bluuebunny/crossref_metadata_2025 huggingface dataset:
Fully Developed Flow of Power-Law Fluid Through a Cylindrical Microfluidic Pipe: Pressure Drop and Electroviscous Effects
Authors: Bharti Ram P. , Harvie Dalton J. E. , Davidson Malcolm R.
Published: July 2009

Pressure drop and electroviscous effects in the axisymmetric, steady, fully developed, pressure-driven flow of incompressible power-law fluids through a cylindrical microchannel at low Reynolds number (Re = 0.01) have been investigated. The Poisson-Boltzmann equation (describing the electrical potential) and the momentum equations in conjunction with electrical force and power-law fluid rheology have been solved numerically using the finite difference method. The pipe wall is considered to have uniform surface charge density (S = 4) and the liquid is assumed to be a symmetric electrolyte solution. In particular, the influence of the dimensionless inverse Debye length (K = 2, 20) and power-law flow behaviour index (n = 0.2, 1, 1.8) on the EDL potential, ion concentrations and charge density profiles, induced electrical field strength, velocity and viscosity profiles and pressure drop have been studied. As expected, the local EDL potential, local charge density and electrical field strength increases with decreasing K and/or increasing S. The velocity profiles cross-over away from the charged pipe wall with increasing K and/or decreasing n. The maximum velocity at the center of the pipe increases with increasing n and/or increasing S and/or decreasing K. The shear-thinning fluid viscosity is strongly dependent on K and S, whereas the shear-thickening viscosity is very weakly dependent on K and S. For fixed K, as the fluid behaviour changes from Newtonian (n = 1) to shear-thinning (n < 1), the induced electrical field strength increases and maximum velocity reduces. On the other hand, the change in fluid behaviour from Newtonian (n = 1) to shear-thickening (n > 1) decreases the electrical field strength and increases the maximum velocity. The non-Newtonian effects on maximum velocity and pressure drop are stronger in shear-thinning fluids at small K and large S, the shear-thickening fluids show opposite influence. Electroviscous effects enhance with decreasing K and/or increasing S. The electroviscous effects show complex dependence on the non-Newtonian tendency of the fluids. The shear-thickening (n > 1) fluids and/or smaller K show stronger influence on the pressure drop and thus, enhance the electroviscous effects than that in shear-thinning (n < 1) fluids and/or large K where EDL is very thin.
Break Up of Viscous Crude Oil Droplets Mixed With Dispersants in Locally Isotropic Turbulence
Authors: Gopalan Balaji , Katz Joseph
Published: July 2009

Our objective is to visualize the breakup of crude oil droplets, mixed with dispersants, in a turbulent flow. The current measurements are performed for a sample crude oil from Alaska National Slope mixed with dispersant COREXIT 9527. The droplet breakup measurements are conducted in a nearly homogeneous and isotropic turbulence facility, the central portion of which is characterized using 2-D PIV. The droplet break up is visualized at high spatial and temporal resolution using one view high speed, in-line digital holography. Subsequent analysis reveals relevant length scales and timescales involved in the break up process.
Observation of a Critical Time Scale for Supercavitation Development and the Effect of Gas Leakage
Authors: Weiland Chris , Vlachos Pavlos
Published: July 2009

A critical time scale that describes the spontaneous growth of small stable cavities into developed supercavitation over blunt free flying cylindrical slug projectiles was observed experimentally. The projectiles were ejected using a modified gas-gun mechanism consisting of a barrel and explosive charge. Upon ignition, high pressure gases translated the projectiles down the launch barrel and into quiescent water where they were digitally imaged for analysis. Results indicate that the initially small cavities appeared downstream of the projectile forebody and grew up the projectile, partially or completely enveloping the projectile. This study introduces a mechanism to explain supercavity development over impulsively translated projectiles. As a projectile is accelerated from rest in the barrel a vortex ring is produced. Small nuclei present in the ambient flow field expand as they encounter the separated flow around the blunt forebody and become entrained in the vortex ring. The subsequent increase in vortex circulation as the projectile continues to accelerate causes the pressure in the vortex ring to drop below the Blake critical pressure, at which point the initially stable cavity rapidly grows. The small cavities grow from aft to fore as the supercavity develops, traveling at speeds up to 4 times the initial projectile velocity.
Effect of Rotational Velocity and Blade Angle of Attack on Mass Flow Rate in an Axial Fan at a Fixed Hub to Tip Ratio
Authors: Izadi Mohammad J.
Published: July 2009

In this investigation an attempt is made to find the best rotational velocity and the best angle of attack of a flat blade at a fixed hub to tip ratio for a maximum mass flow rate in an axial fan in a steady and turbulent conditions. In this study the blade angles are varied from 10 to 80 degrees and the rotational velocity is varied from 500 to 2500 RPM (50 to 200 rad/sec) for a number of blades from 2 to 6, at a fixed hub to tip ratio. The results show that, the maximum flow rate is achieved at the blade angle of attack of about 45 degrees when the number of blades is set equal to 4 at most rotational velocities. The numerical results show that as the rotational velocity increased, the mass flow rate increased, but at very high rotational velocities the mass flow rate remained constant.
Single Droplet Impingment: Effect of Nanoparticles
Authors: Shen Jian , Liburdy James , Pence Deborah , Narayanan Vinod
Published: July 2009

