bluuebunny/crossref_metadata_2025 huggingface dataset:
Turbulent Transport to a Rotating Cylinder for Large Prandtl or Schmidt Numbers
Authors: Smith R. N. , Greif R.
Published: November 2010

The heat or mass transport to a rotating cylinder is obtained by solving the conservation equations for large Prandtl or Schmidt numbers. A modified mixing length, which includes the effect of centrifugal forces in terms of the Richardson number, is used. Explicit relations are presented for the heat or mass transport and a comparison is made with the experimental data over a range of Prandtl and Schmidt numbers from 190 to 11,000.
Determination of Thermal Properties From Steady-State Heat Transfer Measurements on a Heated Tungsten Wire in Vacuum and Helium Gas
Authors: Jody B. J. , Jain P. C. , Saxena S. C.
Published: November 2010

An experimental facility in its developed form is described for the determination of a number of thermal properties as a function of temperature in the range 400–2500 K. These are the resistivity, tensile breaking stress, the total hemispherical emittance of the tungsten wire, and the thermal conductivity of helium. These properties are computed from the knowledge of steady-state heat transfer data from tungsten wire in vacuum and in the presence of helium at pressures covering the temperature-jump and continuum regimes. These measured properties are discussed in the light of literature values wherever available.
On the Interface Temperature of Two Suddenly Contacting Materials
Authors: Kazimi M. S. , Erdman C. A.
Published: November 2010

The interface temperature of two suddenly contacting semi-infinite bodies is developed using the hyperbolic heat-conduction equation. The times for which the non-Fourier effects are important are assessed. A numerical example for a system of uranium dioxide and sodium is considered.
Experiments on the Transfer Characteristics of a Corrugated Fin and Tube Heat Exchanger Configuration
Authors: Goldstein Leonardo , Sparrow E. M.
Published: November 2010

Local and average air-side transfer coefficients have been measured for a one-row corrugated fin and tube heat exchanger configuration. The measurements were accomplished via the heat-mass transfer analogy in conjunction with the naphthalene sublimation technique. The local transfer coefficients revealed the presence of several vortex systems which are activated and strengthened with increasing Reynolds number. The vortices serve to augment the transfer coefficients. The windward or leeward orientation of the facets of the corrugated wall was found to have a decisive effect on the transfer characteristics, with appreciably higher transfer rates prevailing on the windward facets. The average transfer coefficients were compared with those for a corresponding plane-walled heat exchanger configuration. The comparison showed that the augmentation due to the corrugated fin surface increased with Reynolds number. At a Reynolds number of 1000, the average coefficient for the corrugated fin system was about 45 percent greater than that for the plane fin system.
Natural Convection of a Heat-Generating Fluid Within Closed Vertical Cylinders and Spheres
Authors: Kee R. J. , Landram C. S. , Miles J. C.
Published: November 2010

Steady natural convective flow fields were numerically and experimentally characterized for 0.7 Prandtl number fluids having constant, uniformly distributed, internal heat sources. The bounding isothermal walls containing the fluid were considered to be either a sphere or a cylinder of finite height. An instrumented cylinder containing radioactive tritium gas was used to demonstrate experimental and analytical agreement for local temperatures over a range of Grashof numbers. For the spherical geometry, a generalized correlation was obtained for the surface-averaged Nusselt number as a function of a modified Grashof number.
Experiments on the Role of Natural Convection in the Melting of Solids
Authors: Sparrow E. M. , Schmidt R. R. , Ramsey J. W.
Published: November 2010

Experiments are performed whose results convey strong evidence of the dominant role played by natural convection in the melting of a solid due to an embedded heat source. The research encompassed both melting experiments and supplementary natural convection experiments, with a horizontal cylinder as the heat source. For the melting studies, the cylinder was embedded in a solid at its fusion temperature, whereas in the natural convection tests it was situated in the liquid phase of the same solid. A special feature of the experiments was the use of a grid of approximately 100 thermocouples to sense thermal events within the phase change medium. The time history of the heat transfer coefficients for melting was characterized by an initial sharp decrease followed by the attainment of a minimum and then a rise which ultimately led to a steady value. This is in sharp contrast to the monotonic decrease that is predicted by a pure conduction model. The steady state values were found to differ only slightly from those measured for pure natural convection. This finding enables melting coefficients to be taken from results for natural convection. The positions of the solid-liquid interface at successive times during the melting process also demonstrated the strong influence of natural convection. These interfaces showed that melting primarily occurred above the cylinder. In contrast, the interfaces given by the conduction model are concentric circles centered about the cylinder.
Transient Temperature Profile of a Hot Wall Due to an Impinging Liquid Droplet
Authors: Seki M. , Kawamura H. , Sanokawa K.
Published: November 2010

