bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of Radiative Fluxes in an Absorbing, Emitting, and Scattering Vapor Formed by Laser Irradiation
Authors: Erpelding P. , Minardi A. , Bishop P. J.
Published: May 2008

A two-dimensional computer model is developed to determine the radiative heat flux distributions within the vapor formed above a metal target irradiated by a laser beam. An axisymmetric cylindrical enclosure containing a radiatively participating medium is considered. Scattering is assumed to be isotropic and allowances are made for variation of the radiative properties of the medium and boundaries. The P-1 and P-3 spherical harmonics approximations are used to solve the integro-differential radiative transfer equation. The resulting equations are then solved for the radial and axial heat fluxes using a finite-difference algorithm. The most significant factors affecting the results obtained from both the P-1 and P-3 approximations were the optical thickness of the medium and the type of laser profile incident upon the medium. Using different wall reflectivities and scattering albedos had a smaller effect. Changing the medium temperature had an insignificant effect as long as medium temperatures were below 20,000 K.
Optical Diagnostics and Radiative Properties of Simulated Soot Agglomerates
Authors: Ku J. C. , Shim K.-H.
Published: May 2008

The effect of agglomeration on the optical diagnostics and radiative properties of simulated soot agglomerates is investigated, using results from the Jones solution. It is found that agglomeration has a very strong effect on scattering, but only a weak effect on extinction (≅ absorption). An accurate relation has been developed, based on near-forward scattering coefficients, for inferring the number of primary particles in soot agglomerates. General models for both total and differential scattering coefficients have also been established. These results are in general agreement with those predicted for fractal aggregates having a large number of particles. Because of the effect of agglomeration, scattering may not be negligible in treating radiative transport from soot agglomerates.
Combustion of a Fuel Droplet Surrounded by Oxidizer Droplets
Authors: Jiang Tsung Leo , Chiu Huei-Huang
Published: May 2008

The interaction between a burning fuel droplet and satellite oxidizer droplets is studied analytically. The effects of droplet spacing and droplet size ratio on the flame configuration of a burning fuel droplet with a satellite oxidizer droplet are analyzed in a high-temperature oxidizing environment by using the bispherical coordinate system. Three combustion modes including normal combustion, conjugate combustion, and composite combustion are identified at appropriate droplet size ratio and droplet spacing. The burning rate of the fuel droplet is found to be greater than that of an isolated burning fuel droplet, and to increase with the decreasing distance between two droplets. This result has shown a positive effect on the interaction between fuel and oxidizer droplets, in contrast to that of two interacting fuel droplets where the burning rate decreases with decreasing droplet spacing. The combustion configuration of a fuel droplet surrounded by six satellite oxidizer droplets symmetrically is also examined by the method of images. The flame that encloses the fuel droplet is found to be “compressed” and distorted to a nonspherical shape due not only to the group effect among oxidizer droplets but also to the interaction of bipropellant droplets. The results indicate that the burning rate of a fuel droplet increases and the flame size decreases significantly as a result of an increased supply of oxidizer vapor provided by the surrounding oxidizer droplets. Therefore properly optimized bipropellant combustion is potentially able to achieve a desired combustion performance with a much smaller combustor than a conventional spray burner.
Bubble Dynamics in Boiling Under High Heat Flux Pulse Heating
Authors: Asai A.
Published: May 2008

A new theoretical model of bubble behavior in boiling under high heat flux pulse is presented. The essence of the model is nucleation in the superheated liquid followed by instantaneous formation of a vapor film, rapid bubble growth due to the pressure impulse, and cavitation bubble collapse. To check the model, boiling of methanol under 5 ~ 50 MW m−2 heat flux pulse using a small thin film heater has been experimentally investigated. When the heat flux was relatively low (< 20 MW m−2), a bubble grew in a hemispherical shape. When the heat flux was extremely high (> 20 MW m−2), many small bubbles nucleated and combined into a vapor film. The bubble behavior in the latter case is explained well by the model.
Transient Multidimensional Analysis of Nonconventional Heat Pipes With Uniform and Nonuniform Heat Distributions
Authors: Cao Y. , Faghri A.
Published: May 2008

A numerical analysis of transient heat pipe performance including nonconventional heat pipes with nonuniform heat distributions is presented. A body-fitted grid system was applied to a three-dimensional wall and wick model, which was coupled with a transient compressible quasi-one-dimensional vapor flow model. The numerical results were first compared with experimental data from cylindrical heat pipes with good agreement. Numerical calculations were then made for a leading edge heat pipe with localized high heat fluxes. Performance characteristics different from conventional heat pipes are illustrated and some operating limits concerning heat pipe design are discussed.
Experimental Heat Transfer Rates of Natural Convection of Molten Gallium Suppressed Under an External Magnetic Field in Either the X, Y, or Z Direction
Authors: Okada K. , Ozoe H.
Published: May 2008

