bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantification of Discretization Error in Wall Shear Stress Calculations for Aneurismal Flows Using CFD
Authors: Pino-Romainville Francisco A. , Nanduri Jagannath R. , Celik Ismail B. , Rai Ansaar T.
Published: July 2009

Many recent studies suggest that hemodynamic factors such as wall shear stress (WSS) and pressure contribute to the genesis and growth of intracranial aneurysms. Recently there have been a number of computational hemodynamics studies that calculate the values of wall shear stress in arterial and aneurismal flows. However there is a lack of comprehensive error analysis in many of the computational hemodynamics studies. This is perhaps the reason for speculative and ambiguous conclusions drawn by various studies as to the nature of wall shear stress responsible for aneurysm growth. In the current study, geometry involving an actual aneurysm is built from angiogram images. Another geometry consisting of the primary artery where the aneurysm formed is also built by removing the aneurysm volume. The two geometries are meshed using three different grid densities. Second order schemes are used to simulate the pulsatile hemodynamics through each of the geometries. Various representative planes along the geometries are considered and the major flow variables and WSS are plotted as a function of grid densities. The procedure for estimation of discretization error, suggested by ASME Journal of Fluids Engineering, is applied at various representative locations along the aneurysm and arterial geometry. The results suggest high dependence of calculated WSS on local grid density. The contours of WSS in the arterial geometry suggest that high WSS does not necessarily occur at the location where the aneurysm originated. Possible remedies are suggested so that this uncertainty could be eliminated from future studies.
Numerical Analysis on the Performance of the Solid Solar Particle Receiver With the Influence of Aerowindow
Authors: Chen Zhuoqi , Chen Yitung , Tan Taide
Published: July 2009

In this research work, a three dimensional model of the solid solar particle receiver (SPR) with the influence of aerowindow is analyzed. The free-falling down particles will form a solid particle curtain and be directly heated up by the reflected concentrating solar energy which passes through the aperture of the cavity. The mass, momentum and energy exchange between the solid particle phase and gas fluid phase are simulated by the two-way coupling Euler-Lagrange method. A discrete ordinate radiative transfer method has been applied to study the coupling of radiative heat transfer and the falling particle curtain. The realizable κ-ε model is used in the investigation of turbulence flow. In order to predict the performance of the SPR, the aerodynamic behavior of the particles and thermal interaction, which include particle-particle radiation, particle-wall radiation, particle-air convection, and air-wall convection are analyzed and demonstrated in this work. All the investigation on the simulation model is focusing on optimizing the performance of the SPR. The parametric studies of the performance of the SPR with aerowindow are investigated under the different working conditions, such as air injection velocity, particle mass flow rate, and the efficiency of the SPR and exit average particle temperature are compared upon these conditions.
Vibration-Based Fault Diagnosis of Pump Using WPT
Authors: Hong Pan , Yuan Zheng
Published: July 2009

A vibration-based fault diagnosis method of pump units based on wavelet packet transform (WPT) is proposed in this paper. Compared with Fourier transform (FT) and wavelet transform (WT), WPT can subdivide the whole time-frequency domain. It can perform signals with good time resolution at high frequency and vice versa. WPT is considered as a good tool to signal denoising, accounting for its perfect ability in decomposing and reconstructing signal and its characteristic of no redundancy and divulges after denoising. In addition, WPT modulus maximal coefficient provides a simple but accurate method in calculating the Lipschitz exponents, which is the measurement of signal singularity. According to the singularity analysis results of vibration signal, we can recognize the fault pattern of pump units. This paper makes a detail research on signal denoising and singularity analysis based on WPT. Taking the main shaft and thrust bearing vibration signal for example, the experimental results show that WPT is effectively in the fault diagnosis system of pump unit.
Optimized High-Aspect-Ratio Diffusional Micromixers
Authors: Maha Amit , Palaparthy Vamsidhar , Soper Steven A. , Murphy Michael C. , Nikitopoulos Dimitris E.
Published: July 2009

This part of our work has been aimed at designing, manufacturing and characterizing effective micro-mixers which are cheap, durable and easily integrated on a variety of bio-chips with emphasis on those performing Polymerese Chain Reactions (PCR) and Ligase Detection Reactions (LDR). A key contribution is the development of an optimization procedure for the design of passive micro-mixers utilizing high-aspect-ratio micro-channels (HARMC). The optimization procedure identifies the optimum type of mixer on the basis of the flow rate proportions of the mixture constituents and provides for two optimum designs of the selected mixer type for an aspect ratio of choice in two ways: (a) for specified mixture volume and mixer pressure drop the optimum mixer dimensions and operating condition minimize the total production time and (b) for specified mixture volume and a total production time the optimum mixer dimensions and operating condition minimize the mixer pressure drop. The simplest and easiest to manufacture layout of an optimized mixer configuration (X2JC) with two inlet ports and three layers is shown in Figure 1. The injection of compound 1 into the compound 2 main stream is performed through two side-jets in a wider channel to further reduce the pressure loss overhead followed by a contraction into the main mixing channel.
Investigating Behavior of Hydrogen Bubbles in Electro-Chemical Machining
Authors: Tsuboi Ryo , Yamamoto Makoto
Published: July 2009

