bluuebunny/crossref_metadata_2025 huggingface dataset:
Nucleate Boiling in Thermally Developing and Fully Developed Laminar Falling Water Films
Authors: Cerza M. , Sernas V.
Published: October 2009

This paper reports an experimental investigation of nucleate boiling in thin water films falling down the outside of a cylindrical heated tube. A mathematical model for the convective (nonboiling) heat transfer coefficient in the laminar thermal entry length was developed and used as a comparison to the experimental boiling heat transfer coefficients. A heat transfer correlation based on mechanistic arguments is presented and is shown to represent the experimental data fairly well. The experimental data were also compared with existing heat transfer data in the literature. The flow rates utilized in this study corresponded to a Reynolds number range from 670 and 4300 and the heat flux range was 6 to 70 kW/m2.
Stochastic Analysis of Temperature Distribution in a Solid With Random Heat Conductivity
Authors: Tzou Da Yu
Published: October 2009

Stochastic temperature distribution in a solid medium with random heat conductivity is investigated by the method of perturbation. The intrinsic randomness of the thermal conductivity k(x) is considered to be a distribution function with random amplitude in the solid, and several typical stochastic processes are considered in the numerical examples. The formulation used in the present analysis describes a situation that the statistical orders of the random response of the system are the same as those of the intrinsic random excitations, which is characteristic for the problem with extrinsic randomness. The maximum standard deviation of the temperature distribution from the mean value in the solid medium reveals the amount of unexpected energy experienced by the solid continuum, which should be carefully inspected in the thermal-failure design of structures with intrinsic randomness.
Heat Exchanger Shellside Pressure Drop: Comparison of Predictions With Experimental Data
Authors: Kistler R. S. , Chenoweth J. M.
Published: October 2009

A unique set of heat exchanger shellside pressure drop experimental data has become available from experiments at Argonne National Laboratory as a part of an ongoing research program in flow-induced vibration. These data provide overall pressure drop for a number of typical industrial heat exchanger configurations in addition to incremental pressure drop measurements along the shellside path. The test program systematically varied the baffle spacing, the tubefield pattern, and nozzle size for a series of isothermal water tests for segmentally baffled bundles. Also recently a comprehensive method has been published in the Heat Exchanger Design Handbook (HEDH) for the prediction of bundle shellside pressure drops. A search of the literature failed to reveal a complementary method for predicting the shellside nozzle pressure losses. This paper compares the predicted with the measured data and validates the adequacy and limitations of the HEDH method for full bundles of plain tubes. It further applies an extension to the method for no-tubes-in-the-window bundles. Adjustments were indicated to improve the predictions for finned tubes and methods were developed to predict shellside nozzle pressure drops. Overall pressure drop predictions were within plus or minus 20 percent.
Heat Diffusion in Heterogeneous Bodies Using Heat-Flux-Conserving Basis Functions
Authors: Haji-Sheikh A.
Published: October 2009

The generalized analytical derivation presented here enables one to obtain solutions to the diffusion equation in complex heterogeneous geometries. A new method of constructing basis functions is introduced that preserves the continuity of temperature and heat flux throughout the domain, specifically at the boundary of each inclusion. A set of basis functions produced in this manner can be used in conjunction with the Green’s function derived through the Galerkin procedure to produce a useful solution method. A simple geometry is selected for comparison with the finite difference method. Numerical results obtained by this method are in excellent agreement with finite-difference data.
Linear Matrix Operator Formalism for Basic Heat Exchanger Thermal Design
Authors: Pignotti A.
Published: October 2009

The matrix formalism used for the thermal description of heat exchangers is extended to include streams with variable temperature distributions. In this approach, a heat exchanger is described by a temperature-independent matrix operator, which, acting on the inlet temperature distributions, generates the outlet ones. This formalism is particularly useful for the evaluation of the thermal effectiveness of complex heat exchanger configurations that can be broken into simple constitutive parts, linked to each other by unmixed streams. Applications to crossflow configurations of practical interest are shown.
Design of Multipass Heat Exchangers: An Alternative Approach
Authors: Ahmad S. , Linnhoff B. , Smith R.
Published: October 2009

Multipass heat exchangers are often designed according to the rule of thumb FT ≤ 0.75. This criterion can give rise to poor designs. It is the slope (∂FT/∂P)R that is important, not just the absolute value of FT. Furthermore, in multishell arrangements, the number of shells required is usually evaluated by trial and error. This paper introduces an approach based on a new parameter that is an alternative to FT factors. The method is fully compatible with established design practice, takes account of the FT slope, and evaluates the number of shells explicitly in multishell cases.
An Experimental Study on Natural Convection Heat Transfer in an Inclined Square Enclosure Containing Internal Energy Sources
Authors: Lee Jae-Heon , Goldstein R. J.
Published: October 2009

