing domain extends from the inlet of the first stage deep well pump to the outlet of the second stage guide vane. With the Fast Fourier Transform (FFT) analysis, the pressure fluctuation and frequency fluctuation are analyzed under multi-conditions. In this paper, the pressure fluctuation differences between the first stage and secondary are also compared. The numerical results show that the pressure fluctuates at the blade passage frequency, and the maximum amplitude of blade passage frequency occurs in the region from the rotor to the stator when the impeller blade gets close to the guide vane trailing edge, but it decreases rapidly after fluid entering the guide vane. Compared with the steady simulation, the averaged calculated single-stage head of unsteady simulation is more accord with the reality, which is less than the tested head with a relative deviation of 5%.
Numerical Analysis of Rarefaction and Compressibility Effects in Bent Microchannels
Authors: Rovenskaya O. , Croce G.
Published: March 2011

Numerical investigation of a gas flow through microchannels with a sharp, 90 degrees bend is carried out using Navier-Stokes (N-S) equations with the classical Maxwell first-order slip boundary condition, including the tangential gradient effect due to the wall curvature, and Smoluchowski first order temperature jump definition. The details of the flow structure near the corner are analyzed, investigating the competing effects of rarefaction and compressibility on the channel performances. The flow characteristics in terms of velocity profiles, slip velocity distribution along inner and outer wall, pressure, average Mach number along central line of the channel have been presented. The results showed that impact of the bend on the channel performances is smaller at high rarefaction levels. The behaviour of pressure and velocity away from the bend is similar to that of a straight microchannel; however, the asymmetry in the flow at the bend, with high velocities and high velocity gradients on its inner side, has a strong impact on wall slip velocities. The presence of a recirculation is detected on both the inner and outer walls of the corner for larger Reynolds. However, rarefaction may delay the onset of recirculation. It is also observed that the mass flux through a bend microchannel can even be slightly larger than that through a straight microchannel of the same length and subjected to the same pressure difference.
Kinematics of a Free Particle Moving Between Two Parallel Walls
Authors: Champmartin Ste´phane , Ambari Abdlehak , Ben Richou Abderrahim
Published: March 2011

The understanding of some physical phenomena involved in the transport of free particles such as fibers during injection processes is an important issue. To answer some of the questions arising in such problems, we study here numerically the quasi-steady kinematics of a free cylindrical solid particle moving in a Newtonian fluid confined between two parallel plane walls taking the hydrodynamic interactions into account. This is achieved by the use of the resistance matrix technique relating the kinematics of the particle to the forces and the torques exerted on the particle and to the dissipation induced by the motion of this particle. Our approach is confirmed by asymptotical developments and by a comparison with other authors in some cases. The solutions of three practical problems are given. In the first one, the sedimentation of the particle is studied. It is found that the maximum settling velocity of the free particle is obtained at a position off the symmetry plane. The cylinder is observed to rotate counter intuitively against the direction of rolling along the adjacent wall. Moreover the angular velocity has an influence on the settling velocity when the concentration is very high. The second problem concerns the transport of a neutrally buoyant cylindrical particle in a Poiseuille flow. This study reveals that there are relative translational and angular velocities between the free particle and the undisturbed fluid particle contrary to the commonly admitted hypothesis used in several models and numerical codes. Finally the third problem is a combination of the two previous situations: the transport of a non-neutrally buoyant particle in a Poiseuille flow. Depending on the ratio of the buoyancy forces to the viscous ones, different solutions are possible and exposed. Other problems can also be solved with this approach which is less time-consuming than complex methods such as DNS.
Numerical and Experimental Investigations of Cavitating Flow in a Vertical Multi-Hole Injector Nozzle
Authors: He Zhixia , Bai Jing , Wang Qian , Mu Qingmu , Huang Yunlong
Published: March 2011

