Showing papers on "Heat transfer published in 1988"

Calculated thermal properties of metals.

Abstract: The thermal properties of the 14 nonmagnetic cubic metals through the 4d transition series are derived from first-principles electronic-structure calculations coupled with a Debye treatment of the vibrating lattice. Debye temperatures and Gr\"uneisen constants are derived from an analysis of the compressional characteristics of rigid-lattice binding curves and are used to define the contribution of the lattice vibrations to the free energy. A minimization of the resulting free energy with respect to volume yields temperature-dependent lattice separations and coefficients of thermal expansion. Theoretical values of cohesive energies, equilibrium lattice separations, bulk moduli, Debye temperatures, Gr\"uneisen constants, and coefficients of thermal expansion are derived directly from computed electronic-structure results. Good agreement with experiment is found for all computed quantities.

A four-layer model for the heat budget of homogeneous land surfaces

Abstract: The present model envisions the heat balance of a homogeneous land surface in terms of available energy, a set of driving potentials, and parameters for the physical state of the soil and vegetation. Two unique features of the model are: (1) the expression of the interaction of evaporation from the soil and from foliage by changes in the value of the saturation vapor pressure deficit of air in the canopy (the conclusions of this interaction being consistent with field observations); and (2) the treatment of sensible and latent heat exchange between the atmosphere and a soil consisting of two discrete layers.

Droplet vaporization model for spray combustion calculations

Abstract: The re-examination of the classical droplet vaporization model is made in order to develop the simple but sufficiently accurate calculation algorithm which can be used in spray combustion calculations. The new model includes the effects of variable thermophysical properties, non-unitary Lewis number in the gas film, the effect of the Stefan flow on heat and mass transfer between the droplet and the gas, and the effect of internal circulation and transient liquid heating. To evaluate the competing simplified models of the droplet heating, the more-refined, extended model of heat transfer within a moving circulating droplet is considered. A simplified, one-dimensional ‘effective conductivity’ model is formulated for the transient liquid heating with internal circulation. As an illustration, the dynamic and vaporization histories of the droplets injected into the steady and fluctuating hot air streams are analyzed.

Thermal properties of rocks

Abstract: All the important thermal properties of rocks can be estimated from the graphs and tables in this report. Most of the useful published data are summarized herein to provide fairly accurate evaluations of thermal coefficients and parameters of rocks for many engineering and scientific purposes. Graphs of the published data on common rocks and minerals were prepared to show the relationships of thermal conductivity with decimal solidity (one minus decimal porosity), water or air pore content, content of certain highly conducting minerals, and temperature. Tables are given of pressure effect on thermal conductivity of minerals and rocks, anisotropy of conductivity, thermal expansion, heat transfer, density, heat generation in rocks, and activation energies of conduction mechanisms in single crystals of minerals. A series of graphs show the specific heats of rock-forming minerals as a function of temperature; with these graphs the specific heat of a rock can be calculated from its mode as accurately as it can be measured. Calculations of conductivity, diffusivity, and thermal inertia of a rock from its mode are described. Discussions of radiative thermal conductivity, radioactive heat generation, and heat transfer in rocks are provided.

Three-dimensional radiative heat-transfer solutions by the discrete-ordinates method

Abstract: Radiative heat transfer in a three-dimensional participating medium was predicted using the discrete-ordinates method. The discrete-ordinates equations are formulated for an absorbing, anisotropically scattering, and re-emitting medium enclosed by gray walls. The solution strategy is discussed and the conditions for computational stability are presented. Several test enclosures are modeled. Results have been obtained for the S2, S4, S6, and S8 approximation s that correspond to 8, 24, 48, and 80 fluxes, respectively, and are compared with the exact-zone solution and the P3 differential approximation. Solutions are found for conditions that simulate absorbing media and isotropically and anisotropically scattering media. Solution accuracy and convergence are discussed for the various flux approximations. The S4, S6, and S8 solutions compare favorably with the other methods and can be used to predict radiant intensity, incident energy, and surface heat flux. A an bn B C E G / L n q r S x y z a /U,,£,TJ p a a © V Nomenclature = north-south areas, m2 = coefficients of a Legendre series = coefficients of a modified Legendre series = east-west areas, m2 = front-back areas, m2 = emissive power ( = aT4), W/m2 = incident energy, /4w/d6, W/m2 = radiant intensity, W/(m2 • Sr) = enclosure dimension, m = unit normal = heat flux, W/m2 = position vector, m = source term, W/m3 = volume of pth control volume, m3 = weight function in a direction - m (fractional area of a unit sphere) = coordinate, m = coordinate, m = coordinate, m — finite-difference weighting factor = extinction coefficient, a -f K,m~l = surface emittance = absorption coefficient, m"1 = ordinates p = cos0, £ = sin0 sin , TJ = sinG cos = outgoing direction of radiation = phase function = surface reflectance = scattering coefficient, m"1 = Boltzmann's constant, 5.669 X 1(T 8 W/(m2

