bluuebunny/crossref_metadata_2025 huggingface dataset:
Natural Convection in Open-Ended Inclined Channels
Authors: Azevedo L. F. A. , Sparrow E. M.
Published: October 2009

Heat transfer and flow visualization experiments were carried out in water to investigate the effect of inclination on natural convection in a parallel-walled channel. Parametric variations were also made of the dimensionless interwall spacing S/H, the mode of heating, and the wall-to-ambient temperature difference (i.e., the Rayleigh number Ras). The heating modes included: (I) both walls heated and maintained at the same uniform temperature, (II) heating only from above, and (III) heating only from below. The Nusselt number results for top-heated channels inclined at an angle θ and for the vertical one-sided heated channel were perfectly correlated by the single parameter (S/H)Rascosθ. On the other hand, the results for bottom-heated channels displayed a separate dependence on S/H, Ras, and θ. The Nusselt numbers for two-sided heating exceeded those for one-sided heating for vertical and moderately inclined channels, with a mixed trend at high inclinations. The global correlation Nus = 0.645[(S/H)Ras]1/4 represented all the results within ±10 percent. Recirculation zones were present adjacent to the unheated wall of top-heated and one-sided heated channels. In the presence of heating from below, secondary flows in the form of longitudinal vortices existed above a threshold Rayleigh number.
Laminar Mixed Convection in a Concentric Annulus With Horizontal Axis
Authors: Nieckele A. O. , Patankar S. V.
Published: October 2009

Axial laminar flow in a horizontal annular pipe is influenced by the presence of buoyancy-induced secondary flows that are caused by the heat flow from the inner cylinder. A numerical study is presented for the fully developed region of the buoyancy-affected flow. The distributions of the axial and cross-sectional velocities are calculated along with the temperature variation in the cross section. Results are presented for a range of values of the Rayleigh number, the Prandtl number, and the radius ratio of the annulus. The Nusselt number increases significantly with the Rayleigh number; yet the corresponding increase in the friction factor is found to be rather small. Distributions of secondary flow and isotherms over the cross section are presented for different values of the parameters. In each half of the annulus on either side of the vertical centerline, the secondary flow displays a single-eddy pattern at low Rayleigh numbers and changes to a double-eddy pattern at high values.
Heat Transfer Around a Circular Cylinder Near a Plane Surface
Authors: Aiba S.
Published: October 2009

An experimental study has been conducted on the effect of the clearance (c) between a circular cylinder and a plane surface on the heat transfer from the cylinder to a cross flow of air. The test cylinder diameters (d) were 10.1, 15.2, and 25.2 mm. The turbulent boundary layer thickness (δ) along the wall with no cylinder present was varied from 15 to 19 mm. The Reynolds number (Re) based on the undisturbed uniform flow velocity above the wall ranged from 104 to 6.6×104. Variations of the characteristic features of the local and mean Nusselt numbers are discussed in relation to the values c/d, δ/d, and Re investigated.
Thermal Radiation Properties of Acetylene
Authors: Brosmer M. A. , Tien C. L.
Published: October 2009

The spectral absorptivities of the ν3 and ν5 fundamental and the ν4 + ν5 combination bands of acetylene have been measured at low resolution for temperatures between 290 and 600 K. These measurements allow the determination of spectral-mean (narrow-band) parameters for the three bands based on the Elsasser and Goody models and the correlation of the band absorptance data using the Edwards exponential wide-band model. Charts for the total emissivity and Planck mean absorption coefficient have been developed for acetylene based on the wide-band parameters.
Three-Dimensional Formulation of the Radiant Heat Flux Variation on a Cylinder Engulfed in Flames
Authors: Tunc¸ M. M. , Karakas¸ A.
Published: October 2009

A three-dimensional formulation is used to determine the incident radiant heat flux on a cylinder surface which is engulfed in flames. For an axisymmetric horizontal pool fire of a specified flame shape, effective flame radiation temperature and a gray flame absorption coefficient, this analysis computes the variation of the incident radiant heat flux along the length and around the circumference of the tank portrayed as a cylinder, engulfed in flames. The radiant flux density from the flame to the cylinder becomes maximum toward the center of the pool and decreases markedly toward the edges. The points which are receiving the maximum amount of radiation heat flux around the circumference of the cylinder are also determined.
Local Heat Transfer Measurements Using an Electrically Heated Thin Gold-Coated Plastic Sheet
Authors: Baughn J. W. , Takahashi R. K. , Hoffman M. A. , McKillop A. A.
Published: October 2009

This paper describes an experimental technique for measuring the local heat transfer coefficient in complex flows. The technique employs a gold-coated plastic sheet to generate a nearly uniform wall heat flux. The sheet is mounted on an insulated substrate of the desired shape and heating is achieved by passing an electrical current through the gold coating. Three applications of this technique are described: heat transfer downstream of an abrupt expansion, heat transfer from a cylinder in crossflow, and nonuniform circumferential heating in a pipe. For each of these applications the effect of the wall conduction on the surface heat flux is evaluated and found to be small. The effect of nonuniformities in the gold coating, and of the resistance temperature coefficient, are also evaluated and likewise are found to be quite small. Methods of correcting for each of these small effects are presented for the above applications.
Combined Heat and Mass Transfer by Natural Convection in a Vertical Enclosure
Authors: Trevisan O. V. , Bejan A.
Published: October 2009