The presence of cavitation and turbulence in a diesel injector nozzle has significant effect on the subsequent spray characteristics. However, the mechanism of the cavitating flow and its effect on the subsequent spray is unclear because of the complexities of the nozzle flow, such as the cavitation phenomena and turbulence. A flow visualization experiment system with a transparent scaled-up vertical multi-hole injector nozzle tip was setup for getting the experimental data to make a comparison to validate the calculated results from the three dimensional numerical simulation of cavitating flow in the nozzle with mixture multi-phase cavitating flow model and good qualitative agreement was seen between the two sets of data. The critical conditions for cavitation inception were derived as well as the relationship between the discharge coefficient and non-dimensional cavitation parameter. After wards, the testified numerical models were used to analyze the effects of injection pressure, back pressure, cavitation parameter, Reynolds number, injector needle lift and needle eccentricity on the cavitating flow inside the nozzle. Combined with visual experimental results, numerical simulation results can clearly reveal the three-dimensional nature of the nozzle flow and the location and shape of the cavitation induced vapor distribution, which can help understand the nozzle flow better and eventually put forward the optimization ideas of diesel injectors.
Flow of a Thin Viscoelastic Jet
Authors: Ahmed Moinuddin , Khayat Roger E.
Published: March 2011

The influence of elasticity and inertia for steady flow of a thin viscoelastic fluid jet is examined theoretically. The fluid is assumed to emerge from a vertical channel and driven by a pressure gradient and/or gravity. The boundary-layer equations are generalized for a viscoelastic thin film obeying the Oldroyd-b constitutive model. Special emphasis is placed on the initial stages of jet development. The formulation and simulation are carried out for two-dimensional jet flow in order to better understand the intricate wave and flow structures for a viscoelastic jet. In contrast to the commonly used depth-averaging solution method, the strong nonlinearities are preserved in the present formulation as the viscoelastic boundary-layer equations are solved by expanding the flow field in terms of orthonormal shape functions. It is found that for a steady viscoelastic jet, a reduction in inertia or a rise in elasticity leads to the emergence of surface waviness and excessive normal stress, which leads to the formation of sharp gradients in the velocity and shear stress. These gradients can be sufficiently substantial to cause a discontinuity or shock in the flow. During transition, the surface profiles adhere earlier to the shape of the final steady state instead of a traveling wave, the transition between the two states takes the form of a standing wave, which grows essentially in amplitude only.
Investigation of Effects of Radial Distortion on Transonic Fan Behavior
Authors: Voytovych Dmytro M. , Xia Guoping , Lian Chenzhou , Merkle Charles L.
Published: March 2011

The flow analysis around blades of a transonic fan is presented for both clean and radially distorted inlets. Computations are shown for four-blade passages that are accomplished with a second order accurate code using a k-ω turbulence model. The mass flow rate along a speed line is controlled by varying a choked nozzle downstream of the fan. The results show good agreement with data for three speed lines. In the near-stall region, the flow first becomes unsteady and then unstable with the unsteadiness increasing at lower speeds. The four-blade simulations remained stable to lower mass flow rates than the single-blade simulations. In the near-stall vicinity, tip vortex breakdown occurred creating a low momentum zone near the blade tip on the pressure side that grew as the mass flow was decreased until it eventually blocked the passage. The presence of distortion reduced the operational range and moved the stall line to higher mass flow rates. At high speeds distortion reduced both the mass flow rate and total pressure ratio while at lower speeds, the choking mass flow rate was reduced, but the total pressure ratio was slightly improved. The flow separation near the hub on the suction side was caused by the distortion. Its size was decreasing with rotational speed.
Aerodynamic Particle Resuspension due to Human and Model Foot Motions
Authors: Kubota Yoshihiro , Higuchi Hiroshi
Published: March 2011

