bluuebunny/crossref_metadata_2025 huggingface dataset:
Theoretical Study of a Flexible Wiretype Joule Thomson Micro-Refrigerator for Use in Cryosurgery
Authors: Widyaparaga Adhika , Kuwamoto Masashi , Sakoda Naoya , Kohno Masamichi , Takata Yasuyuki
Published: March 2011

We have developed a model capable of predicting the performance characteristics of a wiretype Joule-Thomson microcooler intended for use within a cryosurgical probe. Our objective was to be able to predict evaporator temperature, temperature distribution and cooling power using only inlet gas properties as input variables. To achieve this, the model incorporated changing gas properties due to heat transfer within the heat exchanger and isenthalpic expansion within the capillary. In consideration of inefficiencies, heat in-leak from free convection and radiation was also considered and the use of a 2D axisymmetric finite difference code allowed simulation of axial conduction. Two types of microcoolers differing in inner tube material, poly-ether-ether-ketone (PEEK) and stainless steel, were tested and simulated. CO2 was used as the coolant gas in the calculations and experimental trials for inlet pressures from 0.5 MPa to 2.0 MPa. Heat load trials of up to 550 mW along with unloaded trials were conducted. Comparisons to experiments show that the model was successfully able to obtain a good degree of accuracy. For the all PEEK microcooler in a vacuum using 2.0 MPa inlet pressure, the calculations predicted a temperature drop of 57 K and mass flow rate of 19.5 mg/s compared to measured values of 63 K and 19.4 mg/s therefore showing that conventional macroscale correlations can hold well for turbulent microscale flow and heat transfer as long as the validity of the assumptions is verified.
Creating Small Gas Bubbles in Flowing Mercury Using Turbulence at an Orifice
Authors: Wendel Mark , Abdou Ashraf , Paquit Vincent , Felde David , Riemer Bernard
Published: March 2011

Pressure waves created in liquid mercury pulsed spallation targets have been shown to create cavitation damage to the target container. One way to mitigate such damage would be to absorb the pressure pulse energy into a dispersed population of small bubbles, however, creating such a population in mercury is difficult due to the high surface tension and particularly the non-wetting behavior of mercury on gas-injection hardware. If the larger injected gas bubbles can be broken down into small bubbles after they are introduced to the flow, then the material interface problem is avoided. Research at the Oak Ridge National Labarotory is underway to develop a technique that has shown potential to provide an adequate population of small-enough bubbles to a flowing spallation target. This technique involves gas injection at an orifice of a geometry that is optimized to the turbulence intensity and pressure distribution of the flow, while avoiding coalescence of gas at injection sites. The most successful geometry thus far can be described as a square-toothed orifice having a 2.5 bar pressure drop in the mercury flow of 8 L/s for one of the target inlet legs. High-speed video and high-resolution photography have been used to quantify the bubble population on the surface of the mercury downstream of the gas injection site. Also, computational fluid dynamics has been used to optimize the dimensions of the toothed orifice based on a RANS computed mean flow including turbulent energies such that the turbulent dissipation and pressure field are best suited for turbulent break-up of the gas bubbles.
Numerical Investigation and Geometric Parameterization of Lamination Inlet of Passive Micromixer
Authors: Fan Yanfeng , Hassan Ibrahim
Published: March 2011

A lamination inlet is proposed and optimized in this paper. The perpendicular incoming fluids are applied instead of parallel type. The total mixing length is fixed at 3.2 mm and the depth of channel is fixed at 0.1 mm. The tested Reynolds number is calculated at the entrance of downstream straight channel. The tested Reynolds numbers range from 5 to 200. The perpendicular incoming type enhances the mass-convection and enlarges the interface area. Two parameters, the radius of holes (R) and the distance between two holes (D1), are selected to achieve the optimization. Numerical simulation is used to estimate the mixing performance and flow characteristics. The results show that the vortices are generated in the microchannel. The interface becomes irregular. In order to evaluate the mixing improvement, the parallel lamination is also simulated. The comparison shows that the perpendicular inlet type has better mixing efficiency than the parallel lamination type. This inlet type could be connected with certain mixing element to achieve the applications in biochemistry.
Diffusional Mass Transfer at the Surface of Small Gas Bubbles
Authors: Jeskulke Jan-Peter , Peters Franz
Published: March 2011

A method apt to observe small levitated bubbles in the sub-mm range in liquid is described. The method combines a rotary chamber with a Mie scattering method. The key result of the measurements with this method is the rate at which gas diffuses from the bubble into the liquid. A remarkable result is found for five different gases in water. It turns out that the mass flux density is independent of the radius. This suggests that convective mass transport is not the controlling mechanism.
Mitigating Blockage Effects on Flow Over a Circular Cylinder in an Adaptive-Wall Wind Tunnel
Authors: Bishop Michael , Yarusevych Serhiy
Published: March 2011

