bluuebunny/crossref_metadata_2025 huggingface dataset:
Simultaneous Determination of Temperatures, Heat Fluxes, Deformations, and Tractions on Inaccessible Boundaries
Authors: Dennis B. H. , Dulikravich G. S.
Published: February 2008

A finite element method formulation for the detection of unknown steady boundary conditions in heat conduction and linear elasticity and combined thermoelasticity continuum problems is presented. The present finite element method formulation is capable of determining displacements, surface stresses, temperatures, and heat fluxes on the boundaries where such quantities are unknown or inaccessible, provided such quantities are sufficiently overspecified on other boundaries. Details of the discretization, linear system solution techniques, and sample results for two-dimensional problems are presented.
Numerical Prediction of Transitional Features of Turbulent Forced Gas Flows in Circular Tubes With Strong Heating
Authors: Ezato K. , Shehata A. M. , Kunugi T. , McEligot D. M.
Published: February 2008

In order to treat strongly heated, forced gas flows at low Reynolds numbers in vertical circular tubes, the k-ε turbulence model of Abe, Kondoh, and Nagano (1994), developed for forced turbulent flow between parallel plates with the constant property idealization, has been successfully applied. For thermal energy transport, the turbulent Prandtl number model of Kays and Crawford (1993) was adopted. The capability to handle these flows was assessed via calculations at the conditions of experiments by Shehata (1984), ranging from essentially turbulent to laminarizing due to the heating. Predictions forecast the development of turbulent transport quantities, Reynolds stress, and turbulent heat flux, as well as turbulent viscosity and turbulent kinetic energy. Overall agreement between the calculations and the measured velocity and temperature distributions is good, establishing confidence in the values of the forecast turbulence quantities—and the model which produced them. Most importantly, the model yields predictions which compare well with the measured wall heat transfer parameters and the pressure drop.
Transition of Chaotic Flow in a Radially Heated Taylor-Couette System
Authors: Kedia R. , Hunt M. L. , Colonius T.
Published: February 2008

Numerical simulations have been performed to study the stability of heated, incompressible Taylor-Couette flow for a radius ratio of 0.7 and a Prandtl number of 0.7. As Gr is increased, the Taylor cell that has the same direction of circulation as the natural convection current increases in size and the counterrotating cell becomes smaller. The flow remains axisymmetric and the average heat transfer decreases with the increase in Gr. When the cylinder is impulsively heated, the counterrotating cell vanishes and n = 1 spiral is formed for Gr = 1000. This transition marks an increase in the heat transfer due to an increase in the radial velocity component of the fluid. By slowly varying the Grashof number, the simulations demonstrate the existence of a hysteresis loop. Two different stable states with same heat transfer are found to exist at the same Grashof number. A time-delay analysis of the radial velocity and the local heat transfer coefficient time is performed to determine the dimension at two Grashof numbers. For a fixed Reynolds number of 100, the two-dimensional projection of the reconstructed attractor shows a limit cycle for Gr = −1700. The limit cycle behavior disappears at Gr = −2100, and the reconstructed attractor becomes irregular. The attractor dimension increases to about 3.2 from a value of 1 for the limit cycle case; similar values were determined for both the local heat transfer and the local radial velocity, indicating that the dynamics of the temperature variations can be inferred from that of the velocity variations.
Heat Transfer of Compressed Air Flow in a Spanwise Rotating Four-Pass Serpentine Channel
Authors: Hwang G. J. , Tzeng S. C. , Mao C. P.
Published: February 2008

Convective heat transfer of compressed air flow in a radially rotating four-pass serpentine channel is investigated experimentally in the present study. The coolant air was compressed at 5 atmospheric pressure to achieve a high rotation number and Reynolds number simultaneously. The main governing parameters are the Prandtl number, the Reynolds number for forced convection, and the rotation number for the Coriolis-force-induced cross-stream secondary flow and the Grashof number for centrifugal buoyancy. To simulate the operating conditions of a real gas turbine, the present study kept the parameters in the test rig approximately the same as those in a real engine. The air in the present serpentine channel was pressurized to increase the air density for making up the low rotational speed in the experiment. The air flow was also cooled to increase the density ratio before entering the rotating ducts. Consequently, the order of magnitude of Grashof number in the present study was the same as that in real operating conditions. The local heat transfer rate on the walls of the four-pass serpentine channel are correlated and compared with that in the existing literature.
Combined Natural Convection and Volumetric Radiation in a Horizontal Annulus: Spectral and Finite Volume Predictions
Authors: Kuo D.-C. , Morales J. C. , Ball K. S.
Published: February 2008

