bluuebunny/crossref_metadata_2025 huggingface dataset:
Laminar Incompressible Viscous Flow in Curved Ducts of Regular
Cross-Sections
Authors: Ghia K. N. , Sokhey J. S.
Published: November 2010

The laminar three-dimensional flow in curved ducts has been analyzed for an incompressible viscous fluid. The mathematical model is formulated using three-dimensional parabolized Navier-Stokes equations. The equations are generalized using two indices which permit the choice of Cartesian or cylindrical coordinate systems and straight or curved ducts. The solutions are obtained numerically using an ADI method for a number of duct geometries and flow parameters. The study presents detailed results for developing laminar flow in rectangular curved ducts; also, the effect of longitudinal curvature on secondary flow is fully analyzed. An investigation is made of the occurrence of Dean’s instability and, for curved square ducts, it is found to first appear at Dean number ≃ 143.
Entry Flow in Straight and Curved Channels With Slender Channel
Approximations
Authors: Blottner F. G.
Published: November 2010

The slender channel equations for laminar flow are solved downstream of the entrance of curved channels of variable height. The singularities at the entrance are removed with coordinate transformations which stretch the boundary layer and shrink the core flow. Initial conditions at the entrance are obtained from the governing equations with only the streamwise velocity specified. A modified box scheme is used to develop a finite-difference method which allows the derivatives of the dependent variables across the channel to be discontinuous at the interface between the boundary layer and core flow. Numerical results are presented for several channel geometries and entry conditions.
An Experimental Investigation of Incompressible Channel Flow Near
Transition
Authors: Feliss N. A. , Potter M. C. , Smith M. C.
Published: November 2010

This paper complements an earlier paper by Karnitz, Potter, and Smith [1] (1974) in which the mechanism of the transition of a plane Poiseuille flow between parallel plates was examined. In the present investigation an experimental critical Reynolds number of 7500 (based on average velocity and channel height) was achieved at which the flow became unstable and transition to turbulence occurred. The linear theoretical Reynolds number of 7700 for instability appears to be a simple extrapolation of the present data as the disturbance intensity is allowed to shrink to zero. Bursting (an alternating turbulent to laminar flow) was observed at transition. The transient changes in the velocity profile when the flow is intermittent between a turbulent burst and a laminar flow were observed. The major portion of the burst profile is characteristic of the one-seventh power law profile common to fully turbulent flow. Disturbances were observed to amplify to turbulent bursts in the wall boundary layers in the entrance region of the channel in high Reynolds number flows (the Reynolds number must exceed the critical Reynolds number by a sufficient amount). Thus, the wall boundary layer becomes unstable, resulting in a transition to turbulence before the flow becomes fully developed at sufficiently high Reynolds numbers.
Instability of Elastically Suspended Tainter-Gate System Caused by
Surface Waves on the Reservoir of a Dam
Authors: Ishii Noriaki , Imaichi Kensaku , Hirose Akio
Published: November 2010

In this study, it is theoretically shown that an elastically suspended Tainter-gate system with damping effects possesses the property of a self-excited oscillation, provided that the center of the curved weir plate is not in agreement with the location of the trunnion pin. Moreover, the theoretically obtained characteristics for the self-excited oscillation are confirmed with experiments, and it is shown that the theoretical results are in good agreement with experiments. It is concluded that when designing a dam system with Tainter-gates or other similar devices, more interest and attention to the dynamical behavior of Tainter-gates should be taken in order to prevent disasters such as that which occurred in Japan.
A Three Dimensional Density Field Measurement of Transonic Flow From
a Square Nozzle Using Holographic Interferometry
Authors: Clark L. T. , Koepp D. C. , Thykkuttathil J. J.
Published: November 2010

The three dimensional static density field was measured for transonic flow from a square nozzle using holographic interferometry. These measurements are presented in order to show the efficiency of this method for obtaining accurate experimental data of transonic flows. The accuracy of the measurement was estimated by operating the nozzle at a pressure ratio of 1.89 where the flow should expand to the ambient pressure with no afterexpansion effects. The standard deviation in the static density was approximately 1 percent over the isentropic (potential core) part of the flow. Data are also presented for a pressure ratio of 2.14 where afterexpansion effects are important. The method described represents a significant technical improvement in practical interferometry.
Radiation Heat Transfer for Annular Fins of Trapezoidal Profile
Authors: Keller H. H. , Holdredge E. S.
Published: November 2010

A one-dimensional numerical solution is obtained for the steady-state thermal behavior of annular fins of trapezoidal profile which transfer heat by conduction and radiation. The results obtained are presented as charts relating fin efficiency to the dimensionless group (rT − rB)εσTB3/k cos α, for various values of the dimensionless groups rB/(rT − rB), ZT/(rT − rB), and arctan [(ZB − ZT)/(rT − rB)]. As presented the problem is the general formulation for the problem of radiating fins with flat surfaces.
Natural Convection in Enclosed Porous Media With Rectangular Boundaries
Authors: Chan B. K. C. , Ivey C. M. , Barry J. M.
Published: November 2010

