bluuebunny/crossref_metadata_2025 huggingface dataset:
Demonstration of the Enhanced Mixing and Reaction Ability of an Alternate Pumping Microreactor With Visualization of the Mixing Field and the Reaction Field
Authors: Fujiwara Tamio , Ohue Hiroshi , Urata Takumi
Published: March 2011

In order to enhance the mixing and reaction capabilities of micromixers and microreactors, we had proposed a novel system termed alternate pumping microreactor (APMR) and had demonstrated that the APMR could generate a thin-layered structure under a particular pumping condition. This flow pattern should enhance the abovementioned capabilities. In this paper, we visualized the dilution process of methylene blue solution with water in the APMR and established a method to obtained the concentration field from the captured image according to the relation between the methylene blue concentration and the saturation of the captured color. To assess the reaction field, visualization of the reaction of ferrous sulphate and potassium thiocyanate was adopted. These visualization results suggested that the APMR enhanced the mixing and reacting capabilities and the time and channel length required for the reaction to complete were two order orders of magnitude lesser than those in the case of the ordinary reactor.
Electrostatic and Capillary Effects on the Detachment of Particles With Surface Deformation in Turbulent Flows
Authors: Zhang Xinyu , Ahmadi Goodarz
Published: March 2011

Rolling detachment of micro particles in turbulent flows under the presence of electrostatic and capillary forces was studied. The maximum adhesion resistance model and the effective thermodynamic work of adhesion including the effects of electrostatic and capillary forces were used in the analysis. The JKR and DMT models for elastic interface deformations and the Maugis-Pollock model for the plastic deformation were extended to include the effect of electrostatic and capillary forces. The turbulence burst model was used to evaluate the airflow velocity near the substrate. The critical shear velocities for removal of particles of different sizes were evaluated and the results were compared with those without electrostatic and capillary forces. The relative critical shear velocities as well as the material dependence were also studied. The effect of the direction of the combined Coulomb force was also included. The predictions of the electric detachment fields for particles were compared with the available experimental data and good agreement was observed.
Theoretical Study: Flow Control Mono and Bi-Stable Fluidic Device for Micro-Injection System
Authors: Dennai Brahim , Khelfaoui Rachid , Benyoucef B. , Slimani A. Kader , Asma Abdenbi
Published: March 2011

This paper is focused on the modeling of a micro-injection systems composed of passive amplifier without mechanical part. The micro-system modeling is based on geometrical oscillators form. An asymmetric micro-oscillator design based on a monostable fluidic amplifier is proposed [1, 2]. Several configuration of associate device are simulating to found adequate logical signal form. The characteristic size of the channels is generally about a few hundred of microns.
Fuel Spray Simulation With Collision Jets for Automobile Engines
Authors: Ishii Eiji , Sukegawa Yoshihiro , Yamada Hiroshi
Published: March 2011

Fuel injectors for automobile engines atomize fuel into multi-scale free surfaces: liquid films formed at the fuel-injector outlet, ligaments generated by the liquid-film breakup, and droplets generated from the ligaments within the air/fuel mixture region. We previously developed a fuel spray simulation combining the liquid-film breakup near the injector outlet with the air/fuel mixture. The liquid-film breakup was simulated by a particle method. The fuel-droplet behavior in the air/fuel mixture region was simulated by a discrete droplet model (DDM). In this study, we applied our method to simulate fuel sprays from a fuel injector with collision jets. The simulation results were compared with the measurements—the mean diameter of droplet in spray, D32, was 35 percent larger than measured D32. We also studied the effects of DDM injection conditions on the spray distribution in the air/fuel mixture region—diameter distributions of injected DDM-droplets were given by the liquid-film breakup simulation, or by Nukiyama-Tanazawa’s theory. The diameter distribution of droplets near the injector outlet was found to affect the spray distribution within the air/fuel mixture region, mainly around the leading edge of spray.
Comparative Studies of Turbulence Models Application in Thermal Hydraulic Analysis of Nuclear Reactor Core
Authors: Zeng Heyi , Guo Yun
Published: March 2011

Rod bundles are essential elements of pressurized water nuclear reactors. They consist of tightly packed arrays of rods, which contain the nuclear fuel and are surrounded by flowing liquid coolant. Flow phenomena in the subchannels bounded by adjacent rods are quite complex and exhibit patterns not present in pipe flows. Development of nuclear reactors and of fuel assemblies requires fluid dynamics analysis activities. The detailed prediction of velocity and temperature distributions inside a rod bundle is one of the main objectives of the current research in reactor thermal hydraulics. Computational fluid dynamics (CFD) simulation is of great interest for the design and safety analysis of nuclear reactors since it has recently achieved considerable advancements. In the present studies, numerical simulation were performed on developed turbulent flow through core subchannels with configurations of triangle and square lattice, and impact of different turbulence models built-in software package FLUENT upon simulation results of velocity distribution and hydraulic characteristics in channels with complicated geometry were compared and analyzed. Results show that simulation result greatly depends on turbulence models. Due to the complicated geometric construction, the complicated three-dimensional turbulent flow shows highly anisotropic characteristics. Turbulence models assuming isotropic turbulent viscosity failed to predict secondary flow phenomena during turbulent flow in fuel assembly channel. By solving Reynolds stresses transport equations, more elaborate Reynolds stress model (RSM) can catch secondary flow accurately. The present studies have provided valuable references and guidelines for further investigation on convective heat transfer simulation in complicated geometry and thermalhydrulic analysis of nuclear reactor core.
Transient Numerical Computation of the Temperature of Electronic Devices in Passenger Cars
Authors: Michel Florence , Desmet Bernard
Published: March 2011

