bluuebunny/crossref_metadata_2025 huggingface dataset:
An Experimental Investigation of Ice Formation around an Isothermally Cooled Cylinder in Crossflow
Authors: Cheng K. C. , Inaba Hideo , Gilpin R. R.
Published: October 2009

The problem of steady-state, two-dimensional ice formation around an isothermally cooled circular cylinder in a crossflow is studied experimentally for the ranges of Reynolds numbers, Red, 2.3 × 102 to 8.6 × 104 and cooling temperature ratios, θc, 6.3 to 75.8. The local and average heat transfer coefficients at the ice-water interface are obtained from measured ice profiles by using a series solution of the Laplace equation in the ice. Correlation equations for the average heat transfer are obtained for three regimes of Reynolds numbers. A correlation is also obtained for the cooling capacity that can be stored in the ice layer around a cylinder.
Quasi-Steady-State Temperature Distribution in Periodically Contacting Finite Regions
Authors: Vick B. , O¨zis¸ik M. N.
Published: October 2009

Heat transfer across two surfaces which make and break contact periodically according to a continuous regular cycle is investigated theoretically and exact analytical solutions are developed for the quasi-steady-state temperature distribution for a two-region, one-dimensional, periodically contacting model. The effects of the Biot number, the thermal conductivity and thermal diffusivity of the materials and the duration of contact and break periods on the interface temperature and the temperature distribution within the solids are illustrated with representative temperature charts.
Unsteady Surface Element Method
Authors: Keltner N. R. , Beck J. V.
Published: October 2009

A method for the solution of transient heat conduction problems, called the unsteady surface element (USE) method, is developed and applied to several problems. The method is intended for thermally contacting bodies of similar or dissimilar geometries such as occur in contact conductance and intrinsic thermocouple problems. The method utilizes Duhamel’s integral in several ways. Two different procedures are presented, one utilizing temperature-based kernels and the other uses heat flux-based kernels. One of the given applications is to the intrinsic thermocouple problem. Several solutions are given and the results agree very well with two finite difference solutions.
Natural Convection in the Annulus Between Horizontal Circular Cylinders With Three Axial Spacers
Authors: Kwon S. S. , Kuehn T. H. , Lee T. S.
Published: October 2009

Conjugate natural convection heat transfer in an annulus between horizontal isothermal circular cylinders with three equally spaced axial spacers has been studied theoretically and experimentally. A thin-fin approximation was used to model the thermal boundary condition of the spacers in the two-dimensional finite difference numerical computations. Rayleigh number, Prandtl number, diameter ratio, and location and thermal conductivity of the spacers were varied parametrically to determine the variation in flow patterns, temperature distribution and heat transfer. Spacers of low conductivity can decrease the natural convection heat transfer by as much as 20 percent below that for a simple unobstructed annulus. However, radial conduction through spacers of high conductivity overwhelms the natural convection heat transfer between the cylinders. Two diameter ratios were tested experimentally in a Mach-Zehnder interferometer using air at atmospheric pressure with stainless steel spacers between copper cylinders. The numerical and experimental temperature distributions and local convective heat-transfer coefficients show good agreement.
Heat Transfer by Natural Convection From an Array of Short, Wall-Attached Horizontal Cylinders
Authors: Sparrow E. M. , Cook D. S. , Chrysler G. M.
Published: October 2009

Per-cylinder natural convection Nusselt numbers were measured for an in-line array of short horizontal cylinders that were affixed to a convectively participating vertical plate. The effect of cylinder length-to-diameter ratio, intercylinder spacing, position at which the cylinder is attached to the vertical plate, and Rayleigh number were investigated. The experiments were performed in air. It was found that the extent to which a given cylinder in the array was affected by cylinders situated below it depended on the Rayleigh number, with enhanced heat transfer coefficients being more likely at higher Rayleigh numbers. Greater enhancement occurred at larger intercylinder spacings. The qualitative characteristics of the Nusselt number results were insensitive to the cylinder length-to-diameter ratio, but the longer cylinders exhibited higher values of the Nusselt number. For the most part, the Nusselt numbers for the wall-attached horizontal cylinders fell below those for the classical horizontal cylinder of infinite length.
Free Convection Effects on Laminar Forced Convective Heat Transfer in a Horizontal Isothermal Tube
Authors: Yousef W. W. , Tarasuk J. D.
Published: October 2009

The influence of free convection due to buoyancy on forced laminar flow of air in the entrance region of a horizontal isothermal tube was investigated. The Graetz numbers ranged form 2.5 to 110.0, the Reynolds numbers ranged from 120 to 1200, the Grashof numbers ranged from 0.8 × 104 to 8.7 × 104, and the ratio L/D was varied from 6 up to 46. The average Nusselt numbers based on the log-mean temperature difference, ranged from 2.0 to 25.9. The heat transfer data were correlated according to the influence of free convection which was found to have a significant effect at points close to the entrance to the tube.
Combined Forced and Free Convection in the Entrance Region of an Isothermally Heated Horizontal Pipe
Authors: Hishida Mikio , Nagano Yasutaka , Montesclaros M. S.
Published: October 2009

