bluuebunny/crossref_metadata_2025 huggingface dataset:
Two-Phase Heat Transfer for Flow in Tubes and Over Rod Bundles With Blockages
Authors: Drucker M. I. , Dhir V. K. , Duffey R. B.
Published: October 2009

A study of single- and two-component, two-phase heat transfer mechanisms for vertical flow inside of tubes and over rod bundles with blockages has been made. Existing heat transfer data for air–water flow in tubes with a liquid Reynolds number range of 2000 to 150,000 and void fractions up to 0.40 have been correlated as a function of αGr/Re2. The correlation has also been found to compare well with limited high Prandtl number data obtained with liquids other than water and for flow over rod bundles when an empirical constant is modified. Correlations have also been developed for the heat transfer coefficient in the vicinity of flow blockages in rod bundles. The heat transfer data have been obtained on a four rod bundle with sleeve-type blockages for a Reynolds number range of 230 to 6900 and void fractions up to 0.15. Significant enhancement of the heat transfer coefficient has been observed downstream of the blockages.
Optimization of Cooled Shields in Insulations
Authors: Chato J. C. , Khodadadi J. M.
Published: October 2009

A relatively simple method has been developed to optimize the location, temperature, and heat dissipation rate of each cooled shield inside an insulation layer. The method is based on the minimization of the entropy production rate, which is proportional to the heat leak across the insulation. The results show that the maximum number of shields to be used in most practical applications is three. However, cooled shields are useful only at low values of the overall, cold wall to hot wall absolute temperature ratio. The performance of the insulation system is relatively insensitive to deviations from the optimum values of temperature and location of the cooling shields. Design curves are presented for rapid estimates of the locations and temperatures of cooling shields in various types of insulations, and an equation is given for calculating the cooling loads for the shields.
Simultaneous Heat and Mass Transfer Accompanied by Phase Change in Porous Insulation
Authors: Vafai K. , Whitaker S.
Published: October 2009

This paper analyzes the accumulation and migration of moisture in an insulation material. The problem is modeled as a two-dimensional, transient, multiphase flow in a porous slab. The local volume-averaging technique is used to arrive at a rigorous and fundamental formulation of the heat and mass transfer process in an insulation system. The controlling parameters and assumptions are presented in detail. The equations are solved by devising a two-phase numerical scheme to obtain the condensation regions and the factors which affect the temperature distribution. The phase change process and its effects on the temperature, vapor density, moisture content, liquid content, and the vapor pressure distributions are discussed in detail. The significant transport mechanisms are identified and a simplified formulation of heat and mass transfer, accompanied by phase change, in an insulation system is presented.
Effectiveness of Series Assemblies of Divided-Flow Heat Exchangers
Authors: Pignotti A.
Published: October 2009

Formulas are derived for the effectiveness of a series assembly of two divided-flow exchangers, as a function of the heat capacity rate ratio, and the partial effectivenesses of the components. Six possible connections are discussed: overall parallel flow and counterflow, with either mixing of the intermediate divided streams, or direct or crossed coupling of the same. It is shown that when both exchangers are alike, and direct coupling is used, the simplifying mixing assumption leads to a systematic overestimate of the effectiveness of the assembly. The size of this effect is discussed and illustrated with explicit solutions for TEMA J exchangers with one and two tube passes.
Scaling of Plain and Externally Finned Heat Exchanger Tubes
Authors: Sheikholeslami R. , Watkinson A. P.
Published: October 2009

The performance of copper and mild steel plain heat exchanger tubes and an externally finned mild steel tube was studied under calcium carbonate scaling conditions. Under a constant heat flux for 70-h periods the fouling resistance generally increased linearly with time. The effect of velocity on the rate of scale formation is presented for the three tubes and results compared with the model of Hasson.
Heat Transfer Across a Two-Fluid-Layer Region
Authors: Lienhard J. H. , Catton I.
Published: October 2009

Heat transfer across a two-fluid-layer region is calculated for Rayleigh numbers in excess of the critical value. The method of solution is based on Landau’s comments regarding the onset of turbulence, following Malkus and others. The linear stability problem is solved for its eigenvalues and eigenfunctions, and the eigenfunctions are used to calculate the contribution of secondary motion to heat transfer. Results are obtained in terms of an overall Nusselt number as a function of Rayleigh number, midlayer thickness, and midlayer thermal conductivity.
Enhanced Heat Transfer From a Horizontal Finned Tube Situated in a Vertical Channel
Authors: Sparrow E. M. , Ansari M. A. , Stryker P. C. , Ruiz R.
Published: October 2009

Experiments were performed to determine the heat transfer characteristics of a horizontal finned tube situated in a vertical channel which is open to the ambient at the top and bottom. The heat transfer from the finned tube is by natural convection and radiation. The response of the finned-tube heat transfer to three geometric parameters was investigated: (1) the vertical position of the tube in the channel, (2) the clearance between the fin tips and the channel walls, and (3) the height of the channel. Experiments were also carried out with the finned tube situated in free space. It was found that in-channel positioning of the finned tube gave rise to substantially higher heat transfer rates than did free-space positioning. With the finned tube situated in the channel, the heat transfer was enhanced by: (1) positioning the tube at the bottom of the channel, (2) small tip-to-wall clearances, and (3) tall channels.
Prandtl Number Effect on Be´nard Convection in Porous Media
Authors: Georgiadis J. G. , Catton I.
Published: October 2009