In order to ensure a reliable operation of electronic devices in a passenger car, its thermal situation is evaluated in a digital prototype. Of particular interest is to predict the time period, during which the electronic system embedded in the vehicle works within its optimal operating temperature range, in order to compare it with the vehicle specifications. In the present work, iterative coupling simulation strategies and numerical models to predict the temperature of the electronic equipment in a passenger car under time-dependent operating conditions and thermal loads have been developed and validated. The co-simulation strategies are investigated by means of two complex electronic systems embedded in a passenger car. The comparison with experimental results shows that the parallel discrete coupling strategy provides consistent temperature predictions within reasonable computation times in case of coupled problems for which the characteristic time for heat transport by convection is strongly dependent on the simulation time. As for the serial staggered coupling strategy, it is adapted to coupled problems, for which the characteristic time for convection is much smaller than the characteristic time for conduction. To predict the warm-up of an electronic system over several minutes, this strategy provides an efficient model generation and accurate temperature predictions within 1K.
Numerical Simulation of Cavitation Characteristic Around Hydrofoil NACA0015
Authors: Liu Demin , Liu Shuhong , Wu Yulin , Xu Hongyuan
Published: March 2011

The applicability of numerical prediction method for cavitation around hydrofoil NACA0015 was studied in this paper. For the present study, the mixture fluid methods was adopted for mass transfer between phases. For validation of this approach, simulations for the following problems were carried out: (1) leading edge cavitation on a hydrofoil; and (2)Cavitation performance and flow field analysis for a hydrofoil NACA0015. A full discussion of the results is presented below. This paper modified cavitation mass transfer equation based on the Rayleigh-Plesset equation. The pressure difference, surface tension and the turbulence effects were considered in the new mass transfer equation on the basic of the evaporation and condensation mechanics in the micro-kinetic theory. According to the governing equations for mass, momentum, volume conservation, the hydrofoil NACA0015’s cavitation characteristic was calculated by the new model. The cell-central difference finite element method was employed to discretize the governing equations. The pressure coefficient was contrasted with experiment data to validate the model. The calculation data is identical to the experiment data. As the result, it’s shown that this method can be used for the prediction of the behavior of sheet cavitation of the hydrofoil NACA0015.
Four-Way Coupling of Dense Particle Beds of Black Powder in Turbulent Pipe Flows
Authors: Narayanan Chidambaram , Lakehal Djamel
Published: March 2011

The modeling of particle deposition and transport in pipes is one of the most challenging problems in multiphase flow, because the underlying physics is multi-faceted and complex, including turbulence of the carrier phase, particle-turbulence interaction, particle-wall interactions, particle-particle interactions, two-way and four-way couplings, particle agglomeration, deposition and re-suspension. We will discuss these issues and present new routes for the modeling of particle collision stress. Practical examples like black powder deposition and transport in gas pipelines will be presented and discussed. The model employed is based on dense-particle formulation accounting for particle-turbulence interaction, particle-wall interactions, particle-particle interactions via a collision stress. The model solves the governing equations of the fluid phase using a continuum model and those of the particle phase using a Lagrangian model. Inter-particle interactions for dense particle flows with high volume fractions (from 1% to close packing ∼60%) have been accounted for by mapping particle properties to an Eulerian grid and then mapping back computed stress tensors to particle positions. Turbulence within the continuum gas field was simulated using the V-LES (Very Large-Eddy Simulation) and full LES, which provides sufficient flow unsteadiness needed to disperse the particles and move the deposited bed.
CFD Investigation of Air-Water Test Stand for Three-Stream Airblast Reactor Feed Injector
Authors: Strasser Wayne , Brooker Duane , Earley Joshua , Fanning Paul
Published: March 2011

