Showing papers on "Heat transfer coefficient published in 1986"

Melting and Solidification of a Pure Metal on a Vertical Wall

Abstract: Etude experimentale de l'ecoulement de convection naturelle dans la phase liquide et de son influence sur le mouvement de l'interface liquide-solide et sur le transfert de chaleur au cours de la fusion et de la solidification de gallium a haute purete sur une paroi verticale

Engineering Heat Transfer

Abstract: Fundamental Concepts Mechanisms of Heat Transfer Dimensions and Units Fourier's Law of Heat Conduction Thermal Conductivity Convection Heat Transfer Convection Heat-Transfer Coefficient Radiation Heat Transfer Emissivity and Other Radiative Properties Combined Heat-Transfer Mechanisms Steady-State Conduction in One Dimension One-Dimensional Conduction Equation Plane Geometry Systems Polar Cylindrical Geometry Systems Spherical Geometry Systems Thermal Contact Resistance Heat Transfer from Extended Surfaces Steady-State Conduction in Multiple Dimensions General Conduction Equation Analytical Method of Solution Graphical Method of Solution Conduction Shape Factor Solution by Numerical Methods (Finite Differences) Numerical Method of Solution for Two-Dimensional Problems Methods of Solving Simultaneous Equations Unsteady-State Heat Conduction Systems with Negligible Internal Resistance Systems with Finite Internal and Surface Resistances Solutions to Multidimensional Geometry Systems Approximate Methods of Solution to Transient-Conduction Problems Introduction to Convection Fluid Properties Characteristics of Fluid Flow Equations of Fluid Mechanics Thermal-Energy Equation Applications to Laminar Flows Applications to Turbulent Flows Natural-Convection Problem Dimensional Analysis Convection Heat Transfer in a Closed Conduit Heat Transfer to and from Laminar Flow in Circular Conduit Heat Transfer to and from Turbulent Flow in Circular Conduit Heat-Transfer Correlations for Flow in Noncircular Ducts Convection Heat Transfer in Flows Past Immersed Bodies Boundary-Layer Flow Turbulent Flow over Flat Plate Flow Past Various Two-Dimensional Bodies Flow Past a Bank of Tubes Flow Past a Sphere Natural-Convection Systems Natural Convection on a Vertical Surface: Laminar Flow Natural Convection on a Vertical Surface: Transition and Turbulence Natural Convection on an Inclined Flat Plate Natural Convection on a Horizontal Flat Surface Natural Convection on Cylinders Natural Convection around Spheres and Blocks Natural Convection about an Array of Fins Combined Forced- and Natural-Convection Systems Heat Exchangers Double-Pipe Heat Exchangers Shell-and-Tube Heat Exchangers Effectiveness-Number of Transfer Units Method of Analysis Crossflow Heat Exchangers Efficiency of a Heat Exchanger Condensation and Vaporization Heat Transfer Condensation Heat Transfer Boiling Heat Transfer Introduction to Radiation Heat Transfer Electromagnetic Radiation Spectrum Emission and Absorption at the Surface of an Opaque Solid Radiation Intensity Irradiation and Radiosity Radiation Laws Characteristics of Real Surfaces Radiation Heat Transfer between Surfaces View Factor Methods for Evaluating View Factors Radiation Heat Transfer within Enclosure of Black Surfaces Radiation Heat Transfer within an Enclosure of Diff use-Gray Surfaces Bibliography and Selected References Appendices Index

Heat transfer in nucleate boiling of mixtures

Abstract: An equation for predicting heat transfer coefficients for nucleate boiling of mixtures is derived. This expression contains only one adjustable parameter and the liquid-phase mass transfer coefficient. If the adjustable parameter is put equal to unity, comparison with the most recent data for the SF/sub 6/-CF/sub 2/-Cl/sub 2/ system gives a mass transfer coefficient of 2 X 10/sup -4/ m/s, which is of the same order of magnitude as the value obtained in physical and chemical absorption and in fallingfilm vaporization. The new equation corresponds particularly well with the experimental observation that the heat transfer coefficient is less dependent on the heat flux density and the pressure for nucleate boiling of mixtures than in the case of the pure components.

Heat transfer in circulating fluidized beds

Abstract: Design of heat transfer surfaces is critical to the operation and control of circulating bed reactors. For conditions of practical interest, surface-to- suspension heat transfer coefficients are usually of the order of 150-250 W/m2K. The particle convective component is generally of key importance and is controlled by the particle flux to the heat transfer surface. No existing correlations give consistent agreement with the available data. Radiation tends to be of considerable importance, especially for dilute systems operated at high temperature. Circulating beds are shown to exhibit many of the characteristics of conventional fluidized beds of fine particles: temperature uniformity in the axial direction, rapid heat-up or cool-down of particles to the bulk temperature and small intraparticle temperature gradients.

