bluuebunny/crossref_metadata_2025 huggingface dataset:
Steady-State Temperature Distribution in a Rotating Roll Subject to Surface Heat Fluxes and Convective Cooling
Authors: Patula E. J.
Published: October 2009

With the higher rolling speeds used in modern cold-rolling mills, proper roll cooling has become a critical factor in avoiding problems of excessive roll spalling and poor thermal crowning. Poor thermal crowning of rolls can severely affect the shape and profile of sheet and strip products. To determine the influence of cooling practices on roll temperature, a mathematical model was developed that determines the two-dimensional (radial and circumferential) steady-state temperature distribution in a rotating roll subject to constant surface heat input over one portion of the circumference and convective cooling over another portion of the circumference. The model is analytical in nature, as opposed to a direct numerical simulation, which enables extensive parametric studies to be performed conveniently. The solution technique can be used to solve numerous problems involving any combination of surface boundary conditions that have, at most, a linear dependence with respect to the surface temperature. With the use of the principle of superposition, the present solution can be utilized to solve problems where various regions of the surface have constant heat fluxes. Results of the present analysis indicate that for normal cold-rolling situations during steady operation, the penetration of the effects of the surface heating and cooling that occur during every roll revolution is usually less than 4 percent of the radius. Furthermore, the bulk of the roll is at a uniform temperature that can be calculated quite accurately by neglecting all internal temperature gradients. The location of the cooling regions relative to the heat-input regions has little effect on the bulk roll temperature in this situation. This approximation would be useful for computing bulk roll temperature, which could be utilized in future models for determining thermal crowns, but would not be suited for determining accurate temperatures at the roll surface.
Prediction of Growth Parameters of Frost Deposits in Forced Convection
Authors: White J. E. , Cremers C. J.
Published: October 2009

Experimental investigations of frost deposition under forced convection conditions have shown that in most cases heat and mass transfer rates become constant after an initial transient period. It is shown that, in such cases, approximately half of the mass transfer from a humid air stream to a frost layer diffuses inward, condenses and increases the density of the frost. The other half is deposited at the surface and increases the thickness of the layer. Approximate expressions for density and thickness of the frost layer are derived and compared with data from the literature and also with experimental work reported in this paper. The correlations are shown to work well for a broad range of experimental conditions.
A Methodology of Predicting Cavity Geometry Based on the Scanned Surface Temperature Data—Prescribed Heat Flux at the Cavity Side
Authors: Hsieh C. K. , Su K. C.
Published: October 2009

A methodology is developed to predict a rectangular cavity lying underneath the surface of a plane wall that dissipates heat by convection to the surroundings. This is also the surface whose temperature is scanned. For a prescribed constant heat flux applying on the cavity surface the cavity depth can be predicted by equating the heat in and out of the system. An analytical procedure is developed that permits checking of the assumed cavity wall position based on comparison between the calculated and the measured surface temperatures. The method is also extended to the prediction of holes in a three-dimensional body (parallelepiped). Examples are provided to illustrate applications.
Microconvective Thermal Conductivity in Disperse Two-Phase Mixtures as Observed in a Low Velocity Couette Flow Experiment
Authors: Sohn C. W. , Chen M. M.
Published: October 2009

Eddy transport associated with microscopic flow fields in shearing two-phase flows was investigated. Although such microconvective effects are expected to be present in all disperse two-phase flows, usually they are masked by other collateral mechanisms and could not be studied critically. In the present study, effective thermal conductivities of neutrally buoyant solid-fluid mixtures were measured in a rotating Couette flow apparatus. Low Reynolds numbers were used to avoid the effects of turbulence. Significant enhancement in effective thermal conductivity was observed when the Ped were high. Here Ped = ed2/αf where e is the local mean shear rate, d is the particle diameter, and αf is the thermal diffusivity of the fluid. Volume fractions employed were φ = 0.15 and 0.30 for polyethylene beads (2.9 mm in diameter) in a mixture of silicone oil and kerosene, and φ = 0.15 for polystyrene particles (0.3 mm in diameter) in a mixture of silicone oil and Freon-113. Single-phase liquid mixtures were also measured in various shear rates to show that the thermal conductivity was independent of shear rate and hence the observed phenomenon was not an instrumental artifact. The dependence of conductivity on particle Peclet number appeared to approach a power law relationship ke ∝ Ped1/2 for high Peclet numbers (300 < Ped < 2000).
Mass Transfer from a Rotating Inclined Plate
Authors: Koyama Hitoshi , Ohsawa Sei-ichi , Nakayama Akira
Published: October 2009

An extensive experimental investigation using the Naphthalene Sublimation Technique, has been carried out to explore the mass transfer processes on inclined flat plates at rotation. It has been found that the flows responsible for the transfer processes can be classified into three types, namely, flow without a separated region, flow with a separated region located near the leading edge, and flow with a separated region all over the surface. A wind tunnel experiment on stationary flat plates has been also performed so as to isolate the effects of incidence angle from the rotational effects. A tremendous increase in transfer rate has been observed for the surface of the rotational system exposed to a wake flow.
Heat Transfer During Wind Flow over Rectangular Bodies in the Natural Environment
Authors: Test F. L. , Lessmann R. C. , Johary A.
Published: October 2009