A large-scale parametric air-water test stand (AWTS) study involving more than 40 evaluations was carried out for the purposes of three-stream airblast reactor feed injector optimization; a subset of seven air stream combinations is discussed here. The role of CFD as a supplement to, or a replacement for, air-water testing is of great industrial interest. To this end a set of CFD experiments was carried out to mimic the AWTS study. A compressible geometric reconstruction Volume of Fluid (VOF) method was used to simulate the three-stream interaction. Pressure responses, spray opening characteristics near the feed injector face, and spray distribution were primary measures for both the AWTS and CFD programs. It was found that, over the range of variables studied, there was a partial match between CFD and AWTS results; some measures matched quantitatively, others qualitatively, and some did neither. A self-exciting, pulsatile spray pattern was achieved in CFD and AWTS, and an interesting transition in spray bursting character occurred at moderate inner air flows. Overall, it is shown that the CFD method contained herein can be used to supplement, but not replace, air-water testing for said injector configuration.
Effects of Non-Linearity of the Momentum Conservation Equation During Electrokinetic Transport in Nano and Microchannels
Authors: Bhattacharjee Subir , Quddus Noor Al
Published: March 2011

Electrokinetic transport phenomena, such as electroosmosis, streaming potential, electrophoresis, and sedimentation potential, are central to many micro- and nano-channel flows. During continuum modeling of such phenomena, incorporation of the electrical body force term can make the fluid momentum conservation equation highly non-linear. This non-linearity is often ignored in small-scale electrokinetic flow modeling because of our implicit reliance on the linearity of the Stokes equations for low Reynolds number flows. In this paper, ramifications of this non-linear Stokes equation in electrokinetic flows will be described with examples of our recent studies on pressure driven flows through porous media for electrokinetic power generation, electroosmotic flow of charged entities in nanochannels, and flow of DNA through self-assembled porous media under pulsed electric fields.
Gas Microflows in the Slip Flow Regime: A Review on Heat Transfer
Authors: Colin Ste´phane
Published: March 2011

Accurate modeling of gas microvection is crucial for a lot of MEMS applications (micro-heat exchangers, pressure gauges, fluidic microactuators for active control of aerodynamic flows, mass flow and temperature micro-sensors, micropumps and microsystems for mixing or separation for local gas analysis, mass spectrometers, vacuum and dosing valves…). Gas flows in microsystems are often in the slip flow regime, characterized by a moderate rarefaction with a Knudsen number of the order of 10−2–10−1. In this regime, velocity slip and temperature jump at the walls play a major role in heat transfer. This paper presents a state of the art review on convective heat transfer in microchannels, focusing on rarefaction effects in the slip flow regime. Analytical and numerical models are compared for various microchannel geometries and heat transfer conditions (constant heat flux or constant wall temperature). The validity of simplifying assumptions is detailed and the role played by the kind of velocity slip and temperature jump boundary conditions is shown. The influence of specific effects, such as viscous dissipation, axial conduction and variable fluid properties is also discussed.
Prediction and Measurement of Thermal Transport Across Interfaces Between Isotropic Solids and Graphitic Materials
Authors: Norris Pamela M. , Smoyer Justin L. , Duda John C. , Hopkins Patrick E.
Published: March 2011

Due to the high intrinsic thermal conductivity of carbon allotropes, there have been many attempts to incorporate such structures into existing thermal abatement technologies. In particular, carbon nanotubes (CNTs) and graphitic materials (i.e., graphite and graphene flakes or stacks) have garnered much interest due to the combination of both their thermal and mechanical properties. However, the introduction of these carbon-based nanostructures into thermal abatement technologies greatly increases the number of interfaces per unit length within the resulting composite systems. Consequently, thermal transport in these systems is governed as much by the interfaces between the constituent materials as it is by the materials themselves. This paper reports the behavior of phononic thermal transport across interfaces between isotropic thin films and graphite substrates. Elastic and inelastic diffusive transport models are formulated to aid in the prediction of conductance at a metal-graphite interface. The temperature dependence of the thermal conductance at Au-graphite interfaces is measured via transient thermoreflectance from 78 to 400 K. It is found that different substrate surface preparations prior to thin film deposition have a significant effect on the conductance of the interface between film and substrate.
Analytical Model of Diurnal Temperature for a Radome Enclosed Antenna
Authors: DiCarlo Anthony A.
Published: March 2011

A critical design consideration for the Haystack Ultrawideband Satellite Imaging Radar’s (HUSIR) with respect to its performance at W-band is thermal distortion. This is because thermal distortion affects the surface accuracy of a parabolic reflector. For example, an extremely tight surface tolerance, ∼100 microns root-mean-squared, is required to obtain antenna performance efficiency close to 85 percent. Thermal control is one method for mitigating this distortion. Cost effective thermal control relies on a model that rapidly and accurately predicts the antenna’s temperature. This work develops a simplified analytical model to predict the surface temperature of a metal antenna based on external diurnal temperature variations. The thermal energy balance of the radome/antenna captures the radome enclosed antenna temperature transients. This study also includes a parametric investigation to quantify the sensitivity of the model with respect to convection coefficients. The developed model generates results for four months, (February, April, August, and October). We compare some of these results to experimental measurements.
Water Jet Performance Variation for Intrusion of a Cylinder Central-Body
Authors: Kang Can , Xiao Shengnan , Liu Dong , Zhang Feng
Published: March 2011

