bluuebunny/crossref_metadata_2025 huggingface dataset:
Flame Spread Over Paper in an Air Stream With a Velocity Change
Authors: Sato K. , Miki K. , Hirano T.
Published: October 2009

The behavior of downward flame spread over a sheet of filter paper during and after an increase in ambient air velocity was examined. It was shown that the behavior depends not only on the free-stream velocity but also on its rate of change. The extinction mechanisms when the free-stream velocity is instantaneously increased from that for steady flame spread to that above the steady flame spread limit are discussed, and the conditions for continued flame spreading in an air stream with a velocity fluctuation are pointed out.
Species Concentrations and Turbulence Properties in Buoyant Methane Diffusion Flames
Authors: Jeng S-M. , Faeth G. M.
Published: October 2009

Past measurements of mean velocities and temperatures in buoyant turbulent, axisymmetric methane diffusion flames burning in still air have been extended to include mean species concentrations (CH4, N2, O2, CO2, H2O, CO, and H2) and turbulence quantities. The new measurements were used to evaluate a Favre-averaged, k-ε-g turbulence model of the process—with all empirical constants fixed by measurements in noncombusting flows. Use of the laminar flamelet method to treat scalar properties yielded reasonably good predictions of mean properties. Turbulence predictions were less satisfactory, generally underestimating fluctuation levels and Reynolds stresses in highly buoyant regions of the flows. Measurements indicated significant anisotropy of turbulence properties in the same regions. These findings suggest the need for multistress closure to adequately model turbulence properties in buoyant flames.
Combined Natural and Forced Convective Heat Transfer In Spherical Annuli
Authors: Ramadhyani S. , Zenouzi M. , Astill K. N.
Published: October 2009

This paper presents numerical finite difference solutions of combined natural and forced convective heat transfer in spherical annuli. The flow is assumed to enter the annulus through a port in the bottom of the outer sphere and exit through a diametrically opposite port. The spheres are isothermal and at different temperatures. The governing conservation equations are reduced to dimensionless form and the nondimensional parameters of the problem are identified. The influence of these parameters of the problem are identified. The influence of these parameters on the solution is studied. Details of the flow field and temperature field are presented by means of velocity vector and isotherm maps. Circumferential average and local Nusselt numbers are presented and compared with earlier numerical work in which the effects of natural convection were ignored. It is shown that the buoyancy effects can have a very significant impact on the heat transfer and fluid flow, particularly at low Reynolds numbers.
Boundary Elements for Static Optimal Heating of Solids
Authors: Meric R. A.
Published: October 2009

The static optimal heating of solids by a boundary heat flux has been formulated for a solid of arbitrary geometry. Through the use of a Lagrange multiplier the problem is reduced to an unconstrained optimization problem. The necessary conditions for optimally of a performance index that characterizes the physical objectives are first found by calculus of variations. An iterational numerical procedure is then proposed in which the elliptic equations for the temperature and the Lagrange multiplier are solved by the boundary element method, and better estimates for the boundary heat flux are found by the minimization of the performance index through the conjugate gradient method of optimization. Numerical results are also provided for a two-dimensional problem.
The Effect of Turbulence-Suspended Light Particles on Dryout for Pool Boiling From a Horizontal Surface
Authors: Carey V. P. , Markovitz E. , Chuah Y. K.
Published: October 2009

Experimental measurements are reported which indicate the relationship between particle loading and dryout heat flux for pool boiling from a horizontal surface covered with a mixture of water and light particles. This study specifically examines the dryout conditions for particles which have low settling velocities and are easily suspended by the bubble-generated turbulence in the liquid pool above the surface. Dryout data are presented for pool boiling of mixtures of saturated water and glass beads with diameters ranging from 0.105 mm to 0.475 mm. Data are also presented for methanol and glass beads. At high particle loadings, a portion of the load is suspended, while the remainder forms a layer on the surface. The dryout mechanism apparently is similar to the Helmholtz instability mechanism previously identified as the cause of dryout in shallow beds of heavy particles. However, the suspension of particles in the liquid pool produces very unusual trends in the dryout data. In particular, conditions have been observed in which a decrease in the heat flux can cause dryout to occur. An approximate theoretical model of the particle suspension mechanism is proposed and used to predict the dryout conditions for very light particles. This model explains the trends in the data and predicts dryout conditions which compare favorably with the experimental results for very light particles.
Selecting Optimum Plate Heat Exchanger Surface Patterns
Authors: Focke W. W.
Published: October 2009

With appropriate simplifications, plate heat exchanger dimensions and performance can be described by suitable combinations of the base dimensionless groups: Colburn j factor, friction factor, and Reynolds number. Such combinations are used to construct graphic methods for finding optimum geometries (patterns that minimize the surface area required for heat transfer) subject to various constraints. It was found that the number of potentially optimum geometries increased with increasing number of constraints. In plate heat exchangers, the heat transfer performance is related to the pumping power expended. Therefore, in modular plate heat exchangers, the fixed plate lengths limit design flexibility in that heat transfer and pressure drop cannot be varied independently. This limitation can be partly overcome by using interchangeable chevron-type plates of different corrugation inclination angles in the same plate pack.
The Melting Process of Ice Inside a Horizontal Cylinder: Effects of Density Anomaly
Authors: Rieger H. , Beer H.
Published: October 2009