SCRAPED SURFACE HEAT EXCHANGERS.: A literature survey of flow patterns, mixing effects, residence time distribution, heat transfer and power requirements.

Abstract: In this literature survey flow patterns, mixing effects, heat transfer and power required for rotation in scraped surface heat exchangers (SSHE) are thoroughly discussed, with the emphasis on assumptions and results, while the principal design of different SSHEs are only briefly discussed. The flow patterns control the desired radial mixing and the undesired axial mixing. the flow in a SSHE can be regarded as the sum of an axial flow and a rotational flow. the axial flow is laminar and the rotational flow is laminar or vortical. With laminar flow the radial mixing is poor, which causes poor heat transfer and allows the axial flow profile to control the residence time distribution. the precise onset of vortical flow in a SSHE is hard to predict. the vortical flow makes the radial mixing very efficient, giving good heat transfer and perhaps plug flow behavior. However, vortical flow also causes axial mixing which reduces the apparent heat transfer coefficient and increases the residence time distribution. The power required to rotate the shaft and blades is mainly determined by the design of the blades.

A Theoretical Model of Localized Heat and Water Vapor Transport in the Human Respiratory Tract

Abstract: A steady-state, one-dimensional theoretical model of human respiratory heat and water vapor transport is developed. Local mass transfer coefficients measured in a cast replica of the upper respiratory tract are incorporated into the model along with heat transfer coefficients determined from the Chilton-Colburn analogy and from data in the literature. The model agrees well with reported experimental measurements and predicts that the two most important parameters of the human air-conditioning process are: 1) the blood temperature distribution along the airway walls, and 2) the total cross-sectional area and perimeter of the nasal cavity. The model also shows that the larynx and pharynx can actually gain water over a respiratory cycle and are the regions of the respiratory tract most subject to drying. With slight modification, the model can be used to investigate respiratory heat and water vapor transport in high stress environments, pollutant gas uptake in the respiratory tract, and the connection between respiratory air-conditioning and the function of the mucociliary escalator.

Bulk transfer coefficient over a snow surface

Abstract: The drag coefficient C D and the bulk transfer coefficient for sensible heat C H over a flat snow surface were determined experimentally. Theoretical considerations reveal that C D depends on the friction velocity u * as well as on the geometrical roughness h of the snow surface. It is found that C D increases with increasing u * and/or h. The dependency of C H on u * and h is so small that it is possible to consider C H as a constant for practical purposes: C H, 1 = 2.0 × 10−3 for a reference height of 1 m. The bulk transfer coefficient for water vapor is estimated at C E, 1 = 2.1 × 10−3 for a reference height of 1 m.

Heat Transfer from a Rarefied Plasma Flow to a Metallic or Nonmetallic Particle

Abstract: Heat transfer from a plasma flow to a metallic or nonmetallic spherical particle is studied in this paper for the extreme case of free-molecule flow regime. Analytical expressions are derived for the heat flux due to, respectively, atoms, ions, and electrons and for the floating potential on the sphere exposed to a two-temperature plasma flow. It has been shown that the local or average heat flux density over the whole sphere is independent of the sphere radius and approximately in direct proportion to the gas pressure. The presence of a macroscopic relative velocity between the plasma and the sphere causes substantially nonuniform distributions of the local heat flux and enhances the total heat flux to the sphere. The heat flux is also enhanced by the gas ionization. Appreciable difference between metallic and nonmetallic spheres is found in the distributions along the oncoming flow direction of the floating potential and of the local heat flux densities due to ions and electrons. The total heat flux to the whole sphere is, however, almost the same for these different spheres. For a fixed value of the electron temperature, the heat flux decreases with increasing temperature ratio Te/Th.

Hyperbolic heat conduction with temperature-dependent thermal conductivity

Abstract: Hyperbolic heat conduction in a semi‐infinite slab with temperature‐dependent thermal conductivity is studied numerically, and the results are compared with those obtained from the classical parabolic equation for the following cases: (a) constant applied temperature at x=0.0, (b) constant applied heat flux at x=0.0, and (c) a pulsed heat source released instanteously at t=0.0 in the region 0.0≤x≤Δx adjacent to an insulated boundary. In addition to changing the temperature profiles, the nonlinear thermal conductivity also altered the speed of the thermal front. An increase in the thermal conductivity increased the wave speed, while a decrease in the thermal conductivity decreased the wave speed.