On the Theory of Slow Combustion

Abstract: Publisher Summary Physical theories of slow combustion are usually based on the conception that the transfer of heat to the unburned gaseous mixture from the products of combustion—heated owing to the reaction—is a result of simple thermal conduction. The thickness of the combustion layer separating the region of the initial mixture from that of the products of combustion is then determined completely by thermal conduction in the gas and by purely chemical properties of the given reaction. It is essential that this thickness is independent of the characteristic dimensions of the problem. The characteristic dimensions of the problem to be large in comparison with the thickness of the combustion layer are assumed in the chapter. Then, in determining the hydrodynamical movement of the gas accompanying the combustion process, the whole transition layer is considered as a surface separating the burned and unburned gas. In the considered thermal conduction regime of slow combustion, the rate of propagation of the combustion is certainly small in comparison with the velocity of sound.

Heat transfer and friction characteristics in rectangular channels with rib turbulators

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

Structure of a heat pipe

Abstract: A structure of a loop-type heat pipe is disclosed in which a heat carrying fluid, preferably a bi-phase non-condensative fluid, circulates in a loop form in itself under its own vapor pressure at a high speed within an elongate pipe so as to repeat vaporization and condensation, thus carrying out a heat transfer. A structure of the loop-type heat pipe includes the elongate pipe, both ends thereof being air-tightly interconnected to form a loop-type container, the heat carrying fluid, at least one heat receiving portion and at least one heat radiating portion, both being placed at given portions of a elongate pipe, and at least one check valve for limiting a stream direction of the heat carrying fluid. A check valve(s) propels and amplifies forces generated by the heat carrying fluid and its vapor to move toward the stream direction limited by the check valve(s) so that the heat carrying fluid circulates in the stream direction through the closed-loop passage defined by the elongate pipe at the high speed, repeating vaporization at the heat receiving and radiating portions.

Forced-convection, liquid-cooled, microchannel heat sinks

Abstract: A microchannel heat sink used to cool a high power electronic device such as an integrated circuit comprising a plurality of channels in close thermal contact to the integrated circuit and through which a liquid is passed to create either a developing laminar flow or a turbulent flow. The turbulent flow may be either developing or fully developed. The heat sink features a compensation heater surrounding the integrated circuit and heated at the same rate as the integrated circuit to thereby provide a more uniform temperature at the perimeter of the integrated circuit.

Fluid flow due to a stretching cylinder

Abstract: The fluid flow outside of a stretching cylinder is studied. The problem is governed by a third‐order nonlinear ordinary differential equation that leads to exact similarity solutions of the Navier–Stokes equations. Because of algebraic decay, an exponential transform is used to facilitate numerical integration. Asymptotic solutions for large Reynolds numbers compare well with numerical results. The heat transfer is determined.

Turbulent Transport on the Endwall in the Region Between Adjacent Turbine Blades

Abstract: The complex three-dimensional flow in the endwall region near the base of a turbine blade has an important impact on the local heat transfer. The initial horseshoe vortex, the passage vortex, and resulting corner vortices cause large variations in heat transfer over the entire endwall region. Due to these large surface gradients in heat transfer, conventional measurement techniques generally do not provide in accurate determination of the local heat transfer coefficients. In the present study the heat/mass transfer analogy is used to examine the local transport coefficients for two different endwall boundary layer thicknesses and two free-stream Reynolds numbers. A linear turbine blade cascade is used in conjunction with a removable endwall plate. Napthalene (C{sub 10}H{sub 8}) is cast into a mold on the plate and the rate of naphthalene sublimation is determined at 6,000+ locations on the simulated endwall by employing a computer-aided data acquisition system. This technique allows one to obtain detailed contour plots of the local convection coefficient over the entire endwall. By examining the mass transfer contours, it is possible to infer information on three-dimensional flow in the passage between the blades. Extremely high transport coefficients on the endwall indicate locations of potential overheating and failuremore » in actual turbine.« less