An experiment was made to investigate the heat transfer to a liquid drop impinging on a hot surface. The transient temperature of the heater surface was measured by a thin-film thermometer. The surface temperature fell to a contact temperature immediately after contact with the drop. The contact temperature increased with increasing initial surface temperature T0. In the case of the water drop, however, it was approximately constant for 200°C ≲ T0 ≲ 300°C; and it increased again for T0 ≳ 300°C. The surface temperature at the turning point, i.e., T0 ∼ 300°C, roughly coincided with the Leidenfrost point.
Natural Convection Heat Transfer in Beds of Inductively Heated Particles
Authors: Rhee S. J. , Dhir V. K. , Catton I.
Published: November 2010

Experimental observations of the onset of convective motion in beds of inductively heated particles have been made. Data for the heat transfer coefficient were obtained from water-cooled beds of steel particles. The particulate beds were formed in a 10.4 cm dia glass jar, insulated at the bottom and on the sides. The free surface of a layer of water overlying the bed was maintained at a constant temperature by a copper plate cooled with tap water. In the experiments, the depths of the particulate bed and the overlying layer were varied. The observations showed that increasing the depth of the liquid layer over the bed tended to lower the critical internal Rayleigh number at which the onset of convection occurred. For overlying liquid layer-to-bed depth ratios of one or more, natural convection was observed to begin at R1 ≃ 11.5. The heat transfer data for RI > 11.5 are correlated with Nu = 0.190 RI0.69 However, with no liquid layer on top of the bed, natural convection was observed to occur at RI ≃ 46, which is slightly higher than observed in earlier studies made with Joule heating.
Three-Dimensional, Numerical Analysis of Laminar Natural Convection in a Confined Fluid Heated From Below
Authors: Ozoe H. , Yamamoto K. , Churchill S. W. , Sayama H.
Published: November 2010

An improved model and algorithm were developed for the numerical solution of three-dimensional, laminar natural convection in enclosures. Illustrative calculations were carried out for heating from below in a cubical box, a long channel with a square cross section and in the region between infinite, horizontal plates. The results are in good agreement with prior experimental and theoretical results. For the infinite flat plates the three-dimensional model correctly produces a two-dimensional solution. For the cube the solution produces different stable solutions depending on the initial conditions. A fluid-particle path is shown to be a good method of illustrating the three-dimensional motion. In the cube and in each cubical cell in the channel this streak-line was found to consist of a pair of double helices.
Analysis of Buoyant Surface Jets
Authors: Shirazi M. A. , Davis L. R.
Published: November 2010

To obtain improved prediction of heated plume characteristics from a surface jet, an integral analysis computer model was modified and a comprehensive set of field and laboratory data available from the literature was gathered, analyzed, and correlated for estimating the magnitude of certain coefficients that are normally introduced in these analyses to achieve closure. The parameters so estimated include the coefficients for entrainment, turbulent exchange, drag, and shear. Since there appeared considerable scatter in the data, even after appropriate subgrouping to narrow the influence of various flow conditions on the data, only statistical procedures could be applied to find the best fit. This and other analyses of its type have been widely used in industry and government for the prediction of thermal plumes from steam power plants. Although the present model has many shortcomings, a recent independent and exhaustive assessment of such predictions revealed that in comparison with other analyses of its type the present analysis predicts the field situations more successfully.
The Interaction of a Hot Gas Flow and a Cold Liquid Spray in Channels
Authors: Habib I. S.
Published: November 2010

The coupled interaction of cold liquid sprays and a hot gas stream is analyzed. The effect of liquid droplets introduced into a hot gas stream flowing in channels of constant and of varying areas is investigated as a rapid cooling process for a hot gas discharge. The effects of spray distribution, duct geometry, and wall friction are examined. Variations of gas and liquid spray properties such as gas temperature and velocity, droplets velocity, temperature, and distribution are presented as a function of distance along the duct in the direction of flow. The effectiveness of this rapid cooling process for a hot gas flow is assessed.
Theoretical Solutions for Combined Forced and Free Convection in Horizontal Tubes with Temperature-Dependent Viscosity
Authors: Hong S. W. , Bergles A. E.
Published: November 2010

A boundary layer solution is presented for fully developed laminar flow in a horizontal circular tube, assuming large Prandtl number and temperature-dependent viscosity and density. The solution is given by Nu = C1 Ra1/4, where C1 is a function of a nondimensional viscosity parameter and the heat flux boundary condition. The heat transfer predictions for large values of the viscosity parameter are 50 percent above the constant viscosity predictions. The present analysis is in good agreement with experimental data for water and ethylene glycol flowing in electrically heated tubes which approximate the boundary conditions assumed in the analysis.
Transient Response of Solid Sensible Heat Thermal Storage Units—Single Fluid
Authors: Schmidt F. W. , Szego J.
Published: November 2010

The transient response of a solid sensible heat storage unit which receives or supplies heat to a single flowing fluid is presented. The storage unit is composed of a number of rectangular cross-sectional channels for the flowing fluid, connected in parallel and separated by the heat storage material. The energy equation for the fluid and the transient conduction equation for the storage material are solved using finite difference techniques. The parameters which characterize the transient behavior of these units are identified. Results suitable for the prediction of the rate of heat storage and the outlet temperature of the fluid leaving the storage unit are presented as functions of the identified nondimensional parameters.
The Determination of Stresses and Temperatures in Cooling Bodies by Finite Elements
Authors: Lewis R. W. , Bass B. R.
Published: November 2010