The heat transfer rates of natural convection of molten gallium were measured under various strengths of heating rates and three coordinate directional magnetic fields. Molten gallium (Pr = 0.024) was filled in a cubic enclosure of 30 mm × 30 mm × 30 mm whose one vertical wall was uniformly heated and an opposing wall was isothermally cooled, with otherwise insulated walls. An external magnetic field was impressed either perpendicular and horizontal to the heated wall (x direction) or in parallel and horizontal to the heated wall (y direction) of the enclosure or in a vertical direction (z direction). For the modified Grashof number, based on the heat flux, less than 4.24 × 106 and the Hartmann number less than 461, the average Nusselt numbers were measured. These results proved that our previous three-dimensional numerical analyses for an isothermal hot wall boundary were in good qualitative agreement. A much higher suppression effect is given in the x- and z-directional magnetic fields than that in the y-directional one. The measured heat transfer rates were correlated as follows: NuB−1Nu0−1=1−[1+(aGr1/3/Ha)b]−1/nMagneticfield¯a¯b¯c¯x-directional0.573.191.76y-directional4.192.071.45z-directional0.522.721.44
Comparative Studies on Nonlinear Hyperbolic and Parabolic Heat Conduction for Various Boundary Conditions: Analytic and Numerical Solutions
Authors: Kar A. , Chan C. L. , Mazumder J.
Published: May 2008

With the advent of lasers with very short pulse durations and their use in materials processing, the effect of thermal wave propagation velocity becomes important. Also, localized heating in laser-aided materials processing causes significant variations in the material properties. To account for these two effects, hyperbolic heat conduction is studied in this paper by considering all the thermophysical properties, except the thermal diffusivity, to be temperature dependent. The resulting nonlinear hyperbolic equations are linearized by using Kirchhoff transformation. Both analytical and numerical solutions are obtained for finite domains. Results are presented and compared with parabolic conduction results.
An Experimental Study of Subcooled Film Boiling on a Vertical Surface—Hydrodynamic Aspects
Authors: Vijaykumar R. , Dhir V. K.
Published: May 2008

Interface and liquid velocities near the leading edge of a vertical wall 6.3 cm wide and 10.3 cm high were measured during subcooled film boiling of water at 1 atm pressure. The interface and liquid velocities in the boundary layer adjacent to the interface were measured using the hydrogen bubble flow visualization method. Photographs taken from the front and side showed the existence of a finite vapor layer at the leading edge and the existence of ripples and large-amplitude waves (bulges) on the interface. The bulges and ripples did not slide on the interface but moved in unison with the interface. The wave amplitude and wavelength were also measured. For a given subcooling and wall superheat, the amplitude, the interfacial velocity, and the wavelength were found to attain an equilibrium value several millimeters downstream of the leading edge. The waves were highly nonlinear and the interface velocities, which are found to be governed by the wave amplitude, were much larger than those predicted from the smooth interface, laminar flow theory. Streamlines in the liquid were found to expand into the wave valleys. At the wave peaks the streamlines appeared to be clustered together and the measured interface velocity gradients were high. The overall picture is one of expansion in the wave valleys and contraction (of flow) at the wave peaks. The flow field in turn is found to affect the liquid side heat transfer in subcooled film boiling significantly.
An Experimental Study of Subcooled Film Boiling on a Vertical Surface—Thermal Aspects
Authors: Vijaykumar R. , Dhir V. K.
Published: May 2008

Wall and liquid side heat fluxes near the leading edge of a vertical wall 6.3 cm wide and 10.3 cm high were measured during subcooled film boiling of water at 1 atm pressure. The heat flux from the interface into the liquid and temperature profiles in the liquid thermal layer were measured using real time holographic interferometry. The wall heat flux was measured with thermocouples embedded in a copper block, one face of which served as the heated wall. The role of the leading edge vapor layer, ripples, and large bulges in modifying the liquid side heat transfer is quantified.
Condensation of a Nonazeotropic Refrigerant Mixture R114/R113 in Horizontal Annuli With an Enhanced Inner Tube
Authors: Nozu Sh. , Ozaki K. , Inaba H. , Honda H.
Published: May 2008

Local heat transfer and pressure drop measurements are made during condensation of a nonazeotropic refrigerant mixture R114/R113 in the annuli of horizontal double-tube condensers. The inner tube is a 19.1-mm-o.d. corrugated tube with copper wire fins soldered on the outer surface. The outer tubes are smooth tubes with different i.d. of 29.9 and 25.0 mm. The heat transfer coefficient based on the bulk-vapor to wall temperature difference is considerably smaller for R114/R113 mixtures than for pure R113. An empirical equation for the vapor phase mass transfer coefficient is derived, in which the dimensionless parameters are introduced on the basis of the previous results for turbulent single phase flow in smooth and rough tubes with and without surface suction. The measured condensation heat transfer coefficients for R114/R113 mixtures are correlated by the present model to a mean absolute deviation of 14.3 percent.
Thermal Contact Conductance of Metallic Coated BiCaSrCuO Superconductor/Copper Interfaces at Cryogenic Temperatures
Authors: Ochterbeck J. M. , Peterson G. P. , Fletcher L. S.
Published: May 2008