This study focuses on the dynamics of water and nanofluids droplet surface impingement. Droplets are generated by a piezoelectric driven droplet generator. A high-speed-high-resolution camera is used to record droplets impacting on a smooth heated silicon surface. Droplet impact velocity, spreading diameter, spreading height and dynamic contact angle are measured by image processing. Results of water and nanofluids are compared to determine effects of nanoparticles on spreading dynamics. It is concluded that the nanofluids result in larger spreading rates, larger spreading diameters and an increase in early stage dynamic contact angle.
Flow in Rectangular Cavities With Two Vertical Oscillating Walls
Authors: Ovando Guillermo E. , Beltran Alberto , Ovando Sandy L.
Published: July 2009

Fluid dynamics in a two-dimensional rectangular cavity with vertical oscillatory walls out of phase was studied numerically. The Navier-Stokes equations were solved using the finite element method. We analyzed the behaviour of the velocity fields, the vorticity fields and we also obtained the streaklines of the fluid at the bottom left corner of the domain for one and two cycles, which is associated with the mixing of the fluid. The analysis was carried out for three different Reynolds numbers of 50, 500 and 1000 with constant displacement amplitude of the moving boundaries of 0.2. For this range of parameters the flow is characterized by two kind of symmetries. We found that for lower Reynolds number there is a good local mixing given by cell structures and the smooth behavior of the fluid inside the cavity; however for higher Reynolds number these structures disappear due to the fluid near the vertical walls impinges against the corner of the cavity, then this fluid is dispersed through the whole cavity during the cycle, increasing the global mixing of the fluid.
Microfluidic Device for Synthesis of Lipid Bi-Layers
Authors: Banneyake B. M. R. U. , Banerjee Debjyoti
Published: July 2009

Lipid bi-layers are ubiquitous components of biological cells — and are found in variety of cell components ranging from cell membranes to membranes of organelles inside the cells. In biological membranes, lipid bi-layer membranes carry membrane proteins, which serve as single channel nanopores that are used to study transport of proteins and characterize the properties of proteins. However, lipid bi-layers have very short half lives, which are usually less than an hour. The lipid bi-layers are usually obtained by physico-chemical interactions between a lipid containing organic solvent, an aqueous buffer solution and a hydrophobic surface. We have developed a continuous flow through microfluidic device using pressure driven flow (by means of a tandem syringe pump system) for synthesis of lipid bi-layers. The microfluidic device consists of two glass substrates with micro-channels and microchambers microfabricated using photolithography and wet glass etching. The microchannels in each substrate is in the form of “+” shape and form a mirror image of each other. A Teflon sheet (∼200 microns thickness) is sandwiched between the glass substrates with a ∼200 microns diameter hole etched in the center to communicate with the two sets of microchannels. A lipid solution in an organic solvent (Pentane) and KCl buffer solution are alternately flown through the legs of the microchannel. The conductivity of the buffer is monitored using a current amplifier. The formation of the lipid bi-layer is confirmed by monitoring the resistivity and the impedance to high frequency electrical oscillations. The flow rate in the microfluidic device is optimized to obtain the lipid bi-layer.
Analysis of the Influence of Passage Components on the Efficiency of Bulb Tubular Pumps
Authors: Jin Yan , Liu Chao , Tang Fangping , Zhou Jiren , Cheng Li
Published: July 2009

For large discharge and low lift head, it is especially suitable to use tubular pumps for their economic characteristics. Tubular pumps have high efficiency, small hydraulic loss, compact unit structure, simple construction arrangement and low cost both for construction and running. Recently, in the east route of South to North Water Diversion Project in China, there are many low head and large discharge pump stations using tubular pumps. It is important to analyze the flow characteristics and performance of tubular pump. In this paper CFD method is used to simulate the whole flow passage in a bulb tubular pump which includes inlet passage, outlet passage, guide vane, bulb unit and supportings. Based on the RNG k–ε turbulent model with Wall-Function Law, the SIMPLE algorithm is applied for the solution of the discrete governing equations. The results of the calculation indicate that all of the flow passage components influence the efficiency of the tubular pump, especially the parts of guide vane unit and bulb section. The shape of the bulb and relative position of guide vanes and bulb supportings have important effects on total hydraulic losses of the pump. Reasonable supportings not only improve the turbulent flow, but also reduce circumference velocity. The efficiency of the pump after improving can be increased about 6%.
Self-Assembly of Particles Into 2D Lattices With Adaptable Spacing
Authors: Aubry N. , Nudurupati S. , Janjua M. , Singh P.
Published: July 2009

