bluuebunny/crossref_metadata_2025_split huggingface dataset:
Adaptive Neurocontrol and Minimization of Energy Consumption of a Heat Exchanger Test Facility
Authors: Díaz Gerardo , Sen Mihir , McClain Rodney L. 
Published: November 2021

Abstract
It has been shown that artificial neural networks (ANNs) can be used to simulate and control thermal systems such as heat exchangers. It is known that the characteristics of thermal components such as heat exchangers vary with respect to time mainly due to fouling effects. There is a need of a model that can adapt to the new characteristics of the thermal system. In this work adaptive artificial neural networks are used to control the outlet air temperature of a heat exchanger test facility. The neurocontrollers are adapted on-line on the basis of different criteria. The parameters of the ANNs are modified considering target error and stability conditions of the closed loop system analyzed as a nonlinear iterative map. We also implement a minimization of a performance index that quantifies the energy consumption. It is shown numerically and experimentally that the neural network is able to control the thermal facility, and is also able to adapt to different disturbances applied to the system, while minimizing the amount of energy used.
An Economical Method for Artificial Neural Network Process Modeling by the Model-Modifier Approach
Authors: Bhatikar Sanjay 
Published: November 2021

Abstract
In this paper we present our model-modifier approach as an economical method for the development of accurate manufacturing equipment models. The model modifier method leverages knowledge from one ANN model to another of a similar type, thus reducing the development effort required as compared to starting from scratch. The economy afforded by this knowledge-sharing technique was evaluated on a Chemical Vapor Deposition (CVD) reactor. The results show that the model-modifier approach is a valid method for transferring knowledge between similar ANN models and that significant savings in training data accrue from this approach. In our case, a highly accurate ANN model was developed with a mere one-fifth of the data that would have been required without this approach. Further, we have also shown that an ANN model developed by the model-modifier approach can be easily and reliably utilized for process optimization.
Modeling of Moving Breakdown by Femtosecond Laser Pulses in Dielectrics
Authors: Fan C. H. , Longtin J. P. 
Published: November 2021

Abstract
Laser ablation is becoming increasingly important in the fields of micromaching, thin film formation, and bioengineering applications. In laser ablation, the ablation rates and feature quality strongly depend on the size of the breakdown region in the material. This region is characterized by a high density of free electrons, which absorb a large fraction of energy from the laser pulse that results in material vaporization in solids or liquids. For nanosecond- and picosecond pulses, the breakdown region tends to form near the beam focus and then expand back along the beam path toward the laser; this phenomenon is called moving breakdown. For femtosecond pulses, however, breakdown begins up the beam path and then propagates toward the focal point. A moving breakdown model presented by Docchio et al. (1988a) successfully explains and predicts the time-dependent breakdown region in the nanosecond regime, however it does not adequately describe propagation of the breakdown region at pico- and femtosecond time scales. In the present work, a modified moving breakdown model is proposed that includes the pulse propagation and small spatial extent of ultrafast laser pulses. This revised model shows that pulse propagation becomes significant for pulsewidths less than 10 picoseconds. The new model characterizes the pulse behavior as it interacts with a material within the focal volume in both solids and liquids. The model may also be useful in estimating the time- and space-resolved electron density in the interaction volume, the breakdown threshold of a material, shielding effectiveness, energy deposition, and the temperature increase in the material.
Numerical Simulation of Dendritic Solidification
Authors: Jung Jin-Young , Chen Michael M. 
Published: November 2021

