bluuebunny/crossref_metadata_2025_split huggingface dataset:
Asymmetric Glass Temperature due to Cold-Spots on the Furnace Wall in the Optical Fiber Drawing Process
Authors: Dogu Yahya , Kaminski Deborah A. 
Published: March 2022

Abstract
This study represents a three-dimensional numerical analysis of the effects of wall cold-spots on the temperature fields in an optical fiber draw furnace. Radiation heat transfer was added to the energy equation by using the diffusion approximation inside the glass, and a full enclosure analysis in the gas for surface-to-surface radiation between the glass surface and furnace wall was used. The model includes temperature dependent physical properties. Convective heat transfer was treated by solving the flows in the gas and glass, conjugately. The three-dimensional Navier-Stokes equations and the energy equation were solved within the glass preform and gas simultaneously using the finite element method.
Wall cold-spots at different locations and temperatures were examined and their effects on the furnace temperature were determined. These cold spots cause temperature nonuniformities around the preform circumference and delay the heat up of the preform. Asymmetric glass temperatures on the preform caused by cold-spots located in the upper part of the furnace tended to equilibrate before reaching the end of the furnace. The preform diameter at the furnace exit becomes narrow, thus the circumferential temperature distribution on the fiber becomes more uniform and isothermal. However, although the asymmetric temperature differences were small, the temperature gradients and viscosity changes over the preform cross-sections were rather high. Thus, the glass will flow faster through the hot side of the preform. This may result in a nonuniform consumption of the glass preform and may also cause distortion on the desired form of the symmetric neck-down root shape of the preform. Wall cold-spots must be minimized in temperature and size to prevent their effects on the temperature field and final fiber diameter.
The Role of Heat Transfer Problems in Standard Crystallization Experiments
Authors: Eder Gerhard 
Published: March 2022

Abstract
In most publications dealing with crystallization kinetics also nowadays Avrami’s model from 1939 is used for analyzing experimental data. There have been made many attempts to generalize this isothermal model to arbitrary non-isothermal crystallization processes. The solution of this problem can be found in a work by A.N. Kolmogoroff from 1937. The basic crystallization kinetic quantities in this theory are some crystal growth rate and nucleation rate, which both may depend arbitrarily on time. For analyzing data with such models it is essential to have a good control of the temperature history, since both kinetic quantities are very sensitive with respect to temperature changes. A very popular reason to develop new kinetic models was often the fact, that experimental results could not be described by the classical models. In this paper heat transfer problems are shown to be a decisive source of such deviations.
Estimating the Morphology of Soot Agglomerates by Measuring Their Scattering Matrix Elements
Authors: Manickavasagam S. , Govindan R. , Mengüç M. P. 
Published: March 2022

Abstract
In this study, we introduce a novel approach to identify the structure of soot agglomerates in flames. The idea is based on the use of elliptically-polarized light scattering, which is quite sensitive to the morphology of the scattering particles. First, a numerical procedure is outlined to determine the scattering (Mueller) matrix elements of particles and agglomerates. Results for various fractal-like agglomerates are presented. Following this, an experimental procedure is described to measure the same elements. Then, normalized experimental and numerical results are compared to estimate the fractal morphology of soot agglomerates. The results show that this technique is quite versatile and can be employed effectively to identify the size and structure of soot agglomerates.
Monodisperse Spray Effects on Thermal Explosion in a Gas
Authors: Goldfarb Igor , Goldshtein Vladimir , Kuzmenko Grigory , Greenberg J. Barry 
Published: March 2022

Abstract
The effect of a flammable spray on the thermal explosion in a combustible gas mixture is investigated based on an original physical model. For qualitative analysis of the system an advanced geometric asymptotic technique (integral manifold method) has been used. Possible types of dynamical behavior of the system are classified and parametric regions of their existence are determined analytically. It turns out that there are five main dynamical regimes of the system: slow regimes, conventional fast explosive regimes, thermal explosion with freeze delay and two different types of thermal explosion with delay (the concentration of the combustible gas decreases or increases). Peculiarities of these dynamical regimes are investigated and their dependence on physical system parameters are analyzed. Upper and lower bound estimates for the delay time are derived analitically and compared with results of numerical simulations. The comparison demonstrates satisfactory agreement.
Microscales of Natural Convection
Authors: Arpacı Vedat S. 
Published: March 2022

