bluuebunny/crossref_metadata_2025 huggingface dataset:
Large Heat Transport Due to Spontaneous Gas Oscillation Induced in a Tube With Steep Temperature Gradients
Authors: Yazaki T. , Tominaga A. , Narahara Y.
Published: October 2009

This paper describes experimental studies of heat transfer due to the oscillations of gas columns that are spontaneously induced in a tube with steep temperature gradients. The tube (∼3 m in length) is closed at both ends and bent into U-shaped form at the midpoint. The temperature distribution along the tube is step-functional and symmetrical with respect to the midpoint. The warm part (closed-end sides) is maintained at room temperature and the cold one is immersed in liquid helium (4.2 K). The heat transported from the warm part to the cold is estimated from the evaporation rate of liquid helium. The heat flux by the oscillations is proportional to the square of the pressure amplitude, and the effective heat conductivity can be several orders of magnitude larger than the molecular heat conductivity of gas. The experimental results are compared with the theory of the second-order heat flux proposed by Rott and are found to be in satisfactory agreement with this.
Thermal Convective Instabilities in a Porous Medium
Authors: Kaviany M.
Published: October 2009

The onset of convection due to a nonlinear and time-dependent temperature stratification in a saturated porous medium with upper and lower free surfaces is considered. The initial parabolic temperature distribution is due to uniform internal heating. The medium is then cooled by decreasing the upper surface temperature linearly with time. Linear stability theory is applied to the more formally developed governing equations. In order to obtain an asymptotic solution for transient problems involving very long time scales, the critical Rayleigh number for steady-state, nonlinear temperature distribution is also obtained. The effects of porosity, permeability, and Prandtl number on the time of the onset of convection are examined. The steady-state results show that the critical Rayleigh number depends only on the ratio of porosity to permeability and when this ratio exceeds a value of one thousand, the critical Rayleigh number is directly proportional to this ratio.
Prediction of Nucleate Pool Boiling Heat Transfer Coefficients of Refrigerant-Oil Mixtures
Authors: Jensen M. K. , Jackman D. L.
Published: October 2009

This paper describes an experimental investigation to determine the mechanism governing nucleate pool boiling heat transfer in refrigerant-oil mixtures, the role diffusion plays in this process, and the influence of the fluid mixture properties. Boiling heat transfer data were taken in mixtures of up to 10 percent oil by weight in R-113. Thermophysical properties of the mixtures (density, viscosity, surface tension, specific heat, and contact angle) were measured. The decrease in heat transfer coefficient with increasing oil concentration is attributed to diffusion in an oil-enriched region surrounding the growing vapor bubbles. A correlation based on the postulated mechanism is presented which shows fair agreement with the experimental data from this study and with data obtained from the literature.
Heat Transfer to Separated Flow Regions From a Rectangular Prism in a Cross Stream
Authors: McCormick D. C. , Lessmann R. C. , Test F. L.
Published: October 2009

A series of experiments have been performed to determine the constant surface temperature heat transfer and the corresponding surface pressure variation on a two-dimensional rectangular prism in crossflow whose aspect ratio (chord to height) was 4/1. Results are presented for a surface exposed to both separated and reattached flow and for a wake exposed surface, each for several different angles of attack. Universal Stanton number and pressure coefficient curves result when data are plotted against downstream distance scaled by the length of the near-constant pressure portion of the separated bubble for the reattaching case. This is varified by comparison to other studies involving different geometries. The Nusselt number at reattachment seems to be dependent only on reattachment Reynolds number for these cases. The variation of the local Stanton number across the wake facing surface was found to be a function of angle of attack.
Effects of Free Convection and Axial Conduction on Forced-Convection Heat Transfer Inside a Vertical Channel at Low Peclet Numbers
Authors: Chow L. C. , Husain S. R. , Campo A.
Published: October 2009

A numerical investigation was conducted to study the simultaneous effects of free convection and axial conduction on forced-convection heat transfer inside a vertical channel at low Peclet numbers. Insulated entry and exit lengths were provided in order to assess the effect of upstream and downstream energy penetration due to axial conduction. The fluid enters the channel with a parabolic velocity and uniform temperature profiles. A constant-property (except for the buoyancy term), steady-state case was assumed for the analysis. Results were categorized into two main groups, the first being the case where the channel walls were hotter than the entering fluid (heating), and the second being the reverse of the first (cooling). For each group, heat transfer between the fluid and the walls were given as functions of the Grashof, Peclet, and Reynolds numbers.
A Photographic Investigation of the Stability of a Vapor Nucleus in a Glass Cavity
Authors: Forest T. W.
Published: October 2009

A set of experiments was conducted to observe the stability of a vapor nucleus trapped inside a small glass capillary for water at a uniform superheat. The glass cavity was of a shape that allowed the incipient growth and collapse of the nucleus to be clearly distinguished. Photographs showing the nucleus instabilities are presented at one of three different system pressures used in the experiments. The observed stability of the nucleus and the measured superheats corresponding to the incipient instabilities agree with predictions based on a previous thermodynamic analysis.
Condensation Measurement of Horizontal Cocurrent Steam/Water Flow
Authors: Lim I. S. , Tankin R. S. , Yuen M. C.
Published: October 2009

