bluuebunny/crossref_metadata_2025 huggingface dataset:
Size Effects on Nonequilibrium Laser Heating of Metal Films
Authors: Qiu T. Q. , Tien C. L.
Published: May 2008

Picosecond and sub-picosecond lasers have become important tools in the fabrication and study of microstructures. When the laser pulse duration becomes comparable with or less than the characteristic time of energy exchange among microscopic energy carriers, the excited carriers are no longer in thermal equilibrium with the other carriers, creating a nonequilibrium heating situation. The presence of interfaces in metals provides additional scattering processes for electrons, which in turn affects the nonequilibrium heating process. This work studies size effects, due to both surface scattering and grain-boundary scattering, on the thermal conductivity and the energy exchange between electrons and the material lattice. A simple formula is established to predict the influence of film thickness, grain size, interface scattering parameters, and the electron and lattice temperatures on the effective thermal conductivity of metal thin films. Predictions of the analysis agree with the available experimental data. A three-energy-level model is developed to characterize the energy exchange between electrons and the lattice. This study shows that the size effect reduces the effective thermal conductivity and increases the electron-phonon energy exchange rate. The results are useful for improving processing quality, interpreting diagnostic results, and preventing thermal damage of thin films during short-pulse laser heating.
Uneven Wall Temperature Effect on Local Heat Transfer in a Rotating Two-Pass Square Channel With Smooth Walls
Authors: Han J.-C. , Zhang Y.-M. , Kalkuehler Kathrin
Published: May 2008

The influence of uneven wall temperature on the local heat transfer coefficient in a rotating, two-pass, square channel with smooth walls is investigated for rotation numbers from 0.0352 to 0.352 by varying Reynolds numbers from 25,000 to 2500. The two-pass square channel, composed of 12 isolated copper sections, has a length-to-hydraulic diameter ratio of 12. The mean rotating radius to the channel hydraulic diameter ratio is kept at a constant value of 30. Three cases of thermal boundary conditions are studied: (A) four walls at the same temperature, (B) four walls at the same heat flux, and (C) trailing wall hotter than leading with side walls unheated and insulated. The results for case A of four walls at the same temperature show that the first channel (radial outward flow) heat transfer coefficients on the leading surface are much lower than that of the trailing surface due to the combined effect of Coriolis and buoyancy forces. The second channel (radial inward flow) heat transfer coefficients on the leading surface are higher than that of the trailing surface. The difference between the heat transfer coefficients for the leading and trailing surface in the second channel is smaller than that in the first channel due to the opposite effect of Coriolis and buoyancy forces in the second channel. However, the heat transfer coefficients on each wall in each channel for cases B and C are higher than case A because of interactions between rotation-induced secondary flows and uneven wall temperatures in cases B and C. The results suggest that the effect of uneven wall temperatures on local heat transfer coefficients in the second channel is greater than that in the first channel.
Turbulent Natural Convection From a Vertical Cylinder to an Array of Cooled Tubes
Authors: McEligot D. M. , Stoots C. M. , Christenson W. A. , Mecham D. C. , Lussie W. G.
Published: May 2008

In order to determine whether available correlations are adequate to treat a complicated, turbulent natural convection problem encountered in industrial practice, experiments were conducted by resistively heating a slender, vertical cylinder centered inside a concentric perforated tube, which was, in turn, surrounded by an array of three larger-diameter cooled tubes. The ratio of the test section temperature to the cooling tube temperature was varied up to 2.6; and the Rayleigh number, based on tube diameter and properties evaluated at the cooling tube temperature, ranged from 2.9×104 to 9.2×105. Results indicate that the convective heat transfer parameters for the perforated tube are about 15 percent higher than for the smooth bare tube centered in the same position relative to the array. The Nusselt number for convective heat transfer across the annulus between the heated test section and the perforated tube corresponded approximately to parallel laminar flow (i.e., Nus≈1).
Simulation of Transient Natural Convection Around an Enclosed Vertical Channel
Authors: Shyy W. , Rao M. M.
Published: May 2008

Accurate numerical calculations have been conducted for buoyancy-driven two-dimensional flow of air between two vertical parallel isothermal plates, of aspect ratio 1, placed inside a rectangular enclosure. The Grashof number based on the channel half width is 105. Insights have been obtained regarding the structure of the transient flow and thermal fields in a configuration of particular interest to electronics cooling. In the early stages of the transient the flowfield was found to be highly vortical and the net volume flow rate in the channel displayed an oscillatory behavior, periodically reversing its direction. However, the velocity profile adjacent to the heated plates maintained the same direction throughout the process, and hence the Nusselt number was relatively insensitive to the periodic flow reversal in the channel. Detailed studies of the transient flow field and the heat transfer results are presented.
Interaction of the Nucleation Processes Occurring at Adjacent Nucleation Sites
Authors: Judd R. L. , Chopra A.
Published: May 2008