Abstract
A universal dimensionless number, ΠN∼NN1+Pr-1 ,Pr being the usual Prandtl number and NN the limit of ΠN for Pr → ∞, is introduced for all natural convection processes. For NN=Ra ,Ra being the usual Rayleigh number, ΠN describes buoyancy-driven natural convection. For NN=Ma ,Ma being the usual Marangoni number, ΠN describes thermocapillary-driven natural convection. For NN=TaPr ,Ta being the usual Taylor number, ΠN describes centrifugally-driven natural convection.
In terms of ΠN, a thermal Kolmogorov scale relative to an integral scale, ηθℓ∼ΠN-1/3 is introduced for natural convection including buoyancy, thermocapillary and centrifugally-driven flows. Heat transfer associated with these flows is modeled byNu∼ΠN1/3 ,Nu being the usual Nusselt number. A variety of turbulent natural convection phenomena are shown correlating the model.
Effects of Orifice Geometry on the Heat Transfer Distribution for Impinging Jet Array
Authors: Arjocu Simona C. , Liburdy James A. , Ferland Michele M. 
Published: March 2022

Abstract
The recent technological advances in the areas of gas turbine blades, tempered metals and in particular electronic components, require a rapid rate of removal of heat. With an array of impinging jets a large surface involved in the cooling or heating process can be covered using relatively small flow work, or driving pressure. A properly spaced and configured impinging jet array produces a high heat transfer rate. The present study details the role of impinging jets in the heat transport phenomena. The average and local heat transfer coefficient distribution is mapped using thermochromic liquid crystals for three equal flow area jet orifice geometries in a 3-by-3 submerged impinging water jet square array. The hydrodynamic conditions are established for low Reynolds number values, from 800 to 1500, and impingement distances of 1, 2 and 4 jet hydraulic diameters. The constant temperature jets impinged normally on a constant heat flux surface and liquid crystal images were recorded under thermal and hydrodynamic steady state conditions. The results indicate that there is a Reynolds number dependence of the degree of heat transfer enhancement for different shaped jet orifices. The heat transfer within the central unit cell varies with impingement distance and jet geometry. Two types of heat transfer coefficient spatial variation have been identified: one deals with large scale jet flow characteristics and the other with smaller scale effects caused by flow turbulence. Details are presented illustrating the nonuniformity of the heat transfer for the various geometries.
A Study of the Flow Field and Convective Heat Transfer in a Model Rotor-Stator Cavity
Authors: Roy Ramendra P. , Agarwal Vivek , Devasenathipathy Shankar , He Junru , Meier Lars , Kim Yong W. , Howe Jeff , Ho Ko-Sun 
Published: March 2022

Abstract
Experiments and computations are being carried out with the objective of understanding the turbulent flow field and convective heat transfer in gas turbine disk cavities. An experimental rig which features a configuration of rotor and stator disks simpler than in actual gas turbines but retains the important features of stator vanes, rotor blades, and realistic rim seals on the disks has been constructed for the experiments. The commercial CFD code FLUENT/UNS is used for the computations.
We report measurements, in experiments with mainstream and secondary air flows, of the convective heat transfer coefficient and cooling effectiveness distributions on the rotor disk surface. Also reported are the radial distribution of the time-mean static pressure at the stator disk and the circumferential distribution of the same in the mainstream gas passage. Implications of the cooling effectiveness and static pressure distributions vis-á-vis the ingestion of mainstream gas into the disk cavity are discussed briefly. Computational results are presented and compared with measurements in some cases.
Non-Boussinesq Convection in a Tall Cavity Near the Codimension-2 Point
Authors: Suslov S. A. , Paolucci S. 
Published: March 2022