The phenomenon of natural convection caused by combined temperature and concentration buoyancy effects is studied analytically and numerically in a rectangular slot with uniform heat and mass fluxes along the vertical sides. The analytical part is devoted to the boundary layer regime where the heat and mass transfer rates are ruled by convection. An Oseen-linearized solution is reported for tall spaces filled with mixtures characterized by Le = 1 and arbitrary buoyancy ratios. The effect of varying the Lewis number is documented by a similarity solution valid for Le >1 in heat-transfer-driven flows, and for Le <1 in mass-transfer-driven flows. The analytical results are validated by numerical experiments conducted in the range 1≤H/L≤4, 3.5×105≤Ra≤7×106, −11≤n≤9, 1≤Le≤40, and Pr=0.7, 7. “Massline” patterns are used to visualize the convective mass transfer path and the flow reversal observed when the buoyancy ratio n passes through the value −1.
Measurements of Laminar Mixed Convection Flow Adjacent to an Inclined Surface
Authors: Ramachandran N. , Armaly B. F. , Chen T. S.
Published: October 2009

Measurements of laminar mixed forced and free convection air flow adjacent to an upward and a downward facing, isothermal, heated inclined surface (at 45 deg) are reported. Local Nusselt number and the velocity and temperature distributions are presented for both the buoyancy assisting and the buoyancy opposing flow cases for a range of buoyancy parameter 0 ≤ ξ ≤ 5 (ξ = Grx/Rex2). The measurements are in good agreement with predictions which define a laminar mixed convection regime for buoyancy assisting flow as 0.1 ≤ ξ ≤ 7, and for buoyancy opposing flows as 0.06 ≤ ξ ≤ 0.25 for this inclination angle of 45 deg. Simple mixed convection correlations for the local and average Nusselt numbers for inclined surfaces are also presented and they agree very well with predicted results. As expected, the local Nusselt number increases with increasing buoyancy parameter for assisting flows and decreases for opposing flows. For a given buoyancy parameter and Reynolds number, a downward facing surface provides essentially the same Nusselt number as the upward facing surface for the conditions examined in the experiment.
Heat Transfer Effects of a Longitudinal Vortex Embedded in a Turbulent Boundary Layer
Authors: Eibeck P. A. , Eaton J. K.
Published: October 2009

The heat transfer effects of an isolated longitudinal vortex embedded in a turbulent boundary layer were examined experimentally for vortex circulations ranging from Γ/U∞δ99 = 0.12 to 0.86. The test facility consisted of a two-dimensional boundary-layer wind tunnel, with a vortex introduced into the flow by a half-delta wing protruding from the surface. In all cases, the vortex size was of the same order as the boundary-layer thickness. Heat transfer measurements were made using a constant-heat-flux surface with 160 embedded thermocouples to provide high resolution of the surface-temperature distribution. Three-component mean-velocity measurements were made using a four-hole pressure probe. Spanwise profiles of the Stanton number showed local increases as large as 24 percent and decreases of approximately 14 percent. The perturbation to the Stanton number was persistent to the end of the test section, a length of over 100 initial boundary-layer thicknesses. The weakest vortices examined showed smaller heat transfer effects, but the Stanton number profiles were nearly identical for the three cases with circulation greater than Γ/U∞δ99 = 0.53 cm. The local increase in the Stanton number is attributed to a thinning of the boundary layer on the downwash side of the vortex.
The Effect of Pressure on Dryout of a Saturated Bed of Heat-Generating Particles
Authors: Catton I. , Jakobsson J. O.
Published: October 2009

The results of an experimental investigation of pressure effects on dryout heat flux in a volume-heated porous bed are reported. Several porous beds of near-uniform-sized particles were studied at pressures up to 5 atm. The beds were saturated with water, Freon-113, acetone, and methanol. Simple scaling of the Freon-113 results is used to yield results valid for water pressures from 1 atm to 37.3 atm.
A Prediction Method for Heat Transfer During Film Condensation on Horizontal Low Integral-Fin Tubes
Authors: Honda H. , Nozu S.
Published: October 2009

A method for predicting the average heat transfer coefficient is presented for film condensation on horizontal low integral-fin tubes. Approximate equations based on the numerical analysis of surface tension drained condensate flow on the fin surface are developed for the heat transfer coefficients in the upper and lower portions of the flooding point below which the interfin space is flooded with condensate. For the unflooded region, the equation is modified to take account of the effect of gravity. These equations are used, along with the previously derived equation for the flooding point, to determine the wall temperature distribution, and in turn the average heat transfer coefficient. It is shown that the present model can predict the average heat transfer coefficient within ±20 percent for most of the available experimental data including 11 fluids and 22 tubes.
Flow Visualization Studies on Secondary Flow Patterns in Straight Tubes Downstream of a 180 deg Bend and in Isothermally Heated Horizontal Tubes
Authors: Cheng K. C. , Yuen F. P.
Published: October 2009