In the present investigation heat transfer during melting of ice confined within a heated, horizontal cylinder is studied experimentally and by analysis. Because of the well-known density inversion effect of water in the proximity of the melting point of ice the first-order influence of convection flow for phase change processes becomes obvious. Depending on the inner diameter of the cylinder and on the specific temperature value Tw > 0° of the cylinder wall, quite different shapes of the melting ice body, the flow pattern, and the temperature field were predicted by numerical analysis. Also provided are local and overall heat transfer coefficients, revealing a reasonable agreement between experiments and predicted data. Computations were performed for wall temperatures in the range 4°C ≤ Tw ≤ 15°C and two inner diameters of the cylinder.
Drying Front Movement Near Low-Intensity, Impermeable Underground Heat Sources
Authors: Couvillion R. J. , Hartley J. G.
Published: October 2009

An analytical model of transient, simultaneous heat, water, and air transfer is developed in this paper. The resulting governing differential conservation equations are simplified by dimensional analysis and applied to a semi-infinite moist soil with an impermeable heat source at the boundary. Solutions for moisture and temperature distributions are generated numerically for varying surface heat flux and initial moisture content. Difficulties in using a moving boundary approach are discussed. The solutions predict, without using a moving boundary analysis, that a narrow zone with a steep moisture gradient moves through the soil at a rate such that the volume of soil dried per unit surface heat input is constant for a given initial moisture content.
Laminar Fully Developed Flow and Heat Transfer in Triangular Plate-Fin Ducts
Authors: Baliga B. R. , Azrak R. R.
Published: October 2009

This paper presents a numerical investigation of fully developed flow and heat transfer in triangular cross section plate-fin ducts encountered in compact heat exchangers. Heat conduction in the fin and convection in the fluid are analyzed simultaneously as a conjugate problem. Overall and local results are presented for representative values of the duct aspect ratio and a fin conductance parameter.
Use of Melting Point Surface Coatings for Local Convection Heat Transfer Measurements in Rectangular Channel Flows With 90-deg Turns
Authors: Metzger D. E. , Larson D. E.
Published: October 2009

Centrifugal forces tend to produce secondary flows around and within channel turns that can have significant effects on the convection heat transfer distribution over the channel walls. Local Nusselt number distributions are presented for 90-deg turns of radius ratios 2 and 3 in a 3:1 aspect ratio rectangular cross section duct oriented with the principal walls in the direction of centrifugal force. A method employing the melting phase change of a surface coating was used to determine the local heat transfer rates, and a data analysis procedure needed for quantitative application of the method to internal flows is described.
Heat and Mass Transfer With Liquid Evaporation Into a Turbulent Air Stream
Authors: Kumada T. , Hirota T. , Tamura N. , Ishiguro R.
Published: October 2009

Some of the previously reported heat transfer coefficients with evaporation are fairly large as compared with those of a dry body under similar hydrodynamic conditions. In order to clarify this curious enhancement of heat transfer, a method of error evaluation was developed and applied to correct the experimental errors in the recently reported results. An experimental study was also made on turbulent heat and mass transfer of air flowing over a water surface. The present and the previously reported experimental results revealed that the heat transfer coefficient with evaporation agrees with that of a dry body without evaporation, within experimental error, if the erroneous heat inputs into the liquid are properly corrected according to the proposed method.
Enhancement of Combined Heat and Mass Transfer in a Vertical-Tube Heat and Mass Exchanger
Authors: Webb R. L. , Perez-Blanco H.
Published: October 2009

This paper studies enhancement of heat and mass transfer between a countercurrent, gravity-drained water film and air flowing in a vertical tube. The enhancement technique employed is spaced, transverse wires placed in the air boundary layer, near the air-water interface. Heat transfer correlations for turbulent, single-phase heat transfer in pipes having wall-attached spaced ribs are used to select the preferred wire diameter, and to predict the gas phase heat and mass transfer coefficients. Tests were run with two different radial placements of the rib roughness: (1) at the free surface of the liquid film, and (2) the base of the roughness displaced 0.51 mm into the air flow. The authors hypothesize that the best heat/mass transfer and friction performance will be obtained with the roughness at the surface of the water film. Experiments conducted with both roughness placements show that the authors’ hypothesis is correct. The measured heat/mass transfer enhancement agreed very closely with the predicted values. A unique feature of the enhancement concept is that it does not require surface wetting of the enhancement device to provide enhancement.
Heat Transfer Effects During Cold Dense Gas Dispersion: Wind-Tunnel Simulation of Cold Gas Spills
Authors: Meroney R. N. , Neff D. E.
Published: October 2009

