Showing papers on "Critical heat flux published in 1983"
TL;DR: In this article, the critical heat flux (CHF) was introduced for columnar vapor stems distributed in a liquid layer wetting a heated surface, and a new hydrodynamic model was developed for pool boiling and forced convection boiling.
596 citations
TL;DR: In this article, a theoretically based prediction of CHF has been developed for high velocity flow in tubes, and good agreement was obtained between predictions and experimental data for water flowing in uniformly and nonuniformly heated tubes.
310 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 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 paper, the authors studied the pool boiling heat transfer in a confined space for vertical narrow annuli with closed bottoms and identified three boiling regimes through visual observation: the isolated deformed bubble regime, the coalesced deformed bubbles regime and the boiling regime at high heat flux.
109 citations
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.
96 citations
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.
81 citations
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.
65 citations
TL;DR: In this article, a physically based model for heat transfer to immersed surfaces in large particle fluidized beds is proposed, where large particles are distinguished as those with thermal time constants substantially greater than their residence time at a heat transfer surface.
58 citations
Proceedings Article•
01 Aug 1983
TL;DR: In this paper, a simple heat transfer model consisting of a gas layer exchanging heat with two bounding parallel walls that pulsate against each other in the transverse direction is investigated.
Abstract: Cyclic heat transfer inside closed spaces is investigated analytically using a simple heat transfer model. The model consists of a gas layer exchanging heat with two bounding parallel walls that pulsate against each other in the transverse direction. Correlations for the magnitude and the phase lag of the heat transfer are obtained. Also, an expression for the power loss due to the cyclic heat transfer is presented. It is shown that the loss approaches zero as the heat transfer process approaches either isothermal or adiabatic conditions. The power loss is shown to be a strong function of the phase angle between the bulk gas temperature and the heat transfer.
27 Mar 1983
TL;DR: In this article, a low temperature phase change paint is used to map the heat flux distributions within models of the cooling passages, where the paints change from an opaque coating to a clear liquid at a well defined melting point.
Abstract: This paper reviews the techniques developed jointly by Rolls-Royce Bristol and Oxford University for determining detailed heat transfer coefficient distributions inside turbine blade and vane cooling passages.These techniques make use of a low temperature phase change paint to map the heat flux distributions within models of the cooling passages. The paints change from an opaque coating to a clear liquid at a well defined melting point.Thus, the surface temperature history of a model subjected to transient convective heating is recorded. From this history the heat transfer coefficient distribution is deduced using a transient conduction analysis within the model. The general method may be applied to a range of model thicknesses and geometries. The Rolls-Royce data are usually obtained from the inner surface of thick walled models whereas the Oxford measurements are performed on the outside of thin walls.Results are presented for the detailed heat transfer coefficient distributions within a variety of cooling passages. Firstly, smooth ducts of circular cross section are considered and serve the purpose of validating the experimental techniques. Secondly, results for complex passages with varying cross-sectional area are presented, and the effect of introducing discrete roughness elements and film cooling exhausts into these ducts assessed. Finally, data obtained from a comprehensive examination of a typical engine multi-pass cooling geometry are presented.Copyright © 1983 by ASME
TL;DR: In this article, a new metal hydride container with heat pipes which were able to transfer heat rapidly was constructed and was used to operate the heat storage system with a hydrogen flow of 1.51 min−1 between 3.5 kg beds of CaNi5 and LaNi5.
Abstract: The rate of heat transfer is important in heat storage technology using metal hydrides because the rate of hydrogen transfer depends on the rate of heat transfer. A new metal hydride container with heat pipes which were able to transfer heat rapidly was constructed and was used to operate the heat storage system with a hydrogen flow of 1.51 min−1 between 3.5 kg beds of CaNi5 and LaNi5. The metal hydride beds were located inside cylindrical heat pipes 66 cm long with an inside diameter of 4 cm.
TL;DR: In this article, a simple model for the wave effects on momentum, heat and mass transfer is proposed for the calculation of heat transfer coefficient and flow characteristics of two-phase two-component annular flow.