Combined natural convection and radiation in a two-dimensional horizontal annulus filled with a radiatively participating gray medium is studied numerically by using a control-volume-based finite difference method and a spectral collocation method coupled with an influence matrix technique. The mathematical model includes the continuity equation, the incompressible Navier-Stokes equations, the energy equation, and the radiative transfer equation (RTE), which is modeled using the P1 differential approximation. Computed results for two Rayleigh numbers, Ra = 104 and Ra = 105, for several combinations of the radiation-conduction parameter, NR, and the optical thickness, τ, are presented. The differences observed in the predicted flow structures and heat transfer characteristics are described. Furthermore, an unusual flow structure is studied in detail, and multiple solutions are found. Finally, the potential benefits of applying spectral methods to problems involving radiative heat transfer are demonstrated.
Dynamics and Heat Transfer Associated With a Single Bubble During Nucleate Boiling on a Horizontal Surface
Authors: Son G. , Dhir V. K. , Ramanujapu N.
Published: February 2008

In this study, a complete numerical simulation of a growing and departing bubble on a horizontal surface has been performed. A finite difference scheme is used to solve the equations governing conservation of mass, momentum, and energy in the vapor-liquid layers. The vapor-liquid interface is captured by a level set method which is modified to include the influence of phase change at the liquid-vapor interphase. The disjoining pressure effect is included in the numerical analysis to account for heat transfer through the liquid microlayer. From the numerical simulation, the location where the vapor-liquid interface contacts the wall is observed to expand and then retract as the bubble grows and departs. The effect of static contact angle and wall superheat on bubble dynamics has been quantified. The bubble growth predicted from numerical analysis has been found to compare well with the experimental data reported in the literature and that obtained in this work.
Air-Side Heat Transfer and Friction Correlations for Plain Fin-and-Tube Heat Exchangers With Staggered Tube Arrangements
Authors: Kim N. H. , Youn B. , Webb R. L.
Published: February 2008

This paper deals with heat exchangers having plain fins on a staggered array of circular tubes. Correlations are developed to predict the air-side heat transfer coefficient and friction factor as a function of the Reynolds number and geometric variables of the heat exchanger such as tube diameter, tube pitch, fin spacing, etc. A multiple regression technique was used to correlate 47 sets of heat exchanger data to develop the heat transfer and friction correlation. The correlations are applicable to heat exchangers having small diameter tubes (or large tube pitch to tube diameter ratio), whose performance previous correlations failed to predict adequately. The heat transfer correlation applicable to three or more row configuration predicts 94 percent of the data within ±20 percent, and the heat transfer correlation applicable to one- or two-row configuration predicts 94 percent of the data within ±20 percent. The friction correlation predicts 90 percent of the data within ±20 percent.
Constructal Trees of Convective Fins
Authors: Bejan A. , Dan N.
Published: February 2008

This paper extends to the field of convective heat transfer the constructal theory of optimizing the access of a current that flows between one point and a finite-size volume, when the volume size is constrained. The volume is bathed by a uniform stream. A small amount of high-conductivity fin material is distributed optimally through the volume, and makes the connection between the volume and one point (fin root) on its boundary. The optimization proceeds in a series of volume subsystems of increasing sizes (elemental volume, first construct, second construct). The shape of the volume and the relative thicknesses of the fins are optimized at each level of assembly. The optimized structure emerges as a tree of fins in which every geometric detail is a result of minimizing the thermal resistance between the finite-size volume and the root point (source, sink). Convection occurs in the interstitial spaces of the tree. The paper shows that several of the geometric details of the optimized structure are robust, i.e., relatively insensitive to changes in other design parameters. The paper concludes with a discussion of constructal theory and the relevance of the optimized tree structures to predicting natural self-organization and self-optimization.
Model and Powder Particle Heating, Melting, Resolidification, and Evaporation in Plasma Spraying Processes
Authors: Wan Y. P. , Prasad V. , Wang G.-X. , Sampath S. , Fincke J. R.
Published: February 2008

A comprehensive model is developed to study the heating, melting, evaporation, and resolidification of powder particles in plasma flames. The well-established LAVA code for plasma flame simulation is used to predict the plasma gas field under given power conditions, and provide inputs to the particle model. The particle is assumed to be a spherical and one-dimensional heat conduction equation with phase change within the particle is solved numerically using an appropriate coordinate transformation and finite difference method. Melting, vaporization, and resolidification interfaces are tracked and the particle vaporization is accounted for by the mass diffusion of vapor through the boundary layer around the particle. The effect of mass transfer on convective heat transfer is also included. Calculations have been carried out for a single particle injected into an Ar–H2 plasma jet. Zirconia and nickel are selected as solid particles because of their widespread industrial applications as well as significant differences in their thermal properties. Numerical results show strong nonisothermal effect of heating, especially for materials with low thermal conductivity, such as zirconia. The model also predicts strong evaporation of the material at high temperatures.
Nonlinear Inverse Heat Conduction With a Moving Boundary: Heat Flux and Surface Recession Estimation
Authors: Petrushevsky V. , Cohen S.
Published: February 2008

A one-dimensional, nonlinear inverse heat conduction problem with surface ablation is considered. In-depth temperature measurements are used to restore the heat flux and the surface recession history. The presented method elaborates a whole domain, parameter estimation approach with the heat flux approximated by Fourier series. Two versions of the method are proposed: with a constant order and with a variable order of the Fourier series. The surface recession is found by a direct heat transfer solution under the estimated heat flux.
Coupled Liquid and Vapor Flow in Miniature Passages With Micro Grooves
Authors: Khrustalev D. , Faghri A.
Published: February 2008

