Showing papers on "Heat transfer published in 1982"

Second-Law Analysis in Heat Transfer and Thermal Design

Abstract: This review is devoted to the introduction of second-law analysis in heat transfer and entropy generation minimization in thermal design. The presentation proceeds from the derivation of the Gouy-Stodola theorem, the basis for entropy generation minimization in the conceptual design of heat transfer equipment. Appropriate analytical tools, such as the entropy generation number, are devised for the task of estimating the destruction of available work in the processes involving heat transfer. However, the entropy generation number concept is considerably more general, since it can be used to quantitatively describe the degree of irreversibility of engineering components and processes which do not draw their irreversibility solely from heat transfer. The examples considered in this article range from the irreversibility associated with some of the most fundamental convective heat transfer processes to the minimum irreversibility design of one-dimensional insulations such as the main counterflow heat exchanger of a helium liquefaction plant.

Heat capacity of water at extremes of supercooling and superheating

Abstract: : Low temperature heat capacities for water and deuterium oxide have been remeasured using different sample preparation and data analysis procedures from those used in the original studies of this anomalous region. Self-consistent results have been obtained with reproducibilities of 1%. Comparisons are made with the behavior in the superheated region at 1 atm pressure calculated from a refined equation of state by Haar et al. It appears that the kinetic metastability limit of the liquid (nucleation terminated) at both hot and cold extremes may be reached at the same value of the liquid heat capacity.

Thermo-plastic instability in simple shear

Abstract: A theoretical description of thermo-plastic instability in simple shear is presented in a system of equations describing plastic deformation, the first law of thermodynamics and Fourier's heat transfer rule. Both mechanical and thermodynamical parameters influence instability and it is shown that two different modes of instability may exist. One of them is dominated by thermal softening and has a characteristic time and length, connected to each other by thermal diffusion.A criterion combining thermal softening, current stress, density, specific heat, work-hardening, thermal conductivity and current strain rate is obtained and practical implications are discussed.

Ignition and Combustion of Boron Particles and Clouds

Abstract: PE Nomenclature = heat capacity of the gases = boron heat capacity = oxide heat capacity = heat absorbed by reaction of B2O3 with H2O = heat absorption associated with surface reaction(s) (per unit mass of boron) = heat of vaporization of B2O3 = particle burning mass flux = heat release associated with gas-phase reaction(s) (per unit mass of oxygen) = heat release of B + B2O3 reaction = particle radius = molar rate of boron consumption = molar evaporation rate of boric oxide = molar rate of removal of B2O3 by water reaction = time = particle temperature = effective surroundings radiation temperature = particle surface temperature — ambient temperature = oxide layer thickness = ambient oxygen mass fraction = surroundings absorptivity = particle emissivity = boron density = boric oxide density = density-diffusivity product = Stef an-Boltzmann constant

An efficient algorithm for analysis of nonlinear heat transfer with phase changes

Abstract: A new, simple and effective finite element procedure is presented for the practical solution of heat transfer conditions with phase changes. In this method, a fixed finite element mesh is employed, and a relatively coarse finite element mesh and large time step can be used in the incremental solution. The results of various numerical studies using the algorithm are presented that demonstrate the effectiveness of the procedure.

Human Body Temperature: Its Measurement and Regulation

Abstract: The terminology used in thermal physiology is examined, and principles of heat transfer are discussed, taking into account heat quantity, heat flux, temperature, pressure, quantities used in physiology, a number of common definitions, the equivalence between different forms of energy, the release of potential energy in living tissues, heat transfer without change of state, and heat transfer with change of state. Temperature and humidity measurement are considered along with man and his environment, the temperature distribution in the systems and tracts of the human body, physiological changes affecting the temperature distribution, problems of temperature regulation, questions of heat loss and conservation, acclimatization to heat and cold, and disorders of thermoregulation. Attention is given to possible thermal imaging applications, causes of temperature irregularities in the head and neck, common causes of increased temperatures of upper limbs, and thermography in disease. 193 references.