A numerical study of buoyancy-driven two-dimensional convection in a fluid-saturated horizontal porous layer is reported emphasizing the nonlinear inertial effect on heat transport. The Forchheimer–Brinkman–Darcy–Boussinesq formulation and a single energy equation for the volume-average temperature are used. Closure to the wavenumber selection problem is sought through a criterion based on the Glansdorff and Prigogine theory of nonequilibrium thermodynamics. Good agreement with laboratory data and the analogy with the Rayleigh–Be´nard problem are corroborative facts which justify similar non-Darcian formulations and demonstrate the role of the quadratic inertial terms in decreasing the mean convective heat transfer across the layer.
Pseudo-Steady-State Natural Convection Heat Transfer Inside a Vertical Cylinder
Authors: Lin Y. S. , Akins R. G.
Published: October 2009

The SIMPLER numerical method was used to calculate the pseudo-steady-state natural convection heat transfer to a fluid inside a closed vertical cylinder for which the boundary temperature was spatially uniform and the temperatures throughout the entire system were increasing at the same rate. (Pseudo-steady state is comparable to the steady-state problem for a fluid with uniform heat generation and constant wall temperature.) Stream functions, temperature contours, axial velocities, and temperature profiles are presented. The range of calculation was 0.25 < H/D < 2, Ra < 107, and Pr = 7. This range includes conduction to weak turbulence. A characteristic length defined as 6 × (volume)/(surface area) was used since it seemed to produce good regression results. The overall heat transfer for the convection-dominated range was found to be correlated by Nu = 0.519 Ra0.255, where the temperature difference for both the Nusselt and Rayleigh numbers was the center temperature minus the wall temperature. Correlations using other temperature differences are also presented for estimating the volumetric mean and minimum temperatures.
Higher Order Moments in the Entrainment Zone of Turbulent Penetrative Thermal Convection
Authors: Kumar R. , Adrian R. J.
Published: October 2009

In a simulation of the lifting of an atmospheric inversion layer in the laboratory, measurements have been made to understand the dynamics in the interfacial region capped by a stable, linearly stratified layer. Instantaneous values of vertical and horizontal components of velocity have been measured using a two-component dual-beam laser Doppler anemometer. Temperature fluctuations have been made simultaneously. Detailed measurements of all relevant horizontally averaged one-point moments including heat flux and third-order joint vertical velocity–temperature moments have been obtained. The negative heat flux region is well defined in the entrainment zone, and varies in thickness with different stable layer temperature gradients. The entrainment mechanism is probably most important only in the top part of the interfacial zone. The present data supplement data obtained in the atmosphere, and they compare favorably with the existing data in the literature.
Use of a Cubic Equation to Predict Surface Tension and Spinodal Limits
Authors: Biney P. O. , Dong Wei-guo , Lienhard J. H.
Published: October 2009

The very general Shamsundar–Murali cubic equation is used to interpolate p–v–T data into the metastable and unstable regions. This yields a spinodal line that closely matches the homogeneous nucleation limit predicted by an improved kinetic theory. Only the pressure, the saturated liquid and vapor volumes, and the liquid compressibility at saturation, as well as one compressed liquid data point, are needed to use the cubic equation for the interpolation process. The equation also yields an accurate prediction of the temperature dependence of surface tension when it is substituted in van der Waals’ surface tension formula. Thus, by capitalizing on the inherent relation among the p–v–T equation, the spinodal prediction, and the surface tension—all three—it is possible to obtain each with high accuracy and minimal experimental data.
Critical Heat Flux on a Horizontal Cylinder in an Upward Subcooled and Low-Quality Two-Phase Crossflow
Authors: Jensen M. K. , Pourdashti M.
Published: October 2009

An experimental investigation has been conducted to determine the low-velocity critical heat flux (CHF) behavior on a single horizontal tube in a subcooled and low-quality two-phase crossflow of R-113. Data were obtained over a range of velocities (up to 0.3 m/s), subcooling (0 to 14 K), and qualities (0 < x < +30 percent) at two pressures. There was a linear decrease in the CHF with increasing quality up to about 10 percent quality; then, due to a flow regime transition, the CHF remained relatively constant. A correlation has been developed which predicted well the subcooled and low-quality region CHF condition in the linearly decreasing portion of the curve. Data from the literature are also predicted well.
Reflooding With Steady and Oscillatory Coolant Injection: Part 2—Quench Front and Liquid Carryover Behavior
Authors: Oh S. , Banerjee S. , Yadigaroglu G.
Published: October 2009