Abstract
By means of weakly nonlinear analysis, we investigate the interaction between two physically distinct instability modes arising in the non-Boussinesq convection flow in a differentially heated tall vertical air-filled cavity. It is shown that in the neighborhood of the codimention-2 point the primary parallel flow becomes unstable due to both shear and buoyant disturbances. The flow dynamics is modeled by a system of the two coupled Landau equations. Different possible instability wave patterns are found, and the parameter regions of their existence are discussed. Energy analysis of the interacting instability modes is also presented.
A Stream Function Finite Differences Formulation for Two Dimensional Incompressible Flows
Authors: Bubnovich Valeri I. , Moraga Nelson O. 
Published: March 2022

Abstract
A new implicit algorithm to solve the full Navier Stokes equations for two dimensional unsteady incompressible flows that only makes use of the stream function, without the explicit calculation of the vorticity, is presented. The mathematical model discretized in finite differences, according to the ADI method, results in a system of two algebraic equations involving 11 nodes in each equation. By making an original hyphotesis, a reduction to equations with five nodes allows to obtain the numerical solution via the use of a pentadiagonal matrix algorithm PDMA. An iterative cycle has been implemented to verify the quality of the proposed hyphotesis ant to asses its accuracy and speed of convergence. Numerical results are presented for two classical fluid mechanics problems: induced laminar flow in a square cavity with Re = 100, 400, 1000 and natural convection inside a square cavity for cases where Ra = 1000, 10000 and Pr = 0.1; 1, 10.
The Design and Analysis of Compliant MEMS Using the Pseudo-Rigid-Body Model
Authors: Jensen Brian D. , Howell Larry L. , Gunyan Daniel B. , Salmon Linton G. 
Published: March 2022

Abstract
Because of the difficulty of fabricating rigid-body joints and assembling parts in micro-electro-mechanical systems (MEMS), compliant mechanisms offer several advantages to MEMS designers. However, motion of compliant segments generally involves large, non-linear deflections which are difficult to predict using linear beam theory. This paper discusses MEMS design using the pseudo-rigid-body model. This model has been developed to permit simplified prediction of nonlinear deflections in compliant mechanisms, allowing traditional mechanism theory to be used in design. The design process is validated by testing MEMS structures designed using this model. The model successfully predicted the motion of the compliant MEMS, even for very large deflection paths. The mechanisms designed and tested achieved larger deflections and more complex motion than was previously possible.
Impact of Phonon Dispersion Upon the Size Effect on Thermal Conduction Along Thin Semiconductor Films
Authors: Ju Y. Sungtaek , Goodson Kenneth E. 
Published: March 2022

Abstract
The thermal conductivities of thin crystalline semiconductor films in novel electrical and optical devices can differ from bulk values due to the size effect on lattice thermal conductivity, which is caused by phonon-boundary scattering. For many semiconductors at or above room temperature, the size effect is strongly influenced by the highly dispersive nature of their phonon spectra and the varying contribution of each phonon branch to heat conduction. The present study reviews existing thermal conductivity models for bulk semiconductor samples and examines the impact of the phonon dispersion on the size effect. Based on the observed strong dependence of the size effect on the phonon branch contributions, we demonstrate that the investigation of thin-film thermal conductivity at high temperatures can help the theoretical understanding of lattice thermal conduction. For silicon thin films studied here better agreement between the predicted in-plane thermal conductivity and the existing experimental data is achieved by assuming that longitudinal phonons are the dominant heat carriers. The practically-relevant problem of phonon scattering at the interface between crystalline silicon and amorphous silicon dioxide layers is discussed.
Increasing the Exergy Storage Capacity of Thermal Storages Using Stratification
Authors: Rosen M. A. , Tang R. 
Published: March 2022