This paper presents a finite element method for solving non-linear heat conduction and thermal stress problems. The nonlinearity is caused by the variation of thermo-physical and mechanical properties of the material with respect to temperature. The distribution of temperature and stress in a cooling body can be followed from the onset of solidification. The method is capable of handling complex geometries and initial non-linear boundary conditions.
The Numerical Prediction of Turbulent Flow and Heat Transfer in The Entrance Region of a Parallel Plate Duct
Authors: Emery A. F. , Gessner F. B.
Published: November 2010

Velocity and temperature profiles were computed for turbulent flow, both in the entrance region and the fully developed state, in a duct with heated parallel plates. By starting the calculations at the duct inlet and using a finite difference technique and a three-dimensional mixing length originally defined for corner flows, it was possible to predict axial flow behavior and the nonasymptotic approach to fully developed flow with and without associated heat transfer.
A Comprehensive Model for Nucleate Pool Boiling Heat Transfer Including Microlayer Evaporation
Authors: Judd R. L. , Hwang K. S.
Published: November 2010

The results of an experimental investigation are presented in which dichloromethane (methylene chloride) boiling on a glass surface was studied using laser interferometry and high-speed photography. New data for active site density, frequency of bubble emission, and bubble departure radius were obtained in conjunction with measurements of the volume of microlayer evaporated from the film underlying the base of each bubble for various combinations of heat flux and subcooling. These results were used to support a model for predicting boiling heat flux incorporating microlayer evaporation, natural convection, and nucleate boiling mechanisms. Microlayer evaporation heat transfer is shown to represent a significant proportion of the total heat transfer for the range of heat flux and sub-cooling investigated.
An Investigation of Heat Transport In Oscillatory Turbulent Subcooled Flow
Authors: Roy R. P. , Yadigaroglu G.
Published: November 2010

An experiment has been conducted to investigate transient radial heat transport effects created by oscillatory flow in uniformly heated tubes. Departures from one-dimensional, quasi-steady-state behavior have been quantified in the frequency range of density-wave oscillations. The data show a substantial radial dependence of both the amplitude and the phase of the liquid temperature perturbations even at frequencies as low as 0.1 Hz. The orderly axial enthalpy perturbation propagation breaks down at frequencies above 0.5 Hz. These effects must be taken into consideration in predicting the behavior of the point of net vapor generation in a boiling channel under oscillatory flow conditions.
Mixed Convection in Boundary Layer Flow on a Horizontal Plate
Authors: Chen T. S. , Sparrow E. M. , Mucoglu A.
Published: November 2010

The effects of buoyancy-induced streamwise pressure gradients on laminar forced convective flow and heat transfer over a horizontal flat plate are studied analytically by the local similarity and local nonsimilarity methods of solution. Numerical results for the local surface heat transfer, wall shear stress, and velocity and temperature distributions are presented for gases having a Prandtl number of 0.7. It is found that both the local Nusselt number and the friction factor increase with increasing buoyancy forces for aiding flow and decrease with increasing buoyancy forces for opposing flow. With regard to the heat transfer results, significant buoyancy effects were encountered for Grx/Rex5/2 > 0.05 and < −0.03, respectively, for aiding and opposing flows. The buoyancy-affected velocity profiles for the aiding-flow case exhibited an overshoot beyond the free stream velocity. Results from previously reported series solutions and from an integral momentum/energy solution were found to be accurate only when the buoyancy effects are small. The present study provides results for intermediate range buoyancy force effects, which have not been reported previously.
A Criterion of Onset of Free Convection in a Horizontal Melted Water Layer With Free Surface
Authors: Seki N. , Fukusako S. , Sugawara M.
Published: November 2010

The problem considered in this paper is the determination of the Rayleigh number marking the onset of free convection in a horizontal melted layer of ice heated from above under uniform radiant heat flux. In this analysis, linear perturbation techniques are used to derive a sixth-order differential equation subject to hydrodynamic and thermal boundary conditions. The series-solution method is utilized to obtain an eigenvalue equation for the case where the lower surface (ice surface) is kept at 0°C and the upper free surface is subjected to the general thermal conditions. An experimental determination of the onset of free convection, when the heat transfer mode changes from conduction to convection, is obtained from the fact that the temperature distribution in a melted water layer starts to deviate from its linear profile. At the same time, a peculiar variational inflection of the water-surface temperature occurs. From the present investigation, it can be demonstrated both analytically and experimentally that the critical Rayleigh number Rac in a horizontal melted water layer with a density inversion is dependent on the free water-surface temperature T2 for T2 < 8°C, while Rac for T2 ≧ 8°C is independent of T2.
A Correlating Equation for Forced Convection From Gases and Liquids to a Circular Cylinder in Crossflow
Authors: Churchill S. W. , Bernstein M.
Published: November 2010