An experiment was carried out to study two-dimensional laminar natural convection within an inclined square enclosure containing fluid with internal energy sources bounded by four rigid planes of constant equal temperature. Inclination angles, from the horizontal, of 0, 15, 30, and 45 deg for Rayleigh numbers from 1.0 × 104 to 1.5 × 105 were studied. At inclined angles of 0 and 15 deg, there are two extreme values of temperature and temperature gradient within the fluid, while there is only one at 30 and 45 deg. Local and average Nusselt numbers are obtained on all four walls. As the inclination angle increases, the average Nusselt number increases on the right (upper) and bottom walls, decreases on the left (lower) wall and stays almost constant on the top wall.
Mixed Convection in Stagnation Flows Adjacent to Vertical Surfaces
Authors: Ramachandran N. , Chen T. S. , Armaly B. F.
Published: October 2009

Laminar mixed convection in two-dimensional stagnation flows around heated surfaces is analyzed for both cases of an arbitrary wall temperature and arbitrary surface heat flux variations. The two-dimensional Navier–Stokes equations and the energy equation governing the flow and thermal fields are reduced to a dimensionless form by appropriate transformations and the resulting system of ordinary differential equations is solved in the buoyancy assisting and opposing regions. Numerical results are obtained for the special cases for which locally similar solutions exist as a function of the buoyancy parameter. Local wall shear stress and heat transfer rates as well as velocity and temperature distributions are presented. It is found that the local Nusselt number and wall shear stress increase as the value of the buoyancy parameter increases in the buoyancy assisting flow region. A reverse flow region develops in the buoyancy opposing flow region, and dual solutions are found to exist in that flow regime for a certain range of the buoyancy parameter.
Non-Darcian Convection in Cylindrical Packed Beds
Authors: Hunt M. L. , Tien C. L.
Published: October 2009

Non-Darcian transport describes the nonuniform flow and thermal anomalies often found in flow through packed beds. These effects include the high-flow-rate inertial pressure loss, near-wall porosity variation, solid-boundary shear, and thermal dispersion. Inclusion of these effects significantly alters the velocity and temperature profiles from those predicted by models using uniform or Darcian flow. In this paper, the non-Darcian formulation is used to predict the heat transfer rates for cylindrical packed beds such as chemical reactors. Traditional analyses of chemical reactors assume slug flow and must include a temperature-slip boundary condition to predict the measured temperature profiles. The present analysis predicts similar temperature variations by allowing the velocity and diffusivity to vary across the bed. The results agree with experimental data for chemical reactors and do not depend on the extensive experimental relations needed in conventional reactor models.
Onset of Finger Convection in a Horizontal Porous Layer Underlying a Fluid Layer
Authors: Chen F. , Chen C. F.
Published: October 2009

In the directional solidification of concentrated alloys, the frozen solid region is separated from the melt region by a mushy zone consisting of dendrites immersed in the melt. Simultaneous occurrence of temperature and solute gradients through the melt and mushy zones may be conducive to the occurrence of salt-finger convection, which may in turn cause adverse effects such as channel segregation. We have considered the problem of the onset of finger convection in a porous layer underlying a fluid layer using linear stability analysis. The eigenvalue problem is solved by a shooting method. As a check on the method of solution and the associated computer program, we first consider the thermal convection problem. In this process, it is discovered that at low depth ratios dˆ (the ratio of the fluid layer depth to the porous layer depth), the marginal stability curve is bimodal. At small dˆ, the long-wave branch is the most unstable and the convection is dominated by the porous layer. At large dˆ, the short-wave branch is the most unstable and the convection is dominated by the fluid layer, with a convection pattern consisting of square cells in the fluid layer. In the salt-finger case with a given thermal Rayleigh number Ram = 50, as the depth ratio dˆ is increased from zero, the critical salt Rayleigh number Rasm first decreases, reaches a minimum, and then increases. The system is more stable at dˆ > 0.2 than at dˆ = 0. This rather unusual behavior is again due to the fact that at small dˆ, convection is dominated by the porous layer and, at large dˆ, convection is dominated by the fluid layer. However, in the latter case, the convection pattern in the fluid layer consists of a number of high aspect ratio cells.
Boundary Layer Analysis for Two-Dimensional Slot Jet Impingement on Inclined Plates
Authors: Garg V. K. , Jayaraj S.
Published: October 2009

The laminar boundary layer flow when a two-dimensional slot jet impinges on a flat plate at some angle is analyzed theoretically. The conservation equations in primitive variables are solved using a finite-difference technique. The computed results at 0 and 90 deg angle of impingement are in perfect agreement with the standard solutions available in the literature. The influence of the angle of impingement on the velocity and temperature profiles is studied. The presence of a stagnation point when the plate is not parallel to the oncoming jet is found to affect considerably the local Nusselt number and skin friction coefficient. These parameters attain very large values close to the stagnation point at small angles of impingement. However, far from the stagnation point, they approach values corresponding to a flat plate at zero incidence, irrespective of the angle of jet impingement.
A Two-Equation Model for Heat Transport in Wall Turbulent Shear Flows
Authors: Nagano Y. , Kim C.
Published: October 2009