Condensation of steam on a subcooled water layer was studied in a cocurrent horizontal channel at atmospheric pressure. The heat transfer coefficients were found to vary from 1.3 kW/m2°C to 20 kW/m2°C, depending on whether the liquid interface was smooth or wavy, increased with increasing steam flow rates and water flow rates. For all cases, 50 to 90 percent of the steam condensed within 1.2 m from the entrance. The average Nusselt numbers were correlated with average steam and water Reynolds numbers and average liquid Prandtl numbers, for both smooth and wavy interface flows. Finally, a correlation of the average heat transfer coefficient and condensation rate for wavy interface flow was obtained as a function of inlet conditions and distance downstream.
Two-Dimensional, Combined-Mode Heat Transfer by Conduction, Convection, and Radiation in Emitting, Absorbing, and Scattering Media-Solution by Finite Elements
Authors: Chung T. J. , Kim J. Y.
Published: October 2009

This paper is concerned with a two-dimensional analysis of combined mode heat transfer using finite elements. Conduction, convection, and radiation are coupled in the emitting, absorbing, and scattering medium. The standard Galerkin finite elements can be used if the product of Reynolds number and Prandtl number is equal to or less than 1000. It is shown that the two-dimensional heat flux integration can be efficiently performed via Gaussian quadrature applied to isoparametric finite elements where no limitations to optical thicknesses are imposed. Numerical results are demonstrated for a diverging or converging channel. It is observed that the radiation effect on the temperature profile is more significant in the diverging than in the converging channel. Effects of Reynolds number, Prandtl number, albedo, and optical thickness upon temperature distributions are also investigated.
Adaptive Collocation Method for Simultaneous Heat and Mass Diffusion With Phase Change
Authors: Chawla T. C. , Pedersen D. R. , Leaf G. , Minkowycz W. J. , Shouman A. R.
Published: October 2009

In post-accident heat removal applications, the use of a lead slab is being considered for protecting a porous bed of steel shot in an ex-vessel cavity from direct impingement of molten steel or fuel as released from the reactor vessel following a hypothetical core disassembly accident in an LMFBR. The porous bed is provided to increase the coolability of the fuel debris by the sodium coolant. The present study is carried out to determine melting rates of a lead slab of various thicknesses in contact with sodium coolant and to evaluate the extent of the penetration and the mixing rates of molten lead into liquid sodium by molecular diffusion alone. The study shows that these two calculations cannot be performed simultaneously without the use of adaptive coordinates which cause considerable stretching of the physical coordinates for mass diffusion. Because of the large difference in densities of these two liquid metals, the traditional constant density approximation for the calculation of mass diffusion cannot be used for studying their interdiffusion. The use of the orthogonal collocation method along with adaptive coordinates produces accurate results, which are ascertained by comparing with the existing analytical solutions for concentration distribution for the constant density approximation and for melting rates of infinite lead slab. The analysis further shows that the melting rate progressively increases as the thickness of lead slab decreases. The mixing of two liquid metals by molecular diffusion is extremely slow and the molten lead is likely to stay separated from the sodium coolant unless free convection exists in the sodium. Before any significant mixing takes place, the lead, upon melting, will sink to the bottom of the porous bed and not participate in removing heat from fuel debris lying on the top of the porous steel bed.
A Numerical Heat Transfer Analysis of Strip Rolling
Authors: Tseng A. A.
Published: October 2009

The lack of a practical mathematical model to simulate thermal behavior of the metal rolling process has forced mill operators and designers to rely on plant experience and testing, which is time consuming and expensive. An effective finite difference model has been developed to study the temperature profiles of the work roll and the strip. Several finite difference techniques have been successfully employed to cope with the special characteristics of the rolling process, such as very high velocity, high temperature variation in a very thin layer, curved boundary, and bimaterial interface. Typical rolling conditions were analyzed to provide temperature information on the roll and strip. Both cold and hot rollings were considered, and the effect of changing velocities was also studied. Good correspondence is found when present results are compared with either analytical solutions under simplified rolling conditions or measured data.
Film Condensation of Refrigerant-113 and Ethanediol on a Horizontal Tube—Effect of Vapor Velocity
Authors: Lee W. C. , Rahbar S. , Rose J. W.
Published: October 2009

Heat transfer measurements are reported for condensation of refrigerant-113 and ethanediol (ethylene glycol) on a single horizontal tube with vertical downflow. For refrigerant-113, vapor velocities up to around 6 m/s were obtained, while for ethanediol, velocities in excess of 100 m/s were obtained at low pressure. The results are compared with those of earlier investigators and with theory.
Laminar Combined Convection in Finite Circular Rod Bundles
Authors: Das R. , Mohanty A. K.
Published: October 2009