The reflooding of a tubular test section under oscillatory inlet flow conditions has been investigated experimentally for initial wall temperatures from 316° C to 760°C, oscillation periods from 2 to 6 s, and test section liquid level amplitudes up to 0.76 m. Compared to constant-injection reflooding, the oscillations always increase the liquid carryover rate in the early stages of reflooding. As reflooding progresses, the enhancement diminishes and becomes negative. The crossover point roughly coincides with saturation of the liquid at the quench front. The higher initial liquid carryover increases downstream heat transfer and speeds up quench front propagation, but it also reduces the test section mass accumulation rate, and for this reason delays quench front propagation at later stages. These effects are accentuated at higher oscillation amplitude and frequency. Large oscillations change the reflooding behavior substantially. Quantitative comparisons of quench front velocities and heat transfer immediately downstream of the quench front, obtained through the use of empirical local-condition correlations representing the steady-reflooding rate data, are presented.
An Experimental and Analytical Investigation of Friction Factors for Fully Developed Flow in Internally Finned Triangular Ducts
Authors: Chegini H. , Chaturvedi S. K.
Published: October 2009

Friction factors for fully developed flow in triangular ducts with fins of various height and width are investigated for Reynolds numbers ranging from 150 to 90,000. Two triangular ducts having apex angles of 60 and 38.8 deg are studied. Results are presented in the form of standard plots of friction factor as a function of Reynolds number. Friction factor values for the smooth triangular duct cases are in good agreement with the existing results. For the finned-duct cases, the fully developed axial velocity profiles in laminar flow are determined by solving the x-momentum equation iteratively by the Gauss–Seidel finite-difference technique. The theoretically determined friction factors for these cases are in good agreement with the experimental values of friction factors based on pressure drop measurements.
Heat Transfer and Flow Visualization in Natural Convection in Rapidly Spinning Systems
Authors: Sobel L. , El-Masri M. , Smith J. L.
Published: October 2009

The design of airborne superconducting generators for intermittent duty requires the understanding of some unique free-convection processes in the spinning helium bath. Toward that end, some fundamental experiments on steady and transient free convection in rotating containers of representative geometries have been performed. Heat transfer data from heaters of various geometries mounted on the outer container surface to several fluids are reported. A correlation for steady-state Nusselt number is presented for a wide range of Rayleigh and Prandtl numbers. The heat transfer coefficient was found to be independent of heater size, geometry, and fluid viscosity. Heat transfer measurements during simultaneous thermal transients and sudden increases in rotational speed were also made. They show an enhancement of heat transfer due to the relative counterrotation of the fluid following the acceleration of the container. This persists for a period well below that for fluid spinup. A model based upon the submergence of the thermal boundary layer by the diffusive wave from the wall was successful in correlating this period. Quasi-steady flow visualization experiments indicate that the thermal plumes generate two-dimensional, axially invariant flow fields. Their trajectories are radial relative to the spinning container. Those observations are shown to be consistent with the fact that weak buoyant plumes in containers rotating at small Ekman numbers result in low Rossby number motions. Those are two dimensional according to the Taylor–Proudman theorem. It is shown that the Coriolis and pressure forces on such a thermal column are in azimuthal equilibrium, hence the radial trajectory. Flow visualization following impulsive acceleration in an off-axis, nonaxisymmetric container shows that the flow field is dominated by vortices expelled from corners. The fluid spinup time, however, was found to be the same as that for an on-axis circular cylinder of the same characteristic diameter.
Experimental Investigation of Mixed Laminar Convection in the Entrance Region of Inclined Rectangular Channels
Authors: Morcos S. M. , Hilal M. M. , Kamel M. M. , Soliman M. S.
Published: October 2009

The present experimental study considers the effect of combined forced and free laminar convection on the heat transfer in the entrance region of horizontal and inclined rectangular channels under uniform wall heat flux. The test facility includes electrically heated aluminum rectangular channels having aspect ratios AR = 2.667 and 0.375, with water as the working fluid. The experimental results included the circumferential wall temperature distribution and the axial variation of Nusselt number. Correlations of the experimental results of Nusselt number in the fully developed region were obtained in terms of Rayleigh number, Reynolds number, and inclination angle.
Heat Conduction in a Moving Semi-infinite Solid Subjected to Pulsed Laser Irradiation
Authors: Modest M. F. , Abakians H.
Published: October 2009

Heat conduction in a moving semi-infinite medium subject to laser irradiation is considered. The body of knowledge of exact analytical solutions for Gaussian laser irradiation is expanded to include pulsed lasers, and laser beams that penetrate into the medium with exponential decay. For applications with complicated geometries (laser melting and evaporation), a simple integral method, based on one-dimensional diffusion, is presented, and its range of validity determined.
Structure of Laminar Coflow Methane–Air Diffusion Flames
Authors: Saito K. , Williams F. A. , Gordon A. S.
Published: October 2009

Measured temperature and composition profiles are reported for a number of flames. Implications concerning flame structure are deduced, with emphasis on soot formation and on correlations involving conserved scalars.
Correlation of Melting Results for Both Pure Substances and Impure Substances
Authors: Sparrow E. M. , Gurtcheff G. A. , Myrum T. A.
Published: October 2009