Abstract
It is well known that the dendritic microstructure of alloys is a consequence of morphological instability of the solidification process, which is a result of the coupling of heat and mass transfer with the composition-dependent phase equilibrium condition mediated by the surface energy. There have been many numerical simulations of dendritic solidification. However, many successful simulations of dendritic growth have used non-discrete front tracking method such as artificial source method or phase field method, with demonstrably first order accuracy. Many also found it necessary to continuously inject random noise during simulation. The continuous injection of random noise raises the suspicion that the numerical schemes used may be overly dissipative. The noise is apparently capable of creating nonuniform solidification, but not sufficient to ensure growth with a clear dendritic pattern. In the present study, to rule out the numerical diffusivity as a cause of the damping of dendritic perturbations, artificial perturbations are either not used, or injected only as initial conditions. Under the unstable solidification mode, the initial perturbation triggers the onset of interface instability. Computations were performed for both sub-cooled pure material as well as directional solidification of alloys. The successful simulation of dendritic solidification without the intentional injection of random noise provided evidence that the present method has less numerical diffusion than many existing front tracking methods.
A Volume Radiation Heat Transfer Model for Czochralski Crystal Growth Processes
Authors: Nunes Edmundo M. , Naraghi Mohammad H. N. , Zhang Hui , Prasad Vishwanath 
Published: November 2021

Abstract
Thermal modeling of Czochralski (CZ) crystal growth processes is a challenging task owing to the complex interaction of heat conduction, convection, thermal radiation, fluid flow, and other transport phenomena. A highly innovative, general-purpose computer model for phase-change and free-surface problems, utilizing a multi-zone adaptive grid generation and curvilinear finite volume scheme, is linked to a spectral, volume and surface thermal radiation algorithm to predict the temperature distribution within a Czochralski growth furnace. The radiative transfer model, based upon the Discrete Exchange Factor (DEF) method, is capable of addressing the complexities due to irregularly-shaped axisymmetric geometries and shadowing effects. A unified exchange factor model is used to account for multiple reflection/scattering of radiation within the enclosure. Several numerical trials are performed to simulate the CZ growth of yttrium aluminum garnet (YAG). The effect of the top surface boundary condition on temperature profile, crystal/melt interface shape, and process stability is studied to examine the applicability of this model to control the growth conditions and interface shape. The results show that there exists a temperature range for this surface for which the desirable conditions for crystal growth are possible. This limiting temperature range is, however, dynamic and changes as the growth progresses.
Improved Thermoplastic Composite by Alignment of Vapor Grown Carbon Fiber
Authors: Kuriger Rex J. , Alam M. Khairul , Anderson David P. 
Published: November 2021

Abstract
This paper discusses the properties of an improved thermoplastic composite by alignment of vapor grown carbon fiber (VGCF) suspended in a polypropylene matrix. VGCF provides improved mechanical and electrical properties in composites. In this study an extruder was used to shear mix and extrude VGCF/polypropylene mixtures containing fiber volume fractions of 2.5%, 7% and 11% through a converging-annular die which produces a high degree of fiber alignment along the flow direction. X-ray diffraction analysis performed on the extruded composite strands showed that the fibers were oriented approximately ± 23.7, ± 28.15 and ± 30.0 degrees along the preferred direction for the 2.5%, 7% and 11% specimens, respectively. Tensile tests were done in both the preferred and transverse directions of samples reinforced with pyrolytically stripped VGCF. When compared to polypropylene, there was a 36.5%, 69.4% and 82.0% increase in tensile strength, and a 94.9%, 173.7% and 218.2% increase in modulus for the 2.5%, 7% and 11% VGCF mixtures along the preferred direction, respectively. The tensile strength and modulus in the transverse direction increased as the fiber volume content increased, however, all values were well below that of polypropylene. This behavior could be attributed to stress concentrations in the composite material. Electrical resistivity measurements were made on samples reinforced with two types of VGCF. The results concluded that the electrical conductance of the polymer strands reinforced with a heat-treated VGCF was far superior to those reinforced with a pyrolytically stripped VGCF.
Mechanism and Modeling of Micro-Droplet Impact, Fragmentation, and Solidification
Authors: Zhang H. 
Published: November 2021

