bluuebunny/crossref_metadata_2025 huggingface dataset:
Time and Space Resolved Wall Temperature Measurements During Nucleate Boiling With Constant Heat Flux Boundary Conditions
Authors: Myers Jerry G. , Hussey Sam W. , Yee Glenda F. , Yerramilli Vamsee K. , Kim Jungho
Published: March 2009

The lack of temporally and spatially resolved measurements under nucleate bubbles has complicated efforts to fully explain pool-boiling phenomena. The objective of this current work is to acquire time and space resolved temperature distributions under nucleate bubbles on a constant heat flux surface. This was performed using a microheater array with 100 μm resolution that allowed effectively simultaneous measurements of surface temperature while supplying a constant dissipative heat flux. This data is then correlated with high speed (> 1000Hz) visual recordings of the bubble growth and departure from the heater surface acquired from below and from the side of the heater. The data indicate that a significant source of energy during bubble nucleation and initial growth is the superheated layer around the bubble. Bubble coalescence was not observed to decrease surface temperature as significantly as bubble departure from the surface. Since bubble departure is typically followed by a sharp increase in the heater surface temperature, it is surmised that the departing bubble effectively removes the superheated layer, allowing a higher local heat transfer rate with the bulk fluid through transient conduction/micro-convection during rewetting.
Computations of Flow Structure and Heat Transfer in a Dimpled Channel at Low to Moderate Reynolds Number
Authors: Patrick Wilfred V. , Tafti Danesh K.
Published: March 2009

Time-accurate calculations are used to investigate the three-dimensional flow structure and understand its influence on the heat transfer in a channel with concave indentations on one wall. A dimple depth to channel height ratio of 0.4 and dimple depth to imprint diameter ratio of 0.2 is used in the calculations. The Reynolds number (based on channel height) varies from Re = 280 in the laminar regime to Re = 2000 in the early turbulent regime. Fully developed flow and heat transfer conditions were assumed and a constant heat flux boundary condition was applied to the walls of the channel. In the laminar regime, the flow and heat transfer characteristics are dominated by the recirculation zones in the dimple with resulting augmentation ratios below unity. Flow transition is found to occur between Re = 1020 and 1130 after which both heat transfer and friction augmentation increase to values of 3.22 and 2.75, respectively, at Re = 2000. The presence of large scale vortical structures ejected from the dimple cavity dominate all aspects of the flow and heat transfer, not only on the dimpled surface but also on the smooth wall. In all cases the thermal efficiency using dimples was found to be significantly larger than other heat transfer augmentation techniques currently employed.
Fluid Flow and Heat Transfer in a Lid-Driven Cavity Due to an Oscillatory Thin Fin: Transient Behavior
Authors: Shi Xundan , Khodadadi J. M.
Published: March 2009

A finite-volume-based computational study of transient laminar flow and heat transfer (neglecting natural convection) within a lid-driven square cavity due to an oscillating thin fin is presented. The lid moves from left to right and a thin fin positioned perpendicular to the right stationary wall oscillates in the horizontal direction. The length of the fin varies sinusoidally with its mean length and amplitude equal to 10 and 5 percent of the side of the cavity, respectively. Two Reynolds numbers of 100 and 1000 with a Pr = 1 fluid were considered. For a given convection time scale (tconv), fin’s oscillation periods (τ) were selected in order to cover both slow (τ/tconv>1) and fast (τ/tconv<1) oscillation regimes. This corresponded to a Strouhal number range of 0.005 to 0.5. The number of the cycles needed to reach the periodic state for the flow and thermal fields increases as τ/tconv decreases for both Re numbers with the thermal field attaining the periodic state later than the velocity field. The key feature of the transient evolution of the fluid flow for the case with Re = 1000 with slow oscillation is the creation, lateral motion and subsequent wall impingement of a CCW rotating vortex within the lower half of the cavity. This CCW rotating vortex that has a lifetime of about 1.5τ brings about marked changes to the temperature field within a cycle. The dimensionless time for the mean Nusselt numbers to reach their maximum or minimum is independent of the frequency of the fin’s oscillation and dependent on the distance between the oscillating fin and the respective wall, and the direction of the primary CW rotating vortex. The phase lag angle between the oscillation of the fin and the mean Nusselt number on the four walls increases as the distance between the fin and the respective wall increases.
Effect of Impact Velocity and Substrate Temperature on Boiling of Water Droplets Impinging on a Hot Stainless Steel Surface
Authors: Mehdizadeh N. Z. , Chandra S.
Published: March 2009