Wind-tunnel concentration data were obtained for continuous area releases of ambient temperature Freon–air mixtures, cold N2, cold CO2, and cold CH4 clouds. Heat transfer and humidity effects on model concentration distributions were significant for methane plumes when surface Richardson numbers Ri* were large (i.e., low wind speed and high boiloff rate conditions). At field scales heat transfer and humidity will still play a role in the dispersion of methane spill cases, but plume dilution and liftoff are not expected to be as exaggerated as for the model cases.
Evaporation at a Liquid Surface Due to Jet Impingement
Authors: Sparrow E. M. , Celere S. W. , Azevedo L. F. A.
Published: October 2009

Experiments were performed to determine mass transfer coefficients for evaporation from a water surface on which an air jet impinged. During the course of the experiments, parametric variations were made of the jet velocity and diameter, the separation distance between the jet origin and the water surface, the diameter of the water surface, and the degree of insulation of the water containment pan. It was found that for all of the investigated operating conditions, the dimensionless mass transfer coefficient varied with the 0.8 power of the jet Reynolds number. Furthermore, the transfer coefficient decreased linearly as the separation distance between the jet origin and the water surface increased, with the most significant decreases occurring at relatively small values of the surface-to-jet diameter ratio. At larger diameter ratios, the transfer coefficient was relatively insensitive to the separation. In general, the larger the diameter of the water surface, the lower the transfer coefficient. Comparisons with the literature showed that the dimensionless mass transfer coefficients for impingement on a liquid surface are lower than those for impingement on a solid surface.
Thermal Finite Element Formulation and Solution Versus Experimental Results for Thin-Plate GTA Welding
Authors: Kraus H. G.
Published: October 2009

The problem of steady-state and transient heat transport associated with thin-plate welding is formulated and solved using the finite element method. Phase change is accurately accounted for through an element phase property averaging and quadratic/integral capacitance fitting technique. Three cases of quasi-steady welding of SS (stainless steel) 304 plates were simulated: input powers of 285, 405, and 588 W with corresponding velocities of 0.408 × 10−3, 1.270 × 10−3, and 2.540 × 10−3 m/s. Comparison to experimental results shows good agreement of weld pool size with a shape discrepancy developing as welder power and velocity increase. Arc heat flux and weld pool convection effects are discussed. A review of these results, combined with a survey of current literature, enabled possible causes of these weld pool shape differences to be identified and enabled recommendations for future research to be made.
Radiative Transfer With Dependent Scattering by Particles: Part 2—Experimental Investigation
Authors: Yamada Y. , Cartigny J. D. , Tien C. L.
Published: October 2009

Dependent radiative scattering by particles is experimentally investigated using plane-parallel cells containing latex spheres of 11, 2, and 0.08 μm diameter dispersed in an air or water matrix. The dependent scattering efficiencies and the bidirectional transmittance and reflectance were measured and compared with analytical results. The close-packed 2-μm spheres, which were expected to show dependent scattering from the previous criterion, gave results identical to independent scattering. Measured dependent scattering efficiencies of the small particles tested decrease with increasing particle volume fraction and were compared with those predicted by the theoretical investigation. The bidirectional transmittance and reflectance of dependent scattering were compared with those of independent scattering with the same number of spheres within the test cells. Several different patterns of dependent transmittance and reflectance appeared depending on the optical thickness. Finally, a newly proposed regime map bounding independent and dependent scattering is compared with the present and previous experimental data.
Two-Dimensional Radiative Back-Scattering From Optically Thick Media
Authors: Nelson H. F. , Look D. C. , Crosbie A. L.
Published: October 2009

The theoretical and experimental results of anisotropic back-scattering from an optically thick medium exposed to a laser beam are presented. The laser beam is incident normal to the upper surface of the scattering medium. Uniformly sized latex particles with diameters ranging from 0.046 to 0.35 μm are used for the scattering centers in a water solution. The results are discussed for back-scattered radiation as a function of optical radius from the laser beam and optical thickness of the scattering medium. It is shown that back-scattered radiation in optically thick media is very sensitive to small changes in albedo when the albedo is near unity. The sensitivity increases as the optical radius increases. Also, the isotropic scattering solution yields good agreement with the experimental data at large optical radii when one uses effective optical properties. The agreement between theory and experiment is improved when index of refraction effects at the interface are included.
The Use of Dehumidifiers in Desiccant Cooling and Dehumidification Systems
Authors: Van den Bulck E. , Mitchell J. W. , Klein S. A.
Published: October 2009

The use of rotary dehumidifiers in gas-fired open-cycle desiccant cooling systems is investigated by analyzing the performance of the rotary heat exchanger–rotary dehumidifier subsystem. For a given cooling load, the required regeneration heat supply can be minimized by choosing appropriate values for the regeneration air mass flow rate and the wheel rotation speed. A map is presented showing optimal values for rotational speed and regeneration flow rate as functions of the regeneration air inlet temperature and the process air inlet humidity ratio. This regeneration temperature is further optimized as a function of the process humidity ratio. In the analysis, the control strategy adjusts the process air mass flow rate to provide the required cooling load. Additional control options are considered and the sensitivity of the regeneration heat required to the wheel speed, regeneration air mass flow rate, and inlet temperature is discussed. Experimental data reported in the literature are compared with the analytical results and indicate good agreement.
Analytical Solution of the Transient Response of Gas-to-Gas Crossflow Heat Exchanger With Both Fluids Unmixed
Authors: Gvozdenac D. D.
Published: October 2009