The effects of vapor deposited coatings on the thermal contact conductance of cold pressed, normal state BiCaSrCuO superconductor/oxygen-free copper interfaces were experimentally investigated over a pressure range of 200 to 2000 kPa. Using traditional vapor deposition processes, thin coatings of indium or lead were applied to the superconductor material to determine the effect on the heat transfer occurring at the interface. The test data indicate that the contact conductance can be enhanced using these coatings, with indium providing the greater enhancement. The experimental program revealed the need for a better understanding and control of the vapor deposition process when using soft metallic coatings. Also, the temperature-dependent microhardness of copper was experimentally determined and found to increase by approximately 35 percent as the temperature decreased from 300 to 85 K. An empirical model was developed to predict the effect of soft coatings on the thermal contact conductance of the superconductor/copper interfaces. When applied, the model agreed well with the data obtained in this investigation at low coating thicknesses but overpredicted the data as the thickness increased. In addition, the model agreed very well with data obtained in a previous investigation for silver-coated nickel substrates at all coating thicknesses.
Thickness-Dependent Radiative Properties of Y-Ba-Cu-O Thin Films
Authors: Phelan P. E. , Chen G. , Tien C. L.
Published: May 2008

Some applications of high-temperature superconductors where their radiative behavior is important, such as bolometers, optically triggered switches and gates, and space-cooled electronics, require the superconductor to be in the form of a very thin film whose radiative properties cannot be adequately represented by a semi-infinite analysis. Two properties of particular importance are the film absorptance and the combined film/substrate absorptance, which are crucial to the operation of many devices. Here, calculations of the spectral, normal-incidence absorptance of superconducting-state Y-Ba-Cu-O films on MgO substrates suggest that a decrease in the film thickness often leads to an increase in both the film and the film/substrate absorptance. Furthermore, both can exhibit a maximum at some optimal value of film thickness. Room-temperature experiments verify the qualitative features of the spectral film/substrate absorptance, indicating the assumption that the film is a smooth, continuous slab with a refractive index equal to that of well-aligned bulk Y-Ba-Cu-O is valid, at least in the normal state and for films as thin as 35 nm.
Generalized State-Property Relations for Nonluminous Flame Absorption Coefficients
Authors: Grosshandler W. L. , Thurlow E. M.
Published: May 2008

The work reported here simplifies computing the local Planck-mean absorption coefficient in nonluminous flames as a function of the mixture fraction and fuel composition. Equilibrium is assumed for fuel/air mixtures up to the point where carbon is predicted to condense, beyond which the gaseous products are assumed to be frozen and to be diluted with cold fuel. The resulting algebraic expressions are suitable for inclusion in any turbulent or laminar diffusion flame model predicated on single-step chemistry. The method accounts for the nongray nature of the gaseous combustion products and their variation in concentration and temperature with mixture fraction, at a computational penalty little more than that for estimating variable fluid properties. Nonluminous flames (in air) of H2, CO, CH3OH, CH4 and lean regions of fuels with the general form CxHyOz can be modeled satisfactorily. The effects of pressure-pathlength and heat loss on the absorption coefficient are addressed.
Radiation, Conduction, and Convection From a Sphere in an Absorbing, Emitting, Gray Medium
Authors: Jones P. D. , Bayazitoglu Y.
Published: May 2008

Combined mode heat transfer is solved for an emitting, reflecting sphere in low Peclet number motion through a gray, nonscattering, absorbing, emitting, and conducting infinite medium. The coupled formulation of the energy and radiative transfer equations is solved numerically. The radiative transfer equation is expressed in a unique spatial/directional coordinate system, whose object is to exploit the axisymmetry of the problem. The radiation intensity field is solved using the discrete ordinates method. Results are presented in terms of the Planck and Peclet numbers, and serve as a combined radiation/convection analog to the well-known Nusselt number result for a radiatively nonparticipating medium.
Solidification of an Aqueous Salt Solution in a Circular Cylinder
Authors: Burns A. S. , Stickler L. A. , Stewart W. E.
Published: May 2008

The situation of one-dimensional, transient inward solidification of a binary solution in a circular cylinder is studied numerically. The solution is assumed to be of a hypoeutectic initial concentration and to be initially at a superheated temperature above its initial melting point temperature. The boundary temperature of the cylinder is below that of its heterogeneous nucleation temperature and no supercooling occurs. The boundary temperatures and final solution concentrations are assumed to be above and below, respectively, the eutectic point of the solution. The finite difference numerical model predicts the time for the radial formation of the mush type of ice to reach the center of the cylinder and the time for the entire cylinder to reach the cylinder boundary temperature, based upon the assumptions of negligible diffusion and convection of solute during solidification. The results reveal that closure times are significantly increased for the solutions compared to pure water due to decreased conductivity of the mush compared to ice.
Melting Heat Transfer From a Horizontal Ice Cylinder Immersed in Quiescent Saline Water
Authors: Fukusako S. , Tago M. , Yamada M. , Kitayama K. , Watanabe C.
Published: May 2008