An experimental investigation has been performed to determine the constant temperature heat transfer behavior on the upper surface of a rectangular plate with a chord length of 122 cm (48 in.), a width of 81.3 cm (32 in.) and a thickness aspect ratio of 6/1. Special side attachments were made in order to maintain approximately two-dimensional flow over the finite width body when exposed to varying wind directions. The angle of attack was 40 deg or greater. Quasi-local values of STRe were found to be 200 percent higher than wind tunnel values and 300 percent higher than analytical predictions. The disturbance intensity of the wind flow was in the range of 20 to 50 percent and is thought to be related to the increase in heat transfer since the flow over the plate was found to be laminar.
Theoretical and Experimental Temperature Distribution in Two-Dimensional Turbulent Jet-Boundary Interaction
Authors: Hoch J. , Jiji L. M.
Published: October 2009

A theoretical and experimental study of the temperature characteristics of two-dimensional heated turbulent jets discharging parallel to and in the vicinity of a solid boundary is presented. The model is based on an integral formulation of the basic conservation laws and uses the flow field solutions of corresponding nonbuoyant jets. The theory takes into consideration the effects of free-stream motion and jet offset distance. Theoretical predictions of temperature were found to be in good agreement with experimental data.
Periodic Growth and Decay of a Frozen Crust over a Heat Generating Liquid Layer
Authors: Cheung F. B.
Published: October 2009

A theoretical investigation is made of thermal oscillations in a horizontal layer of liquid heated at high Rayleigh number from within and cooled to freezing from above. The processes of turbulent thermal convection in the liquid layer and transient heat conduction in the solidified layer are modeled and the conditions leading to periodic self-sustained oscillations are identified. The results of this study indicate that there are five independent parameters that control the oscillatory behavior of the system. Effects of these parameters on the behavior of the transient liquid temperature and the instantaneous crust thickness are obtained and discussed. Validity of the present approach is justified based upon the higher-order solutions.
Heat Transfer from a Plate Elevated above a Host Surface and Washed by a Separated Flow Induced by the Elevation Step
Authors: Sparrow E. M. , Samie F. , Lau S. C.
Published: October 2009

Wind tunnel experiments were performed to determine heat transfer coefficients and fluid flow patterns for a thermally active surface elevated above a parallel host surface. The step-like blockage associated with the elevation causes flow separation and recirculation on the forward portion of the thermally active surface. Four parameters were varied during the course of the experiments, including the angle of attack of the oncoming airflow relative to the surface, the step height, the extent of the host surface which frames the active surface (i.e., the skirt width), and the Reynolds number. Flow visualization studies, performed with the oil-lampblack technique, showed that the streamwise extent of the separation zone increases with decreasing angle of attack, with larger step heights and skirt widths, and at higher Reynolds numbers. At larger angles of attack, separation does not occur. The experimentally determined heat transfer coefficients were found to increase markedly due to the flow separation, and separation-related enhancements as large as a factor of two were encountered. The enhancement was accentuated at small angles of attack, at large step heights and skirt widths, and at high Reynolds numbers. A main finding of the study is that the separation-affected heat transfer coefficients are generally greater than those for no separation, so that the use of the latter may underestimate the heat transfer rates. For an application such as a retrofit solar collector, such an underestimation of the wind-related heat loss would yield an optimistic prediction of the collector efficiency.
Application of Mixing Length Theory to Wavy Turbulent Liquid—Gas Interface
Authors: Levy S. , Healzer J. M.
Published: October 2009

A fully developed and adiabatic two-phase annular model with liquid entrainment is derived for flow in a pipe with negligible gravity effects. The model is based upon application of the single phase mixing length theory to a wavy liquid-gas interface. The model subdivides the flow cross section into three regions: a liquid film, a gas core of constant density, and a transition wavy layer between them. The combination of a constant velocity and a density varying exponentially with distance from the wall is employed in the transition layer. This approach plus appropriate logarithmic velocity distributions in the liquid film and gas core make it possible to specify the two-phase pressure drop, volume fraction, wave velocity, and thickness of the liquid film and transition layer. The liquid entrainment is obtained in terms of the exponent of the density profile in the transition layer, and interface stability considerations are used to express this entrainment parameter semiempirically in terms of an apparent Weber number and density ratio. Comparisons of the model are made with air-water and steam-water test data, and the results generally are satisfactory over a wide range of conditions and for all the important characteristics of this flow pattern.
Refilling and Rewetting of a Hot Horizontal Tube—Part III: Application of a Two-Fluid Model to Analyze Rewetting
Authors: Chan A. M. C. , Banerjee S.
Published: October 2009

