bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermal-Hydraulic Behavior and Prediction of Heat Exchanger for Latent Heat Recovery of Exhaust Flue Gas
Authors: Osakabe Masahiro 
Published: December 2021

Abstract
In order to improve the boiler efficiency, latent heat recovery from the flue gas is very important concept. Three kinds of countercurrent cross-flow heat exchangers, which consist of bare tubes, spirally finned tubes of fin pitch 5 and 10mm, were designed and used for the experiment. The heat exchanger of the bare tubes consists of a staggered bank of 5-4 rows and 50 stages. The length, outer and inner diameter of the bare tube is 482, 27.2 and 23.2mm, respectively. The heat exchangers of finned tubes consist of staggered banks of 3-2 rows, 34 stages for the fin pitch 10mm and 20 stages for the pitch 5mm. The length, outer and inner diameter of the base tube welded with the fins is 482, 34 and 28.8mm, respectively. The thickness and height of the plate fin are 1 and 12mm, respectively. The parametric study varying the flue gas flow rate, feed water temperature and flow rate was conducted. The temperature distributions of water and flue gas in the heat exchanger were measured with sheath K-type thermocouples of 1.6 mm in diameter. The pressure loss and the total amount of condensate generated in the heat exchanger were also measured.
Based on the previous basic studies, a prediction method for the heat exchanger was proposed. In the prediction, the flue gas was treated as a mixture of CO2, CO, O2, N2 and H2O, and the one-dimensional heat and mass balance calculation along the flow direction of flue gas was conducted. The heat and mass transfer on tubes was evaluated with a simple analogy correlation. For the finned tubes, the fin efficiency at the condensing region was calculated with a semi-empirical correlation obtained in the previous basic study. The effect of condensate film on the tubes was considered to be negligibly small for the heat transfer and pressure loss calculation. The experimental results for the temperature distributions of water and flue gas in the test heat exchangers with bare and finned tubes agreed well with the prediction.
Simulation of Subcooled Nucleate Boiling in a Vertical Tube With a Bubble-Tracking Model
Authors: Kljenak Ivo , Mavko Borut 
Published: December 2021

Abstract
A three-dimensional bubble-tracking model was developed to simulate subcooled nucleate boiling in a heated vertical cylindrical tube. The behavior of the liquid-vapor system results from motion, interaction and heat transfer mechanisms prescribed mostly at the level of individually-tracked vapor bubbles. The model takes into account bubble nucleation and liquid heating caused by wall heat flux, bubble sliding on tube walls, bubble condensation in the low-temperature tube core region, bubble interaction through wake drift, bubble collisions and coalescence, bubble radial migration towards the tube core region, and turbulent dispersion in the liquid phase. The agreement between calculated void fraction and liquid temperature radial profiles along the flow with experimental results from other authors is promising.
Water Flow Distribution in Horizontal Protruding-Type Header Contaminated With Bubbles
Authors: Horiki Sachiyo , Osakabe Masahiro 
Published: December 2021

Abstract
Flow header for small multiple pipes is commonly used in boilers and heat exchangers. The system contributes to raise the heat transfer efficiency in the components. The flow distribution mechanism of the header for water has been studied and the calculation procedure for the design has been recommended for a single-phase condition. It is also recommended to avoid the bubbles in the header to obtain a uniform water flow rate to each small pipe. But in some cases, the header has to be used to distribute a flow containing bubbles. Distribution behavior of water with a gas-phase was studied experimentally in a horizontal header with four vertical pipes. In the present experimental header, it was possible to protrude the branch pipes inside of the header and the effect of protruding length on the water distribution behavior was studied.
When the protruding length was 0, the water distribution rate to the first pipe rapidly increased and the rates to the others decreased with a small amount of bubbles. As the bubbles in the header were absorbed only into the first pipe, the average two-phase density in the first pipe decreased. The decreased pressure head promotes the rush of water into the first pipe such as in an airlift pump. By increasing the air flow rate in the header inlet further, the flow rate to the first pipe took a maximum and then tended to decrease. The increased air flow rate in the first pipe increased the pressure loss in the pipe and resulted in a reduction in the water flow rate. The more important and serious behavior could be seen in the other pipes where the water flow rate decreased to 1/5 of the uniform distribution rate. By increasing the protruding length, the non-uniform distribution of water was suppressed because the gas-phase entered not only the first pipe but also the others. The best result was obtained when the four branch pipes were protruded into the center of header.
Experimental Study on the Hydraulic Characteristics of Solid-Liquid Slurry Two-Phase Flow in Horizontal Pipelines
Authors: Xu J. L. , Lin C. X. , Ebadian M. A. 
Published: December 2021