The melting characteristics of a horizontal circular ice cylinder immersed in quiescent saline water were determined experimentally. The experiments were carried out in 3.5 wt% saline water for ambient liquid temperatures ranging from 2.8 to 20.3°C. It was observed that the flow consisted of a laminar bidirectional flow at the lower portion of the melting ice cylinder, and an upward turbulent flow at the upper portion of the cylinder, and that the melting ice surface was characterized variously by secondary flow caused by instabilities based on buoyancy forces in the boundary layer flow. It was also found that the melting heat transfer behavior was markedly affected by the character of the flow in the boundary layer.
An Adaptive Inverse Heat Conduction Method With Automatic Control
Authors: Flach G. P. , O¨zis¸ik M. N.
Published: May 2008

An adaptive sequential method is presented for solving the one-dimensional inverse heat conduction problem. The step size, order of parameterization, and amount of the step retained are variable and chosen automatically for each sequence such that optimal, stable results are obtained. A statistical analysis accounting for the stochastic error contributions from both the measured and initial temperatures is derived. Results from the statistical analysis are used to predict stability or instability for a given selection of parameters controlling the inverse method. Simulated experimental applications using inexact data illustrate the practicality of the approach and the effectiveness of the automatic control criteria.
Evaluation of the Stagnation Point Region Overshoot
Authors: Sogin H. H.
Published: May 2008

Stagnation point region overshoot is the augmentation of total heat transfer owing to the presence of insulation at the stagnation point region of an otherwise isothermal body. Evidence summarized by the present work indicates that this paradoxical event can be made to occur. The overshoot is due to the singularly high temperature gradient that is impressed upon the boundary layer just as it arrives at the leading edge of the heated surface after passing over the insulated central portion. The evidence comprises experimental results based on the mass-heat analog using sublimation of naphthalene and on theoretical boundary layer calculations using a method of local similarity. In the experiments, the insulated surfaces were simulated with inert wax, and isothermal regions with active naphthalene. The surfaces were circular disks facing uniform airstreams. The finding was that the total rate of mass transfer would be as much as 10 percent greater than that of a fully active disk if the radius of the central inert region were half the radius of the disk. Put another way, if only the 30-percent annulus at the outer edge of the disk were active, it would transfer mass at the same rate as the completely active disk under the same circumstances of flow. Corresponding results are expected from analogically heated disks operating with Prandtl number near unity and disk Reynolds number ranging from 5000 to 250,000.
Transient Convective Heat Transfer in Planar Stagnation Flows With Time-Varying Surface Heat Flux and Temperature
Authors: Zumbrunnen D. A.
Published: May 2008

Impinging flows are used in a variety of applications where effective and localized heat transfer is mandated by short residence times or by space constraints, as in cooling materials moving along a conveyor or removing heat dissipated within microelectronic circuitry. A wide selection of heat transfer correlations is available for steady-state conditions. However, instantaneous heat transfer coefficients can differ significantly from steady-state values when temporal variations occur in the surface heat flux or surface temperature. Under these conditions, the temperatures of fluid layers near the surface are affected preferentially due to their proximity to the temporal variation. A theoretical model is formulated to assess the importance of a time-varying surface heat flux or temperature on convective heat transfer in a steady, planar stagnation flow. A governing equation for the transient heat transfer response is formulated analytically from the boundary layer equations for momentum and energy conservation in the fluid. Numerical solutions to the governing equation are determined for ramp and sinusoidal changes in the surface heat flux or temperature. Results indicate that the time response is chiefly governed by the velocity gradient in the free stream and to a lesser extent by the Prandtl number. Departures from steady-state Nusselt numbers are larger for more rapid transients and smaller or comparable in size to the magnitude of the imposed variation at the surface.
1990 Max Jakob Memorial Award Lecture: Viscoelastic Fluids: A New Challenge in Heat Transfer
Authors: Hartnett J. P.
Published: May 2008

A review of the current knowledge on the fluid mechanics and heat transfer behavior of viscoelastic aqueous polymer solutions in channel flow is presented. Both turbulent and laminar flow conditions are considered. Although the major emphasis is on fully established circular pipe flow, some results are also reported for flow in a 2:1 rectangular channel. For fully established turbulent channel flow, it was found that the friction factor, f, and the dimensionless heat transfer factor, jH, were functions of the Reynolds number and a dimensionless elasticity value, the Weissenberg number. For Weissenberg values greater than approximately 10 (the critical value) the friction factor was found to be a function only of the Reynolds number; for values less than 10 the friction factor was a function of both Re and Ws. For the dimensionless heat transfer coefficient jH the corresponding critical Weissenberg value was found to be about 100. The heat transfer reduction is always greater than the friction factor reduction; consequently, the heat transfer per unit pumping power decreases with increasing elasticity. For fully established laminar pipe flow of aqueous polymer solutions, the measured values of the friction factor and dimensionless heat transfer coefficient were in excellent agreement with the values predicted for a power law fluid. For laminar flow in a 2:1 rectangular channel the fully developed friction factor measurements were also in agreement with the power law prediction. In contrast, the measured local heat transfer coefficients for aqueous polymer solutions in laminar flow through the 2:1 rectangular duct were two to three times the values predicted for a purely viscous power law fluid. It is hypothesized that these high heat transfer coefficients are due to secondary motions, which come about as a result of the unequal normal stresses occurring in viscoelastic fluids. The anomalous behavior of one particular aqueous polymer solution—namely, polyacrylic acid (Carbopol)—is described in some detail, raising some interesting questions as to how viscoelastic fluids should be classified. In closing, a number of challenging research opportunities in the study of viscoelastic fluids are presented.
The Temperature Field Around a Spherical Ridge or Trough in a Plane
Authors: Fransaer J. , Roos J. R.
Published: May 2008