Based on Karman vortex street principle, central-body nozzle is expected to arouse cavitation in the discharged jet and then result in strong impact on acted object. To discover the influence of central-body on flow characteristics, under the same jet pressure of 15MPa, comparison between the two free water jet fields produced respectively by a central-body nozzle and a round nozzle was conducted. Phase Doppler particle anemometry (PDPA) was applied to measure velocity distribution, turbulent fluctuation and droplet diameter distribution at different traverse sections. Experimental results show that although the annular jet tends to concentrate soon after the central body, the radial diffusion of the jet discharged from the central-body nozzle is more obvious. For the two jets kinetic energy is well remained along the jet direction and high-velocity zone is wider near the jet axis of the central-body nozzle. For the jet discharged from the central-body nozzle, turbulent fluctuation near the jet axis is relatively weak. As for possible cavitation, the position is right after the central body and the reachable distance of cavitation effect is short, which produces an inevitable restriction on the nozzle’s application. And similar Sauter mean diameter (SMD) distribution profiles are found in the two jet fields especially when distance between nozzle and traverse section gets large. The study here provides quantitative and comparative information for the two nozzles and can be referred to in further study and optimal design of central-body nozzle.
Optimization Design of New-Type Deep Well Pump Based on Latin Square Test and Numerical Simulation
Authors: Shi Wei-dong , Wang Hong-liang , Zhou Ling , Zou Ping-ping , Wang Guo-tao
Published: March 2011

In order to develop high efficiency and high head deep well pump of 150QJ20 type, a L18 (37) orthogonal experiment was performed with seven factors and three values including blades numbers, outlet angle, outlet width, etc.18 impellers were designed. The whole flow field of new-type two-stage deep well pump at the operating point for design was simulated by FLUENT using the standard model, SIMPLEC algorithm, second-order upwind scheme to solve, and analyze the independent of the number of the grid. 18 groups of the efficiency and head in design scheme were obtained. The effects of geometrical parameters on efficiency, head were researched using Latin square test method. The primary and secondary factors of the design parameters were acquired by way of variance analysis. According to the test result, an optimum program to further design was put forward. After manufactured and tested, the final optimal design model pump flow at rated efficiency of 66.59% point, single-stage head of 10.9m, match the motor as 5.5 kW, compared to the Chinese national standards (GB/T 2816-2002), which the rated flow point of the efficiency of 64% and matching motor 7.5 kW, the efficiency and head were significantly improved. The productions show good energy saving and material saving characters and can replace traditional pumps for deep well in the future, the comprehensive technical indicators achieve international advanced levels. The results would be instructive to the design of new-type deep well pump with the impeller head maximum approach.
Flow Visualization and PIV Measurements of Flow Around a Sport Utility Vehicle Model
Authors: Lamy Alban , Hamel Amandine , Vanderwel Christina , Tavoularis Stavros , Kourta Azeddine
Published: March 2011

The instantaneous flow structure around a 1:18 scaled model of a square-back sport utility vehicle (Hummer H2) was documented in a low-speed water tunnel. The study comprises both flows with the model fixed on a flat plate and flows with the model’s wheels rolling on an endless belt that moved with the speed of the free stream, thus simulating ground effects. The flow structure was investigated using flow visualization by dye injection as well as particle image velocimetry (PIV) for several Reynolds numbers in the range of 7000 to 27700. The flow along the roof, the sidewalls, and the underbody was observed to separate at the rear edges of the body, creating a recirculation zone at the rear of the vehicle, which is associated with pressure loss and a major contribution to aerodynamic drag. In the vertical plane of symmetry, this recirculation zone appears as two counter-rotating vortices. With a fixed ground, the lower vortex was less energetic than the upper vortex because the boundary layer that developed along the ground upstream of the model reduced the momentum of the flow below the vehicle. This boundary layer was also observed to separate from the ground behind the vehicle, creating a third vortex located further downstream along the ground. This boundary layer separation forced the bottom vortex to remain attached to the base of the vehicle, whereas the upper vortex was advected in the wake. The dimensionless frequency (Strouhal number) of the vortex shedding process from the roof was found to be in the range of 0.1 to 0.9. With a moving ground, the upper vortex behaved similarly to that in the fixed ground configuration; however, in the absence of the boundary layer along the ground, the lower vortex was typically stronger and its location showed some variability. In both configurations, the Reynolds number had little influence on the wake topology, mostly increasing the turbulence intensity without modifying the main flow pattern.
Cavitation Performance Study Based on Numerical Simulation of the Magnetic Driving Pump
Authors: Kong Fanyu , Shen Xiaokai , Zhang Xufeng , Xue Kuanrong , Zhou Shuiqing , Wang Wengti
Published: March 2011