Photographs are presented for secondary flow patterns in a straight tube (x/d = 0 ∼ 70) downstream of a 180 deg bend (tube inside diameter d = 2.54 cm, radius of curvature Rc = 12.7 cm) and in an isothermally heated horizontal tube (tube inside diameter d = 2.54 cm, heated length l = 46.2 cm) with free convection effects. Each test section is preceded by a long entrance length with air as the flowing fluid. For curved pipes, the Dean number range is K = 99 to 384. At the exit of the 180 deg bend, the onset of centrifugal instability in the form of an additional pair of Dean vortices near the central outer wall occurs at a Dean number of about K = 100. The developing secondary flow patterns in the thermal entrance region of an isothermally heated horizontal tube are shown for the dimensionless axial distance z = 0.8 × 10−2 to 1.83 (Re = 3134 ∼ 14) for a range of constant wall temperatures Tw = 55 ∼ 65° C with entrance air temperature at about 25° C. The secondary flow patterns shown are useful for future comparisons with predictions from numerical solutions.
Green’s Function Partitioning Procedure Applied to Foil Heat Flux Gages
Authors: Beck J. V. , Keltner N. R.
Published: October 2009

This paper presents a new procedure for using Green’s functions for transient heat conduction problems. It is developed as part of continuing research on the unsteady surface element (USE) method; the USE method provides a means for combining solutions for two or more different basic geometries. By combining such geometries, problems involving composite media can be solved including problems associated with foil heat flux gages. The new method involves partitioning Green’s function solutions over different time domains for each of which only a few terms are needed to describe the Green’s functions. The method is illustrated for the two-dimensional problem of a circular foil of finite thickness that is uniformly heated over a circular region and otherwise insulated. It is demonstrated that the method has the potential of providing extremely accurate values since six decimal accuracy is provided. Obtaining such accuracy using classical solution procedures is extremely difficult particularly for the extreme aspect ratios covered in this paper.
Exact Solution for Unsteady Conjugated Heat Transfer in the Thermal Entrance Region of a Duct
Authors: Sucec J.
Published: October 2009

By use of the Laplace transformation, an exact analytical solution is developed for the case of transient conjugated heat transfer in the thermal entrance region of a parallel plate duct when the unsteadiness is induced by a sudden change in temperature of the ambient fluid outside the duct walls. The solution is presented for the fastest part of the transient, time domain I, and comparison is made with a finite difference solution and also with the approximate, standard quasi-steady approach which is seen to be appreciably in error for a wide range of conjugation parameter values.
Second-Law Analysis of Heat Transfer in Swirling Flow Through a Cylindrical Duct
Authors: Mukherjee P. , Biswas G. , Nag P. K.
Published: October 2009

A second-law analysis is made on a swirling flow in a cylindrical duct with constant wall temperature. A purely tangential entry of the fluid is considered and a simplified model, consisting of a central air core enclosed by a potential, free vortex region and a boundary layer, is assumed. The approximate hydrodynamic boundary layer equations, and the continuity equation, are set up and solved numerically for the velocity gradients in the boundary layer. Similarly, the temperature gradients within the thermal boundary layer are obtained from the energy equation. The local Nusselt number and rate of entropy generation are calculated and used to evaluate the rate of heat transfer and loss of available energy, respectively. A merit function, defined as the ratio of exergy transferred to the sum of exergy transferred and exergy destroyed, is evaluated for various values of Reynolds number, based on the inlet tangential velocity, and conclusions are drawn about the influence of inlet swirl on irreversibility.
Heat (Mass) Transfer for Circular Jet Impingement on a Confined Disk With Annular Collection of the Spent Air
Authors: Sparrow E. M. , Xu Z. X. , Azevedo L. F. A.
Published: October 2009

Heat (mass) transfer experiments have been performed for a single circular jet impinging perpendicular to a confined disk, with the spent air being collected in an annulus which surrounds the jet delivery tube. This configuration provides precise control of the surface area affected by the impinging jet and also assures complete collection of the spent air. During the course of the experiments, parametric variations were made of the dimensionless separation distance between the jet origin and the impingement disk, of the ratio of disk diameter to the jet diameter, and of the Reynolds number. It was found that the heat (mass) transfer coefficient at the impingement surface increased substantially with a decrease in the jet diameter. Furthermore, for the smaller diameter jet, there was an optimum separation distance at which a maximum value of the heat (mass) transfer coefficient was achieved. For a jet of larger diameter, the transfer coefficient decreased monotonically as the separation distance increased.
Natural Convection From Isothermal Cubical Cavities With a Variety of Side-Facing Apertures
Authors: Clausing A. M. , Waldvogel J. M. , Lister L. D.
Published: October 2009