The effect of wall streamlining on flow development over a circular cylinder was investigated experimentally in an adaptive-wall wind tunnel. Experiments were carried out for a Reynolds number of 57,000 and three blockage ratios of 5%, 8%, and 17%. Three test section wall configurations were investigated, namely, geometrically straight walls (GSW), aerodynamically straight walls (ASW), and streamlined walls (SLW). The results show that solid blockage effects are clearly evident in cylinder surface pressure distributions for the GSW and ASW configurations, manifested by an increased peak suction and base suction. Upon streamlining the walls, pressure distributions for each blockage ratio investigated closely match distributions expected for low blockage ratios. Wake blockage limits wake growth in the GSW configuration at 7.75 and 15 diameters downstream of the cylinder for blockages of 17% and 8%, respectively. This adverse effect can be rectified by streamlining the walls, with the resulting wake width development matching that expected for low blockage ratios. Wake vortex shedding frequency and shear layer instability frequency increase in the GSW and ASW configurations with increasing blockage ratio. The observed invariance of the near wake width with wall configuration suggests that the frequency increase is caused by the increased velocity due to solid blockage effects. For all the blockage ratios investigated, this increase is rectified in the SLW configuration, with the resulting Strouhal numbers of about 0.19 matching that expected for low blockage ratios at the corresponding Reynolds number. Blockage effects on the shear layer instability frequency are also successfully mitigated by streamlining the walls.
On the Heat Transfer Characteristics of Highly Compact Heat Sinks
Authors: Wang Chi-Chuan
Published: March 2011

This study conducts an experimental study concerning the airside performance of highly compact heat sinks under cross flow condition. The test fin patterns can be classified into four categories, namely the base plain fin heat sink (Type I), interrupted fin geometry (Type II), dense vortex generator (Type III), loose vortex generator (Type IV) and their combinations. It is found that the heat transfer performance is strongly related to the arrangement of enhancements. The interrupted and dense vortex generator configurations normally contribute more pressure drop penalty than improvements of heat transfer. This deterioration becomes especially evident at a lower frontal velocity. The oblique VG with cannelure structure shows an appreciable lower pressure drop than that of plain fin geometry. In the meantime, the presence of interrupted surface may also jeopardize heat conduction path due to constriction. The results indicate that the vortex generators operated at a higher frontal velocity is more beneficial than that of plain fin geometry. In summary of the test results, it is therefore concluded that augmentation via various fin patterns like interrupted or vortex generator is quite effective only at developing region. However, the conventional enhanced fin patterns lose its superiority at the fully developed region. To tackle this problem, some techniques employing swing flow or unstable flow field accompanied with the asymmetric design, shows potential to resolve this problem.
Numerical Simulation and Comparsion of Pump and Pump as Turbine
Authors: Yang Sun-sheng , Kong Fan-yu , Shao Fei , Wang Ting , Shen Xiao-kai
Published: March 2011

A numerical comparison of a conventional pump in pump and pump as turbine (PAT) mode is presented. The numerical simulation is carried out with ANSYS CFX software by means of steady state analysis. Through CFD analysis, the relationship of two modes’ performance characteristics, volumetric efficiency, axial thrust and flow field distribution and etc. were acquired. The possible direction for optimization of PAT is clear according to the PAT flow field distribution.
Numerical Study on Droplet Formation in a Microchannel T-Junction Using the VOF Method
Authors: Zadeh Shobeir Aliasghar , Radespiel Rolf
Published: March 2011

The liquid-liquid two-phase flow in a T-junction was numerically investigated applying the VOF method and is compared with experimental results. The geometry was generated and meshed using the software Gridgen, and the corresponding equations for the CFD analysis were solved by using the commercial software Fluent (Fluent 12). The generated mesh consists of block-structured grids with hexahedral elements. Water-Glycerol solution (to-be-dispersed phase) and silicone oil (continuous phase) at room conditions are considered as fluids for this work. The effect of various parameters such as flow rate of the phases, width of the channel, viscosity and surface tension on the droplet formation are investigated and compared with available experimental results [1]. The breakup mechanism of droplets in various capillary-number regimes are explained. The numerical results of the length of the generated droplets as a function of the capillary number (varying the flow rate of the continuous phase) are in good agreement with the experimental values, which were measured using the same geometrical and physical properties. Further studies indicate that at a constant flow rate of the continuous phase, the droplet length rises strongly if the flow rate of the disperse phase increases, whereas the relative effects of the viscosity of the continuous phase, and the surface tension between phases on the length of droplets are moderate.
Simulation of Polymer Crystallization: Role of the Visco-Elasticity
Authors: Boutaous M’hamed , Zinet Matthieu , El Otmani Rabie , Bourgin Patrick
Published: March 2011