It was recently shown in [1–3] that spherical particles floating on a fluid-fluid interface can be self-assembled, and the lattice between them can be controlled, using an electric field. The technique works for a broad range of fluids and particles, including electrically neutral (i.e., uncharged) particles and small particles (micro- and nano-sized particles). In this paper we show that the technique also works for rod-like and cubical particles floating on fluid-fluid interfaces. The method consists of sprinkling particles at a liquid interface and applying an electric field normal to the interface, thus resulting in a combination of hydrodynamic (capillary) and electrostatic forces acting on the particles. It is shown that the relative orientation of two rod-like particles can be controlled by applying an electric field normal to the interface. The lattice spacing of the self-assembled monolayer of rods can be increased by increasing the electric field strength. Furthermore, experiments show that there is a tendency for the rods to align so that they are parallel to each other. The alignment however is not complete. Similarly, the spacing between two cubes, as well as the spacing of a monolayer of cubes, can be adjusted by controlling the electric field strength.
Numerical Simulation of the Backlayer Critical Velocity in the Memorial Tunnel Test (MTFVTP)
Authors: Blanco Eduardo , Cueto Javier , Ferna´ndez Joaqui´n , Barrio Rau´l
Published: July 2009

Road tunnels constitute key elements in the traffic net, especially for the long distance road transportation but also in the large urban areas. Although security preventions have permitted a relatively low index of accidents in tunnels, the analysis of the accidents in road tunnels during the last years shows an increment in both the number of cases and their gravity. In the case of fires, the control of the smoke propagation becomes crucial because the major risk for people is smoke inhalation rather than the direct exposure to the fire itself. Besides, a quick control of the fire requires that the access and evacuation routes are maintained without smoke. However, research in this field has been limited by the difficulties inherent in the problem, and so there are few experimental data available. This paper pursues the study of the control of the smoke propagation in tunnel roads with a longitudinal air stream. The methodology is based on the numerical simulation of the time evolution of the air and smoke flows induced after the onset of localized fires of different magnitude. Specifically, 10, 20, 50 and 100 MW fires were simulated. A general purpose computational fluid dynamics software is used for this investigation, due to its ability to model multi-species three-dimensional unsteady flows. The general purpose of the paper is the refinement and contrast of a numerical procedure for the simulation of fire tunnels with natural and longitudinal ventilation, as the particular case with the most complex and restrictive conditions, and the use of such procedure to study the backlayering phenomenon. The obtained results were compared with the natural and longitudinal ventilation tests of the Memorial Tunnel test as well as with previous studies.
An Analytical and Experimental Study of Rotary-Vane Turbomachinery: Single-Phase Working Fluids
Authors: Mehdizadeh A. , Mahmoud A. M. , Sherif S. A. , Lear W. E.
Published: July 2009

Rotary machines have played an important role for many years in refrigeration and air compression applications because of their inherent simplicity and reliability. They are also very attractive machines since as positive displacement devices; they are more suitable for low flow rates (low specific speeds). In this paper, the thermodynamic and fluid mechanic characteristics of a rotary-vane air-motor are analyzed. The optimum geometrical and operational characteristics of the machine are presented. Experiments are conducted to understand the working principles and operational constraints of the machine. This study also helps formulate design procedures that can be utilized to modify air-motors into optimized expanders for single-phase flow applications. The model has been used to evaluate geometrical parameters such as the optimum intake and exhaust port locations, their spreads and the geometric volume ratio, as well as evaluating performance parameters such as the work produced and the mechanical, isentropic and total efficiencies of the machine. It is anticipated in a follow-up study that the model developed will be the basis for an expander design tool that uses two-phase working fluids in relevant industrial applications.
Performance of a Multi-Path Ultrasonic Flowmeter in Water Flow
Authors: Zheng Yuan , Huang Yu , Tong Chen-Guang , Qu Bo
Published: July 2009

According to the difficulties in the flow measurement of the complicated flow channel in a pump station of China South-to-North Water Transfers project, study on the measuring way for ultrasonic flowmeter working in the complicated flow channel and large flow condition. Simplify the model through CFD numerical calculation, and propose a new method for ultrasonic flowmeter to work in complicated flow channel. Through model experiment, find that in the way which 8 ultrasonic transducers are cross arranged, the weight of each acoustic path is 0.125, and get the proportion of the average velocity measured in the model experiment and the actual flow with this weight, and the proportion is 0.137519. The section to computation the flow in the model is the section whose radius is 0.209m, and the actual section in the field is the section whose radius is 2.09m. The measurement error in the experiment is within ±2%, and the error in the rated condition is ±0.6%, which can satisfy the engineering demand. This proves that it is feasible to measure the flow in a pump station of China South-to-North Water Transfers project with the Model 7510 ultrasonic flowmeter produced by the ACCUSONIC Co. of America, and it can satisfy the accuracy demand of field measurement.
An Active Micromixer Enhances Mixing by Rotating Shuttlecock Rotor
Authors: Dinh Thien Xuan , Ogami Yoshifumi
Published: July 2009