Experiments on rewetting and refilling of hot horizontal tubes [1] indicate that a liquid “tongue” initially runs along the bottom causing significant precooling. The rewetting front follows this tongue, with the bottom of the tube rewetting before the top. Very little precooling is observed at the top and rewetting apparently occurs at quite high temperatures. Rewetting velocities generally decrease with increases in inlet water temperature, initial tube wall temperature and power input into the tube. Rewetting velocities increase with increases in injection flow rate. The data cannot be explained in terms of a conduction controlled rewetting model. Also the rewetting temperature varies considerably between the top and bottom of the tube, and along the tube. The phenomena appear to be hydrodynamically controlled and are well predicted by a two fluid model with reasonable constitutive equations for wall and interfacial friction, and heat transfer. The transverse gravitational force has to be incorporated in the model to account for flow stratification. The most critical constitutive relationship is with regard to the transition from film boiling to a rewet surface at the bottom of the tube. A model based on interfacial instability to signal this transition predicts the experimental results.
A Nondimensional Analysis of Boiling Dry a Vertical Channel with a Uniform Heat Flux
Authors: Sun K. H. , Duffey R. B. , Lin C.
Published: October 2009

A thermal-hydraulic model has been developed for describing the phenomenon of hydrodynamically-controlled dryout, or the boil-off phenomenon, in a vertical channel with a spatially-averaged or uniform heat flux. The use of the drift flux correlation for the void fraction profile, along with mass and energy balances for the system, leads to a dimensionless closed-form solution for the predictions of two-phase mixture levels and collapsed liquid levels. The physical significance of the governing dimensionless parameters are discussed. Comparisons with data from single-tube experiments, a 3 × 3 rod bundle experiment, and the Three Mile Island nuclear power plant show good agreement.
Convective Heat Transfer to Turbulent Droplet Flow in Circular Tubes
Authors: Rane A. G. , Yao Shi-Chune
Published: October 2009

Turbulent droplet flow heat transfer is analyzed for the thermal entrance region of a circular tube. Calculations are performed considering droplet size variation, vapor acceleration and dilution of droplet number density until the single-phase fully developed conditions is reached. Effect of the relevant dimensionless groups on the heat transfer results is studied. The analytical results are compared with the available experimental data. These comparisons show good agreement between the experimental data and the predictions.
Measured Heat Transfer Coefficients at and Adjacent to the Tip of a Wall-Attached Cylinder in Crossflow—Application to Fins
Authors: Sparrow E. M. , Samie F.
Published: October 2009

Wind tunnel studies encompassing both heat transfer measurements and flow visualization were performed for a cylinder in crossflow, with one end of the cylinder attached perpendicular to a wall and with the other end free. The focus of the work was to obtain heat transfer coefficients for the tip of the cylinder, for the tip-adjacent portion of the cylindrical surface, and for a portion of the cylindrical surface where there are no end effects. The flow visualization studies were performed to assist in the explanation and rationalization of the heat transfer results. They revealed the presence of spanwise flows adjacent to both ends of the cylinder, with accompanying modifications of the size of the separated region that washes the rear of the cylinder. The flow passing over the tip separates on the fore portion of the tip, but reattaches on the aft portion. The tip heat transfer coefficients are higher than those for the end-effect-free portion of the cylindrical surface, with deviations which grow with increasing Reynolds number (about a factor of two at Re = 25,000). For the tip-adjacent portion of the cylindrical surface, the coefficients are about fifty percent higher than those uninfluenced by end effects. The ramifications of these findings on the heat transfer analysis of fins are discussed.
The Effect of Thermal Wall Properties on Natural Convection in Inclined Rectangular Cells
Authors: Meyer B. A. , Mitchell J. W. , El-Wakil M. M.
Published: October 2009

The effects of cell wall thickness and thermal conductivity on natural convective heat transfer within inclined rectangular cells was studied. The cell walls are thin, and the hot and cold surfaces are isothermal. The two-dimensional natural convection problem was solved using finite difference techniques. The parameters studied were cell aspect ratios (A) of 0.5 and 1, Rayleigh numbers (Ra) up to 105, a Prandtl number (Pr) of 0.72 and a tilt angle (φ) of 60 deg. These parameters are of interest in solar collectors. The numerical results are substantiated by experimental results. It was found that convection coefficients for cells with adiabatic walls are substantially higher than those for cells with conducting walls. Correlations are given for estimating the convective heat transfer across the cell and the conductive heat transfer across the cell wall. These correlations are compared with available experimental and numerical work of other authors.
Analysis of Solidification Interface Shape Resulting From Applied Sinusoidal Heating
Authors: Siegel R.
Published: October 2009

Maintaining a flat solidification interface is important for forming desired crystal structures in certain types of metal casting processes. This has application in new manufacturing techniques for naturally strengthened composite components such as turbine blades. The solidification interface shape will adjust to be compatible with the spatial distribution of energy being transferred to it. The interface shape must be found that satisfies conditions of simultaneously being at the fusion temperature and having an imposed spatially varying heat flux. Specific results are obtained for the heat transfer from the liquid phase varying along the interface in a cosine fashion. Interface shapes are found as a function of the amplitude and wavelength of the imposed heat transfer variations, and the sensitivity of the interface shape to these variations is examined.
A Non-Self-Adjoint Problem in Heat Conduction
Authors: Ramkrishna D. , Amundson N. R.
Published: October 2009