Pool Boiling Heat Transfer From Enhanced Surfaces to Dielectric Fluids

Abstract: Pool boiling heat-transfer measurements were made using a 15.8 mm o.d. plain copper tube and three copper enhanced surfaces: a Union Carbide High Flux surface, a Hitachi Thermoexcell-E surface and a Wieland Gewa-T surface. The dielectric fluids were Freon-113 and Fluorinert FC-72, a perfluorinated organic compound manufactured to cool electronic equipment. Data were taken at atmospheric pressure, and at heat fluxes from 100 W/m/sup 2/ to 200,000 W/m/sup 2/. Prior to operation, each test surface was subjected to one of three aging procedures to observe the effect of surface past history upon boiling incipience. For Freon-113 the enhanced surfaces showed a two to tenfold increase in the heat-transfer coefficient when compared to a plain tube, whereas for FC-72 an increase of two to five was measured. The High Flux surface gave the best performance over the range of heat fluxes. The Gewa-T surface did not show as much of an enhancement at low fluxes as the other two surfaces, but at high fluxes its performance improved. In fact, it was the only surface tested which delayed the onset of film boiling with FC-72. The degree of superheat required to activate the enhanced surfaces was sensitive to both past history ofmore » the surface and to fluid properties.« less

A mathematical model to calculate temperature distributions in human and rabbit eyes during hyperthermic treatment

Abstract: A mathematical model based on the finite difference method has been developed to calculate transient and steady state temperature distributions in normal unexposed human and rabbit eyes, and human and rabbit eyes heated by various heating techniques. The normal steady state temperature distributions in human and rabbit eyes are given. The model has been experimentally fitted to data obtained from measurements on rabbit eyes. The heat transfer from the choroid to the body core temperature of the rabbit is described by the heat transfer coefficient hs = 65 W m-2 degrees C-1, and from the cornea to the surrounding air temperature by hc = 20 W m-2 degrees C-1. The thermal conductivity and the specific heat of the lens of the rabbit eye were determined empirically to be 0.40 W m-1 degree C-1 and 3.0 J g-1 degree C-1 respectively. The thermal properties of the vitreous humour were taken to be equal to the thermal properties of water.

Stationary nonequilibrium states by molecular dynamics. Fourier's law

Abstract: We have developed a technique to produce stationary nonequilibrium states in a molecular-dynamics system; this method is based on the introduction of stochastic boundary conditions to simulate the contact with a thermal wall. The relaxation times involved in such contact are short enough (\ensuremath{\sim}${10}^{\ensuremath{-}11}$ sec) to make the technique suitable for computer experiments. The method allows the simulation of bulk properties in a system coupled with a heat reservoir and the study of the local thermodynamical equilibrium. Furthermore, it gives a physical description of the heat transfer near a thermal wall. The method has been applied to simulate high thermal gradients in a region of dense fluids ranging from the gas-liquid coexistence line to the freezing line, to check the validity of the linear thermal response (Fourier's law). We have found that the linear region extends at least up to gradients of the order of 1.8\ifmmode\times\else\texttimes\fi{}${10}^{9}$ K/cm for argon. In the bulk region where boundary effects are negligible we have verified the validity of the local equilibrium hypothesis for all simulated gradients.

Experimental Investigation of Natural Convection in Partitioned Enclosures

Abstract: Natural convection heat transfer within a two-dimensional, partitioned enclosure of aspect ratio 1 was investigated experimentally using a Mach-Zehnder interferometer. The vertical walls were maintained isothermal at different temperatures, while the horizontal walls and the partitions were insulated. Local and average heat-transfer coefficients were determined for the air and carbon dioxide filled enclosures both with and without partitions for Grashof numbers between 1.7×105 and 3.0×106 . Good agreement was found between the results in the present study for the nonpartitioned enclosure and those previously published. The partitions were found to significantly influence the convective heat transfer. Observations of the interferometric fringes indicated that the core region is unsteady, with the unsteadiness occasionally affecting the flow along the vertical isothermal walls, beginning at Grashof numbers as low as 5×105 .