A single comprehensive equation is developed for the rate of heat and mass transfer from a circular cylinder in crossflow, covering a complete range of Pr (or Sc) and the entire range of Re for which data are available. This expression is a lower bound (except possibly for RePr < 0.2); free-stream turbulence, end effects, channel blockage, free convection, etc., may increase the rate. In the complete absence of free convection, the theoretical expression of Nakai and Okazaki may be more accurate for RePr < 0.2. The correlating equation is based on theoretical results for the effect of Pr in the laminar boundary layer, and on both theoretical and experimental results for the effect of Re. The process of correlation reveals the need for theoretical results for the effect of Pr in the region of the wake. Additional experimental data for the effect of Pr at small Pe and for the effect of Re during the transition in the point of separation are also needed.
Cooling of Room Fires by Sprinkler Spray
Authors: Kung Hsiang-Cheng
Published: November 2010

Cooling of combustion products and the room by vaporizing water droplets appears to be a promising mechanism in sprinkler control of residential fires. An experimental procedure coupled with an energy balance scheme has been developed to obtain the heat absorption rate of a sprinkler spray. A test room was constructed, 3.05 × 3.66 × 2.45 m high, with a window. Hexane pool fires were selected to simulate room fires. The key parameters of investigation were water-discharge rate and drop size. For the room tested, a correlation has been established between the heat-absorption rate by the sprinkler water and the relative median drop size of the sprinkler spray. It is found that the rate of sprinkler water evaporated is directly proportional to the heat release rate and the water discharge rate, and varies as the minus 0.73 power of the relative median drop size. An extinction criterion for the hexane pool fire in the enclosure, based on the water evaporation rate at the time of sprinkler operation, has also been established.
Friction Factor for Isothermal and Nonisothermal Flow Through Porous Media
Authors: Koh J. C. , Dutton J. L. , Benson B. A. , Fortini A.
Published: November 2010

Measurements were performed to determine the pressure drops for gaseous flow through porous materials of different microstructures, porosities, and thickness under isothermal and nonisothermal conditions at various temperature levels. Results were satisfactorily correlated by a simple equation relating the friction factor to the Reynolds number and porosities.
The Concept of Irreversibility in Heat Exchanger Design: Counterflow Heat Exchangers for Gas-to-Gas Applications
Authors: Bejan A.
Published: November 2010

The thermal design of counterflow heat exchangers for gas-to-gas applications is based on the thermodynamic irreversibility rate or useful power no longer available as a result of heat exchanger frictional pressure drops and stream-to-stream temperature differences. The irreversibility (entropy production) concept establishes a direct relationship between the heat exchanger design parameters and the useful power wasted due to heat exchanger nonideality. The paper presents a heat exchanger design method for fixed or for minimum irreversibility (number of entropy generation units NS). In contrast with traditional design procedures, the amount of heat transferred between streams and the pumping power for each side become outputs of the NS design approach. To illustrate the use of this method, the paper develops the design of regenerative heat exchangers with minimum heat transfer surface and with fixed irreversibility NS.
Experimental Study of Bubble Motion in Mercury With and Without a Magnetic Field
Authors: Mori Y. , Hijikata K. , Kuriyama I.
Published: November 2010

The behavior and hydrodynamical performance of a single bubble rising through mercury with and without magnetic field has been studied experimentally. A new method to measure the rise velocity and the shape of bubble with an electrical triple probe is proposed. When there is no magnetic field, a bubble changes its shape from spherical to elliptic and then to a spherical cap shape, as its equivalent radius Rm changes from 0.1 to 3 mm. The experimental results are found to agree well with the theories reported so far. In the case of a magnetic field, it is found that the effect of intensity of magnetic field B on the rise velocity depends largely on the radius of a bubble. When Rm = 3 mm, the rise velocity decreases monotonically with the increase of B. However, when Rm = 1 mm, the rise velocity increases once but it then starts to decrease afterwards with the increase of B.
Free Convection Effects on the Stokes Problem for an Infinite Vertical Plate
Authors: Soundalgekar V. M.
Published: November 2010

An exact analysis of Stokes’ problem (also Rayleigh’s problem) for the flow past an impulsively started infinite vertical plate is presented. The effects of externally heating or cooling the plate by free convection currents are studied. It is observed that the velocity decreases due to more heating of the plate and increases due to more cooling of the plate. The skin friction increases due to greater heating of the plate and decreases owing to greater cooling of the plate. More cooling of the plate may cause reverse type of flow near the plate in the case of air.
Forced Convection Heat Transfer at an Inclined and Yawed Square Plate—Application to Solar Collectors
Authors: Sparrow E. M. , Tien K. K.
Published: November 2010