Electro-Chemical Machining (ECM) is an advanced machining technology and has been applied to highly specialized fields, such as aerospace, aeronautics, and medical industries. However, some problems remain to be solved. The efficient tool-design, electrolyte processing, and disposal of metal hydroxide sludge are typical problems. To solve such problems, CFD is thought to have potential as a powerful tool. However, a numerical method that can satisfactorily predict the ECM process has not been established because of the complex flow natures. In a previous study, we presented a new model to simulate the flow fields in an ECM process. This model is based on a two-way coupling method, taking the interaction between gas and liquid phases into account. In this coupling method, we assumed that electrolyte and generated hydrogen bubbles over a cathode surface have the same velocity. Therefore, we could simplify the governing equations. Since the flow field had a non-uniform density distribution due to hydrogen bubbles, a low Mach number approximation was applied to solve the pressure Poisson equation. In the present study, we calculate hydrogen bubble trajectories and investigate the distribution and a behavior of hydrogen bubbles. Since hydrogen bubbles follow fluid well, they travel along the stream line. This is because hydrogen bubbles have small density. In the results, around the low velocity region, hydrogen bubbles remain there with making the spiral structure. Hydrogen particles remain more in the suction side than that in the pressure side of the blade.
Transient Calculations of Pump Performance Parameters
Authors: Strongin Mikhail P.
Published: July 2009

The oscillations of pump performance parameters like head and power corresponding to a wide range of flow-rate values are investigated in the present paper. A centrifugal double suction industrial pump is studied with comparison of test, steady state and averaged transient results. Different turbulence closure models, such as k-ω, and k-ω SST were used. The oscillation behavior of the head and the power of pump is studied for three different pump geometries. The pump model consists of suction, impeller and discharge parts which are meshed and calculated together. This, for instance, naturally permits the effects of non uniformity of velocity distribution on the impeller eye and on the inlet of the discharge segment to be taken into account. The commercial code Fluent 6.3.26 is used for the CFD computations. The results show much better agreement of the test data with averaged transient calculations compared with steady state calculations, especially far away from best efficiency point on the performance curve. Besides, an interesting transient effect, doubling of the frequency of pump parameters oscillations (compared with the blade passing frequency w = n*N) is observed.
A Material Interface Transition Algorithm for Multiphase Flow
Authors: Francois Marianne M. , Lowrie Robert B. , Dendy Edward D.
Published: July 2009

Volume tracking method, also referred to as the volume-of-fluid (VOF) method introduces “numerical surface tension” that breaks a filament into a series of droplets whenever the filament is under-resolved. Adaptive mesh refinement can help avoid under-resolution, but a fully-developed flow will still generate filaments that cannot be resolved without enormous computational cost. We propose a complementary new approach that consists of transitioning to a continuous interface representation (i.e. without interface reconstruction) in regions of under-resolved interfacial curvature where volume tracking has become erroneous. The price of the continuous interface treatment is a small amount of numerical mass diffusion, even if the physical interface is immiscible. However, we have found that for certain measures, the overall accuracy is greatly improved by using our transitioning algorithm. The algorithm is developed in the context of the single fluid formulation of the incompressible Navier-Stokes equations. Numerical standard vortices advection test cases and Rayleigh-Taylor instability computations are presented to illustrate the transition algorithm potential.
Annular Flow Experimental Study in Horizontal Pipes Using Radial Proximity Probes
Authors: Libreros Domitilo , Sa´nchez Silva F. , Carvajal Mariscal I. , Polupan G.
Published: July 2009

The development of a new technique to detect and measure the annular flow parameters is presented in this article, the liquid film thickness was detected and measured in eight different radial positions, and the experimental information obtained was used to analyze the liquid film behaviour in order to set the wall regions where the probability to dry is higher. For the above purpose, a measuring system was developed, it was formed by a Digital Signal Processor (DSP) and a proximity circuit based on the embedded technology, it was also implemented a calibration methodology based on the Mandhane map to set the annular flow region in the experimental set up. The Digital Signal Processor (DSP) was also used to interpret and construct the signals according to its time and frequency behaviour. Due to its capacity of making complex operations, including its programming in C language, the device becomes an excellent real time tool to observe and quantify this phenomenon. The measuring and description of the annular flow is carried out through a digital camera, getting time series and visual patterns, creating a data base with hundreds of tests from the experimental system. The liquid film time series are interpreted through lineal transformation with Fourier series, where they are analyzed controlling the frequency and time. Subsequently, they are compared with the original signals to detect measurements uncertainty. The measuring prototype is full described for future applications in the instrumentation and control of the two-phase and multiphase flows experimental studies.
The Low Speed Wind Tunnel at LABINTHAP: Preliminary Evaluation
Authors: Tolentino Eslava R. , Tolentino Eslava G. , Toledo Vela´zquez M.
Published: July 2009