A non-self-adjoint heat conduction problem is solved by an expansion in terms of the root vectors of the conduction operator and its adjoint using their biorthogonality properties. The completeness of the root vectors follows from the fact that the non-self-adjoint boundary conditions satisfy a regularity condition, which is sufficient to guarantee it.
Forced-Convective Post-CHF Heat Transfer and Quenching
Authors: Nelson R. A.
Published: October 2009

Mechanisms in the postcritical heat flux region that provide understanding and qualitative prediction capability for several current force-convective heat-transfer problems are discussed. In the area of nuclear reactor safety, the mechanisms are important in the prediction of fuel rod cooldown and quenches for the reflood phase, blowdown phase, and possibly some operational transients with dryout. Results using the mechanisms to investigate forced-convective quenching are presented. Data reduction of quenching experiments is discussed, and the way in which the quenching transient may affect the results of different types of quenching experiments is investigated. This investigation provides an explanation of how minimum wall superheats greater than the homogeneous nucleation temperature result, as well as how these may be either hydrodynamically or thermodynamically controlled.
Heat Transfer by Natural Convection Across Vertical and Inclined Air Layers
Authors: ElSherbiny S. M. , Raithby G. D. , Hollands K. G. T.
Published: October 2009

Measurements of the heat transfer by natural convection across vertical and inclined air layers are reported. The air layer is bounded by flat isothermal plates at different temperatures and around the edges by a perfectly conducting boundary (i.e., one that takes on a linear temperature distribution between the two plates). Measurements are reported for six aspect ratios between 5 and 110, covering a portion of the range of practical interest for windows, solar collectors, etc. Rayleigh numbers were in the range 102 to 2 × 107. The present measurements permitted the role of aspect ratio to be clearly defined. In addition, correlation equations are presented which allow the heat trnasfer across a vertical or inclined air layer to be calculated.
Radiative Transfer in Packed Fluidized Beds: Dependent Versus Independent Scattering
Authors: Brewster M. Q. , Tien C. L.
Published: October 2009

Experimental measurements are compared with theoretical predictions for radiative transfer in suspensions of 11.0 μ dia Dow latex particles using 0.6328 μ He-Ne laser light. Both absorbing and nonabsorbing particles are studied with particle volume fraction ranging from 0.01 to 0.7 (close-packed). Predictions based on the classical assumptions that particles act as independent point scatterers are shown to give close agreement with experimental data even for close-packed conditions, as long as the interparticle clearance is greater than about 0.3 wavelengths. Evidence is presented indicating that interparticle spacing measured in wavelengths is the most critical parameter to gauge the importance of dependent scattering and that high particle concentration alone is no indication that scattering is dependent. The results have direct application to the design of packed/fluidized bed systems wherein thermal radiation is a significant heat transfer mode.
Determination of Boundary Shape of Cooled Porous Region
Authors: Snyder A. , Siegel R.
Published: October 2009

The shape of a cooled porous wall section is found that will provide a uniform surface temperature, as dictated by material limitations, when the surface is subjected to spatially nonuniform heating. In the analysis, local temperatures and pressures in the porous material are expressed in terms of a potential function. From the imposed thermal conditions, this potential function is governed by the dual constraints of both its value and its normal derivative being specified along the heated surface. The unknown shape of this surface is obtained by meeting these dual conditions. The analytical method uses a generalized conformal mapping procedure that includes a curved boundary. The coolant flow can be compressible or incompressible, and its viscosity can depend on temperature.
Free Convection Diffusion Flames With Inert Additives
Authors: Sibulkin M. , Wang C. Y.
Published: October 2009

An analysis of laminar, free-convection, diffusion flames burning on a vertical fuel surface is presented. The study is directed towards determining the effects of inert additives on the boundary layer structure and burning rates. Results are presented for several classes of inert additives using polymethyl methacrylate burning in air as the base system. The use of a fuel-phase additive to release noncombustible gases is modeled by varying the parameter YFT, the mass fraction of fuel in the gaseous products of pyrolysis. The effects of an additive which promotes char formation is modeled by varying the heat of pyrolysis per unit mass of gaseous pyrolysate released for combustion. The effects of a spray of water droplets on a wall fire is modeled by a combination of the release of a noncombustible gas and a surface heat sink which results from evaporation of water droplets at the fuel surface. The water spray calculations predict an extinction limit which is within a factor of two of experimental results.
Natural Convection Heat Transfer of Water Within a Horizontal Cylindrical Annulus With Density Inversion Effects
Authors: Vasseur P. , Robillard L. , Chandra Shekar B.
Published: October 2009