Numerical methods are used to solve the field equations for heat transfer in a porous medium filled with gas and bounded by plane rectangular surfaces at different temperatures. The results are presented in terms of theoretical streamlines and isotherms. From these the relative increases in heat transfer rate, corresponding to natural convection, are obtained as functions of three-dimensionless parameters: the Darcy number Da, the Rayleigh number Ra, and a geometric aspect ratio L/D. A possible correlation using the lumped parameter Da Ra is proposed for Da Ra greater than about 40.
Effect of Uniform Suction on Laminar Film Condensation on a Porous Vertical Wall
Authors: Yang Ji Wu
Published: November 2010

The problem of film condensation on a porous wall has been solved by a boundary layer treatment. A dimensionless suction velocity parameter β, which is proportional to the uniform suction velocity vw and 1/4th the power of longitudinal coordinate (x1/4), is defined to characterize the process. The results are restricted to small values of β, as the solutions are given by power series expansion in β. The effects of uniform suction on heat transfer, condensation rate, film thickness, and velocity and temperature profiles are demonstrated through various examples. In general, uniform suction causes a substantial increase of heat transfer and condensation rate, especially at low subcooling and at high Prandtl numbers. The problem involves three governing parameters: subcooling, Prandtl number, and suction velocity. Comparison with the previous work of Jain and Bankoff is discussed.
The Transition From Turbulent to Laminar Gas Flow in a Heated Pipe
Authors: Bankston C. A.
Published: November 2010

Experimental results are reported on the heat transfer and fluid friction of heated hydrogen and helium gas flows undergoing transition from turbulent to laminar flow in a circular tube. The entering Reynolds numbers range from 2350 to 12,500 and the nondimensional heat-flux parameter ranges from 0.0021 to 0.0061. Local heat-transfer coefficients and friction factors are obtained, and the flow transition, which is evident in these results, is verified at small heat fluxes by measuring directly the turbulence intensity at the center line with a hot-wire anemometer. At large heat fluxes, laminarization is found to occur at local bulk Reynolds numbers well in excess of the minimum number for fully turbulent adiabatic flow, and the resulting heat-transfer coefficients are much lower than those associated with fully turbulent flow at the same Reynolds number. The relation between laminarization in heated tubes and in severely accelerated external boundary layers is investigated and some similarities are noted. The acceleration and pressure-gradient parameters used to predict boundary-layer laminarization are modified for tube flow and used to correlate the initiation and completion of laminarization in the heated tube.
Heat Conduction With Melting or Freezing in a Corner
Authors: Rathjen Kenneth A. , Jiji Latif M.
Published: November 2010

This paper presents an analytical solution to the two-dimensional free boundary problem of solidification of a liquid, initially at a uniform temperature and filling the quarter-space x, y > 0, subject to a constant wall temperature. The problem is the two-dimensional analog of Neumann’s freezing problem. The solution is characterized by similarity in the variables x/t1/2, y/t1/2 and is obtained by treating the heat of solidification as a moving heat source. A nonlinear, singular, integro-differential equation for the solid-liquid interface is thereby derived and used to establish superhyperbolas to approximate the interface position. Results are presented for a range of the two dimensionless parameters of the problem. The accuracy of the superhyperbolic representation of the interface position is determined by comparison with a finite-difference solution. Equations are given for the calculation of the temperature fields in the solid and liquid regions that are valid for all time (i.e., they are not necessarily short- or long-time solutions).
An Analysis of the Developing Turbulent Hydrodynamic and Thermal Boundary Layers in an Internally Heated Annulus
Authors: Wilson N. W. , Medwell J. O.
Published: November 2010

The problems of the simultaneous growth of the hydrodynamic and thermal boundary layers in the entrance region of a concentric annulus with a uniformly heated core are investigated using the momentum and energy integral equations, along with a modified Reichardt momentum eddy diffusivity variation. A radius ratio range of 0.2 to 0.8 was investigated over a Reynolds number range from 104 to 3 × 105 for a Prandtl number of 0.7. The analysis predicts velocity and temperature profiles and local variations of normalized pressure gradients and Nusselt numbers which are in satisfactory agreement with experimental data. The analysis also shows that the flow is hydrodynamically fully developed within 10 equivalent diameters of the annulus inlet, while a further 30 equivalent diameters are required for the thermal boundary layers to reach the outer insulated wall of the annulus.
A Script-F Matrix Formulation for Enclosures With Arbitrary Surface Emission and Reflection Characteristics
Authors: Bobco R. P.
Published: November 2010

A design-oriented matrix formulation is derived for computing script-F radiative interchange factors in an enclosure of arbitrary geometrical and emissive-reflective complexity. Algorithms are presented for enclosures containing surfaces which emit either diffusely or directionally and reflect diffusely, specularly, or bidirectionally. Inputs to the transfer matrix are bidirectional and diffuse reflectances, conventional shape factors, and exchange factors which account for specular reflections. Rules are given to identify the various elements of the transfer matrix so that it may be constructed mechanically without writing complete equations for emergent directional and hemispherical fluxes. The formulation is illustrated with a closed-form solution and numerical results for a three-surface enclosure consisting of a bidirectionally reflecting area, a perfectly specular reflector, and a perfectly diffuse reflector.
An Evaluation of the Use of the Finite-Element Method in the Computation of Temperature
Authors: Emery A. F. , Carson W. W.
Published: November 2010