The dynamic response of a single-pass crossflow heat exchanger with both fluids unmixed to arbitrary time varying inlet temperatures of fluids is investigated analytically. The initial spatial temperature distribution of the heat exchanger core is arbitrary as well. Analytical solutions for temperature distributions of both fluids and the wall as well as the mean mixed fluid temperatures at the exit are presented. The solutions are found by using Laplace transform method and special functions in the form of series of modified Bessel functions.
Natural Convection From Horizontal Wires to Viscoelastic Fluids
Authors: Ng M. L. , Hartnett J. P. , Kwack E. Y.
Published: October 2009

Natural convection heat transfer from horizontal wires of three different diameters (0.0254, 0.0508, and 0.0826 cm) to a pool of viscoelastic liquid was studied. Aqueous solutions of Natrosol and Polyox constituted the viscoelastic test fluids. The experimental Nusselt numbers were found to agree with the correlations recommended by Fand and Brucker for Newtonian fluids if the zero shear rate viscosity is used in the Rayleigh and Prandtl numbers.
Buoyant Laminar Convection in a Vertical Cylindrical Annulus
Authors: Littlefield D. , Desai P.
Published: October 2009

Solution to natural convective motion in a vertical cylindrical annulus of large aspect ratio is examined, with the inner wall subject to a constant heat flux. Similar transformations of the appropriately simplified Navier–Stokes model of the annular flow are sought. The issue of boundary condition limitations for the considered flow is resolved in terms of acceptable error bounds for valid solutions. Results are generated for a variety of outer wall boundary conditions over various ranges of the Rayleigh number, highlighting the effects on the patterns of streamlines and “heatlines.” Correlations presented for the Nusselt number are shown to be dependent on both the boundary conditions and the geometry.
Deterministic Modeling of Unconfined Turbulent Diffusion Flames
Authors: Hasemi Y. , Tokunaga T.
Published: October 2009

An analytical model of the deterministic properties of turbulent diffusion flames is derived using a similarity analysis. Some parameters appearing in the model are quantified by experiments using porous round burners with propane as the fuel. The validity of the model is verified by experiments as well as by comparing the theory with previous experimental work. The model shows that the deterministic properties are insensitive to material properties.
Natural Convection in a Horizontal Porous Annulus With a Step Distribution in Permeability
Authors: Muralidhar K. , Baunchalk R. A. , Kulacki F. A.
Published: October 2009

A numerical and experimental study of free convective flow and heat transfer in a horizontal annulus containing saturated porous material is reported in the present study. The special case of a step distribution in permeability, resulting in a two-layer system, has been considered. Both isothermal and constant heat flux boundary conditions have been imposed on the inner wall, while the outer wall is kept at a constant temperature. For the case of isothermal boundaries, a simple resistance law gives rise to a model of permeability which collapses the average Nusselt numbers of the variable permeability problem to that of the uniform case. Generally, agreement between experiments and calculation is satisfactory, although under certain circumstances, a systematic divergence of the data is observed. It is deduced in the present work that this is strictly related to non-Darcy effects.
Influence of Pressure on the Leidenfrost Temperature and on Extracted Heat Fluxes in the Transient Mode and Low Pressure
Authors: Testa P. , Nicotra L.
Published: October 2009

In the cooling of a hot surface by means of single water droplets impinging from above, the Leidenfrost temperature was measured as a function of pressure, below atmospheric pressure. Heat fluxes and temperature transients were recorded as functions of pressure, with relatively high time resolution, as allowed by the fast response to thermal transients of the test section and measuring equiqment especially developed for this purpose.
Flow Film Boiling From a Sphere to Subcooled Freon-11
Authors: Orozco J. A. , Witte L. C.
Published: October 2009

The boiling curves for flow boiling of freon-11 from a fluid-heated 3.81-cm-dia copper sphere showed dual maxima. One maximum corresponded to the nucleate peak heat flux while the other was caused by transitory behavior of the wake behind the sphere. Film boiling data were predicted well by the theory of Witte and Orozco. A semi-empirical correlation of the film boiling data accounting for both liquid velocity and subcooling predicted the heat transfer to within +/− 20 percent. The conditions at which the vapor film became unstable were also determined for various sub-coolings and velocities.
Wave Instability of Natural Convection Flow on Inclined Surfaces
Authors: Tzuoo K. L. , Chen T. S. , Armaly B. F.
Published: October 2009