Calculation of Heat and Mass Transfer Coefficients in a Packed Tower Operating With a Desiccant-Air Contact System

Abstract: Packed towers can be used for solar regeneration of aqueous solutions and dehumidification of air using aqueous solutions. These processes involve simultaneous heat and mass transfer with heat effects. In order to design a packed tower for aqueous solution-air contacting operations, heat and mass transfer coefficients for each phase are required. For the present study, aqueous calcium chloride solution is used; ceramic Raschig rings and Berl saddles are used as the packing materials. In this paper air phase transfer coefficients are correlated with flow rates of air and liquid and the temperature of air, whereas liquid phase coefficients are correlated with rates of air and liquid flow, and the temperature and concentration of the liquid.

Determination of heat transfer coefficients during water cooling of metals

Abstract: The heat transfer coefficients for various cooling methods were investigated. Copper, aluminium, and nickel billets were heated and then subjected to cooling by water spray systems and immersion in water and mixtures of water and organic agents. The temperature close to the surface was measured and used for the calculation of the heat transfer coefficient by the implicit finite difference method. The results yielded a defined relation between the heat transfer coefficient and surface temperature, thermophysical material properties, and the intensity of spray cooling or the concentration of the organic agent in the bath. Using this data, a means for analytically formulating the heat transfer coefficient was obtained, enabling easy calculation to be made of the temperature field during quenching or cooling in continuous casting.MST/154

Scaling of Plain and Externally Finned Heat Exchanger Tubes

Abstract: Etude experimentale de la variation des coefficients de transfert de chaleur d'un tube de cuivre, d'un tube d'acier doux et d'un tube d'acier a ailettes externes dans des conditions d'entartrage par une solution de carbonate de calcium soumis a un flux thermique constant pendant des periodes de 70 h. Presentation de l'influence de la vitesse de l'ecoulement sur la vitesse d'entartrage pour les 3 tubes et comparaison des resultats experimentaux avec le modele de Hasson

Effects of random horizontal variations in radiogenic heat source distribution on its relationship with heat flow

Abstract: Lateral conduction resulting from variations in the radiogenic heat generation is known to modify the heat flow-heat generation relation and to bias the evaluation of thickness of radiogenic heat sources. In this paper a statistical approach is used to account for a random horizontal variation in radiogenic heat sources, whereas their vertical variation is simulated by simple models. Relationships between spectral densities and autocorrelation functions of heat generation and heat flow are obtained. When the horizontal scale length of heat generation distribution is not much larger than the vertical one, lateral heat conduction modifies drastically the statistical properties of heat flow distribution, and the apparent thickness obtained from the heat flow-heat generation plot is highly reduced. The procedure is applied to a set of actual heat flow and heat generation data recorded over New Hampshire, U.S.A. Heat production data and especially heat flow data are affected by different types of noise and errors which can be analyzed through their autocorrelation functions. The depth scale of heat generation deduced empirically does not seem to have much relation with any geophysical dimension.

A Comprehensive Examination of Heat Transfer Correlations Suitable for Reactor Safety Analysis

Abstract: Fuel sheath temperatures in water-cooled nuclear reactors are usually near the saturation temperature of water. However, during an accidental increase in power, or a decrease in flow and pressure, deterioration in heat transfer is possible. It occurs when the surface temperature increases to such a high level that the heated surface can no longer support continuous liquid contact. This phenomenon is usually referred to as the boiling crisis (or dryout) and the corresponding heat flux as the critical heat flux (or CHF). The boiling crisis is characterized by either a sudden rise in surface temperature, caused by the heated surface being covered by a stable vapor film (film boiling), or by small surface temperature spikes, corresponding to the appearance and disappearance of dry patches (transition boiling).

Proceedings of the eighth international heat transfer conference

Abstract: This book presents the papers given at a conference on heat transfer. Topics considered at the conference included numerical techniques and modeling, measurement techniques, conduction and thermal insulation, thermal radiation, combustion, internal forced convection, external forced convection, jets, wakes, film cooling, natural and mixed convection, natural convection in confined spaces, vapor condensation, freezing, melting, evaporation, interfacial phenomena, pool boiling, flow boiling, two-phase flow, nuclear reactor heat transfer, particulates and porous materials, heat exchangers, heat transfer augmentation, and special applications.