Mixing performance of an active mixer which mixes two fluids by three-dimensional flow surrounding a rotating shuttlecock rotor in continuous flow is numerically investigated. The mixer consists of a step contraction-expansion microchannel and a shuttlecock micro-rotor placed in the step. The obtained results show that mixing quality of solution does not depend on neither rotation speed nor mean velocity in the mixer, but rather on the ratio of tip paddle velocity of the rotor to the mean velocity (i.e. Strouhal number). Streaklines demonstrate that two fluids from the inlet can penetrate into the space between the paddles of the rotor, and then are mixed here before flowing to the exit channel. In small Strouhal number (∼10) cases, two fluids are twisted 90 degrees after passing the rotor region. In the other words, mixing in downstream flow behind the rotor takes place in the height instead of the width of the exit channel, which makes the mixer applicable for channels with high aspect ratio of the cross section. It is observed that mixing is dominantly enhanced in the rotor region and increasing Strouhal number results in faster mixing in the mixer.
Study on Setting of One-Way Surge Tank in Long Water Supply Engineering
Authors: Hu Jianyong , Zhang Jian , Lu Weihua , Ma Shibo
Published: July 2009

One-way surge tank is an important measure of water hammer protection in long water supply engineering. It can control the negative pressure efficiently and prevent pipeline from column separation. Setting one-way surge tank in proper place along pipeline is relative to the safety of long water supply engineering. Principle of Setting one-way surge tank is made through theoretical analysis detailedly. It is obviously that result of theoretical analysis is conservative because attenuation of water hammer is ignored, but theoretical analysis provide an proper approach for setting one-way surge tank. Based on result of theoretical analysis, optimization setting is obtained through numerical simulation.
ND-YAG Monitoring for DGV Application (Keynote Paper)
Authors: Morrison G. L. , Nelson B.
Published: July 2009

Doppler Global Velocimeters (DGV) requires a narrow bandwidth laser beam which can be accurately tuned to a desired frequency. One laser used for this application is an ND-YAG which is seeded using a laser diode. By adjusting the laser diode output, the frequency of the ND-YAG laser beam can be modified. This technique also narrows the bandwidth of the laser frequency to below 100 MHz. Monitoring this output is difficult due to the 9 ns pulse duration which makes normal interferometry techniques ineffective for the 10 to 20 MHz frequency resolution required. This paper will describe a system constructed to monitor the frequency in real time which can be used in conjunction with a DGV system to correct for laser frequency drift. The particular ND-YAG system response and stability will be presented and discussed in relationship to DGV system accuracy.
Discharge Measurements Using the Classic Gibson Method With Instrumentation Installed Inside a Pipeline
Authors: Adamkowski Adam , Janicki Waldemar , Urquiza Gustavo , Kubiak Janusz , Basurto Miguel
Published: July 2009

The Gibson method (pressure-time method) is one of the basic methods of discharge (flow rate) measurement applied in hydropower plants. Flow rate is determined by integrating the recorded variation of pressure difference between two measuring (hydrometric) sections in a pipeline (penstock). The Gibson method in its classic version consists in direct measurement of pressure difference variation between two hydrometric sections of a pipeline. Particular difficulties, related to application of the method in its various versions, arise in conditions of no access to the hydrometric sections from the outside of a pipeline. In such cases, it is necessary to install dedicated measuring instrumentation inside the pipeline. Such instrumentation has been implemented for the purpose of efficiency tests of two Francis turbines (upgraded and not upgraded) fed from a common penstock of 10 m diameter. The hydrometric sections were furnished with pressure taps connected by means of small copper tubes (impulse tubes) and hermetic manifolds to the differential pressure transducer. The transducer was installed in a hermetic housing and its electric signal was sent from the inside of the penstock to a computer data acquisition system. Using this method, the efficiency characteristics of the tested hydraulic turbines were determined. According to the authors’ knowledge, the pressure-time method has not been used in such an application so far. The method under consideration requires transmitting pressure signals from both penstock sections to the differential pressure transducer by means of impulse tubes. This raises the question on the influence exerted by dynamic properties of the connecting pipes / transducer system on the discharge measurement results. The previously developed computational method incorporating dynamic models of the piping and the transducer has been applied in order to determine this influence. In result of calculations conducted, the piezometric tubes / transducer system has been found to exert a negligible influence on the discharge measurement results.
Acoustic Doppler Current Profiler (ADCP) Measurements of Breaking Waves
Authors: Fullerton Anne M. , Fu Thomas C.
Published: July 2009

Detailed flow measurements of the turbulent multiphase flow associated with wave breaking present a unique instrumentation challenge. Measurement systems must be capable of high sampling rates, large dynamic ranges, and be capable of making measurements in water, air and optically opaque regions. An experiment was performed at the Naval Surface Warfare Center, Carderock Division, in October 2007 to measure various characteristics of the breaking wave generated from a submerged ship transom. The primary objective of this work was to obtain full-scale qualitative and quantitative flow field data of a large breaking transom wave over a range of conditions, specifically transom drafts and Froude numbers. Several types of measurements were made on the transom stern wave during this experiment, however, this paper will focus on the Nortek Acoustic Wave and Current (AWAC) profiler measurements of the stern wake. The AWAC has a center acoustic beam in addition to the three angled beams typically found on an acoustic Doppler current profiler. The trends of the acoustic return from the AWAC and the trends of the bubble density and location on the water surface compare well, and it is anticipated that this return can be related to void fraction and bubble measurements in the future. This type of non-intrusive measurement could be very useful in the evaluation of breaking waves.
Optimization of Stacking Line and Blade Profile for Design of Axial Flow Fan Blade
Authors: Samad Abdus , Lee Ki-Sang , Kim Kwang-Yong
Published: July 2009