We photographed high velocity impact of small water droplets (0.55 mm) on a heated stainless steel surface. To achieve high impact velocities the test surface was mounted on the rim of a rotating flywheel, giving linear velocities of up to 50 m/s. Two cartridge heaters were inserted in the substrate and used to vary substrate temperature. A CCD video camera was used to photograph droplets impinging on the substrate. By synchronizing the ejection of a single droplet with the position of the rotating flywheel and triggering of the camera, different stages of droplet impact were photographed. Substrate temperature was varied from 100–240°C and the impact velocity from 10–30 m/s. High-resolution photographs were taken of vapor bubbles nucleating sites inside the thin films produced by spreading droplets. For a given impact velocity, the extent of droplet spreading increased with substrate temperature. The superheat needed to initiate bubble nucleation decreased with impact velocity. We derived an analytical expression for the amount of superheat required for vapor bubble nucleation as a function of impact velocity.
Filter-Based Unsteady RANS Computations for Single-Phase and Cavitating Flows
Authors: Wu Jiongyang , Shyy Wei , Johansen Stein T.
Published: March 2009

The widely used Reynolds-Averaged Navier-Stokes (RANS) approach, such as the k-ε two-equation model, has been found to over-predict the eddy viscosity and can dampen out the time dependent fluid dynamics in both single- and two-phase flows. To improve the predictive capability of this type of engineering turbulence closures, a consistent method is offered to bridge the gap between DNS, LES and RANS models. Based on the filter size, conditional averaging is adopted for the Navier-Stokes equation to introduce one more parameter into the definition of the eddy viscosity. Both time-dependent single-phase and cavitating flows are simulated by a pressure-based method and finite volume approach in the framework of the Favre-averaged equations coupled with the new turbulence model. The impact of the filter-based concept, including the filter size and grid dependencies, is investigated using the standard k-ε model and with the available experimental information.
Experimental Investigation of Heat Transfer Characteristics of Inkjet Assisted Spray Cooling
Authors: Sharma Ratnesh K. , Bash Cullen E. , Patel Chandrakant D.
Published: March 2009

Increases in microprocessor power density along with an accompanying spatial variation in power density has been well documented in recent years. These combined factors pose a severe challenge for the provisioning of cooling resources at the microprocessor level. The use of thermal inkjet technology to precisely supply coolant onto the surface of a microprocessor has the potential to address this problem in a chip-scale form factor. By providing coolant when and where it is needed on the surface of a chip or package, very high critical heat fluxes can be obtained in an energy efficient manner in a minimum of physical space. In this paper, the unique heat transfer characteristics of inkjet assisted spray cooling of a heated surface are investigated. Sprays of water are used to cool heated surfaces ranging from 281mm2 to 35mm2. Several experiments are conducted at different nozzle-to-surface distances to measure critical heat flux (CHF) at different flow rates and firing frequencies. The impact of volumetric flux variation on CHF is studied. CHF data, measured over broad range of operating conditions is correlated to volumetric flux and liquid properties. Flow visualization studies are also conducted to understand the vapor-liquid interaction at the heater surface and the intermediate region. Jet breakup length studies are carried out to understand the propagation of Rayleigh instabilities in the spray jets and, subsequent, formation of liquid drops. CHF data combined with fluid flow studies have been used to optimize the nozzle-to-surface clearance. Results obtained from these experiments are invaluable for the design of micro scale spray cooling devices for chips.
Flotation and Aerodynamic Instability of Webs in a Dryer
Authors: Nurmi Simo , Zamankhan Piroz , Polashenski William , Heikkila¨ Pertti , Jokioinen Ilkka
Published: March 2009

A mathematical model has been developed as a design optimization tool for the prediction of the aerodynamic behavior of a web in an industrial dryer. In particular the key modeling objective is to examine the propagation of stress waves within the web to determine its lateral motion and hence its stability. Numerical solutions were obtained through a coupling of computational fluid dynamics (CFD) calculations and structural dynamic simulations (SDS). The viscoelastic behavior of the web and the presence of turbulence were found to significantly affect the stability of the web.
Measurements of Gas Entrainment in Evaporating Spray Jets
Authors: Rafique Qureshi Muhammad Mushahid , Lee Tong , Yu Qun , Zhu Chao
Published: March 2009

The jet-induced entrainment can be significantly different for jets with evaporating sprays, compared to those of single-phase jets. The heat and mass transfer properties of a liquid jet could be dominate factors governing the nature of the jet. These factors are mainly associated with the amount of mass of the surrounding air induced into the jet. In this study, we have experimentally investigated the air entrainment by a liquid nitrogen spray jet as well as that by a cold nitrogen gas jet near the liquid nitrogen temperature. An oxygen concentration measurement system was used to determine the local oxygen concentration that is purely due to the jet entrainment while the spray jet velocity was determined using a Laser Doppler Velocimetry system Temperature profiles were also monitored using a mini-sized thermocouple on a traverse. Entrainment velocities as well as mass entrainment rate of surrounding air into the jet were calculated by integrating the product of concentration and velocity within the spray jet boundary. Our results indicate that the jet similarity criterion still holds for two-phase evaporating liquid spray jets for circular nozzles. Experimental results of the entrainment rate and similarity of the single-phase jets were quantitatively compared against those from the classical jet theories. It is found that the mass flow rate of air entrained is significantly increased for the two-phase evaporating spray jets as compared to single-phase jets. Effect of spray evaporation on the spray jet expansion rates is also evaluated by comparing the jet expansion of the single-phase jets and those of two-phase evaporating spray jets.
The Role of Inflow Turbulence for Large Eddy Simulation on Modelling of Bluff Body Flows
Authors: Tutar Mustafa , Celik Ismail , Yavuz Ibrahim
Published: March 2009