An experimental investigation of heat transfer by natural convection from a smooth, isothermal cubic cavity with a variety of side-facing apertures is described in this paper. The study was motivated by the desire to predict the convective loss from large solar thermal-electric receivers and to understand the mechanisms which control this loss. Hence, emphasis is placed on the large Rayleigh number, Ra, regime with large ratios of the cavity wall temperature Tw to the ambient temperature T∞. A cryogenic wind tunnel with test section temperatures which are varied between 80 K and 310 K is used to facilitate deduction of the influences of the relevant parameters and to obtain large temperature ratios without masking the results by radiative heat transfer. A 0.4-m cubic cavity, which is mounted in the side wall of this tunnel, is used. The area of the aperture Aa and its location are key variables in this study. The data which are presented cover the ranges: 1 < Tw/T∞ < 3, L2/18 ≤ Aa ≤ L2, and 3 × 107 < Ra < 3 × 1010.
Radiation-Induced Buoyancy-Driven Flow in Rectangular Enclosures: Experiment and Analysis
Authors: Webb B. W. , Viskanta R.
Published: October 2009

Experiments have been performed to study the rate of internal radiative heating on the natural convective motion in a vertical rectangular enclosure irradiated from the side. A Mach–Zehnder interferometer has been used to determine the temperature field, and a fluorescing dye injection technique was employed to illustrate the flow structure with water as the working fluid. A theoretical model is developed for predicting the absorption of thermal radiation and the subsequent buoyancy-driven flow. Predictions based on spectral calculations for the radiation flux divergence agree well with the experimental data.
Mixed-Convection Flow and Heat Transfer in the Entry Region of a Horizontal Rectangular Duct
Authors: Incropera F. P. , Knox A. L. , Maughan J. R.
Published: October 2009

Entry-region hydrodynamic and thermal conditions have been experimentally determined for laminar mixed-convection water flow through a horizontal rectangular duct with uniform bottom heating. Direct heating of 0.05 mm stainless steel foil was used to minimize wall conduction, and the foil was instrumented to yield spanwise and longitudinal distributions of the Nusselt number. Flow visualization revealed the existence of four regimes corresponding to laminar forced convection, laminar mixed convection, transitional mixed convection, and turbulent free convection. The laminar mixed-convection regime was dominated by ascending thermals which developed into mushroom-shaped longitudinal vortices. Hydrodynamic instability resulted in breakdown of the vortices and subsequent transition to turbulent flow. The longitudinal distribution of the Nusselt number was characterized by a minimum, which followed the onset of mixed convection, and subsequent oscillations due to development of the buoyancy-driven secondary flow.
Experiments on Melting of Unfixed Ice in a Horizontal Cylindrical Capsule
Authors: Webb B. W. , Moallemi M. K. , Viskanta R.
Published: October 2009

Melting of unrestrained ice in a horizontal cylindrical capsule has been investigated experimentally to determine the interaction of fluid flow induced by motion of the solid and natural convection with density inversion of the water–ice system. During the melting process the ice is drawn by buoyancy to the top of the heated cylinder where close-contact melting occurs. Natural convection-dominated melting whose intensity depends on wall temperature prevails in the liquid region below. Three distinct flow regimes were identified for the cylinder wall temperatures of 3.5, 7, and 12° C studied. The flow structure for temperatures below the inversion point is similar to that for melting of unfixed n-heptadecane reported previously. Photographs of flow regimes are presented, and dependence of the solid–liquid interface morphology on the flow structure is discussed.
Transient Melting of a Metal Plate by a Penetrating Plasma Arc
Authors: Hsu Y. F. , Rubinsky B.
Published: October 2009

A study was performed on the heat transfer and the fluid flow during transient melting of a metal plate subjected to stationary, penetrating plasma-arc heating. An integral method of solution was used for this simplified, first-order simulation of plasma-arc metal processing. The results of the study reveal the importance of the workpiece thickness, plasma-penetrating hole size, and gravity on the melting process and the molten fluid flow. The study also shows that plasma-arc metal processing seems to be a low-efficiency manufacturing process with only 7 percent of the plasma energy contributing to the melting.
Condensation of an Accelerating-Decelerating Bubble: Experimental and Phenomenological Analysis
Authors: Lerner Y. , Kalman H. , Letan R.
Published: October 2009

An experimental and theoretical phenomenological study of accelerating–decelerating bubbles, condensing in an immiscible liquid, was conducted. The system consisted of a column of water, and bubbles of freon-113, 4–5×10−3 m in diameter. Shadowgraphing of the process has illustrated the wake formation behind the bubble, wake shedding, forward movement of vortices, and envelopment of the decelerating bubble in its wake. The bubble size, shape, and path were videotaped and analyzed for the collapse rate, and the instantaneous position. The visualized hydrodynamic phenomena provided a phenomenological basis for the theoretical formulations. The theoretical model postulated an eccentrically positioned vapor sphere in the collapsing bubble, a boundary layer and wake over the accelerating bubble, and a concentric vorticular envelope around the decelerating bubble. The theoretical–phenomenological predictions compared well with experiment.
Integral Solution of Diffusion Equation: Part 1—General Solution
Authors: Haji-Sheikh A. , Mashena M.
Published: October 2009

A generalized method is presented that accommodates the linear form of the diffusion equation in regions with irregular boundaries. The region of interest many consist of subregions with spatially variable thermal properties. The solution function for the diffusion equation is decomposed into two solutions: one with homogeneous and the other with nonhomogeneous boundary conditions. The Galerkin functions are used to provide a solution for a diffusion problem with homogeneous boundary condition and linear initial condition. Problems with nonhomogeneous boundary conditions can be dealt with by many other schemes, including the standard Galerkin method. The final solution is a combination of these two solutions.
Turbulent Heat Transfer Downstream of a Contraction-Related, Forward-Facing Step in a Duct
Authors: Garcia A. , Sparrow E. M.
Published: October 2009