This work presents a numerical optimization procedure for a low-speed axial flow fan blade with weighted average surrogate model. Reynolds-averaged Navier-Stokes equations with SST turbulence model are discretized by finite volume approximations and solved on hexahedral grids for flow analyses. The blade profile as well as stacking line is modified to enhance blade total efficiency, i.e., the objective function. Six design variables related to blade lean and blade profile are selected, and a design of experiments technique produces design points where flow analyses are performed to obtain values of the objective function. PBA model is employed as a surrogate model for optimization. A search algorithm is used to find the optimal design in the design space from the constructed surrogate model for the objective function. As a main result, the efficiency is increased effectively by the present optimization procedure.
Unsteady Three-Dimensional Flow Phenomena in an Axial Flow Pump at Different Operating Points
Authors: Benra Friedrich-Karl , Dohmen Hans Josef
Published: July 2009

In highly loaded axial flow pumps considerable changes of the flow behavior are known when altering the flow rate from design point operation to part load operation. The flow structure which is changing from stable operating conditions to stalled flow conditions has been investigated experimental by Kosyna and Stark. The measured results are compared to results obtained by numerical simulations in a previous paper of the authors. Time dependent three dimensional flow fields in this axial flow pump have been investigated by unsteady Reynolds averaged Navier-Stokes simulations. The time resolved flow fields are compared to the time averaged results of the measurements for the design point and also for part load operating conditions. The change in the vortex structure induced by the tip leakage flow is investigated in detail for different conditions of operation. Also the part load recirculation vortex dominating the rotor tip flow at deep stall conditions as well as the cross passage vortex is visualized by evaluating the numerical results.
Observations on Flame Stretching in a Room Model With Natural Vent
Authors: Chow W. K. , Law C. K.
Published: July 2009

Flame stretching in a room with a ceiling vent will be discussed in this short note. A small model was constructed with a pool fire placed inside. Another pool fire of the same size and amount of fuel was burnt outside the model. The flame lengths of the two fires were measured and compared. It is observed that the flame length of the pool fire inside the model was higher than that outside. The value was even double at the later stage of the fire.
Numerical Simulation of Natural Convection Flow in a Cube With a Horizontal Heated Strip
Authors: Alawadhi Esam M.
Published: July 2009

Natural convection flow in a cube with a heated strip is solved numerically. The heated strip is attached horizontally to the front wall and maintained at high temperature, while the entire opposite wall is maintained at low temperature. The heated strip simulates an array of electronic chips The Rayleigh numbers of 104, 105, and 106 are considered in the analysis and the heated strip is horizontally attached to the wall. The results indicate that the heat transfer strongly depends on the position of the heated strip. The maximum Nusselt number can be achieved if the heater is placed at the lower half of the vertical wall. Increasing the Rayleigh number significantly promotes heat transfer in the enclosure. Flow streamlines and temperature contours are presented, and the results are validated against published works.
Experimental and Computational Analysis of Natural Convection Over Flat Plate
Authors: Afroz Farhana , Feroz Chowdhury Md.
Published: July 2009

Natural convection heat transfer over a flat plate with a heat source at bottom side of plate is studied experimentally and numerically. We consider the two-dimensional problem of both steady and unsteady natural convection over the flat plate at vertical, horizontal and inclined position. Experimental analysis is done for three different constant heat fluxes for each angle position. The Navier-Stokes and Energy equations with the Boussinesq approximation are written in Cartesian coordinate system. The problem is solved in the physical variables on the basis of a completely implicit Finite element Method order to examine the heat transfer characteristics. To see the effects of different angle position phenomena of natural convection over flat plate, the computational results presented in the form of streamlines for a wide range of Grashof number at different heat fluxes. The average Nusselt number of heated plate for different angle position has been observed.
Comparison of Vacuum Glazing Thermal Performance Predicted Using Two and Three Dimensional Models and Their Experimental Validation
Authors: Fang Yueping , Hyde Trevor J. , Hewitt Neil , Eames Philip C. , Norton Brian
Published: July 2009

The thermal performance of vacuum glazing was predicted using two dimensional (2-D) finite element and three dimensional (3-D) finite volume models. In the 2-D model, the vacuum space, including the pillar arrays, was represented by a material whose effective thermal conductivity was determined from the specified vacuum space width, the heat conduction through the pillar array and the calculated radiation heat transfer between the two interior glass surfaces within the vacuum gap. In the 3-D model, the support pillar array was incorporated and modeled within the glazing unit directly. The difference in predicted overall heat transfer coefficients between the two models for the vacuum window simulated was less than 3%. A guarded hot box calorimeter was used to determine the experimental thermal performance of vacuum glazing. The experimentally determined overall heat transfer coefficient and temperature profiles along the central line of the vacuum glazing are in very good agreement with the predictions made using the 2-D and 3-D models.
Multidisciplinary Placement Optimization of Heat Generating Semiconductor Logic Blocks
Authors: Suwa Tohru , Hadim Hamid
Published: July 2009

