In this paper a technique for measuring the bidirectional reflectivity of mirrors is presented. An experimental setup is described which allows one to measure the reflecting characteristics at small angles of scattering. These reflectivities are approximated by an exponential relation.
In this paper the results of an investigation into condensation heat transfer of quiescent steam on vertical smooth and profiled tubes with annular grooves are presented. The film REynolds number varied 20 to 3000, the Pradtl number from 1.14 to 1.77. The enhancement of heat transfer during steam condensation on profiled tubes was observed in the all regimes under investigation. Visual observations and photographic recording of condensation revealed a qualitative difference between the condensate film flows on the vertical profiled tube as compared with the smooth one.
This paper reports that heat transfer from a wire operating in crossflow of air at very low Reynolds numbers (Re = 0 to 0.8) was measured. It was found that the behavior of Nu = f(Re) over this range differs strongly from that under free convection conditions. The behavior of Nu = f(Re) at Re {lt} Re{sub r} = 0.05 can be represented by trinomial with constant coefficients, whereas at Re {gt} Re{sub r} the data are best correlated by a binomial equation with variable coefficients which are functions of Re. The effect of free convection can be corrected for by defining Nu{sub 0} as a function of Ra. The effect of variability of physical properties of the flow on the coefficient of heat transfer of the wire is accounted for quite well by employing the log-mean temperature as the reference temperature.
The influence of a number of disturbing factors on the structure of a swirled jet is investigated; great attention is paid to the analysis of turbulent flow characteristics.
This paper describes the variation of the local heat transfer coefficients in the case of combined flow in a vertical pipe, in which forced and free convection act in the same direction, but heat load is varied. The distribution of heat transfer coefficients along the pipe proved to vary with the heat load. At high loads these coefficients are unstable along the pipe even when the effect of thermogravitational forces is low. In addition, certain heat transfer modes, which were not observed in the case of constant physical properties of the flow, occur in the range in which the effect of these forces is moderate. The authors found a general similarity of the heat transfer behavior at different heat loads. The experimental data for the entire range of heat loads were interpreted in terms of the relevant parameters over a broad range of the effect of the thermogravitational forces.
This paper presents experimental results on heat transfer for the cases of impulsively increasing and constant temperatures of the heat transfer fluid. It is established that a temperature increase of the heat transfer fluid is accompanied by a complex of effects: thermal and hydrodynamic unsteadiness and nonisothermicity. It is shown that the heat transfer coefficients decrease by a factor of two and more in comparison with standard quasi-steady values. The effect of a negative longitudinal pressure gradient leads to an attenuation of unsteadiness effects and to a decrease in the heat transfer efficiency in convergent channels.
This paper presents the results of an experimental and computational investigation into the distributions of velocity components, turbulence intensity and of the passive impurity concentration. Satisfactory agreement between the results of calculations and experiments is obtained. The effect of such geometrical parameters as the angle at which the jet swirl in opposing directions and of the degree of channel blocking on the rate of transfer processes in the recirculating zone is investigated. A correlation is derived which connects the mass transfer factor with the parameters of the front device.
Thermal calculation of industrial combustion chambers, based on the assumption that heat transfer in them occurs primarily by radiation, is well understood. Further progress in this area is, however, needed in order to be able to allow for the burnup of the fuel and its aerodynamics in the furnace. The authors' mathematical modeling of furnace processes is based on conservation laws for the time-averaged density, the three velocity components, the energy of turbulence, the enthalpy and concentrations. The authors have simplified the model of the combustion mechanism to a single-stage process of gross oxidation of the fuel. In this paper the authors present the calculations for the combustion of methane, assuming heat flux distribution was calculated in the one-dimensional, but complete approximation.
In this paper equations for predicting the zone of onset of nucleate boiling in pipes are derived. The analytically predicted heat flux densities are compared with experimental data and are found to be in satisfactory agreement.
This paper reports on the spectral luminosity and absorptivity of burning magnesium particles at wave lengths ranging form 0.28 to 32 {mu}m that are determined experimentally; the contribution to the total radiation flux from different zones of a burning particle and the applicability of optical pyrometry methods to two-temperature sources are ascertained; the efficiency of absorption of fine-dispersed magnesium oxide particles at combustion temperatures is measured.