In polymer processing, it is established that the flow causes the polymer chains to stretch and store the energy, by changing their quiescent state free energy. Koscher et al. [1] presented in 2002 an experimental work concerning the flow induced crystallization. They made the assumption that the polymer melt elasticity, quantified by the first normal stress difference, is the driving force of flow-induced extra nucleation. In their work, a constant shear stress is considered, and the first normal stress difference agrees with the use of the trace of the stress tensor. The stored energy due to the flow “Δ Ge” is commonly called elastic free energy and associated to the change in conformational tensor due to flow. By extending the Marrucci theory [2], several studies link this Δ Ge to the trace of the deviatoric stress tensor (first invariant). In this paper, a numerical model able to simulate polymer crystallization is developed. It is based on the assumption that flow induced extra nucleation is linked to the trace of the deviatoric stress tensor. Thus a viscoelastic constitutive equation, the multimode Upper Convected Maxwell (UCM) model, is used to express the viscoelastic extra-stress tensor τVE, and a damping function is introduced in order to take into account the nonlinear viscoelasticity of the material. In Koscher’s work [1], the integral formulation of the Upper Convected Maxwell (UCM) model is used too, but without any damping function, i.e. they assume that the polymer behaves as linear viscoelastic. As an application, a 2D isothermal flow configuration between two plates is simulated. A comparison between the proposed model and the Koscher’s one is then performed, and interesting resultes are pesented: without introducing a damping function, the two models give similar results in the same configurations, but the introduction of a damping function leads to important discrepancies between the two models, seeming that the assumption of a linear viscoelastic behavior is not realistic when the fluid strain and/or stresses are greater than a given values.
Influence of Pressure Fluctuation on Reflux Valve in a Self-Priming Pump With Outer Recirculation
Authors: Li Hong , Shen Zhenhua , Liu Jianrui , Wang Chao
Published: March 2011

The pressure fluctuation caused by impeller-volute interaction is one of the factors which affect the stability of self-priming pump with outer recirculation. Based on the RNG k–ε turbulence model, three-dimensional unsteady turbulence flow in a self-priming pump was simulated in this paper. Pressure fluctuations were obtained at 26 monitor points distributed at eight sections of the volute and on the reflux valve, and the influence on the valve was analyzed. The CFD results show that the main frequency of monitor points is blade passing frequency, and the pressure difference between maximum and average is minimal at the fifth section, which is 1.3%∼2.4%. Using pressure sensors and LabVIEW system, the pressures at third, fifth and seventh sections were tested. The experimental results show that pressure fluctuation layouts are similar as those from CFD, and the pressure difference at the fifth section is 4%, also the minimum. The position also is found with minimal influence on reflux valve. Reflux hole should be placed at 200° ∼ 220° from the tongue along the direction of the impeller rotation. Further, according to the CFD results, the Finite Element Analysis (FEA) of the reflux valve was carried out. FEA shows that the valve can close the reflux hole completely after self-priming process, which gets a good hydraulic performance when the pump runs normally.
Optimal Growth and Transition to Turbulence in Magnetohydrodynamic Duct Flow
Authors: Krasnov Dmitry , Zikanov Oleg , Rossi Maurice , Boeck Thomas
Published: March 2011

We consider the flow of an electrically conducting fluid in a duct in the presence of a constant magnetic field perpendicular to the flow. The technologically relevant approximation of small magnetic Reynolds number is adopted. The focus of investigation is on the nonlinear mechanism of transition consisting of transient growth and subsequent breakdown of finite amplitude perturbations. Numerical analysis demonstrates that the strongest growth is experienced by perturbations localized in the sidewall boundary layers parallel to the imposed magnetic field. This result and the direct numerical simulations of the transition process indicate that the commonly accepted picture of the transition in MHD duct based on the numerical and theoretical analysis of the flow in the Hartmann channel is misleading. The flow may become turbulent within the sidewall layers long before the Hartmann layers on the walls perpendicular to the magnetic field are able to sustain nonlinear transition.
Experimental Characterization of Air-Entrainment in a Plunging Water Jet System Using Particle Image Velocimetry (PIV)
Authors: Qu Xiaoliang , Goharzadeh Afshin , Khezzar Lyes , Molki Arman
Published: March 2011

This paper presents a detailed experimental study of a plunging jet on a free liquid surface. An experimental characterization facility is designed and constructed for generating a vertical round water jet impinging on a free surface of a pool. The experimental analysis focuses on the jet penetration depth, its relation to impact velocity Vj and free jet length Lj. Present results are compared with previous studies. The flowmap for four different regimes, in terms of impact jet velocity is obtained. The details of the two-dimensional velocity field below the pool liquid free surface under a no-entrainment regime, is obtained using Particle Image Velocimetry (PIV) and reveals the entrainment behavior of the impinging jet flow below the interface.
Unsteady Numerical Research Into the Impact of Bleeding on Axial Compressor Performance
Authors: Zhao Bin , Li Shaobin , Li Qiushi , Zhou Sheng
Published: March 2011

The cooling gas of turbine components in aero-engine is extracted from the compressor. Its flow rate is related to the temperature before turbine. The percentage is usually about 3–5% and sometimes up to 25% of the main flow. Very few of the current studies in this field touched on the influence of air bleeding on compressor performance. This paper takes the single stage and low speed axial compressor as the research object, develops a time-accurate numerical method on the compressor overall performance by using the moving mesh to simulate the function of compressor throttle plug. Combined with experimental results, compressor flow field with and without air bleeding are compared and analyzed to study the impact of bleeding on compressor performance. The results show that if a bleeding design can ease the blockage generated by the tip leakage flow and the backflow near the trailing edge, the stall will be effectively postponed and the compressor stability margin will be expanded.
Pressure Drop During Condensation in Microchannels
Authors: Song Tian Yi , Yu Guang Xu , Ma Xue Hu , Rose John W. , Wang Hua Sheng
Published: March 2011