Numerical solutions are given without the aid of a large Prandtl number assumption for combined forced and free laminar convection in the entrance region of a horizontal pipe with uniform wall temperature. The steady-state solutions have been obtained from the asymptotic time solutions of the time-dependent equations of momentum and energy with the Poisson equation for pressure. Results are presented for the developing primary and secondary velocity profiles, developing temperature fields, local wall shear stress, and local and average Nusselt numbers, which reveal how the developing flow and heat transfer in the entrance region are affected by the secondary flow due to buoyancy forces.
Low Rayleigh Number Thermal Convection in a Vertical Cylinder Filled With Porous Materials and Heated From Below
Authors: Bau H. H. , Torrance K. E.
Published: October 2009

Low Rayleigh number (R<500) thermal convection is examined experimentally and analytically for a vertical circular cylinder filled with saturated porous materials. The cylinder is heated from below and cooled from above. The upper boundary is permeable to flow. Results are reported for the critical Rayleigh number at the onset of convection (Rc) and the Nusselt (Nu) versus Rayleigh (R) number correlation. The convective structure is deduced from temperature measurements. The lateral walls have a stabilizing effect and tend to increase Rc relative to the case of a laterally unbounded porous layer. The preferred convective patterns in the cylinder tend to be nonaxisymmetric. The experimental results are in good agreement with analytical predictions. A linear stability analysis is used to calculate Rc and the structure of the convective modes for a range of aspect ratios (radius/height). An integral technique is applied to obtain heat transfer rates for 1 < R/Rc < 5.5.
Analytical and Experimental Investigation of Simultaneous Melting-Condensation on a Vertical Wall
Authors: Taghavi-Tafreshi K. , Dhir V. K.
Published: October 2009

Melting of a vertical wall as a result of condensation of saturated vapor is investigated both analytically and experimentally. Employing similarity transformations, full boundary layer equations governing laminar films of melt and condensate are solved numerically for high Prandtl number liquids. Numerical results for the melting and condensation heat transfer and for the melt-condensate interface temperature are obtained. Experiments are conducted by condensing saturated steam on vertical surfaces of slabs made of naphthalene, biphenyl and stearic acid. The data are found to compare well with the predictions. The analysis is extended to condensation on melting surfaces with shapes yielding variable gravity in the direction of flow.
Frost Formation on Vertical Cylinders in Free Convection
Authors: Cremers C. J. , Mehra V. K.
Published: October 2009

Frost growth on a cooled vertical cylinder in free convective flow was studied experimentally. A correlation that is based on heat transfer considerations was found to be effective in predicting frost growth rates particularly at relative humidities equal to or greater than 65 percent and growing times equal to or greater than 60 min.
Heat Transfer From Combustion Gases to a Single Row of Closely Spaced Tubes in a Swirl Crossflow Stirling Engine Heater
Authors: Bankston C. P. , Back L. H.
Published: October 2009

This paper describes an experimental program to determine the heat-transfer characteristics of a combustor and heat-exchanger system in a hybrid solar receiver which utilizes a Stirling engine. The system consists of a swirl combustor with a crossflow heat exchanger composed of a single row of 48 closely spaced curved tubes. In the present study, heat-transfer characteristics of the combustor/heat-exchanger system without a Stirling engine have been studied over a range of operating conditions and output levels using water as the working fluid. Non-dimensional heat-transfer coefficients based on total heat transfer have been obtained and are compared with available literature data. The results show significantly enhanced heat transfer for the present geometry and test conditions. Also, heat transfer along the length of the tubes is found to vary, the effect depending upon test condition.
Heat-Transfer Augmentation in Rod Bundles Near Grid Spacers
Authors: Yao S. C. , Hochreiter L. E. , Leech W. J.
Published: October 2009

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.
Approximate Calculation of Multidimensional Solidification by Using Conduction Shape Factors
Authors: Shamsundar N.
Published: October 2009

When solidification occurs with conduction controlling and small temperature differences present, quasi-steady models become advantageous. In this paper, the use of conduction shape factors to predict freezing rate and heat transfer in various two-dimensional objects is investigated. Simple equations for calculating these quantities are obtained, and compared to existing results. The use of shape factors to model solidification with time-dependent boundary conditions is illustrated.
Conjugated Heat Transfer in a Laminar Boundary Layer With Heat Source at the Wall
Authors: Brosh A. , Degani D. , Zalmanovich S.
Published: October 2009