Wave instability of nautral convection boundary layer flow adjacent to inclined surfaces is analyzed by a linear theory. The effects of the nonparallelism of the main flow and thermal fields are taken into account in the analysis. Neutral stability results for Prandtl numbers of 0.7 and 7.0 are presented for upward-facing heated surfaces, for angles of inclination ranging from 0 to 90 deg. These results are compared with available analytical wave instability results for small angles of inclination. They are also compared with analytical vortex instability results and with available experimental data.
Drying Rate of Wood Particles With Longitudinal Mass Transfer
Authors: Dorri B. , Emery A. F. , Malte P. C.
Published: October 2009

The drying of small wood particles of shape L:W:t = 3 to 5:2:1 is examined by three numerical models, and results are compared to measurements. (i) A one-dimensional rectangular model has liquid water concentrated in the center of a particle, and this is removed as an evaporation front propagates into the liquid. (ii) The one-dimensional model is also treated by the volume-averaged, or “smeared” approach, for which the moisture at any point is a distribution of liquid and vapor. For the simple rectangular geometry, the frontal and smeared models give similar results. (iii) Equivalent spherical particles are analyzed by a smeared model which includes capillarity. Reasonable agreement is obtained between the spherical results and the measurements, though an overprediction in drying rate occurs for slender particles.
Effect of Wall Heat Conduction on Natural Convection Heat Transfer in a Square Enclosure
Authors: Kim D. M. , Viskanta R.
Published: October 2009

This paper presents numerical and experimental results for buoyancy-induced flow in a two-dimensional, fluid-filled enclosure. Rectangular cavities formed by finite conductance walls of different void fractions and aspect ratios are considered. Parametric heat transfer calculations have been performed and results are presented and discussed. Local and average Nusselt numbers along the cavity walls are reported for a range of parameters of physical interest. The temperatures in the walls were measured with thermocouples, and the temperature distributions in the air-filled cavity were determined using a Mach-Zehnder interferometer. Good agreement has been obtained between the measured and the predicted temperatures in both the solid wall and in the fluid using the mathematical model. Wall heat conduction reduces the average temperature differences across the cavity, partially stabilizes the flow, and decreases natural convection heat transfer.
Natural Convection in Porous Media Bounded by Short Concentric Vertical Cylinders
Authors: Prasad V. , Kulacki F. A.
Published: October 2009

Free-convective heat transfer in short cylindrical annuli filled with saturated porous media has been studied numerically and experimentally. For an annulus whose inner wall is heated at constant temperature and outer wall is isothermally cooled, the top and bottom being insulated, heat transfer results have been obtained numerically for 0.9≥A≥0.3, 1<κ≤11 and Rayleigh number, Ra* up to 104, where A is the aspect (height-to-gap width) ratio and κ is the radius ratio. Introduction of curvature effects diminishes the multicellular flow behavior observed in the case of shallow cavity, and hence, the higher the radius ratio, the lower is the aspect ratio required for multicellular flow to exist. Heat transfer rates for isothermal heating have also been determined experimentally for A=1 and κ=5.338, using water and glass beads (3 and 6 mm dia) as the porous media. The experimental values of Nusselt number agree well with the numerical predictions for Ra* up to 4000. Agreement between the measured temperatures at various locations and the numerically established temperature field is also quite reasonable.
Laser-Induced Natural Convection and Thermophoresis
Authors: Wang C. Y. , Morse T. F. , Cipolla J. W.
Published: October 2009

The influence of axial laser volumetric heating and forced convection on the motion of aerosol particles in a vertical tube has been studied using the Boussinesq approximation. For constant wall temperature, an asymptotic case provides simple temperature and velocity profiles that determine the convection and thermophoretic motion of small aerosol particles. Laser heating induces upward buoyant motion near the tube center, and when forced convection is downward, there may be an inflection in the velocity profile. For constant laser heating (a small absorption limit), a velocity profile may be found that will minimize the distance over which particles are deposited on the wall. Such an observation may have some bearing on the manufacture of preforms from which optical fibers are drawn.
An Experimental Investigation of the Effect of Subcooling on Bubble Growth and Waiting Time in Nucleate Boiling
Authors: Ibrahim E. A. , Judd R. L.
Published: October 2009

The effect of subcooling on bubble waiting time and growth time for water boiling on a copper surface was examined in conjunction with measurements obtained over a range of subcooling from 0 to 15°C and three different levels of heat flux 166, 228, and 291 kW/m2. The growth-time data was successfully correlated with a model that combined the bubble growth theory of Mikic, Rohsenow, and Griffith with the bubble departure diameter relationship of Staniszewski, thereby establishing confidence in the measuring procedure. The waiting time data agreed with the predictions of the Han and Griffith waiting time theory at lower levels of subcooling but then showed a behavior contrary to that predicted for higher levels of subcooling.
Studies on Heat Transfer From a Vertical Cylinder, With or Without Fins, Embedded in a Solid Phase Change Medium
Authors: Kalhori B. , Ramadhyani S.
Published: October 2009

