Showing papers on "Heat transfer coefficient published in 1983"
TL;DR: In this paper, the plate efficiency of an unglazed collector with a corrugated galvanised iron absorber was investigated and shown to improve the plate transfer ratio from 0.63 to 0.72 for a Reynolds number of 40 000.
239 citations
TL;DR: In this paper, a theoretical model of the combined conductive and radiative heat flow through fibrous insulating materials is presented and compared to experimental values of the thermal resistances of several sy...
Abstract: A theoretical model of the combined conductive and radiative heat flow through fibrous insulating materials is presented and compared to experimental values of the thermal resistances of several sy...
183 citations
TL;DR: In this paper, an experimental study was made of critical heat flux in a closed two-phase thermosyphon and the effects of inside diameter, heated length, working liquid, fill charge and inside temperature on the critical heat flow were investigated.
179 citations
TL;DR: In this paper, a correction factor which depends on the Knudsen number was introduced into the expressions for heat fluxes obtained previously based on the continuum approach, and the correction factor was shown to be stronger for smaller particles and it is also more pronounced for an Ar-H2 plasma.
Abstract: The Knudsen effect on heat transfer to a particle exposed to a thermal plasma is important for many practical situations experienced in plasma chemistry and plasma processing. This paper provides theoretical results of this effect based on the “heat conduction potential jump” approach. It is shown that a correction factor which depends on the Knudsen number must be introduced into the expressions for heat fluxes obtained previously based on the continuum approach. The Knudsen effect is stronger for smaller particles and it is also more pronounced for an Ar-H2 plasma (compared to Ar and nitrogen plasmas at the same temperature). Since the Knudsen effect depends on the surface temperature of a particle, calculation of particle heating becomes more complicated.
164 citations
TL;DR: In this article, a theoretical analysis was made of the different phenomena encountered and the assumptions involved in the calculation of the heat transfer rate to a single sphere under plasma conditions, and it was shown that if the integral mean thermal conductivity of the plasma is used in the evaluation of heat transfer coefficient, the Nusselt number for the conduction heat transfer between the plasma and the particle is equal to 2.0.
152 citations
TL;DR: In this paper, the efficiency of a radiative cooling panel is defined for horizontal surfaces with infrared-transparent covers, and plots of efficiency versus a dimensionless temperature difference are shown to be insensitive to variations in air temperature, wind speed and sky radiance.
143 citations
TL;DR: In this article, a 25 mm I.D. copper tube, tightly fitted with helical-wire-coil inserts of varying pitch (p), helix angle (x), and wire diameter (e), was used for heat transfer.
133 citations
TL;DR: In this paper, a theoretical and experimental study of heat flow and solid-state phase transformations during the laser surface hardening of 1018 steel was conducted, where a three-dimensional heat flow model was developed using the finite difference method.
Abstract: A theoretical and experimental study of heat flow and solid-state phase transformations during the laser surface hardening of 1018 steel was conducted. In the theoretical part of the study, a three-dimensional heat flow model was developed using the finite difference method. The surface heat loss, the temperature dependence of the surface absorptivity, and the temperature dependence of thermal properties were considered. This heat flow model was verified with the analytical solution of Jaeger and was used to provide general heat flow information, based on the assumptions of no surface heat loss, constant surface absorptivity, and constant thermal properties. The validity of each of these three assumptions was evaluated with the help of this heat flow model. In the experimental part of the study, on the other hand, a continuous-wave CO2 laser of 15 kW capacity was used in conjunction with a beam integrator to surface harden 1018 steel plates. The beam power and the travel speed of the workpiece were varied, and the onset of surface melting was determined. The configurations of the heat-affected zone observed were compared with those calculated using the heat flow model. The microstructure of the heat-affected zone was explained with the help of the calculated peak temperature, heating, and cooling rates.
123 citations
TL;DR: In this paper, an experimental study on the heat transfer performance of an inclined two-phase closed thermosyphon is described, where water and ethanol have been used as the working fluids.
118 citations
TL;DR: In this article, the authors investigate the heat transfer and fluid flow characteristics of arrays of heat-generating, block-like modules affixed to one wall of a parallel-plate channel and cooled by forced convection airflow.
116 citations
01 Jan 1983
TL;DR: In this paper, the authors present dynamic methods for studying heat and mass transfer in packed beds, including parameter estimation from tracer response measurements, fluid dispersion coefficients, diffusion and reaction in porous catalyst, particle-to-fluid mass, transfer coefficients, steady-state heat transfer thermal response measurements; unsteady-state Heat Transfer models; and particle tofluid heat transfer coefficients.
Abstract: This book presents dynamic methods for studying heat and mass transfer in packed beds. Topics considered include parameter estimation from tracer response measurements; fluid dispersion coefficients; diffusion and reaction in porous catalyst; particle-to-fluid mass; transfer coefficients; steady-state heat transfer thermal response measurements; unsteady-state heat transfer models; and particle-to-fluid heat transfer coefficients.