A study is made of the accuracy and efficiency of the finite-element methods in comparison to the standard finite-difference algorithms used for the computation of temperature. Numerical tests of a linear, a quadratic, and two cubic elements indicate that the quadratic method is the most accurate and desirable of these finite-element models. It is demonstrated that for steady temperature distributions, with or without sources, the finite-element models are equivalent to the finite-difference method in execution time, inferior in core storage requirements, and may be superior in accuracy. The tests also indicate that the normal finite-difference method for variable-property steady-state problems and for constant-property transient problems may be as much as an order of magnitude faster in execution and may require an order of magnitude or more less machine core storage than the finite-element methods. The study suggests that the primary advantages of the finite-element methods are associated with the ease of inputting the required data and the capability of altering the basic accuracy of the method, and its major disadvantages are large core memory requirements and lengthy execution times, particularly for variable-property problems, and some possible inaccuracies associated with the source and transient coefficients.
The Two-Phase Critical Flow of One-Component Mixtures in Nozzles, Orifices, and Short Tubes
Authors: Henry Robert E. , Fauske Hans K.
Published: November 2010

The critical flow of one-component, two-phase mixtures through convergent nozzles is investigated and discussed including considerations of the interphase heat, mass, and momentum transfer rates. Based on the experimental results of previous investigators, credible assumptions are made to approximate these interphase processes which lead to a transcendental expression for the critical pressure ratio as a function of the stagnation pressure and quality. A solution to this expression also yields a prediction for the critical flow rate. Based on the experimental results of single-phase compressible flow through orifices and short tubes, the two-phase model is extended to include such geometries. The models are compared with steam-water, cryogenic, and alkali-metal experimental data.
Free Convection From a Vertical Plate With Discontinuous Wall Temperature
Authors: Kelleher Matthew
Published: November 2010

Free convection from a vertical plate with a step discontinuity in wall temperature is analyzed by using asymptotic series. Expansions for the velocity and temperature profiles are obtained in the region immediately above the discontinuity. By series truncation, the wall heat flux is obtained in terms of a simple polynomial. Calculations are made for Pr = 0.72 and 10.0 and for various wall-temperature ratios. Comparison of the results with experimental data and previous numerical solutions is good.
Internal Laminar Heat Transfer With Gas-Property Variation
Authors: Swearingen T. B. , McEligot D. M.
Published: November 2010

The results of a numerical investigation of internal laminar heat transfer to a gas with temperature-dependent properties are reported. In this investigation the authors obtained numerical solutions to the coupled partial differential equations of continuity, energy, momentum, and integral continuity describing the two-dimensional flow of perfect gas between heated parallel plates. A sequence of numerical solutions was obtained for the case of constant wall heat flux with a fully developed velocity profile at the start of the heated section and pure forced convection. The results may be summarized by Nu=Nuconst.prop.+0.024(Q+)0.3(Gzm)0.75f·Rem=24(Twall/Tbulk) where the subscript “m” refers to properties evaluated at the local mixed-mean (or bulk) temperature.
The Turbulent Boundary Layer on a Porous Plate: Experimental Heat Transfer with Uniform Blowing and Suction, with Moderately Strong Acceleration
Authors: Thielbahr W. H. , Kays W. M. , Moffat R. J.
Published: November 2010

Experimental data are presented for heat transfer to the turbulent boundary layer subjected to transpiration and acceleration at constant values of the acceleration parameter K = (ν/U∞2)(dU∞/dx) of approximately 1.45 × 10−6. This is a moderately strong acceleration, but not so strong as to result in laminarization of the boundary layer. The results for transpiration fractions F of −0.002, 0.0, and +0.0058 are presented in detail in tabular form, and in graphs of Stanton number versus enthalpy thickness Reynolds number. In addition, temperature profiles at several stations are presented. Stanton number results for F = −0.004, +0.002, and +0.004 are also presented, but in graphical form only. The data were obtained using air as both the free-stream and the transpired fluid, at relatively low velocities, and with temperature differences sufficiently low (approximately 40 deg F) that the influence of temperature-dependent fluid properties is minimal. All data were obtained with the surface maintained at a temperature invariant in the direction of flow.
Free-Stream Turbulence Effects on Local Heat Transfer from a Sphere
Authors: Newman L. B. , Sparrow E. M. , Eckert E. R. G.
Published: November 2010