This work presents the solution of the temperature field in a two-dimensional laminar incompressible flow over a conducting solid plate with a line heat source located at the fluid-solid interface perpendicular to the flow direction. A numerical scheme was used to obtain the temperature profiles as a function of the source strength, and of the properties of the fluid and the solid. The heat conduction and forced convection in the fluid and the heat conduction in the solid were solved for the case of moderate temperature rise, where the assumption of constant properties applies. The model enables the improvement of an instrument for the detection of boundary layer separation. It was found that for the actual parameters of the separation detector, a distance of 4 to 24 mm between the sensors gives an indication of 70 percent of the maximum temperature difference.
Numerical Simulation of Natural Convection in Concentric and Eccentric Horizontal Cylindrical Annuli
Authors: Cho C. H. , Chang K. S. , Park K. H.
Published: October 2009

Natural convection heat transfer in concentric and eccentric annuli made of two isothermal horizontal circular cylinders is numerically investigated for Rayleigh numbers less than 5.0 × 104 which is based on the difference of radii. Bipolar coordinates are used for eccentric annuli, and it is found that for very small eccentricity the overall thermal behavior of the annuli exhibits that of the exactly concentric cylinders. The maximum deviation of the local heat-transfer coefficient of the cylinder walls remains, for example, for ε = 0.01, Ri/R0 = 0.3846 and RaL = 1.0 × 104, within a meager 5 percent. The parametric effect on the heat-transfer characteristics is discussed with respect to the diameter ratio for concentric cylinders, and eccentricity and azimuthal angular location of the inner cylinder for eccentric annuli. Output is displayed in terms of streamlines, isothermal contours, radial temperature distribution and equivalent thermal conductivities. Convection patterns are explained in detail.
Laminar and Turbulent Natural Convection in the Annulus Between Horizontal Concentric Cylinders
Authors: Farouk B. , Gu¨c¸eri S. I.
Published: October 2009

Numerical solutions are presented for the steady-state, two-dimensional natural convection in the annulus between two horizontal concentric cylinders which are held at different constant temperatures. Solutions for the laminar case are obtained up to Rayleigh number (based on gap width, L) of 105. Turbulent flow results are presented for the Rayleigh number range of 106–107. the k-ε turbulence model has been applied to obtain the results. Buoyancy effects on the turbulence structure are also accounted for. The results for both the laminar and turbulent cases are in good agreement with available experimental data and other solutions in the literature. All results presented are for the outer cylinder diameter to inner cylinder diameter ratio of 2.6.
Natural Convection in Evaporating Minute Drops
Authors: Zhang Nengli , Yang Wen-Jei
Published: October 2009

Interfacial flow structures in small liquid drops evaporating on flat plates are cinematographically investigated using the methods of direct photography and laser shadowgraphy. Various liquids of relatively low boiling point were evaporated on glass and copper plates at room temperature. The laser shadowgraph records the flow patterns simultaneously at both the liquid-air interface and the liquid-solid interface, from which the evaporation rate is determined. It reveals the existence of three distinct flow structures at the liquid air interface: stable, substable, and unstable. An interfacial flow map is constructed. The direct photography is employed to study the morphology during the entire process of the unstable-interface type evaporation. The mechanism of ripple formation which enhances the evaporation rate is found to be caused by hydrophilicity of the liquid.
Boundary Integral Equation Method Calculations of Surface Regression Effects in Flame Spreading
Authors: Altenkirch R. A. , Rezayat M. , Eichhorn R. , Rizzo F. J.
Published: October 2009

A solid-phase conduction problem that is a modified version of one that has been treated previously in the literature and is applicable to flame spreading over a pyrolyzing fuel is solved using a boundary integral equation (BIE) method. Results are compared to surface temperature measurements that can be found in the literature. In addition, the heat conducted through the solid forward of the flame, the heat transfer responsible for sustaining the flame, is also computed in terms of the Peclet number based on a heated layer depth using the BIE method and approximate methods based on asymptotic expansions. Agreement between computed and experimental results is quite good as is agreement between the BIE and the approximate results.
Pressure Drop During Forced Convection Boiling of R-12 Under Swirl Flow
Authors: Agrawal K. N. , Varma H. K. , Lal S.
Published: October 2009

This investigation deals with the pressure drop during forced convection boiling of R-12 under swirl flow inside a horizontal tube. Plain flow and swirl flow pressure drop data are reported for an electrically heated, horizontal, stainless steel, round test-section fitted with twisted tapes having twist ratios from 3.76 to 10.15. A correlation has been presented expressing the swirl flow boiling pressure drop in terms of the twist ratio and the plain flow boiling pressure drop calculated by the Martinelli-Nelson model. The proposed correlation predicts the swirl flow data to within ± 20 percent of the observed values.
Diffusion in Heterogeneous Media
Authors: Mikhailov M. D. , O¨¸zisik M. N. , Shishedjiev B. K.
Published: October 2009