A new magnetic driving pump with low-NPSHR had been developed to ensure leakage-free for transporting fluid. In hydraulic design, several common measures, according to the equation of cavitation, were applied to lower down the NPSHR of the pump. Moreover, a variable-pitch inducer whose pitch increases gradually was installed at the inlet of impeller. Cavitation performance of the magnetic driving pump and the reasons why the NPSHR was reduced by installing a variable-pitch inducer were analyzed according to the simulation predicted flow field at the pump inlet and inducer. The test of cavitation performance showed that the magnetic driving pump had the excellent cavitation performance, and met the design requirements in flow, head and vibration. The magnetic driving pump presented the reliability after a long period of operation in a petrochemical corporation. Therefore, magnetic driving pumps with low-NPSHR would have a great future in petrochemical, shipping and other important fields.
Simulation of Two-Phase Flow Using Conservative Level-Set Method Without Re-Initialization Process
Authors: El Otmani Rabie , Boutaous M’hamed , Benhadid Hamda
Published: March 2011

Multiphase flows are generated in several industrial domains. The numerical simulation of such flows need to have an exact tracking of the different phase interfaces. The level set method is one of the simplest methods used to study the moving front of the flow. But it is known that this method generates a non mass conservation, and do not respect the uniformity of the signed distance function. Several corrections are usually proposed to solve these problems when using the Level set method. In this paper, a novel two steps correction method is proposed in order to guarantee the flow mass conservation and the exact shape of the flow front. The first step concerns the correction of the mass loss. It consists to add in the transport equation, a penalty or constraint term, built to force the velocity field to satisfy the mass balance or to preserve the conservative property. This term is multiplied to an adjustable penalty factor (β). The second step consists to impose that the isocontours of the level set function (φ) always respect the same distance. With this way, the costly reinitialization procedure is eliminated. The performance of the method is demonstrated and validated using several cases involving two-phase flow. The numerical experiments show that the accuracy and performances of our method is drastically improved compared to other methods. The approach will then applied to track an air-liquid interface in a case of an air bubble moving in a constant volume of liquid. In this case, the classical level set method reveals to be not conservative. A solution is then proposed in order to introduce a correction. To do, Navier-Stokes, continuity and energy equations are coupled to describe the flow and its thermal behavior. A finite element method is used to solve the equations. The solution is also verified by solving the dam-break problem, and bubble rising in water. Good agreements with referenced solutions are demonstrated for all tow investigated problems.
Measurement of Interfacial Area Production and Permeability Within Porous Media
Authors: Crandall Dustin , Ahmadi Goodarz , Smith Duane
Published: March 2011

An understanding of the pore-level interactions that affect multi-phase flow in porous media is important in many subsurface engineering applications, including enhanced oil recovery, remediation of dense non-aqueous liquid contaminated sites, and geologic CO2 sequestration. Standard models of two-phase flow in porous media have been shown to have several shortcomings, which might partially be overcome using a recently developed model based on thermodynamic principles that includes interfacial area as an additional parameter. A few static experimental studies have been previously performed, which allowed the determination of static parameters of the model, but no information exists concerning the interfacial area dynamic parameters. A new experimental porous flow cell that was constructed using stereolithography for two-phase gas-liquid flow studies was used in conjunction with an in-house analysis code to provide information on dynamic evolution of both fluid phases and gas-liquid interfaces. In this paper, we give a brief introduction to the new generalized model of two-phase flow model and describe how the stereolithography flow cell experimental setup was used to obtain the dynamic parameters for the interfacial area numerical model. In particular, the methods used to determine the interfacial area permeability and production terms are shown.
Bed Height Effects on Fluidized Bed Hydrodynamics
Authors: Escudero David R. , Heindel Theodore J.
Published: March 2011

Characterizing the hydrodynamics of a fluidized bed is of vital importance to understand the behavior of these multiphase flow systems. Minimum fluidization velocity and gas holdup are two important factors used to understand the hydrodynamics of a fluidized bed. Experimental studies on the effects of bed height on the minimum fluidization velocity and gas holdup were carried out using a 10.2 cm diameter cylindrical fluidized bed filled with 500–600 μm glass beads. In this study, four different bed height-to-diameter ratios were used: H/D = 0.5, 1, 1.5, and 2. Minimum fluidization velocity was determined for each H/D ratio using pressure drop measurements. Local time-average gas holdup was determined using non-invasive X-ray computed tomography imaging. Results show that minimum fluidization velocity is not affected by the change in bed height, while local gas holdup does appear to be affected by the change in bed height.
Experimental Characterization of Hydraulic Solid Particle Transportation in Horizontal Pipelines Using PIV
Authors: Liang Wang , Goharzadeh Afshin , Rodgers Peter
Published: March 2011