Laminar combined free and forced convection in flow through a finite rod array is investigated using a finite difference scheme. The geometrical dimensions simulate those of a CANDU-type pressurized water reactor. The rods are deemed to dissipate heat uniformly, whereas the shell wall is maintained adiabatic. Temperature of the inner rod surface at a non-nodal and nonorthogonal intersection is estimated using a six-point interpolation scheme. Velocity and temperature profiles together with transport rates are presented indicating variations due to buoyancy, power skew, eccentricity, and number of rods in the array.
The Optical Constants of Coal, Char, and Limestone
Authors: Brewster M. Q. , Kunitomo T.
Published: October 2009

The infrared optical constants, n and k, (n˜ = n − ik) of swelling and nonswelling coals, their respective char products, and limestone at room temperature have been obtained by a particle extinction technique using compressed KBr tablets. By assuming spherical particles and using Mie theory for the particle extinction measurements in conjunction with normal specular reflectance measurements from polished specimens, it is possible to obtain more accurate values for n and k than if the usual Fresnel reflectance technique is misapplied to samples that may appear specular but do not satisfy the stringent conditions necessary for invoking the Fresnel equations. Values of k for coal were found to be an order-of-magnitude smaller than previously reported values, with absorption due mainly to molecular vibration. The results for char evidenced that a significant increase in absorption by free electrons takes place upon devolatization and carbonization of coal. The limestone results demonstrated pronounced molecular absorption bands characteristic of CaCO3.
Discrete-Ordinates Solutions of the Radiative Transport Equation for Rectangular Enclosures
Authors: Fiveland W. A.
Published: October 2009

The Sn discrete-ordinates method is used to find numerical solutions in a two-dimensional rectangular enclosure with a gray absorbing, emitting, and isotropically scattering medium. Results are obtained for the S2, S4, and S6 approximations that correspond to 4, 12, and 24 flux approximations, respectively, and are compared with exact solutions, numerical Hottel’s zone results, P3 differential approximations, and an approximation method developed by Modest. The S2 approximation solutions were found to be applicable only for several specific cases and are not recommended for general use. The S4 and S6 solutions compare favorably with other methods and can be used to predict radiant intensity and surface heat transfer rate for various surface and optical conditions.
Fire Plume Along Vertical Surfaces: Effect of Finite-Rate Chemical Reactions
Authors: Chen C. H. , T’ien J. S.
Published: October 2009

Fire plume along a vertical wall is analyzed using a laminar boundary layer model, including finite-rate, gas-phase chemical kinetics. The chemical reactions include two semiglobal steps: In the first, fuel is oxidized to form carbon monoxide and water vapor, and in the second, carbon monoxide is oxidized to form carbon dioxide. Several important nondimensional kinetic parameters are identified and a parametric study is given. The computed results indicate that by slowing down the relative kinetic rates in the gas-phase reactions, the total surface heat transfer rate and the preheating distance are decreased. Furthermore, slowing down the kinetics also increases the amount of unreacted combustibles that escape from the flame.
Shell-and-Tube Side Heat Transfer Augmentation by the Use of Wall Radiation in a Crossflow Shell-and-Tube Heat Exchanger
Authors: Yamada Y. , Akai M. , Mori Y.
Published: October 2009

The heat transfer performance of a crossflow shell-and-tube heat exchanger for high-temperature use in which heat transfer is augmented by the use of wall radiation in both shell and tube sides, is studied. Radiation plates are inserted in the shell side, and twisted cross-tapes in the tube side. Overall heat transfer coefficients are measured to be about a maximum 80 percent larger than those without radiation, where the inlet temperatures of the hot gas range up to 800 °C, while those of the cold gas are about room temperature. Analytical results agree well with experimental results, and an approximate calculation procedure is found to be simple and accurate enough for practical use.
Rotary Heat Exchangers With Time Varying or Nonuniform Inlet Temperatures
Authors: Brandemuehl M. J. , Banks P. J.
Published: October 2009

The performance of a counterflow, rotary heat exchanger operating with either transient or nonuniform inlet temperatures is investigated. The effect of transient inlet temperatures is analyzed in terms of the response of the outlet fluid temperatures to a step change in temperature of one of the inlet fluid streams. The effect of temperature nonuniformities is analyzed in terms of the change in steady-state effectiveness due to a circumferential temperature distribution in one of the inlet fluid streams. These temporal and spatial variations are explored using three different methods of analysis. An equilibrium analysis, assuming infinite heat transfer coefficients, is developed from kinematic wave theory. It is used to qualitatively describe the heat transfer process and define the upper limit of performance. A finite difference model of the governing differential equations, using finite transfer coefficients, is employed to obtain a detailed numerical analysis of heat exchanger performance. Results for the complete range of matrix to fluid capacity rate ratio are presented for a balanced and symmetric regenerator. At moderate capacity rate ratios, the numerical analysis predicts unusual temporal periodicity in the transient response. An experimental analysis has also been conducted using a counterflow, parallel passage, rotary heat exchanger made from polyester film. The results are used to substantiate predictions of the numerical model.
Heat Transfer and Friction in Channels With Two Opposite Rib-Roughened Walls
Authors: Han J. C.
Published: October 2009

