bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Studies on the Optimization Design of a Low Specific Speed Centrifugal Pump
Authors: Zhang Jinfeng , Yuan Ye , Yuan Shouqi , Lu Weigang , Yuan Jianping
Published: June 2012

For a low specific speed centrifugal pump with the requirement of high efficiency of 68% and non-overload power characteristics, series experimental studies, by matching 9 volutes with 19 impellers were done. By combining the former research results about the splitters and the non-overload theory in centrifugal pump, the theoretical conditions to achieve the property of non-overload in a centrifugal pump with splitters was analyzed, and formulas to estimate the maximum shaft power and its position are derived. Based on the requirement of high efficiency and non-overload, blade outlet angle β2, blade outlet width b2, volute throat are Ft and the inlet diameter of splitters Di were chosen with three levels to design a normal L9 (34) orthogonal test scheme. After the optimized design scheme was determined, and corresponding test was done also, it demonstrates that the experiment purpose was achieved and the design method to combine the splitters and non-overload theory is reasonable, which can get the property of high efficiency and non-overload. A BP artificial neural network (BPANN) model was built to predict the efficiency and head of centrifugal pumps with splitters in MATLAB toolbox. Eighty five groups of test results were used to train and test the network model, where the Levenberg–Marquardt algorithm was adopted to train the neural network model. Five parameters Q, Z, β2, Di, b2 were chosen as the input layer parameters, η and H were the output factors. Through the analysis of prediction results, the conclusion was got that, the accuracy of the BP ANN is good enough for performance prediction. And the BP ANN can be used for assisting design of centrifugal pumps with splitters, which can shorten research time and cost.
Experimental Study on the Performance and Pressure Fluctuations of a Regenerative Gas Blower for Different Design Parameters
Authors: Kim Younghoon , Kang Shin Hyoung , Noh Yonggyu
Published: June 2012

A regenerative gas blower design for fuel cell vehicle is presented. Two issues studied concern non-dimensional performance characteristics under various design parameters and the noise of the blower due to unsteady pressure fluctuation. Non-dimensional performance curves were measured at various rotating speeds and gas mixture ratios. Blower models using different design parameters such as the stripper angle, blade aspect ratios and blade thickness ratios were tested. The effects that aforementioned parameters had on performance were investigated. Surface pressure fluctuations were measured in the channel close to both ends of the stripper using fast-response pressure transducers. A sharp blade increases the maximum isentropic total enthalpy coefficient and the maximum efficiency because the pressure loss coefficient of the circulatory flow is reduced. A small stripper angle enhanced the maximum isentropic total enthalpy coefficient and the maximum efficiency because working sections was lengthened. The enlarged stripper angle and the low pressure difference across the stripper reduce the magnitude of pressure fluctuation at the blade passing frequency.
Numerical Study on Unsteadiness of Tip Clearance Flow and Performance Prediction of Axial Compressor
Authors: Hwang Yoojun , Kang Shin-Hyoung
Published: June 2012

Numerical calculations were performed to investigate unsteady features of tip clearance leakage flow in an axial compressor. The first stage rotor of a low speed axial compressor with a large tip clearance was examined. It was confirmed that the numerically calculated performance data were in good agreement with the experimentally measured performance data. Using frequency analysis, the flow characteristic near the casing induced by tip clearance leakage flow was found to be not associated with the rotating speed of the rotor. This characteristic is called rotating instability or self-induced unsteadiness. We found that the circumferential length scale of the rotating instability of the compressor was longer than a pitch of a blade passage; therefore, a multi-blade passage was adopted to study the flow structure more precisely. The flow characteristic was described by the frequency, the circumferential length, and the phase velocity, and was changed by operating points toward stall. The behavior of the flow was characterized by circumferentially traveling waves. Hence, the mechanism governing the development of the unsteady feature was further examined in terms of the rotating wave pattern of the pressure distribution. Furthermore, the unsteady feature of the tip clearance leakage flow affected the prediction of compressor performance by altering blockage, flow turning, and loss near the casing.
Study of Heat Transfer Characteristics for the Fuel Cell System of the Humidifier due to Analysis and the Hot Testing
Authors: Kim Seon-hwa , Lee Jae-jun , Oh Young-min , Lee Sang-hoon , Kim Jae-sik
Published: June 2012

The MCFC system of BOP (Balance of Plant) is contained various mechanical equipments. One of the equipments of the heat exchangers is important component for efficiency and cost. In MCFC system, several heat exchangers are used according to the application. Most typical heat exchanger is the humidifier in BOP for MCFC, which is named for the humidifier because it is to preheat the fuel and water so that a reactor will convert some of the incoming fuel to hydrogen. Then, hot side fluid service is used the exhausted gas from the fuel cell and cold side fluid service is the fuel and water. The operation temperature range is about 25∼500 Celsius Degree.[1] This heat exchanger has the problems of multiphase fluid and phase change heat transfer. So it is necessary to analyze the heat transfer characteristics and to propose the reasonable design methodology for the humidifier. In this study, the thermal characteristic for the humidifier is estimated by using commercial tool of heat exchanger design, rating and simulation. Also this study presents the results for test facility of fabrication and for testing.
6-DOF Numerical Simulation of the Vertical-Axis Water Turbine
Authors: Wang Xin , Luo Xianwu , Zhuang Baotang , Yu Weiping , Xu Hongyuan
Published: June 2012