Abstract
A flow loop that contains a mixing tank, pump, horizontal pipeline, and corresponding measurement transducers has been constructed at Florida International University’s Hemispheric Center for Environmental Technology (FIU-HCET). Several slurry simulants that include liquid and five or six chemical solid species were applied in the tests. New data were provided on the pressure gradient and volume concentration across a vertical cross-section. It was found that the flow characteristics are quite distinct from the classical characteristics of coal-water or sand-water slurry flowing in horizontal pipelines. An apparent transition point occurs in the curve of the pressure gradient versus velocity. Flow observation identified that the solid particles settle down at the velocities of the corresponding transition points. The velocities at the transition points are classified as the limit deposition velocity. Lower velocity than the limit deposition velocity will result in a stationary bed flow. Weight concentration measurements in a heterogeneous flow regime indicate that there is no weight concentration gradient along the axial distance. However, within the present parameter range, the weight concentration is always higher at the top point than that at the bottom point.
Analysis of Fluid Flow in Composite Channels: Comparision of Analytical and Numerical Approaches
Authors: Kuznetsov A. V. , Xiong Ming 
Published: December 2021

Abstract
In this work, comparisons between the numerical solutions for forced convective flow in composite channels, partly occupied by a homogeneous (clear) fluid and partly by a fluid saturated porous medium, and the exact solutions for the same problems are carried out. This is done to establish limitations of the single-domain approach utilized to obtain the numerical solutions. These limitations result from the assumptions which are implicitly invoked once the single-domain approach is utilized to model fluid flow in the interface region between the porous medium and a clear fluid. It is shown that the single-domain approach results in correct matching of the shear stress at the porous/fluid interface only if the adjustable coefficient in the representation for the excess stress equals zero and also if the effective viscosity of the porous medium equals to the fluid viscosity.
A Hyperbolic Phase-Field Approach for Solidification With Supercooling
Authors: Chen Yuqi , McDonough James M. , Tagavi Kaveh A. 
Published: December 2021

Abstract
This report concerns the solidification of a “supercooled” liquid, whose temperature is initially below the equilibrium melt temperature, Tm of the solid. A new approach, the phase-field method, will be applied for this Stefan problem with supercooling, which simulates the solidification process of a pure material into a supercooled liquid in a spherical region. The advantage of the phase-field method is that it bypasses explicitly tracking the freezing front. In this approach the solid-liquid interface is treated as diffuse, and a dynamic equation for the phase variable is introduced in addition to the equation for heat flow. Thus, there are two coupled partial differential equations for temperature and phase field. In the reported study, an implicit numerical scheme using finite-difference techniques on a uniform mesh is employed to solve both Fourier phase-field equations and non-Fourier (known as damped wave or telegraph) phase-field equations. The latter gurantees a finite speed of propagation for the solidification front. Both Fourier (parabolic) and non-Fourier (hyperbolic) Stefan problems with supercooling are satisfactorily simulated and their solutions compared in the present work.
A Numerical Study of the Development of Convective Motion in a Bottom Heated Square Enclosure Containing Ice and Water
Authors: Oosthuizen P. H. 
Published: December 2021