A new proposal for closing the energy equation is presented at the two-equation level of turbulence modeling. The eddy diffusivity concept is used in modeling. However, just as the eddy viscosity is determined from solutions of the k and ε equations, so the eddy diffusivity for heat is given as functions of temperature variance t2, and the dissipation rate of temperature fluctuations εt, together with k and ε. Thus, the proposed model does not require any questionable assumptions for the “turbulent Prandtl number.” Modeled forms of the t2 and εt equations are developed to account for the physical effects of molecular Prandtl number and near-wall turbulence. The model is tested by application to a flat-plate boundary layer, the thermal entrance region of a pipe, and the turbulent heat transfer in fluids over a wide range of the Prandtl number. Agreement with the experiment is generally very satisfactory.
Three-Dimensional Unsteady Flow With Heat and Mass Transfer Over a Continuous Stretching Surface
Authors: Lakshmisha K. N. , Venkateswaran S. , Nath G.
Published: October 2009

A numerical solution of the unsteady boundary layer equations under similarity assumptions is obtained. The solution represents the three-dimensional unsteady fluid motion caused by the time-dependent stretching of a flat boundary. It has been shown that a self-similar solution exists when either the rate of stretching is decreasing with time or it is constant. Three different numerical techniques are applied and a comparison is made among them as well as with earlier results. Analysis is made for various situations like deceleration in stretching of the boundary, mass transfer at the surface, saddle and nodal point flows, and the effect of a magnetic field. Both the constant temperature and constant heat flux conditions at the wall have been studied.
Heat Transfer Characteristics From a Flat Plate to a Gas–Solid Two-Phase Flow Downstream of a Slit Injection
Authors: Obi S. , Hishida K. , Maeda M.
Published: October 2009

The behavior of fine glass particles and their influence on fluid motion are investigated in a flow over a flat plate downstream of a two-dimensional slit injection. Heat transfer characteristics are examined in terms of the mass loading ratio of the particles ranging up to 0.8 and particle size varying from 68.6 to 148 μm in mean diameter. The particles promote turbulence of the fluid in a weakly turbulent flow, but suppress turbulence in a strongly turbulent flow. The heat transfer characteristics along the wall are well correlated to the variation of turbulent flow field due to the effect of the particles.
Electrically Induced Shape Oscillation of Drops as a Means of Direct-Contact Heat Transfer Enhancement: Part 2—Heat Transfer
Authors: Kaji N. , Mori Y. H. , Tochitani Y.
Published: October 2009

The heat transfer enhancement caused by the application of a low-frequency (1 ∼ 16 Hz) alternating field having the sinusoidal waveform has been studied experimentally with water drops in a medium of silicone oil. The heat transfer coefficient has been found to peak at three particular frequencies. The data newly obtained with the sinusoidal waveform are compared with earlier results obtained with electric fields having other waveforms. The waveform and the frequency that yield the largest enhancement of heat transfer are sought.
The Influence of Availability Costs on Optimal Heat Exchanger Design
Authors: Witte L. C.
Published: October 2009

Optimizing heat exchangers based on second-law rather than first-law considerations ensures that the most efficient use of available energy is being made. In this paper, second-law efficiency is used to develop a new technique for optimizing the design of heat exchangers. The method relates the operating costs of the exchanger to the destruction of availability caused by the exchanger operation. The destruction of availability is directly related to the second-law efficiency of the exchanger. This allows one to find the NTU at which the benefits of reduced availability losses are offset by the costs of added area; this is the optimal point. It can be difficult to determine the proper cost of irreversibility to be used in the optimization process. This issue can be handled by including the irreversibility cost in a dimensionless parameter that represents the ratio of annual ownership costs to annual operating costs that include irreversibility costs. In this way, each heat exchanger designer can estimate the costs of irreversibilities for his particular system, and then use the generalized method that is developed herein for determining the optimal heat exchanger size. The method is applicable to any heat exchanger for which the ε-NTU-R relationships are known.
Combined Forced and Free Laminar Convection in the Entrance Region of an Inclined Isothermal Tube
Authors: Choudhury D. , Patankar S. V.
Published: October 2009

An analysis is made of the combined forced and free convection for laminar flow in the entrance region of isothermal, inclined tubes. This involves the numerical calculation of the developing flow with significant buoyancy effects. Three independent parameters are introduced: the Prandtl number Pr, a modified Rayleigh number Ra*, and Ω, a parameter that measures the relative importance of free and forced convection. The inclination angle does not appear explicitly in the formulation. Numerical results are obtained for Pr = 0.7, 5, and 10, and representative values of Ra* and Ω. The axial development of the velocity profiles, temperature field, local pressure gradient, and the Nusselt number are presented. These results reveal that the buoyancy effects have a considerable influence on the fluid flow and heat transfer characteristics of the development flow. A comparison of the numerical results with the available experimental data is also presented.
Flows in Vertical Channels With Asymmetric Wall Temperatures and Including Situations Where Reverse Flows Occur
Authors: Ingham D. B. , Keen D. J. , Heggs P. J.
Published: October 2009