Melting experiments were performed encompassing both pure and impure substances. The pure substances included n-octadecane paraffin and n-eicosane paraffin, while the impure substances were mixtures synthesized from the pure paraffins. The experiments were carried out in a closed vertical tube whose wall was subjected to a step-change increase in temperature to initiate the melting. For each impure substance, supplementary measurements were made of two characteristic temperatures: the temperature T** at which melting of the solid phase first begins and the lowest temperature T* at which the melting can go to completion. For a pure substance, T** = T*. The time-dependent melting results for all the investigated substances, both pure and impure, were well correlated as a function of FoSte**(Gr**)1/8 alone, where the ** signifies the presence of T** in the temperature difference which appears in Ste and Gr. This correlation enables melting rates for impure substances to be determined from melting rates for pure substances. The T** values needed for the implementation of the correlation can be obtained from simple experiments, obviating the need for the complete equilibrium phase diagram.
Natural Convection Experiments in a Stratified Liquid-Saturated Porous Medium
Authors: Reda D. C.
Published: October 2009

Natural convection heat transfer from a constant-flux cylinder, immersed vertically through a stratified (two-layer) liquid-saturated porous medium, was investigated experimentally. Measured radial temperature profiles and heat transfer rates agreed well with numerical predictions based on the work of Hickox and Gartling. The 1:6 permeability-ratio interface existing between the two layers was found to effectively trap buoyancy-driven fluid motion within the high-permeability region, beneath the interface. Within this high-permeability region, Nusselt number versus Rayleigh number data were found to correlate with previously measured results, obtained for the same basic geometry, but with a fully permeable upper-surface hydrodynamic boundary condition. In both cases, the vertical and radial extent of the region under study were large compared to the radius of the heat source. Combined results indicate that, for a given Rayleigh number in the Darcy-flow regime, heat transfer rates from cylinders immersed vertically in uniform liquid-saturated porous media of large vertical and radial extent potentially approach limiting values. Variable-porosity effects which occur in unconsolidated porous media adjacent to solid boundaries were investigated numerically for cases where the particle-to-heater diameter ratio was small (≈ 10−2). Results showed variable-porosity effects to have a negligible influence on the thermal field adjacent to such boundaries under conditions of Darcy flow.
Electric Field Effects on Natural Convection in Enclosures
Authors: Nelson D. A. , Shaughnessy E. J.
Published: October 2009

The enhancement of convective heat transfer by an electric field is but one aspect of the complex thermoelectric phenomena which arise from the interaction of fluid dynamic and electric fields. Our current knowledge of this area is limited to a very few experimental studies. There has been no formal analysis of the basic coupling modes of the Navier–Stokes and Maxwell equations which are developed in the absence of any appreciable magnetic fields. Convective flows in enclosures are particularly sensitive because the limited fluid volumes, recirculation, and generally low velocities allow the relatively weak electric body force to exert a significant influence. In this work, the modes by which the Navier–Stokes equations are coupled to Maxwell’s equations of electrodynamics are reviewed. The conditions governing the most significant coupling modes (Coulombic forces, Joule heating, permittivity gradients) are then derived within the context of a first-order theory of electrohydrodynamics. Situations in which these couplings may have a profound effect on the convective heat transfer rate are postulated. The result is an organized framework for controlling the heat transfer rate in enclosures.
Effect of Plate Inclination on Natural Convection From a Plate to Its Cylindrical Enclosure
Authors: Singh P. , Liburdy J. A.
Published: October 2009

Presented in this paper are the local and mean heat transfer coefficients for an inclined, thin, heated flat surface enclosed in a long isothermal cylinder. Holographic interferometry was used to identify variations of the convective coefficient on both sides of the plate. There are significant local variations when the surface is oriented at different angles to the gravitation vector. An overall heat transfer coefficient is identified which is influenced by opposing inclination effects on either side of the surface. Results are significantly different from those of a surface in an infinite environment due to the recirculation required by the enclosure geometry. The effects of inclination become minor at angles greater than 60 deg from the horizontal.
Numerical Investigation of Variable Property Effects on Laminar Natural Convection of Gases Between Two Horizontal Isothermal Concentric Cylinders
Authors: Mahony D. N. , Kumar R. , Bishop E. H.
Published: October 2009

A numerical finite difference investigation has been conducted to determine the effects of variable properties on the laminar natural convection of gases between horizontal isothermal concentric cylinders. Velocity profiles, temperature profiles, and heat transfer rates have been computed for diameter ratios of 1.5, 2.28, 2.6, and 5.0 and Rayleigh numbers based on gap width up to 1.8 × 105. The temperature difference ratio θo was varied from 0.2 to 3.0, and the range of validity of the Boussinesq approximation was determined to be θo = 0.2. A volume-weighted mean temperature was shown to be the most effective reference temperature to reduce the heat transfer data for each diameter ratio to a single curve of the form keq = C RaLn, for 0.2 ≤ θo ≤ 3.0 and RaL = 2.0 × 105.
The Buoyant Plume-Driven Adiabatic Ceiling Temperature Revisited
Authors: Cooper L. Y. , Woodhouse A.
Published: October 2009