Non-Newtonian Fluids in Circular Pipe Flow

Abstract: Publisher Summary This chapter focuses on heat transfer behavior of viscoelastic fluid in turbulent pipe flow Although the asymptotic values of the heat transfer and friction factor can be calculated, there exist no firm criteria for determining whether asymptotic conditions exist Predictions of the intermediate values of the friction and heat transfer are not yet possible, even if the rheology and the thermal properties of the aqueous polymer solution are known To deals with the problems, the Weissenberg or Deborah number has to be taken into account The behavior of viscoelastic fluids flowing turbulently in noncircular channels or over external surfaces represents a relatively unexplored area of fluid mechanics Open channel flow of viscoelastic fluid is another interesting field currently being investigated The chapter concludes that to approach turbulent heat transfer behavior analytically, the usual and simplest method is to solve the uncoupled energy equation using the empirically determined velocity profile Hence, it is essential to understand the fluid mechanics of non-Newtonian fluids as well as the rheology

Heat-Transfer Augmentation in Rod Bundles Near Grid Spacers

Abstract: Heat-transfer augmentation by straight grid spacers in rod bundles is studied for single-phase flow and for post-critical heat flux dispersed flow. The heat transfer effect of swirling grid spacers in single-phase flow is also examined. Governing heat-transfer mechanisms are analyzed, and predictive formulations are established. For single-phase flow, the local heat transfer at a straight spacer and at its upstream or downstream locations are treated separately. The effect of local velocity increasing near swirling spacer is considered. For post critical heat flux (CHF) dispersed flow, the heat transfer by thermal radiation, fin cooling, and vapor convection near the spacer are calculated. The predictions are compared with experimental data with satisfactory agreement.

A numerical simulation of the D.C. continuous casting process including nucleate boiling heat transfer

Abstract: The steady-state thermal problem associated with the direct-chill continuous casting of A6063 aluminum cylindrical ingots is solved using the numerical finite element technique. Excellent correlation is demonstrated between the numerical model and experimental data from ingots cast at two different speeds. By application of the model, effective heat transfer coefficients are calculated as a function of vertical position on the outside surface of the ingot. It is shown that direct application of these coefficients to the modeling of different casting situations will produce substantial errors in the region in which heat transfer is by nucleate boiling. Using theories of nucleate boiling with forced convection and film cooling, a method is developed to calculate the external boundary conditions in the submold region of the ingot, thus making it possible for the first time to define explicitly all of the thermal boundary conditions associated with this casting configuration. These theories are incorporated into the numerical model, and a subsequent simulation shows excellent agreement with experimental data from a third ingot.

Thermal Convection in Non-Newtonian Fluids*

Abstract: Publisher Summary This chapter presents the field of thermal convection in non-Newtonian fluids. The thermal convection in external flows of inelastic fluids is relatively well understood in the chapter. Thermal convection in viscoelastic fluids has been studied only in a restricted way. An approximate correlating equation for mixed convection in external flows on non-Newtonian fluids is presented. The chapter explores the theoretical indications to show that there are likely to be tremendous advantages in adding drag-reducing polymers to impart viscoelastic properties to materials undergoing the process of thermal convection under turbulent conditions. The problem of buoyancy-induced secondary flow in heated horizontal tubes appears to be most challenging from a theoretical viewpoint. There are certain equations that correlate heat transfer data empirically, but the situation is not wholly satisfactory. The possibilities of oscillatory convection in viscoelastic fluids appear to exist under certain circumstances. The chapter concludes that thermal convection experiments are difficult to conduct, therefore there appears to be a massive generation of data correlating overall heat transfer coefficients with process variables but practically very little information on the velocity and temperature fields.

Hyperbolic heat transfer with reflection

Abstract: The non-Fourier model for heat transfer leads to a hyperbolic evolution problem describing the temperature solution. A one-dimensional case is considered for such a propagating heat wave reflected at a boundary. A primary goal is investigation of the effectiveness of numerical solution techniques for the case of a propagating heat front and the influence of different boundary conditions. Finite elements are employed in space and alternative time integration schemes are studied, including ordinary differential equation system integrators. The effect of solution “roughness” on the error and oscillations before and after reflection is examined and rates of convergence are numerically determined.