Heat transfer from a flat surface to an oblique impinging jet

Abstract: Experiments are conducted to determine the heat transfer to a jet impinging at different oblique angles to a plane surface The main portion of the test plate contains a composite sheet of temperature-sensitive liquid crystal, which is sandwiched between a thin metallic-foil heater and a specially designed liquid bath The results indicate a displacement of the peak heat transfer from the geometric center of the jet origin, the displacement being a function primarily of impingement angle Contours of constant heat transfer coefficient are obtained and correlated with an empirical equation that permits determination of average Nusselt numbers over areas of interest

A Two-Equation Model for Heat Transport in Wall Turbulent Shear Flows

Abstract: A new proposal for closing the energy equation is presented at the two-equation level of turbulence modeling. The eddy diffusivity concept is used in modeling. However, just as the eddy viscosity is determined from solutions of the k and {var epsilon} equations, so they eddy diffusivity for heat is given as functions of temperature variance t{sup 2}, and the dissipation rate of temperature fluctuations {var epsilon}{sub t}, together wtih k and {var epsilon}. Thus, the proposed model does not require any questionable assumptions for the turbulent Prandtl number. Modeled forms of the t{sup 2} and {var epsilon} equations are developed to account for the physical effects of molecular Prandtl number and near-wall turbulence. The model is tested by application to a flat-plate boundary layer, the thermal entrance region of a pipe, and the turbulent heat transfer in fluids over a wide range of the Prandtl number. Agreement with the experiment is generally very satisfactory.

Microchannel heat sinks

Abstract: Microchannel heat sinks useful in the cooling of diode laser arrays have been fabricated from InP and exhibit a thermal resistance as low as 0072 C/(W/sq cm), corresponding to the dissipation of heat loads in excess of 1 kW/sq cm and representing a two-orders-of-magnitude reduction of levels achievable by current methods The pumping power required to force liquid coolants through microchannel heat sinks can be kept as low as as 10 W/sq cm Attention is presently given to a thermal- and fluid-performance model for these heat sinks, as well as to illustrative examples of microchannel fabrication for both InP and aluminum 19 references

Thermal and stress analysis of semiconductor wafers in a rapid thermal processing oven

Abstract: Results are presented from studies of heat transfer in a rapid thermal processing (RTP)-type oven used for several semiconductor wafer processes. These processes include: (1) rapid thermal annealing; (2) thermal gradient zone melting; and (3) lateral epitaxial growth over oxide. The heat transfer studies include the measurement of convective heat transfer in a similar apparatus, and the development of a numerical model that incorporates radiative and convective heat transfer. Thermal stresses that are induced in silicon wafers are calculated and compared to the yield stress of silicon at the appropriate temperature and strain rate. Some methods for improving the temperature uniformity and reducing thermal stresses in the wafers are discussed. >

Solutions of the bio-heat transfer equation.

Abstract: A solution of the bio-heat transfer equation for a 'step-function point source' is presented and discussed. From this basic solution one can, in principle, obtain the temperature field resulting from a general heat source distribution by superposition. As an example, the method is used to calculate the temperature on the body surface at a point where therapeutic ultrasound is applied. Comparison is made with experimental results recently published by Williams and co-workers.

Heat Transfer During Melting and Solidification of Metals

Abstract: Discussion relative aux processus de transfert de chaleur fondamentaux lors de la transformation de phase solide-liquide et comparaison entre donnees experimentales et previsions de modeles mathematiques numeriques. Role important joue par l'ecoulement du liquide induit par la poussee. Identification des problemes necessitant des recherches

Thermal Radiation in Packed and Fluidized Beds

Abstract: Etude du transfert radiatif dans les lits fluidises ou a garnissage. Presentation des techniques experimentales existantes pour la determination des proprietes radiatives. Analyse de l'interaction du rayonnement avec d'autres modes de transfert de chaleur