An analytical solution, which describes the temperature field around a single spherical particle partly embedded in a plane or around a trough making an arbitrary contact angle with a plane, is presented here. The temperature distributions for three cases are studied: the temperature distribution around a conducting bowl or trough, the temperature distribution around a non-conducting bowl or trough present in a conducting plane, and the temperature profile around a conducting bowl or trough conducting heat toward a sink at infinity. The normalized heat flux distribution on the plane and particle is presented. The various incremental resistances caused by a single and a dilute planar random array of truncated spherical particles are also derived.
Local Heat Transfer in a Rotating Serpentine Flow Passage
Authors: Yang Wen-Jei , Zhang Nengli , Chiou Jeff
Published: May 2008

An experimental study is performed on the internal cooling of a rotating serpentine flow passage of square cross section with throughflow. The test section is not proceeded by a hydrodynamic calming region, i.e., a leading arm, and is rotated at low Rossby numbers. The local heat transfer coefficients along the flow passage, including the leading wall, trailing wall, and sidewalls, are determined together with the circumferentially averaged values. The Reynolds, Rossby, and rotating Rayleigh numbers are varied to determine their effects on heat transfer performance. It is disclosed that heat transfer augmentation is significant at all sharp turns due to the presence of strong secondary flow. The rotational effect is very obvious and complicated in the local heat transfer performance but it is very minor on the average heat transfer performance. The throughflow rate plays an important role on the heat transfer performance. The results may serve as a baseline for comparison with the results from a model with a leading arm to determine the effects of a hydrodynamic calming section on the heat transfer performance of a rotating serpentine flow passage.
An Experimental Study of Free Convection Heat Transfer From an Array of Horizontal Cylinders Parallel to a Vertical Wall
Authors: Al-Alusi T. R. , Bushnell D. J.
Published: May 2008

An experimental investigation of heat transfer from an array of three horizontal cylinders aligned vertically parallel to a single wall is presented. Three different cylinder center-to-center spacings for the array cylinders were examined, CC= 1.5D, 2D, and 4D. The wall-array spacings were varied from 0.081D to infinity. The cylinders were placed in a still air medium at atmospheric pressure and maintained at constant heat flux. Modified Rayleigh number, based on the diameter of the cylinders, ranged from 6.2 × 104 to 1.2 × 106. Results indicate that heat transfer is generally enhanced, but for some wall spacing to cylinder configurations the heat transfer can be minimally decreased. For cases where the heat transfer was enhanced the top cylinder in the array was observed to have the highest enhancement (22 percent) and the lowest cylinder was enhanced the least (5 percent). Flow visualization studies showed that the wall generated a chimney effect between the wall and the cylinders.
Exciplex Fluorescence Thermometry of Falling Hexadecane Droplets
Authors: Hanlon T. R. , Melton L. A.
Published: May 2008

Exciplex fluorescence thermometry has been used to measure the temperature of 283 micron hexadecane droplets falling through a quiescent, oxygen-free, approximately 500°C ambient. After a period of negligible change, the derived droplet temperatures exhibit a sharp rise of about 100°C followed by a gentle increase to approximately 200°C. The derived temperatures, although averaged over most of the volume of the droplet, still provide some evidence of internal processes in the droplet due to the partially selective optical sampling of the droplet volume, in which fluorescence from the region between 0.50 and 0.75 of the droplet radius contributes disproportionately. At longer times, the droplet is presumed to be approximately homogeneous, and the exciplex fluorescence thermometry measurements provide accurate, interpretable temperatures for the freely falling droplets.
Measurement of Radiative Properties of Ash and Slag by FT-IR Emission and Reflection Spectroscopy
Authors: Markham J. R. , Best P. E. , Solomon P. R. , Yu Z. Z.
Published: May 2008

This article presents laboratory measurements of the radiative properties of ash and slag deposits that have been extracted from combustion devices. The measurements were made by a technique employing a sample heating device that is coupled to a Fourier Transform Infrared (FT-IR) spectrometer to measure the sample’s emission and directional-hemispherical reflection. By this technique, the temperature at the measurement point and the spectral emittance of the surface are both obtained. These measurements are then related to the physical and chemical properties of the surface to determine what controls the radiative properties. The measurements have shown that the physical state of a deposit (i.e., fused, sintered, or packed particles) greatly influenced the measured spectral emittance. The results were in agreement with mathematical models that account for the physical properties.
Effective Propagation Constant of Fibrous Media Containing Parallel Fibers in the Dependent Scattering Regime
Authors: Lee Siu-Chun
Published: May 2008