In previous works, convective heat transfer from buoyant plume-driven ceiling jets to unconfined ceilings has been estimated using a formula for the temperature distribution below an adiabatic ceiling Tad obtained from experimental data in the range 0 ≤ r/H < 0.7 (r is the radial distance from the plume and H is the plume source-to-ceiling distance). The present study re-evaluates these data, and develops an independent estimate for Tad. The analysis takes account of the effect of ceiling surface reradiation, and use is made of the previously established similarity between plume/ceiling- and jet/wall-driven heat transfer phenomena. The latter similarity is the basis of a correlation of recently reported free jet-wall jet “recovery temperature” data into a normalized Tad distribution. All of the analysis leads to new formulae for estimating the convective heat transfer to ceilings during enclosure fires. These new results confirm previous formulae, and extend them into the larger range 0 ≤ r/H ≤ 2.2.
Mass Transfer at the Base of a Cylindrical Cavity Recessed in the Floor of a Flat Duct
Authors: Sparrow E. M. , Misterek D. L.
Published: October 2009

Experiments involving either sublimation or evaporation at the base surface of a cylindrical cavity were performed respectively using naphthalene and water as the transferred vapor. The cavity was mounted in the lower wall of a flat rectangular duct through which turbulent air was passed. Supplementary experiments were also carried out using a cavity with a constricted opening (i.e., a Helmholtz resonator). The base surface mass transfer did not decrease monotonically with increasing cavity depth. Rather, there were two local maxima, respectively at about 0.06D and 0.5D (D = cavity diameter). Of these, the first is due to the reattachment of the shear layer on the cavity base. For the second, both fluid-elastic and fluid-resonant oscillations were ruled out as causes on the basis of definitive experimental data, leaving fluid-dynamic oscillations as a possible cause. The base surface Sherwood number was well correlated by power-law dependences on the Reynolds and Schmidt numbers. Fluid flow experiments encompassing oil-lampblack flow visualization, helium bubble flow visualization, and spectral analysis of the pressure field at the cavity base were also carried out.
Growth of Flame Front Turbulence
Authors: Tsuruda T. , Harayama M. , Hirano T.
Published: October 2009

An experimental study was performed on the growth of flame front turbulence by stimulating a laminar propagating flame with weak pressure waves, which were generated by sudden breaking of the membrane separating a small chamber from the combustion chamber. The flame front behavior was explored by using high-speed schlieren photography. About one millisecond after the first weak pressure wave passed the flame front, a very fine disturbance appeared at the central part of the flame front, where no effect of the wall turbulence could appear. Then, the area and strength of the disturbance were observed to increase rapidly. The effects of the pressure wave intensity, fuel concentration, and fuel type on the growth of this type of flame front turbulence were examined in detail.
Water Droplet Size Measurements in an Experimental Steam Turbine Using an Optical Fiber Droplet Sizer
Authors: Tatsuno K. , Nagao S.
Published: October 2009

An optical fiber droplet sizer which is applicable to droplet size measurements in a steam turbine has been developed. This sizer uses the forward scattering method. The performance of the droplet sizer was verified by 0.1–5.7 μm average diameter polystyrene particles. Using this sizer, droplet size measurements were made at the last stage moving blade outlet in a 10 MW experimental steam turbine. Average diameters between 0.2 and 1.0 μm, which depend on wetness (6–14 percent) and locations in the radial direction of the blade, were obtained.
Film Condensation of Steam on Horizontal Finned Tubes: Effect of Fin Spacing
Authors: Wanniarachchi A. S. , Marto P. J. , Rose J. W.
Published: October 2009

The film condensation heat transfer performance of six externally finned copper tubes has been evaluated. All tubes had rectangular-shaped fins with a height and thickness of 1 mm. The spacing between fins was 0.5, 1.0, 1.5, 2.0, 4.0, and 9.0 mm. Data were also obtained for a smooth tube whose outside diameter of 19.0 mm was equal to the diameter at the base of the fins for all of the finned tubes. Tests were performed both at atmospheric pressure and under vacuum (∼ 11.3 kPa). Steam flowed vertically downward with a velocity of approximately 1 and 2 m/s at atmospheric pressure and under vacuum, respectively. The smooth tube was fitted with wall thermocouples for the evaluation of the water-side heat transfer coefficient. This was used, subsequently, to determine the steam-side heat transfer coefficient for the finned tubes for which only overall measurements were made. Strenuous efforts were made to obtain high-accuracy data; in particular, the coolant temperature rise was determined by both quartz-crystal thermometers and a 10-junction thermopile. The two temperature-rise measurements always agreed to within ± 0.03 K. Care was taken to avoid errors due to the presence of noncondensing gases and to ensure that filmwise condensation conditions prevailed over the entire tube throughout all tests. The steam-side heat transfer coefficient for the smooth tube agreed closely with values found by other recent workers. Maximum steam-side enhancement was found for the tube with a fin spacing of 1.5 mm. At this fin spacing, the heat transfer enhancement ratios were around 3.6 and 5.2 for low-pressure and atmospheric pressure runs, respectively.
Heat Transfer and Pressure Drop of Typical Air Cooler Finned Tubes
Authors: Eckels P. W. , Rabas T. J.
Published: October 2009