The effect of density inversion on steady natural convection heat transfer of cold water, between two horizontal concentric cylinders of gap width, L, is studied numerically. Water near its freezing point is characterized by a density maximum at 4°C. Numerical solutions are obtained for cylinders with nonlinear Rayleigh numbers RA ranging from 2 × 103 to 7.6 × 104, a radius ratio 1.75 ≤ ra ≤ 2.6 and an inversion parameter γ, relating the temperature for maximum density with the cavity wall temperatures, between −2 and 2. The results obtained are presented graphically in the form of streamline and isotherm contour plots. The heat transfer characteristics, velocity profiles, and local and overall Nusselt numbers are studied. The results of the present study were found qualitatively valid when compared with an experimental investigation carried out in the past.
Soot Volume Fraction Profiles in Forced-Combusting Boundary Layers
Authors: Beier R. A. , Pagni P. J.
Published: October 2009

A multiwavelength laser transmission technique is used to determine soot volume fraction fields and aproximate particle size distributions in a forced flow combusting boundary layer. Measurements are made in diffusion flames of polymethylmethacrylate (PMMA) and five liquid hydrocarbon fuels (n-heptane, iso-octane, cyclohexane, cyclohexene, and toluene) with ambient oxygen mass fractions in the range of 0.23 ≲ Y0∞ ≲ 0.50. Soot is observed in a region between the pyrolyzing fuel surface and the flame zone. Soot volume fraction increases monotonically with Y0∞, e.g., n-heptane and PMMA are similar with soot volume fractions, fν, ranging from fν ∼ 5 × 10−7 at Y0∞ = 0.23 to fν ∼ 5 × 10−6 at Y0∞ = 0.50. For an oxygen mass fraction the same as air, Y0∞ = 0.23, soot volume fractions are approximately the same as values previously reported in pool fires and a free combusting boundary layer. However, the shape of the fν profile changes with more soot near the flame in forced flow than in free flow due to the different y-velocity fields in these two systems. For all fuels tested, a most probable particle radius is between 20 nm and 80 nm, and does not appear to change substantially with location, fuel, or oxygen mass fraction.
Low Reynolds Number Flow Between Interrupted Flat Plates
Authors: Roadman R. E. , Loehrke R. I.
Published: October 2009

The flow between pairs of flat plates was studied experimentally to gain insight into the operation of compact heat exchangers with interrupted surfaces. The plates were tested at low Reynolds number in both water and air streams. The investigation focused on the region of transition from steady to unsteady laminar flow between plates. A critical velocity was determined at which periodic oscillations were first observed. This velocity depends strongly on the thickness of the plates, t, plate length, L, and plate separation distance and weakly on flow disturbance level. Data for a range of geometries, 4 ≤ L/t ≤ 159, are correlated using plate wake width as a single plate length scale. The downstream plate was found to have a pronounced upstream influence on the critical velocity. In a low-disturbance-level stream the critical velocity may be lower than that required to produce detectable oscillations at the same point in the upstream plate wake in absence of the second plate. This feedback effect may be responsible for the relative insensitivity of the results to the turbulence level in the free stream.
Heat Transfer From Interrupted Plates
Authors: Zelenka R. L. , Loehrke R. I.
Published: October 2009

The forced convection heat transfer from two plates aligned with the flow direction in a wind tunnel was measured. The effects of leading edge bluntness, plate spacing distance, and Reynolds number on the leading and trailing plate average heat transfer rate were studied. The low Reynolds number, steady laminar and transitional flow regimes investigated are typical for compact heat exchangers. The measured heat transfer rate from the leading plate agrees well with laminar theory for thin plates when the leading edge is rounded. The heat transfer rate from the leading plate with a blunt nose ranges from slightly below theoretical at a Reynolds number which gives a long, steady separation bubble to well above theoretical under conditions of laminar separation and turbulent reattachment. The heat transfer rate from the second plate is influenced by the leading edge configuration of the first plate only at small plate spacing distances and high Reynolds number. At large spacings the mixing provided by the unsteady wake of the first plate dominates that due to the turbulence formed by leading edge separation on the first plate. The leading edge configuration of the second plate is important only at large values of plate spacing. The heat transfer rate from the second plate is generally higher than that predicted by theory for laminar, steady flow over thin plates and may be higher than that on the leading plate.
Approximate Phase Change Solutions for Insulated Buried Cylinders
Authors: Lunardini V. J.
Published: October 2009

The conduction problem for cylinders embedded in a medium with variable thermal properties cannot be solved exactly if phase change occurs. New, approximate solutions have been found using the quasi-steady method. These solutions consider heat flow from the entire pipe surface, rather than from a single point, as has been assumed in the past. The temperature field, phase change location, and pipe surface heat transfer can be evaluated using graphs presented for parametric ranges of temperature, thermal properties, burial depth, and insulation thickness. The theoretical results show good agreement with complete numerical solutions. The accuracy of the method increases as the Stefan number decreases and the results are of particular value for insulated hot pipes or refrigerated gas lines.
Interaction of the Nucleation Phenomena at Adjacent Sites in Nucleate Boiling
Authors: Sultan M. , Judd R. L.
Published: October 2009