TL;DR: In this article, a composite consisting of a plastic sheet coated with liquid crystal, another sheet with a thin layer of a conducting material (gold or carbon), and copper bus bar strips were evaluated and found to provide a simple, convenient, accurate, and low-cost measuring device for use in heat transfer research.
Abstract: Commercially available elements of a composite consisting of a plastic sheet coated with liquid crystal, another sheet with a thin layer of a conducting material (gold or carbon), and copper bus bar strips were evaluated and found to provide a simple, convenient, accurate, and low-cost measuring device for use in heat transfer research. The particular feature of the composite is its ability to obtain local heat transfer coefficients and isotherm patterns that provide visual evaluation of the thermal performances of turbine blade cooling configurations. Examples of the use of the composite are presented.
TL;DR: In this paper, the effects of varying the spacing between the corrugated walls and of different fluid flow inlet conditions were determined experimentally for water flowing in a corrugation-wall duct.
TL;DR: In this article, a new method for predicting the variation of nucleate pool boiling heat transfer coefficients with composition for binary liquid mixtures is presented, where the rise in the local boiling point of the liquid adjacent to the heated surface caused by preferential evaporation of the volatile component has a limit at the peak nucleate heat flux.
TL;DR: Etude experimentale du transfert de chaleur et de la perte de charge dans une conduite rectangulaire aplatie munie de barres transversales adjacentes a une paroi a repartition periodique as discussed by the authors.
Abstract: Etude experimentale du transfert de chaleur et de la perte de charge dans une conduite rectangulaire aplatie munie de barres transversales adjacentes a une paroi a repartition periodique
Abstract: Etude experimentale dans une soufflerie a faible vitesse du transfert de chaleur dans l'ecoulement laminaire d'air a l'aval de gradins de 1,27-0,64 et 0,38 cm de haut. Mesure du champ de temperatures a l'aide d'un interferometre Mach-Zehnder. Etablissement d'une correlation pour le transfert de chaleur
TL;DR: In this paper, the authors measured the local heat transfer from a flat plate to arrays of impinging circular air jets and averaged numerically to obtain spanwise and streamwise-spanwise averaged heat transfer coefficients.
Abstract: Measurements are made of the local heat transfer from a flat plate to arrays of impinging circular air jets. Fluid from the spent jets is constrained to flow out of the system in one direction. Two different jet-to-jet spacings, 4 and 8 jet diameters, are employed. The parameters that are varied include jet-orifice-plate to impingement-surface spacing and jet Reynolds number. Local heat transfer coefficients vary periodically both in the flow direction and across the span with high values occurring in stagnation regions. Stagnation regions of individual jets as determined by local heat transfer coefficients move further in the downstream direction as the amount of crossflow due to upstream jet air increases. Local heat transfer coefficients are averaged numerically to obtain spanwise and streamwise-spanwise averaged heat transfer coefficients.
TL;DR: In this paper, two experiments have been conducted to study radiative heat transfer in light-weight fibrous insulations (LWFI), and the experimental results are compared with the theoretial values calculated according to the analytical models.
Abstract: Two experiments have been conducted to study radiative heat transfer in light-weight fibrous insulations (LWFI). The spectral extinction coefficients for a commercial LWFI have been measured via transmission measurements, and a guarded hot plate apparatus has been used to measure the radiant heat flux as well as the total heat flux in the insulation. The experimental results are compared with the theoretial values calculated according to the analytical models are useful in Part I of this paper. The comparisons reveal that the analytical models are useful in giving representative values for the radiative properties of typical LWFI. However, only qualitative agreements have been obtained for the heat transfer results.
01 Mar 1983
TL;DR: In this paper, scaling criteria for a natural circulation loop under single phase and two-phase flow conditions have been derived for a LOFT facility under one-dimensional area average forms, and preliminary conclusions on the feasibility of the facility have been obtained.
Abstract: Scaling criteria for a natural circulation loop under single phase and two-phase flow conditions have been derived. For a single phase case the continuity, integral momentum, and energy equations in one-dimensional area average forms have been used. From this, the geometrical similarity groups, friction number, Richardson number, characteristic time constant ratio, Biot number, and heat source number are obtained. The Biot number involves the heat transfer coefficient which may cause some difficulties in simulating the turbulent flow regime. For a two-phase flow case, the similarity groups obtained from a perturbation analysis based on the one-dimensional drift-flux model have been used. The physical significance of the phase change number, subcooling number, drift-flux number, friction number are discussed and conditions imposed by these groups are evaluated. In the two-phase flow case, the critical heat flux is one of the most important transients which should be simulated in a scale model. The above results are applied to the LOFT facility in case of a natural circulation simulation. Some preliminary conclusions on the feasibility of the facility have been obtained.
01 Oct 1983
TL;DR: In this paper, an equation for predicting heat transfer coefficients for nucleate boiling of mixtures is derived, which contains only one adjustable parameter and the liquid-phase mass transfer coefficient.