Numerical investigations are conducted into steady laminar combined convection flows in vertical parallel plate ducts with asymmetric constant wall temperature boundary conditions. The streamwise diffusion terms in the governing equations are neglected and the resulting parabolic equations are expressed in an implicit finite difference scheme and solved using a marching technique. In certain situations the combination of the size of the ratio |Gr/Re| and the difference in temperature between the walls of the duct is such that the fully developed flow profile, as the streamwise coordinate tends toward infinity, includes reverse flow in the vicinity of the cold wall. Techniques first used in a previous study are employed in finding a solution through the whole domain of the fluid for those situations involving reverse flow in the fully developed region. Comparisons with existing data near the duct entrance and far along the duct show very good agreement.
Network Thermodynamic Modeling With Bond Graphs for Membrane Transport During Cell Freezing Procedures
Authors: Diller K. R. , Beaman J. J. , Montoya J. P. , Breedfeld P. C.
Published: October 2009

Freezing procedures for preservation of living cells create osmotic stresses associated with the addition and removal of cryoprotective agents and with ice formation in the extracellular solution, causing a concomitant segregation of electrolytes into the remaining liquid phase. When these osmotic stresses are introduced, coupled flows of water and permeable solute are induced across the plasma membrane. A network thermodynamic model of this process is presented, based on development according to the principles of bond graphs. The model is a complete representation of the equations that describe the process, and the bond graph can be interpreted directly in terms of the relevant energy flows during membrane transport and the topology of the system. Determination of the transient cell volume during addition of glycerol to an erythrocyte suspension is used to demonstrate the model.
Recent Developments in Contact Conductance Heat Transfer
Authors: Fletcher L. S.
Published: October 2009

The characteristics of thermal contact conductance are increasingly important in a wide range of technologies. As a consequence, the number of experimental and theoretical investigations of contact conductance has increased. This paper reviews and categorizes recent developments in contact conductance heat transfer. Among the topics included are the theoretical/analytical/numerical studies of contact conductance for conforming surfaces and other surface geometries; the thermal conductance in such technological areas as advanced or modern materials, microelectronics, and biomedicine; and selected topics including thermal rectification, gas conductance, cylindrical contacts, periodic and sliding contacts, and conductance measurements. The paper concludes with recommendations for emerging and continuing areas of investigation.
Some Perspectives on Enhanced Heat Transfer—Second-Generation Heat Transfer Technology
Authors: Bergles A. E.
Published: October 2009

During the past twenty-five years, heat transfer enhancement has grown at a rapid rate to the point where it can be regarded as a major field of endeavor, a second-generation heat transfer technology. After some historical background, mention of the driving trends, and a review of the various convective enhancement techniques, four areas of major contemporary interest are discussed: structured surfaces for shellside boiling, rough surfaces in tubes, offset strip fins, and microfin tubes for refrigerant evaporators and condensers. The review concludes with developments in the major areas of application.
On the Computation of Convective Heat Transfer in Complex Turbulent Flows
Authors: Launder B. E.
Published: October 2009

The paper summarizes current strategies for computing heat transfer coefficients in complex turbulent flows based on numerical solution of the averaged equations for momentum and enthalpy and corresponding equations for averaged properties of the turbulent flow field. It argues that, for accuracy and width of applicability, a fine-grid low-Reynolds-number treatment should be employed near the wall in place of wall functions, despite the attractive simplicity of the latter approach. Several examples are provided that bring out the benefit from adopting second-moment closures, in which attention is focused on the turbulent stresses and heat fluxes themselves rather than on effective viscosities and thermal diffusivities. Directions for future research are briefly discussed, an important contribution to this effort being the direct numerical simulation of the near-wall dynamic and thermal turbulence field.
Thermal Radiation in Packed and Fluidized Beds
Authors: Tien C. L.
Published: October 2009

The present work gives an overview of the existing knowledge on radiative transfer in packed and fluidized beds. Special emphasis is given to the proper usage and determination of radiation characteristics of the particles in these systems. Models that treat the particulate bed as a continuum are discussed along with those that consider the system as discontinuous, i.e., accounting for the phase boundaries between the gas and the particles. Existing experimental techniques for determining the radiative properties are presented, and the published bed transmittance and reflectance data are discussed and compared with the theoretical predictions. Interaction of radiation with other modes of heat transfer is also examined.
Natural Circulation Loops
Authors: Greif R.
Published: October 2009

Natural circulation loops encompass a broad range of applications and phenomena. Basic experimental and theoretical studies as well as overall performance and systems testing and analyses have been carried out on natural circulation loops. Research in this important area is being vigorously conducted throughout the world and a number of representative works and programs are discussed.
Convection Near the Temperature of Maximum Density for High Rayleigh Number, Low Aspect Ratio, Rectangular Cavities
Authors: Ivey G. N. , Hamblin P. F.
Published: October 2009