An experimental investigation to explore the interaction between bubbles forming at adjacent nucleation sites is presented. The results obtained are consistent with the results of Calka’s and Knowles’ experimental investigations and confirm that nucleation site activation/deactivation, whereby a bubble growing at a nucleation site is able to promote/hinder the formation of a bubble at an adjacent nucleation site by depositing/displacing a vapor nucleus in the nucleation cavity, is instrumental in determining how a bubble forming at a nucleation site influences the nucleation of the subsequent bubble at an adjacent nucleation site.
Boiling Heat Transfer in a Horizontal Small-Diameter Tube
Authors: Wambsganss M. W. , France D. M. , Jendrzejczyk J. A. , Tran T. N.
Published: May 2008

Results of a study on boiling heat transfer of refrigerant R-113 in a small-diameter (2.92 mm) tube are reported. Local heat transfer coefficients are measured for a range of heat flux (8.8–90.75 kW/m2), mass flux (50–300 kg/m2s), and equilibrium mass quality (0–0.9). The measured coefficients are used to evaluate 10 different heat transfer correlations, some of which have been developed specifically for refrigerants. High heat fluxes and low mass fluxes are inherent in small channels, and this combination results in high boiling numbers. In addition, based on a flow pattern map developed from adiabatic experiments with air-water mixtures, it has been shown that small-diameter channels produce a slug flow pattern over a large range of parameters when compared with larger-diameter channels. The effects of high boiling number and slug flow pattern lead to domination by a nucleation mechanism. As a result, the two-phase correlations that predicted this dominance also predicted the data the best when they properly modeled the physical parameters. The correlation of Lazarek and Black (1982) predicted the data very well. It is also shown that a simple form, suggested by Stephan and Abdelsalam (1980) for nucleate pool boiling, correlates the data equally well; both correlations are within a mean deviation of less than 13 percent. Results are applicable to boiling in compact heat exchangers.
Diffusion Layer Theory for Turbulent Vapor Condensation With Noncondensable Gases
Authors: Peterson P. F. , Schrock V. E. , Kageyama T.
Published: May 2008

In turbulent condensation with noncondensable gas, a thin noncondensable layer accumulates and generates a diffusional resistance to condensation and sensible heat transfer. By expressing the driving potential for mass transfer as a difference in saturation temperatures and using appropriate thermodynamic relationships, here an effective “condensation” thermal conductivity is derived. With this formulation, experimental results for vertical tubes and plates demonstrate that condensation obeys the heat and mass transfer analogy, when condensation and sensible heat transfer are considered simultaneously. The sum of the condensation and sensible heat transfer coefficients becomes infinite at small gas concentrations, and approaches the sensible heat transfer coefficient at large concentrations. The “condensation” thermal conductivity is easily applied to engineering analysis, and the theory further demonstrates that condensation on large vertical surfaces is independent of the surface height.
A Thermal Barrier With Adaptive Heat Transfer Characteristics
Authors: Furmanski P. , Floryan J. M.
Published: May 2008

A thermal barrier with adaptive heat transfer characteristics for applications in zero gravity environments is considered. The barrier consists of a mixture of fluid with a small volume fraction of arbitrarily oriented, randomly distributed particles of ellipsoidal shape. Heat flux control is obtained by changing the orientation of the particles. Heat flow may be increased up to several hundred times by rotating the particles from being parallel to the walls to being transverse to the walls and by increasing their aspect ratio, volume fraction, and relative thermal conductivity. An increase in the size of the particles results in the appearance of wall effects, which may substantially reduce heat flow as compared to the case of an infinite medium. Very large temperature variation is found to occur near the walls where an apparent “slip” of temperature occurs for barriers whose thickness is large compared to the particle size.
An Experimental Investigation of the Augmentation of Tube-Side Heat Transfer in a Crossflow Heat Exchanger by Means of Strip-Type Inserts
Authors: Hsieh Shou-Shing , Kuo Ming-Tzung
Published: May 2008

The results of an experimental investigation of the augmentation of heat transfer in a crossflow heat exchanger by means of strip-type inserts are presented and discussed. Three kinds of strip type inserts—longitudinal strip (LS), crossed-strip (CS), and regularly interrupted strip (RIS)—are studied. Correlations for friction factor and Nusselt number are also developed. It is shown that on the basis of both constant pumping power and constant heat duty, LS-inserts perform better than CS- and RIS-inserts for tube-side Reynolds numbers above 19,000. At tube-side Reynolds numbers below 12,000, CS-inserts perform better than LS- and RIS-inserts. Furthermore, flow visualization was made for shell-side hot air and cold air flow in the plenum to advance the qualitative understanding of the physical phenomena of this type of crossflow heat exchanger.
Solidification of Liquid Metal Droplets Impacting Sequentially on a Solid Surface
Authors: Kang B. , Zhao Z. , Poulikakos D.
Published: May 2008

In this paper, a combined theoretical and experimental study is reported on the process of solidification of two liquid metal droplets impacting sequentially one on top of the other on a cold substrate. The process of interest is directly related to the splat-quenching regime in the spray deposition of metal droplets. The theoretical part of the study is focused on the heat transfer aspects of the solidification process and the difference in the behavior of the solidification of the first and second droplet. The experimental part of the study aims at the characterization of the structure of solidified splats composed of one or two droplets. It is found that the solidification of the second droplet exhibits drastically slower cooling rates compared to the first droplet. As a result, the grain structure of the top of a two-droplet splat is considerably coarser than the structure of the top of a single droplet splat. The findings of the present study imply that in splat cooling severe limitations need to be imposed on the thickness of the resulting solid product (ribbon or coating, for example) to ensure rapid solidification and fine grain structure. In addition, it is shown that the temperature field in the substrate is two dimensional and radial conduction in the substrate should not be neglected in the modeling of the process.
Forced Convection in a Porous Channel With Localized Heat Sources
Authors: Hadim A.
Published: May 2008