Experiments involving both heat-transfer and turbulence-field measurements were performed to determine the influence of free-stream turbulence on the local heat transfer from a sphere situated in a forced-convection airflow. The research was facilitated by a miniature heat-flux sensor which could be positioned at any circumferential location on the equator of the sphere. Turbulence grids were employed to generate free-stream turbulence with intensities of up to 9.4 percent. The Reynolds-number range of the experiments was from 20,000 to 62,000. The results indicate that the local heat flux in the forward region of the sphere is uninfluenced by free-stream turbulence levels of up to about 5 percent. For higher turbulence levels, the heat-flux increases with the turbulence intensity, the greatest heat-flux augmentation found here being about 15 percent. Furthermore, at the higher turbulence intensities, there appears to be a departure from the half-power Reynolds-number dependence of the stagnation-point Nusselt number. Turbulent separation occurred at Reynolds numbers of 42,000 and 62,000 for a turbulence level of 9.4 percent, these values being well below the transition Reynolds number of 2 × 105 for a sphere situated in a low-turbulence flow.
Thermal Effects of Power Plants on Lakes
Authors: Moore F. K. , Jaluria Y.
Published: November 2010

The natural thermal cycle of a stratified water body used for power-plant cooling will be disturbed both by heat addition and the mixing effect of withdrawal and return. A perturbation analysis for these effects is made with a model based on the assumption that a Richardson number is constant at the base of any stratified layer. On a further assumption about the profiles of wind-driven return currents, constant heat flux from that layer is inferred. This heat flux, and the diffusion coefficient at the thermocline, are the critical parameters of the simple one-dimensional line-segment model, and are chosen to give good imitation of the known natural cycle of Cayuga Lake. The model is then perturbed in terms of both heat flux and diffusion to give power-plant impact for that lake. Both transient and final cycle changes of summer and winter temperatures and stratification and overturn are calculated. It is shown that the heat and diffusion effects are comparable, and that the latter may be dominant if the discharge is diluted to meet a thermal standard. Certain implications as to strategy of water use are developed.
Experimental Investigation of Heat Transfer from Partially Ionized Argon with an Applied Transverse Magnetic Field
Authors: Roschke E. J.
Published: November 2010

Wall heat transfer measurements were obtained for laminar flow of partially ionized argon flowing within the conducting walls of a square channel, with and without an applied transverse magnetic field. Tests were conducted for subsonic flows and for flows which were supersonic before a magnetic field was applied. Increases in Stanton number by a factor of as much as six were observed at field strengths approaching 10 kG as compared to values at zero magnetic field. These large increases in heat transfer are believed to have been due to (1) a small amount of joule heating augmented or accompanied by (2) magnetically induced ionization. Heat transfer and flow data were used to estimate effective values of the joule heating parameter, Hall coefficient, and current density. The experimental data have been compared to theoretical predictions for several limiting cases.
Impingement Heat-Transfer Rates from Torch Flames
Authors: Schulte E. H.
Published: November 2010

The heat-transfer profiles of small natural gas–oxygen and acetylene–air flames to flat cooled surfaces were experimentally determined. Results show that the heat-transfer profiles can be relatively flat over a given area and that the best operating condition must be determined experimentally.
The Vaporization of Superheated Sodium in a Vertical Channel
Authors: Singer Ralph M. , Holtz Robert E.
Published: November 2010

Measurements of the vapor growth patterns and rates following the nucleation of superheated sodium in a vertical rectangular channel are presented and discussed. The vapor was found to grow as a single bubble for incipient bulk-liquid superheats greater than about 10 deg C, and this single bubble tended to completely fill the channel cross section (except for a thin liquid film on the walls) and to grow as a vapor slug for incipient bulk-liquid superheats greater than about 50 deg C. The temperature gradients in the liquid both normal and parallel to the channel axis prior to nucleation were found to have an important effect upon the dynamics of the vapor slug. Experimental data on the vapor growth and collapse rates and the associated pressure transients are presented for boiling pressures up to 1 atm and incipient superheats up to about 180 deg C.
The Influence of Thermocapillary Flow on Heat Transfer in Film Condensation
Authors: Cary J. D. , Mikic B. B.
Published: November 2010

The influence of fluid flow—induced by surface-tension forces—on heat transfer through a condensate film broken by non-wetting strips was considered. The film was modeled as a two-dimensional layer on an isothermal, vertical flat surface; the layer has a flat midsection with circular arcs at the edges. The solution was obtained by a finite-difference technique for several values of the Marangoni number (Nm) which provides a relative measure of the surface-tension forces and of the Biot number (Bi) which provides a relative measure of the heat transfer at the liquid–vapor interface. The range of parameters covered by this work transcends the limits of most practical interest for water. The results show that internal thermocapillary circulation causes modest increases in heat transfer. It is concluded that thermocapillary flow might be an important factor in determining the geometry of channeled condensate films.
Heat Transfer in Fire
Authors: Emmons H. W.
Published: November 2010

The essential role played by heat and mass transfer processes in fire is discussed, and the need for the development of an understanding of fire through the application of analysis and modeling techniques so successful in heat transfer is indicated. Practical design for fire protection today stands where heat transfer design stood 50 years ago. Many of the same techniques that changed heat transfer design from an empirical to a rational process can similarly transform fire safety design and fire control operations.
Leidenfrost Temperature—Its Correlation for Liquid Metals, Cryogens, Hydrocarbons, and Water
Authors: Baumeister K. J. , Simon F. F.
Published: November 2010