Human foot motions such as walking and foot tapping detach the particulate matter on the floor and redistribute it, increasing the particle concentration in air. The objective of this paper is to experimentally investigate the mechanism of particle resuspension and redistribution due to human foot motion. In particular, generation and deformation of vortex produced by the foot motion and how they are affected by the shape of sole have been examined. The experiments were carried out by particle flow visualization and the Particle Image Velocimetry (PIV) measurements in air, and dye flow visualization in water. The flow visualizations with human foot tapping and stomping were also carried out in order to elucidate the particle resuspension in real situations. In a laboratory experiment, the foot was modeled either as an elongated plate or a foot wearing a slipper, moving normal to the ground downward or upward. To focus on the aerodynamic effect, the model foot was stopped immediately above the floor before contacting the floor. The results indicated that the particles were resuspended both in downward motion and in upward motion of the foot. The particle resuspension and redistribution were associated with the wall jet between the foot and floor and the vortex dynamics. With an elongated plate, three-dimensional vortex structure strongly affected the particle redistribution.
Immersed Boundary Method for Generalised Finite Volume and Finite Difference Navier-Stokes Solvers
Authors: Pinelli A. , Naqavi I. Z. , Piomelli U.
Published: March 2011

In Immersed Boundary Methods (IBM) the effect of complex geometries is introduced through the forces added in the Navier-Stokes solver at the grid points in the vicinity of the immersed boundaries. Most of the methods in the literature have been used with Cartesian grids. Moreover many of the methods developed in the literature do not satisfy some basic conservation properties (the conservation of torque, for instance) on non-uniform meshes. In this paper we will follow the RKPM method originated by Liu et al. [1] to build locally regularized functions that verify a number of integral conditions. These local approximants will be used both for interpolating the velocity field and for spreading the singular force field in the framework of a pressure correction scheme for the incompressible Navier-Stokes equations. We will also demonstrate the robustness and effectiveness of the scheme through various examples.
Prediction of Chemical Reaction Yield in a Microreactor and Development of a Pilot Plant Using the Numbering-Up of Microreactors
Authors: Togashi Shigenori , Asano Yukako , Endo Yoshishige
Published: March 2011

The chemical reaction yield was predicted by using Monte Carlo simulation. The targeted chemical reaction of a performance evaluation using the microreactor is the consecutive reaction. The main product P1 is formed in the first stage with the reaction rate constant k1. Moreover, the byproduct P2 is formed in the second stage with the reaction rate constant k2. It was found that the yield of main product P1 was improved by using a microreactor when the ratio of the reaction rate constants became k1/k2 >1. To evaluate the Monte Carlo simulation result, the yields of the main products obtained in three consecutive reactions. It was found that the yield of the main product in cased of k1/k2 >1 increased when the microreactor was uesd. Next, a pilot plant involving the numbering-up of 20 microreactors was developed. The 20 microreactor units were stacked in four sets, each containing five microreactor units arranged. The maximum flow rate when 20 microreactors were used was 1 × 104 mm3/s, which corresponds to 72 t/year. Evaluation of the chemical performance of the pilot plant was conducted using a nitration reaction. The pilot plant was found to capable of increasing the production scale without decreasing the yield of the products.
Mercury Scaling of a Swirling Jet Micro-Bubble Generator
Authors: Walker Stuart , Ruggles Arthur
Published: March 2011

Swirling jets with co-axial gas filament flow have been used for production of small bubbles in environmental and chemical processing industries for some time. The modeling of the physics for the gas filament break-up is not well established, and this impedes scaling of the device to use with fluids other than water and organics where data is available. High speed photographic studies of the gas filament break-up are used to examine the physical phenomena, and support model development for the bubble production that may be used to scale the device to alternate applications, such as bubble production in liquid metals. Bubble break-up models based on energy dissipation generate a power-law, with exponent of α = 8/5, relating Weber number to Reynolds number at the nozzle exit. Those models are compared to empirical models found in the literature providing a link between mechanistic models, scaling arguments, and legacy empirical models.
A Combined Experimental and Numerical Study of Flow Past a Single Step Cylinder
Authors: Morton Chris R. , Yarusevych Serhiy
Published: March 2011