A random flow generation (RFG) technique for large eddy simulation (LES) is successfully adopted into a finite element based conventional fluid flow solver to generate the required inflow/initial turbulence boundary conditions for the LES computations of viscous incompressible turbulent flow over a two-dimensional circular cylinder at Reynolds number of 140,000. The effect of generated turbulent inflow boundary conditions on the transitional nature of the flow regime is studied during the early development of the very near wake of the cylinder. The numerical results obtained from the Smagorinsky sub-grid scale (SGS) model based simulations are compared with each other and with the experimental data for varying degree of inflow turbulence to discuss the issues such as the inflow turbulence effects on the time evolution of the local flow structures in the very near wake and on the integral flow parameter predictions such as separation points, transient fluid forces that the cylinder experience, and the local flow resolutions in the vicinity of the cylinder wall and the free shear layer. The influence of mesh resolution on the quality of the predicted results is also investigated. The comparison of present LES results with those of case without inflow turbulence and the experimental data indicates that the present LES approach coupled with the suggested RFG technique enhance the resolution of the turbulent flow and can be used with a confidence for a bluff body problem where the inflow turbulence is significant.
Water Hammer Pressure Transients in a Closed Loop System
Authors: Leishear Robert A. , Morehouse Jeffrey H.
Published: March 2009

The effects of fluid transients, or water hammer, in closed loop systems are somewhat different than those observed in open ended systems. The open loop system has received much attention in the literature, not so for the closed system. The generally accepted method of characteristics (MOC) technique was applied herein to investigate closed loop systems. The magnitudes of the pressures during fluid transients were investigated for examples of rapid valve closures, and the operations of parallel pumps. The effects of trapped air in the system were also considered for these examples. To reduce the pressures caused by the transients, the installation of slow closing valves were evaluated for different conditions.
LES and Unsteady RANS Computations for a Periodically-Perturbed Separated Flow Over a Backward-Facing Step
Authors: Dejoan Anne , Jang Yong-Jun , Leschziner Michael A.
Published: March 2009

Large eddy simulation and statistical turbulence closure are used to investigate and contrast the ability of both strategies to represent the effects arising from the unsteady perturbation of a separated backward-facing-step flow by means of a slot jet injected periodically at zero net mass-flow rate into the flow at the step edge at an angle of 45 degrees relative to the flow direction. Experimental data show the effects to depend non-linearly on the perturbation frequency, the strongest response arising at a Strouhal number of 0.2, which is the condition investigated herein. The principal response is a shortening of the separation bubble by almost 30%, a result that is highly pertinent to active flow control. As the injection frequency lies within the low-frequency range of the large scales of the turbulence spectrum, an issue of particular interest that is addressed is the ability of the statistical models, operating within a phase-averaged URANS framework, to reproduce the experimental observations and the response derived from the simulation.
Passive Cooling of Conducting and Insulating Heat Generating Cylinders in Enclosures With Openings
Authors: Tsivyan V. , Dubovsky V. , Weiss Y. , Aharon J. , Ziskind G. , Letan R.
Published: March 2009

The objective of this paper is to study cooling by induced convection of a vertical cylinder in an enclosed space with openings. The enclosed space has various configurations: it is either horizontal only, or combined vertical-horizontal, but its width remains constant. The study in general aims at finding the preferable configuration in which the maximum and mean temperature of the cylinder would be the lowest, and to compare the results for conducting and insulating cylinders, made either of stainless steel or cement. A laboratory-scale model is studied both experimentally and numerically. Each cylinder is 50mm in diameter and 100 mm high. It is heated from inside by a cartridge heater, installed in a drill along the cylinder axis and connected to an external power source. Temperature measurements are performed at various locations inside the cylinders by fine thermocouples using a multi-channel data acquisition unit. Numerical simulations are performed for the velocity and temperature fields in the enclosure, using the Fluent 5.5 software, accounting for both convection and radiation. The cylinders are modeled as they were built in reality: they had a heat-generating core and conducting body. Comparison of the experimental results with the numerical predictions is presented and discussed.
Laminar Convection on a Vertical Heated Plate Placed in a Chimney
Authors: Farber A. , Dubovsky V. , Ziskind G. , Letan R.
Published: March 2009