The radiative properties of a particulate medium are strongly influenced by the particle concentration and wavelength of the incident radiation. Independent scattering prevails at very low particle concentration, such that the spacing between the particles is much larger than the particle size and incident wavelength. As the particle spacing decreases, near-field multiple scattering and far-field interference of the scattered waves become increasingly pronounced. These dependent scattering effects cause the extinction efficiency and the phase velocity of electromagnetic waves, which are related to the effective propagation constant of the medium, to deviate from those in the independent scattering regime. This paper presents the theoretical formulation of the effective propagation constant of a nondissipative medium containing closely spaced parallel fibers. The dispersion relations for oblique incidence are derived for a transverse magnetic and a transverse electric mode incident wave. Numerical results for Rayleigh limit fibers are presented to illustrate the effect of fiber volume fraction on the propagation constant and extinction efficiency of the medium.
Developing Heat Transfer and Friction in a Ribbed Rectangular Duct With Flow Separation at Inlet
Authors: Liou Tong-Miin , Hwang Jenn-Jiang
Published: May 2008

The local heat transfer and pressure drop characteristics of developing turbulent flows in a rectangular duct with an abrupt-contraction entrance and repeated square-rib pairs on the two opposite walls have been investigated experimentally. Both entrance-region and periodic-fully-developed-region results were obtained. Laser holographic interferometry was employed in the local and average heat transfer measurements. The Reynolds number was varied from 5.0 × 103 to 5.0 × 104; the rib pitch-to-height ratios were 10, 15, and 20; and the rib height-to-duct height ratio was kept at a value of 0.13. The results allowed the entry length to be determined and the regions susceptible to hot spots to be located. Semi-empirical heat transfer and friction correlations for the periodic fully developed region were developed. Moreover, performance comparisons between the ribbed and smooth ducts were made under two types of constraint, namely equal mass flow rate and equal pumping power. Finally, the effect of thermal entry length on the length mean Nusselt number was also investigated. The results showed that the length mean Nusselt number ratio was a function of only the duct length and independent of PR and Re, and could be further correlated by an equation of the form Num/Nup = 1 + 1.844/(X/De).
Heat Transfer in the Non-Newtonian Axisymmetric Flow in the Neighborhood of a Sudden Contraction
Authors: Carvalho M. S. , Souza Mendes P. R.
Published: May 2008

The flow pattern at low Reynolds number in the neighborhood of a sudden contraction is very sensitive to the mechanical behavior of the flowing fluid. A large extensional viscosity leads to vortex enhancement in the corner region of the flow of a non-Newtonian fluid in such geometry. In the corresponding flow of a Newtonian fluid, these vortices are much weaker and smaller. Moreover, the extension-thickening behavior of most polymeric liquids leads to higher viscous dissipation effects in the predominantly extensional flow, as compared to typical shear flows. The flow and temperature fields for this problem have been obtained from numerical integration of the conservation equations, aiming at applications related to extrusion and capillary rheometry of polymeric liquids. To account for the flow dependence of the stress tensor, a generalized Newtonian model has been employed, including the dependence of the viscosity function on both the second and the third invariants of the rate-of-deformation tensor. The numerical solutions have been obtained via a finite-volume method. The case of a 4:1 circular contraction was investigated, with uniform temperature distribution at the solid boundaries. The fluid inlet temperature is equal to the temperature at the walls, so that thermal gradients in the fluid are due to viscous dissipation effects only. Comparisons between Newtonian and non-Newtonian results showed that the combined effect of viscous dissipation and enhancement of vortex activity significantly affects the temperature field. The practical significance of the results is discussed for extrusion processes and capillary rheometry.
Numerical Calculation of Convective Heat Transfer Between Rotating Coaxial Cylinders With Periodically Embedded Cavities
Authors: Hayase T. , Humphrey J. A. C. , Greif R.
Published: May 2008

A numerical study has been performed for the flow and heat transfer in the space between a pair of coaxial cylinders with the outer one fixed and the inner one rotating. Of special interest is the case where either one of the cylinders has an axially grooved surface resulting in twelve circumferentially periodic cavities embedded in it. The ends of the cylinder are bounded by flat impermeable walls that are either fixed to the outer cylinder or rotate with the inner one. Such a geometry is common in electric motors where an improved understanding of thermophysical phenomena is essential for analysis and design. Discretized transport equations are solved for two-dimensional and three-dimensional, steady, constant property laminar flow using a second-order accurate finite volume scheme within the context of a SIMPLER-based iterative methodology. The two-dimensional calculations reveal a shear-induced recirculating flow in the cavities. For supercritical values of the Reynolds number, the three-dimensional calculations show how the flow in a cavity interacts with Taylor vortices in the annular space to enhance heat transfer. Relative to coaxial cylinders with smooth surfaces, for the conditions of this study the transport of momentum and heat is raised by a factor of 1.2 in the case of cavities embedded in the inner cylinder and by a factor of 1.1 in the case of cavities embedded in the outer cylinder.
Direct Numerical Simulation of Passive Scalar Field in a Turbulent Channel Flow
Authors: Kasagi N. , Tomita Y. , Kuroda A.
Published: May 2008