The present investigation is an original study in nucleate pool boiling heat transfer combining theory and experiment in which water boiling at atmospheric pressure on a single copper surface at two different levels of heat and different levels of subcooling was studied. Cross spectral analysis of the signals generated by the emission of bubbles at adjacent nucleation sites was used to determine the relationship of the time elapsed between the start of bubble growth at the two neighbouring active sites with the distance separating them. The experimental results obtained indicated that for the lower level of heat flux at three different levels of subcooling, the elapsed time and distance were directly related. Theoretical predictions of a temperature disturbance propagating through the heating surface in the radial direction gave good agreement with the experimental findings, suggesting that this is the mechanism responsible for the activation of the surrounding nucleation sites.
Heat Transfer and Fluid Flow Experiments With a Tube Fed by a Plenum Having Nonaligned Inlet and Exit
Authors: Sparrow E. M. , Bosmans L. D.
Published: October 2009

Local turbulent heat transfer coefficients for airflow were measured in a tube situated downstream of a cylindrical plenum chamber in which the inflow was radial and the outflow was axial. Pressure drop measurements and flow visualization were performed to supplement the heat transfer experiments. The plenum length and diameter were varied systematically during the experiments, and the Reynolds number ranged from 10,000 to 60,000. Substantially higher Nusselt numbers in the tube were encountered for the present nonaligned plenum inlet/exit configuration than for a plenum with axially aligned inlet and exit or for an upstream hydrodynamic development section. For a given Reynolds number, the Nusselt numbers corresponding to the present plenum configuration were quite insensitive to the investigated geometrical parameters. The thermal development length was found to be substantially elongated due to swirl carried into the tube from the plenum; the presence of the swirl was confirmed by flow visualization. The net pressure loss due to the presence of the plenum was about 1.75 velocity heads and was guite insensitive to the geometrical parameters and to the Reynolds number.
Radiative Heat Transfer in Fibrous Insulations—Part I: Analytical Study
Authors: Tong T. W. , Tien C. L.
Published: October 2009

The purpose of this work is to develop models for predicting the radiant heat flux in lightweight fibrous insulations (LWFI). The radiative transport process is modeled by the two-flux solution and the linear anisotropic scattering solution of the equation of transfer. The radiative properties of LWFI consistent with these solutions have been determined based on extinction of electromagnetic radiation by the fibers. Their dependence on the physical characteristics of fibrous insulations has been investigated. It has been found that the radiant heat flux can be minimized by making the mean radius of the fibers close to that which yields the maximum extinction coefficient. The results obtained in this study are useful to those concerned with the design and application of LWFI.
Buoyancy Effects on a Boundary Layer Along an Infinite Cylinder With a Step Change of Surface Temperature
Authors: Yao L. S.
Published: October 2009

The laminar boundary layer induced by a horizontal forced flow along an infinite vertical cylinder with a step change of surface temperature is studied by a finite-difference method. Close to the thermal leading edge, the buoyancy force induces a strong free-convection boundary layer. Slightly above the thermal leading edge, the boundary layer starts to separate at the rear stagnation line (φ = 180 deg). The region of separated flow grows toward the forward stagnation line and becomes stationary at φ = 104 deg as one moves upward. In other words, free convection dominates the heat transfer along the thermal leading edge. The importance of forced convection increases as one moves vertically from the thermal leading edge and eventually becomes the dominant mode. The numerical results show that the free-convection boundary layer is suppressed at the forward stagnation line and is carried toward the rear stagnation line by the forced convection. The phenomenon shares many similarities with a thermal plume affected by forced convection.
Shape Change of an Initially Vertical Wall Undergoing Condensation-Driven Melting
Authors: Taghavi-Tafreshi K. , Dhir V. K.
Published: October 2009

Condensation-driven melting of an initially vertical wall is studied both analytically and experimentally. It is shown that a vertical surface undergoing simultaneous melting-condensation will not stay vertical and will go through a series of transient shapes before attaining a steady-state shape. Numerical solutions are obtained both for the transient shapes of the wall and the heat transfer. The steady-state shape of the wall is found to be the one which yields a constant melting rate along the wall. The total melting rate is shown to increase during the time the shape change occurs such that the steady-state shape yields about 35 percent more melting rate than the initial vertical wall. Experiments are conducted at one atmosphere pressure by condensing saturated steam on vertical surfaces of slabs made of naphthalene, biphenyl, and stearic acid. The heat transfer and shape change data are found to compare well with the predictions.
Experiments on Transient Thermal Convection With Internal Heating—Large Time Results
Authors: Keyhani M. , Kulacki F. A.
Published: October 2009

Experimental data and correlations are presented for the time scales of developing and decaying thermal convection with volumetric heating in a horizontal layer. The layer is bounded by rigid surfaces, with an insulated lower boundary and an isothermal upper boundary. The time for complete flow development/decay, as a result of a step change in volumetric heat generation, is simply parameterized in terms of the Fourier number for the layer, the step change in Rayleigh number, ΔRa, and the initial/final dimensionless maximum core temperature. For developing flows, ΔRa > 0, results are in good agreement with existing experiments and an approximate boundary layer theory. In decaying flows, Fourier numbers are larger than those of previously reported experiments for a motionless final state. Data for turbulent-to-turbulent transitions when ΔRa < 0 suggests that the approximate boundary layer theory underestimates the Fourier number. Experimental uncertainties on measured Fourier numbers are generally well within the limits of uncertainty allowed by the approximate theory.
Stationary Thermal Ignition of Particle Suspensions
Authors: Khalil H. , Shultis J. K. , Lester T. W.
Published: October 2009