A numerical study is performed to analyze steady laminar forced convection in a channel filled with a fluid-saturated porous medium and containing discrete heat sources on the bottom wall. Hydrodynamic and heat transfer results are reported for two configurations: (1) a fully porous channel, and (2) a partially porous channel, which contains porous layers above the heat sources and is nonporous elsewhere. The flow in the porous medium is modeled using the Brinkman-Forchheimer extended Darcy model. Heat transfer rates and pressure drop are evaluated for wide ranges of Darcy and Reynolds numbers. Detailed results of the evolution of the hydrodynamic and thermal boundary layers are also provided. The results indicate that as the Darcy number decreases, a significant increase in heat transfer is obtained, especially at the leading edge of each heat source. For fixed Reynolds number, the length-averaged Nusselt number reaches an asymptotic value in the Darcian regime. In the partially porous channel, it is found that when the width of the heat source and the spacing between the porous layers are of the same magnitude as the channel height, the heat transfer enhancement is almost the same as in the fully porous channel while the pressure drop is significantly lower. These results suggest that the partially porous channel configuration is a potentially attractive heat transfer augmentation technique for electronic equipment cooling, an end that motivated this study.
Melting Solid Plug Between Two Coaxial Pipes by a Moving Heat Source in the Inner Pipe
Authors: Fomin S. A. , Wei P. S. , Chugunov V. A.
Published: May 2008

Melting of a solid plug in the gap between two coaxial pipes by inserting a moving heat source in the inner pipe is investigated. Using a scale analysis, closed-form solutions for temperatures of liquid in the inner pipe, solid plug and liquid in the annular gap, and the surrounding medium around the outer pipe are determined. It is shown that eight independent dimensionless parameters are required to specify the entire process. The effects of independent parameters on the shapes of the molten region in the gap are found. The analysis and results provided are useful for the design of oil pipes.
Direct Simulation of Phonon-Mediated Heat Transfer in a Debye Crystal
Authors: Peterson R. B.
Published: May 2008

A direct simulation of phonon-mediated heat transfer is described and preliminary results are reported. The method is derived from past work in simulating gas-dynamic flow and uses a linear array of cells for modeling a one-dimensional heat transfer problem. Central to the development of the technique is the Debye model for heat capacity of a crystal. The energy equation for this type of solid is presented and a phonon frequency distribution is obtained leading to a simulation technique that naturally takes into account changes in heat capacity. Using the linear array of cells, two fundamental problems are investigated. The first deals with the time evolution of the temperature profile in an array of 40 cells where the initial temperature distribution is 300 K, and at time zero the temperature of the first cell is raised to 500 K and maintained at this value. The second problem involves determining the steady-state heat transfer through an array of 20 cells where the two boundary cells are held at 500 K and 300 K. In this latter problem, the phonon mean free path is varied for each run and the results compared to both a continuum and radiation model for the heat transfer. Considering the simplistic approach used in modeling the phonon collisions, the results from both the time evolution problem and the steady energy transfer one are encouragingly close to predictions made with analytical solutions.
The Interfacial Pressure Distribution and Thermal Conductance of Bolted Joints
Authors: Mittelbach M. , Vogd C. , Fletcher L. S. , Peterson G. P.
Published: May 2008

Experimental interface pressure distributions and thermal conductance data are presented for a bolted joint. The variables considered included the bolt torque and associated axial load, the upper and lower plate thicknesses, and the mean interface temperature within the bolt radius. For 7.62-cm-dia Aluminum 6061-T6 plates, axial loads of 6.69 to 13.425 kN (1500 to 3000 lb), three heat fluxes, and mean junction temperatures of up to 310 K were considered. Pressure distribution data obtained with a pressure-sensitive film compared favorably with both theoretical predictions and published experimental data. Thermal conductance data obtained at three radial locations for the bare interface compared favorably with published data. These data also were compared with a previously published correlation for heat transfer in bolted joints. Thermal conductance data for high-conductivity elastomeric gasket materials were obtained to ascertain their suitability for thermal enhancement. The results of this investigation will be useful in the thermal analysis of bolted and riveted joints.
Approximate Analytical Solution of Forced Convection Heat Transfer From Isothermal Spheres for All Prandtl Numbers
Authors: Refai Ahmed G. , Yovanovich M. M.
Published: May 2008