Recent years, the vertical-axis water turbine (VAWT) is widely used for converting the kinetic energy of the moving water in open flow and with low static head like river and tidal sites. Conventional numerical methods such as disk-stream tube method and vortex panel method have some drawbacks to predict the behaviors and characteristics of the vertical-axis tidal stream turbine. This paper had treated the hydrodynamic performance of a VAWT model experimentally and numerically. Based on the present research, a 6-DOF method coupled with CFD suitable to simulate the rotor movement and predict the hydraulic performance for a VAWT was proposed. Compared with the experiments, the numerical results for the performance of the VAWT model were reasonable. It is also noted that there is a maximum power coefficient near tip speed ratio of 2.5 for the test model.
Investigation of the Performance for a Heat Generator Using Hydrodynamic Cavitation
Authors: Pyun Kwon Bum , Kwon Woo Chul , Oh Kyoung Taek , Yoon Joon Yong
Published: June 2012

Cavitation occurs typically when pressure is lower than the saturated vapor pressure. Generally, cavitation used to be a phenomenon engineer should avoid when they design fluid machinery because it creates erosion, vibration and noise that make performance of the machineries worse. Recently, study about generating energy with cavitaion is being proceeded like heat generating machinery which is the most typical. There is little academic research, although study about these has some commercial documents or patents. In this study, we proceed experimental study for the heat generator connected to electrical motor which generates heat from cavitaion using a fast rotating device. We used 15 kW and 55 kW electric motors to rotate the generator. The experiments performed changing flow conditions such as pressure at entering position by using a booster pump and rotating velocity of the motors by an inverter. We analyzed heat production and thermal efficiency according to the flow conditions. The front cover of the heater is made of acrylic plate so that we can use high speed photography to observe the relation between cavitation and generator shape. We made sure that these conditions can affect performance and especially pressure at entrance or rotating velocity affect heat production. Existing theory of cavitation and results of this study were discussed. These results could be useful for design process of the machine using cavitation such as a cavitation heat generator and a chemical reactor etc.
Detached Eddy Simulation of Unsteady Flow Field and Prediction of Aerodynamic Sound in a Half-Ducted Propeller Fan
Authors: Kusano K. , Jeong J. H. , Yamada K. , Furukawa M.
Published: June 2012

Three-dimensional structures and unsteady nature of vortical flow fields in a half ducted propeller fan have been investigated by a detached eddy simulation (DES) based on k-ω two-equation turbulence model. The validity of the numerical simulation performed in the present study was demonstrated by the comparison to LDV measurement results. The simulation shows the tip vortex is so strong that it dominates the flow field near the rotor tip. The tip vortex does not impinge on the pressure surface of the adjacent blade directly, however it interacts with the shroud surface and induces a separation vortex on the shroud. Furthermore, this separation vortex interacts with the pressure surface of the adjacent blade. These flow structures cause high pressure fluctuation on the shroud surface and the blade pressure surface. Besides, sound pressure levels were predicted by Ffowcs William-Hawkings equation based on Lighthill’s acoustic analogy using the unsteady surface pressure data obtained by DES. As a result, the degree of contribution by each flow structure to overall sound has been estimated quantitatively.
Flow Analysis and Deterministic Decoupling in a Squirrel Cage Fan
Authors: Ferna´ndez Oro Jesu´s Manuel , Velarde-Sua´rez Sandra , Guerras Colo´n Israel , Argu¨elles Di´az Katia M. , Gonza´lez Jose´
Published: June 2012

Squirrel cage fans are often used as blowers for automobile applications or for small industrial equipment. The flow in this kind of fans happens to be quite complex and with unsteady features, that makes it quite difficult to be studied. In particular, unsteady flow separation at the machine inlet or at the impeller blades and a variety of flow induced vibrations is found for most of the operation conditions. The deterministic stress analysis becomes an interesting tool in analyzing the main flow features from an existing numerical model. In this paper, the analysis of the internal flow and the periodic phenomena resulting from a deterministic study is intended. To accomplish this goal, a series of numerical routines were performed for different flow rates, including also failing operating modes of the fans (blocked inlets as a typical problem for this type of arrangements). The squirrel cage fan studied is a small centrifugal fan with a twin impeller configuration, each with 23 forward curved blades. The blades chord is 0.013 m and each impeller has a diameter of 0.08 m and a width of 0.09 m. The performance curves (head, power and efficiency versus flow rate) was obtained numerically in previous works and confirmed experimentally in normalized test campaigns. These tests have shown a nominal flow rate at around 352 m3/h and a specific speed ns = 1.9. The main goal of the paper consists on the evaluation of the non-uniformities induced by the volute tongue over the blade to blade distributions within the impeller. As a consequence, fluctuation levels in the blade loadings, derived from deterministic non-uniformities can be provided in the relative frame of reference. The practical applications of the conclusions do imply a progress in the knowledge of the working parameters for machines that affect in a direct way to the passengers comfort.
Efficiency Improvement at Part Load of Multistage Centrifugal Compressor for Turbo Chiller
Authors: Kawaguchi Daisuke , Okada Takeshi , Nakamura Yasushi , Terasaki Masatoshi
Published: June 2012