Abstract
A numerical study of the steady state flow in a square enclosure with two vertical walls which are adiabatic and with two horizontal isothermal walls has been undertaken. The enclosure contains water and the upper wall is maintained at a uniform temperature that is below the freezing point of water while the lower wall is maintained at a uniform temperature that is above the freezing point of water. The upper portion of the enclosure is thus filled with ice and the lower portion is filled with water. The conditions considered in the present study are such there can be significant natural convection in the water and the effect of the density maximum that exists in the water at approximately 4°C can have a significant effect on this flow. The main aim of the study was to determine how far above 4°C the hot wall temperature can be before significant convective motion develops in the water. The governing equations have been expressed in dimensionless form and solved using a finite element procedure. The effect of the various governing parameters on the mean Nusselt number has mainly been considered and the effect of the lower surface temperature has, in particular, been studied. The results obtained, which indicate that convective motion does not occur until the lower hot wall temperature is well above the maximum density temperature, can be used to determine the actual hot wall temperature at which significant convective motion develops.
An Accuracy Evaluation for the Madejski Splat-Quench Solidification Model
Authors: Aceves Salvador M. , Shapiro Arthur B. , Sahai Vivek 
Published: December 2021

Abstract
Development of methods to spray form materials by precisely controlled deposition of droplets can result in new manufacturing processes which offer improved metallurgical performance and reduced production costs. These processes require a more detailed knowledge of the fluid mechanics, heat transfer and solidification that occur during droplet spreading. Previous work using computer simulations of this process have been difficult to implement and have required long running times. This paper examines the use of an alternative, simplified, method developed by Madjeski for solving for the problem of droplet spreading and solidification. These simplifications reduce the overall splat spreading and solidification problem to a closed-form differential equation. This differential equation is then solved under various conditions as reported from recent publications of experimental and numerical results of drop analysis. The results from the model are compared in terms of maximum splat diameter, minimum splat thickness, and time for the droplet spreading to reach 95% of the maximum diameter. The results indicate that the accuracy of the model can be improved by accounting for energy losses in the initial rate of droplet spreading. The model results show that the predictions of experimental results are improved to within 30% over a wide range of conditions.
Numerical Simulation of Blend Combustion of Coal and Feedlot Waste in a Swirl Burner
Authors: Sami Muhammad , Annamalai Kalyan , Dhanapalan Senthil , Wooldridge Margaret 
Published: December 2021

Abstract
In many coal combustion simulations, only one mixture fraction is used to model the coal-off gases. This assumption, however, is not accurate because the coal char and coal volatiles have considerable differences in composition. In the case of a coal:manure blend combustion, the use of one mixture fraction to describe the off gases from the coal and the manure yields inaccurate predictions. The inaccuracy is due to the fact that coal and manure have substantially different compositions and heating values. In the present work three mixture fractions are used separately to account for primary air, secondary air, coal off-gas and manure off-gas in a numerical simulation of blend combustion in a swirl burner. In the near burner region, significant differences in gas temperature and burnout are predicted when compared with a coal only base case. Secondary air and fuel flow rates are changed to keep the same equivalence ratio. The effects of these changes on the gas temperatures and burnout are determined.
Char Oxidation Model Validation in Detailed Coal Simulations
Authors: Domino Stefan P. , Smith Philip J. 
Published: December 2021

Abstract
The controlling mechanisms governing the amount of unburned carbon in fly ash from practical pulverized coal combustion systems have been studied by incorporating elements of the carbon burnout kinetic model (CBK) proposed by Hurt et al. in a computational fluid dynamics based combustion, cfd, simulator. An experimental data set from The International Flame Research Foundation are compared to evaluate mechanistic variations in the carbon burnout processes. Simulation results comparing total exit LOI (defined as the residual weight of carbon in the ash) and centerline carbon burnout indicates that use of a char oxidation submodel, including the effects of a statistical reactivity distribution, thermal annealing of active oxidation sites and a developing ash film resistance layer, is necessary to predict experimentally measured exit LOI and centerline burnout profiles.
Radiation Mechanism for a Single Bubble Sonoluminescence
Authors: Jeon Jin-Seok , Yang Ik-Jun , Na Jung-Hee , Kwak Ho-Young 
Published: December 2021