A new, simple and approximate analytical method based on linearization of the energy equation is proposed to develop solutions for forced convection heat transfer from isothermal spheres. Furthermore, heat transfer correlations from spheres are proposed in the range of Reynolds number, 0 ≤ ReD ≤ 2 × 104, and all Prandtl numbers. This technique is performed as follows. The first step is to approximate the energy equation to the form of a transient heat conduction equation that has an existing solution. The second step is to evaluate the effective velocity through scaling analysis in the limit of Pr → ∞ and Pr → 0 and then resubstitute the effective velocity into the solution of the energy equation. Finally, a “blending method” is used to provide a general model for all Prandtl numbers. Comparison of the heat transfer correlations for NuD versus ReD from the present study with the available correlations in the literature reveals very good agreement.
Effect of Flow Pulsations on the Cooling Effectiveness of an Impinging Jet
Authors: Sheriff H. S. , Zumbrunnen D. A.
Published: May 2008

An experimental investigation has been performed to study the effect of flow pulsations on local, time-averaged convective heat transfer to an impinging water jet. Sinusoidal and square-pulse waveforms were considered. For the square waveform, the flow was completely halted for a portion of the pulsation cycle. Hot-film anemometry was used to characterize both the steady and the pulsating flows with regard to turbulence level and the spatial uniformity in the velocity profile across the nozzle width in order to assess separately the influence of flow pulsation on convective heat transfer. Pulse magnitude, which was defined as the ratio of the mean-to-peak velocity change to the mean flow velocity, was varied from 0.5 to 100 percent. Pulse frequencies ranged from 5 to 280 Hz, which corresponded to Strouhal numbers based on jet width and velocity of 0.014 to 0.964. Observed effects on convective heat transfer are explained in terms of nonlinear dynamic responses of the hydrodynamic and thermal boundary layers, boundary layer renewal, and bulges in the jet free surface.
Mass Transfer With Flow Through an Array of Rectangular Cylinders
Authors: Cho H. H. , Jabbari M. Y. , Goldstein R. J.
Published: May 2008

The mass transfer from an array of naphthalene-coated parallel rectangular cylinders, through which air passes in a slitlike flow, has been measured. The local Sherwood numbers indicate that the flow pattern is asymmetric in spite of using an array of two-dimensional, equally spaced identical cylinders. Smoke-wire flow visualization verifies this asymmetry, showing alternate short and long wakes around the cylinders, due probably to the instability of vortex shedding. On the side surfaces of the cylinders with the short wakes, the airflow deflects and reattaches, resulting in a high mass transfer. Also, a strong impinging effect is observed on the leeward (back) surface of these cylinders at high Reynolds numbers. Reattachment is not observed on the side surface for cylinders with the long wakes. On these, however, the mass transfer on the leeward surface is higher than on the short wake cylinders. This may be due to the relatively low naphthalene vapor concentration in the long wakes. The distribution of the short wakes (and the long wakes) is periodic and relatively stable. However, their position can be changed from one cylinder to the adjacent one by a disturbance. Measurements were taken over a moderate Reynolds number range of 300 to 3000 (based on the cylinder-to-cylinder pitch and approaching velocity). The laminar, transition, and turbulent nature in the wake flows can be inferred from the results.
Mixed Convection From Simulated Electronic Components at Varying Relative Positions in a Cavity
Authors: Papanicolaou E. , Jaluria Y.
Published: May 2008

A numerical study of the combined-forced and natural convective cooling of heat-dissipating electronic components, located in a rectangular enclosure, and cooled by an external throughflow of air is carried out. A conjugate problem is solved, describing the flow and thermal fields in air, as well as the thermal field within the walls of the enclosure and the electronic components themselves. The interaction between the components is of interest here, depending on their relative placement in the enclosure, and different configurations are considered. For Re = 100 laminar, steady flow is predicted for up to Gr/Re2 = 10, but a single-frequency oscillatory behavior is observed for most of the configurations studied, at Gr/Re2 = 50. Heat transfer results are presented for both the laminar and the oscillatory domains. The mixed convection regime, where the buoyancy effects are comparable to the forced flow, occurs at values of Gr/Re2 between 0.01 and 10. The results are of value in the search for a suitable placement of electronic components in an enclosed region for an effective heat removal.
The Cylindrical Electrostatic Liquid Film Radiator for Heat Rejection in Space
Authors: Kim H. , Bankoff S. G. , Miksis M. J.
Published: May 2008

A new space radiator concept has been proposed (Kim et al., 1991, 1992a, b, 1993) in which a thin film of hot liquid, flowing along the inside of a closed membrane, rejects waste heat by radiation to the surroundings. In previous versions, the radiator rotates, supplying most of the driving force for the liquid flow. In the present design, the cylinder is stationary, and the liquid flows circumferentially under its initial momentum. Moderately large Reynolds numbers are required to overcome viscous drag, and prevent excessive thickening of the film. The major design consideration involves the application of an internal electrostatic field to pull the liquid away from the site of a membrane puncture due to micrometeorite impact. Calculations are presented that show that leaks can be stopped with a safety factor of two or more, while the surface wave thus produced is washed harmlessly out of the system. Some preliminary heat transfer performance characteristics are presented. The advantages of this concept include the absence of moving parts and the ease of deployment, compared to rotating units, and a factor of at least three for the reduction of the weight per unit surface area compared to heat pipes.
Recirculation in an Annular-Type Jet Pump
Authors: Elger Donald F. , Taylor Sam. J. , Liou Chyr P.
Published: May 2008