Solid particle transport in pipelines by fluids is encountered in a wide variety of industry processes, such as oil production, mining and chemical industry. In contrast to the intensive research effort that has investigated transport modes for suspended solid particles in pipeline flow, limited studies have been published on solid transportation mechanism generated from an initial stationary particle bed. Consequently the underlying mechanisms responsible for bed-load and saltation transport phenomena have not been extensively assessed, particularly for low velocity hydraulic conveying pipe flows. This paper presents an experimental investigation into sand particle transportation from a stationary horizontal particle bed under hydraulic conveying flow for bed-load and saltation transport phenomena. Experiments were undertaken in a laboratory environment using a 14 m long transparent plexiglas loop of 24 mm internal diameter to permit optical access. High speed digital photography was employed to study the morphologic characteristics of sand bed transportation, with Particle Image Velocimetry (PIV) used to characterize the near surface flow structure at the fluid-solid interface. Experimental results characterize the influence of water flow on sand dune formation for one bed thickness and particle size. Flow field velocity distributions revealed the presence of vortex structures that strongly influence the dynamics of sand dunes. The results presented on the combined study of flow field and bed formation interaction provide a fundamental insight into the physics of fluid-solid interaction in a closed conduit that can also serve as benchmark data for computational fluid dynamics based predictions.
Analytical Design of Helically Coiled Heat Exchangers Used for Transient Heat Transfer Applications
Authors: Salimpour Mohammad Reza , Bahiraee Farid , Akbari Soheil
Published: March 2011

In the present study, a special application of a helical heat exchanger, i.e. its usage in the cooling process of a reservoir’s hot fluid at a specified finite time was considered. An analytical approach was developed to anticipate the required heat transfer area of the heat exchanger. Also, the effects of the various flow and geometry parameters of the heat exchanger like the mass and initial and target temperatures of the reservoir fluid, mass flow rate and inlet temperature of the tube-side fluid, the diameter, curvature and pitch of the coiled tube, etc, and also the finite time allocated to heat transfer were investigated. Next, the effects of different parameters upon the required length were examined in appropriate curves. It was generally observed that transition from laminar to turbulent regime, enhanced heat transfer coefficient and consequently, reduced the required length of the heat exchanger.
Transient Numerical Computation of the Temperature of Electronic Devices in Passenger Cars: Flow Simulation in Electronics Cavities
Authors: Michel Florence , Desmet Bernard
Published: March 2011

To compute the temperature of an electronic system submitted to time-dependent thermal loads, the problem of multi-scale coupled heat transfer modes is solved by means of co-simulation strategies. These coupling strategies use adapted codes for the prediction of each transfer mode, e.g. a CFD code for the computation of convection and a FE code for conduction. In this paper, numerical models to solve the flow in typical electronic enclosures are investigated, in particular regarding mesh requirements and turbulence modeling. First, the accuracy of a steady-state approach for the computation of natural convection in a cavity heated from below is examined for a large range of Rayleigh number covering time-dependent convection. Then, a steady-state method for fan flow simulation is presented and validated in comparison with the fan performance curve measured in a test-rig. Finally, different numerical models for flow computation through thin grills of an electronic system are discussed regarding the fan mass flow rate and the establishing pressure distribution.
Computational Study of Aerial Sprays Used for Forest Protection
Authors: Ryan Sydney D. , Gerber Andrew G. , Holloway Gorden A. L. , Bagherpour Ali
Published: March 2011

The efficacy of pesticide sprays is strongly dependent on the accuracy of the droplet size spectrum. Over estimates of droplet size may result in excessive drift or ineffective doses, while under estimates of droplet size result in excessive releases. This situation is not only bad for the environment; it incurs large operating costs (spray usually accounts for 30% of total cost). This paper describes the study of droplet sprays commonly used in the agriculture and forestry management. It combines experimental wind tunnel testing and Computational Fluid Dynamic (CFD) methods to develop a fundamental understanding of droplet generation and dispersion in the wake of the atomizer spray system. The results will assist designers of spray technology and applicators in delivering pesticide to its target. The CFD models that are developed and calibrated will further allow the wind tunnel data to be generalized; thus, allowing less wind tunnel testing and eventually direct simulation of droplet dispersion in aircraft wakes. The CFD models are developed for the poly-dispersed sprays released from a Micronair AU4000 atomizer (a standard atomizer used for forest protection) at an airspeed of 67 m/s. Simulations are performed using a Lagrangian (droplet phase) - Eulerian (fluid phase) procedure and include droplet drag/body forces and turbulent dispersion of droplets. The Base-line Reynolds Stress Model (BSL RSM) turbulence model is used to compute turbulence levels in the air phase. The CFD simulations include the sprayer and a large portion of the wind tunnel geometry in order to facilitate in validation. The computational results are compared to full scale experimental measurements of pressure, gas phase velocity, droplet velocity, and droplet size spectra measured using Phase Doppler Interferometry (PDI) and Hotwire Anemometry. Measurements are available along radial lines at 0.5, 1, 2 and 4 m downstream of the atomizer.
Advances in Design Methods and Characteristics of Internal Flow for Centrifugal Pumps
Authors: Yuan Shouqi , Yuan Jianping , Liu Houlin , Tang Yue , Zhang Jinfeng , Pei Ji
Published: March 2011