Experiments were performed to investigate the axial distribution of the heat transfer coefficient downstream of an abrupt contraction in a flat rectangular duct. The contraction was created by the presence of a forward-facing step in one of the walls of the duct. The flow arriving at the step was hydrodynamically developed and isothermal. In the contracted duct, the duct wall that constituted the continuation of the step was maintained at a uniform temperature different from that of the entering flow, while the other walls were adiabatic. During the course of the experiments, the Reynolds number of the flow in the contracted duct ranged from 4000 to 24,000, while the ratio of the post-contraction to the precontraction duct heights took on values of 1 (no contraction), 0.8, 0.6, and 0.4. In the presence of the contraction, the axial distribution of the Sherwood number increased at first, attained a maximum, and then decreased monotonically to a fully developed value. In contrast, the no-contraction Sherwood number decreased monotonically and subsequently became fully developed. At a given Reynolds number, the peak Sherwood number for the contraction case was virtually independent of the contraction ratio and exceeded the largest measured Sherwood number for the no-contraction case by about a factor of two.
Entropy Generation in Convective Heat Transfer and Isothermal Convective Mass Transfer
Authors: San J. Y. , Worek W. M. , Lavan Z.
Published: October 2009

The irreversible generation of entropy for two limiting cases of combined forced-convection heat and mass transfer in a two-dimensional channel are investigated. First, convective heat transfer in a channel with either constant heat flux or constant surface temperature boundary conditions are considered for laminar and turbulent flow. The entropy generation is minimized to yield expressions for optimum plate spacing and optimum Reynolds numbers for both boundary conditions and flow regimes. Second, isothermal convective mass transfer in a channel is considered, assuming the diffusing substance to be an ideal gas with Lewis number equal to unity. The flow is considered to be either laminar or turbulent with boundary conditions at the channel walls of either constant concentration or constant mass flux. The analogy between heat and mass transfer is used to determine the entropy generation and the relations for optimum plate spacing and Reynolds number. The applicable range of the results for both limiting cases are then investigated by non-dimensionalizing the entropy generation equation.
Turbulence Structure of Vertical Adiabatic Wall Plumes
Authors: Lai M.-C. , Faeth G. M.
Published: October 2009

Weakly buoyant turbulent adiabatic wall plumes along vertical surfaces were studied. Instantaneous velocities and concentrations were measured using laser-Doppler anemometry and laser-induced fluorescence, Earlier work reported mean properties and their comparison with predictions of simplified mixing-length and k–ε–g turbulence models. Velocity and concentration fluctuations and their correlations are reported in the present paper. The results show considerable deficiencies in the simplified models concerning turbulence properties, e.g., anisotropy of turbulence properties, lack of coincidence of maximum velocity and zero Reynolds stress points, and variability of the turbulence Prandtl/Schmidt number. Density/velocity correlations were found which provide a means of estimating differences between Reynolds and Favre averages, effects of turbulence fluxes on conserved quantities, and effects of buoyancy/turbulence interactions on turbulence properties.
Marangoni Convection in Radiating Fluids
Authors: Bayazitoglu Y. , Lam T. T.
Published: October 2009

The onset of Marangoni convection driven by surface tension gradients in radiating fluid layers is studied. The system considered consists of a fluid layer of infinite horizontal extent which is confined between a free upper surface and a rigid isothermal lower surface. The radiative boundaries of black–black, mirror–mirror, and black–mirror are considered. The critical conditions leading to the onset of convective fluid motions in a microgravity environment are determined numerically by linear stability theory. The perturbation equations are solved as a Bolza problem in the calculus of variations. The results are presented in terms of the critical Marangoni number and optical thickness for a wide range of some radiative parameters, including the Planck number, nongrayness of the fluid, and the emissivity of the boundaries. It is found that radiation suppresses Marangoni convection during material processing in space.
Modeling of the Two-Phase Closed Thermosyphon
Authors: Reed J. G. , Tien C. L.
Published: October 2009

A comprehensive model is developed to predict the steady-state and transient performance of the two-phase closed thermosyphon. One-dimensional governing equations for the liquid and vapor phases are developed using available correlations to specify the shear stress and heat transfer coefficients. Steady-state solutions agree well with thermosyphon flooding data from several sources and with film thickness data obtained in the present investigation. While no data are available with which to compare the transient analysis, the results indicate that, for most systems, the governing time scale for system transients is the film residence time, which is typically much longer than the times required for viscous and thermal diffusion through the film. The proposed model offers a versatile and comprehensive analysis tool which is relatively simple.
Drag Coefficients Associated With a Moving Drop Experiencing Condensation
Authors: Huang Lin Jie , Ayyaswamy P. S.
Published: October 2009