Natural convection in rectangular cavities with the vertical endwalls differentially heated about the temperature of maximum density of water was studied in the laboratory. In order to control heat losses, the experiments were conducted in a large cold room with the air temperature maintained at 4°C. The Rayleigh number was varied over the range 105 to 108 and the aspect ratio over the range 0.1 to 0.5. The flow field consisted of a double cellular circulation, and the observed temperature field, flow field, and heat transfer rates were compared with analytical predictions in the diffusive regime. The experiments demonstrated that the interior sinking flow was unstable for Ra > 107.
Flow Reversal in Opposing Mixed Convection Flow in Inclined Pipes
Authors: Lavine A. S. , Kim M. Y. , Shores C. N.
Published: October 2009

An experimental investigation of opposing mixed convection in an inclined pipe has been conducted. Dye injection reveals the existence of flow reversal regions. There is an optimal tilt angle that yields maximum flow reversal length. Flow reversals are seen to cause early transition to turbulence. Temperature profiles are measured across the tube cross section near the entrance to the heated section, and show the effect of tube inclination. Temperature measurements exhibit periodic behavior in the flow reversal region under some conditions, generally characterized by low tilt angle and moderate to high Reynolds and Grashof numbers. Flow visualization indicates that this periodic behavior is due to the intermittent breakdown of the flow reversal region.
The Fundamentals of Sliding Contact Melting and Friction
Authors: Bejan A.
Published: October 2009

This paper focuses on the phenomenon of melting and lubrication by the sliding contact between a phase-change material and a smooth flat slider. The first part of the study considers the limit in which the melting is due primarily to “direct heating,” that is, to the temperature difference between the solid slider and the melting point of the phase-change material. It is shown that in this limit the relative motion gap has a uniform thickness and that the friction factor decreases as both the normal force and the temperature difference increase. The second part considers the limit where the melting is caused mainly by the frictional heating of the liquid formed in the relative motion gap. This gap turns out to have a converging-diverging shape that varies with the parameters of the problem. As the normal force increases, a larger fraction of the melt is pushed out through the upstream opening of the relative motion gap. Means for calculating the melting speed, the friction factor, and the temperature rise along the slider surface are developed.
Planar Imaging of Vortex Dynamics in Flames
Authors: Gutmark E. , Parr T. P. , Parr D. M. , Schadow K. C.
Published: October 2009

The interaction between the fluid dynamics and the combustion process in an annular diffusion flame was studied experimentally using the Planar Laser Induced Fluorescence (PLIF) technique. The local temperature and OH radical fluorescence signals were mapped in the entire flame cross section. The flame was forced at different instability frequencies, thus enabling the study of the evolution and interaction of large-scale structures in the flame shear layer. The present study of the effect of fluid dynamics on combustion is part of a more comprehensive program aimed at understanding and controlling the effect of heat release, density variations, and reaction parameters on the shear layer evolution.
An Inverse Convection Problem
Authors: Moutsoglou A.
Published: October 2009

The nature of inverse problems in convective environments is investigated. The ill-posed quality inherent in inverse problems is verified for free convection laminar flow in a vertical channel. A sequential function specification algorithm is adapted for the semiparabolic system of equations that governs the flow and heat transfer in the channel. The procedure works very well in alleviating the ill-posed symptoms of inverse problems. The performance of a simple smoothing routine is also tested for the prescribed conditions.
Heat Transfer and Pressure Drop Characteristics of an Assembly of Partially Segmented Plates
Authors: Lee Y. N.
Published: October 2009

The heat transfer and pressure drop characteristics of an assembly of plates in a rectangular duct, with part of each plate segmented transversely and the segments inclined at 25 deg to the flow, have been investigated experimentally in the range of Reynolds numbers between 900 and 4000. The segmented-to-total width ratios β were 0.81 and 0.61. Mass transfer measurements of naphthalene were made to obtain the heat transfer coefficient. A new spray technique is described for preparing the mass transfer models, which are so complex that previously reported techniques cannot be applied. The mass transfer models simulate louvered fin surfaces used currently in industries. The heat transfer coefficient is found to be a strong function of the segmented-to-total plate width ratio β, and it decreases as β decreases. The heat transfer coefficient of an existing louver fin heat exchanger whose geometries are in close proximity to one of the model configurations was compared with that of the model, and good agreement was obtained between the two. The pressure drop (through the plate assembly) measurements showed that the pressure drop is mainly due to inertia loss in the experimental range of the present work, and that the streamwise, per-row pressure drop coefficient Kp is a function of only β and independent of the Reynolds number NRe,Dh. It was found, for a fixed blower power, that there exists an optimum Reynolds number (NRe,Dh)opt for maximum Nusselt number at a given segmented-to-total width radio β. A similar trend is also found for a fixed pressure drop.
Cavity Heat Transfer on a Transverse Grooved Wall in a Narrow Flow Channel
Authors: Metzger D. E. , Bunker R. S. , Chyu M. K.
Published: October 2009