For some annular-type jet pump applications, it is important to avoid formation of a recirculation zone in the mixing region. The goals of this research were to find (i) when recirculation occurs and (ii) the size and location of the resulting recirculation zone. Experiments were performed using air in a straight-walled, annular-type, ducted jet. Area ratio Aj/As varied from 0.39 to 0.89; here, A is flow area, and j and s identify the jet and secondary flows, respectively. Data showed that recirculation correlates with J, where J ≈ Pj/(Pj + Ps), and P is rate of momentum. For the area ratios studied, recirculation begins when J exceeds a value ranging from 0.89 to 0.94. This paper also presents data showing the recirculation zone boundaries and presents a discussion of jet pump design.
Numerical Simulation of a Dilute Particulate Flow (Laminar) Over Tube Banks
Authors: Jun Yong-Du , Tabakoff Widen
Published: May 2008

This paper presents an investigation of numerical simulation for a dilute particle laden flow (laminar) over in-line tube banks. Particles behavior of two different sizes and density (100 μm sand and 40 μm fly ash) is demonstrated through the present study for a fixed geometry and flow condition, that is, a square in-line tube bank of two rows deep with pitch-to-diameter ratio of two at Reynolds number 400. Dilute particulate flow assumption is used and the drag force is considered as the only external force term that affects the particles behavior in the flow. Experimental rebounding data and semiempirical equation for the erosion estimation are used. It was found through the present simulation that the particles behavior of the different sizes and density in tube bank system is quite different in their trajectories, impact and the erosion pattern. The protective role of the first row of cylinders could be supported with respect to the particles collision on the cylinder but not necessarily to the erosion point of view. Also the information at impact such as the impact velocity and the impact angle which affect the erosion (Tabakoff et al., 1988) can be estimated by using the numerical simulation shown in the present study.
Particle Mixing and Volumetric Expansion in a Vibrated Granular Bed
Authors: Hunt M. L. , Hsiau S. S. , Hong K. T.
Published: May 2008

The present experiments are an investigation of the expansion and mixing that occur in a horizontal bed of particles subjected to vibrational accelerations in the direction parallel to gravity. The particles are colored-glass balls of uniform size; three different bed heights are examined of 6, 9, and 12 particle diameters. The vibrational frequency and amplitude are controlled separately to cover a range of acceleration levels from 1 to 5.5 times gravitational acceleration. The expansion results show that above a critical frequency, the bed begins to expand and the bed solid fraction decreases. This result is independent of the vibrational amplitude. Above a second critical frequency, the thickest beds show a further decrease in solid fraction; the minimum value of solid fraction for all bed heights is approximately 0.21 ± 0.03. The mixing results indicate that the mixing times decrease significantly with the expansion of the bed. However, the mixing times are greater as the bed depth increases. Unlike the expansion results, the mixing times depend on the amplitude of the vibration. A simple analysis of the flow is performed using a self-diffusion coefficient developed from dense-gas kinetic theory. The analysis qualitatively agrees with the experiments for the largest vibrational velocities and for the thinnest beds.
Spin-Up From Rest of a Two-Layer Liquid in a Cylinder
Authors: Kim Kwan Yeop , Hyun Jae Min
Published: May 2008

A numerical and analytical study is made of spin-up from rest of a two-layer liquid in a rapidly rotating cylinder. The overall system Ekman number is small. The density of the top layer is smaller than that of the bottom layer (ρ1/ρ2<1.0), but the ratio of the individual layer kinematic viscosities is arbitrary (v1/v2<1.0 or v1/v2>1.0). The highlights of the analytical model, which is based on amended formulations of the Wedemeyer-Gerber-Homicz flow configurations, are briefly recapitulated. Comprehensive numerical solutions are secured to the time-dependent Navier–Stokes equations. The numerical solutions are validated by comparing the maximum interface displacements with the available experimental data as well as the analytical model predictions. Descriptions are made of the prominent characteristics of the interface shape for the two regimes of v1/v2<1.0 and v1/v2 > 1.0. Details of the azimuthal and meridional flow structures are illustrated by exploiting the numerical solutions. The computed meridional flows are compatible with the basic assumptions embedded in the development of the analytical model. Sequential plots of the radial profiles of azimuthal velocities are presented. These show that the global spin-up process is substantially accomplished over (En−1/2Ω−1), where En denotes the value of the smaller Ekman number of the two layers. The numerical study gives credence to the reliability and accuracy of the simplified analytical model.
Computational Study of Disk Driven Rotating Flow in a Cylindrical Enclosure
Authors: Lang E. , Sridhar K. , Wilson N. W.
Published: May 2008