This study deals with heat transfer from a vertical electrically heated plate, which is symmetrically placed in an experimental modular chimney of variable height. The chimney is made of Perspex in order to enable observation and recording of the flow. The inner horizontal cross-section of the chimney is a rectangle, 110 by 20 mm, where the larger dimension is along the plate and the smaller one is normal to it. Three main approaches are used in parallel: temperature measurement, flow visualization, and numerical simulation. Temperature measurements are done by thermocouples distributed inside the plate and through the chimney. Visualization is performed using the smoke of incense sticks, with video recording and consequent image processing. It indicates that the flow inside the chimney remains laminar under the conditions of the present study. Computer simulations of flow and temperature fields are performed in 3D and compared with the measurements and visualization.
Fluid Transients in Mercury and Mercury-Helium Flows
Authors: Sawyer Aaron , Ruggles Art
Published: March 2009

Mercury flow is used in chemical and nuclear systems. The sound speed of mercury is similar to that of water, but the density is over an order of magnitude greater, making the consequences of fluid transients like fluid column separation followed by fluid-hammer much more severe in mercury systems than in water systems. Fluid transients in a mercury flow loop are considered and fluid transients in a loop filled with mercury and 0.5% by volume helium bubbles are evaluated. The helium bubbles add compressibility, which helps mitigate consequences of some transients of concern to nuclear applications.
Cryogen Droplet Impingement Onto Indented Surfaces Relevant to Dermatologic Laser Surgery Therapies
Authors: Liu Jie , Franco Walfre , Nelson J. Stuart , Aguilar Guillermo
Published: March 2009

To protect the epidermis during selected dermatological laser surgeries, Cryogen Spray Cooling (CSC) is used as an auxiliary procedure to remove the heat generated in the epidermis by laser irradiation. The impingement of cryogen droplets onto the skin determines not only the effective amount of cryogen deposited on the surface, but also the dynamic behavior of the cryogen layer that forms on the skin surface and thus, it strongly affects the heat extraction process. Recently, it has been shown that the force of the spray alters the skin surface producing an indentation that in turn affects CSC efficiency. To achieve a better understanding of cryogen spray deposition, the impingement of a single cryogen (R-134a) droplet onto indented skin phantoms was experimentally studied. We first built an experimental pressure chamber where the pressure may be raised slightly above the saturation pressure of R-134a (600 kPa), with the objective to suppress and control the rapid evaporation that cryogen droplets undergo as they are released from the nozzles into ambient pressure. This allows us to focus on individual droplet impingement. Two nozzles of different outer diameters were used to generate droplets of different outer diameters were used to generate droplets of different sizes, which fall by gravity onto various indented skin phantoms. To maintain similarity, the range of Weber (We) and Reynolds (Re) numbers measured at the point of impact for typical cryogen spurts were matched with the We and Re of the individual droplets under study. A high-speed digital camera (500 fps) recorded the droplet impingement on indented surfaces resembling in vivo skin indentation measurements. Different indentation geometries were used since studies have shown that skin deformation depends on factors such as nozzle-to-skin distance, skin type and anatomical location. Experimental results showed different droplet impingement dynamics for droplets of two different sizes but same velocity. For We = 130 and Re = 25000 the amount of cryogen left at the bottom of the indentation after two droplets impinged consecutively was equivalent to the total mass of one droplet, whereas for We = 96 and Re = 18500, the amount of cryogen left at the bottom of indentation was twice as much as that after first droplet impingement. The effect of the depth and radius of curvature of the indentations appeared to have small effect on the droplet impingement behavior, compared to that associated with the droplet size (We and Re), as confirmed by the high speed videos.
Mixing in Large Scale Tanks: Part II — Full Scale Pump Testing
Authors: Stefanko David B. , Dimenna Robert A. , Leishear Richard A. , Lee Si Y.
Published: March 2009

Velocities in the discharge jet of a submerged Advanced Design Mixer Pump (ADMP) were measured in an eighty-five foot diameter tank, and were successfully compared to predictions from a computational fluid dynamics (CFD) model. The ADMP is a 10400 gallon per minute, dual nozzle pump ultimately used to mix the contents of a nuclear waste tank prior to further processing. The pump was initially installed, operated, and tested in a full-diameter test facility tank containing seventy inches of water. The horizontal discharge jets of the pump established a steady flow pattern in the tank, and the resulting velocities were measured throughout the tank. The data from these measurements were statistically averaged to obtain local velocities at each of the measured points in the tank. This experimental velocity mapping was compared to the results of a CFD model and showed good agreement with the calculated velocities.
Experimental Measurements of Heat and Mass Transport in Heat Pipe Wicks
Authors: Iverson Brian D. , Garimella Suresh V.
Published: March 2009

A novel experimental approach is developed for characterizing the performance of heat pipe wick structures. Mass transport measurements of the working fluid are obtained in addition to the temperature field in the porous wicks, under the action of a discrete heat source (evaporator). Open, partially submerged wicks are studied under partially saturated conditions, simulating normal heat pipe operation. The submerged portion of the wick simulates the condenser in a heat pipe. A vertical wick orientation, where the lift is in opposition to gravity, was selected to test the wicks under the most demanding conditions. The working fluid, supplied from the condenser pool, evaporates from the wick surface, and is condensed and collected into a collector separate from the pool, to yield mass flow rate results. Thus the liquid-pumping capability of the wick, coupled with flow impedance, can be measured with this approach at various applied heat fluxes. A simplified analytical model for the heat flow paths in the wick structure is also presented to explain the experimental measurements.
Modeling of the Mist Dynamics and Heat Transfer at Various Ambient Pressures
Authors: Issa Roy J. , Yao S. C.
Published: March 2009