The paper reports preliminary results from a new research programme for making accurate heat transfer and pressure drop measurements during condensation in microchannels. While commissioning the apparatus a dummy test section was used with identical channel and header geometry to that to be used in the main test program (The final test section will comprise a relatively thick copper test section containing 98 accurately located thermocouples for measuring the temperature distribution from which local heat flux and temperature at the microchannel surface will be obtained). While using the dummy test section (without embedded thermocouples) the opportunity was taken to make accurate pressure drop measurements while measuring the vapor flow rate and total heat transfer rate based on coolant measurements. Data have been obtained for FC72 and steam. Approximate comparisons with available pressure drop calculation methods are presented.
Hydraulic Design of Micro-Irrigation Subunit Based on Genetic Algorithm
Authors: Wang Xinkun , Xu Wenbo
Published: March 2011

With the difference between average discharge and design discharge of emitter to be the objective function, a based-genetic-algorithm model for micro-irrigation subunit hydraulic design is established, which takes the node pressure in the submain end as a decision variable and applies bisection algorithms and back step method to handle the hydraulic calculation of submain and laterals. Simulation results show that the model and algorithm possess excellent solving efficiency, accuracy, and good versatility and practical value. In the meanwhile, it can be also obtained that discharge and pressure distribution of submain and laterals some characteristic value and their orifice location such as average discharge, maximum discharge and minimum discharge of emitter, determine pressure variation, discharge variation, uniformity and other indicators. This model can be applied to hydraulic analysis and design of the micro-irrigation subunit with non-uniform slope, varied-diameter, varied-spacing and so on, and also used to check or evaluate the micro-irrigation subunit which has been designed or completed.
Modeling of a Micro-Channel Water-Gas Shift Reactor
Authors: Akbari M. H. , Asaee S. A. , Roohi R.
Published: March 2011

Hydrogen purification through water-gas shift (WGS) is a favored option in fuel processing for hydrogen fuel cells. A three-dimensional single channel model is developed to simulate the behavior of a water-gas shift micro reactor. The flow regime is assumed to be steady and laminar; furthermore, it is presumed that the walls are isothermal. A water-gas shift reaction rate model is utilized to simulate the surface reaction on Pt/TiO2 catalyst. The gas feed composition is taken as the efflux of a typical auto-thermal reforming (ATR) reactor. A parametric study is conducted to investigate the effect of gas feed temperature, gas space velocity and channel length on water-gas shift micro reactor performance. The study resulted in an optimum water-gas shift micro reactor design. It should be noted that a water-gas shift micro reactor is an essential part of a reactor train to remove carbon monoxide from a hydrogen rich mixture. Such a mixture can be used as fuel for a PEM fuel cell in portable devices. The results of these simulations revealed that the optimum reactor consists of a square cross section channel with 100 μm hydraulic diameter, 20 mm length, space velocity of 1000 h−1 and gas feed temperature of 270°C. The carbon monoxide mole fraction in the efflux is in a range suitable for a typical preferential oxidation (PROX) reactor.
Flow Instabilities and Heat Transfer in Buoyancy Driven Flows of Inelastic Non-Newtonian Fluids in Inclined Rectangular Cavities
Authors: Siginer Dennis , Khezzar Lyes
Published: March 2011

Steady two-dimensional natural convection in rectangular two dimensional cavities filled with non-Newtonian power law-Boussinesq fluids is numerically investigated. The conservation equations of mass, momentum and energy are solved using the finite volume method for varying inclination angles between 0° and 90° and two cavity height based Rayleigh numbers, Ra = 104 and 105, a Prandtl number of Pr = 102 and two cavity aspect ratios of 1, 4. For the vertical inclination of 90°, computations were performed for two Rayleigh numbers Ra = 104 and 105 and three Prandtl numbers of Pr = 102, 103 and 104. In all of the numerical experiments, the channel is heated from below and cooled from the top with insulated side-walls and the inclination angle is varied. A comprehensive comparison between the Newtonian and the non-Newtonian cases is presented based on the dependence of the average Nusselt number Nu on the angle of inclination together with the Rayleigh number, Prandtl number, power law index n and aspect ratio dependent flow configurations which undergo several exchange of stability as the angle of inclination O̸ is gradually increased from the horizontal resulting in a rather sudden drop in the heat transfer rate triggered by the last loss of stability and transition to a single cell configuration. Despite significant differences in the heat transfer rate and flow configurations both Newtonian and non-Newtonian fluids of the power law type exhibit qualitatively similar behavior.
Numerical Simulation of Mixing in Microchannels With Rough Surface
Authors: Yang Dayong
Published: March 2011