Flow behavior in Thermal Engineering and Applied Hydraulics Laboratory (LABINTHAP) wind tunnel was investigated by measuring the velocity profiles, turbulence intensity and wall effects with a Hot Wire Anemometer. Measurements were carried out at 5, 15 and 30 m/s in planes located at 1.8, 2.6 and 3.4 m from flow inlet to the test section. The flow showed a good quality with a velocity variation less than 1%, turbulence intensity lower than 4% and the wall effects allow having an excellent work area in the test section for the velocities evaluated.
Computational Study of a Subsonic Aircraft Design: Basic CFD Methods and CAD Designs
Authors: Winkelmann Scott , Amano Ryoichi S.
Published: July 2009

This investigation explores the methodology, using various computational tools and processes, involved in designing the fuselage of an aircraft. The design begins using 3-Dimensional modeling software and a basic understanding of aerodynamics. The form of the aircraft is built using only a few simple features and is then ready for the meshing process. Picking a simple tetrahedral mesh, rather than a more complicated hexahedral mesh, will allow this process to proceed even faster and also requires only a basic understanding of meshing. Once the geometry is completed the mesh may be moved into Computational Fluid Dynamics software and a wind tunnel simulation can be preformed. Developing a connection between each of these steps will allow the design to be manipulated in many different ways.
Design of Small Wind Turbine
Authors: Amano R. S. , Malloy Ryan
Published: July 2009

The project has been completed, and all of the aforementioned objectives have been achieved. An anemometer has been constructed to measure wind speed, and a wind vane has been built to sense wind direction. An LCD module has been acquired and has been programmed to display the wind speed and its direction. An H-Bridge circuit was used to drive a gear motor that rotated the nacelle toward the windward direction. Finally, the blade pitch angle was controlled by a swash plate mechanism and servo motors installed on the generator itself. A microcontroller has been programmed to optimally control the servo motors and gear motor based on input from the wind vane and anemometer sensors.
Is There an Asymptotic Effect of Initial and Upstream Conditions on Turbulence?
Authors: George William K.
Published: July 2009

More than two decades ago the first strong experimental results appeared suggesting that turbulent flows might not be asymptotically independent of their initial (or upstream) conditions [1]. And shortly thereafter the first theoretical explanations were offered as to why we came to believe something about turbulence that might not be true [2]. It was recognized immediately that if turbulence was indeed asymptotically independent of its initial conditions, it meant that there could be no universal single point model for turbulence [2], [3], certainly consistent with experience, but not easy to accept for the turbulence community. Even now the ideas of asymptotic independence still dominate most texts and teaching of turbulence. This paper reviews the substantial additional evidence — experimental, numerical and theoretical — for the asymptotic effect of initial and upstream conditions that has accumulated over the past 20 years. Emphasis has been placed on the canonical turbulent flows (especially wakes, jets, and homogeneous decaying turbulence), which have been the traditional building blocks for our understanding. Some of the implications for the future of turbulence modeling and research, especially LES and turbulence control, are also considered.
Experimental Measurements and Numerical Modeling for the Air-Mist Cooling of a Heated Cylinder
Authors: Issa Roy J. , Hunt Emily M. , Davis Freddie J.
Published: July 2009

Experimental measurements and numerical simulations are conducted to investigate the effect of mist on the spray heat transfer and fluid dynamics in the cooling of a low-carbon steel cylindrical surface heated to the nucleate boiling temperature range. Multiple tests are performed to investigate the effect of the droplet size, and liquid-to-air loading on the spray heat transfer along the circumference of the annulus cylinder. Infrared imaging is used to capture the effect of the spray flow conditions on the droplets transportation process around the heated cylinder. A computational fluid dynamics model is also developed to simulate the spray transportation process, droplets impaction and evaporation over the cylinder surface. The model takes into consideration droplet-to-surface interaction and water-film accumulation on the surface. Simulation results show the wetting of the cylinder depends on the droplet size and liquid-to-air loading. The smaller the droplets, the closer to the surface they remain. For high liquid-to-air loadings and high air velocities, droplet wetting of the cylinder back surface dramatically increases due to the increase in the flow turbulence. An overall good agreement is observed between the experimental measurements, numerical simulations and the thermal images. The results of this study shall lead to a better understanding of the multiphase heat transfer enhancement that plays an important role in the design of heat exchangers using multiphase cooling.
Experimental Observation of the Dynamic Micro- and Macro-Layer During Pool Boiling
Authors: Gerardi Craig , Buongiorno Jacopo , Hu Lin-Wen , McKrell Thomas
Published: July 2009