A numerical model is developed to simulate the dynamics of the droplet-wall interaction and heat transfer mechanisms at sub-atmospheric to elevated ambient pressures, and for surface temperatures ranging from nucleate to film boiling. This is the first time a general model is developed to study these phenomena over a wide range of ambient pressures. The model provides insight to the optimal flow conditions, and droplet size distribution for best heat transfer enhancement. Simulations are provided for single stream droplet impactions, and for full conical sprays using nozzles that dispense a spectrum of non-uniform droplets. The model simulation was compared against available test data for single stream of droplets at non-atmospheric conditions, and the simulation compared favorably well with the test data.
Characterization of Fluid Flow and Taylor Vortex Onset in Partially-Obstructed Annular Space With Inner Cylinder Rotation
Authors: Loureiro B. V. , Souza Mendes P. R. , Azevedo L. F. A.
Published: March 2009

The present work studies the characteristics of the flow field inside an annular space formed by two concentric cylinders with rotation of the inner cylinder. The annular space was partially blocked by a plate parallel to the axis of rotation, thereby destroying the circumferential symmetry of the annular space geometry. This flow configuration encounters application on the modeling of drilling of horizontal petroleum wells where a bed of cuttings is formed at the bottom part of the annulus. This bed was modeled in the present work by a flat plate inserted into the annular space. The velocity field was investigated both numerically and experimentally. The equations governing the three-dimensional, laminar flow of a Newtonian fluid were solved via a finite-volume technique. The instantaneous and time-averaged flow fields over two-dimensional meridional sections of the annular space were measured employing the particle image velocimetry technique (PIV). Attention was focused on the determination of the onset of secondary flow in the form of distorted Taylor vortices. The results demonstrated that the critical rotational Reynolds number is directly influenced by the degree of obstruction of the flow given by the cylinder-to-plate gap. The smaller the gap, the larger the critical Taylor number. The gap dimensions control the width of the vortices. The calculated steady state axial flow profiles results agreed well with measurements. Transitions values of the rotational Reynolds numbers were also well predicted by the computations. Differences were found between measured and predicted values for the length of the Taylor vortices. Transverse flow maps revealed a complex interaction between Taylor vortices and zones of recirculating flow, for moderate to high degrees of flow obstruction.
Effective Thermal Conductivity of Fully-Saturated High Porosity Metal Foam
Authors: Schmierer Eric N. , Paquette Jason , Razani Arsalan , Kim Kwang J.
Published: March 2009

Geometric models are used to simplify the complex, three-dimensional geometry of metal foams for calculations of effective thermal conductivity. The first is based on a conventional three-dimensional cubic lattice and the second is a tetrakaidecahedronal model. The models consist of interconnecting ligaments with a spherical node at their intersections. The geometry of the foam is determined based on two dimensionless parameters: 1) the porosity and 2) the product of the specific surface area of the foam and the length of the interconnecting ligaments. A free parameter represents the size of the lumps at the ligament interconnections. It is shown that the remaining unknown geometric parameters of the models can be obtained as a solution of a cubic equation that has only one acceptable solution. From the cubic lattice model, a one-dimensional heat conduction analytical model is used to find the effective thermal conductivity of fully saturated metal foam. A three-dimensional finite element calculation of the effective thermal conductivity for the cubic lattice is then compared to the one-dimensional model. In the case of the tetrakaidecahedronal model, a similar three-dimensional finite element calculation is performed to find the effective thermal conductivity. Anisotropy of the models is explored. The results of the models are compared with experimental results from this study and the literature to substantiate their accuracy. The experimental results are reported for fully saturated aluminum metal foam in air, water, and oil. Results show that both the cubic lattice model, which is less complex, and the tetrakaidecahedronal model can both be used to represent one-dimensional effective thermal conductivity. Finally, the dimensionless surface areas for each geometric model are compared. The models produce significantly different surface areas, and therefore do not both represent the density and specific surface area of foam accurately.
Forced Convection in a Square Cavity With Inlet and Outlet Ports
Authors: Saeidi S. M. , Khodadadi J. M.
Published: March 2009