Abstract
The increase in exergy storage capacity that is attained in thermal storages through stratification is assessed. A design-oriented temperature distribution model for vertically stratified thermal storages that facilitates the evaluation of storage energy and exergy contents is utilized. The paper is directed towards demonstrating the thermodynamic benefits achieved through stratification, and increasing the utilization of exergy-based performance measures for stratified thermal storages. A wide range of realistic storage-fluid temperature profiles is considered, and for each the relative increase in exergy content of the stratified storage compared to the same storage when it is fully mixed is evaluated. The results indicate that, for all temperature profiles considered, the exergy storage capacity of a thermal storage increases when it is stratified, and increases as the degree of stratification, as represented through greater and sharper spatial temperature variations, increases. Furthermore, the percentage increase in exergy capacity is greatest for storages at temperatures near to the environment temperature, and decreases as the mean storage temperature diverges from the environment temperature (to either higher or lower temperatures). It is concluded that (i) the use of stratification in thermal storage designs should be considered as it increases the exergy storage capacity of a thermal storage, and (ii) exergy analysis should be applied in the analysis and comparison of stratified thermal storage systems.
New Humidification Concept for Evaporative Gas Turbine Cycles Applied to a Modern Aeroderivative Gas Turbine
Authors: Aagren Niklas D. , Cavani Adrin , Westermark Mats O. 
Published: March 2022

Abstract
A new humidification concept in evaporative gas turbine cycles is presented. This involves a humidfication column with multiple sections of counter-current humidification with different water flows in each section. The advantages of multiple sections are analyzed in combination with part-flow humidification, where less than 50% of the compressed air from the air compressor is led through the humidification column and the rest is passed on directly to the recuperator. The part flow humidification is a concept that noticeably reduces mass and heat transfer equipment costs in the EvGT cycle. It is shown that, for a part flow configuration, a more efficient cycle can be attained than in a system with customary single-section humidification.
In this paper an EvGT system is modeled in the GATE/CYCLE gas turbine simulation program. The simulations are based on the modem aeroderivative gas turbine Rolls Royce Trent in non-intercooled mode. The results include performance data as well as dimensions and design considerations of the humidification column and the heat exchangers.
The Effect of Thermoelectric Cooler Mounting Orientation on Cooling Efficiency
Authors: Welling Thomas E. , Bell Cheryl A. , Al-Ubaidi Muthar 
Published: March 2022

Abstract
This paper documents an experiment designed to evaluate the effect of heat sink location on cooling system efficiency. Increasing cost and regulation of CFCs, as well as environmental concerns, have resulted in the widespread use of alternative cooling systems, including Thermoelectric Coolers (TECs). These small, solid state heat pumps require heat sinks to increase their effective surface area. Their physical geometry precludes the use of more efficient flow-through heat exchangers. This fact encourages designs in which the cooling process occurs in a duct, raising the question, “How does the position of the heat sinks in a cooling duct affect system efficiency?”
This experiment documents a difference in cooling efficiency between identical sets of four thermoelectrically cooled heat sinks mounted serially in a duct and four similarly cooled heat sinks mounted peripherally in the duct.
This experiment proves that heat sink location in duct cooling applications should be optimized to increase system efficiency and reduce operating costs.
Absorption Heat Pump Performance Improvement Through Ground Coupling
Authors: Garimella Srinivas 
Published: March 2022

Abstract
The present study investigates the improvement in the performance of an absorption heat pump for residential space-conditioning due to the use of the ground as the heat source in the heating mode and the heat sink in the cooling mode. A baseline air-coupled single-effect ammonia-water heat pump is first designed to deliver 10.55 kW (36,000 Btu/hr) of cooling load at the ARI rating conditions. Particular attention is paid to incorporating many realistic details of an operating system such as fuel combustion efficiencies of the burner, non-equilibrium conditions, and moist air processes in the air-coupled heat exchangers. A range of parametric studies is also conducted to investigate the variation in performance of this system with ambient conditions in the heating and cooling modes. The same system is then analyzed in a ground-coupled configuration. The instantaneous COP for the ground-coupled system is compared with the COP of the air-coupled system as a function of the time of the year and the corresponding variations in ambient and ground temperatures using thirty-year average climate data for various locations from the National Weather Service. Improvements in COP of up to twenty percent over the air-coupled system values (cooling mode COP of 0.495 at 35°C (95°F) and heating mode COP of 1.20 at 8.33°C (47°F)) are demonstrated in diverse geographic locations with widely varying heating and cooling loads. These improvements indicate that an efficient ground-coupled heat pump could be developed for residential space-conditioning applications using simple thermodynamic cycles and existing technology for the heat and mass exchange components.
Nondestructive Evaluation of Graphite/Aluminum Composites Using Acousto-Ultrasonics
Authors: Quattlebaum Gene J. , Raju P. K. 
Published: March 2022