The heat transfer and pressure drop performance of heat exchangers fabricated from helically wrapped finned tubes with an equilateral triangular pitch arrangement are reported for one through five rows. Two finned tube types were tested, one with a “T” foot and the other with an overlapped “L” foot. The dimensions of both finned tubes were similar and were typical of those used in air-cooling applications. The tube diameter was 25.4 mm; the fin height was 15.87 mm; the fin number was 0.41/mm; and the fin-tip clearance was 6.35 mm. The fin base thickness was 0.38 mm and was tapered to half the base thickness at the fin outside diameter. No difference in the thermal performance of the two finned tube types could be detected. Both the heat transfer coefficient and pressure drop were found to increase with the number of tube rows. These results were then compared to other published data.
Firestorms
Authors: Carrier G. F. , Fendell F. E. , Feldman P. S.
Published: October 2009

Quantitative criteria are sought for onset of firestorms, severe stationary (non-propagating) holocausts arising via merger of fires from multiple simultaneous ignitions in a heavily fuel-laden urban environment. Within an hour, surface-level radial inflow from all directions sustains a large-diameter convective column that eventually reaches altitude of about 10 km (e.g., Hamburg, Dresden, Hiroshima). As the firestorm achieves peak intensity (a couple of hours after the ignitions), inflow speeds are inferred to attain 25–50 m/s; typically 12 km2 are reduced to ashes, before winds relax to ambient levels in six-to-nine hours. Here the firestorm is interpreted to be a mesocyclone (rotating severe local storm). Even with exceedingly large heat release sustained over a concentrated area, in the presence of a very nearly autoconvectively unstable atmospheric stratification, onset of vigorous swirling on the scale of 2 hrs requires more than concentration of circulation associated with the rotation of the earth; rather, a preexisting, if weak, circulation appears necessary for firestorm cyclogenesis.
A Method to Solve Conjugate Heat Transfer Problems: The Case of Fully Developed Laminar Flow in a Pipe
Authors: Barozzi G. S. , Pagliarini G.
Published: October 2009

A simple, fast, and rather general procedure combining the superposition principle with a finite element method is proposed to deal with conjugate heat transfer problems. The method is employed to consider the wall conduction effect on heat transfer to fully developed laminar flow through a pipe whose exterior boundary is uniformly heated along a finite length. Results are given for two values of each of the four parameters determining the relative importance of axial conduction: the Peclet number of the fluid, the wall to fluid conductivity ratio, and the dimensionless thickness and length of the heated section of the pipe.
Liquid Diffusion in Fibrous Insulation
Authors: Motakef S. , El-Masri M. A.
Published: October 2009

Vapor condensation in insulated structures degrades their physical properties as well as thermal performance. Motion of the condensate within the insulation is a crucial factor in analyzing annual moisture retention in building shells. The diffusion of liquid can be caused by several driving potentials. A model for isothermal liquid transport in fibrous insulation is presented. The model relates liquid diffusion to the characteristics of the insulation. These are identified as void-fraction and its spatial distribution, mean fiber radius, directionally index, and tortuousity factor. Due to the anisotropic layered structure of the fiberglass insulation, liquid diffusion along the three principal directions are studied. The diffusion of liquid from one layer to the next is controlled by liquid diffusion along the layers and the tortuosity factor. Diffusion along the layers is caused by the suction potential and retarded by the viscous forces. By balancing the suction and the viscous forces, a model for transient diffusion in terms of the five medium properties is obtained. An electrical resistance probe for in-situ measurement of liquid content in insulation samples of high voidage has been developed. Data on liquid diffusion under isothermal concentration gradients for commercial fiberglass insulations have been acquired. The experimental data show consistent agreement with the model predictions.
Heat Transfer From Rectangular Plates Inclined at Different Angles of Attack and Yaw to an Air Stream
Authors: Motwani D. G. , Gaitonde U. N. , Sukhatme S. P.
Published: October 2009

Average heat transfer coefficients during forced convection air flow over inclined and yawed rectangular plates have been experimentally determined. Tripping wires at the edges ensured that a turbulent boundary layer prevailed over the plates. The experiments were carried out for a constant surface temperature and covered two plates of different aspect ratios, angles of attack from 0 to 45 deg, angles of yaw from 0 to 30 deg, and Reynolds numbers from 2 times; 104 to 3.5 times; 105. The results show that the average heat transfer coefficient is essentially insensitive to the aspect ratio and angle of yaw. However, it is a function of Reynolds number and the angle of attack. Correlation equations for various angles of attack are suggested.
Vaporization of Drops of a Denser, Volatile Liquid Dropped Onto a Surface of Another Liquid
Authors: Nosoko T. , Mori Y. H.
Published: October 2009