A prediction technique for the Leidenfrost and minimum temperatures is presented which considers the effects of the critical temperature of the liquid, thermal properties of the solid, surface energy of the liquid, and surface energy of the solid. The prediction technique is in good agreement with data for liquid metals, cryogens, hydrocarbons, and water.
A Mathematical Model for Transient Subchannel Analysis of Rod-Bundle Nuclear Fuel Elements
Authors: Rowe D. S.
Published: November 2010

This paper presents a mathematical method for analyzing transient flow and enthalpy transport in rod-bundle nuclear fuel elements during both boiling and nonboiling conditions. A mathematical model is formulated by dividing the bundle flow area into flow subchannels that are assumed to contain one-dimensional flow and are coupled to each other by turbulent and diversion crossflow mixing. The mathematical model neglects sonic velocity propagation and neglects temporal and spatial acceleration in the transverse momentum equation. A semiexplicit finite-difference scheme is used to perform a boundary-value solution where the boundary conditions are the inlet enthalpy, inlet flow rate, and exit pressure. Calculations are presented to show the effect of rapid changes in heat flux, inlet enthalpy, and inlet flow rate on the subchannel flow and enthalpy distribution in rod bundles.
Heat or Mass Transfer in Laminar Flow in Conduits With Constriction
Authors: Chow J. C. F. , Soda K.
Published: November 2010

Analytical solutions are obtained on the effects of boundary constriction on heat or mass transfer at the entrance region in a well-developed steady laminar flow in symmetric and axisymmetric conduits subjected to uniform wall temperature or mass concentration. The solutions are limited to the fluids of constant properties with negligible viscous dissipation, moderate Reynolds number, and large Peclet or Schmidt number, and the spread of the wall constriction is large compared to the mean width or radius of the conduits. It is found that both the bulk temperature and heat transfer rate at the wall are oscillatory in nature, and their amplitudes decrease drastically as the fluid moves away from the entrance. Near thermal entry length, the bulk fluid temperature approaches its mean value with vanishing oscillation, but the heat transfer rate at the wall stays oscillatory in nature due to the irregularity of the wall. The thermal entry length changes very little from the corresponding straight-wall conduits. These results are also true for the mass transfer.
The Effect of Thermal Contact Resistance on Heat Transfer Between Periodically Contacting Surfaces
Authors: Howard J. R. , Sutton A. E.
Published: November 2010

An analog-computer study is made of one-dimensional heat conduction through two bars whose axes are in line and whose adjacent ends make and break contact periodically. The work extends a previous study to take account of imperfect thermal contact at the contact interface. The effect of frequency and duration of contact are also discussed.
Velocity, Temperature, and Turbulence Measurements in Air for Pipe Flow With Combined Free and Forced Convection
Authors: Carr A. D. , Connor M. A. , Buhr H. O.
Published: November 2010

Experimental results are presented for velocity and temperature profiles and for the turbulence quantities vz′ t′ and vzt, for up-flow of air in a vertical pipe with constant heat flux at Reynolds numbers of 5000 to 14,000. The measurements show that, with increasing heat flux, superimposed free convection effects cause marked distortion of the flow structure at low Reynolds numbers, with the velocity maximum moving from the tube center to a position near the wall. The axial turbulence intensity, vz′, is depressed by increasing heat flux while the temperature intensity, t′, first decreases and then rises, with a shift in the position of the peak intensity away from the wall. On the basis of an analysis developed for heated turbulent flow, the turbulent shear stress and heat flux distributions are calculated from the experimental results. As the flow field becomes appreciably distorted on heating, it is found that the turbulent shear stress becomes very small, while the heat flux distribution suggests an increase in the width of the viscous sublayer.
Diffusion Through Laminated Composite Cylinders Subjected to a Circumferentially Varying External Heat Flux
Authors: Lockwood J. D. , Mulholland G. P.
Published: November 2010

The diffusion equation for the temperature distribution in each of k sections of a hollow laminated composite cylinder with a circumferentially varying external heat flux is solved. The composite consists of k discrete cylinders each of a different material with perfect thermal contact at each of the k-1 interfaces. The cylinders have an arbitrary initial temperature distribution and the temperature on the inside surface of the composite is an arbitrary function of time. The solution is obtained by using a Fourier integral transformation and a dependent variable substitution. This produces a new partial differential equation with homogeneous boundary conditions. This new equation is then solved by using a type of orthogonality relationship developed by Vodicka.
Controlled Transpiration Cooling of the Anode in a High Intensity Arc
Authors: Boffa C. V. , Pfender E.
Published: November 2010

A high intensity arc plasma torch with controlled transpiration cooling of the anode has been developed. The plenum chamber surrounding the porous anode is subdivided into several independent compartments which allow for individual control of the pressure and of the ensuing mass flow rates through the corresponding anode segments. In this way, the inherent instabilities of transpiration cooling may be alleviated. Arc performance characteristics are determined utilizing a porous carbon anode and argon at atmospheric pressure as working fluid. It is shown that the temperature distribution of the porous anode segments depends only on the transpiring mass flow rate and on the pressure drop through the porous material. Theoretical predictions compare favorably with experimental results. By using a two-step temperature model, the arc attachment size on a particular anode segment may be estimated. The torch efficiency which is a measure of the effectiveness of transpiration cooling on net anode losses and the mean enthalpy of the emanating plasma jet are measured as a function of mass flow rate and power input.
Heat and Mass Transfer in Beds of Particles Undergoing Sublimation Dehydration
Authors: Hardin L. L. , Dyer D. F.
Published: November 2010