A finite-volume-based computational study of steady laminar forced convection inside a square cavity with inlet and outlet ports is presented. Given a fixed position of the inlet port, the location of outlet port is varied along the four walls of the cavity. The widths of the ports are equal to 5, 15 and 25 percent of the side. By positioning the outlet ports at 9 locations on the walls for Re = 10, 40, 100 and 500 and Pr = 5, a total of 101 cases were studied. For high Re and with the shortest distance between the inlet and outlet ports along the top wall, a primary CW rotating vortex that covers about 70 to 80 percent of the cavity is observed. Similar cases with smaller Re exhibit identical flow patterns but with weaker vortices as Re is lowered. As the outlet ports is lowered along the right wall, the CW primary vortex diminishes its strength; however a CCW vortex that is present next to the top right corner covers a greater portion of the cavity. With the outlet port moving left along the bottom wall, the CW primary vortex is weakened further and the CCW vortex occupies nearly the right half of the cavity. The temperature fields are directly related to the presence of the multiple vortices in the cavity. Regions of high temperature gradient are consistently observed at the interface of the throughflow and next to the solid walls on both sides of the outlet port. Local Nusselt numbers are low at 3 corners when no outlet port is present in their vicinity, whereas intense heat transfer rate is observed on the two sides of the outlet port. Between these minima and maxima, the local Nusselt number can vary drastically depending on the flow and temperature fields. By placing the outlet port with one end at the 3 corners, maximum total Nusselt number of the cavity can be achieved. Minimum total heat transfer of the cavity is achieved with the outlet port located at the middle of the walls.
Study on Erosive Wear and Novel Wear-Resistant Materials for Centrifugal Slurry Pumps
Authors: Liu Juan , Xu Hongyuan , Qi Longhao , Li He
Published: March 2009

The erosive wear of the impellers and liner of centrifugal slurry pumps was investigated. The eroded material surfaces of different parts in impellers and liner have been studied by using scanning electron microscopic (SEM). The examination shows that the eroded surface pattern and eroded degree of different parts in slurry pump are different. The microstructure SEM analysis provides insights into the erosive wear mechanisms in pumps. The material removal processes include chipping out of lateral cracks caused by impact of the erodent particles, grain boundary cracking and grain pull out, as well as plastic deformation caused by the repeated sliding and impact of the particles. A new kind of anti-erosive wear material- Al2O3 engineering ceramic has been made. Engineering ceramics have a high application potential for wear-protection of different working parts used for slurry pumps and mineral industries. Measurements of the erosive wear of various materials used in centrifugal slurry pumps have been studied in a simple slurry pot tester in aqueous slurry of silicon carbide grits. Effects of varying the size distribution and volume content of erodent particle are investigated.
Simulations of Heat Transport During Transient Electrostatic Discharge Events in a Sub-Micron Transistor
Authors: Narumanchi Sreekant V. J. , Murthy Jayathi Y. , Amon Cristina H.
Published: March 2009

The thermal problem associated with the transient electrostatic discharge phenomena in sub-micron silicon transistors is fast becoming a major reliability concern in IC packages. Currently, Fourier diffusion and some simple models based on the solution to the phonon Boltzmann transport equation (BTE) are used to predict failure (melting of silicon) in these transistors. In this study, a more comprehensive model, based on the phonon BTE and incorporating considerable details of phonon physics, is proposed and used to study the ESD problem. Transient results from the model reveal very significant discrepancies when compared to results from the other models in the literature.
Experimental Research for Unsteady Separated Flow in an Annular Cascade
Authors: Tang Hongfen , Li Yong , Wu Yulin
Published: March 2009

To study unsteady-fluid characteristic of inner flow in fluid machines is very important for reducing losing and enhancing lift force. In an annular cascade, when incidence angle changed, separation and vortex may happen. Under the designed incidence, separating section is narrower and blended with main fluid quickly. When the incidence angle decreases greatly, wider separating section, and stronger vortex appear. Similar phenomenon happens when incidence angle increases to a big positive value, expect that the vortex intensity is higher than that of the former. Experiment with pressure probe shows that aerodynamic performance of the annular cascade would be improved obviously by adding proper external acoustic excitation. In order to develop an in-depth study on configuration and characteristic of separate flow and effects of external unsteady excitation, PIV (Particle Image Velocimetry) was used to analyze the inner flow field through an annular cascade. Tests have been taken under different incidence cases in the tested range, with and without external acoustic excitation. The distribution of flow velocity, vorticity and streamline are obtained. Other important parameters like circumferential velocity, turbulent kinetic energy can be calculated from the original experimental data. Detailed configuration of separate flow in the annular cascade was acquired, and obvious difference of separation configuration due to different incidence angle can be seen from the results. Moreover, when proper external acoustic excitation added, vorticity and range of separating in the tested range decreases obviously. These results are important for research of flow control and may lead to some ideas on optimizing the design.
Numerical Investigation on Cooling Strategies in a Commercial Blast Furnace Hearth
Authors: Patnala Anil K. , Zhou Chenn Q. , Zhao Yongfu
Published: March 2009