Measurements are presented of local convection heat transfer for the case of flow through a narrow slot-type channel where one of the bounding walls contains a transverse rectangular cavity. The experimental situation is a stationary modeling of some salient features of flow through the clearance gap at the grooved tips of axial turbine blades. Cavity depth-to-width ratios of 0.1, 0.2, and 0.5 are included for each of clearance-to-width ratios of 0.05, 0.10, and 0.15. Overall heat transfer on the cavity floor is in general reduced as cavity depth is increased, but reduction with the deepest cavity tested is essentially the same as that of the intermediate depth cavity. Resistance to flow through the gap is increased as cavity depth is increased, but again the change between the deepest and intermediate depth cavities is small. In addition to the stationary experiments, heat transfer in the cavity with a moving as well as stationary shroud is modeled with a finite-difference method. The numerical results indicate that, within the range of parameters considered, heat transfer characteristics in the cavity are virtually unaffected by the shroud movement. This is in agreement with a previous finding for heat transfer on ungrooved blade tips.
The Enthalpy Method for Heat Conduction Problems With Moving Boundaries
Authors: Hunter L. W. , Kuttler J. R.
Published: October 2009

The purpose of this paper is to demonstrate how an enthalpy method for heat conduction problems with moving boundaries associated with phase changes can be combined with Kirchhoff and coordinate transformations to put these problems in a particularly simple form. All nonlinearities in density, conductivity, and specific heat can be concentrated in the functional relation between enthalpy and the generalized temperature. Convection in the fluid is neglected. A simple numerical example is included.
On Natural Convection Heat Transfer From Three-Dimensional Bodies of Arbitrary Shape
Authors: Hassani A. V. , Hollands K. G. T.
Published: October 2009

A simple expression is developed for the natural convection heat transfer from three-dimensional bodies of arbitrary shape immersed in an extensive fluid. The expression applies to both laminar and turbulent regimes and requires the calculation of purely geometric properties of the bodies. Experiments were performed with air, covering a Rayleigh number (Ra) range of from 10 to 108, on different body shapes oriented in various directions: for example, circular or square disks, a short circular cylinder of height equal to diameter and a similar cylinder but with hemispherical ends, prolate and oblate spheroids of various aspect ratio, and an “apple core” shape. Comparison between the predictions of the expression and the experimental results of this work and those gathered from several other sources ranging up to Ra = 1014 showed very good agreement, with an average rms difference of 3.5 percent for Ra < 108 and 22 percent for 108 < Ra < 1014.
Numerical Investigation of Near-Wall Turbulent Heat Transfer Taking Into Account the Unsteady Heat Conduction in the Solid Wall
Authors: Kasagi N. , Kuroda A. , Hirata M.
Published: October 2009

The deterministic near-wall turbulence model developed by Kasagi et al. (1984b) is used in a numerical analysis of turbulent heat transfer, in which the unsteady heat conduction inside the wall associated with the turbulent flow unsteadiness is taken into account. Unlike the typical methodology based on Reynolds decomposition, the algebraic expressions for the three fluctuating velocities given by the model are directly introduced into the governing energy equation. From the numerical results of the unsteady conjugate heat transfer, the statistical quantities, such as temperature variance, turbulent heat flux, and turbulent Prandtl number, are obtained for fluids of various Prandtl numbers. It is demonstrated that the near-wall behavior of these quantities is strongly influenced by the thermal properties and thickness of the wall. In addition, the budget of the temperature variance associated with coherent turbulence structure is calculated and, except for dissipation, each budget term is in qualitative agreement with the experiment.
Theory of Melting With Natural Convection in an Enclosed Porous Medium
Authors: Bejan A.
Published: October 2009

This paper reports a complete theory of the melting that occurs in a confined porous medium saturated with phase-change material and heated from the side. Darcy flow characteristics are assumed for the liquid phase. The solid phase is isothermal and at the melting point. The first part of the paper reports a matched boundary layer solution for natural convection dominated melting in the quasi-steady regime. The second part reports a solution for the heat transfer during the two earlier regimes, pure conduction followed by mixed conduction and convection. Together, the two solutions cover the entire history of transient heating administered from the side. This theory shows that the liquid-side Stefan number has a profound effect on the heat transfer and melting rates.
Upward Turbulent Flame Spread on Wood Under External Radiation
Authors: Saito K. , Williams F. A. , Wichman I. S. , Quintiere J. G.
Published: October 2009