The effect of variable inlet guide vanes in the multistage centrifugal compressor for the turbo chiller on the part load efficiency improvement was analyzed by using CFD (computational fluid dynamics). The area we analyzed targeted two stages including the first and second variable inlet guide vanes arranged upstream of each compressor. The numerical simulation involved three-dimensional, steady, and compressible flow analysis with ANSYS-CFX. The flash gas injected from the intermediate inlet of the economizer passage was taken into account. The part-load efficiency was measured while changing the opening ratio for the first and second variable inlet guide vanes. The predicted part-load efficiency corresponded to the one that was measured. The predicted flow pattern indicated that higher efficiency could be obtained by adjusting the opening ratio for the first and second variable inlet guide vanes to suppress excessive prewhirl from the first impeller and stall from the second impeller.
Development of Prediction Method for Wind Noise Caused by Airflow Around Front Pillar
Authors: Okutsu Yasuhiko , Hamamoto Naoki , Powell Robert , Wu Long
Published: June 2012

To control high frequency wind noise upper than 1 kHz is important to ensure the comfort for a driver and passengers when vehicles cruise at high speed. Therefore the prediction method for high frequency wind noise inside a cabin has been required for development of a vehicle. This paper describes about the prediction method for high frequency wind noise from numerical simulation results. In this study, wind noise caused by airflow around a front pillar is predicted. We have predicted wind noise by visualizing noise sources and pressure fluctuation on vehicle surfaces in recent years. Although an inferior-to-superior relationship can be predicted from these results, it was difficult to estimate quantitative interior noise level. In this research, the SEA code is examined to predict such noise level. The SEA code has confirmed showing a qualitative and almost quantitative consistency of measured and calculated SPL at the head area of a front passenger seat.
The Development and Implementation of Model-Based Control Algorithm of Urea-SCR Dosing System for Improving De-NOx Performance and Reducing NH3-Slip
Authors: Jeong Soo-Jin , Kim Woo-Seung , Park Jung-Kwon , Lee Ho-Kil , Oh Se-Doo
Published: June 2012

The selective catalytic reduction (SCR) system is a highly-effective aftertreatment device for NOx reduction of diesel engines. Generally, the ammonia (NH3) was generated from reaction mechanism of SCR in the SCR system using the liquid urea as the reluctant. Therefore, the precise urea dosing control is a very important key for NOx and NH3 slip reduction in the SCR system. This paper investigated NOx and NH3 emission characteristics of urea-SCR dosing system based on model-based control algorithm in order to reduce NOx. In the map-based control algorithm, target amount of urea solution was determined by mass flow rate of exhaust gas obtained from engine rpm, torque and O2 for feed-back control NOx concentration should be measured by NOx sensor. Moreover, this algorithm cannot estimate NH3 absorbed on the catalyst Hence, the urea injection can be too rich or too lean. In this study, the model-based control algorithm was developed and evaluated based on the analytic model for SCR system. The channel thermo-fluid model coupled with finely tuned chemical reaction model was applied to this control algorithm. The vehicle test was carried out by using map-based and model-based control algorithms in the NEDC mode in order to evaluate the performance of the model based control algorithm.
Potential of Fuel Stratification for Reducing Pressure Rise Rate in HCCI Engines Fueled With DME/n-Butane
Authors: Lim Ocktaeck , Jamsran Narankhuu , Jeong Soojin , Pyo Youngduck , Park Kyuyeol
Published: June 2012

We investigated the efficacy of fuel stratification in a pre-mixture of di-methyl ether (DME) and n-Butane, which have different auto-ignition characteristics, for reducing the pressure rise rate (PRR) of homogeneous charge compression ignition (HCCI) engines. A new chemical reaction model was created by mixing DME and n-Butane and compared to existing chemical reaction models to verify the effects. The rate of maximum pressure rise depends on mixture ratio. When DME was charged with stratification and n-butane was charged with homogeneity, the maximum PRR was the lowest. The calculations were performed using the SENKIN application of CHEMKIN-II.
Analytic Study of Lubricity of DME as Alternative Fuel
Authors: Lim Young-Kwan , Kim Jong-Ryeol , Jung Choong-Sub , Lee Joung Min , Yim EuiSoon
Published: June 2012

In recent years, there have been increased concerns for the global warming and the exhaustion of resources caused by the heavy consumption of the fossil fuel. For this reason, biomass has been brought to great attention as a renewable source of energy to mitigate the situation. In this particular area, DME (dimethyl ether) fuel produced from biomass, biogas, and coal is expected to be useful as one of the eco-friendly synthetic fuel alternatives to petrodiesel. Diesel engine need fuel lubricity due to their severe condition (high pressure and temperature) but DME have low lubricity. In this study, we developed the analytic system for DME lubricity test which is pressurized chambered tester. Also we synthesized various of biodisel from 12 kinds of vegetable oil under base catalyst system. Oxygen compounds definitely contributed to the natural lubricity of fuel, biodiesel have ester group which is polar oxygenated functional group. After prepared test system and biodiesel as lubricant, we analyzed the lubricity of neat DME, neat biodiesels and DME-lubricant blended (100 ppm to 2000 ppm) fuel.
Noise Prediction in HVAC Squirrel-Cage Fans by Unsteady Reynolds Navier-Stokes Computation
Authors: Guerras Colo´n Israel , Velarde-Sua´rez Sandra , Ballesteros-Tajadura Rafael , Ferna´ndez Oro Jesu´s Manuel , Gonza´lez Jose´
Published: June 2012