An experimental investigation of melting and cyclic melting and freezing around a vertical cylinder is reported. The studies encompass two cases: a plain vertical cylinder, and a vertical cylinder with fins. In the melting studies, the total heat transfer from the cylinder was measured as a function of time. In addition, measurements have been made of the solid-liquid interface shape after various melting times. In these studies, the solid phase was initially isothermal and either at its fusion temperature or subcooled below the fusion point. The experiments reveal the important influence of natural convection in the liquid phase in both unfinned and finned situations. Subcooling of the solid phase is observed to strongly inhibit heat transfer in the unfinned situation. In the experiment on cyclic melting and freezing, subcooling of the solid phase is once again found to have an important effect on the unfinned situation. Heat transfer from the finned cylinder is much less affected by solid-phase subcooling. All the experiments were performed with 99 percent pure n-eicosane paraffin.
Oscillatory Conductive Heat Transfer for a Fiber in an Ideal Gas
Authors: Kuntz H. L. , Perreira N. D.
Published: October 2009

A description of the thermal effects created by placing a cylindrical fiber in an inviscid, ideal gas, through which an acoustic wave propagates, is presented. The fibers and the gas have finite heat capacities and thermal conductivities. Expressions for the temperature distribution in the gas and in the material are determined. The temperature distribution is caused by pressure oscillations in the gas which, in turn, are caused by the passage of an acoustic wave. The relative value of a dimensionless parameter is found to be indicative of whether the exact or approximate equations should be used in the solution. This parameter is a function of the thermal conductivities and heat capacities of the fiber and gas, the acoustic frequency, and the fiber diameter.
Transient Response of a Coupled Conduction and Convection Heat Transfer Problem
Authors: Friedly J. C.
Published: October 2009

Systems of dynamic models involving the coupling of both conduction and convection offer significant theoretical challenges because of the interaction between parabolic and hyperbolic types of responses. Recent results of state space theory for coupled partial differential equation models are applied to conjugate heat transfer problems in an attempt to understand this interaction. Definition of a matrix of Green’s functions for such problems permits the transient responses to be resolved directly in terms of the operators’ spectral properties when they can be obtained. Application of the theory to a simple conjugate heat transfer problem is worked out in detail. The model consists of the transient energy storage or retrieval in a stationary, single dimensioned matrix through which an energy transport fluid flows. Even though the partial differential operator is nonself-adjoint, it is shown how its spectral properties can be obtained and used in the general solution. Computations are presented on the effect of parameters on the spectral properties and the nature of the solution. Comparison is made with several readily solvable limiting cases of the equations.
Turbulent Heat Transfer Computations for Rearward-Facing Steps and Sudden Pipe Expansions
Authors: Gooray A. M. , Watkins C. B. , Aung Win
Published: October 2009

Results of numerical calculations for heat transfer in turbulent recirculating flow over two-dimensional, rearward-facing steps and sudden pipe expansions are presented. The turbulence models used in the calculation are the standard k – ε model and the low-Reynolds number version of this model. The k – ε models have been improved to account for the effects of streamline curvature and pressure-strain (scalar) interactions including wall damping. A sequence of two computational passes is performed to obtain optimal results over the entire flow field. The presented results consist of computed distributions of heat transfer coefficents for several Reynolds numbers, emphasizing the low-to-moderate Reynolds number regime. The heat transfer results also include correlations of Nusselt numnber for both side and bottom walls. The computed heat transfer results and typical computed fluid dynamic results are compared with available experimental data.
Thermophoretic Deposition of Particles in Natural Convection Flow From a Vertical Plate
Authors: Epstein M. , Hauser G. M. , Henry R. E.
Published: October 2009

An analysis is made for thermophoretic transport of small particles through a free-convection boundary layer adjacent to a cold, vertical deposition surface. The gas-particle, boundary layer equations are solved numerically for both laminar and turbulent flow. The numerical results indicate that, for a fixed set of boundary conditions and physical properties, the particle concentration at the wall in the laminar flow is very close to that in turbulent flow. A simple expression is suggested relating the particle transport rate to the heat transfer coefficient for the laminar and turbulent flow regimes.
Investigation of Turbulators for Fire Tube Boilers
Authors: Junkhan G. H. , Bergles A. E. , Nirmalan V. , Ravigururajan T.
Published: October 2009

This paper summarizes an experimental study of three popular “turbulator” inserts for fire tube boilers. An electrically heated flow facility was developed to deliver hot air to a water-cooled steel tube instrumented to derive sectional average heat transfer coefficients for four regions of the tube. Reference data for the empty tube are in excellent agreement with the accepted correlation. Two commercial turbulators, consisting of narrow, thin metal strips bent and twisted in zig-zag fashion to allow periodic contact with the tube wall, displayed 135 and 175 percent increases in heat transfer coefficient at a Reynolds number of 10,000. A third commercial turbulator, consisting of a twisted strip with width slightly less than tube diameter, provided a 65 percent increase in heat transfer coefficient. The friction factor increases accompanying these heat transfer coefficient increases were 1110, 1000, and 160 percent, respectively, for the same Reynolds number. These data should be useful in assessing overall performance gains to be expected when turbulators are used in actual boilers.
Effect of Fin Spacing on the Performance of Horizontal Integral-Fin Condenser Tubes
Authors: Yau K. K. , Cooper J. R. , Rose J. W.
Published: October 2009