Friction factor coefficients for liquid flow in a rectangular micro-groove coupled with the vapor flow in a vapor channel of a miniature two-phase device were calculated using finite element analysis. The results show that the effect of the vapor-liquid frictional interaction on the liquid flow decreases with curvature of the liquid-vapor interface. Shear stresses at the liquid-vapor interface are significantly nonuniform, decreasing towards the center of the liquid-vapor meniscus.
Heat Transfer in Fin Assemblies: Significance of Two-Dimensional Effects—A Reexamination of the Issue
Authors: Thomas L. C.
Published: February 2008

The purpose of this paper is to reexamine the significance and nature of two-dimensional effects in fin assemblies. In particular, consideration is given to concerns expressed in the literature that the standard approach commonly leads to large errors due to two-dimensional effects. In addition, for the purpose of establishing a practical means of evaluating the level of significance of two-dimensional effects, an approximate first-order two-dimensional thermal circuit approach to analyzing heat transfer in fin assemblies is developed.
Effect of Buoyancy, Susceptor Motion, and Conjugate Transport in Chemical Vapor Deposition Systems
Authors: Chiu W. K. S. , Jaluria Y.
Published: February 2008

The fluid flow and heat transfer in the chemical vapor deposition (CVD) manufacturing process are studied numerically. Several crucial aspects such as thermal buoyancy, continuous processing, and conjugate transport are considered. For each aspect, the predicted heat transfer rate and the susceptor temperature are computed and qualitatively linked with the rate and uniformity of film deposition. It is shown that buoyancy effects in helium carrier gas commonly used in diffusion-limited CVD has a negligible effect on deposition rates. Susceptor motion is shown as a feasible alternative to improving the productivity. Conjugate heat transfer effects that arise demonstrate that reactor wall thickness and material may be judiciously chosen to improve temperature uniformity and enhance heat transfer rates, thereby improving deposition rate, film uniformity, and quality.
Heat Transfer in Discretely Heated Side-Vented Compact Enclosures by Combined Conduction, Natural Convection, and Radiation
Authors: Yu E. , Joshi Y. K.
Published: February 2008

A three-dimensional investigation of combined conduction, natural convection, and radiation in a side-vented compact enclosure is carried out. The focus of the study is on the enhancement of overall heat transfer through the opening, and the roles of the various modes in achieving it. A discrete heat source, flush-mounted centrally on a vertical substrate, is placed in the enclosure with a single rectangular opening on the opposite vertical wall. Steady-state computations are carried out for Rayleigh numbers, Ra, at 2.6 × 106 and 2.0 × 107. The results show that radiation plays a significant role in the overall heat transfer, and the radiative transport is even more pronounced for lower Ra. It is found that natural convection is weakened by radiation, however, contrary to the existing studies on top vented enclosures, the overall heat transfer is enhanced when radiation is included in the computations. Flow recirculation by radiative heating of enclosure walls is predicted, and is also observed experimentally. Heat spreading in the substrate is found to effect both convection and radiation. The numerical solutions on an extended computational domain are found in good agreement with the experimental data, when the conjugate effects are accounted for.
Modeling of Fluid Flow and Heat Transfer in a Hydrothermal Crystal Growth System: Use of Fluid-Superposed Porous Layer Theory
Authors: Chen Q.-S. , Prasad V. , Chatterjee A.
Published: February 2008

Hydrothermal synthesis, which uses aqueous solvents under high pressure and relatively low temperature, is an important technique for difficult to grow crystalline materials. It is a replica of crystal growth under geological conditions. A hydrothermal growth system usually consists of finely divided particles of the nutrient, predetermined volume of a solvent and a suitably oriented crystal seed (Fig. 1) under very high pressures, generally several thousand bar. The nutrient dissolves at a higher temperature in the lower region, moves to the upper region due to buoyancy-induced convective flows, and deposits on the seed due to lower solubility if the seed region is maintained at a lower temperature. The system can be modeled as a composite fluid and porous layer using the Darcy-Brinkman-Forchheimer flow model in the porous bed. Since the growth process is very slow, the process is considered quasi-steady and the effect of dissolution and growth is neglected. This first study on transport phenomena in a hydrothermal system therefore focuses on the flow and temperature fields without the presence of the seed and mass transfer. A three-dimensional algorithm is used to simulate the flow and heat transfer in a typical autoclave system. An axisymmetric flow pattern at low Grashof numbers becomes three-dimensional at high Grashof numbers. A reduction in the porous bed height for fixed heated and cooled regions can result in oscillatory flows. These results, for the first time, depict the possible flow patterns in a hydrothermal system, that can have far reaching consequences on the growth process and crystal quality.
The Time Delay for a Perceptible Thermal Disturbance in a Slab
Authors: Davies M. G.
Published: February 2008