Electroosmotic flow is widely used to transport and mix fluids in microfluidics. Aiming at the parallel-plate microchannel with sinusoidal surface roughness, this paper solved the governing equations using the finite element method and the effects of roughness height and frequency on mixing efficiency are investigated. The simulation results indicate that the mixing efficiency increases with the roughness height and frequency, which is approximately proportional to the roughness height. The results can provide valuable insights into the efficient mixing in microfluidics with rough surface and the optimal design of microchannel.
Large Eddy Simulations of Taylor-Go¨rtler Instabilities in Transitional and Turbulent Boundary Layers
Authors: Gordeev Sergej , Stieglitz Robert , Heinzel Volker
Published: March 2011

Free surface liquid metal targets are considered in several high power targets as a tool to produce secondary particles, since their power density exceeds material sustainable limits. Many target designs consider due to the high power deposited in the liquid a concave formed back plate in order to yield a higher boiling point. Upstream the free surface target domain the liquid metal flow is conditioned by a nozzle. However, a back-wall curvature as well as a concave shaped exit nozzle contour can lead to the occurrence of secondary motions in the flow caused by Taylor-Go¨rtler (TG) instabilities. These motions may impact the hydrodynamic stability the flow and also lead to an undesired heat transfer from the hottest region produced within the liquid target towards the uncooled back plate. In this study, the suitability of the Large Eddy Simulation (LES) technique to simulate the formation, development and destruction TG instabilities in transitional and turbulent boundary layers was tested by comparing the simulation results with experimental data reported in literature. All comparisons exhibit a qualitative and quantitative good agreement between experimental data and numerical predictions regarding the mean flow parameters and unsteady large-scale structures caused by TG instabilities.
Microfluidic Magnetic Multi-Cell Sorting
Authors: Tsai Scott S. H. , Stone Howard A.
Published: March 2011

We propose a cell sorting system that uses permanent magnets in a microfluidic device. Functionalized magnetic beads attached to cells and take on different trajectories based on the magnetic forces acting on them.
Numerical Studies on Non-Boiling Two-Phase Flows in Microtubes and Microchannels: A Review
Authors: Talimi V. , Muzychka Y. S.
Published: March 2011

Numerical studies on the hydrodynamic and heat transfer characteristics of two-phase flows in small tubes and channels are reviewed. These flows are gas-liquid and liquid-liquid slug flows. The review is categorized into two groups of studies: circular and non-circular channels. Different aspects such as slug formation, slug shape, flow pattern, pressure drop and heat transfer are of interest. According to this review, there are some large gaps in the research literature, including pressure drop and heat transfer in liquid-liquid slug flows. Gaps in research are also found in applications of non-circular ducts, pressure drop and heat transfer in meandering microtubes and microchannels for both of gas-liquid and liquid-liquid two-phase flows.
Numerical Simulation and Experimental Study of the Pressure Fluctuation in Water Turbines
Authors: Gong Ru-Zhi , Wang Hong-Jie , Liu Wan-Jiang , Qin Da-Qing , Li Feng-Chen
Published: March 2011

Pressure fluctuation is a common problem in large-scale hydraulic turbine, which will affect the performance of the water turbines, such as negatively affecting the efficiency, increasing the damage of related components and decreasing the life span, bringing up great potential troubles to the operation safety of large-scale water turbines. The mechanism how the pressure fluctuation appears is due to the low-frequency pressure pulsation in the draft tube and the mid-frequency pressure pulsation generated by dynamic and static interferences before the runner transmit upstream, and the low-frequency and mid-frequency pressure pulsation in the front of the runner, guide vanes, fixed vanes and the inlet of the volute. To study the relationship between the capacity and the pressure fluctuation of the water turbine, the CFD calculation was performed on the water turbine and the results of the calculation were compared with the measurements in this study. The model of water turbine studied in this paper is Baihetan HEC_1014-type. The computations were carried out in the whole runner blade passage and the boundary conditions were set as the same as the experimental conditions. The unsteady state flow of the turbine was computed. The effects of turbulence were modeled with standard κ-ε turbulence model. The inner flow field and the pressure fluctuation were obtained from the calculation using the solver of Fluent. And the results of simulation are compared with the experimental results.
Numerical Simulation of the Flow in a Large-Scale Thrust Bearing
Authors: Wang Hong-Jie , Gong Ru-Zhi , Lu De-Ping , Wu Zhong-De , Li Feng-Chen
Published: March 2011

Thrust bearing is a key component of large-scale water turbine. It closely relates to the efficiency of large-scale water turbines, and even determines whether the large-scale turbine can operate normally. With the development of the capacitance of water turbines, thrust bearing will develop to the direction of high speed and heavy load. The structure, strength, lubrication and the characteristic of heat radiation of large-scale thrust bearing were often researched in the past. To study the flow condition of the large-scale thrust bearing and analyze the load characteristics, CFD simulation was carried out on the model of thrust bearing. In this study, CFD method was used to simulate the internal flow field of the large-scale thrust bearing. The model researched was a thrust bearing for 1000MW water turbines. The diameter of the thrust bearing was over 5.8 meters, and the maximum thrust load of the bearing can reach to 60MN. The thin gap between the runner and the pad was usually neglected in the published CFD calculations of thrust bearing. But the thin gap was taken into account in this investigation. 1/12 of the model was used as the computational field and periodic boundary was used in the calculation. The standard κ-ε turbulence model was used to simulate the thrust bearing model, and the flow field in the thrust bearing was obtained. The thin gap between the runner and the pad is a wedge. The pressure and velocity distribution in the thrust bearing and thin gap was calculated respectively with conditions of different thin gaps and different rotational speeds of runner. After that, the relationship between carrying capacity and the size of clearance or the speed of the runner through analyzing the data has been obtained from the results of the calculation.
A Validation Database for Flow in a Parallel Triangular Heat Exchanger Tube Array
Authors: Mahon John , Meskell Craig
Published: March 2011