Abstract
A mechanism of light emission from a single bubble sonoluminescence (SBSL) was formulated by assuming that the source for the light emission is bremsstrahlung in partially ionized gases. Also the spectrum was measured and the observed results were compared with the calculated ones. Calculated and experimental results yield common spectral behavior in the visible region: the spectral radiance shows power-law dependence on wavelength with an exponent of −2.5. The SBSL spectrum which is characterized by the continuous one with no major peaks has been confirmed experimentally.
Analysis of the Heat Transfer Capacity of a Micromachined Loop Heat Pipe
Authors: Hoelke A. , Henderson H. T. , Gerner F. M. , Kazmierczak M. 
Published: December 2021

Abstract
For on-chip electronic cooling, a micromachined silicon LHP (Loop Heat Pipe) is being developed, with a Coherent Porous Silicon (CPS) wick as the central part. The present work is a lumped-element network analysis of the overall heat removal performance of such a device. A heat flux of more than 100 W/cm2 is predicted for a micromachined baseline LHP. Moreover, this system-level model shows that a higher performance could be achieved by optimizing the vapor-removing duct. This would be possible without severe microfabrication challenges. The predicted performance of an optimized LHP with reduced turbulent flow losses in the evaporator exceeds 1000 W/cm2.
A Coupled Stagnation Flow and Knudsen Layer Analysis for Laser Drilling
Authors: Batteh John J. , Chen Michael M. , Mazumder Jyoti 
Published: December 2021

Abstract
The application of lasers in industrial drilling processes is rapidly increasing. Consequently there is a great need to understand the fundamental physics of the laser drilling process. Recent experiments have shown that material removal occurs via the combined action of vaporization and melt expulsion due to the vaporization-induced recoil pressure. The authors (Batteh et al., 1998) developed a quasi-steady stagnation flow analysis to study the physical mechanisms of laser drilling by examining the heat transfer and fluid flow in the molten metal. This paper presents an extension of that analysis by including the effects of nonequilibrium vaporization. A Knudsen layer analysis is used to model the nonequilibrium evaporation at the liquid-vapor interface and the compressible flow outside the Knudsen layer. The analysis gives the pressure, temperature, and density jumps across the Knudsen layer. Numerical results for the combined stagnation flow and Knudsen layer analysis are shown for several different materials over a range of laser intensities commonly used in laser drilling. Drilling trends are shown as functions of the laser energy and beam radius. The results show that a significant portion of the material removed occurs through melt expulsion due to the vaporization-induced recoil pressure. The results from both the equilibrium and Knudsen layer models for vaporization are compared, and the validity of equilibrium vaporization models are discussed.
Transient, Three-Dimensional Heat Transfer Model for Partially Stabilized Zirconia Undergoing Laser-Assisted Machining
Authors: Pfefferkorn Frank E. , Incropera Frank P. , Shin Yung C. 
Published: December 2021

Abstract
A three-dimensional, unsteady heat transfer model has been developed for predicting the temperature field in partially stabilized zirconia (PSZ) undergoing laser-assisted machining (LAM). PSZ is a semi-transparent ceramic which volumetrically absorbs, emits and scatters radiation across a spectral region extending from approximately 0.5 to 8 μm. As a first approximation, it is treated as optically thick within this spectral band, and the high density of scattering centers, as well as the random orientation of grain boundaries, permits the assumption of isotropic scattering. Accordingly, the Rosseland diffusion approximation is used to model internal radiative transfer. Since most of the CO2 laser radiation (λ = 10.6 μm) is absorbed in the first layer of control volumes adjacent to the surface, incident laser radiation is treated as a surface phenomenon.
The equivalent radiation conductivity of PSZ is strongly temperature dependent and enhances thermal energy transfer within regions of the workpiece which are close to the location of laser irradiation. However, the effective thermal conductivity of PSZ remains relatively low, even at the highest temperatures achieved during LAM, and is responsible for large temperature gradients near the irradiated surface of the workpiece. For representative operating conditions, comparative calculations are performed with and without the radiation model to assess the influence of volumetric radiation effects on the temperature field. Numerical simulations are also performed to consider the effect of operating conditions, such as the laser power, laser/tool feed and depth-of-cut, on thermal conditions in close proximity to the material removal zone. The results are contrasted with those for silicon nitride, which is an opaque ceramic that exhibits quasi-plastic deformation when its temperature is raised above a threshold value at the depth-of-cut and can therefore be machined with a cutting tool.
Emission and Laser-Induced Fluorescence Spectroscopy of Laser-Ablated Titanium Plume
Authors: Chu Schubert S. , Grigoropoulos Costas P. 
Published: December 2021