If a thermal disturbance such as a step change in temperature is applied at each surface of a homogeneous slab of thickness 2L, the effect of cooling at x = +L at first has no effect at x = −L but is clearly evident after a time described by a Fourier number F0 = λt/ρcpL2 of around 0.2. To establish the time of a perceptible change the minimum value of φi − (φ1 + (φ2) is sought, where φ1 is the flux into a semi-infinite solid and φ1 and φ2 are the first and second eigenfunction contributions to the solution for a slab of finite thickness. Cooling throughout the slab is determined virtually by the first eigenfunction alone after F0 = 0.22. For a fluid-cooled slab these values are larger.
Onset of Convection in a Fluid Saturated Porous Layer Overlying a Solid Layer Which is Heated by Constant Flux
Authors: Wang C. Y.
Published: February 2008

The thermoconvective stability of a porous layer overlying a solid layer is important in seafloor hydrothermal systems and thermal insulation problems. The case for constant flux bottom heating is considered. The critical Rayleigh number for the porous layer is found to increase with the thickness of the solid layer, a result opposite to constant temperature heating.
Free Drawing and Polymer Coating of Silica Glass Optical Fibers
Authors: Paek U. C.
Published: February 2008

The paper is primarily to highlight the current issues concerning fiber drawing and coating. The main emphasis is on high-volume production of silica-based optical fibers by using a large preform and a high-speed drawing. The commercial application of these processes has led to increasing the productivity in fiber manufacturing and resulted in a low cost of produced fibers. In order to systematically address the problems associated with the fiber manufacturing process, the fiber drawing system was divided into three major functional sections: heating, cooling, and coating zones. The governing equations at each section were formulated to describe the process mechanics and to identify the key control parameters for drawing and coating. These process parameters are the basic elements of implementing a streamline production system of optical fibers.
Heat Transfer Enhancement and Vortex Flow Structure Over a Heated Cylinder Oscillating in the Crossflow Direction
Authors: Gau C. , Wu J. M. , Liang C. Y.
Published: February 2008

Experiments are preformed to study the flow structure and heat transfer over a heated oscillating cylinder. Both flow visualization using a smoke wire and local heat transfer measurements around the cylinder were made. The excitation frequencies of the cylinder are selected at Fe/Fn = 0, 0.5, 1, 1.5, 2, 2.5, and 3. These include excitations at harmonic, subharmonic, superharmonic, and nonharmonic frequencies. Synchronization of vortex shedding with the cylinder excitation occurs not only at Fe/Fn = 1 but also at Fe/Fn = 3, which can greatly enhance the heat transfer. The simultaneous enhancement of heat transfer at the stagnation point, its downstream region, and the wake region of the flow suggests that different modes of instabilities occurring in the shear layer of the near wake are actually initiated and amplified far upstream in the stagnation point, which were suppressed in the accelerated flow region and re-amplified in the decelerated flow region. As long as the dominant mode of the instability is amplified by the excitation of cylinder, enhancement of heat transfer can be obtained. During the experiments, the Reynolds numbers vary from 1600 to 4800, the ratios of oscillation amplitude to diameter of the cylinder from 0.064 to 0.016.
Coupling Between Heat and Momentum Transfer Mechanisms for Drag-Reducing Polymer and Surfactant Solutions
Authors: Aguilar G. , Gasljevic K. , Matthys E. F.
Published: February 2008

Drag-reducing solutions exhibit simultaneous friction and heat transfer reductions, yet it has been widely believed that there is no direct coupling between the two. In this work, we have conducted a study to re-examine this issue, using measurements of friction and heat transfer over a wide range of flow conditions from onset to asymptotic, various pipe diameters, and several polymer and surfactant solutions. Contrary to some earlier suggestions, our tests show that no decoupling of the momentum and heat transfer mechanisms was seen at the onset of drag reduction, nor upon departure from the asymptotes, but rather that the friction and heat transfer reductions change simultaneously in those regions. For asymptotic surfactant and polymer solutions, the ratio of heat transfer and drag reductions was seen to be constant over a large range of Reynolds numbers, if modified definitions of the reduction parameters are used. In the nonasymptotic region, however, the ratio of heat transfer to drag reductions is higher and is a function of the reduction level, but is approximately the same for polymer and surfactant solutions. This variation is consistent with the concept of a direct coupling through a nonunity constant Prt, as also suggested by our local measurements of temperature and velocity profiles. We also saw that our diameter scaling technique for friction applies equally well to heat transfer. These findings allow us to predict directly the heat transfer from friction measurements or vice versa for these drag-reducing fluids, and also suggest that a strong coupling exists between the heat and momentum transfer mechanisms.
The Effect of Drainage Configuration on Heat Transfer Under an Impinging Liquid Jet Array
Authors: Garrett K. , Webb B. W.
Published: February 2008