A direct numerical simulation (DNS) of the fully developed thermal field in a two-dimensional turbulent channel flow of air was carried out. The isoflux condition was imposed on the two walls so that the local mean temperature increased linearly in the streamwise direction. With any buoyancy effect neglected, temperature was considered as a passive scalar. The computation was executed on 1,589,248 grid points by using a spectral method. The statistics obtained were root-mean-square temperature fluctuations, turbulent heat fluxes, turbulent Prandtl number, and dissipation time scales. They agreed fairly well with existing experimental and numerical simulation data. Each term in the budget equations of temperature variance, its dissipation rate, and turbulent heat fluxes was also calculated. It was found that the temperature fluctuation θ′ was closely correlated with the streamwise velocity fluctuation u′, particularly in the near-wall region. Hence, the distribution of budget terms for the streamwise and wall-normal heat fluxes, u′θ′ and v′θ′, were very similar to those for the two Reynolds stress components, u′u′ and u′v′.
Three-Dimensional Mach-Zehnder Interferometric Tomography of the Rayleigh-Be´nard Problem
Authors: Michael Y. C. , Yang K. T.
Published: May 2008

A three-dimensional experimental technique based on axial tomography is demonstrated in this study for the Rayleigh-Be´nard convection problem. The technique can perform under severe blockage conditions and with a small number of projections. The major requirement of the technique is an adequate initial guess of the field and the use of an iterative inversion algorithm. In this study, five views are used to study the steady-state natural convection inside a three-dimensional rectangular cavity filled with water at Ra = 5470 ± 100 and Ra = 6140 ± 100. The reconstructed results are estimated to be accurate with a standard deviation of about 0.01°C. The temperature measurements show strong three-dimensional features in the flow.
Partial Coherence Theory of Thin Film Radiative Properties
Authors: Chen G. , Tien C. L.
Published: May 2008

A new approach based on the partial coherent theory of light is introduced to predict the radiative properties of a thin film. General expressions obtained for the normal reflectance and transmittance of a thin film not only degenerate into the limiting results of the wave and the geometric optics in the coherent and incoherent cases, but also apply for all partial coherent states between the limits. The key element in the formulation is the complex degree of coherence, for which a general integral expression is obtained and further approximated algebraically for nearly monochromatic radiation. Limiting criteria and regime maps are established to demonstrate the range of applications for the various methods.
Infrared Refractive Index of Thin YBa2Cu307 Superconducting Films
Authors: Zhang Z. M. , Choi B. I. , Le T. A. , Flik M. I. , Siegal M. P. , Phillips J. M.
Published: May 2008

This work investigates whether thin-film optics with a constant refractive index can be applied to high-Tc superconducting thin films. The reflectance and transmittance of YBa2Cu3O7 films on LaAlO3 substrates are measured using a Fourier-transform infrared spectrometer at wavelengths from 1 to 100 μm at room temperature. The reflectance of these superconducting films at 10 K in the wavelength region from 2.5 to 25 μm is measured using a cryogenic reflectance accessory. The film thickness varies from 10 to 200 nm. By modeling the frequency-dependent complex conductivity in the normal and superconducting states and applying electromagnetic-wave theory, the complex refractive index of YBa2Cu3O7 films is obtained with a fitting technique. It is found that a thickness-independent refractive index can be applied even to a 25 nm film, and average values of the spectral refractive index for film thicknesses between 25 and 200 nm are recommended for engineering applications.
Heat Transfer Regimes in Microstructures
Authors: Flik M. I. , Choi B. I. , Goodson K. E.
Published: May 2008

Submicron dimensions are the hallmark of integrated electronic circuits, photovoltaic cells, sensors, and actuators. The design of these devices requires heat transfer analysis. Often it is not known to the designer whether a given microstructure can be analyzed using macroscale heat transfer theory, i.e., a method not considering the size dependence of a transport property such as thermal conductivity. This study develops regime maps showing the boundary between the macroscale and microscale heat transfer regimes. The maps relate the geometric dimension separating the two regimes to temperature for conduction in solids, to temperature, pressure, and Reynolds number for convection in gases, and to the temperature of the emitting medium for radiative transfer. The material purity and defect structure strongly influence the regime boundaries. Microstructures pertaining to a given technology are marked on these maps to determine whether macroscale heat transfer theory is applicable. By marking regions on the maps for the expected future development of microtechnologies, research needs in microscale heat transfer can be anticipated.
Solidification With a Throughflow in a Porous Medium
Authors: Banerjee T. , Chang C. , Wu W. , Narusawa U.
Published: May 2008

A steady throughflow in a porous medium is studied in the presence of a solidified layer due to cooling of the walls. Under the assumption of a moderately sloped melt-solid interface, analytical solutions are obtained for both a flow between parallel plates and a circular pipe. Differences and similarities are examined between the Darcian and the Brinkman porous media, as well as the effects of various parameters, such as the Peclet number, the ratio of diffusivities in the longitudinal and the lateral directions, and a parameter indicating the degree of wall cooling and flow heating, on thermofluid structure of a flow in porous media accompanied by solidification.
Accurate Heat Transfer Measurements for Condensation on Horizontal, Integral-Fin Tubes
Authors: Briggs A. , Wen X.-L. , Rose J. W.
Published: May 2008