Abstract
Pulsed laser deposition (PLD) of thin films has evolved into a well-recognized technique for a wide range of materials and in a variety of devices. There is great interest in the energy characterization of the ablated plume because this is a key parameter in determining the quality of the deposited film. Spectroscopic techniques, such as optical time-of-flight (TOF,) emission spectroscopy, and laser-induced-fluorescence (LIF) are excellent methods for this purpose since they offer temporal and spatial resolution as well as the capability of distinguishing different species. The effects of laser fluence and background gas pressure on the kinetic energies of the ablated species were found by the optical time-of flight technique and by emission imaging. Furthermore, laser-induced-fluorescence was employed for spectrally resolved imaging. The results provide additional data on the kinetic energy and the distribution of neutral titanium. The axial velocity of neutral titanium was found to be as high as 2 × 104 m/s. The distribution of species within the plume was also determined.
Transient Elastic Stress Development During Laser Scribing of Ceramics
Authors: Mallison Thomas M. , Modest Michael F. 
Published: December 2021

Abstract
Lasers are emerging as a valuable tool for shaping and cutting hard and brittle ceramics. Unfortunately, the large, concentrated heat flux rates that allow the laser to efficiently cut and shape the ceramic also result in large localized thermal stresses in a small heat-affected zone. These notable thermal stresses can lead to micro-cracks, a decrease in strength and fatigue life, and possibly catastrophic failure. In order to assess where, when, and what stresses occur during laser scribing, an elastic stress model has been incorporated into a three-dimensional scribing and cutting code. First, the code predicts the temporal temperature fields and the receding surface of the ceramic. Then, using the scribed geometry and temperature field, the elastic stress fields are calculated as they develop and decay during the laser scribing process. The analysis allows the prediction of stresses during continuous wave and pulsed laser operation, a variety of cutting speeds and directions, and various shapes and types of ceramic material. The results of the analysis show substantial tensile stresses develop over a thick layer below and parallel to the surface, which may be the cause of experimentally observed subsurface cracks.
The Dispersion in Finite Element Solutions to the One-Dimensional Heat Equation
Authors: Emery Ashley F. , Dauksher Walter 
Published: December 2021

Abstract
A method for evaluating the numerically introduced dispersion in finite element solutions to the one-dimensional heat equation is presented. The dispersion is quantified for linear and quadratic elements as a function of time step, mesh refinement and capacitance matrix formulation. It is demonstrated that an analysis of the dispersion is a useful tool in estimating the accuracy and in understanding the behavior of the numerical algorithm.
Prediction of Humid Air Heat Exchanger Performance Using Artificial Neural Networks
Authors: Pacheco-Vega Arturo , Sen Mihir , Yang K. T. , McClain Rodney L. 
Published: December 2021

Abstract
In the present study we apply an artificial neural network to predict the operation of a humid air-water fin-tube compact heat exchanger. The network configuration is of the feedforward type with a sigmoid activation function and a backpropagation algorithm. Published experimental data, corresponding to humid air flowing over the heat exchanger tubes and water flowing inside them, are used to train the neural network. After training with known experimental values of the humid-air flow rates, dry-bulb and wet-bulb inlet temperatures for various geometrical configurations, the j-factor and heat transfer rate predictions of the network were tested against the experimental values. Comparisons were made with published predictions of power-law correlations which were obtained from the same data. The results demonstrate that the neural network is able to predict the performance of this heat exchanger much better than the correlations.