Abstract
Acousto-ultrasonic (AU) is a nondestructive testing technique for evaluating composites and composite like materials. The name is based on the fact that advantages of the acoustic emission and ultrasonic testing techniques are combined in this NDE technique. In previous research, AU has been used to evaluate carbon/carbon and GFRP composite materials. The work reported in this paper uses Au to examine the adhesive bond strength of lap-jointed graphite/aluminum composite structures. The Stress Wave Factor (SWF), an AU parameter, was used to quantify the strengths of the two types of adhesives used in this research. Also, AU was used to identify delaminations present in the bond area. AU was used to see if the transverse tensile strength of these composites could be determined and to see if this NDE technique was sensitive to progressive damage. The results indicate that AU can be used to effectively identify the bond strength, the transverse tensile strength, and progression of damage in transverse specimens.
Boundary Element Analysis of Mufflers With an Improved Four-Pole Method
Authors: Wu T. W. , Zhang P. , Cheng C. Y. R. 
Published: March 2022

Abstract
When a muffler is modeled by the boundary element method (BEM), the transmission loss (TL) can be evaluated by either the conventional four-pole method or the recently developed three-point method. The three-point method produces only the TL, and nothing else. On the other hand, the four-pole method has the advantage of retaining the transfer matrix of the muffler, which contains important parameters when the muffler is connected to another muffler or other components in the exhaust system. However, the major drawback of the conventional four-pole method is that it requires two separate boundary element runs due to the two different boundary conditions imposed on the outlet boundary. Therefore, it can take twice as much of the CPU time as the more efficient three-point method. In this paper, an improved four-pole method is introduced. This improved four-pole method does not require solving the boundary element matrix twice. Therefore, it is as efficient as the three-point method and it also retains the important four-pole transfer matrix. The boundary element analysis is done by the direct mixed-body BEM. Two different transfer impedance formulas for perforated tubes are used. Numerical results are compared to experimental data.
Flexible Monitoring Strategies for Milling Operations
Authors: Klocke Fritz , Reuber Martin , Rehse Michael 
Published: March 2022

Abstract
Frequently changing machining operations are a characteristic feature in one-off and small batch size production and require a high degree of flexibility in the production processes and facilities. Process monitoring systems applied in such a production environment have to be able to supply reliable process information under varying machining conditions. Therefore, generic and flexible monitoring solutions are needed, adaptable to the requirements of specific machining applications with minimum efforts. In this paper the requirements for such generic and flexible monitoring approaches are critically discussed. In the second part, monitoring strategies for a process state analysis in face milling, end milling and drilling operations is described, adaptable to varying machining conditions by combining several sensing and evaluation methods.
Prediction of Thermal Deformation of Machine Tool With Strain Sensor
Authors: Moriwaki Toshimichi , Shamoto Eiji , Kawano Masahiro 
Published: March 2022

Abstract
A new approach is presented to estimate the thermal deformation of machine tool, which is generally defined by the relative displacement between the tool and the workpiece. Unlike the conventional approaches based on measurement of the temperature distribution with thermocouples, the new approach is based on measurement of strain distribution, which is considered to give more accurate information about the deformation. A new sensor is developed to measure the true strain including the thermal influence, since it can not be measured by the conventional strain gauge sensors. The developed sensor is applied to estimation of the thermal deformation of a machining center. Fundamental properties of the sensor and the estimated results of thermal deformation are reported.