Small centrifugal and axial fans are used in automobile applications, as it is the case for HVAC systems for public transport. Typically, these fans are used to work at high speed (over 4000 rpm) and variable operation conditions, even at extreme off-design points. Flow instabilities, low efficiency and high levels of noise and vibrations appear in these machines due to these working characteristics and the need of low fabrication costs. However, lower noise levels are required today to improve the passengers comfort. Aiming to solve these problems, it is interesting to develop a computer application to predict the generated noise level (especially at the blade passing frequency BPF), which could be used during the design phase of the fans. In this paper, using Computational Fluid Dynamics (CFD) tools, the three-dimensional (3D) internal flow in a small squirrel-cage fan is computed unsteadily. Based upon the data acquired from the pressure fluctuations at the surfaces of 46 rotating blades and the volute tongue, the Ffowcs Williams-Hawkings analogy, which has been successfully applied in other types of turbomachines, is used to predict noise levels at the BPF. On the other hand, in order to validate the predicted numerical results, an experimental noise characterization in a semi-anechoic chamber using capacitive microphones and a real-time frequency analyzer is performed.
On Uncertainty and Local Sensitivity Analysis for Transient Conjugate Heat Transfer Problems
Authors: Rauch Christian
Published: June 2012

The need for simulating real-world behavior of automobiles has led to add more and more sophisticated models of various physical phenomena for being coupled together. This increases the number of parameters to be set and, consequently, the required knowledge of their relative importance for the solution and the theory behind them. Sensitivity and uncertainty analysis provides the knowledge of parameter importance. In this paper a thermal radiation solver is considered, that performs conduction calculations and receives heat transfer coefficient and fluid temperate at a thermal node. The equations of local, discrete, and transient sensitivities for the conjugate heat transfer model solved by the finite difference method are being derived for some parameters. In the past, formulations for the boundary element method and the finite element method have been published. This paper builds on the steady-state formulation published previously by the author. A numerical analysis on the stability of the solution matrix is being conducted. From those normalized sensitivity coefficients dimensionless uncertainty factors are calculated. On a simplified example the relative importance of the heat transfer modes at various locations are then investigated by those uncertainty factors.
Large Eddy Simulation on the Unsteady Aerodynamics of a Heavy Duty Truck in Wind Gust
Authors: Tsubokura Makoto , Das Prasanjit , Matsuuki Tomofuyu , Nakashima Takuji
Published: June 2012

Unsteady aerodynamic forces acting on a full-scale heavy duty truck were investigated using a large-eddy simulation technique. The numerical method adopted was first validated on a static condition measured at the DNW German-Dutch wind tunnels. After the correction of the blockage ratio in the wind tunnel, the drag coefficient obtained by our numerical method showed good agreement with the experimental data within the errors of less than 5%. Effect of an air deflector mounted on the top of a cabin was also discussed. Then the method was applied to non-stationary conditions in which the truck was subjected to ambient perturbation of approaching flow. The perturbation of the flow is a model of atmospheric turbulence and sinusoidal crosswind velocity profiles were imposed on the uniform incoming flow with its wavelength comparable to the vehicle length. As a result, it was confirmed that when the wavelength of the crosswind is close to the vehicle length, averaged drag increases by more than 10% and down-force decreases by about 60%, compared with the case without perturbation.
Numerical Simulation of a New Typed Sprinkler Irrigation System
Authors: Zhu Xingye , Wang Xinkun , Liu Junping
Published: June 2012

It has important significance and practical value for studying Sprinkler Irrigation System. In this study, numerical simulation was carried out. According to the selected materials and setting modes, both the pressure and the velocity distribution along the lateral were calculated out. Experimental study was carried out for this system to verify the correctness of numerical simulation. The following parameters were measured in the experiments: the flow-rate, rotational speed of the pump, and working pressure for the sprinklers. The numerical simulation results agreed to the experimental results within 5 percent. It supplied a foundation for the reasonable application of sprinkler irrigation system for the future. It can be concluded that structural optimization approach can be effectively implement by CFD simulation.
Opposition Control of Turbulent Taylor-Couette Flow
Authors: Le Dauphin Christophe , Fukagata Koji
Published: June 2012