An experimental study of fully developed turbulent air flow in square ducts with two opposite rib-roughened walls was performed to determine the effects of the rib pitch-to-height and rib height-to-equivalent diameter ratios on friction factor and heat transfer coefficients with Reynolds number varied between 7000 and 90,000. Based on the four-sided, smooth-duct correlation and the four-sided, ribbed-duct similarity law, a general prediction method for average friction factor and average Stanton number in rectangular ducts with two smooth and two opposite ribbed walls was developed. There was good agreement between prediction and measurements. The results may be useful for gas turbine blade internal cooling design.
Analysis of Low-Peclet Heat Transfer During Slug Flow in Tubes With Axial Wall Conduction
Authors: Soliman H. M.
Published: October 2009

An exact solution is presented for the temperature distribution during slug flow inside an infinitely long tube with a finite heated length. The solution takes into consideration axial conduction in the fluid and tube wall, which are characterized by Peclet number and a wall conduction parameter, respectively. Results of bulk and wall temperatures, convective heat flux and Nusselt number are presented for low and high Peclet numbers using a range of values for the wall conduction parameter. It is concluded that wall conduction can have substantial effects on the heat transfer characteristics in the areas surrounding the beginning and end of direct heating. These effects can be much more pronounced than the effects of fluid conduction.
Local Heat Transfer Downstream of an Abrupt Expansion in a Circular Channel With Constant Wall Heat Flux
Authors: Baughn J. W. , Hoffman M. A. , Takahashi R. K. , Launder B. E.
Published: October 2009

Measurements have been made of the local heat transfer coefficients to an air flow downstream of an axisymmetric abrupt expansion in a circular pipe with a constant wall heat flux. The experimental technique uses an electrically heated thin gold film on a plastic substrate. The flow upstream of the expansion was unheated and fully developed. Runs were made with small diameter to large diameter ratios of 0.267 to 0.800 and over the Reynolds numbers range of 5,300 to 87,000 (based on downstream diameter). The results include measurements near the expansion corner region where no previous measurements have been reported. These provide clear evidence of a secondary recirculation. Comparisons are also made with previous experimental results in the region of reattachment.
Effect of a Protuberance on Thermal Convection in a Square Cavity
Authors: Kaviany M.
Published: October 2009

Thermal convection resulting from a temperature difference between two vertical surfaces of a square cavity is considered. The effects of a semicylindrically shaped protuberance, located at the bottom of the cavity, on total and local heat transfer rates are examined numerically. The numerical results are for a Prandtl number of 0.71 and for Rayleigh numbers up to 104. The results show that the presence of the protuberance leads to a decrease in heat transfer rates in the lower part of the cavity. This relative decrease initially becomes more pronounced as the Rayleigh number increases, but is less significant as the Rayleigh number increases past a critical value. This critical Rayleigh number depends on the radius of the protuberances and its value increases as the radius increases. These results are in general agreement with those found in other investigations dealing with the effects of partitions.
An Experimental Study of Transition and Film Boiling Heat Transfer in Liquid-Saturated Porous Bed
Authors: Fukusako S. , Komoriya T. , Seki N.
Published: October 2009

Experimental investigations of transition and film boiling in a liquid-saturated porous bed are reported. The porous bed contained in a vertical circular cylinder is made up of packed spherical beads whose diameters range from 1.0 to 16.5 mm, while the depth of the bed overlying the heating surface varies from 10 to 300 mm. Water and fluorocarbon refrigerants R-11 and R-113 are adopted as testing liquids. Special attention is focused on the effect of the diameter of spherical beads on boiling heat transfer in the transition boiling region. It is found that for the small bead diameters the steady boiling heat transfer rises monotonically with temperature from nucleate boiling through the film boiling region, without going through a local maximum.
A Mechanistic Explanation of Channels in Debris Beds
Authors: Reed A. W.
Published: October 2009

A mechanistic explanation of channeling during boiling in unconsolidated particulate debris beds is formulated by combining a free-body force diagram and the capillary pressure-saturation curve for porous media. The model is consistent with the principles of two-phase flow in porous media and provides boundary conditions for the flow equations in the unchanneled region. Experimental evidence for spherical particles presented here implies that the solid matrix in the channeled region cannot maintain a shear force and therefore behaves like a fluid without being fluidized in the classical sense.
Natural Convection Characteristics of Pool Penetration Into a Melting Miscible Substrate
Authors: Epstein M. , Grolmes M. A.
Published: October 2009