A calculational method is presented for the stationary thermal ignition of pulverized coal suspensions based on radiative energy transport in a heat generating medium. A diffusion-limited, Arrhenius model for heat generation is used in the description of the heterogeneous ignition and combustion of particles with the gases in which they are dispersed. The discrete ordinates method, which is used to solve numerically the radiative transfer equation, is combined with an iterative procedure to obtain both the temperature and radiation intensity distributions throughout the reacting system. Numerical examples are presented to show the variation in the critical behavior of a system in plane geometry with wall temperature and reflectivity, optical thickness of the system, particle size, optical parameters, anisotropy of the scattering, and the parameters of the heat generation model.
Transient Nonsimilarity Nonlinear Heat Diffusion Solutions
Authors: Cheung F. B.
Published: October 2009

An approximate analytical method for treating parabolic type nonlinear heat diffusion equations is descibed in this study. The method involves transformation of the partial differential equations along with their initial and boundary conditions in terms of several pseudo-similarity variables followed by numerical solution of a system of quasi-ordinary differential equations. One obvious advantage of the approach is that the solution at a particular time can be found independently of the previous history of the temperature field. The simplicity and directness of the method are illustrated by solving the problem of combined conduction and thermal radiation in a large, heat-generating, particulate bed in contact with a solid. Comparison of the present analytical results is made with available finite difference solutions and found to be good.
Transient Response of a Composite Straight Fin
Authors: Chu Hsin-Sen , Weng Cheng-I , Chen Chao-Kuang
Published: October 2009

The transient response of a straight fin composed of two different materials is analyzed. The Laplace transformation and eigenfunction expansion methods are used in the analysis. The inverse Laplace transform is solved by utilizing the Fourier series technique. It is shown that the conductivity ratio plays an important role on both the heat transfer rate and the time to reach the steady state. However, the effect of diffusivity ratio is found to be insignificant on the transient response when the conductivities are constant.
On the Presentation of Performance Data for Enhanced Tubes Used in Shell-and-Tube Heat Exchangers
Authors: Marner W. J. , Bergles A. E. , Chenoweth J. M.
Published: October 2009

As the efforts to produce more efficient heat transfer equipment continue, an increasing number of augmented surfaces are being produced commercially. Consequently, the designer faces an almost overwhelming task in comparing and evaluating the performance of various surfaces because of the many different ways in which the test data are currently presented in the literature. Thus, a uniform format for presenting pressure drop and heat transfer data for enhanced surfaces has become a necessity. This paper is concerned with one important aspect of this problem, namely, that of tubular enhanced surfaces used in shell-and-tube heat exchangers. As an initial step, the subject is limited to single-phase pressure drop and heat transfer; however, both tubeside and shellside flow are taken into consideration. A comprehensive list of commerical augmented tubes which may be considered for use in shell-and-tube exchangers is given, along with a survey of the performance data which are available in the literature. A standardized data format which uses the inside and outside envelope diameters as the basis for presenting the various geometrical, flow, and heat transfer parameters for all tubular enhanced surfaces is proposed and discussed.
Crystalline Fouling Studies
Authors: Ritter R. B.
Published: October 2009

In a study of fouling of heat exchangers, aqueous solutions of CaSO4 and Li2SO4 were circulated through electrically heated tubes at controlled conditions. Measured induction periods and fouling rates of both salts were found to be primarily functions of the supersaturation of the solutions. Secondary correlating parameters were surface temperature for the Li2SO4 solutions and mass transfer coefficients for the CaSO4 solutions.
Laminar Natural Convection in an Inclined Rectangular Box With the Lower Surface Half-Heated and Half-Insulated
Authors: Chao P. K.-B. , Ozoe H. , Churchill S. W. , Lior N.
Published: October 2009

The pattern of circulation and the rate of heat transfer were determined experimentally and also by three-dimensional, finite-difference calculations for an inclined 2 × 1 × 1 rectangular enclosure with a 1 × 1 segment of the lower 2 × 1 surface at a uniform temperature, the other 1 × 1 segment and four side walls insulated, and the upper surface at a lower uniform temperature. As contrasted with an enclosure heated and cooled on the horizontal surfaces, a fluid motion occurs and the rate of heat transfer exceeds that for pure conduction for all temperature differences and orientations. The effects of elevation of the heated and insulated segments were investigated, as well as of inclination about the longer dimension. Despite differences in the Prandtl and Rayleigh numbers, the observed and predicted patterns of circulation are in good agreement, and the measured and predicted rates of heat are in qualitative agreement.
Natural Convection Along a Vertical Wavy Surface
Authors: Yao L. S.
Published: October 2009