Navier-Stokes and energy equations, supplemented by the Prandtl-Kolmogorov turbulence model of the second type, are solved numerically by the familiar finite-difference method. It was found in the course of the numerical analysis that modifications of the {kappa}-{epsilon} model with wall functions produce flow descriptions superior to those derived from the standard model. The calculations were performed for longitudinal flow of air over a circular cylinder and a plate. The velocity in the recirculatory flow produced by flow separation from the leading edge of the body averages 40 percent of the free-stream velocity. At 10{sup 3} {lt} Re {lt} 10{sup 5}, the length of the separation bubble reaches its asymptotic value of about 1.5d (Tu {le} 1 percent). For flow over a plate, the values of these parameters are 30 percent and 3.5h, respectively. When the inlet Tu is increased to 10 percent, the length of the separation bubble because of 0.85d, and when {Lambda} is increased from 0.1 to 0.4, the bubble length drops to 0.75d. The decrease of Tu along the pipe is demonstrated numerically. The predicted values of the average flow and heat transfer parameters fit the experimental results published in the paper.
In this paper, the mechanisms of self-excitation of thermoacoustic vibrations in two-phase bubble flows are described. It is shown that a theory of this process must take into consideration the work performed by bubbles traveling in the acoustic wave. The results of the theory herein developed agree with previous experimental data of the author.
This paper presents numerical models of conjugate heat and mass transfer in ducts, in which the flow is described by the familiar, time-averaged two-dimensional Navier-Stockes equations. The equations modeled are those of continuity, of the two velocity components, of the kinetic energy of turbulence, of the rate of dissipation of the kinetic energy, of the enthalpy and of the concentration of the reactants. The above set of equations is complemented by functional relationships expressing the dependence of thermophysical properties of the fluid on the temperature, pressure and reactant concentrations, as well by the temperature dependence of the properties of the reactor walls. The heating of the flow by radiation from the reactor walls is corrected for in the formulation of the problem in terms of a one-dimensional approximation. The computations were performed for three cylindrical reactors with different inside diameters and different wall thicknesses. The quantitative results illustrating the contributions of conjugate heat and mass transfer are presented. The effects of radiation and chemical kinetics on heat transfer in the reactors are analyzed in the case of pyrolysis of methane. It appears that the authors' procedure for evaluating conjugate problems of heat and mass transfer can be applied to analysismore » of a broad range of practical problems.« less
In this paper turbulent flow in the boundary layer of a convergent nozzle is considered. On the basis of the Prandtl two-layer model expressions are obtained for determining the relative laws of friction, heat transfer, velocity and enthalpy profiles taking into account the mutual effect of such disturbing factors as nonisothermicity, compressibility and a negative pressure gradient.
In this paper, a mathematical model and certain results of numerical analysis of drying and pyrolysis of pulverized low-ash brown coal at high heat input rates are presented. It is shown that a high gage pressure exists in coal particles, and is most probably responsible for their breakdown to dust during the drying stage.
In this paper the mechanism of transition boiling and of the film boiling crisis is set out and the structural form of calculational relations is obtained. Empirical computational relations are presented for determining the heat flux and the boundaries of transition boiling, the mean time of wall contact with the liquid and vapor as well as the temperature of the film boiling crisis.
In this paper, the test unit, burners and technique of simulating fuel-bound nitrogen are described, as are the errors of the experiments. The experiments involved injecting water or recycled flue gases into combustion chambers where diesel fuel with FBN (fuel-bound nitrogen) contents of 0 and 0.5 to 0.65 percent was burned with air, and measuring the decrease in NO{sub x} content of the flue gases, the authors found that injection of water or flue gases increased the percentage of fuel-bound nitrogen converted to oxides, but that in some cases the NO{sub x} concentration in flue gases dropped. The flame temperature proved to be the factor controlling the NO{sub x} concentration in flue gases, and can be brought down to the same extent by water or flue-gas injection.
The paper presents the results of a computational-experimental study and makes recommendations on the calculation of heat transfer and hydraulic resistance of saturated and superheated vapors of different liquids condensing in vertical tubes and coils. A procedure is suggested for generalizing the local heat transfer with the use of the film thickness as the determining linear dimension as well as providing a technique for generalizing the mean condensation heat transfer in tubes and coils. Single relations are obtained to calculate hydraulic resistances in wide ranges of geometrical and operational parameters.
In this paper experimental and analytic results on high-temperature heat transfer to liquid n-paraffins (n-octane and n-nonane) flowing in cylindrical tubes are described. The experiments were performed in unit with replaceable tubes, to avoid possible carbon deposition on walls. The two-phase flow of these high-molecular weight hydrocarbons were also simulated numerically in the homogeneous-medium approximation. A fairly simple iterative prediction procedure was made possible by assuming that the degree of vaporization of the liquid in the tube is a linear function of the distance it travels. The kinetics of pyrolysis were incorporated into the model by means of semiempirical stoichiometric relationships.
In this paper a method is suggested for determining local and average irradiation coefficients for selective systems divided into volumetric and surface zones.