A multidisciplinary optimization methodology for placement of heat generating semiconductor logic blocks on integrated circuit chips is presented. The methodology includes thermal and wiring length criteria, which are optimized simultaneously using the genetic algorithm. An effective thermal performance prediction methodology based on a superposition method is used to determine the temperature distribution on a silicon chip due to multiple heat generating logic blocks. Using the superposition method, the predicted temperature distribution in the silicon chip is obtained in much shorter time than with a detailed finite element model and with comparable accuracy. The main advantage of the present multidisciplinary design and optimization methodology is its ability to handle multiple design objectives simultaneously for optimized placement of heat generating logic blocks. Capabilities of the present methodology are demonstrated by applying it to several standard benchmarks. The multidisciplinary logic block placement optimization results indicate that the maximum temperature on a silicon chip can be reduced by up to 7.5°C, compared with the case in which only the wiring length is minimized.
Numerical Simulation on Melting and Solidification of a Phase-Change Material in an Aluminum Plate-Fin Thermal Storage
Authors: Lv Minhui , Peng Hao , Ling Xiang
Published: July 2009

The numerical simulation on melting and solidification process of a phase-change material (PCM) in an aluminum plate-fin thermal storage was performed in this paper. The phase-change material-naphthalene was stored in the stacked passages with fins while water flew along other adjacent passages with fins as the heat transfer fluid (HTF). The PCM stored or released a large amount of heat during melting or solidification. A three-dimensional numerical model was performed to investigate the effect of flow parameters (inlet temperature and flow velocity of HTF) on the melting and solidification time. The results indicated that the rate of phase change was strongly dependent on the inlet temperature and flow velocity of HTF during storing or releasing heat. And the detail description of solidification process were discussed and presented.
Josef Stefan and His Contributions to Heat Transfer
Authors: Crepeau John
Published: July 2009

Josef Stefan was a professor of physics at the University of Vienna between 1863 and 1893. During his time in Vienna he was a fruitful researcher in many scientific fields, but he is best known for his work in heat transfer. He was a gifted experimentalist and theoretician who made contributions to conduction, convection and radiation heat transfer. Stefan was the first to accurately measure the thermal conductivity of gases, using a device he invented called the diathermometer. He also determined the diffusion of two gases into each other, a process now known as Maxwell-Stefan diffusion. His work provided experimental verification of the newly formulated kinetic theory of gases published by the great Scottish physicist James Clerk Maxwell. Stefan also experimentally studied the motion of gases induced by evaporation along a liquid surface, a phenomenon known as Stefan flow. In addition, Stefan received data from various expeditions on ice formation in the arctic seas. From that solid/liquid phase change data, he formulated solutions to the moving boundary problem, now called the Stefan problem. The work for which he is most famous is the T4 radiation law which he deduced from the experimental work of a number of investigators. However, his theory was not widely accepted until his former student, Ludwig Boltzmann, derived the same relation from first principles. In their honor, the T4 radiation equation is called the Stefan-Boltzmann law. Despite his varied contributions, little is known about Stefan the man. This paper gives some details on his life and describes the seminal work he performed in broad areas of heat transfer.
Pyrolysis Modeling in a Woodstove
Authors: Gupta Rajesh
Published: July 2009

A simple empirical model for predicting the pyrolysis rate of fuel packed bed of a woodstove has been presented. The thermolytic behavior of the fuel bed has been approximated by a pseudo-first order reaction. The reaction rate constant has been determined as function of temperature. The effect of orientation of twigs in the fuel bed arrangement and twig diameter on the reaction rate constant has been analyzed. It has been concluded that the effect of twig orientation is insignificant while the peak magnitude of reaction rate constant increased with increasing twig diameter.
Development of a Flow Regime Map for a Horizontal Pipe With the Multi-Classification Support Vector Machines
Authors: Tam L. M. , Ghajar A. J. , Tam H. K. , Tam S. C.
Published: July 2009