Direct numerical simulations (DNS) of an opposition-controlled turbulent Taylor-Couette (TC) flow is performed. Opposition control is then applied. Significant drag reduction is achieved by opposition control and the skin friction drag is decreased up to 31% with the wall-normal control. Strong modifications of the turbulence statistics in the near-wall region are observed. The streamwise velocity fluctuation is greatly reduced and shows a more symmetric profile. The origin of the boundary layers seems to undergo a displacement toward the middle of the flow. Besides, the visualization of the coherent flow structures shows a significant reduction of their number when the control is applied. In a further step, the combination of wall-normal and spanwise control, as well as the influence of the gain on the input response are investigated. The efficiency of this control strategy is then compared with the opposition control.
Large Eddy Simulation of the Flow Field in the Hudson River
Authors: Phan Tuy N. M. , Wells John C. , Kirkey William D. , Islam Mohammad S. , Bonner James S.
Published: June 2012

Large-eddy simulation (LES) has been conducted under idealized conditions in two river reaches of the Hudson River (New York, USA), with near-bank resolution set to some 5 meters in order to resolve large-scale motions of turbulence in the near-bank regions. To simplify analysis, simulation is performed at a constant discharge corresponding to a typical ebb tide. A standard Smagorinsky model is implemented in the commercial package FLUENT, with buoyancy neglected and bottom roughness set to zero. We perform Proper Orthogonal Decomposition (POD) on the LES results. POD modes are orthogonal flow fields that capture the kinetic energy in an optimally convergent fashion. Results show that only a few POD modes are enough to describe the most energetic flow dynamics. In a reach around the Indian Point power plant, the second and third modes reflect an interesting generation of separating eddies on the western bank, which we do not find with a URANS (standard k-ε) computation on the same grid. To test our simulation, a comparison of simulation results with other simulation results and Acoustic Doppler Current Profiler (ADCP) data measured at West Point, New York will be presented.
Turbulence Length Scales in a Vortical Flow
Authors: Habchi Charbel , Lemenand Thierry , Della Valle Dominique , Peerhossaini Hassan
Published: June 2012

Laser Doppler velocimetry is used to investigate the velocity spectra and turbulence length scales in a turbulent vortical flow. The turbulent vortical flow is ensured by vorticity generators (VG) inserted into a straight circular pipe. Each VG generates a complex flow that is mainly the combination of a steady streamwise counter-rotating vortex pair and a periodic sequence of hairpin-like structures caused by the Kelvin-Helmholtz instability in the shear layer ejected from the VG trailing edges. These primary structures induce a secondary vorticity in the wake of the VG. The aim of the study is to analyze the velocity spectra and turbulent length scales for the different coherent structures in the flow. Thus, the Kolmogorov and Taylor microscales, the Liepmann-Taylor microscale and the viscous length scale are determined in different locations in the VG streamwise direction. The evolution of the length scales with respect to the Taylor-Reynolds number is compared with theoretical trends in a variety of flows in the open literature.
Spatio-Temporal Characteristics of Heat Transfer in Separated and Reattaching Flows
Authors: Nakamura Hajime , Takaki Sayaka , Yamada Shunsuke
Published: June 2012

Spatio-temporal characteristic of heat transfer accompanied by the flow separation and reattachment was investigated using a high-speed infrared thermograph that recorded the temperature fluctuation on a heated thin-foil. In this study, the heat transfers behind a backward-facing step, behind a forward-facing step, and on a blunt plate were investigated. In all configurations, the heat transfer in the flow reattaching region had spot-like characteristics, which spread with time and overlapped with others to form a complex feature in terms of spatio-temporal characteristics of the heat transfer. The mean Nusselt number distribution behind the reattaching region was approximately proportional to 2/3 power of Reynolds number, as indicated in the previous researches. The time-space distribution of the heat transfer had a typical spanwise wavelength and fluctuating frequency in the reattaching region, which was likely to be related to the dimension of the separation region (characteristic length H or the separation length xR). This suggests that the origin of these periodicities is not the instability upstream of the flow separation, but due to some instability, which is accompanied by the flow separation and reattachment.
Numerical Study on Fluid Flow and Heat Transfer of Mixed Convection to a Stagnation Region From an Upward-Facing Horizontal Plate
Authors: Mitsuishi Akihiko , Kitamura Kenzo
Published: June 2012

Mixed convection heat transfer from an upward-facing horizontal semi-infinite plate to a stagnation region is studied by means of direct numerical simulation. All the cases studied are simulated under constant heat flux condition on the plate. Assuming that the working fluid is air at room temperature and pressure, the Prandtl number is kept at 0.71. The Reynolds and the modified Grashof numbers are in the ranges of 102−103 and 107−108, respectively. Longitudinal vortical structure, which was discovered in the recent experimental study, is successfully simulated. The typical structure appears as a pair of counter-rotating vortices being elongated over the plate. The relationship between this structure and the heat transfer rate is clarified. Characteristics of the vortices are investigated in detail.
Length Efficiency of the Etoile Flow Straightener: Numerical Experimentation
Authors: Laribi Boualem , Youcefi Abdelkader , Matene Elhacene
Published: June 2012