In most earlier experimental investigations of condensation on low-fin tubes, vapor-side heat transfer coefficients have been found from overall (vapor-to-coolant) measurements using either predetermined coolant-side correlations or “Wilson plot” methods. When the outside resistance dominates, or is a significant proportion of the overall resistance, these procedures can give satisfactory accuracy. However, for externally enhanced tubes, and particularly with high-conductivity fluids such as water, significant uncertainties may be present. In order to provide reliable, high-accuracy data, to assist in the development of theoretical models, tests have been conducted using specially constructed plain and finned tubes fitted with thermocouples to measure the tube wall temperature, and hence the vapor-side heat transfer coefficient, directly. The paper describes the technique for manufacturing the tubes and gives results of systematic heat transfer measurements covering the effects of fin height, thickness, and spacing, tube diameter, and vapor velocity. The tests were carried out with steam, ethylene glycol, and R-113, with vertical vapor downflow. The heat flux was measured using an accurately calibrated 10-junction thermopile and paying particular attention to coolant mixing and isothermal immersion of thermocouple junctions. Care was taken to avoid errors due to the presence in the vapor of noncondensing gas and the occurrence of dropwise condensation. Smooth, consistent, and repeatable results were obtained in all cases. The data are presented in easily accessible form and are compared with the results of previous investigations, where indirect methods were used to determine the vapor-side data, and with theory.
A Spectral Line-Based Weighted-Sum-of-Gray-Gases Model for Arbitrary RTE Solvers
Authors: Denison M. K. , Webb B. W.
Published: May 2008

This paper presents an approach for generating weighted-sum-of-gray gases (WSGG) models directly from the line-by-line spectra of H2O. Emphasis is placed on obtaining detailed spectral division among the gray gases. Thus, for a given model spectrum, the gray gas weights are determined as blackbody fractional functions for specific subline spectral regions at all temperatures. The model allows the absorption coefficient to be the basic radiative property rather than a transmissivity or band absorptance, etc., and can be used with any arbitrary solution method for the Radiative Transfer Equation (RTE). A single absorption cross section spectrum is assumed over the entire spatial domain in order to fix the subline spectral regions associated with a single spectral calculation. The error associated with this assumption is evaluated by comparison with line-by-line benchmarks for problems of nonisothermal and nonhomogeneous media.
Measurements of the Thermal Radiative Properties of Liquid Uranium
Authors: Havstad M. A. , McLean W. , Self S. A.
Published: May 2008

Measurements of the thermal radiative properties of liquid uranium have been made using an instrument with two optical systems, one for measuring the complex index of refraction by ellipsometry, the other for measuring the normal spectral emissivity by direct comparison to an integral blackbody cavity. The measurements cover the wavelength range 0.4–10 μm with sample temperatures between 1410 and 1630 K. Two 5-KeV ion sputter guns and an Auger spectrometer produce and verify, in situ, atomically pure sample surfaces. Good agreement between the two methods is observed for the normal spectral emissivity, which varies with wavelength in a manner typical of transition metals. The two components of the complex index of refraction—the index of refraction and the extinction coefficient—increase with wavelength, from ~3 at 0.4 μm to ~20 at 9.5 μm. Both components of polarized reflectivity are shown for visible to infrared wavelengths.
Microscale Heat and Mass Transfer of Vascular and Intracellular Freezing in the Liver
Authors: Bischof J. C. , Rubinsky B.
Published: May 2008

A set of heat and mass transfer equations is developed to predict vascular as well as intracellular ice formation during freezing in liver tissue. A modified Krogh unit with vascular and cellular compartments is used. In the model intracellular ice formation is predicted by a probability integral with functional dependence on cell compartment volume, temperature, and time. Finite difference computer simulations qualitatively predict the amount and location of vascular and intracellular ice, the temperature distribution in the tissue, and the position of the partial and total freezing interfaces at any time.
Heat Transfer Mechanisms During Short-Pulse Laser Heating of Metals
Authors: Qiu T. Q. , Tien C. L.
Published: May 2008

This work studies heat transfer mechanisms during ultrafast laser heating of metals from a microscopic point of view. The heating process is composed of three processes: the deposition of radiation energy on electrons, the transport of energy by electrons, and the heating of the material lattice through electron-lattice interactions. The Boltzmann transport equation is used to model the transport of electrons and electron-lattice interactions. The scattering term of the Boltzmann equation is evaluated from quantum mechanical considerations, which shows the different contributions of the elastic and inelastic electron-lattice scattering processes on energy transport. By solving the Boltzmann equation, a hyperbolic two-step radiation heating model is rigorously established. It reveals the hyperbolic nature of energy flux carried by electrons and the nonequilibrium between electrons and the lattice during fast heating processes. Predictions from the current model agree with available experimental data during subpicosecond laser heating.