For horizontal circular pipes under uniform wall heat flux boundary condition and three different inlet configurations (re-entrant, square-edged, bell-mouth), Ghajar and Tam (1995) developed flow regime maps for the determination of the boundary between single-phase forced and mixed convection using experimental data of Ghajar and Tam (1994). Based on the ratio of the local peripheral heat transfer coefficient at the top and the bottom, the heat transfer data was classified as either forced or mixed convection among the different flow regimes. The forced-mixed convection boundary was then obtained by empirical correlations. From the flow maps, heat transfer correlations for different flow regimes were recommended. Recently Trafalis et al. (2005) used the Multiclass Support Vector Machines (SVM) method to classify vertical and horizontal two-phase flow regimes in 4 pipes with good accuracy. In this study, the SVM method was applied to the single-phase experimental data of Ghajar and Tam (1994) and new flow regime maps were developed. Five flow regimes (forced turbulent, forced transition, mixed transition, forced laminar, mixed laminar) were identified in the flow maps using Reynolds and Rayleigh numbers as the identifying parameters. The flow regimes on the boundaries of the new maps were represented by the SVM decision functions. The results show that the new flow regime maps for the three types of inlets can classify the forced and mixed convection experimental data in different flow regimes with good accuracy.
Thermal-Structural Analysis of the MacArthur Maze Freeway Collapse
Authors: Noble Charles R. , Wemhoff Aaron P. , McMichael Larry D.
Published: July 2009

At approximately 3:41 AM on the morning of April 29, 2007, a tractor-trailer rig carrying 8,600 gallons (32.6 m3) of fuel overturned on Interstate 880 in Oakland, CA. The resultant fire weakened the surrounding steel superstructure and caused a 50-yard (45.7 m) long section of the above connecting ramp from Interstate 80 to Interstate 580 to fail in approximately 18 minutes. In this study, we performed a loosely-coupled thermal-structural finite element analysis of the freeway using the LLNL Engineering codes NIKE3D, DYNA3D and TOPAZ3D. First, we applied an implicit structural code to statically initialize the stresses and displacements in the roadway at ambient conditions due to gravity loading. Next, we performed a thermal analysis by approximating the tanker fire as a moving box region of uniform temperature. This approach allowed for feasible calculation of the fire-to-structure radiative view factors and convective heat transport. We used a mass scaling methodology in the thermal analysis to reduce the overall simulation time so an explicit structural analysis could be used, which provided a more computationally efficient simulation of structural failure. Our approach showed structural failure of both spans due to thermal softening under gravity loading at approximately 20 minutes for a fixed fire temperature of 1200°C and fixed thermal properties. When temperature-dependent thermal properties were applied, the south and north spans collapsed at approximately 10 minutes and 16 minutes, respectively. Finally, we performed a preliminary fully-coupled analysis of the system using the new LLNL implicit multi-mechanics code Diablo. Our investigation shows that our approach provides a reasonable first-order analysis of the system, but improved modeling of the transport properties and the girder-box beam connections is required for more accurate predictions.
Transient Natural Convection From a Vertically Embedded Heat Source in a Thermally Stratified Porous Layer
Authors: Zhang J. , Lai F. C.
Published: July 2009

Numerical results are presented for transient natural convection from a heat source vertically embedded in a saturated porous layer. The porous layer is initially thermally stratified with a negative temperature gradient. The effects of the source strength and its buried depth on the penetration of convective flows are investigated. The results, which include the buoyancy-induced flow patterns and temperature profiles, as well as the heat transfer coefficient in terms of the Nusselt number, are presented for a wide range of base Rayleigh number and stratification parameter. The results thus obtained have important implications for applications in geothermal energy and underground disposal of nuclear wastes.
Optimization of Combined Cycle Power Plant Using Sequential Quadratic Programming
Authors: Meigounpoory Mohammad Reza , Ahmadi Pouria , Ghaffarizadeh Ahmad Reza , Khanmohammadi Shoaib
Published: July 2009

The thermal-economic optimization of a combined cycle power plant (CCPP) which can provide 140 MW of electrical power is discussed in this paper. The CCPP is composed of a gas turbine cycle (including, air compressor, combustion chamber, gas turbine), heat recovery steam generator (HRSG), steam turbine, condenser system, and a pump. The design parameters of such a plant are compressor pressure ratio (rAC), compressor isentropic efficiency (ηAC) gas turbine isentropic efficiency (ηGT), and turbine inlet temperature (T3), pinch difference temperature (ΔTpinch), steam turbine inlet temperature (Ta), steam turbine isentropic efficiency (ηST), and pump isentropic efficiency (ηPUMP). The objective function was the total cost of the plant in terms of dollar per second, including sum of the operating cost related to the fuel consumption, and the capital investment for equipment purchase and maintenance costs. The optimal values of decision variables were obtained by minimizing the objective function using sequential quadratic programming (SQP). The effects of change in the demanded power and fuel price on the design parameters werestudied for, 100, 120, and 140MW of net power output.
Thermal Homogenization in Spherical Reservoir by EHD Conduction Phenomenon
Authors: Yazdani Miad , Seyed-Yagoobi Jamal
Published: July 2009

Electrohydrodynamic (EHD) conduction phenomenon involves the interaction of electric field and flow field in a dielectric fluid medium via the process of dissociation and recombination of free charges. This paper numerically studies the effect of electric conduction phenomenon on the mixing mechanism of two fluids with identical physical properties but separated due to the non-homogeneity of the temperature field. The fluid is designated to be restored in a spherical reservoir and it is not spontaneously mixed since the reservoir is predicted to be located in non-gravity environment. The electrodes are embedded on the reservoir surface such that the resultant electric body force causes the fluid with higher temperature mixes with the colder fluid and vice versa. The electric field and electric body force distribution and the resultant velocity field are presented. The results are illustrated in the form of time evolution of temperature distribution inside the reservoir. The effects of primary dimensionless numbers on the mixing time are studied.
A Novel Gas-Water Heat Exchanger With Minichannels
Authors: Chen Yang , Lundqvist Per , Palm Bjo¨rn
Published: July 2009