For a moving liquid drop experiencing condensation, three different drag coefficients govern the motion and the transport. These coefficients are associated with friction, pressure, and condensation. Unlike situations involving the motion of a rigid sphere or a liquid drop without the presence of condensation, there is a large pressure recovery in the rear of a moving drop experiencing condensation. As a consequence, the pressure drag coefficient exhibits interesting behavior. While the coefficients for the friction drag and the condensation drag increase with the level of condensation, the pressure drag coefficient decreases rapidly. In this note, the roles played by the various drag forces in condensing situations are delineated. Results for the variation of average condensation heat transfer with vertical-fall height of the drop are presented.
Analytical Solution of Transient Response of Gas-to-Gas Parallel and Counterflow Heat Exchangers
Authors: Gvozdenac D. D.
Published: October 2009

This paper shows how the transient response of gas-to-gas parallel and counterflow heat exchangers may be calculated by an analytical method. Making the usual idealizations for analysis of dynamic responses of heat exchangers, the problem of finding the temperature distributions of both fluids and the separating wall as well as the outlet temperatures of fluids is reduced to the solution of an integral equation. This equation contains an unknown function depending on two independent variables, space and time. The solution is found by using the method of successive approximations, the Laplace transform method, and special functions defined in this paper.
A Wall Function for the Temperature Variance in Turbulent Flow Adjacent to a Diabatic Wall
Authors: Sinai Y. L.
Published: October 2009

By assuming simple initial conditions for a surface-renewal calculation of thermal coupling between a thick solid and a well-mixed, low-Prandtl-number fluid, it has been possible to approximate the temperature variance near the wall in terms of a straightforward quadrature. Comparisons have been made with several experiments. The results are aimed at numerical solutions of the turbulent variance transport equation, which has thus far been solved with ad-hoc boundary conditions applied at solid walls.
Steady and Transient Analyses of Natural Convection in a Horizontal Porous Annulus With the Galerkin Method
Authors: Rao Y. F. , Fukuda K. , Hasegawa S.
Published: October 2009

Steady and transient analytical investigation with the Galerkin method has been performed on natural convection in a horizontal porous annulus heated from the inner surface. Three families of convergent solutions, appearing one after another with increasing RaDa numbers, were obtained corresponding to different initial conditions. Despite the fact that the flow structures of two branching solutions are quite different, there exists a critcal RaDa number at which their overall heat transfer rates have the same value. The bifurcation point was determined numerically, which coincided very well with that from experimental observation. The solutions in which higher wavenumber modes are dominant agree better with experimental data of overall heat transfer.
Dispersion Phenomenology of LNG Vapor in the Burro and Coyote LNG Spill Experiments
Authors: Morgan D. L.
Published: October 2009

Various physical phenomena affecting LNG vapor dispersion were observed in LNG spill experiments conducted by the Lawrence Livermore National Laboratory. Understanding the phenomena is necessary in predicting the size of the hazardous region of vapor concentration following a spill. Gravity flow of the cold dense vapor increased cloud width while density stratification and heat flow from the ground had substantial effects on the mixing rate with air. Density stratification inhibits turbulent mixing while heat flow into the cloud promotes it through a number of processes including buoyancy. Some possible instances of buoyancy were observed in the experiments, and calculations indicate that modest amount of additional heat might substantially increase cloud dispersion. In the experiments, these phenomena led to a dependence of the maximum distance ℒ to the lower flammability limit on source rate, wind speed, and atmospheric stability that was substantially different from the prediction of the Gaussian plume model. Including these phenomena in predictive models is important for their accuracy. Time-dependent features of the concentration field due to turbulence and rapid phase-transition explosions, which also affect ℒ, were examined by applying a space-time interpolation scheme to the concentration data.
Two-Phase Boundary Layer Treatment for Subcooled Free-Convection Film Boiling Around a Body of Arbitrary Shape in a Porous Medium
Authors: Nakayama A. , Koyama H. , Kuwahara F.
Published: October 2009

The two-phase boundary layer theory was adopted to investigate subcooled free-convection film boiling over a body of arbitrary shape embedded in a porous medium. A general similarity variable which accounts for the geometric effect on the boundary layer length scale was introduced to treat the problem once for all possible two-dimensional and axisymmetric bodies. By virtue of this generalized transformation, the set of governing equations and boundary conditions for an arbitrary shape reduces into the one for a vertical flat plate already solved by Cheng and Verma. Thus, the numerical values furnished for a flat plate may readily be tranlsated for any particular body configuration of concern. Furthermore, an explicit Nusselt number expression in terms of the parameters associated with the degrees of subcooling and superheating has been established upon considering physical limiting conditions.
Turbulent Thermal Convection in an Enclosure With Internal Heat Generation
Authors: Farouk B.
Published: October 2009

Numerical results are presented for turbulent thermal convection, driven by uniform volumetric energy sources for two-dimensional flows in a rectangular enclosure. Rigid adiabatic sides and a rigid isothermal upper surface are considered. For the rigid bottom surface, zero heat flux boundary conditions are used. Computations are carried out for Prandtl number = 6.5 and Rayleigh number (based on enclosure depth L) range of 106 to 1010. The aspect ratio (L/X) of the enclosure was maintained at 0.5 for all cases. The turbulence model used in this study is a k–ε model, which characterizes turbulence through the kinetic energy and its volumetric rate of dissipation. Buoyancy effects on the turbulence structure are accounted for. Results show the transition from well-ordered multicellular flow to fully turbulent flow within the enclosure as the Rayleigh number increases.
A Physical Model of the Evaporating Meniscus
Authors: Mirzamoghadam A. , Catton I.
Published: October 2009