Abstract
New applications have been identified for thermal spraying using micro-droplets. Mechanisms of impact, fragmentation, and solidification developed for millimeter size droplets are no longer applicable for micro-droplets due to the significance of the surface tension and wall interaction. New fragmentation mechanisms and advanced numerical modeling are required to develop a better understanding of the transport phenomena for droplet spreading and solidification. In this paper, the existing fragmentation mechanisms have been reviewed, and a new mechanism is proposed. The proposed mechanism considers the effects of flow instability, wettability, surface roughness, surface chemistry, and moisture absorption. This mechanism has been incorporated into an advanced numerical model that consists of a multizone adaptive grid generation used for tracking the movement of the solidification interface and a curvilinear level-set method for capturing the movement of free surface. Impact, fragmentation, and solidification of a molybdenum micro-droplet has been simulated, and the fragmentation morphology has been predicted.
System Characterization and Plasma-Particle Distribution Analysis for Development of a Closed Loop Control for Plasma Spray
Authors: Gevelber M. , Wroblewski D. , Fincke J. , Swank W. D. 
Published: November 2021

Abstract
This paper investigates the need to develop an advanced control system for plasma spray deposition. The limitations and performance capability of both feed forward and real-time control are evaluated. Critical system characteristics for developing such controllers are experimentally identified including dominant nonlinearalities; dynamics, cross-coupling, distributions, and sensor issues.
Pool Boiling Critical Heat Flux on a Downward-Facing Convex Surface
Authors: Howard Alicia H. , Mudawar Issam 
Published: November 2021

Abstract
Heat transfer measurements and photographic studies were performed to capture the detailed evolution of liquid-vapor interfacial behavior near critical heat flux (CHF) for a 90-degree downward-facing convex surface. The test surface, with a width of 3.2 mm and a 102.6-mm radius, consisted of a series of nine heaters which dissipated equal power. Instrumentation within each heater facilitated localized heat flux and temperature measurements along the convex surface, and transparent front and back windows enabled optical access to a fairly two-dimensional liquid-vapor interface. Near CHF, vapor behavior along the convex surface was cyclical in nature and somewhat similar to that observed in pool boiling on horizontal downward-facing flat surfaces. The vapor repeatedly formed a stratified layer at the bottom of the convex surface, which stretched as more vapor was generated, and then departed from the surface. Subsequently, the bottom (downward-facing) heaters, followed by the other heaters, were wetted with liquid before the nucleation/coalescence/stratification/release process repeated itself. Prior to CHF, the surface was adequately cooled by the liquid wetting. At CHF, the surface was still wetted for a brief period, but the wetting time was too short to allow adequate cooling of the downward-facing heaters, and the temperature of these heaters began to rise. This study proves that despite the pronounced thickening of the vapor layer as it propagates upwards along the convex surface, CHF always commences on the downward-facing heaters.
Transient Convective Heat Transfer in a Helical Tube With Steam-Water Two-Phase Flow Under Pressure Drop Type Oscillations
Authors: Guo Lie-Jin , Feng Zi-Ping 
Published: November 2021

Abstract
In the present paper the experiments for subcooled water flow and steam-water two-phase flow were conducted to investigate the effects of pulsation upon transient heat transfer characteristics in a closed-circulation helical-coiled tube steam generator. The non-uniform property of local heat transfer with steady flow was also examined. The secondary flow mechanism and the effect of interaction between the flow oscillation and secondary flow were analyzed on the basis of the experimental data. Some new phenomena were observed and explained. A series of correlations were proposed for the average and local heat transfer coefficients both under steady and oscillatory flow conditions. The results showed that there were considerable variations in local and peripherally time-averaged Nusselt numbers for pulsating flow in a wide range of parameters. Systematic investigations of pressure drop type oscillations and their thresholds for steam-water two-phase flow in a uniformly heated helical tube were also reported.
Subcooled Boiling of Surfactant Solutions
Authors: Hetsroni G. , Gurevich M. , Mosyak A. , Rozenblit R. , Yarin L. P. 
Published: November 2021