Experiments have been performed to determine the average heat transfer coefficients for forced convection airflow over a square plate that is inclined and yawed relative to the oncoming flow. The experiments involved mass transfer and were carried out via the naphthalene sublimation technique, with air as the working fluid. By means of the analogy between heat and mass transfer, the results are presented in a form that can be used directly for heat transfer applications. The experiments encompassed a wide range of angles of yaw and angles of attack, and extended over a Reynolds number range from about 20,000 to 100,000. It was found that owing to three dimensional flow effects, the transfer coefficients were remarkably insensitive to both the angle of attack and the angle of yaw. This enabled all the results to be correlated by the equation j = 0.931Re−1/2 (where j = (h/ρcpU∞)Pr2/3) with an accuracy of ±2 1/2 percent. The correlation equation was applied to the determination of the heat transfer coefficient for wind-related heat losses from a flat plate solar collector. It was demonstrated that the currently standard computational equation (which is, in reality, not well suited to the application) substantially overestimates the heat transfer coefficient.
An Experimental and Theoretical Investigation Into Thermally Governed Transient Flow Surges in Two-Phase Condensing Flow
Authors: Wedekind G. L. , Bhatt B. L.
Published: November 2010

The specific transient phenomenon under consideration is the outlet flowrate of subcooled liquid from a tube-type condenser where complete condensation takes place. Experimental data are presented which indicates that a small change in the inlet vapor flow-rate will momentarily cause a very large transient surge in the outlet flowrate of subcooled liquid. These experimentally measured flow transients are predicted quite accurately using a system mean void fraction model. Also, some preliminary results are presented which indicate the influence of throttling at the condenser outlet as a means of attenuating the transient overshoot characteristics.
Heat Transfer in Curved Tubes With Pulsatile, Fully Developed, Laminar Flows
Authors: Simon H. A. , Chang M. H. , Chow J. C. F.
Published: November 2010

A perturbation analysis is carried out to include the second order solution for fluid flow and heat transfer for a wide range of excitation parameters and Prandtl numbers. The results show an increase in the time averaged Nusselt number in curved pipes with pulsatile flow over that achieved in straight pipes with pulsatile flow. The increases are most evident at high Prandtl numbers, high excitation relative amplitudes, and low excitation frequencies.
Film Cooling With Large Density Differences Between the Mainstream and the Secondary Fluid Measured by the Heat-Mass Transfer Analogy
Authors: Pedersen D. R. , Eckert E. R. G. , Goldstein R. J.
Published: November 2010

The effect of large density differences on film cooling effectiveness was investigated through the heat-mass transfer analogy. Experiments were performed in a wind tunnel where one of the plane walls was provided with a porous strip or a row of holes with three-diameter lateral spacing and inclined 35 deg into the main stream. Helium, CO2, or refrigerant F-12, was mixed with air either in small concentrations to approach a constant property situation or in larger concentration to produce a large density difference and injected through the porous strip or the row of holes into the mainstream. The resulting local gas concentrations were measured along the wall. The density ratio of secondary to mainstream fluid was varied between 0.75 and 4.17 for both injection systems. Local film effectiveness values were obtained at a number of positions downstream of injection and at different lateral positions. From these lateral average values could also be calculated. The following results were obtained. The heat mass-transfer analogy was verified for injection through the porous strip or through holes at conditions approaching a constant property situation. Neither the Schmidt number, nor the density ratio affects the film effectiveness for injection through a porous strip. The density ratio has a strong effect on the film effectiveness for injection through holes. The film effectiveness for injection through holes has a maximum value for a velocity ratio (injection to free stream) between 0.4 and 0.6. The center-line effectiveness increases somewhat with a decreasing ratio of boundary layer thickness to injection tube diameter.
Steady State Temperature Distribution in a Solid Cylinder Moving in the Direction of its Axis Through a Cross-Flow of Hot Gas
Authors: Hunter L. W. , Favin S.
Published: November 2010

A range of boundary value problems is solved that describe the steady state temperature distribution in a solid circular cylinder of infinite length, moving in the direction of its axis. The cylinder is heated by a hot gas flowing perpendicularly to the cylinder. The problems differ in complexity depending on whether or not the cylinder is radially isothermal and the gas temperature uniform. Dimensionless charts are presented. This work pertains to the “moving wire techniques” for studying polymer flammability and measuring heat transfer from gases.
Natural Convection in a Horizontal Porous Medium Subjected to an End-to-End Temperature Difference
Authors: Bejan A. , Tien C. L.
Published: November 2010

Natural convection in a porous medium filling a slender horizontal space with an end-to-end temperature difference is studied analytically. The end-to-end temperature difference gives rise to a horizontal counterflow pattern augmenting the heat transfer rate through the porous medium. Two basic geometries are considered: horizontal layer confined between two adiabatic and impermeable parallel plates, and horizontal cylinder surrounded by an adiabatic and impermeable cylindrical surface. Nusselt number relations are derived in terms of the Rayleigh number and the cavity aspect ratio. The end-wall permeability is shown to affect the heat transfer rate through the medium.
Forced Convection Heat Transfer from Nonisothermal Thin Needles
Authors: Chen J. L. S. , Smith T. N.
Published: November 2010