Experiments were performed with single R 113 (C2Cl3F3) drops dropped onto the surface of immiscible ethylene glycol or water, or miscible n-tridecane in contact with the common vapors of the two liquids. Five different vaporization modes were distinguished in the immiscible systems: film boiling on the surface, film boiling in the bulk (only in R 113/ethylene glycol system), and three other modes in which the two liquids make direct contact. The latter three were replaced, in the miscible system, by an immediate dissolving of drops into the medium. The details of dynamic process in each mode have been revealed with the aid of high-speed cinephotography. Operational conditions required for the occurrence of respective modes and heat transfer characteristics in those modes have also been discussed.
An Integral Treatment of Laminar and Turbulent Film Condensation on Bodies of Arbitrary Geometrical Configuration
Authors: Nakayama A. , Koyama H.
Published: October 2009

A general solution procedure has been developed for laminar and turbulent film condensation problems. The procedure is designed to deal with both plane and axisymmetric isothermal bodies of arbitrary geometrical configuration. Inertia effects are fully considered by introducing a new parameter associated with the flow acceleration. A closed-form expression for the local Nusselt number is obtained for both laminar and turbulent flows. Calculations are carried out for laminar and turbulent condensate layers developed on flat plates, horizontal circular cylinders, and spheres. The results are compared with available predictions and measurements.
Melting Around a Migrating Heat Source
Authors: Moallemi M. K. , Viskanta R.
Published: October 2009

The problem of melting around a moving heat source arises in many different situations such as nuclear reactor technology (i.e., “self-burial” process of nuclear waste materials and reactor core “melt-down”), process metallurgy, and geophysics. Experiments were undertaken with a horizontal cylindrical heat source that melted its way through a phase-change material (n-octadecane) under its own weight. The heat source velocity and solid-liquid interface motion for a constant surface temperature source were measured. Effects of heat source density and surface temperature as well as the effects of the initial subcooling of the solid were investigated and are reported. The flow structure in the melt was visualized using a dye. Timewise variation of temperature distribution in the solid and the melt were also measured and are discussed. Results for the heat source migration velocity and the volume of the material melted are correlated in terms of the relevant problem parameters.
Differential Approximation to Radiative Transfer in Semitransparent Media
Authors: Azad F. H.
Published: October 2009

Radiative transfer in a semitransparent medium is treated using the differential approximation. Boundary conditions are formulated to accommodate direction-dependent reflection and refraction at a dielectric interfaces. The approximate results are compared to numerical solution of the exact integral equation. Also, a modification based on the exact formulation of the integrated intensity at the interface is presented that significantly improves the accuracy of the differential approximation in the optically thin regimes.
Heat Transfer in Gas-Solids Drag-Reducing Flow
Authors: Kane R. S. , Pfeffer R.
Published: October 2009

Heat transfer coefficients of air-glass, argon-glass, and argon-aluminum suspensions were measured in horizontal and vertical tubes. The glass, 21.6 and 36.0-μ-dia particles, was suspended at gas Reynolds numbers between 11,000 and 21,000 and loading ratios between 0 and 2.5. The presence of particles generally reduced the heat transfer coefficient. The circulation of aluminum powder in. the 0.870-in.-dia closed loop system produced tenacious deposits on protuberances into the stream. In the vertical test section, the Nusselt number reduction was attributed to viscous sublayer thickening; in the horizontal test section to particle deposition.
Natural Convection Heat Transfer for a Concentric Tube Thermosiphon
Authors: Steimke J. L.
Published: October 2009

Natural convection heat transfer for a single-phase thermosiphon formed by two concentric tubes and a central rod filled with water is studied theoretically and experimentally. The two annuli between the tubes and the rod are joined at the top and bottom and form a flow loop. The middle tube is heated while the outer tube is cooled. In this one-dimensional model equations for continuity, momentum, and energy for steady laminar flow are written and solved numerically. There is reasonably good agreement between the analytically and experimentally determined temperatures and convective velocities in the thermosiphon.
A Study of Free Convective Heat Transfer in a Horizontal Annulus With a Large Radii Ratio
Authors: Hessami M. A. , Pollard A. , Rowe R. D. , Ruth D. W.
Published: October 2009

Steady laminar natural convective heat transfer in a horizontal annulus with a large radii ratio (R) of 11.4 (and inner-cylinder diameter Di of 1.27 cm) has been investigated. Experimental data for air, glycerin, and mercury in the ranges of 0.023 ≤ Pr ≤ 10,000 and 0.03 ≤ GrDi ≤ 3 × 106 are reported. The influence of the variation of fluid properties as compared to the usual assumption of constant fluid properties has been explored numerically for air and glycerin. The heat transfer computations for air do not change with variation of fluid properties, whereas for glycerin significant differences in the local heat transfer distributions and flow patterns are observed. The experimental data have been correlated with some other data from the literature for smaller values of R, and it has been shown that the heat transfer from the inner cylinder should be almost the same as that in an infinite medium when R ≥ 10.
Experimental Investigation of Free Convection in a Vertical Rod Bundle—A General Correlation for Nusselt Numbers
Authors: Keyhani M. , Kulacki F. A. , Christensen R. N.
Published: October 2009