TL;DR: In this article, a high thermal capacity copper test section placed at the end of a heating tube is used for investigating the critical heat flux and heat transfer characteristics during rewetting process for Freon-113 upward flow at mass velocities of 357, 627, 1035 and 1465 kg m−2 s−1.
TL;DR: In this article, the heat flux from a constant temperature hot film mounted flush with the surface of a plane insulating wall is examined numerically assuming that the thermal boundary layer theory is applicable everywhere and at all times.
TL;DR: In this paper, an analytical model for heat transfer in nucleate pool boiling at high heat flux, near the critical value, is proposed and the results of the analysis have been compared with some experimental results and the agreement is found to be reasonably good.
Patent•
10 Aug 1983
TL;DR: In this paper, a building having a number of separately-controlled zone heat pumps includes a circulation conduit for heating or cooling a heat transfer fluid circulated throughout the system, and individual heat pumps for each of the controllable zones.
Abstract: A heating and cooling system for a building having a number of separately-controlled zone heat pumps includes a circulation conduit for heating or cooling a heat transfer fluid circulated throughout the system, and individual heat pumps for each of the controllable zones. Prior to dissipation of excess system heat by use of the cooling means, an additional heat pump in heat transfer contact with the circulation loop extracts heat for storage in a separate reservoir, at a temperature higher than that of the circulating fluid. The stored heat may be returned to the circulation conduit, or otherwise recovered as necessary for heating potable water or the like.
TL;DR: In this article, a simple heat balance has been used to analyze conditions for flame propagation in ducts and a heat flow parameter coupled with the critical heat flux for ignition was used to define the ignition and extent of flame propagation for duct lining materials.
TL;DR: In this paper, an experimental study was made on rewetting of a hot stainless steel tube by a Freon 113 liquid film at atmospheric pressure, and the effects of liquid film flow rate, initial wall temperature and wall thickness on the wet front velocity were presented.
TL;DR: Analyse du transfert de chaleur de fluides newtoniens et non-newtoniens dans un tube, avec conduction axiale and production de chalur.
Abstract: Analyse du transfert de chaleur de fluides newtoniens et non newtoniens dans un tube, avec conduction axiale et production de chaleur. Application d'une condition limite a l'entree, qui tient compte de l'effet de la conduction axiale. Influence du nombre de Peclet, de l'indice du modele a loi de puissance et de la production de chaleur sur le champ des temperatures et le nombre de Nusselt
TL;DR: The heat and mass transfer characteristics of a thermochemical energy storage system based on solid-gas reactions have been studied through the example of the borax dehydration reaction in an apparatus simulating uni-dimensional heat transfer as discussed by the authors.
TL;DR: For certain postulated severe accident conditions such as loss of piping integrity and a loss of heat sink in connection with liquid-metal fast breeder reactor safety analysis, the process of dec...
Abstract: For certain postulated severe accident conditions such as a loss of piping integrity and a loss of heat sink in connection with liquid-metal fast breeder reactor safety analysis, the process of dec...
TL;DR: In this paper, a tube-wall reactor is cooled by an annular heat pipe arrangement, which exhibits flatter temperature profiles and uniform redistribution of the imposed heat load, and is more temperature stable, more flexible and more productive than cooling by conventional means.
Abstract: Cooling a tube-wall reactor using an annular heat pipe (AHP) is more temperature-stable, more flexible and more productive than cooling by conventional means. Tube-wall reactors cooled by an annular heat pipe arrangement exhibit flatter temperature profiles and uniform redistribution of the imposed heat load. The combination of tube-wall reactor and annular heat pipe is subject to the usual capacity limitations of the heat pipe: sonic flow, boiling heat transfer, liquid entrainment, and capillary flow of the working fluid.
01 May 1983
TL;DR: In this article, a fully implicit upwind finite difference numerical scheme has been proposed to investigate the characteristics of thermal entrance heat transfer in laminar pipe flows subject to a step change in ambient temperature.