Centrifugal pump is widely used in various fields of the national economy. Pumps, of which 70% are centrifugal pumps, consume 20.9% of the total electricity generation nationwide in China in 2009, according to the statistics. In this paper, the research advances in design methods and characteristics of internal flow fields for centrifugal pumps, carried out by the Research Center of Fluid Machinery Engineering and Technology of Jiangsu University, is introduced. First of all, the Greater Flow Design method, Non-Overload Design method and Splitter Blade Offset Design method are fully discussed through systematically studies. In addition, three methods of performance prediction for centrifugal pumps are adopted, and a CAD/CFD software for hydraulic design and analysis is initially developed. Secondly, to deepen the understanding of characteristics of internal flow in centrifugal pumps, the numerical simulation and PIV measurement investigation have been done. Then the unsteady flow induced vibration and noise are studied considering fluid-structure interaction and fluid-sound interaction. The control of the unsteady flow in centrifugal pumps is also attempted to optimize the design method for centrifugal pumps. In addition, the pressure pulsation and vibration behaviors under both cavitation and non-cavitation conditions are obtained and analyzed. Finally, some detecting methods and criterion for cavitation incipiency and development are put forward.
Theoretical and Experimental Study on Device Characteristics of Sprinkler Irrigation System
Authors: Zhu Xingye , Yuan Shouqi , Liu Jianrui , Wang Xinkun , Cai Bin
Published: March 2011

The resistance loss of sprinkler irrigation system is an important parameter, it has significance and practical value for studying its device characteristics. In this study, according to the selected materials and setting modes, both the pressure drop along the pipe and the local resistance loss were calculated out. The theoretical device characteristics of one sprinkler irrigation system was analyzed. A calculating schema has been carried out in order to apply the method to any sprinkling system. Experimental study was carried out for this system. Water distribution maps for the sprinklers were drawn using Matrix Laboratory (MATLAB). The hydraulic characteristics were as follow, 7.2, 3.0, 10.0 mm/h was the average, minimum, and maximum irrigated intensity, respectively. It supplied theoretical foundation for the reasonable application of sprinkler irrigation system for the future.
Design of an Experimental Setup to Study Mass Transport in Micro-Nano Capillaries and Porous Media
Authors: Pant Lalit M. , Secanell Marc , Mitra Sushanta K.
Published: March 2011

Study of gas diffusion is critical in understanding the process of mass transfer in porous media, which is an integral part of polymer electrolyte membrane fuel cells (PEMFCs). An experimental method is presented to study the mass transfer processes in micro-nano capillaries, which is further extended to study the transport in the porous media of fuel cells. A diffusion bridge setup, similar to the one presented by Remick and Geankoplis [1] has been used. The experimental setup facilitates the study of binary and multicomponent mixture transport through micro-nano capillaries and porous media. The setup can perform studies for two cases viz., pure diffusion and convection-diffusion. Using pressure controls in both channels, the pressure gradient across the capillaries is varied to study the convection diffusion process in detail. The results obtained from the study will be used to review various models of mass transport available in literature.
Reentrant Motion in Cloud Cavitation due to Cloud Collapse and Pressure Wave Propagation
Authors: Sato Keiichi , Wada Youhei , Noto Yoshitaka , Sugimoto Yasuhiro
Published: March 2011

It is well known that reentrant jet motion in periodic cloud cavitation means upward flow from the cavity closure area of cloud cavitation. However the mechanism of reentrant motion seems to remain unsolved clearly. In the present study some experiments were conducted about the mechanism of reentrant motion in a fixed type cavity for a convergent-divergent nozzle. High speed video observation and image analysis based on the frame difference method were made about unsteady cloud cavitation with a periodic structure of cavitation cloud shedding. As a result, the main points are experimentally found as follows; 1) a typical pattern of reentrant motions can be caused by the pressure wave propagation from the collapse of cavitation cloud shed downstream and 2) the frame difference method is very useful in an image analysis for high speed video observation of cavitating flow because the trajectory of pressure waves can be clearly visualized by the method.
The Dynamic Behavior of an Adaptive Liquid Microlens Driven by a Ferrofluidic Transducer
Authors: Xiao Wenjia , Hardt Steffen
Published: March 2011

Ferrofluids are superparamagnetic suspensions of nanoparticles that can be used as transducers in microfluidic systems, among others. In corresponding setups a microscopic enclosure such as a microchannel is filled with a ferrofluid that is acted on by an external magnetic field. The induced motion of the ferrofluid is utilized to pump or manipulate minute amounts of liquids. Here the dynamic behavior of an adaptive liquid microlens driven by a ferrofluidic transducer is studied. Adaptive microlenses based on that principle promise a number of advantages over existing concepts, such as an increased tuning range of the focal length. It is shown that the delay time of the deformation of the lens surface to the displacement of the magnet producing the external field increases with increasing magnet speed. Dynamic leakage of the lens liquid around the ferrofluid plug, on the other hand, only occurs when the magnet speed exceeds a threshold value and further increases from that point onwards. When the viscosity of the lens liquid increases, both the delay time and the dynamic leakage increase.
Mixing Considerations in Stirred Tank Bioreactors When Using Fluid Property Altering Microorganisms
Authors: Kadic Enes , Heindel Theodore J.
Published: March 2011