Experiments were performed to obtain histories of surface temperatures and rates of upward flame spread for vertically oriented, thermally thick wood slabs exposed to surface fluxes of thermal radiation up to 2.6 W/cm2. Above a critical irradiance sustained upward flame spread occurred for Douglas-fir particle board with pilot initiation at the base of the fuel face. Data obtained included temperatures, flame heights, pyrolysis-front heights, combustion duration, and char-layer thickness for various irradiances and preheat times. The measurements were compared with theory.
Thermal Measurements in Large Pool Fires
Authors: Gregory J. J. , Keltner N. R. , Mata R.
Published: October 2009

During the summer of 1983, a series of pool fire tests was conducted in which the test item was a 1.4-m-dia, 6.4-m-long, mild steel calorimeter with a mass of approximately 10,000 kg. The purpose of these tests was to study the thermal response of a large test item in a specified fire configuration, to define thermal boundary conditions, and to assess the repeatability of the fire environment. While the calorimeter used in the tests simulated a nuclear waste transportation cask, the results of the study have broader application to the truck and rail transport of hydrocarbon fuels and hazardous chemicals.
Acoustic Temperature Profile Measurement Technique for Large Combustion Chambers
Authors: Venkateshan S. P. , Shakkottai P. , Kwack E. Y. , Back L. H.
Published: October 2009

Measurement of times of flight of sound waves can be used to determine temperatures in a gas. This paper describes a system, based on this principle, that is capable of giving the temperature profile in a nonisothermal gas volume, for example, prevalent in a large furnace. The apparatus is simple, rugged, accurate, and capable of being automated for process control applications. It is basically an acoustic waveguide where the outside temperature profile is transferred to a chosen gas contained inside the guide.
The Peak Boiling Heat Flux in Saturated Ethanol–Water Mixtures
Authors: Reddy R. P. , Lienhard J. H.
Published: October 2009

The present work provides original measurements of the burnout heat flux in saturated ethanol–water mixtures, over the full range of concentrations. These data were obtained at atmospheric pressure on horizontal cylinders, ranging from 0.51 to 2.16 mm in diameter. They reveal significant improvements of the peak heat flux for mixtures, over that which would be expected from pure fluids with the properties of the mixture. This improvement is most pronounced at low ethanol mass fractions. McEligot has suggested that the improved heat flux results from a subcooling created by selective distillation at the liquid–vapor interface. Combining this idea with a recent correlation of subcooled burnout, we estimate the extent of effective subcooling qualitatively and discuss the use of this estimate to correlate burnout in binary mixtures. Two dimensionless groups are proposed to characterize this effective subcooling, both based on appropriate characterizations of the phase equilibrium diagram.
An Approximate Analysis for General Film Condensation Transients
Authors: Flik M. I. , Tien C. L.
Published: October 2009

This work presents a simple, powerful technique for analyzing a broad class of film condensation transients. The analysis shows that general film condensation transients are governed by the propagation of a kinematic wave along the film. Scaling arguments establish conditions for the use of quasi-steady profiles in the integral conservation equations. An elementary method permits simple solutions of the governing hyperbolic equation for time-step changes with arbitrary initial conditions. The application of this method yields closed-form solutions for step changes of body force, vapor shear, and wall temperature for a laminar film and for step changes of body force and wall temperature for a film within a porous medium. These approximate results agree excellently with numerical solutions of the complete boundary-layer equations. This technique has applications to a wide class of film condensation transients and to film boiling and convective vaporization transients.
Horizontal-Tube Falling-Film Evaporation With Structured Surfaces
Authors: Chyu M.-C. , Bergles A. E.
Published: October 2009

Extensive experimental tests for tubes with commercial structured surfaces in a horizontal single-tube falling-film evaporator were conducted. The test sections were hollow copper cylinders with GEWA-T, Thermoexcel-E, or High Flux surfaces electrically heated by inserted cartridge heaters. A smooth surface cylinder was also tested for reference. All tubes were tested in both pool boiling and falling-film evaporation with water. The results reveal that falling-film evaporation provides much higher heat transfer coefficients than pool boiling in the low heat flux, convective region. The GEWA-T surface enhances heat transfer through its increased and accessible area, while Thermoexcel-E and High Flux demonstrate high heat transfer performances because of enhanced nucleate boiling. The falling-film evaporation data for the structured surfaces either merge or show a tendency to merge with the respective pool boiling curves at high heat fluxes. Unusual incipient boiling behavior of Thermoexcel-E and the effects of factors such as surface aging, surface subcooling, film flow rate, liquid feed height, and rate of heat flux change, are described.
Approximate Solution—One-Dimensional Energy Equation for Transient, Compressible, Low Mach Number Turbulent Boundary Layer Flows
Authors: Yang J. , Martin J. K.
Published: October 2009

Unsteady surface heat-flux and temperature profiles in the transient, compressible, low Mach number, turbulent boundary layer typically found in internal combustion engines have been determined by numerically integrating a linearized form of the one-dimensional energy equation. An empirical relation for μt/μ has been used to consider turbulent conductivity. Approximate solutions have been acquired by multiparameter fits to the numerical solutions. Comparisons of the approximate solutions with motored engine experiments show good agreement.
Flow and Heat Transfer in the Space Between Two Corotating Disks in an Axisymmetric Enclosure
Authors: Chang C. J. , Schuler C. A. , Humphrey J. A. C. , Greif R.
Published: October 2009