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.
TL;DR: In this article, the authors presented heat transfer measurements for free convection in a vertical annulus wherein the inner cylinder is at constant surface heat flux and the outer cylinder at constant temperatuare.
Abstract: Heat transfer measurements are presented for free convection in a vertical annulus wherein the inner cylinder is at constant surface heat flux and the outer cylinder is at constant temperatuare. Overall heat transfer data re corrected for thermal radiation in the annulus. Rayleigh numbers span the conduction, transition and boundary layer regimes of flow, and average heat transfer coefficients are obtained with air and helium as the working fluids. The range of Rayleigh number is 10/sup 3/
TL;DR: In this article, boundary layer solutions are presented to study the steady state heat transfer from a semi-infinite flat plate to a micropolar fluid, where boundary conditions of isothermal wall, constant surface heat flux and insulated wall with viscous dissipation effects have been treated.
TL;DR: In this article, a model of heat transfer in a coke-oven charge is presented, which uses, as submodels, the descriptions of the physical properties and chemical changes in coal during its decomposition to coke as given previously.
TL;DR: The Dundas Island polynya is a natural laboratory for the study of atmospheric turbulence and heat exchange between the Arctic Ocean and the atmosphere in extreme (20-34°C) sea-air temperature differences as mentioned in this paper.
Abstract: The Dundas Island polynya is a natural laboratory for the study of atmospheric turbulence and heat exchange between the Arctic Ocean and the atmosphere in extreme (20–34°C) sea-air temperature differences. A sonic anemometer-thermometer measured wind and temperature fluctuations at a height of 4.4 m at the downwind edge, where turbulent heat flux was characteristic of the surface flux from the polynya. Profiles of wind, temperature, and temperature fluctuations were also measured. Temperature ramps associated with the passage of convective plumes give skewed temperature distributions. Sensible heat flux is related to wind speed and sea-air temperature difference by a stability-dependent bulk coefficient. Formulas describing turbulence structure in convective boundary layers in terms of ‘similarity’ theory are verified and compared with published results taken in less extreme temperature gradients. By using these formulas, heat flux can be estimated from either temperature variance or temperature spectra.
TL;DR: In this paper, a solution methodology has been employed that enables the fully developed regime in a duct of periodically varying cross section to be determined without dealing with the entrance region of the duct.
Abstract: A solution methodology has been employed that enables the fully developed regime in a duct of periodically varying cross section to be determined without dealing with the entrance region. ...
TL;DR: In this paper, the parametric behavior of radial temperature variations within the charge during crystal growth in a Bridgman-Stockbarger configuration is derived by a two-dimensional heat transfer model.
TL;DR: In this article, a flame-spread model is analyzed in which heat release occurs at the planar interface of two media, each of which moves with a different but constant velocity, subject to a prescribed temperature distribution on the downstream half of the interface and continuity of the normal heat flux on the upstream half.
Abstract: A flame-spread model is analyzed in which heat release occurs at the planar interface of two media, each of which moves with a different but constant velocity. The steady-state, two-dimensional equations for conservation of energy in each medium are solved subject to a prescribed temperature distribution on the downstream half of the interface and continuity of the normal heat flux on the upstream half. Differing thermal conductivities in normal and streamwise directions are allowed in each medium. The approach involves introduction of Fourier transforms in the streamwise coordinate and use of the Wiener-Hopf technique. The model is shown to be equivalent to that of de Ris with radiant transfer neglected and also may be interpreted in terms of distributed electrical or radiant heating without combustion. Parametric results are obtained for various heat fluxes and for spread rates. The study helps to improve understanding of mechanisms of flame spread under conditions controlled by heat transfer.
Patent•
07 Jun 1983
TL;DR: In this paper, a high thermal capacitance multilayer thermal insulation structure is described, which is of particular utility for thermal protection against exposure to alternate high and low radiant heat flux levels, and comprises a laminate of alternate metal foil or metallized plastic foil layers and layers of material which are characterized by phase change upon the absorption of heat.
Abstract: A high thermal capacitance multilayer thermal insulation structure is described, which is of particular utility for thermal protection against exposure to alternate high and low radiant heat flux levels, and which comprises a laminate of alternate metal foil or metallized plastic foil layers and layers of material which are characterized by phase change upon the absorption of heat, the foil layers providing high reflectance and reradiation of the heat flux, and the phase change layers providing for absorption and storage of heat during periods of high heat flux for reradiation during periods of low heat flux.
TL;DR: In this article, a generalized coordinate transformation is employed to analyze the temperature field in a laminar boundary layer for the body with a step change in the surface temperature distribution, and the solution to the governing equations are obtained as universal functions which are independent of the geometry of the problem.
TL;DR: In this paper, an experimentally studied transient boiling heat transfer under forced convection was conducted, where an exponential increasing heat input was supplied to a platinum wire in water flowing upward in a round tube at pressures from 0.143 to 1.503 MPa.