The problem of steady laminar flow in a stationary cylinder driven by a rotating disk at the top was studied numerically. Three governing equations in cylindrical coordinates were solved by the spatially second-order and temporally first-order accurate ADI method. The flow was characterized by three bulk quantities, namely the torque coefficient and the primary and secondary volumetric flow rates. Calculation of the torque coefficient presented a difficulty because the velocity gradient is singular where the rotating disk and the stationary cylinder meet. This problem was overcome by specifying a gap between the disk and cylinder in the boundary conditions. The results obtained compared favourably with previous experimental results. The relevant parameters for the problem were the rotational Reynolds number, the aspect ratio and the gap. The ranges investigated were as follows: Reynolds number from 1 to 105; aspect ratio from 0.02 to 3; and gap size from 0.1 to 10 percent of the cylinder radius. The results showed that the bulk quantities were dependent on the Reynolds number and the aspect ratio. The torque coefficient was also dependent on the gap, while the volumetric flow rates were only weakly dependent on the gap. For high aspect ratios, the bulk quantities approached constant values.
Performance Analysis of Viscous Flow Computations on Various Parallel Architectures
Authors: Drikakis D. , Schreck E. , Durst F.
Published: May 2008

A study on the performance of parallel viscous flow computations on various parallel architectures is presented. An implicit computational fluid dynamics code was utilized to solve the axisymmetric compressible Navier-Stokes equations, and parallelization of the code was obtained by the grid partitioning technique. Several hardware and software issues, such as, different communication possibilities and their effect on the parallel performance, the numerical and parallel efficiency for single grid and mesh-sequencing solutions, double and single precision calculations, and the effect of the number of processors on the computing time and the parallel performance, were investigated. Calculations for laminar and turbulent benchmark cases were performed on four parallel platforms and the results were compared with corresponding computations done on the Cray Y-MP utilizing only one processor. A theoretical model for the prediction of the parallel efficiency was also derived and it was verified for single grid and mesh-sequencing solutions by comparing the measured efficiencies with those of the predicted ones.
Unsteady Flow in Diffusers
Authors: Kwong A. H. M. , Dowling A. P.
Published: May 2008

The flow in a diffuser is unsteady in the range of optimum pressure recovery; diffusers can therefore be a major source of noise in pipework systems. A theory is developed to predict the frequency of this noise and good agreement with experimental results, for both conical and rectangular diffusers, is demonstrated. The acoustics of the duct to which a diffuser is connected are found to have a crucial effect on the unsteady flow within the diffuser, a point which has been overlooked previously in the literature. Once this is recognized, it is possible to reconcile experimental results for air and water diffusers.
Computational Study of Resonance Suppression of Open Sunroofs
Authors: Ota D. K. , Chakravarthy S. R. , Becker T. , Sturzenegger T.
Published: May 2008

A 2-D computational study of flow over a fully open sunroof of a car with a passenger compartment has been done on a scalar workstation. The critical velocity for resonance in the passenger compartment has been determined. A wind deflector angle study has been done to determine an adequate angle to suppress the resonance. A validation case of computing the resonance condition of the flow over a 3:1 depth to length rectangular cavity has also been done. These resonance studies show the potential of using scalar workstations for a CFD design study.
Condensation in a Porous Region Bounded by a Cold Vertical Surface
Authors: Chung J. N. , Plumb O. A. , Lee W. C.
Published: May 2008

The problem of condensation in a porous medium near a cold vertical surface is investigated numerically and experimentally. Numerical solutions to the mathematical model, which assumes that a distinct two-phase zone exists between the liquid and the vapor phases, compare favorably with the experimental results. Experiments were performed for steam condensing in packed beds of glass beads of three different sizes. In the numerical model, the effect of the vapor flow in the two-phase zone is included. The interfacial velocity was determined through the matching of shear stress and a total mass balance. The predicted interfacial velocities are around one to two orders of magnitude smaller than the Darcy velocity. The calculated liquid film thicknesses are on the order of the diameter of the glass beads. The results, presented in dimensionless format, are applicable to transport processes in geothermal reservoirs, steam-driven enhanced petroleum recovery, and a number of industrial applications.
A Study of Thermal Energy Storage Systems With Conjugate Turbulent Forced Convection
Authors: Cao Y. , Faghri A.
Published: May 2008

A phase-change energy storage module with a turbulent transport fluid is studied. The forced convection due to the turbulent transport fluid is solved with the k–ε model and coupled with the phase-change solution in the phase-change material (PCM). The numerical method is first compared with previous investigations, then conjugate computations for the energy storage module with different cases are conducted. A correlation for the energy storage capacity is derived and its empirical constants are determined by the numerical data. The correlation provides a reference for the module design and parameter optimization.
Optimization of Multiprobe Cryosurgery
Authors: Keanini R. G. , Rubinsky B.
Published: May 2008

This paper describes a general technique for optimizing cryosurgical procedures. The method, which is based on the simplex minimization algorithm, minimizes unnecessary freezing by optimizing various surgical parameters. The optimization procedure is illustrated using a simplified model of prostatic cryosurgery. In this illustrative case, the function to be minimized, F, defined as the volume of healthy tissue destroyed during complete freezing of the prostate, is assumed to depend on three parameters: the number of cryoprobes used, the freezing length per cryoprobe, and the cryoprobe diameter. Using an iterative procedure, the optimization algorithm first alters these parameters, then calculates F by solving a three-dimensional bioheat transfer model of multiprobe cryosurgery, and finally determines whether F is minimized. The iterative procedure continues until unnecessary freezing is minimized. For the model considered here, the optimization code indicates that unnecessary freezing during cryoprostatectomy is minimized using approximately 5 cryoprobes, each 7.5 mm in length and 4 mm in diameter.
Thermal Constriction Resistance of Phase-Mixed Metallic Coatings
Authors: Chung K. C. , Sheffield J. W. , Sauer H. J.
Published: May 2008