The steady laminar forced convection heat transfer from nonisothermal thin needles in nonuniform incompressible flows is investigated analytically. Similarity temperature fields and heat transfer characteristics for needles with power-law thermal variations in (1) wall temperature, and (2) surface heat flux, are obtained. The influence of needle size and Prandtl number on the thermal behavior of the flow is examined for a uniform as well as an accelerating flow.
An Experimental Investigation of Heat Transfer and Buoyancy Induced Transition from Laminar Forced Convection to Turbulent Free Convection over a Horizontal Isothermally Heated Plate
Authors: Imura H. , Gilpin R. R. , Cheng K. C.
Published: November 2010

The flow over a horizontal isothermally heated plate at Reynolds numbers below that at which hydrodynamic instabilities exist, is characterized by a region of laminar forced convection near the leading edge, followed by the onset of longitudinal vortices and their growth to a finite amplitude and finally a transition to a turbulent flow regime. Results are presented for the temperature profiles, the thermal boundary layer thickness, and the local Nusselt number. They are used to identify the various flow regimes. It was found that the transition from laminar forced convection to turbulent convection was characterized by the parameter Grx/Rex1.5 falling in the range 100 to 300. For values of this parameter greater than 300 the heat transfer rates were independent of Reynolds number and typical of those for turbulent free convection from a horizontal surface.
Experimental Study on Bubble Nucleation in the Oscillating Pressure Field
Authors: Hijikata K. , Mori Y. , Nagatani T.
Published: November 2010

In bubble nucleation under the oscillating pressure field, when the oscillation period τ is of the same order of magnitude as the characteristic time τn of bubble nucleation, it is expected that the distribution of radius of bubble embryo in liquid will be largely affected by the pressure oscillation and the degree of superheat limit may change. In order to clarify this point, superheat limits of homogeneous nucleation under the oscillating pressure field generated by ultrasonic oscillators are measured for propane with and without dissolved carbon dioxide by the floating droplet method. From the experimental results it is found that when τ > τn the measured superheat limit agrees with that calculated by the conventional theory where the quasi-steady state is assumed, but the bubble nucleation occurs at temperature lower than that preducted by the theory when τ nearly equals τn. It is also found that the characteristic time of bubble nucleation is changed by the amount of dissolved carbon dioxide.
Early Response of Hot Water to Sudden Release from High Pressure
Authors: Lienhard J. H. , Alamgir Md. , Trela M.
Published: November 2010

The very early stages of blowdown are observed with the aid of a novel quick-opening mechanism. Water at pressures and temperatures up to PWR conditions is released from a long, one-half in. (1.27 cm) ID pipe. Depressurization rates up to 1.62 × 106 atm/s are achieved. As a consequence of the rapidity of depressurization, the water reaches pressures far below saturation (even approaching the spinodal line) before nucleation occurs. The performance of the opening device is described quantitatively, and implications of the response of the water are discussed in relation to nuclear safety problems.
Performance Ranking of Plate-Fin Heat Exchanger Surfaces
Authors: Soland J. G. , Mack W. M. , Rohsenow W. M.
Published: November 2010

The Kays-London [4] way of presenting heat exchanger performance is modified to use the data in the simplified analysis of La Haye, et al. [5] which was extended to permit the ready comparison of the performance of the various plate-fin surfaces. Based on the four comparison criteria considered, the wavy finned 17.8–3/8 W surface of Kays-London is the best.
Heat Transfer During Piston Compression
Authors: Nikanjam M. , Greif R.
Published: November 2010

An experimental and theoretical study has been carried out to determine the unsteady heat transfer from a nonreacting gas to the end wall of a channel during the piston compression of a single stroke. A thin platinum film resistance thermometer records the surface temperature of the wall during the compression. A conduction analysis in the wall, subject to the measured surface temperature variation, then yields the unsteady heat flux. A separate analysis based on the solution of the laminar boundary layer equations in the gas provides an independent determination of the heat flux. The two results are shown to be in good agreement. This is true for measurements that were made in air and in argon. Results for the heat transfer coefficient as a function of time are also presented and exhibit a nonmonotonic variation.
Laminar Natural Convection Heat Transfer in a Horizontal Cavity with Different End Temperatures
Authors: Bejan A. , Tien C. L.
Published: November 2010

The heat transfer by free convection in a horizontal cavity with adiabatic horizontal walls and differentially heated end walls is studied analytically. The paper develops three models for explaining and predicting the heat transfer mechanism in a cavity with the height/length aspect ratio considerably smaller than one. The three models are: 1) the regime of vanishing Rayleigh numbers, 2) the intermediate regime, and 3) the boundary layer regime. The transition from one model to the next occurs as the Rayleigh number increases. The Nusselt number prediction based on the three-regime theory agrees very well with available numerical and experimental heat transfer data.
Reduction of Heat Transfer to High Velocity Gun Barrels by Wear-Reducing Additives
Authors: Ward J. R. , Brosseau T. L.
Published: November 2010