Heat or mass diffusion problems of finite heterogeneous media are characterized by a set of partial differential equations for temperatures or mass concentrations, Tk (x, t), (k = 1, 2, . . . , n), in every point in space, which are coupled through source-sink terms in the equations. In the present analysis, appropriate integral transform pairs are developed for the solution of the n-coupled partial differential equations subject to general linear boundary conditions. Three-dimensional, time-dependent solutions are presented for the distributions of the potentials (i.e., temperatures or mass concentrations), Tk (x, t), (k = 1, 2, . . . , n), as a function of time and position for each of the n-components in the medium. The results of the general analysis are utilized to develop solutions for the specific cases of one-dimensional slab, long solid cylinder, and sphere. Numerical results are presented for the dimensionless potentials (i.e., temperature or mass concentration), Tk (x, t), (k = 1, 2, 3), at the center of the slab, long solid cylinder, or sphere for each of the three components of a three-component system.
Particulate Fouling on the Gas-Side of Finned Tube Heat Exchangers
Authors: Bott T. R. , Bemrose C. R.
Published: October 2009

A 0.3-m (12-in.) square vertical wind tunnel has been built to provide airflows in the range 2.4–5.8 m/s (490–1140 fpm) for fouling studies. Precipitated calcium carbonate dust can be fed into the airstream (which may be heated) prior to a heat exchanger model. The paper reports results on a four-row, four-pass spiral wound finned tube heat exchanger. Fouling tests have been carried out primarily near the extremes of surface heat flux available (1000 W/m2 to −700 W/m2). The results have been analyzed by the general method of Kays and London to give an effective nondimensional airside heat transfer parameter (StPr2/3) and a friction factor. Tests have covered the Reynolds number range from 1350 to 3800. Normalization of fouling data to fixed Reynolds numbers has given friction factor curves which increase to an asymptotic level between 1.4 and 2.5 times the initial value, whilst StPr2/3 values tend to fall by only 10–20 percent during the same time
Evaluation of a Method for Heat Transfer Measurements and Thermal Visualization Using a Composite of a Heater Element and Liquid Crystals
Authors: Hippensteele S. A. , Russell L. M. , Stepka F. S.
Published: October 2009

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.
Influence of Free-Stream Turbulence on Turbulent Boundary Layer Heat Transfer and Mean Profile Development, Part II—Analysis of Results
Authors: Blair M. F.
Published: October 2009

An experimental research program was conducted to determine the influence of free-stream turbulence on zero pressure gradient, fully turbulent boundary layer flow. In Part I of this paper, convective heat transfer coefficients, boundary layer mean velocity and temperature profile data, as well as wall skin friction coefficient distribution data were presented for five flow conditions of constant free-stream velocity (30 m/s) and free-stream turbulence intensities ranging from approximately 1/4 to 7 percent. These data indicated that the turbulence had significant effects on both the turbulent boundary layer skin friction and heat transfer. In the current paper, these new data are compared to various independent experimental data and analytical correlations of free-stream turbulence effects. This analysis has shown that the effects documented in Part I were a function of the freestream turbulence intensity, the turbulence length scale, and the boundary layer momentum thickness Reynolds number. In addition, the Reynolds analogy factor (2St/cf) was shown to increase by just over 1 percent for each 1 percent increase in free-stream turbulence level. New correlations for the influence of free-stream turbulence on skin friction, heat transfer, and the Reynolds analogy factor are presented.
Heat Transfer Coefficients and Patterns of Fluid Flow for Contacting Spheres at Various Angles of Attack
Authors: Sparrow E. M. , Prieto R. F.
Published: October 2009

Wind tunnel experiments were performed to determine heat transfer coefficients and fluid flow patterns for two contacting spheres. The experiments were carried out at three different angles of attack and for Reynolds numbers in the range from 4000 to 26,000. Three heat transfer conditions were considered: (a) both spheres thermally active, (b) forwardmost sphere thermally active and rearmost sphere adiabatic, and (c) forwardmost sphere adiabatic and rearmost sphere thermally active. Complementary experiments for a single sphere, encompassing the same parameter ranges, yielded baseline information for comparison with the two-sphere results. It was found that the largest effects of the sphere-to-sphere interaction on the heat transfer occurred when the two spheres were in line. At this orientation and for higher Reynolds numbers in the investigated range, there was substantial enhancement of the heat transfer with respect to that for the single sphere. At the other angles of attack, there was lesser enhancement. The visualization studies revealed such key fluid flow features as the reattachment of the separated flow from the first sphere on the second, the presence of strong recirculations, and the delay of separation due to pressure-driven transverse flows.
Radiation-Natural Convection Interactions in Two-Dimensional Complex Enclosures
Authors: Chang L. C. , Yang K. T. , Lloyd J. R.
Published: October 2009