This paper presents the results of an experimental study on nucleate pool boiling. Experiments were performed using vapor-deposited thin films which were electrically heated. High-speed infrared and visible cameras simultaneously observed bubble growth from the heater surface. Possible experimental confirmation of microlayer dynamics is presented.
Experimental Apparatus for Measuring in Tube Condensation Heat Transfer Coefficient and Pressure Drop Using Smooth and Micro-Fin Tubes for HFC Refrigerants
Authors: Patil Pradeep A. , Sapali S. N.
Published: July 2009

An experimental test facility is designed and built to calculate condensation heat transfer coefficients and pressure drops for HFC-134a, R-404A, R-407C, R-507A in a smooth and micro-fin tube. The main objective of the experimentation is to investigate the enhancement in condensation heat transfer coefficient and increase in pressure drop using micro-fin tube for different condensing temperatures and further to develop an empirical correlation for heat transfer coefficient and pressure drop, which takes into account the micro-fin tube geometry, variation of condensing temperature and temperature difference (difference between condensing temperature and average temperature of cooling medium). The experimental setup has a facility to vary the different operating parameters such as condensing temperature, cooling water temperature, flow rate of refrigerant and cooling water etc and study their effect on heat transfer coefficients and pressure drops. The hermetically sealed reciprocating compressor is used in the system, thus the effect of lubricating oil on the heat transfer coefficient is taken in to account. This paper reports the detailed description of design and development of the test apparatus, control devices, instrumentation, and the experimental procedure. It also covers the comparative study of experimental apparatus with the existing one from the available literature survey. The condensation and pressure drop of HFC-134a in a smooth tube are measured and obtained the values of condensation heat transfer coefficients for different mass flux and condensing temperatures using modified Wilson plot technique with correlation coefficient above 0.9. The condensation heat transfer coefficient and pressure drop increases with increasing mass flux and decreases with increasing condensing temperature. The results are compared with existing available correlations for validation of test facility. The experimental data points have good association with available correlations except Cavallini-Zecchin Correlation.
Modeling Flash Diffusivity Experiments in Two Dimensions for Thick Samples
Authors: McMasters Robert L.
Published: July 2009

The laser flash method for measuring thermal diffusivity is well established and has been in use for many years. Early analysis methods employed a simple model, in which one dimensional transient conduction was assumed, with insulated surfaces during the time subsequent to the flash. More recently, models of grater sophistication have been applied to flash diffusivity experiments. These models have been matched to experimental data using nonlinear regression and assume one-dimensional conduction. The advanced models have achieved highly accurate agreement with experimental data taken from thin samples, on the order of one millimeter in thickness. As samples become thicker, models which neglect edge losses can lose some conformity to the experimental data. The present research involves the application of a two dimensional model which allows for penetration of the laser flash into the sample. The accommodation of the flash penetration is important for porous materials, where the coarseness of the porosity is more than one percent of the sample thickness. Variability of the area of incidence of the flash is also investigated to determine the effect on the model and the results. Statistical methods are used in order to make a determination as to the validity of the two dimensional model, as compared with the one dimensional analysis method.
A Visual Study of Phase Change Heat Transfer in Horizontal Bottom Heating Beads Packed Porous Structures
Authors: Li C. H.
Published: July 2009

An experimental investigation was conducted to study the influence of the sphere material and size on the bubble generation, growth, and detachment on nucleate pool boiling heat transfer in two different sphere-packed porous media, copper sphere and glass sphere at the same size of 3 mm diameter, respectively. By measuring the heating surface temperatures and visualizing the bubble dynamics over a wide range of heat flux, an effort was made to find the relationship between the normalized bubble dynamics process and the factors of sphere material and size. By comparing the experimental results of two different sphere material porous media, the interfacial heat and mass transport will be analyzed to provide the information how the bubble generation, growth, detachment and the liquid replenished process were influence by the liquid/copper and liquid/glass interfaces in different size porous media.
Development of the Loop Heat Pipe (LHP)
Authors: Tanaka K.
Published: July 2009

First, I describe the basic equations that resolve the physical development of the LHP and how to estimate the maximum heat transfer capability of the LHP. Second, I describe the outline of experimental manufacture of the LHP. This LHP is made from copper. The evaporator is φ19×95mm, the vapor tube is φ5×300mm, the condenser is φ3.5×600mm and the liquid tube is φ3.5×300mm. The wick is made from the sintering cupper. The working fluid is methanol. Finally, I briefly describe the test result of heat transfer capability of this LHP.
Theoretical Evaporation Model of a Single Droplet in Laser Treatment of PWS in Conjunction With Cryogen Spray Cooling
Authors: Zhou Zhifu , Xin Hui , Chen Bin , Wang Guo-Xiang
Published: July 2009