The dependence of heat transfer performance on fin spacing has been investigated for condensation of steam on horizontal integral-fin tubes. Thirteen tubes have been used with rectangular section fins having the same width and height (0.5 mm and 1.6 mm) and with fin pitch varying from 1.0 mm to 20.5 mm. For comparison, tests were made using a plain tube having the same inside diameter and an outside diameter equal to that at the root of the fins for the finned tubes. All tests were made at near-atmospheric pressure with vapor flowing vertically downward with velocities between 0.5 m/s and 1.1 m/s. The observed heat transfer enhancement for the finned tubes significantly exceeded that to be expected on grounds of increased area. Plots of enhancement against fin density were repeatable and showed local maxima and minima. The dependence of enhancement on fin density did not depend appreciably on vapor velocity or condensation rate for the ranges used. The maximum vapor-side enhancement (i.e., vapor-side heat transfer coefficient of finned tube/vapor-side coefficient for plain tube) was found to be around 3.6 for the tube with a fin spacing of 1.5 mm.
Corresponding States Correlations for Pool and Flow Boiling Burnout
Authors: Sharan A. , Lienhard J. H. , Kaul R.
Published: October 2009

The peak pool boiling heat flux can be nondimensionalized so the dimensionless peak heat flux is a function of a Bond or Laplace number that characterizes the system geometry. The dimensionless peak heat flux can be interpreted as the product of a geometrical function (given by previous investigations), universal functions of the reduced saturation pressure, and the Pitzer acentric factor. The latter universal functions are constructed by correlation. These are combined to give a single prediction of the peak heat flux that applies to all the common geometrical heater configurations. The probable error of the prediction, when it is compared with the available peak heat flux data, is 6.1 percent for substances whose dipole moment is not high. The method is also extended to create a comparable correlation for flow boiling burnout during crossflows over cylinders. There is a lack of data with which to check this correlation fully.
Heat and Mass Transfer Associated With Condensation on a Moving Drop: Solutions for Intermediate Reynolds Numbers by a Boundary Layer Formulation
Authors: Sundararajan T. , Ayyaswamy P. S.
Published: October 2009

Condensation heat and mass transfer to a liquid drop moving in a mixture of saturated vapor and a noncondensable have been evaluated. The Reynolds number of the drop motion is 0(100). The quasi-steady, coupled, boundary layer equations for the flow field and the transport in the gaseous phase are simultaneously solved. The heat transport inside the drop is treated as a transient process. Results are presented for the heat and mass transport rates to the drop, the surface shear stress, the velocity profiles across the boundary layer, and the temperature-time history of the drop. The comparisons of results with experimental data, where available, show excellent agreement. Tables summarizing results appropriate to a wide range of condensation rates have been included. Local heat and mass transfer rates have also been presented. These features will make the paper useful to the designer of direct contact heat transfer equipment.
Prediction of Flow Patterns During Condensation of Binary Mixtures in a Horizontal Tube
Authors: Tandon T. N. , Varma H. K. , Gupta C. P.
Published: October 2009

In the present paper, experimental flow pattern data during forced convection condensation of binary mixtures of R-22 and R-12 inside a horizontal tube are reported for the first time. These visually observed flow patterns were plotted on existing condensing flow as well as on Baker’s adiabatic flow map. The mixture flow pattern data were found to best correlate on a flow regimes map suggested earlier by the present authors [8] with dimensionless gas velocity Jg* and (1 − α)/α coordinates (α is the void fraction). The criteria to delineate different flow regimes for mixtures have also been found to be the same as those proposed earlier for pure refrigerants.
Enhanced Heat Conduction in Fluids Subjected to Sinusoidal Oscillations
Authors: Kurzweg U. H.
Published: October 2009

Enhanced conduction heat transfer via sinusoidal oscillatory flow through circular tubes connecting two fluid reservoirs maintained at different temperatures is examined. Using a multiscale expansion technique for the solution of the governing partial differential equation, the spatial and temporal temperature variation within the tubes is determined for low values of α2 Pr, where α is the Womersley number and Pr the fluid Prandtl number. From this result, a calculation of the effective thermal diffusivity is made and used to determine the enhanced conduction heat transfer from the high- to low-temperature reservoir. The enhanced heat transfer produced by the oscillations is shown to be proportional to the square of the oscillation amplitude and a function of the Prandtl number, the frequency, and the tube radius. Values of effective conductivity in liquid metals three orders of magnitude greater than the normal heat conductivity are shown to be readily obtainable under typical experimental conditions.
Optimization of Thermal Conductivities of Isotropic and Orthotropic Solids
Authors: Meric R. A.
Published: October 2009