Abstract: A fully implicit upwind finite difference numerical scheme has been proposed to investigate the characteristics of thermal entrance heat transfer in laminar pipe flows subject to a step change in ambient temperature. In order to demonstrate the results more clearly, a modified Nusselt number is introduced. The unsteady axial variations of modified Nusselt number, bulk fluid temperature, and wall temperature and the transient temperature profiles at certain axial locations are presented graphically for various outside heat transfer coefficients. The effects of the outside heat transfer coefficient on the heat transport processes in the flow are examined in detail. The results can be comprehensively explained by the interaction between the upstream convective heat transfer and the diffusion heat transfer in the radial direction. Steady state is reached when the axial convection balances the radial diffusion.
01 Jan 1983
TL;DR: In this article, a small heat flux meter was used to measure local values of the heat transfer coefficient in the impingement zone, and these local values were integrated to yield space average values.
Abstract: High velocity, impinging, air jets are commonly used for heating, cooling, drying etc., because of the high heat transfer coefficients which occur in the impingement region. To provide data for design, a variety of slot nozzles has been tested to determine the effect on heat transfer of both nozzle shape and slot width. A small heat flux meter was used to measure local values of the heat transfer coefficient in the impingement zone, and these local values were integrated to yield space average values.As a necessary preliminary to the heat transfer investigation, the discharge coefficients of the nozzles were measured. From the first test series it was found that heat transfer results from differently shaped nozzles could be satisfactorily correlated provided that the effective slot width was used to characterize nozzle shape. From the second test series it was found that for geometrically similar arrangements, narrower slots gave higher heat transfer coefficients.
TL;DR: In this paper, a method for predicting steady state dispersed vertical upflow film boiling heat transfer under constant heat flux conditions is presented, which is dependent upon knowledge of conditions at the dryout point only.
Abstract: A method for predicting steady state dispersed vertical upflow film boiling heat transfer under constant heat flux conditions is presented. Differential transport equations and accepted heat transfer correlations are used to form a solution dependent upon knowledge of conditions at the dryout point only. Thermal nonequilibrium is included in the analysis and the actual flow quality is determined from local equilibrium conditions. A nondimensional grouping is derived which indicates the extent of nonequilibrium present in the flow. Results of this analysis are compared to data of three fluids in tube geometry: Freon 12, nitrogen, and steam. Predictions compare favorably with data from all three fluids.
TL;DR: In this paper, the authors investigated the contribution of flow oscillation on the decrease in critical heat flux (CHF) with forced convection under an oscillating acceleration condition and showed that in the high exit quality region deteriotation of CHF could almost wholly be attributed to the variation of inlet flow rate induced by motion.
Patent•
26 May 1983
TL;DR: In this paper, a method for the determination of the heat transfer coefficient on a heat transferring surface, including the steps of arranging a layer for measuring the surface temperature and heat flux on the heat-transfer surface so that the layer can change the original temperature and flux to a negligible extent only, providing for the slight and properly slow changeability of the surface heat flux density within a cycle time which is by several orders of magnitude longer than the time constants of both the heat flux measuring layer and the boundary layer.
Abstract: A method for the determination of the heat transfer coefficient on a heat transferring surface, including the steps of arranging a layer for measuring the surface temperature and heat flux on the heat transferring surface so that the layer can change the original temperature and heat flux to a negligible extent only, providing for the slight and properly slow changeability of the surface heat flux density within a cycle time which is by several orders of magnitude longer than the time constants of the heat flux measuring layer and of the heat transferring boundary layer, by using a supplementary heating element and performing a practically unlimited number of measuring cycles, using the steps of deflecting the surface heat flux density and temperature relative to the condition in which no measurement takes place. The time-functions of the changes of the surface temperature ΔT and of the surface heat flux density Δq are determined, and the heat transfer coefficient is defined as the approximate limit value H of the quotients Δq/ΔT corresponding to the zero surface heat flux density or temperature deflection.