A blast furnace is the predominant iron-producing process in the U.S. It is widely believed that the blast furnace hearth refractory is the most dominant factor affecting the campaign life of a blast furnace. The hearth, where the liquid metal is collected, is made of carbon bricks. Cooling water is normally applied to the outside wall of the hearth. Wear of the carbon refractory occurs primarily because of erosion, which is related to the operating conditions of the hearth, such as the liquid flow in the hearth and the heat duty to the walls. Evaluation of fluid flow, heat transfer, and erosion patterns in the hearth are critical to the extension of the campaign life of a blast furnace, leading to the increase of productivity and saving of costs significantly. Advanced computational fluid dynamics (CFD) modeling techniques make it possible for providing detailed information on furnace conditions and parametric effects on performance. In this research, the blast furnace No. 13 at U.S Steel has been simulated using a comprehensive CFD model. The model was validated using the temperatures measured by thermocouples in the wall refractories of the furnace. The effects of cooling water on the temperature distributions as well as erosion patterns were evaluated. The results provide useful information for the furnace operations.
Design Optimization of Forward-Curved Blades Centrifugal Fan With Response Surface Method
Authors: Seo Seoung-Jin , Kim Kwang-Yong
Published: March 2009

This paper presents the response surface optimization method using three-dimensional Navier-Stokes analysis to optimize the shape of a forward-curved blades centrifugal fan. For numerical analysis, Reynolds-averaged Navier-Stokes equations with k-ε turbulence model are discretized with finite volume approximations. In order to reduce huge computing time due to a large number of blades in forward-curved blades centrifugal fan, the flow inside of the fan is regarded as steady flow by introducing the impeller force models. Three geometric variables, i.e., location of cut off, radius of cut off, and width of impeller, and one operating variable, i.e., flow rate, were selected as design variables. As a main result of the optimization, the efficiency was successfully improved. And, optimum design flow rate was found by using flow rate as one of design variables. It was found that the optimization process provides reliable design of this kind of fans with reasonable computing time.
Computations of Boiling Flows
Authors: Tryggvason Gre´tar , Esmaeeli Asghar
Published: March 2009

Numerical simulations of boiling flows are discussed. The change of phase from liquid to vapor and vice-versa usually takes place in a highly unsteady manner where the phase boundary is very convoluted. Direct numerical simulations therefore require the accurate solution of the Navier-Stokes equations and the energy equation in each phase and the correct incorporation of the unsteady phase boundary. Such simulations, where the motion of an unsteady phase boundary is followed for a sufficiently long time to allow computation of average heat transfer are very recent. Here, we will describe one method that has been used successfully to simulate boiling flows and show a few examples of studies using the method.
Droplet Formation From a Pulsed Vibrating Nozzle
Authors: Yang Guozhong , Liburdy James A.
Published: March 2009

Droplet formation from a passive vibrating nozzle driven by a pulsed pressure wave is numerical simulated. The nozzle is an orifice in a thin walled plate which is allowed to vibrate due to the pressure loading on the plate. The analysis couples the fluid flow from the nozzle and the resultant droplet formation with the nozzle vibration calculated using large deflection theory. A one-dimensional fluid flow model is used where droplet formation is driven by a short step change in applied pressure. The problem is made nondimensional based on the capillary parameters of time, velocity and pressure. The nozzle material properties are varied to alter the vibration characteristics of the orifice plate used to form the nozzle. It is determined that the vibration of the nozzle only weakly affects the droplet break-off time and size, but greatly affects the droplet velocity. The resultant filament after drop break-off is also significantly affected by the nozzle vibration, resulting in variations in satellite droplet formation. Higher vibration amplitudes, which correspond to more flexible plates, result in larger total satellite volume.
General Formulations for Rhie-Chow Interpolation
Authors: Zhang Sijun , Zhao Xiang
Published: March 2009

In this paper, general formulations for Rhie-Chow interpolation on co-located grid are derived. Unlike the standard Rhie-Chow interpolation, the general formulations are applicable for any flow conditions. It has observed that the original momentum-based interpolation due to Rhie and Chow has serious deficiency, such as under-relaxation factor dependence, failure to suppress saw-tooth pressure solutions with small time step size for unsteady state problems and wrong solutions or divergence with discontinuities. Thus the derivation of Rhie-Chow interpolation is first recalled, then the errors of numerical discretization are analyzed, finally, new formulations and some improvements are given.
Parallel CFD-DEM for Fluid-Particle Systems
Authors: Zhao Xiang , Wang Jun , Zhang Sijun
Published: March 2009

This paper presents numerical methods and parallel algorithms for modeling the fluid-particle flow in gas fluidization of multi-sized particles. This work involves combined Computational Fluid Dynamics (CFD) and Discrete Element Method (DEM) to describe continuum flow of fluids and discrete flow of solid particles, respectively. Such simulations are extremely computationally intensive. To meet the challenge and produce high-performance, state-of-the-art computational tools capable of simulating the industrial fluid-particle systems, the parallel computing techniques are used with special emphasis of domain decomposition, dynamic load balancing and parallel algorithm. A study of the implementation of a parallel algorithm is also presented, together with performance measurements on PC cluster machines. The results obtained validate not only the parallel algorithm, but also the potential role of such computer systems in industrial fluid-particle flow simulations.
An Aid to Learn Computational Fluid Dynamics: Immersed-Boundary-Based Simulation of 2D Flow
Authors: Lee Sungsu , Yang Kyung-Soo , Hwang Jong-Yeon
Published: March 2009