The heat transfer characteristics of single and dual-exit drainage configurations for arrays of liquid jets impinging normal to a heated isoflux plate has been studied experimentally. The interaction of drainage channel crossflow from upstream jets and the stagnation jets and its impact on heat transfer was the focus of the investigation. Infrared thermography was used to measure the local temperature distribution on the heated plate, from which local heat transfer coefficients were determined. A single jet diameter was used, and jet arrays with jet-to-jet spacings of 4.8, 6, 8, and 12 jet diameters were studied. Average jet Reynolds numbers in the range 400–5000 were investigated for jet nozzle-to-impingement plate spacings of 1, 2, and 4 jet diameters for fully flooded (submerged) drainage flow. A single jet-to-plate spacing large enough to yield free-surface jets was also studied. The data reveal a complex dependence of local and average Nusselt numbers on the geometric parameters which describe the problem configuration.
Local Heat Transfer in a Rotating Square Channel With Jet Impingement
Authors: Hsieh S.-S. , Huang J.-T. , Liu C.-F.
Published: February 2008

The influence of rotation and jet mass flow rate on the local heat transfer coefficient for a single confined impinging round jet with a fixed jet-to-wall spacing of H/d = 5 was studied for the jet Reynolds number from 6500 to 26,000 and the rotational Reynolds number from 0 to 112,000. The local heat transfer coefficient along the surface is measured and the effect of the rotation on the stagnation (peak) point, local and average Nusselt number, is presented and discussed. Furthermore, a correlation was developed for the average Nusselt number in terms of the parameters of Rej and ReΩ. In general, the combined jet impingement and rotation effect are shown to affect the heat transfer response. Rotation decreases the average Nusselt number values from 15 to 25 percent in outward and inward radial flow, respectively. Finally, comparisons of the present data with existing results for multijets with rotation were also made.
Inverse Natural Convection Problem of Estimating Wall Heat Flux Using a Moving Sensor
Authors: Park H. M. , Chung O. Y.
Published: February 2008

The inverse problem of determining heat flux at the bottom wall of a two-dimensional cavity from temperature measurement in the domain is considered. The Boussinesq equation is used to model the natural convection induced by the wall heat flux. The inverse natural convection problem is posed as a minimization problem of the performance function, which is the sum of square residuals between calculated and observed temperature, by means of a conjugate gradient method. Instead of employing several fixed sensors, a single sensor is used which is moving at a given frequency over the bottom wall. The present method solves the inverse natural convection problem accurately without a priori information about the unknown function to be estimated.
Mixture Fraction Statistics of Plane Self-Preserving Buoyant Turbulent Adiabatic Wall Plumes
Authors: Sangras R. , Dai Z. , Faeth G. M.
Published: February 2008

Measurements of the mixture fraction properties of plane buoyant turbulent adiabatic wall plumes (adiabatic wall plumes) are described, emphasizing conditions far from the source where self-preserving behavior is approximated. The experiments involved helium/air mixtures rising along a smooth, plane and vertical wall. Mean and fluctuating mixture fractions were measured using laser-induced iodine fluorescence. Self-preserving behavior was observed 92–155 source widths above the source, yielding smaller normalized plume widths and near-wall mean mixture fractions than earlier measurements. Self-preserving adiabatic wall plumes mix slower than comparable free line plumes (which have 58 percent larger normalized widths) because the wall prevents mixing on one side and inhibits large-scale turbulent motion. Measurements of probability density functions, temporal power spectra, and temporal integral scales of mixture fraction fluctuations are also reported.
The Role of Bubble Waiting Time in Steady Nucleate Boiling
Authors: Judd R. L
Published: February 2008

Experimental results previously reported by Ibrahim and Judd were examined in order to determine the role of bubble waiting time in steady nucleate boiling. The analysis identified that the time elapsed between the formation of bubbles at a nucleation site is the time required for the liquid which replaced the previous bubble to acquire sufficient energy to sustain the growth of the subsequent bubble, and not the time required to establish the conditions required to enable the nucleus, which formed at the nucleation site, to commence growing into a bubble.
Analysis of the Polarity Influence on Nucleate Pool Boiling Under a DC Electric Field
Authors: Zaghdoudi M. C. , Lallemand M.
Published: February 2008

An experimental study of the action of an intense electric field on the pool boiling of n-pentane is presented. By the application of a 25 kV/cm electric field strength, a threefold heat transfer enhancement is obtained. The effect of the electric field polarity has been researched. In nucleate boiling, the negative polarity allows to obtain a heat transfer enhancement, which is better than the one obtained in positive polarity. However, in natural convection and near the critical heat flux, the polarity of the electric field has a low influence on the heat transfer. The interpretations of the observed results are based on the action of the electric field on the boiling phenomenon and more particularly on the analysis of the electric field distribution between the electrodes. The influence of the space charge injection and the effect of the temperature on the electric field distribution have been investigated. The results obtained in the two cases of polarity are discussed in terms of effects of electrical and thermal phenomena on the distribution of the electric field between the electrodes.
A Heat and Mass Transfer Analysis of the Ignition and Extinction of Solid Char Particles
Authors: Phuoc T. X. , Annamalai K.
Published: February 2008