Free convection in two vertical, enclosed rod bundles has been experimentally investigated for a wide range of Rayleigh numbers. A uniform power dissipation per unit length is supplied to each rod, and the enclosing outer cylinder is maintained at constant temperature. Nusselt numbers for each rod, as well as an overall value for each bundle, have been obtained as a function of Rayleigh number. Comparison of the results for air and water as the working fluid indicate that, for a fixed Rayleigh number, an increase in the Prandtl number produces a reduction in the Nusselt number. This is contrary to what has been reported for vertical cavities and is attributed to curvature effects. Furthermore, the data reveal the interesting fact that it is quite possible for the individual rods in the bundle to exchange energy with the working fluid via different but coexisting regimes at a given power dissipation. Also, as the Rayleigh number is increased, the rods each tend to assume nearly the same heat transfer coefficient. Finally, a correlation for the overall convective Nusselt number is developed in terms of Rayleigh number and geometric parameters.
Transition Boiling Heat Transfer on a Vertical Surface
Authors: Bui T. D. , Dhir V. K.
Published: October 2009

Transition boiling heat transfer on a vertical surface in a pool of saturated water is investigated experimentally. Local heat transfer rates are obtained on a 6.3-cm-wide and 10.3-cm-high surface which was machined from a large block of copper. Experiments conducted with water show that even for relatively slow transient cooling rates (|dT/dt| < 11 K/s), the transient maximum heat fluxes are as much as 60 percent lower than the maximum steady-state heat fluxes. It is found that transition boiling heat transfer is very sensitive to the surface condition as well as to the history of the process. Two distinct transition boiling curves are observed during transient heating and cooling of clean surfaces. However, the difference between the two curves diminishes as the wettability of the surface increases. A correlation is developed to relate the transient quenching and steady-state peak heat fluxes for the range of temperature transient rates and surface conditions used in this investigation. Although the transient transition boiling curves obtained during heating and cooling are distinct because of different initial conditions, it is found that they possess the same rate of change of heat transfer coefficient with surface temperature when a correction factor equal to the ratio of steady to transient maximum heat fluxes is used.
Thermosyphon Boiling in Vertical Channels
Authors: Bar-Cohen A. , Schweitzer H.
Published: October 2009

The high heat flux capability and modest temperature differences associated with boiling heat transfer make immersion cooling one of the primary candidates for VHSIC and VLSI microelectronic component thermal control. While the literature contains many references to pool boiling heat transfer from single integrated circuit packages or transistor cans, there is as yet little information on ebullient thermal transport from vertical arrays of parallel, densely packaged Printed Circuit Boards or ceramic modules. The present study represents an attempt to explore the thermal performance of such ebullient cooling systems by analytically and empirically investigating boiling heat transfer in water from a pair of flat, isoflux plates. Experimental results for wall temperature as a function of axial location, heat flux, and plate spacing are presented. A theoretical model for liquid flow rate through the channel is developed and used as a basis for correlating the rate of heat transfer from the channel walls.
Heat Transfer Enhancement Due to Electrically Induced Resonant Oscillation of Drops
Authors: Kaji N. , Mori Y. H. , Tochitani Y.
Published: October 2009

By applying a low-frequency alternating field with a specially designed waveform, we succeeded in making water drops in a medium of silicone oil undergo a resonant shape oscillation of the second mode. The resonant oscillation was found to be quite effective for enhancing heat transfer between the medium and drops.
Natural Convection in an Externally Heated Vertical or Inclined Square Box Containing Internal Energy Sources
Authors: Acharya S. , Goldstein R. J.
Published: October 2009

A numerical investigation has been made of two-dimensional natural convection of air in an externally heated vertical or inclined square box containing uniformly distributed internal energy sources. Results have been obtained for Rayleigh numbers (both internal and external) up to 107 and inclination angles of 30, 60, and 90 deg from the horizontal. Two distinct flow pattern systems are observed: one, when the external Rayleigh number is larger than the internal Rayleigh number and the other, when the internal Rayleigh number is considerably greater than the external Rayleigh number. The average heat flux ratio (convective heat flux/corresponding conduction heat flux) along the hot surface is observed to undergo large variations in the external Rayleigh number range associated with the transition from one flow pattern to another. The average heat flux ratio along the cold plate is found to increase with increasing external Rayleigh number and decreasing internal Rayleigh number. The local heat flux ratio along a surface attains its maximum value in the vicinity of the region where the heated (or cooled) fluid from the opposite wall or from the interior encounters the surface.
Effect of Destabilizing Heating on Go¨rtler Vortices
Authors: Kamotani Y. , Lin J. K. , Ostrach S.
Published: October 2009

Experimental investigations of the effect of destabilizing heating on the vortex instability in a laminar boundary-layer flow of air along a concave surface are reported. The ranges of the parameters studied herein are Gr (Grashof number) from 0 to 70 and G (Go¨rtler number) from 0.46 to 9.0. The wavelength of the vortices remains unchanged with heating but the strength of the vortices is enhanced by heating. The amplitude of the vortices increases almost exponentially with the combined parameter (G2 + f Gr)1/2, where f is found to be between 0.3 and 0.4, until the nonlinear effects become important. In the nonlinear region the original sinusoidal wave form of the vortices becomes distorted and they meander in the lateral direction.