Experiments were performed to gain an understanding of the convective heat transfer process occurring in a warm liquid pool as it penetrates into an underlying meltable solid of less dense material, for the case where the molten phase of the solid and pool liquid are mutually miscible. Previous experimental work on downward melting penetration made use of warm aqueous salt solution pools overlying solid polyethylene glycol (PEG) or ice, or pools of heated organic liquids with benzene as the frozen substrate. Owing to the complexity of the melting trends observed in these studies, particularly with PEG substrates, a sufficiently definitive theory of the phenomenon has not yet emerged. As part of the present study, an attempt was made to reproduce the previous experimental results for salt-solution-pool penetration into PEG. An unexpected strong effect of initial solid PEG temperature on melting rate was uncovered for this polymer material. It was found that the unconventional melting trends reported previously at high pool-to-substrate density ratios could be eliminated if careful control of the initial PEG temperature is maintained. These new experimental data indicate that the melting of PEG by an overlying pool of heavier salt solution has much in common with classical, turbulent, thermal convection above a horizontal surface. Additional experiments were conducted which seem to support this conclusion for other pool–substrate material pairs as well.
On the Convective Heat Transfer in a Tube of Elliptic Cross Section Maintained Under Constant Wall Temperature
Authors: Ebadian M. A. , Topakoglu H. C. , Arnas O. A.
Published: October 2009

The convective heat transfer problem along the portion of a tube of elliptic cross section maintained under a constant wall temperature where hydrodynamically and thermally fully developed flow conditions prevail is solved in this paper. The successive approximation method is used for the solution utilizing elliptic coordinates. Analytical expressions for temperature distribution and Nusselt number corresponding to the first cycle of approximation are obtained in terms of the ellipticity of the cross section. In the case of a circular section, the first cycle approximation of the Nusselt number is obtained as 3.7288 compared to the exact value of 3.6568. Representative temperature distribution curves are plotted and compared to those corresponding with constant wall heat flux conditions.
Multinode Unsteady Surface Element Method With Application to Contact Conductance Problem
Authors: Litkouhi B. , Beck J. V.
Published: October 2009

The unsteady surface element method is a powerful numerical technique for solution of linear transient two- and three-dimensional heat transfer problems. Its development originated with the need of solving certain transient problems for which similar or dissimilar bodies are attached one to the other over a part of their surface boundaries. In this paper a multinode unsteady surface element (MUSE) method for two arbitrary geometries contacting over part of their surface boundaries is developed and formulated. The method starts with Duhamel’s integral (for arbitrary time and space variable boundary conditions) which is then approximated numerically in a piecewise manner over time and the boundaries of interest. To demonstrate the capability of the method, it is applied to the problem of two semi-infinite bodies initially at two different temperatures suddenly brought into perfect contact over a small circular region. The results show excellent agreement between the MUSE solution and the other existing solutions.
A Stochastic Approach for Radiative Exchange in Enclosures With Directional-Bidirectional Properties
Authors: Naraghi M. H. N. , Chung B. T. F.
Published: October 2009

The concept of multiple Markov chains is applied to the study of radiative heat transfer problems. A stochastic method for calculating radiative interchange in enclosures consisting of a number of isothermal surfaces with directional-bidirectional properties is developed. In this work, the Monte Carlo method is employed for calculating the multiple transition probabilities. Numerical examples have been presented to demonstrate the usefulness of the present approach.
Developing Flow and Flow Reversal in a Vertical Channel With Asymmetric Wall Temperatures
Authors: Aung Win , Worku G.
Published: October 2009

Numerical results are presented for the effects of buoyancy on the hydrodynamic and thermal parameters in the laminar, vertically upward flow of a gas in a parallel-plate channel. Solutions of the governing parabolic equations are obtained by the use of an implicit finite difference technique coupled with a marching procedure. It is found that buoyancy dramatically increases the hydrodynamic entry length but diminishes the thermal development distance. At a fixed wall temperature difference ratio, buoyancy enhances the heat transfer on the hot wall but has little impact on the cool wall heat transfer. Flow reversal is observed in some cases. Based on an analytical solution for fully developed flow, criteria for the occurrence of flow reversal are presented. The present numerical solutions yield results that asymptotically approach those from the analytical solution.
Transient Behavior of a Radiatively Heated Double-Diffusive System
Authors: Bergman T. L. , Incropera F. P. , Viskanta R.
Published: October 2009

A mathematical model is developed to predict the transient response of a salt-stratified, double-diffusive system which is destabilized by radiation absorption at its bottom boundary. An accepted k-ε turbulence model is used to predict the response of the salt-stratified solution to bottom heating, and a discrete ordinates solution of the radiative transfer equation is used to predict the radiation field. Verification is achieved through comparisons of predicted and measured temperature distributions, which have been previously reported. Parametric calculations are performed to investigate the influence of the radiation source temperature, bottom surface reflectivity, optical extinction coefficient, and top surface boundary condition on system response.
Numerical Analysis of Heat and Mass Transfer From Fluid Spheres in an Electric Field
Authors: Sharpe L. , Morrison F. A.
Published: October 2009

Steady-state heat or mass transfer to a drop in an electric field at low values of the Reynolds number is investigated. The energy equation is solved using finite difference techniques; upwind differencing is used in approximating the convective terms. Far from the sphere, a “transmitting” boundary condition is introduced; the dimensionless temperature is held at zero for inward radial flow and the dimensionless temperature gradient is held at zero for outward radial flow at a fixed distance from the sphere’s surface. Numerical solutions are obtained using an iterative method. Creeping flow heat transfer results are obtained for Peclet numbers up to 103.
Heat Transfer and Pressure Drop in a Helically Coiled Rectangular Duct
Authors: Kadambi V. , Levy E. K. , Neti S.
Published: October 2009