In order to understand how wear-reducing additives such as TiO2/wax and polyurethane foam liners reduce erosion, a series of gun firings was made in a 105 mm tank cannon equipped with thermocouples to measure the heat transferred to the gun barrel both in the presence and in the absence of the additives. Four thin thermocouples (0.13 mm diameter) were placed at different radial distances from the bore surface. Each thermocouple was placed at the same axial distance along the gun barrel. From the temperature distribution measured 100 milliseconds after propellant ignition, the total heat transferred in the gun barrel was determined. On the basis of single shot measurements, both the polyurethane foam and the TiO2/wax liner reduced the heat transferred to the gun barrel by ten percent. Repeated firings with TiO2/wax liners afforded steadily increasing reduction in heat transfer which was attributed to the formation of an insulating layer of TiO2 and unreacted wax on the bore surface. This also accounts for the twenty-five fold increase in wear life of the M68 tank cannon firing rounds equipped with TiO2/wax liners. This thermocouple technique is now used to design optimum weight and location of wear-reducing additives in other gun systems, since the efficacy of the wear-reducing liner can be deduced from a few shots.
Transient Thermal Analysis of Epoxy-Impregnated Superconducting Windings in Linearly Ramped Fields
Authors: Laskaris T. E.
Published: November 2010

Heat is generated in superconducting windings whenever the magnetic field changes. During these transient periods, the current carrying capability of the superconductor is limited by the temperature distribution inside the winding, especially in epoxy-impregnated winding composites that have limited thermal conductance. A finite-difference transient thermal analysis of a superconducting winding composite is presented. The analysis is employed to predict the critical current of a cylindrical coil and a modular racetrack winding under linear ramping of the magnetic field, when eddy current losses and hysteresis losses prevail. The dependence of these losses on the magnetic field and temperature is properly accounted for. The analytical predictions are compared to experimental data and the agreement is excellent.
Thermosyphon Models for Downhole Heat Exchanger Applications in Shallow Geothermal Systems
Authors: Kreitlow D. B. , Reistad G. M. , Miles C. R. , Culver G. G.
Published: November 2010

The analysis of downhole heat exchangers used to extract energy from relatively shallow geothermal wells leads to the consideration of several interesting problems of buoyancy-driven heat transfer in enclosures. This paper considers thermosyphoning through and around the wellbore casing which is perforated at two or more depths. Analytical models are developed for thermosyphoning in the cased well both with and without a heat exchanger installed. Theoretical results are compared with experimental values. These comparisons show that the observed energy extraction rates and flow rates through the well casing are possible with thermosyphoning as the only circulation mechanism within the well bore. The model with a heat exchanger installed is parametrically evaluated to illustrate the sensitivity of the model to estimated parameters and the effect of changes in design variables or constraints.
Low-Velocity Heat Transfer to a Flat Plate in The Presence of a Corona Discharge in Air
Authors: Velkoff H. R. , Godfrey R.
Published: November 2010

A study was conducted to determine the enhancement in convection heat transfer that could be achieved using the corona wind over a range of stream velocities. A heated flat plate mounted in a flow channel was placed in a Mach-Zehnder interferometer. Corona wires were placed above the active plate surface. Data were taken over a range of stream velocities. The results showed the expected large increase in heat transfer at low velocities and that this gain in heat transfer decreased to zero at high stream velocities.
Structure of Turbulent Velocity and Temperature Fluctuations in Fully Developed Pipe Flow
Authors: Hishida M. , Nagano Y.
Published: November 2010

An experimental investigation of the turbulent structure of velocity and temperature fields has been made in fully developed pipe flow of air. In the near-wall region, the coherent quasi-ordered structure plays a dominant role in the turbulent heat transport process. The turbulent axial heat flux as well as the intensities of velocity and temperature fluctuations reach their maximums in this region, but these maximum points are different. The nondimensional intensities of velocity and temperature fluctuations are well described with the “logarithmic law” in the turbulent part of the wall region where the velocity-temperature cross-correlation coefficient is nearly constant. In the turbulent core, the velocity and temperature fluctuations are less correlated. The spectra of velocity and temperature fluctuations present −1 slope at low wavenumbers in the wall region and −5/3 slope in the inertial subrange. The temperature spectrum for the inertial-diffusive subrange indicates the −8/3 power-law.
Heat Transfer Downstream of a Fluid Withdrawal Branch in a Tube
Authors: Sparrow E. M. , Kemink R. G.
Published: November 2010

Experiments have been performed to study how fluid withdrawal at a branch point in a tube affects the turbulent heat transfer characteristics of the main line flow downstream of the branch. Air was the working fluid. The experiments were carried out for several fixed test section Reynolds numbers and at each Reynolds number the ratio of the withdrawn flow to the test section flow (hereafter designated as the flow split number) was varied systematically. Local heat transfer coefficients were determined both around circumference and along the length of the tube, and circumferential average coefficients were also evaluated. The circumferential average Nusselt numbers in the thermal entrance region are much higher than those for a conventional turbulent pipe flow having the same Reynolds number, and the differences are accentuated at higher values of the flow split number. When normalized by the corresponding fully developed value, the axial distribution of the circumferential average Nusselt number is relatively insensitive to the Reynolds number for a fixed flow split. The thermal entrance lengths, based on a five percent approach to fully developed conditions, are in the 20 to 30 diameter range, which is substantially greater than that for conventional turbulent air flows. Circumferential variations on the order of ±20 percent are induced by the fluid withdrawal process. For the most part, these variations are dissipated upstream of x/D = 10.
Perturbation Solutions to Phase Change Problem Subject to Convection and Radiation
Authors: Yan M. M. , Huang P. N. S.
Published: November 2010