Cryogen spray is an effective cooling technique used for laser treatment of Port Wine Stain. The cooling process involves complex droplet evaporation and strong convective heat and mass transfer, therefore a deep understanding of spray characteristics is essential in order to optimize the nozzle design and improve the cooling efficiency of the spray. This paper improves a theoretical model to describe the equilibrium evaporation process of a single cryogen droplet in cryogen spray. The results of comparative analysis of gas phase models for single droplet heating and evaporation are presented. Six different semi-theoretical models based on various assumptions are compared and their effects on a single droplet heating and evaporation characteristics in the process of cryogen R-134a spray cooling are compared. It is pointed out that the gas phase model, in which the effect of superheat is taken into account, predicts the evaporation process closest to the experimental data. Finally, a parametric study of the influences of initial diameter and velocity on the droplet evaporation is then carried out. The results can be used to guide the Cryogen Spray Cooling of laser therapy.
Simulation of Radiation Heat Transfer of Three Dimensional Participating Media by Radiative Exchange Method
Authors: Bordbar Mohammad Hadi , Hyppa¨nen Timo
Published: July 2009

This paper describes the theoretical bases of the Radiative Exchange Method, a new numerical method for simulating radiation heat transfer. By considering radiative interaction between all points of the geometry and solving the radiation balance equation in a mesh structure coarser than the structure used in computational fluid flow calculation, this method is able to simulate radiative heat transfer in arbitrary 3D space with absorbing, emitting and scattering media surrounded by emitting, absorbing and reflecting surfaces. A new concept is introduced, that of the exchange factors between the different elements that are necessary for completing the radiative balance equation set. Using this method leads to a set of algebraic equations for the radiative outgoing power from each coarse cell being produced and the result of this set of equations was then used to calculate the volumetric radiative source term in the fine cell structure. The formulation of the exchange factor for a three-dimensional state and also a mesh size analysis that was conducted to optimize the accuracy and runtime are presented. The results of this model to simulate typical 3D furnace shape geometry, is verified by comparison with those of other numerical methods.
Mean-Field Bounds and the Classical Nature of Thermal Conduction in Nanofluids
Authors: Eapen Jacob
Published: July 2009

The initial promise of nanofluids as an advanced, nanoengineered coolant has been tempered in the recent years by a conspicuous lack of consensus on its thermal conduction mechanism. Several new mechanisms have been hypothesized in the recent years to characterize the thermal conduction behavior in nanofluids. In this presentation, we show that a large set of nanofluid thermal conductivity data is enveloped by the well-known Hashin and Shtrikman (H-S) mean-field bounds for inhomogeneous systems. The thermal conductivity in nanofluids, therefore, is largely dependent on whether the nanoparticles stays dispersed in the base fluid, form linear chain-like configurations, or assume an intermediate configuration. The experimental data, which is strikingly analogous to those in most solid composites and liquid mixtures, provides a strong evidence for the classical nature of thermal conduction in nanofluids.
Dual Pump Femtosecond Laser Induced Plasma
Authors: Mahat Meg , Choi Tae Y. , Seifolah Nasrasadani , Neogi Arup
Published: July 2009

Laser-induced breakdown spectroscopy (LIBS) can provide a noncontact way of inspecting a specimen including distinct signature of atomic composition of the sample. Ultra-short pulse laser enables characterization of any materials by utilizing the multiphoton process, which is a dominant carrier generation mechanism for dielectric materials. Additionally, femtosecond LIBS yields low background and better defined atomic lines than the nanosecond LIBS. We have performed a time-resolved emission intensity measurement for an iron oxide (Fe3O4, magnetite). The emission intensity has the peak value at 100 ps time delay, signifying that the succeeding pump beam is interacting with the plasma generated in the vicinity of the sample by the preceding beam. The dual pulses significantly enhance the atomic emission as compared to single pulse excitation and enables ultrafast time-resolved spectroscopy.
Electron and Focused Ion Beams in Thermal Science and Engineering
Authors: Choi Tae-Youl , Poulikakos Dimos
Published: July 2009

Focused-ion-beam (FIB) is a useful tool for defining nanoscale structures. High energy heavy ions inherently exhibit destructive nature. A less destructive tool has been devised by using electron beam. FIB is mainly considered as an etching tool, while electron beam can be used for deposition purpose. In this paper, both etching and deposition method are demonstrated for applications in thermal science. Thermal conductivity of nanostructures (such as carbon nanotubes) was measured by using the FIB (and electron beam) nanolithography technique. Boiling characteristics was studied in a submicron heater that could be fabricated by using FIB.
Design of Fin Plate Heat Exchanger for Increasing Micro Turbine Efficiency and Introduction of Fin Plate Heat Exchanger Design Software (KhoshNasr) for this Purpose
Authors: Nasrabadi Mehdi , Haghighi Khoshkhoo Ramin
Published: July 2009