The present paper deals with experiments using air in three helically coiled rectangular ducts of mean diameters 12.7 cm, 17.8 cm, and 22.8 cm, respectively, made of rectangular wave-guide tubing of dimensions 1.27 cm × 0.64 cm. Pressure variations observed around the ducts were qualitatively in agreement with the expectations for secondary flow. The friction factors change gradually with increasing Reynolds numbers over the range 1200–10,000 without exhibiting a sudden transition from laminar flow to turbulence. At all Reynolds numbers, these are higher than those for a straight duct by 20–100 percent. The heat transfer coefficient is also higher than that for straight ducts ranging between 20–300 percent, depending on the Reynolds number. The largest increases are seen in the Reynolds number range 1200–2500.
Exact Transient Solutions of Parallel-Current Transfer Processes
Authors: Li Chung-Hsiung
Published: October 2009

Exact transient solutions of parallel-current transfer processes are obtained by the use of the Laplace transformation. Solutions are valid for a finite or an infinite transfer zone. The solutions are verified with steady-state solutions. Exact transient solutions of this study are applicable to liquid-to-liquid and liquid-to-gas heat exchangers in which the thermal capacitance of the core is negligible (zero) compared to the thermal capacitance of the stepped liquid contained in the exchanger.
Mixed and Free Convection Over a Rotating Sphere With Blowing and Suction
Authors: Lien Fue-Sang , Chen Cha’o-Kuang , Cleaver J. W.
Published: October 2009

An analysis is performed to study the flow and heat transfer characteristics for the case of laminar mixed convection and pure free convection about a rotating permeable sphere. The transformed conservation equations of the nonsimilar boundary layers are solved by an efficient finite difference method. It is found from the numerical results that both the local friction factor and the local Nusselt number increase with increasing rotation parameter and buoyancy force for aiding flow. The agreement of solutions obtained by the present method with others is found to be good.
Flow Excursion-Induced Dryout at Low Heat Flux Natural Convection Boiling
Authors: Khatib-Rahbar M. , Cazzoli E. G.
Published: October 2009

Flow excursion-induced dryout at low heat flux natural convection boiling, typical of liquid metal fast breeder reactors, is addressed. Steady-state calculations indicate that low-quality boiling is possible up to the point of the Ledinegg instability, leading to flow excursion and subsequent dryout in agreement with experimental data. A flow regime-dependent critical heat flux relationship based upon a saturated boiling criterion is also presented. Transient analyses indicate that premature flow excursion cannot be ruled out and the boiling process is transient dependent. Analysis of a loss-of-flow transient at high heat flux forced convection shows a significantly faster flow excursion leading to dryout, which is in excellent agreement with the results of the two-dimensional THORAX code.
Heat Transfer Around Sharp 180-deg Turns in Smooth Rectangular Channels
Authors: Metzger D. E. , Sahm M. K.
Published: October 2009

Measured Nusselt numbers are presented for forced convection within and around sharp 180-deg turns in smooth channels of rectangular cross section. Separately determined top wall, bottom wall, and side wall values are presented individually along with azimuthal averages. The geometry of the channels and connecting turn is characterized by the parameters W*, the ratio of upstream and downstream channel widths; D*, the nondimensional channel depth; and H*, the nondimensional clearance at the tip of the turn. Results from nine combinations of these parameters are presented at several values of channel Reynolds number to illustrate the effect of turn geometry on the heat transfer distributions.
Hybrid Analytical/Numerical Computation of Heat Transfer in a Gas-Driven Fracture
Authors: Griffiths S. K. , Nilson R. H. , Morrison F. A.
Published: October 2009

In gas-driven hydraulic fractures, as occur in rock blasting and underground nuclear testing, the high-temperature gases (1000 to 30,000 K) are radically cooled by heat transfer to the host material. This significantly reduces both the maximum extent and rate of fracture growth. The coupled processes of fluid flow, heat transfer, and rock deformation governing fracture growth are calculated here by a hybrid analytical/numerical procedure. The gas motion along a fracture of increasing length and aperture is described by a finite-difference form of the one-dimensional transport equations; fluid friction, advective heat transfer, and heat loss to the walls of the fracture are considered. Lateral heat losses are evaluated in a quasi-analytical fashion, based on an integral method that accounts for the convective film resistance between the fluid and fracture wall, as well as the conductive resistance within the surrounding medium. The calculations are performed on a difference grid that expands to maintain a fixed number of points uniformly distributed along the fracture. The present numerical results agree, within appropriate limits, with known similarity solutions. Beyond this, new nonsimilar solutions for early-time fracture growth are presented.
Combined Mode Heat Transfer Analysis Utilizing Radiation Scaling
Authors: Lee H. , Buckius R. O.
Published: October 2009