The present work studies the ignition and extinction of a spherical solid fuel particle exposed to a quiescent, hot, oxygen-containing environment. Using particle sizes and ambient temperature and oxygen concentration as parameters, the ignition, burning, and extinction of particles were parametrically analyzed by studying the relative heat production and heat-loss rates. For a given ambient condition, the results showed that it is possible that both large and small particles might not ignite at all. When a particle burns, its size decreases with time and its combustion characteristics are altered. The extinction condition may be reached due solely to the diminishing size of the particle. The particle extinction diameter was calculated. It strongly depends on the ambient condition and the reaction rate, but not on the initial particle size.
The Leidenfrost Point: Experimental Study and Assessment of Existing Models
Authors: Bernardin J. D. , Mudawar I.
Published: February 2008

This study presents a detailed and thorough parametric study of the Leidenfrost point (LFP), which serves as the temperature boundary between the transition and film boiling regimes. Sessile drop evaporation experiments were conducted with acetone, benzene, FC-72, and water on heated aluminum surfaces with either polished, particle blasted, or rough sanded finishes to observe the influential effects of fluid properties, surface roughness, and surface contamination on the LFP. A weak relationship between surface energies and the LFP was observed by performing droplet evaporation experiments with water on polished copper, nickel, and silver surfaces. Additional parameters which were investigated and found to have negligible influence on the LFP included liquid subcooling, liquid degassing, surface roughness on the polished level, and the presence of polishing paste residues. The accumulated LFP data of this study was used to assess several existing models which attempt to identify the mechanisms which govern the LFP. The disagreement between the experimental LFP values and those predicted by the various models suggests that an accurate and robust theoretical model which effectively captures the LFP mechanisms is currently unavailable.
Phonon Wave Heat Conduction in Thin Films and Superlattices
Authors: Chen G.
Published: February 2008

Heat conduction in thin films and superlattices is important for many engineering applications such as thin-film based microelectronic, photonic, thermoelectric, and thermionic devices. Past modeling efforts on the thermal conductivity of thin films were based on solving the Boltzmann transport equation that treats phonons as particles. The effects of phonon interference and tunneling on the heat conduction and the thermal conductivity of thin films and superlattices remain to be explored. In this work, the wave effects on the heat conduction in thin films and superlattices are studied based on the consideration of the acoustic wave propagation in thin film structures and neglecting the internal scattering. A transfer matrix method is used to calculate the phonon transmission and heat conduction through these structures. The effects considered in this work include the phonon interference, tunneling, and confinement. The phonon dispersion is considered by introducing frequency-dependent Lamb constants. A ray-tracing method that treats phonons as particles is also developed for comparison. Sample calculations are performed on double heterojunction structures resembling Ge/Si/Ge and n-period superlattices similar to Ge/Si/n(Si/Ge)/Ge, It is found that phonon confinements caused by the phonon spectra mismatch and by the total internal reflection create a dramatic decrease of the overall thermal conductance of thin films. The phonon interference in a single layer does not have a strong effect on its thermal conductance but for superlattice structures, the stop bands created by the interference effects can further reduce the thermal conductance. Tunneling of phonon waves occurs when the constituent layers are 1–3 monolayer thick and causes a slight recovery in the thermal conductance when compared to thicker layers. The thermal conductance obtained from the ray tracing and the wave methods approaches the same results for a single layer. For superlattices, however, the wave method leads to a finite thermal conductance even for infinitely thick superlattices while the ray tracing method gives a thermal conductance that decreases with increasing number of layers. Implications of these results on explaining the recent thermal conductivity data of superlattices are explored.
Instability of Ultra-Thin Water Films and the Mechanism of Droplet Formation on Hydrophilic Surfaces
Authors: Majumdar A. , Mezic I.
Published: February 2008

This paper presents a new theory of droplet formation during condensation of water on a hydrophilic surface. The theory uses hydration, electrostatic, van der Waals, and elastic strain interactions between a hydrophilic solid surface and a water film, and shows that contributions to the disjoining pressure are dominated by hydration forces for films thinner than 3 nm. The equilibrium film thickness is found to remain almost constant at about 0.5 nm for a wide range of relative humidity, although it increases sharply as the relative humidity approaches unity. The competition between strain energy on one hand, and hydration, van der Waals, and liquid-vapor surface tension on the other, induces instability for films thicker than a critical value. The critical wavelength of instability, Lcr is also predicted as a function of film thickness. The theory proposes that as the relative humidity increases, nucleation initially occurs in monolayer fashion due to strong hydration forces. Using nucleation thermodynamics it predicts a critical nucleus size, d*, and internuclei spacing, I, as a function of subcooling, ΔT, of the solid surface and shows that both length scales decrease with increasing subcooling. Since these monolayer nuclei are formed on the adsorbed water film, it is shown that when the internuclei spacing is larger than the critical wavelength, l > Lcr instability occurs in the film resulting in droplet formation. The theory predicts that beyond a certain value of subcooling, the interdroplet spacing is “choked” and cannot decrease further.
A New Method for Evaluation of Heat Transfer Between Solid Material and Fluid in a Porous Medium
Authors: Ichimiya K.
Published: February 2008