A theoretical analysis as well as an experimental study of sublimation freeze-drying is reported. The theoretical and experimental results compare within 10 percent for a test case. In addition, the theoretical work confirms that drying rates increase linearly with bed thickness for particle bed drying, as reported in earlier experiments. Drying times for a slab and particle beds with the same mass and dryer surface area are compared. It is shown that the drying time for the particle bed can be reduced by more than a factor of two compared to the equivalent slab. It is also shown that the optimum way to increase the drying rate of particle beds is to increase the number of layers rather than the size of particles.
Prediction of Momentum, Heat and Mass Transfer in Swirling, Turbulent Boundary Layers
Authors: Koosinlin M. L. , Launder B. E. , Sharma B. I.
Published: November 2010

The paper presents the outcome of finite-difference calculations of turbulent flow near spinning cones, disks, and cylinders. The turbulence model used is a version of the mixing-length hypothesis in which the mixing length which would prevail in the absence of swirl is made a linear function of the local “swirling flow” Richardson number. Agreement with available experimental data for these geometries is generally good. At high swirl rates, however, a few systematic differences between experiment and calculation become evident which are probably attributable to the nonisotropic nature of the effective viscosity in such complex strain fields.
Concurrent Reduction of Draft Height and Heat-Exchange Area for Large Dry Cooling Towers
Authors: Moore F. K. , Hsieh T.
Published: November 2010

A procedure is outlined to meet simultaneous requirements to reduce overall size of a dry cooling tower for a large power plant, and to reduce the size (surface area) of the associated air-water heat exchanger. First, tower exit dimensions (or fan power) are specified as attainable fractions of their theoretical minima as found from a draft equation. Then a heat-exchanger type is chosen, having as small an air hydraulic diameter as feasible. Appropriate equations and assumptions dealing with air side and water side heat exchange and water pumping power then yield a full description of tower and heat-exchanger characteristics for a given tower duty. A specific example is worked out and compared with the tower at Rugeley, England. We find that a very open heat exchanger, of shallow depth (one in or less) results from our analysis, and in a proposed configuration of acceptable header loss gives a 1/3 height reduction and a four-fold reduction of heat-exchanger area.
Adaptation of the Surface Renewal Approach to Momentum and Heat Transfer for Turbulent Pulsatile Flow
Authors: Thomas L. C.
Published: November 2010

This paper presents a surface renewal based formulation for convective heat transfer for hydrodynamically and thermally fully developed turbulent flow in a tube. Based on the modeling concept presented in this paper, turbulent pulsatile flow is categorized according to the hydrodynamically unsteady mean residence time, τ(t).
Spontaneous Ignition: Finite Element Solutions for Steady and Transient Conditions
Authors: Anderson C. A. , Zienkiewicz O. C.
Published: November 2010

Steady-state and transient ignition problems are solved by the finite element method. Discretized equations for the reactive heat equation are set down using Galerkin’s method. The steady-state discretized equations are solved by an incremental Newton-Raphson procedure using the Frank-Kamenetskii parameter as the incremented or “loading” variable. Critical values of the Frank-Kamenetskii parameter are given for both common and unusual shapes using isoparametric finite elements to describe the geometrical features of the bodies. The transient ignition problem is solved by using the finite element spatial description together with a midinterval time differencing scheme.
An Experimental Investigation of the Temperature Field Produced by a Cryosurgical Cannula
Authors: Cooper T. E. , Petrovic W. K.
Published: November 2010

Liquid crystals, a material that exhibits brilliant changes in color over narrow temperature bands, have been successfully used to study the temperature field that is produced by a cryosurgical cannula (cryoprobe). Cryoprobe tip temperatures ranging from −36 to −117 C were used to produce frozen regions in a clear gel. Experimental results compare within experimental uncertainty with results of a one-dimensional analytical solution for predicting ice growth rates.
Natural Convection Adjacent to Horizontal Surface of Various Planforms
Authors: Lloyd J. R. , Moran W. R.
Published: November 2010

Natural convection adjacent to horizontal surfaces of circular, square, rectangular, and right triangular planforms has been studied experimentally. Electrochemical techniques were employed involving a fluid with a Schmidt number of about 2200. The results encompass a wide range of Rayleigh numbers thus providing information on both the laminar and the turbulent regimes. The data for all planforms are reduced to a single correlation in the laminar and turbulent regimes using the characteristic length, as recommended by Goldstein, Sparrow, and Jones. L* = A/p, where A is the surface area and p is the surface perimeter. The laminar data for all planforms are correlated by the expression Sh=0.54Ra1/4(2.2×104≤Ra≤8×106) and the data for the turbulent regime are correlated by the expression Sh=0.15Ra1/3(8×106≤1.6×109) Transition is found to occur at about Ra = 8 × 106. The present work thus significantly extends the Rayleigh number range of validity for the use of L* through the 1/4 power laminar regime into the turbulent 1/3 power regime. It also demonstrates the validity of the use of L* to correlate natural convection transfer coefficients for highly unsymmetrical planforms, which heretofore had not been demonstrated. Comparisons to analytical solutions and other experimental heat and mass transfer data are presented.
An Experimental Investigation of Natural Convection With a Low Prandtl Number Fluid in a Vertical Channel With Uniform Wall Heat Flux
Authors: Colwell R. G. , Welty J. R.
Published: November 2010