An experimental parametric study of the surface pressure on a cylinder in the sixth row of a rotated triangular tube array (P/d = 1.375) with air cross flow has been conducted. A range of static displacements were examined. Jet switching was observed in this array and resulted in the large asymmetry observed in the pressure distribution around the static cylinder even in a geometrically symmetric configuration. The large fluctuations in lift force due to jet switching suggest that it should be more seriously considered when designing against fatigue failure. The effect of jet switching on the pressure distribution data was mitigated by deconstructing the pressure distribution into two modes. Forces were calculated from the pressure measurements offering an insight into the fluid mechanics generating the forces. No simple parameterisation was found for either the lift or drag force, but it was found that the drag force was only weakly affected by the tube displacement. The dataset presented here compliments the data previously presented for normal triangular arrays and represents a valuable reference for validation of simulations and flow-induced vibration models.
Two Phase Heat Transfer of Ammonia in a Mini/Micro Channel
Authors: Maqbool M. Hamayun , Palm Bjo¨rn , Khodabandeh R. , Ali Rashid
Published: March 2011

Experiments have been performed to investigate heat transfer in a circular vertical mini channel made of stainless steel (AISI 316) with internal diameter of 1.70 mm and a uniformly heated length of 245 mm using ammonia as working fluid. The experiments are conducted for a heat flux range of 15 to 350 kW/m2 and mass flux range of 100 to 500 kg/m2s. The effects of heat flux, mass flux and vapour quality on the heat transfer coefficient are explored in detail. The experimental results show that the heat transfer coefficient increases with imposed wall heat flux while mass flux and vapour quality have no considerable effect. Experimental results are compared to predictive methods available in the literature for boiling heat transfer. The correlations of Cooper et al. [1] and Shah [3] are in good agreement with our experimental data.
Experimental and Theoretical Studies of Pulsed Micro Flows Pertinent to Continuous Subcutaneous Insulin Infusion (CSII) Therapy
Authors: Wang Bin , Hu Hui , Demuren Ayodeji , Gyurcsko Eric
Published: March 2011

Continuous subcutaneous insulin infusion (CSII) therapy, also known as insulin pump therapy, has become an important advancement in diabetes therapy to improve the quality of life for millions of diabetes patients. Insulin delivery failures caused by the precipitations of insulin within micro-sized CSII tubing systems have been reported in recent years. It has also been conjectured that the flow of insulin through an insulin infusion set may be reduced or inhibited by air bubbles entrained into the capillary CSII tubing system during the typical three- to five-day operation between refills. Currently, most solutions to insulin occlusion related problems are based on clinical trials. In the present study, an experimental and theoretic study was conducted to investigate the pulsed flows inside the micro-sized CSII tubing system. A micro-PIV system was used to provide detailed flow velocity field measurements inside the capillary CSII tubing system to characterize the transient behavior of the micro-flows upon the pulsed actuation of the insulin pump used in CSII therapy. It was found that the microflow inside the CSII tubing system is highly unsteady, which is much more interesting than the creeping flow that the nominal averaged flow rates would suggest. A theoretic frame work was also performed to model the pulsed micro-flows driven by the insulin pump to predict the transient behavior of the microflows and velocity distributions inside the micro-sized CSII tubing system. The measurement results and the theoretic predictions were compared quantitatively to elucidate underlying physics for a better understanding of the microphysical process associated with the insulin delivery in order to provide a better guidance for troubleshooting of insulin occlusion in CSII therapy.
An Experiment Study of Wall Slot Jets Pertinent to Trailing Edge Cooling of Turbine Blades
Authors: Yang Zifeng , Kumar Anand Gopa , Igarashi Hirofumi , Hu Hui
Published: March 2011

An experimental study was conducted to quantify the flow characteristics of wall jets pertinent to trailing edge cooling of turbine blades. A high-resolution stereoscopic PIV system was used to conduct detailed flow field measurements to quantitatively visualize the evolution of the unsteady vortex and turbulent flow structures in cooling wall jet streams and to quantify the dynamic mixing process between the cooling wall jet streams and the main stream flows. The detailed flow field measurements are correlated with the adiabatic cooling effectiveness maps measured by using pressure sensitive paint (PSP) technique to elucidate underlying physics in order to improve cooling effectiveness to protect the critical portions of turbine blades from the harsh ambient conditions.
Experimental Investigation of Dielectrophoretic Behavior of Myoglobin and Silica Particles on a Microelectrode Chip
Authors: Kumar Gunda Naga Siva , Kumar Mitra Sushanta
Published: March 2011