The current study investigates flow past a step cylinder for ReD = 1050 and D/d = 2 using both experimental and numerical methods. The focus of the study is on the vortex shedding and vortex interactions occurring in the step cylinder wake. Flow visualization with hydrogen bubble technique and planar Laser Induced Fluorescence has shown that three distinct spanwise vortex cells form: a single vortex shedding cell in the wake of the small cylinder and two vortex shedding cells in the wake of the large cylinder. Vortex connections form between the spanwise vortices in these cells downstream of the step, and vortex dislocations occur at cell boundaries. Complementary to the experimental tests, an LES-RANS hybrid numerical simulation is used to model the flow development. A comparison of the experimental and numerical results indicates that the numerical approach adequately models vortex dynamics in the wake of a step cylinder and, thus, may be used to analyze time dependent, three-dimensional flow topology which is difficult to characterize quantitatively using experimental methods.
An Experimental Study of Flow Past a Dual Step Cylinder
Authors: Morton Chris R. , Yarusevych Serhiy
Published: March 2011

Flow past a dual step cylinder has been investigated using experimental flow visualization methods. The dual step cylinder model is comprised of a small diameter cylinder (d) and a large diameter cylinder (D) mounted at the mid-span of the small cylinder. The experiments have been performed for ReD = 1050, D/d = 2, and a range of large cylinder aspect ratios (L/D). The focus of the study is on vortex shedding and vortex interactions occurring in the large and small cylinder wakes. A flow visualization study completed using hydrogen bubble technique and planar laser induced fluorescence has shown that the flow development is highly dependent on the aspect ratio of the large cylinder, L/D. The results identify four distinct flow regimes: (i) for L/D ≥ 17, three vortex shedding cells form in the wake of the large cylinder, one central cell and two cells of lower frequency extending over about 4.5D from the large cylinder ends, (ii) for 7 < L/D ≤ 14, a single vortex shedding cell forms in the wake of the large cylinder, whose shedding frequency decreases with decreasing L/D, (iii) for 2 ≤ L/D ≤ 7, vortex shedding in the wake of the large cylinder is highly three-dimensional, such that each vortex deforms while it is shed into the wake, (iv) for 0.2 ≤ L/D ≤ 1, only small cylinder vortices are shed in the wake and often form vortex connections across the wake of the large cylinder.
Bubble Formation on Top of Submerged Needle and Substrate Plates
Authors: Vafaei Saeid , Angeli Panagiota , Wen Dongsheng
Published: March 2011

The purpose of this investigation is to conduct a comparative study on the formation of bubble on top of a stainless steel needle nozzle and two substrate plate nozzles. The experimental study is conducted on a submerged needle nozzle with internal diameter of 0.51 mm and 0.155 mm thickness, and two stainless steel substrate plates with nozzle diameter of 0.4 mm and 0.51mm respectively. The experiment is carried out under low gas flow rates (0.015 ∼ 0.85 ml/min). The bubble formation is recorded by a high speed video camera and detailed characteristics of bubble formation such as the variations of instantaneous contact angles, bubble heights and the radii of contact lines are obtained, which show a weak dependence on the flow rate under the conditions of current work. Using experimentally captured values of the height of bubble and the radius of contact line, the Young-Laplace equation is solved, which is found to be able to predict bubble evolution quite well until the last milliseconds before the detachment. Interestingly, it is found that the trends of the variation of bubble volume expansion rate from the stainless steel needle and the substrate plate are different, however, the rest of bubble characteristics such as radius of contact line, bubble height, contact angle, and radius of curvature of bubble apex follow same trends as the time and bubble volume change for formation of bubble on top of needle and substrate nozzles. A force analysis of bubble formation reveals that the observed variations of contact angles and other characteristics during the bubble growth period are associated with the relative contribution of surface tension, buoyancy and gravitational forces.
Modeling of Blood Flow in the Human Brain
Authors: Hossain Md. Shahadat , Dalal Bhavin , Fischer Ian S. , Singh Pushpendra , Aubry Nadine
Published: March 2011