An experimental program was conducted to study the heat transfer characteristics of mercury in laminar natural convection flow within a vertical open-ended channel over a range of channel widths. Two sets of boundary conditions were investigated separately: (1) uniform heat flux at one wall with the other insulated, and (2) both walls symmetrically and uniformly heated. A decrease in channel width caused a decrease in channel wall temperature in the developing portion of the flow. This unexpected phenomenon persisted until the channel height-to-width ratio, Ar, reached a value greater than 18. Hence, the buoyancy induced flow of a low Prandtl number fluid in a channel is more thermally efficient than a single heated plate. Temperature data have been correlated into local Nusselt versus modified Grashof number plots, based on streamwise position, for several aspect ratios. The effect of aspect ratio on channel temperature is displayed on NuL versus Ar curves for several GrL*. The infinite spacing limit is compared to previous work with temperature profiles and local heat transfer results. Expressions for local and average heat transfer correlations are presented, with suggested limits on their application. The effect of flow in from the sides of the channel was investigated by affixing plastic side plates to the channel.
The Diffusion Stratification Effect in Bunsen Flames
Authors: Sivashinsky G. I.
Published: November 2010

The thermal diffusion flame model for a bimolecular reaction under stoichiometry conditions of the fresh mixture was examined. The structure of the flame tip of the Bunsen cone was studied. A local breakdown in the stoichiometry in the vicinity of the reaction zone was found such that the light component is always insufficient. For Lewis numbers greater than unity, the flame front is continuous. The temperature at the exit from the reaction zone exceeds the adiabatic temperature of the combustion products. For a Lewis number of the light component less than unity, either a flame with a continuous front, the temperature of which is less than the adiabatic temperature, or a flame with an exposed tip is possible. The problem is solved on the assumption of a strong temperature dependence of the reaction rate.
Radiation Induced Thermal Stratification in Surface Layers of Stagnant Water
Authors: Snider D. M. , Viskanta R.
Published: November 2010

Analysis is developed for the time dependent thermal stratification in surface layers of stagnant water by solar radiation. The transient temperature distribution is obtained by solving the one-dimensional energy equation for combined conduction and radiation energy transfer using a finite difference method. Experimentally, solar heating of water is simulated using tungsten filament lamps in parabolic reflectors of known spectral characteristics. The transient temperature distribution resulting from radiant heating of pure water in a glass-walled test cell is measured with a Mach-Zehnder interferometer. Measured and predicted temperature profiles show good agreement, thus verifying the radiation and total energy transfer models in stagnant water. It is found that the boundary condition at the air-water interface and internal radiant heating rate must be correctly specified in order to properly model stratification of water by radiation.
Analysis of Flow Field and Impingement Heat/Mass Transfer Due to a Nonuniform Slot Jet
Authors: Sparrow E. M. , Lee L.
Published: November 2010

An analysis is made of the fluid flow and heat transfer characteristics associated with the impingement of a slot jet which issues from a delivery duct with a nonuniform velocity profile. Consideration is given to velocity profiles similar to that for a fully developed laminar channel flow. The velocity field within the impinging jet is solved for within the framework of an inviscid flow model. Results from the inviscid solution are used as input for the analysis of the boundary layer heat or mass transfer on the impingement surface. The stagnation point heat (or mass) transfer coefficients corresponding to the initially nonuniform velocity profile are found to be almost twice as large as those for an initially flat velocity profile. Furthermore, the transfer coefficients are insensitive to the separation distance between the duct exit and the impingement surface, within the range investigated. The analytical results compared satisfactorily with experimentally determined mass transfer coefficients.
Natural Convection in a Horizontal Fluid Layer With Volumetric Energy Sources
Authors: Kulacki F. A. , Nagle M. E.
Published: November 2010

Natural convection with volumetric heating in a horizontal fluid layer with a rigid, insulated lower boundary and a rigid, isothermal upper boundary is experimentally investigated for Rayleigh numbers from 114 to 1.8 × 106 times the critical value of linear stability theory. Joule heating by alternating current passing horizontally through the layer provides the volumetric energy source. Layer aspect ratios are kept small to minimize the effects of side walls. A correlation for mean Nusselt number is obtained for steady heat transfer, and data are presented on fluctuating temperatures at high Rayleigh numbers and on developing temperature distributions when the layer is subjected to a step change in power.
Analysis of Multidimensional Conduction Phase Change Via the Enthalpy Model
Authors: Shamsundar N. , Sparrow E. M.
Published: November 2010