A phase-mixed coating using plasma-enhanced deposition onto a cold surface can offer excellent characteristics of adhesion of coatings to a wide range of base materials, and very close control of coating thickness. These physical characteristics are of great importance to the control of surface contact situations and in particular to the thermal constriction resistance of contact joints, with many applications in thermal control systems. Analytical expressions were developed for the thermal constriction resistance of cylindrical contact spots in such coatings. The thermal constriction parameter was presented in the dimensionless form as a function of the contact geometry, coating thickness, and thermal conductivity ratio of the two different coating materials. Finally, the results of analytical thermal constriction resistance were compared with experimental investigation using copper-carbon and silver-carbon phase-mixed coating materials. Conclusions on selecting phase-mixed coating materials were based solely on the thermal point of view
Heat Transfer With Very High Free-Stream Turbulence: Part I—Experimental Data
Authors: Maciejewski P. K. , Moffat R. J.
Published: May 2008

The present research investigates boundary layer heat transfer with very high freestream turbulence, a problem of primary interest in the gas turbine industry where existing boundary layer correlations and codes underpredict local heat transfer rates on first-stage turbine blades and vanes by as much as a factor of three for some engine designs. The problem was studied experimentally by placing a constant-temperature heat transfer surface at various locations in the margin of a turbulent free jet and measuring both the surface heat transfer rate and the turbulence in the free stream. In this experiment, free-stream turbulent fluctuations 20 to 60 percent relative to the mean velocity augment heat transfer 1.8 to 4 times that which would be predicted locally using accepted correlations for turbulent boundary layers at the same Reynolds number.
Analysis of a Screen Heat Exchanger
Authors: Jones G. F. , Prenger F. C.
Published: May 2008

Heat transfer in a fluid-to-fluid screen heat exchanger is analyzed from first principles. The screens are treated as an ensemble of pin fins and an empirical heat transfer coefficient accounts for convection heat transfer at the fin surface. Pressure drop and simultaneous axial conduction in the screen matrix and the wall separating the fluid streams are modeled. Expressions are obtained that relate dimensionless length ratios to exchanger effectiveness and pressure drop. The “mesh ratio,” defined as the ratio of fin diameter (d) to spacing (s), prevails throughout the results. The key findings are: (1) the existence of an optimal ratio of fin length (a) to fin diameter that maximizes thermal performance (arising from the competition between the fin-length dependent heat transfer coefficient and fin surface area), (2) increasing a/d greater than optimal increases exchanger length and reduces pressure drop; for a/d less than optimal heat transfer is depressed and pressure drop increased, and (3) the pressure drop is linear with overall Ntu and varies as d−2, (1 + d/s)6, and approximately the square of the mass flow rate per width of exchanger. An exact solution for axial conduction is presented that is valid in the limit of large Ntu and equal fluid capacity rates. Axial conduction is seen to decrease with increasing Ntu and mass flow rates and reduced fin a/d ratio. Predictions from the model are validated by comparing with published effectiveness and pressure-drop data.
Prediction of Heat Transfer and Friction for the Louver Fin Geometry
Authors: Sahnoun A. , Webb R. L.
Published: May 2008

This paper is concerned with prediction of the air-side heat transfer coefficient of the louver fin geometry used in automotive radiators. An analytical model was developed to predict the heat transfer coefficient and friction factor of the louver fin geometry. The model is based on boundary layer and channel flow equations, and accounts for the “flow efficiency” in the array, as previously reported by Webb and Trauger. The model has no empirical constants. The model allows independent specifications of all of the geometric parameters of the louver fin. This includes the number of louvers over the flow depth, the louver width and length, and the louver angle. The model was validated by predicting the heat transfer coefficient and friction factor of 32 louver arrays tested by Davenport, which spanned hydraulic diameter based Reynolds numbers of 300–2800. At the highest Reynolds number, all of the heat transfer coefficients were predicted within a maximum error of −14 / + 25 percent, and a mean error of ± 8 percent. The high Reynolds number friction factors were predicted with a maximum error −22 /+ 26 percent, with a mean error of ± 8 percent. The error ratios were slightly higher at the lowest Reynolds numbers.
Three-Dimensional Natural Convection in a Vertical Porous Layer With a Hexagonal Honeycomb Core
Authors: Asako Y. , Nakamura H. , Yamaguchi Y. , Faghri M.
Published: May 2008

Numerical solutions are obtained for a three-dimensional natural convection heat transfer problem in a vertical porous layer with a hexagonal honeycomb core. The porous layer is assumed to be long and wide such that the velocity and temperature fields repeat themselves in successive enclosures. The natural convection problem is solved for only one honeycomb enclosure with periodic thermal boundary conditions. The porous layer is assumed to be homogeneous and isotropic and the flow is obtained by using the Darcian model. The numerical methodology is based on an algebraic coordinate transformation technique, which maps the hexagonal cross section onto a rectangle. The transformed governing equations are solved with the SIMPLE algorithm. The calculations are performed for the Darcy–Rayleigh number in the range of 10 to 103 and for eight values of the aspect ratio (H/L = 0.25, 0.333, 0.5, 0.7, 1, 1.4, 2, and 5). Two types of thermal boundary condition for the honeycomb core wall are considered: conduction and adiabatic honeycomb core wall thermal boundary conditions. The results are presented in the form of average and local heat transfer coefficients and are compared with the corresponding values for two and three-dimensional rectangular enclosures.
Radiative Properties of Y-Ba-Cu-0 Films With Variable Oxygen Content
Authors: Choi B. I. , Zhang Z. M. , Flik M. I. , Siegrist T.
Published: May 2008