Dielectrophoresis (DEP) is one of the nondestructive electrokinetic techniques that has immense capability for manipulating nano-sized biomolecules like myoglobin. The present study investigates the behavior of myoglobin molecules on a microelectrode surface under the influence of dielectrophoresis. Microelectrodes are fabricated in transparent borofloat glass wafers with a sequence of microfabrication steps like piranha cleaning, metal deposition, optical lithography and etching. A detailed description of experimental setup to conduct DEP experiments on myoglobin is presented with a brief overview of myoglobin preparation. Silica particles are used to mimic the myoglobin molecules. Both positive DEP and negative DEP effects on silica particles is observed and positive DEP effect on myoglobin is also observed. Positive DEP on silica particles is observed at applied voltage range of 5–10V and frequency range of DC to 1KHz. Negative DEP effect on silica particles is observed at 10V applied voltage and 10KHz to 40KHz frequency range. The positive DEP effect of myoglobin is observed at applied voltage of 5V and frequency of 5kHz.
Models for Gaseous Slip Flow in Circular and Noncircular Microchannels
Authors: Duan Zhipeng , Yovanovich M. M.
Published: March 2011

Slip flow in noncircular microchannels has been examined and a simple model for normalized Poiseuille number is proposed to predict the friction factor and Reynolds number product fRe for slip flow. The developed model for normalized Poiseuille number has an accuracy of 4.2 percent for all common duct shapes. As for slip flow, no solutions or graphical and tabulated data exist for most geometries, the developed simple model can be used to predict friction factor, mass flow rate, and pressure distribution of slip flow in noncircular microchannels for the practical engineering design of microchannels such as rectangular, trapezoidal, double-trapezoidal, triangular, rhombic, hexagonal, octagonal, elliptical, semielliptical, parabolic, circular sector, circular segment, annular sector, rectangular duct with unilateral elliptical or circular end, annular, and even comparatively complex doubly-connected microducts.
Active Control of Air Flow in Vehicle Underhood Compartment: Temperature and Heat Flux Analysis
Authors: Khaled Mahmoud , Harambat Fabien , Yammine Anthony , Peerhossaini Hassan
Published: March 2011

An experimental analysis of the aerothermal phenomena in the vehicle underhood is given using temperature measurements and separate measurements of convective and radiative heat fluxes. The vehicle underhood used for these measurements is instrumented by 120 surface and air thermocouples and 20 fluxmeters. Measurements are carried out on a passenger vehicle in wind tunnel S4 of Saint-Cyr-France for three thermal functioning conditions. In particular, it is shown for some components that outside air entering the engine compartment (for cooling the different components by convection) can in fact heat other components. This problem results from the underhood architecture, specifically the positioning of some components downstream of warmer components in the same airflow. To avoid this undesired situation, an optimized thermal management procedure is proposed that uses static and dynamic air deflectors during the constant-speed driving (rooting) phase of a vehicle. Much of the present paper is devoted to fluxmetric analysis of underhood thermal behavior (especially the absorption of convective heat flux); we also describe a new control procedure for implementing air deflectors in the actual car underhood.
Fluxmetric Analysis of Car Inclination Effects on the Thermal Management of Underhood Top Region
Authors: Khaled Mahmoud , Harambat Fabien , Hamadi David , Yammine Anthony , Peerhossaini Hassan
Published: March 2011

It is now well established that car inclination influences component temperatures in the car underhood compartment [1, 2]. This study presents an analysis of these effects by measurement of the heat flux that enters or leaves the underhood components. We report underhood thermal measurements carried out in wind-tunnel S4 of Saint-Cyr l’Ecole on a passenger vehicle. The underhood compartment is instrumented with 40 surface and air thermocouples and 20 fluxmeters of normal gradients. Three configurations of car positions are investigated: the flat, the up-hill and the down-hill inclinations. Measurements are carried out for three different car thermal functioning points.
Numerical Investigation of the Impact of Calcasieu Ship Channel on the Hydrodynamics and Water-Substance Transport in Calcasieu Lake and Surrounding Wetlands
Authors: Zhang Ning , Yadagiri Saikiran
Published: March 2011

Calcasieu Lake is located in the heart of the Chenier Plain coastal wetland area, which is a geographical region that extends from Vermillion parish of Louisiana to Chambers county of Texas. On the north side of Calcasieu Lake, there is a heavily industrialized area and the Port of Lake Charles. A ship channel, Calcasieu Ship Channel, was constructed through the Calcasieu Lake connecting Lake Charles and Gulf of Mexico for safe navigation of crude oil, gasoline, and other products for local industries. Due to the increased size of the vessel, the ship channel was widened and deepened in recent years. However, the presence of the wide, deep ship channel made significant impact on the hydrodynamics and water-substance transport in the lake and surrounding wetlands. The impact includes frequent flooding and abnormal salinity, nutrient and pollutant concentrations. In this study, numerical simulations were conducted to study the impact. An unsteady depth-averaged shallow water equation set was implemented to simulate the hydrodynamics (1–4), while for the scalar particulate phase an unsteady depth-averaged scalar transport equation was implemented for the water-substance transport simulations. The results of flow phase agreed well with measurement data (5). The simulations with and without the ship channel were conducted and the results were compared to study the impact.
Near-Wall RANS Modelling in LES of Heat Transfer in Backward-Facing Step Flows Under Conditions of Constant and Variable Fluid Properties
Authors: Jakirlic´ S. , Kniesner B.
Published: March 2011