Development of geometry-independent computational method and educational codes for simulation of 2D flows around objects of complex geometry is presented. Referred as immersed boundary method, it introduces virtual forcing to governing equations to represent the effect of physical boundaries. The present method is based on a finite-volume approach on a staggered grid with a fractional-step method to solve Navier-Stokes equation and continuity equation. Both momentum and mass forcings are introduced on and inside the object to satisfy no-slip condition and mass conservation. Since Cartesian grid lines in general do not coincide with the immersed boundaries, several interpolation schemes are employed. Several examples are simulated using the method presented in this study and the results agree well with other results. Both user-friendly preprocessor with GUI and FORTRAN-based solver are open to the public for educational purposes.
Coherent Structures in Open-Channel Flows Over a Fixed Dune
Authors: Yue Wusi , Lin Ching-Long , Patel Virendra C.
Published: March 2009

Turbulent open-channel flow over a two-dimensional laboratory-scale dune is studied using large eddy simulation. Free surface motion is simulated using a level set method. Two subgrid scale models, namely dynamic Smagorinsky and dynamic two-parameter models, are employed. The present numerical predictions of mean flow field and turbulence statistics are in good agreement with experimental data. Streaky structures are observed in the wall layer after flow reattachment. Quadrant two events dominate near-wall and near-surface motions. Coherent structures are produced behind the dune crest by strong shear layer riding over the recirculation zone. These tube-like vortical structures are transported downstream with the mean flow and most are destroyed before arriving at the next crest.
Development of a Multiple Absorption Coefficient Zonal Method (MACZM) for Application to Radiative Heat Transfer in Multi-Dimensional Inhomogeneous Non-Gray Media
Authors: Yuen Walter W.
Published: March 2009

The formulation of a multiple absorption coefficient zonal method (MACZM) is presented. The method can be directly applied to a fine-grid finite-difference or finite-element computation and is thus an effective approach to generate accurate assessment of the importance of radiative heat transfer in multi-dimensional inhomogeneous, non-gray media. The feasibility of the method is demonstrated by calculating the radiative exchange between a high temperature (∼3000 K) molten nuclear fuel (UO2) and water (with a large variation in absorption coefficient from the visible to the infrared) in a highly 3-D and inhomogeneous environment simulating the premixing phase of a steam explosion.
Experimental Thermal Behavior of Electronic Chips in a Channel During Pump-On Transient Period
Authors: Bhowmik H. , Tou K. W. , Tso C. P.
Published: March 2009

Experiments are performed to study the heat transfer characteristics during the pump-on transient period from an array of 4 × 1 flush mounted discrete heat sources in a vertical rectangular channel using water as the working fluid. The experimental data covers the flow regime with Reynolds number based on heat source length ranging from 1050 to 2625. The applied uniform heat fluxes to the chips are 1, 3, 5 and 7 W/cm2. The effects of heat flux, flow rates and chip numbers are investigated and empirical correlations are developed for investigated and empirical correlations are developed for individual chips as well as for overall data in the transient regime. The transient correlation recommended is Nul/(Pel)1/3 = 3.5(Fo)1/4.
Numerical Analysis of Two-Dimensional Experiment of Shipping Water on Deck Using Particle Method
Authors: Koshizuka S. , Go S. , Oka Y. , Tanizawa K.
Published: March 2009

A two-dimensional computer code is developed for shipping water on deck using a particle method. The method used in Moving Particle Semi-implicit (MPS) method which can be applied to incompressible flow with free surfaces. Since grids are nor necessary, fluid separation and merging are calculated without grid distortion. Numerical diffusion does not take place due to Lagrangian description of the moving particles. An experiment is carried out in two dimensions in order to verify the code. The developed code is applied to this experiment. A linear wave of 7cm height and 69cm width is generated with the average depth of 30cm. A rectangular step of 32cm height is located in front of the wave. The step is covered with water when the wave impinges on the step. The calculated water behaviour agrees well with that of the experiment. The volume of shipping water is also in good agreement with the experiment. Sensitivities with respect to spatial resolution, the number of waves and the wave height are studied.
Numerical Simulation of Heat and Fluid Flow in a Basic Pulse-Tube Refrigerator
Authors: Koshimizu Takao , Kubota Hiromi , Takata Yasuyuki , Ito Takehiro
Published: March 2009

The working principle of refrigeration in basic pulse-tube refrigerators (BPTR) has been explained by the mechanism called surface heat pumping (SHP) that heat is conveyed from the cold end to the hot end of the pulse tube by the successive heat exchange between the working gas and the wall. In this study, a numerical simulation has been performed to clarify the effect of the wall in BPTRs by comparing the numerical results in two physical models; one is the model considering the heat exchange between the working gas and the wall (HE model), and the other is the model ignoring that (AW model). As a result, the importance in the effect of the wall was shown clearly. In addition, the mechanism of refrigeration other than the SHP was made clear in the AW model.