A heat exchanger is a part of micro turbines, which can improve thermal efficiency of micro turbines up to 30 percent. Some important factors in design of heat exchangers are low cost, high efficiency, small size, low weight and high performance. In this paper, design of a heat exchanger with consideration of Iranian industry’s capability has been investigated. A survey of different types of gas to-gas heat exchangers is presented and then fin-tube heat exchanger, fin-plate heat exchanger, shell & tube heat exchanger and regenerator are designed. Also, the effect of thermo hydraulic parameters on the efficiency of the three heat exchangers is investigated. Effects of these heat exchangers on the efficiency of a 100 kW micro turbine are studied and the heat exchanger with the highest efficiency is selected. The algorithm for design and modeling of the selected heat exchanger is then presented. After research on all types of heat exchangers, fin plate heat exchanger appeared to be the optimum choice for manufacturing in Iran industry. A new design program was written in MATLAB based on our suggested algorithm. Since there were some practical charts about heat transfer and pressure drop in design of the heat exchanger, all the existing experimental curves related to heat transfer and pressure of fins (required in the design of the heat exchanger) were converted to data (using “Image Processing” technique in MATLAB) and implemented in the design program.
Prediction of Bundle Shell Side Condensation Heat Transfer Coefficient
Authors: Chen Tailian
Published: July 2009

Prediction of condenser bundle performance is of great interest to chiller design engineers and tube developers as well. Depending on their locations in a condenser bundle, tubes are subjected to inundation or flooding of condensate coming from those above them. The tubes located in the top portion of the bundle are not or slightly inundated whereas the tubes located deep in the bundle experience larger degree of inundation; those in the bundle bottom are the most severely inundated. For a condenser bundle to have good performance, it is necessary for the tubes to perform well in both non-inundated and inundated conditions. In this paper, the outside condensation heat transfer coefficient and its sensitivity to inundation for a condenser tube of enhanced 3-dimensional (3D) outside fins were measured. Based on the single tube measurements, shell side condensation performance of a condenser bundle was predicted. The predicted bundle outside heat transfer coefficient has a reasonable agreement with that of a condenser tested in a 500-ton chiller.
Evaluating the Thermal Characteristics of Copper-II and Zinc-Oxide Nanofluids Flowing Over a Heated Flat Plate
Authors: McCants Dale A. , Khan Jamil A. , Hayes Andrew M. , Shaaban Aly
Published: July 2009

Thermal characteristics of CopperII and Zinc-Oxide nanofluids have been investigated for flow over a heated flat plate. Fluid containing different volume-percents nanoparticles flow over a heated flat plate at specified laminar flow velocities. The heated plate experienced a constant heat flux from cartridge heaters spaced evenly along the length of the plate. The flow channel’s cross-sectional area was a square of dimensions 5cm × 5cm. Investigation of the heat transfer occurring in a plane along the centerline of the plate in the direction of the flow was performed. The heat transfer coefficients were calculated and plotted verses the Reynolds number and compared with the results obtained from distilled de-ionized water. Nanoparticle size from the fluids was investigated to inspect for possible agglomeration using both a transmission electron microscope (TEM) and a dynamic light scattering system (DLS).
Argon Thermal Conductivity by Anharmonic Lattice Dynamics Calculations
Authors: Turney J. E. , McGaughey A. J. H. , Amon C. H.
Published: July 2009

Lattice dynamics calculations are used to investigate thermal transport in the face-centered cubic Lennard-Jones (LJ) argon crystal between temperatures of 20 and 80 K. First, quasi-harmonic lattice dynamics calculations are used to find the frequencies and mode shapes of non-interacting phonons [1]. This information is then used as input for anharmonic lattice dynamics calculations. Anharmonic lattice dynamics is a means of computing the frequency shift and lifetime of each phonon mode due to interactions with other phonons [2]. The phonon frequencies, group velocities, and lifetimes, determined with the lattice dynamics methods, are then used to compute the thermal conductivity. The thermal conductivities predicted by the lattice dynamics methods are compared to predictions from molecular dynamics simulations. The two methods are found to agree well at low temperature but diverge at higher temperatures (i.e., near the melting point). The properties of individual phonon modes are used to identify the modes that dominate thermal transport.
Experimental Validation of Passenger Car Underhood Simulation in the Presence of Convective and Radiative Heat Flux
Authors: Suzzi Daniele , Lechner Bernhard , Rauch Christian , Jagsch Sebastian , Almbauer Raimund
Published: July 2009

The numerical prediction of underhood local temperatures represents a challenging field in the development of passenger cars. The reliability of computational fluid dynamics (CFD) results is depending upon numerics and employing appropriate physical models which can strongly affect the quality of results and the overall simulation time. The purpose of this paper is to analyze and validate the simulation of heat transfer phenomena in a vehicle’s underbody through the comparison with experimental data. The measurements are obtained from thermal sensors mounted on a passenger car during a highway drive. Furthermore, the radiative boundary conditions are defined through the post-processing of thermographic camera images. The numerical results of a commercial CFD code are finally compared with the experimental data on surface temperatures of the vehicle’s underbody.
Effects of Syngas Ash Particle Size on Deposition and Erosion of a Film Cooled Leading Edge
Authors: Rozati Ali , Tafti Danesh K. , Sreedharan Sai Shrinivas
Published: July 2009