The basis of the enthalpy model for multidimensional phase change problems in media having a distinct phase change temperature is demonstrated, and subsequent numerical applications of the model are carried out. It is shown that the mathematical representation of the enthalpy model is equivalent to the conventional conservation equations in the solid and liquid regions and at the solid-liquid interface. The model is employed in conjunction with a fully implicit finite-difference scheme to solve for solidification in a convectively cooled square container. The implicit scheme was selected because of its ability to accommodate a wide range of the Stefan number Ste. After its accuracy had been established, the solution method was used to obtain results for the local and surface-integrated heat transfer rates, boundary temperatures, solidified fraction, and interface position, all as functions of time. The results are presented with SteFo (Fo = Fourier number) as a correlating parameter, thereby facilitating their use for all Ste values in the range investigated. At low values of the Biot number, the surface-integrated heat transfer rate was relatively constant during the entire solidification period, which is a desirable characteristic for phase change thermal energy storage.
Transient Temperature Distributions in Heat-Generating Transpiration-Cooled Tubes and Plates
Authors: Burch D. M. , Peavy B. A.
Published: November 2010

This paper investigates the transient temperature distribution in transpiration-cooled porous matrices, after sudden initiation of uniform internal heat generation. Analytic solutions are derived for the tube and plate geometries that include the effect of forced convection heat transfer at the gas-exit surface where the conventional heat-transfer coefficient is used to define the boundary condition.
Multihole Cooling Film Effectiveness and Heat Transfer
Authors: Mayle R. E. , Camarata F. J.
Published: November 2010

Adiabatic film effectiveness and heat transfer measurements with injection of secondary air through arrays of holes in a flat plate into a turbulent boundary layer are presented. Measurements were taken both within and downstream of the multihole pattern for different hole pitch-to-diameter ratios and blowing rates. The hole configurations considered were regular patterns of staggered holes. The holes were angled 30 deg to the plate’s surface and 45 deg to the mainstream. A comparison between the measured adiabatic film effectiveness and a model based on the superposition of point heat sinks is made.
Natural Convection in a Porous Medium: Effects of Confinement, Variable Permeability, and Thermal Boundary Conditions
Authors: Ribando R. J. , Torrance K. E.
Published: November 2010

Two-dimensional numerical calculations are reported for natural convection of a fluid in a porous, horizontal layer heated from below. Effects of the following parameters are examined: rigid (impermeable) and constant-pressure (permeable) upper boundaries; isothermal and uniform heat flux at the lower boundary; and permeabilities which are constant, or which vary with depth to simulate compaction of a porous medium or property variations of real fluids within the medium. Steady-state results are presented for the heat flux distribution on the upper surface, as well as for flow and temperature fields in the interior.
Combined Radiation and Developing Laminar Free Convection Between Vertical Flat Plates With Asymmetric Heating
Authors: Carpenter J. R. , Briggs D. G. , Sernas V.
Published: November 2010

A numerical investigation of the interaction of radiation with developing laminar free convective heat transfer in vertical parallel plate channels with asymmetric heating is presented. A unique iterative-marching technique is developed to solve the resulting nonlinear partial differential field equations and the integrodifferential radiation constraint equations. The introduction of radiation leads to five dimensionless parameters (heat flux ratio, Rayleigh number, aspect ratio, emissivity, and radiation number) which affect wall temperature and heat transfer performance. Radiation to the inlet-exit and the cooler opposing entrance wall significantly alters the nonradiation results by reducing the maximum wall temperature by as much as 50 percent. The nonradiation fully developed flow solution often could not be obtained with radiation present. Under certain conditions the Nusselt number actually becomes negative indicating a large radiative loss to the exit and a subsequent heating of the wall by the high local fluid temperature. The numerical results are verified experimentally.
Experiments and Universal Growth Relations for Vapor Bubbles With Microlayers
Authors: Theofanous T. G. , Bohrer T. H. , Chang M. C. , Patel P. D.
Published: November 2010

Solutions for bubble growth rates including the effects of inertia, heat transfer, and microlayer evaporation were obtained in generalized coordinates. Experimental growth rate data, covering a wide range of superheats, were obtained under precisely controlled conditions. The theoretical development appears to provide a satisfactory a priori prediction of these data. In particular, the Γ-effect predicted earlier is fully corroborated by these data which are the first to cover an extended range of this parameter.
Free Convective Heat Transfer Across Inclined Air Layers
Authors: Hollands K. G. T. , Unny T. E. , Raithby G. D. , Konicek L.
Published: November 2010

This paper presents new experimental measurements on free convective heat transfer rates through inclined air layers of high aspect ratio, heated from below. The Rayleigh number range covered is from subcritical to 105; the range of the angle of inclination, φ measured from the horizontal is: 0 < φ < ∼70 deg. Although it was anticipated that the results might be identical to the results for the horizontal layer if one replaced Ra by Ra cos φ, significant departures from this behavior were observed, particularly in the range 1708 < Ra cos φ < 104, 30 deg ≤ φ < 60 deg. A recommended relationship giving the Nusselt number as a function of Ra cos φ and φ is reported. This relationship fits all data closely.