A numerical finite-difference study has been carried out for the two-dimensional radiation-natural convection interaction phenomena in square enclosures with equal vertical finite-thickness partitions located at the centers of the ceiling and floor. Both participating gases (CO2 and NH3) and nonparticipating gas (air) are considered. In the radiation calculations, the nongray exponential wide-band models for CO2 and NH3 are used, together with a radial flux method utilizing a more realistic polar description for the radiation exchange in the enclosure. Results on the effects of both surface and gas radiation on the velocity and temperature fields and the overall heat transfer rates as functions of the partition heights at two levels of the Grashof number are presented and discussed in terms of the physical phenomena.
Surface Temperature Measurement Errors
Authors: Keltner N. R. , Beck J. V.
Published: October 2009

Mathematical models are developed for the response of surface mounted thermocouples on a thick wall. These models account for the significant causes of errors in both the transient and steady-state response to changes in the wall temperature. In many cases, closed form analytical expressions are given for the response. The cases for which analytical expressions are not obtainable can be easily evaluated on a programmable calculator or a small computer.
Laminar Forced Convection Heat Transfer in Spherical Annuli
Authors: Ramadhyani S. , Torbaty M. M. , Astill K. N.
Published: October 2009

An analysis is presented of forced convection heat transfer in spherical annuli bounded by isothermal surfaces at different temperatures. Flow enters the annulus through a port in the outer sphere and exits through a diametrically opposite port. The conservation equations of mass, momentum, and energy are reduced to dimensionless form, and the governing parameters of the problem are identified. Solutions are obtained for several values of each of the governing parameters via a numerical finite-difference procedure. It is found that very complex flow patterns can prevail within the annulus, particularly at high Reynolds numbers. Details of the flow field are presented by means of velocity and pressure profile plots. The effect of the flow patterns on the heat transfer phenomena is discussed by examining temperature profiles and variations of the local Nusselt number along the spherical surfaces. In addition, the circumferential average Nusselt numbers at the two spherical surfaces are presented as functions of the governing parameters of the problem. These graphs of average Nusselt numbers constitute information that could be used in the design of spherical annulus heat transfer equipment.
Critical Flashing Flows in Nozzles With Subcooled Inlet Conditions
Authors: Abuaf N. , Jones O. C. , Wu B. J. C.
Published: October 2009

Examination of a large number of experiments dealing with flashing flows in converging and converging-diverging nozzles reveals that knowledge of the flashing inception point is the key to the prediction of critical flow rates. An extension of the static flashing inception correlation of Jones [16] and Alamgir and Lienhard [17] to flowing systems has allowed the determination of the location of flashing inception in nozzle flows with subcooled inlet conditions. It is shown that in all the experiments examined with subcooled inlet regardless of the degree of inlet subcooling, flashing inception invariably occurred very close to the throat. A correlation is given to predict flashing inception in both pipes and nozzles which matches all data available, but is lacking verification in intermediate nozzle geometries where turbulence may be important. A consequence of this behavior is that the critical mass flux may be correlated to the pressure difference between the nozzle inlet and flashing inception, through a single phase liquid discharge coefficient and an accurate prediction of the flashing inception pressure at the throat. Comparison with the available experiments indicate that the predicted mass fluxes are within 5 percent of the measurements.
An Experimental Study of Free Corrective Heat Transfer in a Parallelogrammic Enclosure
Authors: Seki N. , Fukusako S. , Yamaguchi A.
Published: October 2009

Experimental measurements are presented for free convective heat transfer across a parallelogrammic enclosure with the various tilt angles of parallel upper and lower walls insulated. The experiments covered a range of Rayleigh numbers between 3.4 × 104 and 8.6 × 107, and Prandtl numbers between 0.70 and 480. Those also covered the tilt angles of the parallel insulated walls with respect to the horizontal, φ, of 0, ±25, ±45, ±60, and ±70 deg under an aspect ratio of H/W = 1.44. The fluids used were air, transformer oil, and water. It was found that the heat transfer coefficients for φ = −70 deg were decreased to be about 1/18 times those for φ = 0 deg. Experimental results are given as plots of the Nusselt number versus the Rayleigh number. A correlation equation is given for the Nusselt number, Nu, as a function of φ, Pr, and Ra.
Natural Convection Heat Transfer Between Bodies and Their Spherical Enclosure
Authors: Powe R. E. , Warrington R. O.
Published: October 2009

The natural convective heat transfer phenomena which occur between a body and its spherical enclosure have been experimentally investigated. Bodies of several different shapes were employed, so the results should have broad applicability. New temperature field and heat transfer results, in the form of natural convection from cubical inner bodies to a spherical enclosure, have been combined with previously available enclosure data. By considering all of the data combined, trends in the behavior of the convective heat transfer phenomena have been established, thus enabling a much more reliable analysis of enclosed body problems than is now possible. A very general heat transfer correlation has been developed which predicts the natural convection heat transfer from spheres (concentric and eccentric), cylinders, and cubes to a spherical enclosure with an average deviation of less than 12 percent. Although these results are strictly valid only for a spherical outer body, they should give a preliminary indication of expected behavior for other shapes.
Heat Transfer From a Heated Pool to a Melting Miscible Substrate
Authors: Catton I. , Brinsfield W. A. , Ghiaasiaan S. M.
Published: October 2009