Perturbation solutions are obtained for one-dimensional phase change problem in a finite region subject to convective and radiative boundary condition at the fixed boundary. The radiative term is first approximated by Taylor’s series expansion, then the perturbation technique is used. Analytical expressions for total solidification time and the rate of solidification as well as the temperature distributions are obtained. Close agreement is observed between the present analysis and that of an early work.
Effect of Finite Width on Heat Transfer and Fluid Flow about an Inclined Rectangular Plate
Authors: Sparrow E. M. , Ramsey J. W. , Mass E. A.
Published: November 2010

Wind tunnel experiments were performed to study the heat transfer and fluid flow characteristics for finite-width rectangular plates inclined at various angles of attack to an oncoming airflow. Plates having ratios of spanwise width to streamwise length of 0.4 and 2.5 were employed, and the angle of attack was varied from 90 deg (normal incidence) to 25 deg. The Reynolds number range extended from about 20,000 to 90,000. The naphthalene sublimation technique was used in the transfer coefficient determinations, and the fluid flow patterns adjacent to the plate were made visible by the oil/lampblack technique. The flow field was found to be highly complex and three dimensional, with stronger three-dimensional effects in evidence for the narrow plate. A stagnation zone, centered in the plate cross section at normal incidence, moved forward and ultimately disappeared as the plate was inclined at smaller angles of attack. The dimensionless heat (mass) transfer coefficient, expressed in terms of the Colburn j-factor, varied as the square root of the Reynolds number for all angles of attack, both for the narrow and the wider plates. For the wider plate, the transfer coefficients are completely independent of the angle of attack in the range investigated, while for the narrow plate there is an overall variation of twenty percent. An algebraically simple correlation of all the results, accurate to ± 10 percent, is given to facilitate their use in applications such as the wind-related heat loss from flat plate solar collectors.
Measurements of Developing and Fully Developed Heat Transfer Coefficients along a Periodically Interrupted Surface
Authors: Cur N. , Sparrow E. M.
Published: November 2010

The heat transfer and pressure drop characteristics for an array of colinear, equally spaced plates aligned parallel to the flow in a flat rectangular duct have been studied experimentally. The periodic interruptions (i.e., the gaps between the plates) preclude the attainment of hydrodynamic and thermal development of the type that is encountered in conventional duct flows, but a periodic fully developed regime can exist. Measurements of the heat transfer coefficients for the successive plates of the array affirmed the periodically developed regime and demonstrated the developmental pattern leading to its attainment. The thickness of the plates in the array was varied parametrically. In general, the Nusselt number increases with plate thickness. Thickness-related increases in the fully developed Nusselt number of up to 65 percent were encountered. The presence of the interruptions serves to augment the heat transfer coefficients. In the fully turbulent regime, the heat transfer coefficients are on the order of twice those for a conventional duct flow. The pressure drop also increases with the plate thickness.
Stability of a Horizontal Porous Layer with Timewise Periodic Boundary Conditions
Authors: Chhuon B. , Caltagirone J. P.
Published: November 2010

The stability of a horizontal porous layer bounded by two impermeable planes is investigated. A time dependent periodic temperature profile is imposed on the lower boundary while the upper plane is kept at constant temperature. Starting from the preconvective temperature distribution, and using the linear stability theory, a criterion for the onset of convection is defined as a function of the perturbation wavenumber and of the amplitude and frequency of the temperature oscillation. Experimental work with a setup allowing both the amplitude and the frequency of the thermal signal to vary is done. Finally, the equations are also solved numerically and the results are compared to the previous ones. A synthesis of all results is included.
A Generalized Procedure for the Design and Optimization of Fluted Gregorig Condensing Surfaces
Authors: Webb Ralph L.
Published: November 2010

This paper summarizes the general theory of the Gregorig fluted condensing surface, and includes advances since Gregorig’s original publication. These include Bromley, et al.’s mathematical description for the geometrical shape of the convex surface, and definition of the “optimum” fluted surface geometry established by Zener and Lavi. However, their optimization is applicable to only one of a family of possible convex surface shapes. This paper extends the work of Zener and Lavi to define the optimum geometry as a function of the included angle of the convex surface. This broader optimization analysis will support calculation of economically optimum fluted surface designs. Calculated results are presented for ammonia condensing on vertical fluted tubes and compared with existing experimental data. The expected performance of real condensers is discussed, relative to the idealized conditions assumed in the analysis. Finally, the paper outlines a step-by-step procedure for the design of the fluted surface and construction of the convex surface profile.