Scaling laws have been formulated to predict the radiant heat flux in anisotropically scattering, one-dimensional planar media [1, 2]. The radiation portion of the problem is reduced to an equivalent nonscattering problem by the scaling. The same scaling laws are applied to problems when radiation is combined with other modes of heat transfer, requiring the solution of the energy equation for a temperature profile. The average incident intensity is accurately scaled by a multilayer approach. Results presented for radiation/conduction and the thermally developing Poiseuille flow problems show very good agreement between exact and scaled solutions for heat fluxes and temperature distributions.
Freezing of Liquid-Saturated Porous Media
Authors: Weaver J. A. , Viskanta R.
Published: October 2009

The paper reports on an experimental and analytical study of freezing of a liquid-saturated porous medium. Experiments have been performed in a cylindrical capsule cooled from the outside and oriented vertically and horizontally to obtain quantitative temperature distribution and fusion front motion and shape data. Different-size glass and aluminum spherical beads were used for the porous medium, and distilled water was used as the phase-change material. A mathematical model, based on a one-dimensional analysis which considered heat conduction as the only mode of heat transfer in both the solid and liquid regions, has been developed and sensitivity studies have been carried out. Comparison of experimental data with predictions of the solid–liquid interface position and temperature distribution shows good agreement and thus confirms the mathematical model for a system of glass beads and water. However, for a system of aluminum beads and water the thermophysical property model is inadequate, and agreement between predictions and data is relatively poor.
Characteristics of a Simple Energy Absorption Transducer
Authors: Beck B. T. , Wedekind G. L.
Published: October 2009

This paper presents the results of an investigation into a simple technique developed primarily for evaluating surface coating effectiveness for the absorption of a nonuniform laser radiation heat flux. Analysis suggests that if the transducer sensor is designed appropriately, and the experimental data analyzed in a particular manner, the temperature–time history of the transducer need be measured at only a single arbitrary location. These conclusions are also supported by experimental measurements of laser radiation absorption at a wavelength of 10.6 μm for polished copper, polished steel, and for a manganese–phosphate coating on a steel substrate. The absorptivities measured for the polished copper and steel agree well with other experimental data in the literature. Limitations of the measurement technique, resulting from the temperature dependence of the transducer material properties, radiation absorptivity, and combined convective and radiative heat flux, are also investigated theoretically and experimentally.
An Inverse Finite Element Method for the Analysis of Stationary Arc Welding Processes
Authors: Hsu Y. F. , Rubinsky B. , Mahin K.
Published: October 2009

An inverse finite element computer code was developed to facilitate the experimental analysis of two-dimensional stationary arc welding processes. The method uses transient temperature data from thermocouples imbedded in the solid region of the work piece to determine through a Newton–Raphson interpolation procedure the transient position of the solid–liquid interface and the transient temperature distribution in the solid region of the work piece. The accuracy of the method was demonstrated through comparison with results obtained with a direct finite element code and through comparison with experiments.
Natural Convection in an Inclined Rectangular Channel Heated From the Bottom Surface
Authors: Inaba H.
Published: October 2009

The phenomenon of natural convection in an inclined rectangular channel heated from the bottom surface has been experimentally investigated. The experiments covered a range of modified Rayleigh numbers Rad*, by using the shortest distance d between two opposing side walls as a representative length, between 1.8 × 102 and 6 × 105, and a range of inclination angles of the side wall with respect to the horizontal θ between 30 deg and 90 deg. Air was used as the working fluid. An experimental correlation equation is given for the Nusselt number Nud as a function of sin θ and Rad* for W/l (width to length of the channel) = 0.1–0.5.
Three-Dimensional Analysis of Natural Convection in a Toroidal Loop: Effect of Tilt Angle
Authors: Lavine A. S. , Greif R. , Humphrey J. A. C.
Published: October 2009

A three-dimensional numerical analysis of natural convection in a toroidal thermosyphon has been performed. The results confirm the experimental observations of three dimensionality, streamwise flow reversal, and secondary motion. The flow reversals reduce the wall friction and buoyancy forces, and consequently have a strong effect on the average axial velocity.
Numerical Prediction of Turbulent Flow and Heat Transfer Within Ducts of Cross-Shaped Cross Section
Authors: Nakayama A. , Koyama H.
Published: October 2009

Calculations were carried out for fully developed turbulent flows within ducts of cross-shaped cross section using the numerical method based on the pressure correction method developed by Patankar and Spalding. The Reynolds stress driven secondary flows were simulated successfully by Launder and Ying’s algebraic stress model coupled to the k–ε turbulence model. A parametric study was made on the friction and heat transfer characteristics in terms of the parameter α associated with the decrease in the cross-sectional area, namely, α = 0 for a square duct, and α → 1 for infinite parallel plates. Through performance evaluations, it has been found that both the Reynolds analogy factor and the heat transfer coefficient under equal pumping power decrease slightly, while the heat transfer coefficient obtained with equal mass flow rate increases appreciably with α, suggesting effective turbulent heat transfer within ducts of cross-shaped cross section.
Finite Element Solution of Laminar Combined Convection From a Sphere
Authors: Wong King-Leung , Lee Shun-Ch’ing , Chen Cha’o-Kuang
Published: October 2009