Melting a miscible substrate by a heated overlying pool of higher density is studied experimentally. The heated pool is either carbon tetrachloride or diiodomethane, and the substrate is frozen benzene. By performing the experiments with heated pools of different densities the effects of pool-to-substrate temperature differences and pool-density to melt-density ratios on melting heat transfer are independently studied. Heat transfer rates are reported as a function of both temperature difference and density ratio. A model is postulated and compared with experimental results. The downward heat flux is found to be essentially independent of temperature differences, while being an increasing function of the density ratio between the pool and the melting solid for large density rations. For low-density ratios a buoyant plume analysis was used to obtain a correlation.
Evaporation of Water From a Horizontal Surface by Natural Convection
Authors: Sparrow E. M. , Kratz G. K. , Schuerger M. J.
Published: October 2009

Experiments were performed to measure the mass transfer coefficients for natural convection evaporation from a horizontal water layer. Owing to the latent heat requirements of the evaporation process, the temperature of the water layer is depressed relative to the ambient temperature. This gives rise to a buoyancy which overpowers the oppositely directed buoyancy associated with the concentration gradient of the water vapor. The experiments encompassed two orders of magnitude in the Rayleigh number and, in addition, the effects of two geometrical parameters were investigated. One of these is the size of a horizontal annular frame which surrounds the water containment pan, while the other is the step caused by the difference between the water level and the height of the pan sidewall. Both the presence of the frame and of the step decrease the mass transfer coefficient. Narrow frames give rise to a sharp decrease, but further enlargements of frame size have little additional effect. The step-height effect was found to be independent of both the Rayleigh number and the frame size, enabling a universal correlation. Furthermore, for all of the investigated steps and frames, Sh ∼Ra0.205.
Heat Transfer in Porous Media Heated From Above With Evaporation, Condensation, and Capillary Effects
Authors: Udell K. S.
Published: October 2009

Heat and mass transfer characteristics of a sand-water-steam system heated at the top and cooled at the bottom were studied. It was found that at steady-state conditions the system segregated into three regions. The top region was conduction-dominated with the voids containing a stationary superheated steam. The middle region was convection-dominated, nearly isothermal, and exhibited an upward flow of the liquid by capillary forces and a downward flow of steam due to a slight pressure gradient. The bottom portion contained a stationary compressed liquid and was also conduction dominated. The length of the two-phase convection zone was evaluated through the application of Darcy’s equations for two-phase flow and correlations of relative permeabilities and capillary pressure data. The model was in excellent agreement with the observed results, predicting a decreasing two-phase zone length with increasing heat flux. The thermodynamics of the two-phase zone were also analyzed. It was found that the vapor phase was in a superheated state as described by the Kelvin equation for vapor pressure lowering. Also, it was evident that the liquid must also be superheated for thermodynamic equilibrium to result. A stability analysis demonstrated that the superheated liquid can exist in an unconditionally stable state under conditions typical of porous systems. The degree of liquid superheat within the two-phase zone of these experiments was obtained.
Maldistributed Inlet Flow Effects on Turbulent Heat Transfer and Pressure Drop in a Flat Rectangular Duct
Authors: Sparrow E. M. , Cur N.
Published: October 2009

The effects of flow maldistribution caused by partial blockage of the inlet of a flat rectangular duct were studied experimentally. Local heat transfer coefficients were measured on the principal walls of the duct for two blockages and for Reynolds numbers spanning the range between 6000 and 30,000. Measurements were also made of the pressure distribution along the duct, and the fluid flow pattern was visualized by the oil-lampblack technique. Large spanwise nonuniformities of the local heat transfer coefficient were induced by the maldistributed flow. These nonuniformities persisted to far downstream locations, especially in the presence of severe inlet flow maldistributions. Spanwise-average heat transfer coefficients, evaluated from the local data, were found to be enhanced in the downstream portion of the duct due to the flow maldistribution. However, at more upstream locations, where the entering flow reattached to the duct wall following its separation at the sharp-edged inlet, the average coefficients were reduced by the presence of the maldistribution.
Heat Transfer of Power Law Fluid at Low Peclet Number Flow
Authors: Dang Vi-Duong
Published: October 2009

An exact solution is presented for the temperature distribution and local Nusselt number of power law fluid in conduit at low Peclet number flow by considering axial conduction in both the upstream and the downstream regions while keeping the wall at constant temperature. Solutions are also reported for the parallel plate geometry for the aforementioned heat transfer condition and for constant wall heat flux boundary condition. The order of importance of axial conduction is established for different geometries and different boundary conditions. The effect of axial conduction is more significant when power law model index, s, increases for constant wall heat flux case, but the effect changes with Peclet number for constant wall temperature case.
Measurement of Fusion Boundary Energy Transport During Arc Welding
Authors: Landram C. S.
Published: October 2009