Transport phenomena associated with the heating of a stationary fluid near saturation by an inclined, partially submerged copper plate were studied analytically. Under steady-state evaporation, the meniscus profile was derived using an appropriate liquid film velocity and temperature distribution in an integral approach similar to boundary layer analysis. Derivation of the meniscus profile led to predicting heat transfer and performance as a function of angle of inclination of the plate.
Experimental Measurement of Water Evaporation Rates Into Air and Superheated Steam
Authors: Haji M. , Chow L. C.
Published: October 2009

The rates of evaporation of water from a horizontal water surface into a turbulent stream of hot air or superheated steam at different free-stream mass fluxes and modulated temperatures were experimentally measured. The pressure of the free stream was atmospheric. For steam, the experimental results are mostly within 10 percent of the available analytical results. Two previous experimental results are about 50 percent and 300 percent higher than the analytical results. For air, the measured evaporation rates are consistently higher than the analytical results. An estimate of the conduction heat transfer from the walls of the test section to water was made for several air tests. If the conduction heat transfer were subtracted from the total heat transfer, the measured evaporation rates are actually quite close to the analytical results. The present experiment also confirms the existence of a temperature, called the inversion temperature, below which the water evaporation rate is higher in air than in steam, but above which the opposite is true. The inversion temperature is in good agreement with the analytical prediction. The results for both air and superheated steam show that a certain scaled expression for the evaporation rate is independent of the free-steam mass flux, also in agreement with the analytical prediction.
Methodology for Comparison of Inverse Heat Conduction Methods
Authors: Raynaud M. , Beck J. V.
Published: October 2009

The inverse heat conduction problem involves the calculation of the surface heat flux from transient measured temperatures inside solids. The deviation of the estimated heat flux from the true heat flux due to stabilization procedures is called the deterministic bias. This paper defines two test problems that show the tradeoff between deterministic bias and sensitivity to measurement errors of inverse methods. For a linear problem, with the statistical assumptions of additive and uncorrelated errors having constant variance and zero mean, the second test case gives the standard deviation of the estimated heat flux. A methodology for the quantitative comparison of deterministic bias and standard deviation of inverse methods is proposed. Four numerical inverse methods are compared.
Shellside Waterflow Pressure Drop Distribution Measurements in an Industrial-Sized Test Heat Exchanger
Authors: Halle H. , Chenoweth J. M. , Wambsganss M. W.
Published: October 2009

Throughout the life of a heat exchanger, a significant part of the operating cost arises from pumping the heat transfer fluids through and past the tubes. The pumping power requirement is continuous and depends directly upon the magnitude of the pressure losses. Thus, in order to select an optimum heat exchanger design, it is is as important to be able to predict pressure drop accurately as it is to predict heat transfer. This paper presents experimental measurements of the shellside pressure drop for 24 different segmentally baffled bundle configurations in a 0.6-m (24-in.) diameter by 3.7-m (12-ft) long shell with single inlet and outlet nozzles. Both plain and finned tubes, nominally 19-mm (0.75-in.) outside diameter, were arranged on equilateral triangular, square, rotated triangular, and rotated square tube layouts with a tube pitch-to-diameter ratio of 1.25. Isothermal water tests for a range of Reynolds numbers from 7000 to 100,000 were run to measure overall as well as incremental pressure drops across sections of the exchanger. The experimental results are given and correlated with a pressure drop versus flowrate relationship.
Numerical Analysis of Laminar Forced Convection in the Entrance Region of Tubes With Longitudinal Internal Fins
Authors: Rustum I. M. , Soliman H. M.
Published: October 2009

Steady, laminar, forced convection heat transfer in the thermal entrance region of internally finned tubes is investigated numerically for the case of fully developed hydrodynamics using the (H1) and (T) thermal boundary conditions. Results are presented for 16 geometries including the local Nusselt number and developing length corresponding to each boundary condition. These results indicate that internal finning influences the thermal development in a complicated way, which makes it inappropriate to extend the smooth tube results to internally finned tubes on a hydraulic diameter basis.
Heat Transfer and Friction Characteristics in Rectangular Channels With Rib Turbulators
Authors: Han J. C.
Published: October 2009

The effect of the channel aspect ratio on the distribution of the local heat transfer coefficient in rectangular channels with two opposite ribbed walls (to simulate turbine airfoil cooling passages) was determined for a Reynolds number range of 10,000 to 60,000. The channel width-to-height ratios (W/H, ribs on side W) were 1/4, 1/2, 1, 2, and 4. The test channels were heated by passing current through thin, stainless steel foils instrumented with thermocouples. The local heat transfer coefficients on the ribbed side wall and on the smooth side wall of each test channel from the channel entrance to the fully developed regions were measured for two rib spacings (P/e = 10 and 20). The rib angle-of-attack was kept at 90 deg. The local data in the fully developed region were averaged and correlated, based on the heat transfer and friction similarity laws developed for ribbed channels, to cover the ranges of channel aspect ratio, rib spacing, rib height, and Reynolds number. The results compare well with the published data for flow in a square channel with two opposite ribbed walls. The correlations can be used in the design of turbine airfoil cooling passages.
Measurements in the Transition Vortex Flow Regime of Mixed Convection Above a Horizontal Heated Plate
Authors: Moharreri S. S. , Armaly B. F. , Chen T. S.
Published: October 2009