Abstract
During subcooled boiling of pure water and water with cationic surfactants, the motion of bubbles and the temperature of the heated surface were recorded by both a high-speed video camera and an infrared radiometer. The results show that the bubble behavior and the heat transfer mechanism for the surfactant are quite different from those of clear water. Bubbles formed in Habon G solutions were much smaller man those in water and the surface was covered with them faster. Boiling hysteresis is found for degraded solutions. Dependencies of heat transfer coefficient for various solutions were obtained and compared. The boiling curves of surfactant are quite different from the boiling curve of pure water. Experimental results demonstrate that the heat transfer coefficient of the boiling process can be enhanced considerably by the addition of a small amount of Habon G. The experiments show that the limitations of the ER technique with respect to frequency response are outweighed by its unique capacity to measure wall temperature distribution with high spatial resolution over an area encompassing many nucleation sites and over long periods.
Some Aspects of Critical-Heat-Flux Enhancement in Tubes
Authors: Doerffer S. S. , Groeneveld D. C. , Rudzinski K. F. , Pioro I. L. , Martin J. W. 
Published: November 2021

Abstract
This paper summarizes the effects of various types or numbers of critical-heat-flux (CHF)-enhancing inserts in tubular geometries. The impact of inserts on CHF is frequently expressed by an enhancement ratio K: the ratio of CHF with an insert to the CHF in a bare tube for the same local flow conditions. The impact on K of the following parameters was investigated: (i) fluid type (Freon-134a, water), (ii) axial spacing between inserts, (iii) shape of the insert, (iv) flow blockage of the insert, (v) number of similar/dissimilar insert planes upstream, and (vi) impact of flow conditions. The spacing and flow-obstruction area were found to be the major geometric factors that affected K: by decreasing the relative spacing, L/D, to 16, K can reach a value of from 2 to 3, depending on the flow-obstruction area. Among flow parameters, the critical quality, xc, usually has a strong effect on K: K can increase from a value of 1 to 3, when xc increases from 0 to 0.4 for a mass flux G ≥ 2 Mg/m2s. For G &lt; 2 Mg/m2s, CHF enhancement can disappear or become negative (K &lt; 1). No cumulative effect was found on K for a series of upstream insert planes. CHF enhancement does not depend on fluid type, provided that the conditions in the fluids meet the CHF fluid-to-fluid modelling requirements.
Shock Waves in Liquids With Bubbles Containing Evaporating Drops
Authors: Khabeev Nail S. , Bertelsen Arnold F. , Ganiev Oleg R. 
Published: November 2021

Abstract
An investigation of wave processes in liquids with bubbles containing evaporating drops is presented. A model is used which takes into account both the liquid radial inertia due to medium volume changes, and the temperature distribution inside and around the bubbles. An analysis of the microsopic fields of physical parameters is aimed at closing the system of equations for averaged characteristics. The evolution of non-steady shock waves in liquids with bubbles containing evaporating drops is studied by numerical methods. The effect of the initial conditions, shock strength, volume fraction, dispersity of the vapor phase, initial static pressure and of the thermophysical properties of the phases on shock-wave structure and evolution is studied.
The possible enhancement of disturbances in the region of their initiation is shown. The phenomenon of the nonlinear anomalous enhancement of waves reflected from a wall is established.
Stacked Microchannel Heat Sinks for Liquid Cooling of Microelectronic Components
Authors: Wei X. , Joshi Y. 
Published: November 2021

Abstract
A novel heat sink based on a multi-layer stack of liquid cooled microchannels is investigated. For a given pumping power and heat removal capability for the heat sink, the flow rate across a stack of microchannels is lower compared to a single layer of microchannels. Numerical simulations using a computationally efficient multigrid method [1] were carried out to investigate the detailed conjugate transport within the heat sink. The effects of the microchannel aspect ratio and total number of layers on thermal performance were studied for water as coolant. A heat sink of base area 10 mm by 10 mm with a height in the range 1.8 to 4.5 mm (2–5 layers) was considered with water flow rate in the range 0.83×10−6 m3/s (50 ml/min) to 6.67×10−6 m3/s (400 ml/min). The results of the computational simulations were also compared with a simplified thermal resistance network analysis.
Fire Resistance Characteristics of Fire Protection Materials With High-Water Content
Authors: Asako Y. , Otaka T. , Yamaguchi Y. 
Published: November 2021