A numerical investigation was undertaken to characterize the laminar flow and heat transfer in axisymmetric coaxial corotating shrouded disk configurations. Attention was focused on calculation conditions favoring steady, stable, symmetric solutions of the conservation equations. The justification for this is based on velocity measurements obtained in a test section that matches the numerical configuration. Calculations were performed to investigate the dependence of the flow characteristics on disk angular velocity, disk spacing, and the disk–shroud gap width. Conditions involving a radial throughflow (blowing) and/or an axially directed disk–shroud gap flow were also predicted. In the region of the shroud the results show a strong sensitivity of the flow and heat transfer to variations in the flow Reynolds number (rotation) and Rossby number (blowing). By contrast, the flow was found to be less dependent on the disk spacing and the disk–shroud gap width for the conditions investigated. The introduction of an axially directed disk–shroud gap flow significantly alters the flow and heat transfer characteristics in the region between two disks. This finding is important for the improved design and control of corotating disk systems.
Analysis of Volumetric Absorption of Solar Energy and Its Interaction With Convection
Authors: Thynell S. T. , Merkle C. L.
Published: October 2009

A theoretical analysis of the interaction of volumetric absorption of concentrated solar radiation and convection in a two-dimensional, axisymmetric absorption chamber is presented. Previous analytical works on the absorption of the radiant energy in such chambers have employed one-dimensional models to show that very high temperatures and therefore high thermodynamic efficiencies are achievable. In this work, the effects of using collimated as opposed to isotropic irradiation on the absorption efficiency are investigated for the one-dimensional case, and the effects of employing a more realistic two-dimensional model on the absorption efficiency are studied. The model is based on the assumptions that the velocity profile is uniform and that conduction within the fluid is negligible compared to convective and radiative transports of energy. Several parameter surveys are performed and compared with the results of previous one-dimensional models.
Condensation on Coherent Turbulent Jets: Part II—A Theoretical Study
Authors: Kim S. , Mills A. F.
Published: October 2009

Condensation on coherent turbulent liquid jets was investigated theoretically. The governing conservation equations were obtained using an order of magnitude analysis, and were solved numerically using a finite difference method. The Boussinesq hypothesis was invoked to model turbulent transport. Various eddy diffusivity models, of varying degrees of complexity, were evaluated through comparison with experimental data, and shortcomings noted. An ad hoc model, which allows for axial decay of turbulence by viscosity, and radial decay by both surface tension and viscosity, is shown to be in reasonable agreement with experiment. Numerical solutions were also obtained for laminar jets, and are essentially exact; these solutions are used to give some insight into the nature of the jet heat transfer problem.
Effective Thermal Conductivity Within Packed Beds of Spherical Particles
Authors: Duncan A. B. , Peterson G. P. , Fletcher L. S.
Published: October 2009

An investigation of the effective thermal conductivity of packed beds of spherical particles was conducted. Included is a brief review of related analytical and experimental investigations, along with a description of the results from an experimental program. Five beds of different materials were evaluated to determine the effective thermal conductivity as a function of the mechanical load on the bed, the conductivity of the bed material, and the interstitial gaseous environment surrounding the bed particles. The effective thermal conductivity of the packed beds were found to be dependent upon the thermal conductivity of the bed material and the axial load. The presence of an interstitial gas increased the effective thermal conductivity of the bed by a factor of two in almost all cases. The experimental results obtained for vacuum conditions were compared with two existing analytical models that assumed elastic deformation of the spheres. The analytical models slightly under-predicted the effective thermal conductivity for hard materials with low thermal conductivities below the elastic limit, and slightly overpredicted the effective thermal conductivity above the elastic limit for these materials. For soft materials with relatively high thermal conductivities, the analytical models overpredicted the effective thermal conductivity by as much as an order of magnitude.
Turbulent Heat Transport in a Circular Duct With a Narrow Strip Heat Flux Boundary Condition
Authors: Baughn J. W. , Dingus C. A. , Hoffman M. A. , Launder B. E.
Published: October 2009

Experiments and computations have been performed for turbulent air flow in a circular duct in which uniform heating is applied over a 60 deg arc of the circumference. The results are compared to those for both a uniform heat flux around the full circumference of the duct and for a uniform heat flux around half the circumference. The flow was hydrodynamically fully developed at the start of heating and there were negligible buoyancy effects. Both the experimental results and the computations show that the local heat transfer coefficients for the narrow strip (60 deg wide) are less than the values for uniform heating around the full circumference but greater than the values for uniform heating around half the circumference (180 deg). This rather surprising result is a consequence of the temperature distribution in the fluid and the definition of the local heat transfer coefficient, which is based on the bulk temperature.