The purpose of this investigation is to study the flow and heat transfer characteristics of laminar combined convection from an isothermal sphere. The full Navier–Stokes and energy equations are solved by a finite element method. The variations of surface shear stress, pressure, and Nusselt number are obtained over the entire surface of the sphere including the zone beyond the separation point. The predicted values of average Nusselt number, location of separation point, total drag shear force, and some plots of the flow and temperature fields are also presented. The results are compared with those of previous numerical and experimental investigations and the agreement is satisfactory.
The Influence of Coupled Molecular Diffusion on Double-Diffusive Convection in a Porous Medium
Authors: Rudraiah N. , Malashetty M. S.
Published: October 2009

The effect of coupled molecular diffusion on double-diffusive convection in a horizontal porous medium is studied using linear and nonlinear stability analyses. In the case of linear theory, normal mode analysis is employed incorporating two cross diffusion terms. It is found that salt fingers can form by taking cross-diffusion terms of appropriate sign and magnitude even when both concentrations are stably stratified. The conditions for the diffusive instability are compared with those for the formation of fingers. It is shown that these two types of instability will never occur together. The finite amplitude analysis is used to derive the condition for the maintenance of fingers. The stability boundaries are drawn for three different combinations of stratification and the effect of permeability is depicted.
Local Heat Transfer Coefficients for Horizontal Tube Arrays in High-Temperature Large-Particle Fluidized Beds: An Experimental Study
Authors: Goshayeshi A. , Welty J. R. , Adams R. L. , Alavizadeh N.
Published: October 2009

An experimental study is described in which time-averaged local heat transfer coefficients were obtained for arrays of horizontal tubes immersed in a hot fluidized bed. Bed temperatures up to 1005 K were achieved. Bed particle sizes of 2.14 mm and 3.23 mm nominal diameter were employed. An array of nine tubes arranged in three horizontal rows was used. The 50.8 mm (2 in.) diameter tubes were arranged in an equilateral triangular configuration with 15.24 cm (6 in.) spacing between centers. The center tube in each of the three rows in the array was instrumented providing data for local heat flux and surface temperature at intervals of 30 deg from the bottom to the top—a total of seven sets of values for each of the center tubes. The three sets of data are representative of the heat transfer behavior of tubes at the bottom, top, and in the interior of a typical array. Data were also obtained for a single horizontal tube to compare with the results of tube bundle performance. Superficial velocities of high-temperature air ranged from the packed-bed condition through approximately twice the minimum fluidization level. Comparisons with results for a single tube in a bubbling bed indicate only slight effects on local heat transfer resulting from the presence of adjacent tubes. Tubes in the bottom, top, and interior rows also exhibited different heat transfer performance.
Subcooled-Boiling and Convective Heat Transfer to Heptane Flowing Inside an Annulus and Past a Coiled Wire: Part I—Experimental Results
Authors: Mu¨ller-Steinhagen H. , Watkinson A. P. , Epstein N.
Published: October 2009

Heat transfer coefficients for subcooled heptane were measured in two flow geometries for different heat fluxes, flow rates, bulk temperatures, and system pressures. Regimes of convective heat transfer and of nucleate boiling were delineated for a concentric annular test section containing an internally heated rod, and for a resistance-heated coiled wire mounted in crossflow. Second-order effects such as flow direction, hysteresis, and method of pressurization were also investigated.
On the Stability and Flow Reversal of Pressure-Driven Flow in an Asymmetrically Heated U-Shaped Tube
Authors: Zhou Kun-Ying , Bau H. H.
Published: October 2009

Experimental and theoretical results are reported about the stability of pressure-driven flow in a vertical U-shaped loop to whose descending leg heat is supplied. The stability of the flow depends on a nondimensional number B, which represents the ratio between the buoyancy and the pressure heads. As long as BBcr, the flow ceases to be stable, the flow rate oscillates with increasing amplitude and then the flow reverses direction. The end result consists of stable ascending flow in the heated section. That is, the flow is driven by the buoyancy force and opposed by the pressure head. Two types of loops are considered: one containing single-phase fluid; and the other, saturated porous media (packed bed). A marginal stability curve is constructed using linear stability analysis. Finite difference numerical simulation suggests that the same curve is also valid for finite amplitude disturbances. The theoretical results are compared with experimental data.
Heat Transfer and Pressure Drop Performance of Finned Tube Bundles
Authors: Eckels P. W. , Rabas T. J.
Published: October 2009

The heat transfer and pressure drop performance of two types of finned tubes used in the air-conditioning industry are reported for 14 different bundle configurations. Twelve of these configurations contained a new type of finned tube called K-Y and two contained a more conventional pin fin. A unique characteristic of all these configurations is zero or negative fin-tip clearances. A comparison of the performance of these air-conditioning type finned tubes with negative fin-tip clearance is then made with the performance of typical air-cooled heat exchanger tubes used in the process and power industries. Both the heat transferred and the pressure drop are substantially higher with the air-conditioning configurations; the heat transfer coefficient is superior even to plain tubes. The very high heat transfer performance is more the result of the negative fin-tip clearance than the fin shape or type.