The room-temperature radiative properties of YBa2Cu3O7−δ superconducting films with varying oxygen content (δ = 0 to 1) on a LaAlO3 substrate are investigated. The fitting of reflectance spectra using thin-film optics and the Drude-Lorentz model function with multiple oscillators determines the optical constants. The film with high oxygen content (δ = 0) has a metallic optical behavior. A decrease in the oxygen content causes a removal of free carriers, and the film with low oxygen content (δ = 1) acts like a dielectric with a very weak free-electron contribution. Knowledge of the optical constants of oxygen-deficient YBa2Cu3O7-δ films facilitates accurate substrate temperature measurement and control during the film deposition process.
In Vitro Activity of Ferroquine Is Independent of Polymorphisms in Transport Protein Genes Implicated in Quinoline Resistance in
Plasmodium falciparum
Authors: Henry Maud , Briolant Sébastien , Fontaine Albin , Mosnier Joel , Baret Eric , Amalvict Rémy , Fusaï Thierry , Fraisse Laurent , Rogier Christophe , Pradines Bruno
Published: May 2008

The in vitro activity of ferroquine (FQ) (SR97193), a 4-aminoquinoline antimalarial compound that contains a ferrocenic nucleus, against 15
Plasmodium falciparum
strains was assessed and compared with those of chloroquine (CQ), quinine (QN), monodesethylamodiaquine (MDAQ), and mefloquine (MQ). These 15 strains were genotyped for polymorphisms in quinoline resistance-associated genes such as Pf
crt
, Pf
mdr1
, Pf
mrp
, and Pf
nhe-1
. FQ was highly active against CQ-resistant parasites or in parasites with reduced susceptibility to QN, MDAQ, or MQ. Encouragingly, we did not find a correlation between responses to FQ and those to other quinoline drugs. These results suggest that no cross-resistance exits between FQ and CQ or quinoline antimalarial drugs. Mutations in codons 74, 75, 76, 220, 271, 326, 356, and 371 of the Pf
crt
gene; codons 86, 184, 1034, 1042, and 1246 of the Pf
mdr1
gene; and codons 191 and 437 of the Pf
mrp
gene were not significantly associated with
P. falciparum
susceptibility to FQ. Neither the number of ms4760 DNNND or DDNHNDNHNN repeats in Pf
nhe-1
nor the profile of ms4760 was significantly associated with the FQ in vitro response. These data suggest the FQ may not interact with transport proteins in quinoline-resistant parasites. The present results justify further clinical trials of FQ in multidrug resistance areas.
Amphipathic DNA Polymers Exhibit Antiherpetic Activity In Vitro and In Vivo
Authors: Bernstein David I. , Goyette Nathalie , Cardin Rhonda , Kern Earl R. , Boivin Guy , Ireland James , Juteau Jean-Marc , Vaillant Andrew
Published: May 2008

Phosphorothioated oligonucleotides have a sequence-independent antiviral activity as amphipathic polymers (APs). The activity of these agents against herpesvirus infections in vitro and in vivo was investigated. The previously established sequence-independent, phosphorothioation-dependent antiviral activity of APs was confirmed in vitro by showing that a variety of equivalently sized homo- and heteropolymeric AP sequences were similarly active against herpes simplex virus type 1 (HSV-1) infection in vitro compared to the 40mer degenerate parent compound (REP 9), while the absence of phosphorothioation resulted in the loss of antiviral activity. In addition, REP 9 demonstrated in vitro activity against a broad spectrum of other herpesviruses: HSV-2 (50% effective concentration [EC50], 0.02 to 0.06 μM), human cytomegalovirus (EC50, 0.02 to 0.13 μM), varicella zoster virus (EC50, <0.02 μM), Epstein-Barr virus (EC50, 14.7 μM) and human herpesvirus types 6A/B (EC50, 2.9 to 10.2 μM). The murine microbicide model of genital HSV-2 was then used to evaluate in vivo activity. REP 9 (275 mg/ml) protected 75% of animals from disease and infection when provided 5 or 30 min prior to vaginal challenge. When an acid-stable analog (REP 9C) was used, 75% of mice were protected when treated with 240 mg/ml 5 min prior to infection (P< 0.001), while a lower dose (100 mg/ml) protected 100% of the mice (P< 0.001). The acid stable REP 9C formulation also provided protection at 30 min (83%,P< 0.001) and 60 min (50%,P= 0.07) against disease. These observations suggest that APs may have microbicidal activity and potential as broad-spectrum antiherpetic agents and represent a novel class of agents that should be studied further.