An experimental technique is presented to identify fusion boundary (liquid/solid interface) energy transport mechanisms during welding procedures. The gas-tungsten-arc spot-welding procedure, using a low melting point specimen material (lead), was chosen to demonstrate the methods. Vaporization energy losses were found to be important during the growth of the fusion boundary. Significant thermal convection was absent within the weld pool for applied currents less than about 100 A, and for such cases the location of the fusion boundary was found to be governed primarily by heat conduction. At the current levels of almost 300 A, significant weld pool convection was found to exist, especially at the (inner) stagnation point, causing a deeper penetration of the fusion boundary there.
Experiments on a Crossflow Heat Exchanger With Tubes of Lenticular Shape
Authors: Ruth E. K.
Published: October 2009

Measurements of pressure losses and heat transfer rates were made for an unconventional crossflow heat exchanger with tubes of lenticular cross section so spaced to reduce variation in the velocity of the fluid outside the tubes, thus reducing separation and drag. The results of these experiments are reported for various tube spacing and demonstrate that the performance of the lenticular tube heat exchanger is superior to that of conventional circular tubes by 20 percent at Reynolds numbers of 20,000 to 50,000.
Heat Transfer Mechanisms and Performance in Multiple Parallel Disk Assemblies
Authors: Mochizuki S. , Yang Wen-Jei , Yagi Y. , Ueno M.
Published: October 2009

Heat transfer and frictional loss performance in radial flow through multiple parallel disk assemblies are experimentally studied by a modified single-blow transient test method. The mechanisms of heat transfer enhancement are determined in the four flow regimes which are characterized by different combinations of flow patterns: pure laminar, laminar-oscillating-laminar, laminar-oscillating-turbulent-laminar, and laminar-oscillating-turbulent type convection. The fifth convective regime is predicted. The results of a condensation-heated disk core are incorporated for discussion and performance comparison. The effects of the disk spacing and size and influx disturbance on the transfer performance are investigated. It is concluded that the disk device has the performance characteristics comparable to high-performance plate-fin type surfaces that are commonly employed in compact heat exchangers.
The One-Dimensional Analysis of Fin Assembly Heat Transfer
Authors: Manzoor M. , Ingham D. B. , Heggs P. J.
Published: October 2009

The design of finned surfaces is conventionally performed in two stages. First the fin efficiency is determined by simultaneously analyzing the conductive heat flow within the fin, and the convective heat dissipation from the surface of the fin. Then, the effects of the thermal interaction between the supporting interface and the fins and the convective heat exchange at the plain side of the supporting interface are incorporated by employing a technique based on electric circuit theory. In this study, it is shown that this technique in fact has a mathematically rigorous foundation. It is also shown that, for design purposes, there is a far superior alternative to the fin efficiency.
Two-Phase Vessel Blowdown of an Initially Saturated Liquid—Part 2: Analytical
Authors: Hutcherson M. N. , Henry R. E. , Wollersheim D. E.
Published: October 2009

Analytical models are presented to predict the internal vessel conditions during the decompression regimes of an initially saturated liquid. A subcooled blowdown analysis considers the elasticity of both the liquid and vessel. A bubble growth analysis for the intermediate period of blowdown is based on thermally dominated bubble growth from a solid surface into a superheated liquid. A dispersed analysis for the latter decompression period assumes the vapor bubbles have grown sufficiently so the liquid is uniformly distributed within the vapor phase. The sub-cooled analysis predicts the initial period of blowdown reasonably well. The bubble growth analysis predicts the rise in system pressure above that value to which it initially falls after the end of subcooled blowdown. It considers an initially “slow” depressurization rate (less than 400 MPa/s) where nucleation and bubble growth is the dominate volume producing, and thus pressure recovery, mechanism. It provides insight into why the system pressure initially drops below the saturation pressure, and it also offers an explanation for the subsequent recovery of the system pressure toward the saturation pressure. The thermodynamic equilibrium analysis provides a reasonable prediction of the latter stage of decompression. The combination of these three models predicts the overall two-phase decompression phenomenon reasonably well.
The Prediction of Pressure Drop and CCFL Breakdown in Countercurrent Two-Phase Flow
Authors: Ostrogorsky A. G. , Gay R. R. , Lahey R. T.
Published: October 2009

A steady-state analytical model has been developed to predict channel pressure drop as a function of inlet vapor flow rate and applied heat flux during conditions of countercurrent two-phase flow. The interfacial constitutive relations utilized are flow structure dependent and allow for the existence of either smooth or wavy liquid films. A computer code was developed to solve the analytical model. Predictions of Δp versus vapor flow rate were found to agree favorably with experimental data from adiabatic, air/water systems. In addition, the model was used to predict countercurrent flow conditions in heated channels characteristic of a BWR/4 nuclear reactor fuel assembly.
Local Heat Transfer Coefficients for Condensation in Stratified Countercurrent Steam-Water Flows
Authors: Kim H. J. , Bankoff S. G.
Published: October 2009