The non-Newtonian properties of blood, i.e., shear thinning and viscoelasticity, can have a significant influence on the distribution of Cerebral Blood Flow (CBF) in the human brain. The aim of this work is to quantify the role played by the non-Newtonian nature of blood. Under normal conditions, CBF is autoregulated to maintain baseline levels of flow and oxygen to the brain. However, in patients suffering from heart failure (HF), Stroke, or Arteriovenous malformation (AVM), the pressure in afferent vessels varies from the normal range within which the regulatory mechanisms can ensure a constant cerebral flow rate, leading to impaired cerebration in patients. It has been reported that the change in the flow rate is more significant in certain regions of the brain than others, and that this might be relevant to the pathophysiological symptoms exhibited in these patients. We have developed mathematical models of CBF under normal and the above disease conditions that use direct numerical simulations (DNS) for the individual capillaries along with the experimental data in a one-dimensional model to determine the flow rate and the methods for regulating CBF. The model also allows us to determine which regions of the brain would be affected relatively more severely under these conditions.
Modeling of Particles Dispersion on Liquid Surfaces
Authors: Gurupatham Sathishkumar , Dalal Bhavin , Nudurupati Sai , Fischer Ian S. , Singh Pushpendra , Joseph Daniel D.
Published: March 2011

When small particles (e.g., flour, pollen, etc.) come in contact with a liquid surface, they immediately disperse. The dispersion can occur so quickly that it appears explosive, especially for small particles on the surface of mobile liquids like water. This explosive-like dispersion is the consequence of capillary forces pulling particles into the interface causing them to accelerate to a relatively large velocity. The maximum velocity increases with decreasing particle size; for nanometer-sized particles (e.g., viruses and proteins), the velocity on an air-water interface can be as large as 47 m/s. We also show that particles oscillate at a relatively-high frequency about their floating equilibrium before coming to stop under viscous drag. The observed dispersion is a result of strong repulsive hydrodynamic forces that arise because of these oscillations.
On the “Early-Time” Evolution of Variables Relevant to Turbulence Models for the Rayleigh-Taylor Instability
Authors: Rollin Bertrand , Andrews Malcolm J.
Published: March 2011

We present our progress toward setting initial conditions in variable density turbulence models. In particular, we concentrate our efforts on the BHR turbulence model [1] for turbulent Rayleigh-Taylor instability. Our approach is to predict profiles of relevant variables before fully turbulent regime and use them as initial conditions for the turbulence model. We use an idealized model of mixing between two interpenetrating fluids to define the initial profiles for the turbulence model variables. Velocities and volume fractions used in the idealized mixing model are obtained respectively from a set of ordinary differential equations modeling the growth of the Rayleigh-Taylor instability and from an idealization of the density profile in the mixing layer. A comparison between predicted profiles for the turbulence model variables and profiles of the variables obtained from low Atwood number three dimensional simulations show reasonable agreement.
Formation of Sand Ripples Under Turbulent Flow Simulated by LES
Authors: Cui Yan , Wells John C. , Nguyen Y. Quoc
Published: March 2011

To simulate the initial formation of sedimentary bedforms, constrained to be in hydraulically smooth turbulent flows under bedload conditions, a numerical model based on Large Eddy Simulation (LES) in a doubly periodic domain has been developed. The numerical model comprises three parts. Given the instantaneous bed geometry, the bed shear stress distribution is obtained from a Large-Eddy-Simulation (LES) method coupled with an Immersed-Boundary-Method (IBM). Flux is estimated by the van Rijn’s formula [1]. Finally, evolution of the bed surface is described by the Exner equation. “Two-dimensional bed” [2] and “three-dimensional bed” models employ, respectively, transversely averaged bed shear stress and instantaneous local shear stress to estimate the bedload flux. Based on this model, the evolution of an initial sand wave has been successfully computed. Compared to the “two-dimensional” [2] model, the three-dimensional model leads to a slightly slower propagation and a smaller sand wave. The tendency of the sand wave evolution in three-dimensional model is two-dimensional during the simulated interval.
Effect of Air Flow on Dust Particles Resuspension From Common Flooring
Authors: Goldasteh Iman , Ahmadi Goodarz , Ferro Andrea
Published: March 2011