This article presents a numerical investigation of the development and the establishment of the flow in the presence of the Etoile flow straightener recommended in ISO 5167 (ISO 5167. Measurement of fluid flow by means of orifice plates, nozzles and venture plates inserted in circular cross-section conduits running full, 2003). The objective of this study is to examine the effectiveness length of the Etoile flow straightener, recommended by ISO 5167 with length of two pipe diameters, on the development and the establishment of the flow. The flow is produced by air in a 100mm pipe diameter and 40D of length with a Reynolds number of 2.5×105. The disturbance is a valve maintained at 100% and 50% open. The flow parameters examined are velocity profile, turbulence intensity profile, and the gyration of the fluid. Several measuring stations upstream and downstream of the unit are done. The code CFD Fluent is used for this simulation. The results obtained are compared according to directives of the standard ISO 5167. However, they show that for position valve 100% open the various lengths of the Etoile flow straightener do not present differences for the three flow parameters. On the other hand, for the valve position 50% open, the Etoile flow straightener with 2D length which presents the best performances according the standard.
Numerical Investigation of New Design of the Etoile Flow Straightener
Authors: Laribi Boualem , Youcefi Abdelkader , Belkacemi Djelloul
Published: June 2012

Flow metering of industrial fluids remains the concern of several researchers and exporting countries of gas and oil in the world. It is in this context that a vast numerical investigation is done in our laboratory of Industrial Fluids Measurements and Applications (FIMA). This article examines numerically a new design of the Etoile flow straightener which is described by the standard ISO 5167. This new design consists in removing the central part of the Etoile which, according to researchers, leads to a very high level of turbulence. Our intervention relates to the development and the establishment of the flow parameters downstream the Etoile with and without central part. The flow is produced by air in a 100mm pipe diameter and 40D of length with a Reynolds number of 2.5×105. The disturbance is a valve maintained 100%, 50% and 30% open. The flow parameters examined are velocity profile, turbulence intensity profile, and the fluid gyration angle. The code CFD Fluent is used for this simulation. The results obtained are compared according to directives of the standard ISO 5167. The results obtained show that for the valve settings 30% and 50% open, upstream the Etoile, we have a high turbulence level and a velocity profile with recirculation zones more significant for the valve 30% open than for the valve 50% open. It is also noted that the valve develop very high fluid gyration angle apart from the standard values. The flow behavior downstream the central part of Etoile described by the ISO 5167 is well simulated with the valve open at 100%, with a deficit of flow and a very high degree of turbulence. At this stage for the two designs, the noticed results seem so identical beyond a certain stations downstream the Etoile.
Effect of Tee and Valve on the Flow Measurement Accuracy for Turbulent Pipe Flow With Flow Conditioner
Authors: Laribi Boualem , Bouricha Nahla
Published: June 2012

This work describes the effect of a Tee and a Valve on the flow measurement accuracy and the performances of the E´toile flow straightener described by the standard ISO 5167 to produce the fully developed pipe flow with these disturbances. Simulation is carried out for an air flow in 100mm pipe diameter with a Reynolds number between 104 and 106. The code used for this work is Fluent V6.3, where the Navier-Stokes equations are solved by the finite volumes method with K-ε model like turbulent model. The results show that for the disturbance valve 50% closed, the length of establishment seems to be reached at 25D downstream the E´toile where the flow gyration angle is reduced practically to zero value. But for the Tee disturbance the results show that the flow needs more than 25D to reach the profiles requested by the standards. An experimental study is essential to validate these results for choosing a standard disturbance which will be examined with conditioners quoted in standard 5167 and thereafter the development of a new flow conditioner.
Experiments on Swirling Flow in a Vertical Circular Tube
Authors: Chang Tae-Hyun , Kil Sang-Cheol , Doh Deog Hee , Kim Sang youn
Published: June 2012

Swirling flows are related to spiral motion in the tangential direction in addition to the axial and radial direction using several swirl generators. These kinds of flows are used for combustion chambers to improve the flame stability, heat exchanger enhancing heat transfer coefficients, agricultural spraying machines and some vertical pipes to move slurries or conveying of materials. But, few papers have dealt with three dimensional velocities profiles in a vertical pipe. In this paper, 3 dimension PIV technique has employed to measure velocities profiles in water along a vertical circular pipe for Re = 3000 ∼ 13,000. The swirl generator to be used is tangential inlet condition to produce the flow. The velocities and flow noise have been measured with swirl in the water and air along the test tube.
Creation of Transparent Flow Passage to Measure the Biomedical Flow Inside Human Body by PIV
Authors: Kim Sung Kyun , Seo Anna , Jang Jiwon , Chung Kangsoo
Published: June 2012

Knowledge of flow characteristics in human airway and blood vessel is essential to understand the physiological and pathological aspects of respiratory and circulatory systems. Creating an accurate transparent flow passage is indispensable for the successful investigation on the flow inside a complex flow passage of human organ by PIV. The Web-based communication system between multi-researchers and medical doctors is established for making the post-surgery models and to discuss surgery plans. We also introduced a semi-automatic segmentation technique to reconstruct accurate three dimensional computer models from CT data rapidly and conveniently.
On Boundary Conditions for Cavitation CFD and System Dynamics of Closed Loop Channel
Authors: Nohmi Motohiko , Ikohagi Toshiaki , Iga Yuka
Published: June 2012