Abstract
It is well known that moist fire protection materials show good fire resistance characteristics. For this reason, these materials are usually made of mixtures of cement mortar and high-water content materials such as silica gels or moist perlites. The latent heat of water plays an important role in the resistance of heat propagation in these materials. In this study, the thermal conductivity of mixtures of perlite-mortar and super-absorbent polymer gel to increase its water storage capacity, were measured. Also, the water content of the test materials was measured. Using the measured thermal properties of such fire protection materials, the numerical simulation for the fire resistant test were conducted. The effects of mixing ratio of the gels and the perlite-mortar on the fire resistance characteristics are discussed.
Simulation of Turbulent Flow Through Hybrid Porous Medium: Clear Fluid Domains
Authors: de Lemos Marcelo J. S. , Pedras Marcos H. J. 
Published: November 2021

Abstract
Turbulent flow in a channel, totally and partially filled with a porous medium, is simulated with a proposed turbulence model. Two cases are analyzed, namely clear flow past a porous obstacle and flow through a porous medium having a cavity with a higher porosity. Mean and turbulence quantities were solved within both computational domains using a single numerical technique. The control volume approach was used to discretize the governing equations. In the first case analyzed, the flow penetration into the porous substrate is accompanied by generation of turbulence kinetic energy within the obstacle. In the second geometry, the flow is pushed towards the cavity as porosity increases.
Measurement and Prediction of Temperature Distributions in Optical Elements in the Millikelvin Regime
Authors: Ambrose Jay , Hashemi Ab , Schneider Julie , Stubbs Dave , Aaron Kim , Shao Michael , VanZandt Tom 
Published: November 2021

Abstract
This paper describes analytical and experimental thermal results for a 33.5 cm diameter plano mirror under conditions of small thermal perturbations (steady-state temperature gradients of 10–100 mK). These tests are intended to support verification of specific thermal requirements for a space interferometer. The primary thermal requirement is knowledge/control of temporal changes in mirror gradients to the 1 mK (0.001 K) level. Tests were performed with small heat inputs to the back of the mirror, which was suspended in a thermally-uniform shroud. Correlation of thermal models for both conductively and radiatively-heated test configurations were performed, and results indicate very good agreement between the thermal model predictions and the temperature measurements. The modeling uncertainty based on the test correlation is estimated to be ±3 mK for absolute temporal comparisons. Comparisons for temporal change of gradient are shown to be within 1 mK for small perturbations. The paper describes the test setup, test results, model correlation and uncertainty estimates.
Application of Computational Fluid Dynamics to Protective Clothing System Evaluation
Authors: Gibson Phillip W. , Charmchi Majid 
Published: November 2021

Abstract
Convection, diffusion, and phase change processes influence heat and mass transfer through textile materials used in clothing systems. For example, water in a hygroscopic porous textile may exist in vapor or liquid form in the pore spaces or in bound form when it has been absorbed by the solid phase, which is typically some kind of hydrophilic polymer. Phase changes associated with water include liquid evaporation/condensation in the pore spaces and sorption/desorption from hydrophilic polymer fibers. Certain materials such as encapsulated paraffins may also be added to textiles; these materials are designed to undergo a solid-liquid phase change over temperature ranges near human body temperature, which influences the perceived comfort of clothing. Additional factors such as the swelling of the solid polymer due to water imbibition, and the heat of sorption evolved when the water is absorbed by the polymeric matrix, can all be incorporated into the appropriate conservation and transport equations describing heat and mass transfer through clothing layers. These physical factors, nonlinear material properties, and complex multiphase flows make the task of modeling and predicting levels of protection and comfort of various clothing designs difficult and elusive. Computational fluid dynamics (CFD) has proven to be useful at several levels of material and system modeling to evaluate and design protective clothing systems and material components. This paper summarizes current and past work aimed at utilizing CFD techniques for protective clothing applications.