Experimental results covering the transition vortex flow regime of mixed convection over a heated, horizontal flat plate are presented. A criterion for the onset of vortex instability as a function of critical Reynolds and Grashof numbers was established with the aid of a flow visualization technique. The three-dimensional nature of this flow regime was documented through both velocity and temperature measurements using laser-Doppler and hot/cold-wire anemometers, respectively. A higher buoyancy force, through a higher plate temperature or a larger downstream distance, and/or a lower free-stream velocity, intensifies the strength of the vortices. Velocity and temperature profiles through vortex peaks and valleys are reported to quantify the behavior of these vortices. It has been found from these measurements that the two-dimensional laminar mixed convection flow changes into a transitional three-dimensional vortex flow in a relatively short distance from the leading edge of the plate. The vortex three-dimensional flow continues to intensify as the buoyancy force increases and then develops into a two-dimensional fully turbulent flow at the end of the transition regime. These findings place an upper limit on the applicability of the two-dimensional, laminar boundary layer flow analysis for mixed convection over a heated horizontal flat plate.
Heat Transfer in a Countercurrent, Gas–Solid, Packed Column
Authors: Saatdjian E. , Large J. F.
Published: October 2009

A theoretical model has been used, in conjunction with pressure drop and solid holdup data, to predict correctly the thermal efficiency of a countercurrent, gas–solid, packed heat exchanger. In the model, the ideal efficiency is multiplied by a ratio of particles in contact with the gas to the total amount of particles in the packed section. The Ergun equation is used to obtain both an effective packing porosity and the number of particles in contact with the gas. The results show that the model correctly gives the efficiency versus gas velocity curve for different packing heights and solids mass fluxes. The calculated and experimental velocities for which exchanger efficiency is a maximum are also in agreement.
Mixed Convective Heat Transfer From a Heated Horizontal Plate in a Porous Medium Near an Impermeable Surface
Authors: Oosthuizen P. H.
Published: October 2009

Two-dimensional flow over a horizontal plate in a saturated porous medium mounted near an impervious adiabatic horizontal surface and subjected to a horizontal forced flow has been numerically investigated. The plate is heated to a uniform temperature that is higher than the temperature of the flowing fluid. The conditions considered are such that the buoyancy forces have an effect on the flow and, therefore, on the heat transfer rate from the plate. The full governing equations, written in dimensionless form, have been solved for a range of values of the governing parameters using the finite element method. The heat transfer rate from the plate is influenced both by the dimensionless depth of the plate below the surface and the importance of the buoyancy forces, the latter having been characterized by a parameter which is equal to the ratio of the Darcy–Rayleigh number to Peclet number. The conditions under which these parameters have a negligible effect on the heat transfer rate are discussed.
Developing Laminar Mixed Convection With Solidification in a Vertical Channel
Authors: Bennon W. D. , Incropera F. P.
Published: October 2009

Solidification of both high and low Prandtl number fluids (n-octadecane and aluminum) is considered for downward, mixed convection in the entrance region between vertical parallel plates symmetrically cooled below the fusion temperature. A continuum model is used to formulate a set of steady, two-dimensional partial differential equations, which include the influences of both axial diffusion and thermal buoyancy. The equations are solved using a fully elliptic, control-volume-based finite-difference scheme. Results reveal that, for a given phase change system, conditions are uniquely determined by a Grashof-to-Reynolds number ratio, Gr/Re, a Peclet number Pe, and a characteristic dimensionless temperature. Limiting cases involving both large and small values of Pe have been considered, and the effect of Gr/Re on thermally induced flow reversal in the fluid core has been determined.
Experiments for the Determination of Convective Diffusion Heat/Mass Transfer to Burner Rig Test Targets Comparable in Size to Jet Stream Diameter
Authors: Santoro G. J. , Go¨kog˘lu S. A.
Published: October 2009

The application of a recently formulated vapor transport theory to predict deposition rates of corrosive salts from alkali-seeded combustion gases of a small-capacity, high-velocity, atmospheric-pressure burner rig was hampered by the relatively large dimensions of the cylindrical deposit collector compared to the diameter of the combustion gas stream. The relative dimensions led to a highly nonadiabatic combustion gas flow around the collector and necessitated two series of experiments. In the first series, mass transfer coefficients were determined by utilizing the naphthalene sublimation technique. The second series of experiments determined the dilution effect on the sodium species concentrations due to the entrainment of ambient air. This second series involved the measurement of the temperature variation along the surface of the collector under steady-state conditions. Vapor deposition rates were determined exploiting this information and the results were found to compare favorably with experimentally obtained rates.