The author proposes a new method to estimate the heat transfer between fluid gas and solid material in a porous medium. In the first stage, the local Nusselt numbers on the heated wall of a flow passage with a porous medium are numerically obtained in advance for the parameter Ha including the volumetric heat transfer coefficient, hv between the fluid and the solid material in a porous medium. In the second stage, the experimental Nusselt numbers on the heated wall are obtained by measuring wall temperatures and heat flux. The volumetric heat transfer coefficient, hv, is evaluated by comparing experimental Nusselt numbers with numerical ones. This method also gives the longitudinal characteristics of the heat transfer in a porous medium.
Kinematic Synthesis of Deployable-Foldable Truss Structures Using Graph Theory, Part 2: Generation of Deployable Truss Module Design Concepts
Authors: Warnaar D. B. , Chew M.
Published: February 2008

A special type of truss structures, called truss modules, is presented. Graphs of this class of structures form a subset of the graphs that are generated using the approach presented in Part 1. Two procedures are presented that are applied to recognize these graphs among graphs of truss structures. The procedures also generate information on the relative lengths of the links in a truss module by examining the graph it represents. This enables the generation of numerous novel (deployable) truss modules as well as those that have been reported in the literature. Promising alternatives to existing designs are identified.
New Methods for the Dynamic Analysis of Flexible Single-Input and Multi-Input Cam-Follower Systems
Authors: Dresner T. L. , Barkan P.
Published: February 2008

The need to limit system vibrations makes the dynamic behavior of flexible highspeed cam-follower systems (as well as other machines subject to periodic motion) an important topic in the design of any such system. Researchers have worked extensively on this subject since before the turn of the century, both to determine dynamic behavior, and to improve and control that behavior. The goals in these analyses are to: 1) predict when and if the follower jumps off the cam; 2) determine the cam contact forces; 3) determine the linkage forces; 4) establish the closing spring requirements; 5) determine the magnitude of any follower impact with its seat; and 6) help optimize the system’s dynamic response. This paper provides the following: a brief review of the literature on the dynamic analysis of flexible cam-follower systems; a recommended method for the analysis of such systems; and an extension of this analysis method to multi-input systems.
Minimizing Residual Vibrations in High-Speed Cam-Follower Systems Over a Range of Speeds
Authors: Chew M. , Chuang C. H.
Published: February 2008

A direct procedure, based on the generalized Lagrange multiplier method, will be presented for designing high-speed cam-follower systems over a range of cam speeds. With this method residual vibrations at the end of the rise of a Dwell-Rise-Dwell (DRD) cam motion are minimized for any specified range of rise times. A minimum of boundary conditions on the cam displacement function will be specified to reduce unnecessary constraints on the cam displacement function. The applicability of rules of thumb generally accepted in designing for minimum vibrations will be discussed and compared to the results from this approach.
A Formula for Determining Limit Noninterference Curvature in Pure Rolling Conjugation Gears by Using Geometro-Kinematical Concepts
Authors: Chen Chih-Hsin
Published: February 2008

Pure rolling conjugation gears are very useful in the cases where lubrication is difficult to implement, such as in cryogenic and/or vacuum environments, and at slow operating speeds. The main problem confronted in the design of the pure rolling conjugation gears is to determine the limit noninterference curvature of one gear when the curvature of the conjugate gear is prescribed. The way of solving this problem becomes very complicated when using the conventional concepts from the classical differential geometry. However, when using the geometro-kinematical concepts from the theory of conjugate surfaces, this problem can be solved explicitly and simply. In this paper, these concepts are introduced, and a closed-form formula for determining the limit noninterference curvature is derived. A numerical example is cited.
Geometric Tolerancing in Mechanical Design Using Fractal-Based Parameters
Authors: Srinivasan R. S. , Wood Kristin L.
Published: February 2008

The submacrogeometric (tolerance) variations of mechanical components have an important impact on product function. The problem of combining tolerance assignment in engineering design with tolerance control in manufacturing and quality assurance presents a continuing challenge to researchers. This paper illustrates the feasibility of using fractal-based methods for the problem of tolerance specification in engineering design. Error data are generated as a function of the fractal dimension using the fractional Brownian motion model and are superposed on an ideal profile of a slider bearing. The consequent changes in performance parameters are studied and the detrimental effect of large variations perceived. This simple case study indicates the potential of the method to be extended for more complex problems.
Optimally Directed Truss Topology Generation Using Shape Annealing
Authors: Reddy G. M. , Cagan J.
Published: February 2008

This paper presents a technique for the generation and optimization of truss structure topologies based on the shape annealing algorithm. Feasible truss topologies are generated through a shape grammar in an optimally directed manner using simulated annealing for minimum weight, subject to stress and Euler buckling constraints.
Object Extent Determination for Algebraic Solid Models
Authors: Ganter M. A. , Storti D. W.
Published: February 2008