Optimization of thermal conductivities of isotropic and orthotropic solids is treated as a steady-state optimal control problem. Nonlinear necessary optimum conditions are first derived for the so-called material optimization problem, and a general numerical method of solution is then proposed. The iterative numerical procedure solves the linearized state and co-state equations by the finite element method and minimizes the performance index by the conjugate gradient method. Numerical solutions, checked with exact results when possible, are given for an isotropic infinite plate and a cylinder.
Enhancement of Thermal Contact Conductance by Metallic Coatings: Theory and Experiment
Authors: Antonetti V. W. , Yovanovich M. M.
Published: October 2009

A thermomechanical model for nominally flat, rough contacting surfaces coated with a metallic layer is developed. The model is shown to agree quite well with thermal test data obtained using nickel specimens, with one side of the contact coated with silver and the other side glass-bead blasted. In addition, it is demonstrated that a coated joint can be reduced to an equivalent bare joint by employing an effective hardness and an effective thermal conductivity. Using this technique, 61 coated test points were correlated, with an RMS difference of ± 12.6 percent between the data and a correlation which had previously been used only for bare contacts.
A Method for the Solution of Heat Transfer Problems With a Change of Phase
Authors: Frederick D. , Greif R.
Published: October 2009

A method of broad applicability is presented which can be used to obtain solutions to problems involving a phase change. The solution in one of the phases is specified as a known single-phase solution; an inverse analysis then determines the solution for the other phase. Two problems are studied: The first yields the similarity solution for the planar geometry and the second gives the exact solution to a more general problem. Convergence is shown and error bounds are given. The method can accommodate convection, heat generation, variable properties, nonplanar, and multidimensional systems.
Combined Analysis and Optimization of Extended Heat Transfer Surfaces
Authors: Hrymak A. N. , McRae G. J. , Westerberg A. W.
Published: October 2009

This study presents an efficient numerical method to discover the optimal shape for a fin subject to both convective and radiative heat loss. Problem formulation is a finite element approximation to the conduction equation embedded within and solved simultaneously with the shape optimization problem. The approach handles arbitrary equality and inequality constraints. Grid points move to conform to the fin shape during the problem solution, reducing the number of elements required in the solution.
On the Heat Transfer of a Moving Composite Strip Compressed by Two Rotating Cylinders
Authors: Yuen W. Y. D.
Published: October 2009

Two influential parameters in rolling mill analysis are the heat loss to the rolls and the strip temperature distribution. In this paper, the heat transfer process occurring in rolling is modeled by a moving three-layer composite strip, compressed between two rotating cylinders. It is shown that, for the range of parameters representative of strip rolling, the problem can be reduced, to leading order, to one of heat transfer beween slabs with plane parallel boundary contact. The heating effects due to deformation energy generated in the strip, friction energy generated at the strip/cylinder interfaces, and the strip/cylinder bulk temperature difference are considered. Application of the results to rolling analysis is demonstrated.
A Numerical Study of Laminar and Turbulent Heat Transfer in a Periodically Corrugated Wall Channel
Authors: Amano R. S.
Published: October 2009

A numerical study is reported on hydrodynamic and heat transfer characteristics in a periodically corrugated wall channel for both laminar and turbulent flows. For turbulent flows the k-ε turbulence model with a refined near-wall model is adopted for the computation of the flow field for step ratios H/W ranging from two to four. The Reynolds number considered in this study varies from 10 to 25,000. The solution method of the governing transport equations is based on the modified hybrid scheme. As a result of extensive computations, the complex flow patterns in the perpendicularly corrugated wall channel are clarified and the mechanisms of heat transfer are explained relating to the flow phenomena of separation, deflection, recirculation, and reattachment. Finally it was observed that the effect of the step ratio on the local Nusselt number is minor. Moreover, it was found that both skin friction and heat transfer patterns change drastically from laminar to turbulent flows.
Measurements and Predictions of Laminar Mixed Convection Flow Adjacent to a Vertical Surface
Authors: Ramachandran N. , Armaly B. F. , Chen T. S.
Published: October 2009

Measurements and predictions of laminar mixed forced and free convection air flow adjacent to an isothermally heated vertical flat surface are reported. Local Nusselt numbers and the velocity and temperature distributions are presented for both the buoyancy assisting and opposing flow cases over the entire mixed convection regime, from the pure forced convection limit (buoyancy parameter ξ = Grx/Rex2 = 0) to the pure free convection limit (ξ = ∞). The measurements are in very good agreement with predictions and deviate from the pure forced and free convection regimes for buoyancy assisting flow in the region of 0.01 ≤ ξ ≤ 10 and for opposing flow in the region of 0.01<ξ< 0.2. The local Nusselt number increases for buoyancy assisting flow and decreases for opposing flow with increasing value of the buoyancy parameter. The mixed convection Nusselt numbers are larger than the corresponding pure forced and pure free convection limits for buoyancy assisting flow and are smaller than these limits for opposing flow. For buoyancy assisting flow, the velocity overshoot and wall shear stress increase, whereas the temperature decreases but the temperature gradient at the wall increases as the buoyancy parameter increases. The reverse trend is observed for the opposing flow. Flow reversal near the wall was detected for the buoyancy opposing flow case at a buoyancy parameter of about ξ = 0.20.