The paper investigates the deposition and erosion caused by Syngas ash particles in a film cooled leading edge region of a representative turbine vane. The carrier phase is predicted using Large Eddy Simulation for three blowing ratios of 0.4, 0.8 and 1.2. Three ash particle sizes of 1, 5, and 10 microns are investigated using Lagrangian dynamics. The 1 micron particles with momentum Stokes number St = 0.03 (based on approach velocity and cylinder diameter), follow the flow streamlines around the leading edge and few particles reach the blade surface. The 10 micron particles, on the other hand with a high momentum Stokes number, St = 3, directly impinge on the surface, with blowing ratio having a minimal effect. The 5 micron particles with St = 0.8, show the largest receptivity to coolant flow and blowing ratio. On a number basis, 85–90% of the 10 micron particles, 40–50% of 5 micron particles and less than 1% of 1 micron particles deposit on the surface. Overall there is a slight decrease in percentage of particles deposited with increase in blowing ratio. On the other hand, the potential for erosive wear is highest in the coolant hole and is mostly attributed to 5 micron particles. It is only at B.R. = 1.2 that 10 micron particles contribute to erosive wear in the coolant hole.
Analytic Solution of Thermal Spreading Resistance: Generalization to Arbitrary-Shape Heat Sources on a Half-Space
Authors: Sadeghi E. , Bahrami M. , Djilali N.
Published: July 2009

Thermal spreading resistance is an important phenomenon in contacting bodies and local heating e.g. laser heating. In contacting bodies, the real area of contact is typically less than 2% of the nominal contact area. In practice, due to random nature of contacting surfaces, the actual shape of microcontacts is unknown; therefore, it is advantageous to have a model applicable to any arbitrary-shape heat source. Starting from a half-space representation of the heat transfer problem, a compact model is proposed based on the generalization of the analytical solution of the spreading resistance of an elliptical source on a half-space. Using a “bottom-up” approach, unified relations are found that allow accurate calculation of spreading resistance over a wide variety of heat source shapes under both isoflux and isothermal conditions.
The Effect of Pore Shape to the Effective Thermal Conductivity of Thermal Barrier Coatings
Authors: Altun Ozge , Bo¨ke Y. Erhan
Published: July 2009

Effective thermal conductivity is an important parameter for the design of porous ceramic coatings that are exposed to high temperatures. Pore shapes which change in relation with the coating parameters and coating method affect the effective thermal conductivity significantly. In this study the effective thermal conductivity of 8 wt % yttria stabilized ZrO2 coating deposited by air plasma spraying have been calculated by finite element method using digital images. The effects of pore shape on effective thermal conductivity have been discussed.
Natural Convective Heat Transfer From an Inclined Narrow Isothermal Flat Plate
Authors: Oosthuizen Patrick H. , Kalendar Abdulrahim
Published: July 2009

Natural convective heat transfer rate from an isothermal flat plate inclined at moderate angles to the vertical has been numerically studied. When the plate is wide compared to its height the flow can be adequately modeled by assuming two-dimensional flow. However, when the width of the plate is relatively small compared to its height, the heat transfer rate can be considerably greater than that predicted by these two-dimensional flow results. The heat transfer from a narrow isothermal plate embedded in a plane adiabatic surface, the adiabatic surface being in the same plane as the heated plate and inclined at an angle to the vertical has been numerically considered. Results for both positive and negative inclination angles have been numerically determined here. Attention was restricted to results for a Prandtl number of 0.7; this being approximately the value existing in the application that originally motivated this study. It has been assumed that the fluid properties are constant except for the density change with temperature which gives rise to the buoyancy forces, this having been treated by using the Boussinesq approach. It has also been assumed that the flow is symmetrical about the vertical centre-plane of the plate. The solution has been obtained by numerically solving the full three-dimensional form of the governing equations, these equations being written in dimensionless form. The solution was obtained using a commercial finite element method based code, FIDAP. The solution has the Rayleigh number, the dimensionless plate width, the angle of inclination, and the Prandtl number as parameters. Results have been obtained for Rayleigh numbers between 103 and 107 for ratios of the plate width to the plate height of between 0.3 and 1.5 and for angles of inclination between +45° and −45°.
Reverse Monte-Carlo Ray-Tracing Method Combined With Full-Spectrum K-Distribution Method for Radiative Heat Transfer
Authors: Sun Xiaojing , Smith Philip J.
Published: July 2009