This paper presents methods for determination of spatial extent of algebraic solid models. Algebraic solid models are a variation of implicit solid models defined by implicit polynomial functions with rational coefficients. Spatial extent information, which can be used to enhance the performance of visualization and property evaluation, includes silhouettes, outlines and profiles. Silhouettes are curves on the surface of the solid which separate portions of the surface which face towards or away from a given viewpoint. The projection of the silhouette onto the viewing plane gives the outline of the solid, and the bivariate implicit function which defines the area enclosed by the outline is called the profile. A method for outline determination is demonstrated using concepts from algebraic geometry including polar surfaces and variable elimination via the Gro¨bner basis method and/or resultants. Examples of outline generation are presented and a sample profile function is constructed.
Optimal Curved Fences for Part Alignment on a Belt
Authors: Brokowski M. , Peshkin M. , Goldberg K.
Published: February 2008

In automated packing or assembly it is often necessary to bring randomly oriented parts into uniform alignment. Mechanical methods such as vibratory bowl feeders are often used for this purpose, although there is no theory for the systematic design of such feeders. A slanted “fence” attached to the stationary sides of a conveyor belt is also capable of orienting a stream of parts and a sequence of such fences has been shown [17] to function as a systematically designable linear parts feeder. A limitation of fence alignment is that once a part has left contact with a fence, its final orientation is confined to a narrow range of angles but is not unique. Here we consider the design of a single fence, consisting of a straight slanted section followed by an optimal curved tail. The straight section selectivity aligns certain edges of the part, while the curved tail preserves this alignment precisely as the part leaves contact with the fence. We have found the shortest tail which guarantees alignment. Optimal curved fences may be used individually for alignment of parts on a conveyor belt. They also lend themselves to systematic design of multi-fence linear parts feeders [8], [17].
Be´zier Curves on Riemannian Manifolds and Lie Groups with Kinematics Applications
Authors: Park F. C. , Ravani B.
Published: February 2008

In this article we generalize the concept of Be´zier curves to curved spaces, and illustrate this generalization with an application in kinematics. We show how De Casteljau’s algorithm for constructing Be´zier curves can be extended in a natural way to Riemannian manifolds. We then consider a special class of Riemannian manifold, the Lie groups. Because of their group structure Lie groups admit an elegant, efficient recursive algorithm for constructing Be´zier curves. Spatial displacements of a rigid body also form a Lie group, and can therefore be interpolated (in the Be´zier sense) using this recursive algorithm. We apply this alogorithm to the kinematic problem of trajectory generation or motion interpolation for a moving rigid body. The orientation trajectory of motions generated in this way have the important property of being invariant with respect to choices of inertial and body-fixed reference frames.
Distance Metrics on the Rigid-Body Motions with Applications to Mechanism Design
Authors: Park F. C.
Published: February 2008

In this article we examine the problem of designing a mechanism whose tool frame comes closest to reaching a set of desired goal frames. The basic mathematical question we address is characterizing the set of distance metrics in SE(3), the Euclidean group of rigid-body motions. Using Lie theory, we show that no bi-invariant distance metric (i.e., one that is invariant under both left and right translations) exists in SE(3), and that because physical space does not have a natural length scale, any distance metric in SE(3) will ultimately depend on a choice of length scale. We show how to construct left- and right-invariant distance metrics in SE(3), and suggest a particular left-invariant distance metric parametrized by length scale that is useful for kinematic applications. Ways of including engineering considerations into the choice of length scale are suggested, and applications of this distance metric to the design and positioning of certain planar and spherical mechanisms are given.
The Study of Design Research Methodology
Authors: Reich Y.
Published: February 2008

Studies on design research methodology are infrequent, although there is a consensus that more effort is needed for improving design research quality. Previous calls for exercising better research methodology have been unsuccessful. As numerous studies reveal, there is no single scientific methodology that is exercised in science or in any other research practice. Rather, research methodologies are socially constructed. Since some constructions are better than others for different purposes, it becomes valuable to study different methodologies and their influence on research practice and results. Proposals for such studies are offered.
Design Variation Simulation of Thick-walled Cylinders
Authors: Eggert R. J.
Published: February 2008

Thick-walled cylinders exposed to high, static internal pressures may experience both elastic and plastic deformation. Primary design considerations include loads, geometry and material properties. However, variations in geometry and material properties due to conventional manufacturing processes, and variations of internal pressure due to actual usage patterns, propagate through the system resulting in off-design stresses and strains which may cause failure. These variations can be evaluated using probabilistic methods which are discussed in this paper. Von Mises-distortion energy yield theory is presented to predict elastic, plastic and residual stresses in thick-walled cylinders. The design variation simulation method using Monte Carlo simulation and available statistical information is used to design a pressure vessel for servo-hydraulic experiments. The use of autofrettage to induce favorable compressive stresses at the inner bore, thereby improving the margin of safety and overall reliability, is also presented.