The unsteady two dimensional CFD for the cavitation in a orifice passage were carried out by using a commercial software ANSYS-CFX. The mass flow rate and the static pressure were controlled at the inlet and the outlet boundaries respectively. The CFD result showed periodic fluctuation of the cavitation flow. The time derivative of the cavitation volume showed relatively good agreement with the difference of the inlet and the outlet volume flow rate. The periodic fluctuation was ceased by the extension of the passage length downstream of the cavitation. The periodic fluctuation of cavitation flow was also induced by the fluctuation of the inlet volume flow rate or the fluctuation of the outlet static pressure. The dynamic flow behavior of the closed loop system including the orifice were analyzed by using the orifice cavitation CFD with the inlet and the outlet boundary conditions derived from the lumped parameter system dynamics for the tank, the pump and the pipes in the loop.
Fundamental Exercises in Mechanical Systems Engineering Using Robot Manipulator
Authors: Takanobu Hideaki
Published: June 2012

A five degrees-of-freedom (5-DOF) robot manipulator is used for the basic learning of mechanical system engineering. Students learned the forward kinematics as concrete applications of the mathematics, especially linear algebra. After making a manipulator, baton relay contest was done to understand the inverse kinematics by controlling the manipulator using a manual controller having five levers.
3D Tomographic Transition of Particle Distribution in Microchannel
Authors: Choi Je-Eun , Takei Masahiro
Published: June 2012

The three dimensional cross-sectional particle concentrations of particle-liquid two phase flows in the two cross-seciton of microchannel has been reconstructed using process tomography. In the obtained 3D (2D space and time) reconstruction image, the dielectric particle-injected area appears to have a high particle concentration, and the deionized water-injected area appears to have a low particle concentration. Dielectric particles as the solid phase and non-conductive deionized water as the liquid phase are non-uniformly injected to the microchannel. The comparison between the qualitative result of 3D reconstruction image and the quantitative result of particle concentration in flow direction transition is that the particle is reasonably distributed in the particle injected area of the cross-section. Based on the reconstructed particle distribution image, it is easy to estimate the particle diffusion behaviors in microchannel.
Forced Convection Heat Transfer Characteristics of V-Bent Circular Fin-Tube Heat Exchanger
Authors: Lee Jong Hwi , Kang Hie Chan
Published: June 2012

The purpose of the present study is to investigate the flow resistances and heat transfer characteristics of V-bent circular fin-tube heat exchangers. Two types of V-bent fin, in which the fin areas are identical but the type of bend is different (uni- and bi-directional), have been tested numerically. The heat transfer, pressure drop, fin temperature, and fin efficiency are discussed. The uni-directional bent fin showed higher flow resistance and better heat transfer performance than the bi-directional fin. With a 37% V-bent design, the heat transfer coefficient of the uni-directional fin was up to 33% higher than that of the plain circular fin in the present test range.
Natural Convection Correlations of Circular Finned Tube Heat Exchanger
Authors: Kang Hie Chan , Jang Hyun Soon
Published: June 2012

An experimental study has been conducted on natural convection heat transfer for seventeen kinds of circular finned tube heat exchanger. The transient method was used to obtain the heat transfer coefficient. The experimental data were presented and their characteristics lengths were discussed. The experimental data were presented and correlated in the ranges of 27 < RaDh < 2300, 1.2 < Do/Di < 2.8, and 0.12 < Pf/Di < 0.26. The Nusselt number correlated with the quarter power of the Rayleigh number, based on the hydraulic diameter, for the small diameter fins, the same as laminar natural convection; however, the correlation was with the half power for the large fin diameters and small fin pitches.
Parallel Simulation of Multiphase Flows Using the Volume-of-Fluid Method
Authors: Fuster Daniel , Hoepffner Jerome , Popinet Stephane , Zaleski Stephane
Published: June 2012

This article numerically investigates the appearance of instabilities in two planar coflowing liquids sheets. As a function of the momentum ratio, two different regimes are distinguished. At low momentum ratios the frequency of the waves appearing in the primary atomization region are influenced by the liquid velocity, whereas an asymptotic regime is obtained for large momentum ratios. In this regime, the gas velocity and the ratio between the gas boundary layer and the thickness of the separator plate influence the observed frequency. Current computational results are in agreement with Ben Rayana’s experimental observations [1].
Droplet Traffic Control in Microchannel by Droplet Bistability
Authors: Lee Beomjoon , Yoo Jung Yul
Published: June 2012

This paper presents novel methods for precisely controlling water droplets by use of a microfluidic bifurcation channel with outlet restrictions, based on droplet bistability which utilizes the Laplace pressure due to interfacial tension arising when a droplet encounters a narrow restriction. We implement droplet bistable geometry, which has two symmetric branches and restrictions, to operate as capillary valves, so that a droplet can be trapped in front of a restriction and released through it when the next droplet arrives at the other restriction. It is observed that this trap-and-release occurs repeatedly and regularly by the succeeding droplets. It is also found that there is a critical flow rate to achieve droplet bistability which occurs only when the apparent Laplace pressure surpasses the pressure drop across the droplet. By adopting a simplified hydrodynamic resistance model, droplet bistable mechanism is clearly explained. Droplet bistability enables simple and precise control of droplets at a bifurcation channel. Thus, by an appropriate channel design to induce droplet bistability, precise control of droplet traffic is achieved at a bifurcation channel connected with a single inlet channel and two outlet channels. In particular, we are able to distribute droplets at a junction in a manner of perfect alternation between the two outlet channels. Bistable components can be used as an elaborately embedded droplet traffic signal for red light (trap) and green light (release) in complex microfluidic devices, where droplets provide both the chemical or biological materials and the processing signal.
Molecular Dynamics Study of Oxygen Permeation Through the Ionomer of PEFC Catalyst Layer
Authors: Sakai Kiminori , Tokumasu Takashi
Published: June 2012