Stirred tank reactors are one of the standard reactors in the chemical industry and have been widely implemented for biological applications. They are used with viscous liquids, slurries, very low gas flow rates, and large liquid volumes. Stirred tank bioreactors are popular because a well-mixed state, required or preferred for numerous biological processes, is usually achieved in such situations; however, many production processes using microorganisms tend to experience fluid property alterations, which significantly impact mixing, operational parameters, and process results. The most troubling issues occur when a fluid gradually undergoes a viscosity change and/or slowly exhibits non-Newtonian behavior due to microorganism growth since these will alter the flow conditions and possibly limit the conversion rate or production scale. This paper provides an overview of the relevant mixing issues in stirred tank bioreactors when using a range of fluid viscosities, surface tensions, and/or non-Newtonian fluids.
A Fluid Dynamics Study of a Modified Low-Reynolds-Number Flapping Motion
Authors: Amiralaei M. R. , Alighanbari H. , Hashemi S. M.
Published: March 2011

The objective of the present study is to investigate the low Reynolds number (LRN) fluid dynamics of an elliptic airfoil performing a novel figure-eight-like motion. To this mean, the influence of phase angle between the pitching and translational (heaving and lagging) motions and the amplitude of translational motions on the fluid flow is simulated. Navier-Stokes (NS) equations with Finite Volume Method (FVM) are used and the instantaneous force coefficients and the fluid dynamics performance, as well as the corresponding vortical structures are analyzed. Both the phase angle and the amplitudes of horizontal and vertical motions are of great importance to the fluid dynamic characteristics of the model as they are shown to change the peaks of the fluid forces, fluid dynamic performance, and the vortical patterns around the model.
Effect of Surface Roughness on the Pressure Drop of Liquid Flow in Micro-Channels
Authors: Zhou Guobing , Yao Shi-Chune
Published: March 2011

Experimental results in the literature of the surface roughness effect on pressure drop of liquid flow in mini and micro channels were examined. Also, three prominent theories, which are the constricted flow model, the constricted model considering roughness distribution, and the roughness viscosity model are reviewed based upon this broad data base. It is found that all the normalized data of fRe can be predicted, within an error of about ±15%, by the classical pressure drop theory with the channel dimension using the constricted flow model. On the other hand, it appears that the viscosity model is difficult to use generally and the roughness distribution information is frequently hard to obtain for natural rough-surfaces. However, the data, which supports these two theories, can also be predicted well by the constricted flow method at a similar accuracy. It is possible that the viscosity model and the constricted model with roughness distribution can be further developed to become easier to use, for the time being the simple constricted flow model could be a general and reliable method for mini and micro channel pressure drop predictions.
Heat Transfer Limitations of Gas-Liquid Exothermic Reactions in Microchannels
Authors: Kockmann Norbert , Gottsponer Michael
Published: March 2011

Chemical reactions in gas-liquid systems are often occurring and embrace many issues, especially the contacting of the gas and liquid stream and generation of gas bubbles. Continuous mixing and generation of a large interface between the phases is very important for maintaining and intensifying a chemical reaction between the two phases. The generated heat from the chemical reaction has to be removed very quickly from the flowing stream, which is also a challenging task. Recent applications of microreactors at Lonza Ltd. are described with gas-liquid mass transfer and highly exothermic chemical reactions. The proper description and understanding of convective flow, heat transfer and reaction kinetics are essential for the successful application of microstructured devices.
Application of a Zonal K-ε Model on Simulation of Turbulent Mixed Convection
Authors: Shahraeeni Mehdi , Raisee Mehrdad
Published: March 2011

Fluid flow and heat transfer in a vertical tube under constant heat flux have been studied and effect of buoyancy force on the heat transfer coefficient is investigated. The finite volume method is used to study turbulent flow in both upward and downward directions. For the turbulence modeling, a zonal k-e model is employed and the numerical results are compared with available experimental data. The results of the simulation show that for the downward flow, heat transfer is enhanced and for strong buoyancy force, flow reversal is observed. In contrast, for the heated upward flow, heat transfer can be either impaired or enhanced by the buoyancy force depending on its strength. Partial laminarization is caused by the buoyancy in the case of modest buoyancy force. For the condition of stronger buoyancy force, a sudden decrease in the fully-developed Nusselt number is evident in the experimental data and well predicted by the numerical solution. In general, the quantitative agreement between the numerical results and the experimental data is satisfactory.