Particle resuspension from flooring in connection with increased indoor air pollution was studied. Earlier efforts hypothesized that during the gait cycle, high speed airflow is generated at the floor level that would lead to particle resuspension. The details of the mechanism of the particle resuspension, however, are not well understood. Earlier models were mainly developed for spherical particle detachment from smooth surfaces, but in reality, dust particles are irregular in shape and have a wide size distribution. The resuspension of dust particles thus depends on their shape and size and the nature of their contact with the surface. In this work, a wind tunnel study of dust particle resuspension from common flooring was performed and the critical air velocities for particle detachment were measured. The main goal of the present experimental work is to understand the main mechanism of dust particle resuspension under real conditions by systematically investigating a range of airflow speeds. The other goal of the study is to provide information on the role of the airflow on dust particle detachment from common floorings.
Sequence of Courses on Particle Transport, Deposition and Removal and Engineering of Nano/Micro-Scale Systems
Authors: Ahmadi Goodarz , Cetinkaya Cetin
Published: March 2011

Small (nano-/micro-scale) particle transport, deposition and removal are of critical importance in many industries including semiconductor manufacturing, imaging, pharmaceutical and food processing. In addition, numerous environmental processes involve particle transport, deposition and removal. In the last decade, significant research progress in the areas of nano- and micro-particle transport, deposition and removal has been made. In this project, a series of courses was developed to make these class of new important research findings available to seniors and graduate students in engineering through developing and offering of specialized curricula at Clarkson University. The project involved integration of particle transport, deposition and removal numerical simulations and experiments in the developed courses. The course materials are mostly made available on the web and some courses have been taught at Clarkson University and Syracuse University campuses simultaneously. Based on the course materials, a series of short courses was also offered at several countries. The first two courses on particle transport, deposition and removal are composed of four modules: (i) fundamental of particle transport, dispersion, deposition and removal, (ii) computational modeling of particle transport, deposition and removal, (iii) experimental study of particle transport, deposition and removal, and (iv) industrial applications of particle transport, deposition and removal. Based on this course development experience, more recently, a new undergraduate course (Nano/Micro-scale Systems Engineering) was developed. The course development and implementation was supported a grant from NSF under the Nanotechnology Undergraduate Education program following an initial grant from Clarkson University. The chief instructional objective of the new course is to familiarize the students to the design, analysis, simulation and implementation/fabrication of nano/micro-scale engineering systems. This nanotechnology course consists of three main components to address a set of its well-defined educational objectives: (i) lectures developed and delivered by a multidisciplinary team at Clarkson University, (ii) instructions on computational design/analysis and simulation tools, and (iii) a hands-on workshop for gaining experience with cleanroom procedures and fabrication facilities. The second component has been developed with help of a software company. The third component is being realized through collaboration with the NNIN supported CNF facility at Cornell University as a hands-on workshop for the Clarkson students. An outline of this ongoing course development activity has been given and main features of the course has been discussed.
Fiber Transport and Deposition in Human Upper Tracheobronchial Airways
Authors: Tian L. , Ahmadi G. , Hopke P. K. , Cheng Y.-S.
Published: March 2011

Transport and deposition of inhaled asbestos fibers has been studied in the past few decades due to its pathological response in living being. Of the earlier study, in vitro and vivo experiments in human and animal subjects were conducted and measurements were made where carcinogenicity of these particles was investigated. In this work, the transport and deposition of elongated ellipsoidal fibers were numerically simulated in a physiological realistic multi-level lung model. Detailed motion of the inhaled fibers and their interaction with the surrounding environment were reproduced by solving the system of coupled nonlinear equations governing the fibers’ translational and rotational motion. This information has never been revealed in past studies. Correlations between the deposition pattern, fiber characteristics, breathing conditions, and airway morphology in human upper tracheobronchial airways were analyzed. The results were compared with experimental measurements, and carcinogenicity of these fibers was discussed.