In the current study, a novel gas water heat exchanger with minichannels is designed, built and tested. The heat exchanger is mainly composed of a number of concentric ring shaped plates, which are made up of several heat exchanger tubes. The ring shaped plates are arranged in parallel and placed in a shell. The heat exchanger is designed as a counter current heat exchanger with laminar flow on the heat exchanger’s shell-side (gas side) and therefore has a very low pressure drop on the shell side. The heat exchanger was tested with water and hot air on its tube-side and shell-side respectively. All the necessary parameters like inlet and outlet temperatures on tube-side and shell-side as well as the pressure drop, flow rate of fluids, etc. were measured. Different existing correlations were used to calculate the overall heat transfer coefficient and the results were compared with the measured value. The measured results show that the new designed heat exchanger can achieve a good heat transfer performance and also maintain a low pressure drop on shell-side (gas side).
Heat Transport Capability and Fluid Flow Neutron Radiography of Three-Dimensional Oscillating Heat Pipes
Authors: Borgmeyer B. , Wilson C. , Winholtz R. A. , Ma H. B. , Jacobson D. , Hussey D.
Published: July 2009

An experimental investigation into the parameters affecting heat transport in two three-dimensional oscillating heat pipes (OHP) was implemented. A three-dimensional OHP is one in which the center axis of the circular channels containing the internal working fluid do not lie in the same plane. This novel design allows for more turns in a more compact size. The OHPs in the current investigation is made of copper tubing (3.175 mm OD, 1.65 mm ID) wrapped in a three-dimensional fashion around two copper spreaders that act as the evaporator and condenser. The two OHPs have 10 and 20 turns in both the evaporator and condenser. The 20 Turn OHP was filled to 50% of the total volume with high performance liquid chromatography (HPLC) grade water. Transient and steady state temperature data was recorded at different locations for various parameters. Parameters such as heat input, operating temperature, and filling ratio were varied to determine its effect on overall heat transport. Neutron radiography was simultaneously implemented to create images of the internal working fluid flow at a rate of 30 frames per second (fps). Results show the average temperature drop from the evaporator to condenser decreases at higher heat inputs due to an increase in temperature in the condenser region caused by greater oscillations. These large oscillations were visually observed using neutron radiography. As the operating temperature is increased, the thermal resistance is reduced due to increased fluid flow caused by changes in fluid properties. A decrease in filling ratio tends to create more steady fluid motion; however, the heat transfer performance is reduced.
Measurements of Bubble Nucleation Characteristics in Pool Boiling of a Wetting Liquid on Smooth and Roughened Surfaces
Authors: McHale John P. , Garimella Suresh V.
Published: July 2009

Quantitative measurements are obtained from high-speed visualizations of pool boiling at atmospheric pressure from smooth and roughened surfaces, using a perfluorinated hydrocarbon (FC-77) as the working fluid. The boiling surfaces are fabricated from aluminum and prepared by mechanical polishing in the case of the smooth surface, and by electrical discharge machining (EDM) in the case of the roughened surface. The roughness values (Ra) are 0.03 and 5.89 micrometers for the polished and roughened surfaces, respectively. The bubble diameter at departure, bubble departure frequency, bubble terminal velocity, and active nucleation site density are measured from the monochrome movies, which are recorded at 8000 frames per second with a digital CCD camera and magnifying lens. Results are compared to predictions from existing models of bubble nucleation behavior in the literature. Wall superheat, heat flux, and heat transfer coefficient are also reported.
Reverse Monte Carlo Modeling of Signal Transport in Light-Pipe Radiation Thermometers
Authors: Erturk Hakan , Ezekoye Ofodike A. , Howell John R.
Published: July 2009

Rapid thermal processing (RTP) has been widely used by the semiconductor manufacturing industry. Light-pipe radiation thermometers are the predominant method to monitor the wafer temperature during rapid thermal processing. The errors associated with light-pipe measurements are great concerns across the industry due the extreme temperature sensitivity of the processes used to fabricate semiconductor devices during rapid thermal processing. Modeling of the light-pipes has helped understand the signal transport process and errors associated with the light pipe measurements. However, due to the smaller size of the light-pipe sensor area with respect to the total system area full scale modeling of such a system including the light pipe thermometer have not been possible due to the computational demand. In this paper, a reverse Monte Carlo method is developed to model the signal transport through a light-pipe thermometer used in a RTP system. The Monte Carlo model considers the spectral and angle dependent optical properties of the chamber and quartz materials. The reverse Monte Carlo model is applied to a simpler system with a quartz light pipe probe for verification against a model developed using a forward Monte Carlo method.