A study of steam condensation in countercurrent stratified flow of steam and subcooled water has been carried out in a rectangular channel inclined 33 deg to the horizontal. The variables in this experiment were the inlet water and steam flow rates, and the inlet water temperature. Condensation heat transfer coefficients were determined as functions of local steam and water flow rates, and the degree of subcooling. Correlations are given for the local Nusselt number for the smooth and for the rough interface regimes, and also for the dimensionless wave amplitude. A turbulence-centered model is also developed. It is shown that better agreement with the data can be obtained if the characteristic scales in the turbulent Nusselt number and Reynolds numbers are related to measured interfacial parameters rather than the bulk flow parameters. The important effect of interfacial shear, missing in previous eddy-transport models, is thus implicitly included.
Reflux Condensation and Transition to Natural Circulation in a Vertical U-Tube
Authors: Banerjee S. , Chang J-S. , Girard R. , Krishnan V. S.
Published: October 2009

Reflux and natural circulation condensation in vertical inverted U-tube steam generators form an important heat removal mechanism for nuclear reactors in certain accidents. As a first step in understanding the behavior of such steam generators, condensation was studied in a single vertical tube with a cooling jacket. Steam was fed into the tube from an inlet plenum and condensed in the jacketed region. The inlet and outlet pressures and cooling jacket conditions were controlled to give well-defined boundary conditions. The amount of steam condensed and the flow patterns obtained were determined. The steam flow rate into the tube initially increased with pressure differences between the inlet and outlet plenums. The condensate ran back to the inlet plenum countercurrent to the steam flow (reflux flow). At a certain pressure difference, no further increase in steam inlet flow rate was observed though pure refluxing was maintained. Instead, a column of liquid formed above the two-phase condensing region. The length of this column increased as the pressure difference was increased. At a sufficiently large pressure difference the liquid column carried over the top of the vertical U-bend and there was a dramatic change in flow regime to natural circulation condensation in which the bulk of the condensate flowed cocurrently with the steam. The behavior of the system was explained by postulating that “flooding” conditions were reached at the inlet when the pressure difference became large enough for a liquid column to form above the condensing region. A small perturbation analysis of the stability of the condensing and liquid column regions was done using a lumped parameter approach and constant pressure boundary conditions. Experimental results on the frequency of oscillations in a single tube followed the qualitative trends predicted by the linear analysis, but the predicted frequencies were about twice as high as those observed.
The Use of Porous Baffles to Control Acoustic Vibrations in Crossflow Tubular Heat Exchangers
Authors: Byrne K. P.
Published: October 2009

This paper describes how a single porous baffle can be used to prevent the occurrence of acoustic vibration in a crossflow tubular heat exchanger. A method for determining the optimum location and the optimum specific flow resistance of the porous baffle is presented. Finally, a description of how a porous baffle was successfully applied to control acoustic vibration which was occurring in the heat recovery region of a 375-MW brown coal steam generator is given.
The Stability of Vertical Buoyancy-Induced Flow in Cold Water
Authors: Higgins J. M. , Gebhart B.
Published: October 2009

Calculations of the stability of the buoyancy-induced flow of cold water, adjacent to a vertical surface, have been carried out. The disturbance equations, for an isothermal boundary condition, have been formulated with a new density relation for pure and saline water, of very high accuracy. Buoyancy terms in the base flow and disturbance equations, thereby, accurately express the buoyancy forces in water at low temperatures. Stability results are presented for a Prandtl number of 12.6 for a variety of ambient and surface temperature conditions. The anomalous cold water density behavior was found to produce important differences in stability from the Boussinesq solutions. The Boussinesq approximation consistently overpredicts the buoyancy force in upflow circumstances. The resulting neutral stability prediction lies upstream of the accurate ones. For temperature conditions which result in downflow, the predictions lie downstream of the accurate values. The effects may be very large.
Analysis of Turbulent Thermal Convection Between Horizontal Plates
Authors: Kaviany M. , Seban R.
Published: October 2009

The one-equation model of turbulence is applied to the turbulent thermal convection between horizontal plates maintained at constant temperatures. A pseudo-three-layer model is used consisting of a conduction sublayer adjacent to the plates, a turbulent region within which the mixing length increases linearly, and a turbulent core within which the mixing length is a constant. It is assumed that the Nusselt number varies with the Rayleigh number to the one-third power. As a result, the steady-state distributions of the turbulent kinetic energy and the mean temperature are obtrained and presented in closed forms. These results include the effects of Prandtl number. The predictions are compared with the available experimental results for different Prandtl and Rayleigh numbers. Also included are the predictions of Kraichnan, which are based on a less exact analysis. The results of the one-equation model are in fair agreement with the experimental results for the distribution of the turbulent kinetic energy and the mean temperature distribution. The predictions of Kraichnan are in better agreement with the experimental results for the mean temperature distribution.