Two backward-facing step (BFS) flow configurations associated with the heat transfer under the conditions of constant and variable fluid properties were investigated computationally by means of LES and a zonal Hybrid LES/RANS (HLR) method. The latter scheme couples a RANS (Reynolds-Averaged Navier-Stokes) model with large-eddy simulation (LES) within a two-layer framework. A differential near-wall eddy-viscosity model resolves the wall layer and the LES model the remainder of the flow domain. As an introductory heat-transfer case a fully-developed channel flow at Re number Rem = 24000 (DNS: Abe et al., 2004) was computed. In both presently investigated BFS cases the flow is subjected to increasingly enhanced wall heating. Whereas the first considered case (ReH = 28000, ER = 1.25), treated experimentally by Vogel and Eaton (1985) - reference LES is due to Keating et al., 2004, deals with a passive scalar transport, the high-intensity heat flux introduced into the flow domain through the step wall in the second investigated configuration (ReH = 5540, ER = 1.5; reference LES by Avancha and Pletcher, 2002; corresponding isothermal experiment by Kasagi and Matsunaga, 1995) leads to large temperature gradients causing a strong variation of the flow properties. An important feature of the latter flow is a substantial increase of the friction coefficient magnitude with the wall heating intensification in both the flow reversal and recovery region, associated with the local flow acceleration in the immediate wall vicinity. The results obtained by the present simulations with respect to the mean velocity and temperature fields, friction factor and Stanton number variations follow closely the reference experimental and LES databases.
Three Dimensional Simulation of Suspension Flow in a Mold Cavity
Authors: Oumer Ahmed N. , Ali Ahmed M. S. , Mamat Othman B.
Published: March 2011

This paper presents three-dimensional simulation of fiber suspension flows in a cavity using the Finite Volume Method (FVM). The numerical simulation model described makes it possible to predict the propagation of the fiber-polymer solution and fiber orientation during the filling phase. Therefore, the objective of the work is to develop a Computational Fluid Dynamics (CFD) model to simulate and characterize the fiber suspension flow in three dimensional cavities. The model is intended to describe the fiber orientation distribution in three dimensional mold cavities. The continuity, momentum, energy and the fiber orientation equations are solved using the FVM. The flow is considered to be incompressible, non-isothermal, transient, and to behave as non-Newtonian fluid. A numerical analysis is presented to illustrate the application of the FVM to dilute suspension flows in injection molding processes. The volume-of-fluid method is employed to describe the flow of the two incompressible, immiscible phases, i.e., liquid suspension and air. Since the flow is a non-Newtonian, the Cross model is used to describe the shear-thinning behavior of the suspension. The governing equations of the flow and the fiber are implemented and solved by means of the open source code OpenFOAM. The evolution equation of the fiber orientation contains a fourth order orientation tensor which is approximated in terms of second order tensor through the use of appropriate closure rules. In this study the Hybrid closure model of Advani and Tucker is used to approximate the fourth order orientation tensor. To validate the numerical algorithm, test cases of suspension flow in a rectangular cavity are modeled for different fiber-polymer matrices. The numerical results are compared with available experimental findings and with those of Newtonian flows.
Molecular Dynamics Simulations of Liquid Flow in and Around Carbon Nanotubes
Authors: Nicholls William D. , Borg Matthew K. , Reese Jason M.
Published: March 2011

Using recently-developed fluid state controllers [1], we apply continuum fluid boundary conditions to molecular dynamics (MD) simulations of liquid argon flow past a carbon nanotube (CNT) and through a CNT membrane. Advantages of this method are that: it is not dependent on periodic boundary conditions; it can accurately generate fluid transport without any geometrical constraints; and it is capable of performing as an essential part of a hybrid continuum/atomistic technique. In our simulations, a pressure gradient is applied across a CNT membrane by controlling the densities of two reservoirs located either side of the membrane. Fluid velocity and density distributions are reported and compared to other published data where possible.
Non-Overload Design of Low Specific Speed Submersible Pump
Authors: Shi Wei-dong , Long Fei , Li Yue , Leng Hong-fei , Zou Ping-ping
Published: March 2011

Based on the design of low specific speed submersible pump, the influence of impeller geometrical parameter on shaft power of pump is analyzed in this paper. Under the condition of the maximum value of shaft power being no more than the input power of matching electromotor, the method of reducing the maximum value of pump power is researched further in order to reduce the power of the matching electromotor. Then the design correlation formula of the geometrical parameters of impeller is presented. The value of shaft power was predicted by the software FLUENT. The results show that the ratio of maximum power of pump to the power at designing condition is less than 1.2 when the correlation formula presented is used. The experimentation of prototype shows that the maximum value of shaft power of pump reduces greatly whilst every parameter meets the rated requirements. The results demonstrated the guiding role of the discriminated formula in practice, so the desired aim was achieved.