Accurate prediction of radiative heat transfer plays a key role in many high temperature applications, such as combustion devices and fires. Among various simulation methods, the Monte-Carlo Ray-Tracing (MCRT) has the advantage of solving the radiative transfer equation (RTE) for real gas mixtures with almost no approximations; however, it has disadvantage of requiring a large computational effort. The MCRT method can be carried out with either the Forward MCRT or the Reverse MCRT, depending on the direction of ray tracing. The RMCRT method has advantages over the FMCRT method in that it uses less memory, and in a domain decomposition parallelization strategy, it can explicitly obtain solutions for the domain of interest without the need for the solution on the entire domain.
Experimental Research on Heat Transfer Characteristics of Pulsating Heat Pipe
Authors: Jia Li , Li Yan
Published: July 2009

Experimental research was conducted to understand heat transfer characteristics of pulsating heat pipe in this paper. The PHP is made of high quality glass capillary tube. The heat transfer rate and many other influence factors, the flow patterns were observed in the start-up, transition and stable stage under different fill ratio. The effects of heating position on heat transfer were discussed. The experimental results indicate that no annular flow appeares in top heating condition. The flow pattern in PHP is transferred form bulk flow to semi-annual flow and annual flow, and the performance of heat transfer is improved for down heating case under different fill ratios and heat transfer rate. The experimental results show that the total heat resistant of PHP is increased with fill ratio, and heat transfer rate achieves optimum at filling rate 50%. But for pulsating heat pipe with changing diameters the thermal resistance is higher than that with uniform diameters.
Investigation of Melting in a Vertical Circular Tube: Local Heat Fluxes
Authors: Shmueli H. , Ziskind G. , Letan R.
Published: July 2009

The present study explores the process of melting of a phase change material (PCM) in a vertical circular tube. A detailed analysis of the digital experimental pictures, obtained in previous investigations, is performed. In this analysis, the tubes are subdivided by horizontal planes into 1cm high slices. The melt fraction as a function of time is calculated separately for each slice, yielding the local heat transfer rates into the solid. The flow patterns that cause these effects are obtained from the numerical simulation. The simulation provides a detailed heat flux distribution on the inner wall of the tube. The numerical simulations, performed using the Fluent 6 software, model the same commercially available paraffin-type material that was used in the previous experimental investigations.. The simulation results, along with the analysis of the experimental pictures, reveal the effects of convection in the liquid phase, which make heat transfer from the wall to the melting PCM essentially non-radial. Thus, the analysis adopted in the present study provides a comprehensive picture of melting in vertical circular tubes at various locations and instants.
Explorations of Carbon Nanotube Wick Structure for High Heat Flux Cooling
Authors: Cai Qingjun , Chen Chung-Lung , Xiong Guangyong , Ren Zhifeng
Published: July 2009

Multiwall carbon nanotube (MCNT) has high thermal conductivity, nano size pores and high capillary pressure. All these physical properties make it an ideal candidate as a wick structure in a micro sized heat pipe/spreader. In this paper, experimental investigations evaluate heat transfer performance of the carbon nanotube (CNT) wick and demonstrate its ability to handle high heat flux cooling. The CNT wick structure used for high heat flux experiments employs the bi-wick structure design to overcome high flow resistance in CNT clusters. The wick fabrication technique integrates both microelectromechanical systems (MEMS) patterning and thermal chemical vapor deposition (CVD) CNT growth processes. In high heat flux experiments, the CNT cluster functions as the first order wick structure and provides a large capillary force. The spacing among CNT clusters acts as the second order wick structure thus setting up low resistance liquid supply channels and vapor ventilation paths. Preliminary experiments are conducted in an open chamber system with vertical CNT bi-wick sample setup. Heat flux, as high as 400W/cm2, is demonstrated over 0.16mm2 heating area. Dryout was not observed, whereas the heater soft-bonding material fails at the higher testing heat flux. The experimental results indicate that the CNT bi-wick structure is capable of high heat flux cooling and promises to be the heat transfer element in new generation microelectronics cooling systems.
Performance Comparison of Particle Swarm Optimization and Genetic Algorithm in Rolling Fin-Tube Heat Exchanger Optimization Design
Authors: Han Wutao , Tang Linghong , Xie Gongnan , Wang Qiuwang
Published: July 2009

A method for optimization designs of rolling fin-tube heat exchangers was put forward with Particle Swarm Optimization (PSO) and Genetic Algorithm (GA), respectively. The length of tube bundles, the row numbers of tubes, the width of heat exchanger core and fin pitch were used as the optimization variables. The allowable pressure drop and heat exchange requirements were considered as restrictive conditions. According to specific design requirements, the volume, weight or pressure drop may be chosen as the optimization objective function. In the same design parameters, ranges of the search variables and restrictive conditions, optimization results compared with GA, the minimum volume, weight and pressure drop PSO could decrease by 3.34%, 4.31% and 14.04%, respectively, and corresponding CPU time could be reduced by 32.39%, 40.23% and 33.45%, respectively. In the fields of optimization designs of heat exchanger, Particle Swarm Optimization is a promising optimization method.