A transformation method is applied to study the natural convection along irregular vertical surfaces. A sinusoidal surface is used as a specific example to demonstrate the advantages of the transformation method, and to elucidate the heat transfer mechanism near such surfaces. The numerical results show that the frequency of the local heat transfer rate is twice that of the wavy surface. The amplitude of the oscillating local Nusselt number gradually decreases downstream where the natural convection boundary layer grows thick.
Numerical Prediction of Wall Temperatures for Near-Critical Para-Hydrogen in Turbulent Upflow Inside Vertical Tubes
Authors: Bellmore C. P. , Reid R. L.
Published: October 2009

Presented herein is a method of including density fluctuations in the equations of turbulent transport. Results of a numerical analysis indicate that the method may be used to predict heat transfer for the case of near-critical para-hydrogen in turbulent upflow inside vertical tubes. Wall temperatures, heat transfer coefficients, and velocities obtained by coupling the equations of turbulent momentum and heat transfer with a perturbed equation of state show good agreement with experiments for inlet reduced pressures of 1.28–5.83.
Transient Response of Gas-to-Gas Crossflow Heat Exchangers With Neither Gas Mixed
Authors: Romie F. E.
Published: October 2009

The transient mixed mean temperatures of the two gases leaving a crossflow heat exchanger are found for a unit step increase in the entrance temperature of either gas. The temperature responses are given in graphical form for the range of parameters: Ntu from 1 to 8, capacity rate ratio from 0.6 to 1.67, and conductance, ratio from 0.5 to 2.0. The solutions are found using the Laplace transform method and apply to single-pass crossflow exchangers with neither gas mixed.
Mean Temperature Difference in Multipass Crossflow
Authors: Pignotti A. , Cordero G. O.
Published: October 2009

A procedure is developed to obtain analytical expressions for the mean temperature difference in crossflow heat exchangers with arbitrary number of passes and rows per pass. The influence of air mixing, along with different flow arrangements for the tube fluid between passes, is analyzed, both in co- and counter-crossflow.
Finite Analytic Numerical Solution Axisymmetric Navier-Stokes and Energy Equations
Authors: Chen Ching-Jen , Yoon Young Hwan
Published: October 2009

Connective heat transfer for steady-state laminar flow in axisymmetric coordinates is considered. Numerical solutions for flow pattern and temperature distribution are obtained by the finite analytic numerical method applied to the Navier-Stokes equations expressed in terms of vorticity and stream function, and the energy equation. The finite analytic numerical method differs from other numerical methods in that it utilizes a local analytic solution in an element of the problem to construct the total numerical solution. Finite analytic solutions of vorticity, stream function, temperature, and heat transfer coefficients for flow with Reynolds numbers of 5, 100, 1000, and 2000, and Prandtl numbers of 0.1, 1.0, and 10.0 with uniform grid sizes, are reported for an axisymmetric pipe with a sudden expansion and contraction. The wall temperature is considered to be isothermal and differs from the inlet temperature. It is shown that the finite analytic is stable, converges rapidly, and simulates the convection of fluid flow accurately, since the local analytic solution is capable of simulating automatically the influence of skewed convection through the element boundary on the interior nodal values, thereby minimizing the false numerical diffusion.
Two-Phase Vessel Blowdown of an Initially Saturated Liquid—Part 1: Experimental
Authors: Hutcherson M. N. , Henry R. E. , Wollersheim D. E.
Published: October 2009

Experimental blowdown results for initially isothermal, saturated water from a small pressure vessel containing internal geometry are presented. This experiment simulated a break in a large duct of approximately three diameters in length which exited from the vessel. Choking only occurred at the exit of the discharge duct, and the instantaneous internal vessel pressure distribution was nearly uniform. Most of the fluid within the vessel immediately after the initiation of the blowdown became superheated liquid. This thermodynamic state together with the activated wall cavities inside the vessel maintained a nearly constant internal vessel pressure history early in the blowdown. However, in the latter stage of the depressurization, the remaining fluid within the vessel was essentially in thermodynamic equilibrium. A nonuniform distribution of fluid quality within the vessel was also detected in this experiment. In addition, this experiment illustrates that transient, two-phase, critical flow in large diameter ducts is similar to steady, two-phase, critical flow in small diameter ducts.
Numerical Modeling of Wet Cooling Towers—Part 2: Application to Natural and Mechanical Draft Towers
Authors: Majumdar A. K. , Singhal A. K. , Reilly H. E. , Bartz J. A.
Published: October 2009

This paper presents several applications of the mathematical model described in Part 1 of the paper. Natural and mechanical draft towers of counterflow and crossflow arrangement have been considered. Predicted thermal performances compare well with the available data from operating towers. The distributions of air velocities, pressure, temperature, moisture fraction, and water temperature have been assessed from the considerations of physical plausibility only, since no experimental data are available for comparison. Some sample parametric computations for a mechanical draft crossflow tower are also presented. The parameters studied are: (a) air travel dimension of fill; (b) aspect ratio of fill; (c) fan power; and (d) atmospheric pressure. The results are self-consistent and demonstrate the applicability of the model as an analysis tool.