Polymer electrolyte membrane fuel cell (PEFC) is focused worldwide as the energy conversion device of next generation. In the PEFC cathode catalyst layer, an ionomer with which the catalyst is covered is very important on the point of transferring protons to the catalytic surface on the cathode side. On the other hand, it is said that an ionomer interferes with oxygen permeation to the catalytic surface. The mechanism of oxygen permeation through an ionomer was not analyzed in detail because it is too small to research by experiment. Moreover molecular dynamics simulation of the catalyst layer and oxygen permeability has not yet studied. In this research, we constructed the system including nafion, water, oxonium ion, platinum layers by using molecular dynamics study, and studied about the effect of the water content of the ionomer on the structure of the ionomer and permeability of the oxygen molecule. As the results, a lot of oxygen molecules permeated through a dried ionomer and reached to the catalytic surface but there were few oxygen molecules that permeated through a hydrated ionomer and reached there. In addition, it is found that the shape of the ionomer in the case of water content rate γ = 3, 7, 11 changed.
Micro Rod Mixer Using AC Electric Field Induced Flow
Authors: Obara Hiromichi , Tashiro Shinichi
Published: June 2012

A novel rod mixer, using a micro-scale flow structure induced with electrokinetics under an AC electric field, is proposed for three-dimensional micro-scale processing of biological applications. Flow structures around the micro-rod mixer are demonstrated using the micro-particle image velocimetry method and the particle-tracking velocimetry method. Characteristics of the flow structure and mixing property are investigated for several electric field intensities and frequencies. It is observed that the micro-mixing flow structures induced with an AC electric field at the appropriate intensity and frequency conditions which are intermediate conditions between a dielectrophoresis and an electrolysis. A source-type three-dimensional flow structure is generated around the tip of the micro-rod electrode installed in the sample liquid. Furthermore it is possible to control the scale of the flow structure by adjusting the supplied AC electric field intensity and frequency. The mixing characteristics are also discussed.
Prediction of Flow Crossover in the GDL of PEFC Using Serpentine Flow Channel
Authors: Saha L. K. , Oshima N.
Published: June 2012

A serpentine flow channel is one of the most common and practical channel layouts for PEFCs since it ensures the removal of water produced in the cell with an acceptable parasitic load. The operating parameters such as temperature, pressure and flow distribution in the flow channel and GDL has a great influence on the performance of PEFCs. It is desired to have an optimum pressure drop because a certain pressure drop helps to remove excess liquid water from the fuel cell, too much of pressure drop would increase parasitic power needed for the pumping air through the fuel cell. In order to accurately estimate the pressure drop precise calculation of mass conservation is necessary. Flow crossover in the serpentine channel and GDL of PEFC has been investigated by using a transient, non-isothermal and three-dimensional numerical model. Considerable amount of cross flow through GDL is found and its influence on the pressure variation in the channel is identified. The results obtained by numerical simulation are also compared with the experimental as well as theoretical solution.
Electrical Detection of Pollen Allergen Using Electrode-Embedded-Micro-Channel
Authors: Kawaguchi Chihiro , Taniguchi Masateru , Tsutsui Makusu , Kawano Satoyuki , Kawai Tomoji
Published: June 2012

Hay fever is a disease that approximately 20 percent of the world population develop. Providing appropriate treatment for this plant-specific pollen allergy requires a method to identify various types of pollen. Here we introduce a technique that can be used for direct detections of single biological macromolecules such as pollen. Our method is based on two-probe current measurements using a microfluidic-channel-embedded-electrode system. A fabrication procedure of the device is as follows. First, we formed two gold nanoelectrodes by standard electron beam lithography and lift-off processes. The interelectrode gap distance was designed to be 500 nm. We then deposited a SiO2 layer. After that, we fabricated Cr etching mask. Finally, we dry-etched the sample by reactive ion etching and obtained a microfluidic-channel-embedded-electrode structure. We flowed HEPES(2-[4-(2-Hydroxyethyl)-1-piperazinyl] ethanesulfonic acid) solution containing pollen of 500 nm size into the micro-channel and simultaneously measured current flowing through the two electrodes. Characteristic spike-like signals were observed; sharp rise of the current followed by a rather smooth decrease to the base current level. We exhibited control experiments in a HEPES solution wherein no pollen was added and observed only featureless current traces. We anticipate that the sharp current rise is associated with trapping of a single cedar pollen between the electrodes whereas the gradual current decrease represents the pollen detrapping. We propose the technique for identifying several kinds of pollens based on the height and the width of the current spikes.