bluuebunny/crossref_metadata_2025 huggingface dataset:
Sensor/Model Fusion for Improved Process Understanding and Control in Injection Molding
Authors: Chien Li-Jen , Thomas Charles L. , Lawson Del R.
Published: March 2022

Many types of sensors have been investigated to monitor the process conditions in an injection mold during the molding process. Sensors such as thermocouples, pressure sensors, optical sensors, and ultrasonic sensors have been used to monitor the material, mold, and machine status during molding. Users have always found disadvantages or constrains in application for each type of sensor. Certain sensors can only be applied below a certain temperature. They may be hard to install at a critical location, or have difficulty in making an on-line measurement. A model of the process can predict molding conditions and polymer behavior at any location in the process, but the result is not on-line and the accuracy may be unacceptable. In this work, the signals from a cavity pressure sensor and an ultrasonic sensor are used in conjunction with a finite difference model to predict conditions in an injection mold during molding. The combination improves the model predictions and allows monitoring of variables that are not easily measured. Using this system one sensor is used to provide feed back to improve the model accuracy, while the model acts as a “virtual sensor” predicting the output of a variable that is not as easily measured.
New Ultrasonic Solidification Sensing Techniques for Injection Molding
Authors: Jiang Mingwen , Thomas Charles L. , Peterson Rob , Bur Anthony J.
Published: March 2022

An ultrasonic transducer installed facing a pressure transducer in the cavity of a rectangular plaque injection mold shows new sensitivities to the solidification of the polymer in the mold. Features of the amplitude variation of a pulse transmitted twice through the polymer are sensitive to the flow rate and solidification state of the polymer at the transducer face. The signal from a normal incidence shear transducer gives a direct indication of solidification. A model was developed to describe the changing amplitude of a pulse transmitted through the polymer. The model illustrates how temperature, pressure, flow rate, and signal frequency affect the measured echo amplitude.
Modeling Race Tracking Effects in Liquid Composite Molding
Authors: Chan Albert W. , Morgan Roger J.
Published: March 2022

Fabrication of polymer composite components for automotive applications typically involve the injection of a reactive polymer resin into a preform placed in a closed mold. This process, generally referred to as liquid composite molding, offers the opportunity for part consolidation and fabrication of large, complex shaped parts in a single molding step. A problem often encountered in the molding of composite components is the channeling flow (or race tracking) of resin along the periphery of the preform. This race tracking flow occurs as a result of a small clearance between the preform periphery and the mold. The resistance to flow in the peripheral clearance is much smaller than that in the bulk preform; hence, resin preferentially flows through this region.

This paper will present an integrated approach to modeling flow (both in the preform and along the periphery) in the mold cavity. The objective is to model race tracking as part of the overall flow problem. The solution essentially involves the interfacing of the two flow domains along the preform periphery. An integrated approach will not only lead to more accurate model predictions, but will also lead to improved computational efficiency. Example case studies will be presented to illustrate the importance of including race tracking in modeling liquid composite molding operations.
Green’s Function Approach to the Analysis of Functionally Graded Materials
Authors: Nomura Seiichi , Sheahen Donna M.
Published: March 2022

A micromechanical approach is adopted to systematically obtain numerical Green’s function for functionally graded materials (FGMs) which enables expressing thermomechanical fields in FGMs as a convolution type of integrals between the Green’s function and a source function. The numerical Green’s function is sought by the eigenfunction expansion method. Computer algebra systems are essential to derive admissible functions that satisfy the given boundary conditions and manipulation of the algebra involved. Using the Green’s function for FGMs, physical fields in FGMs can be expressed semi-analytically while retaining all the relevant parameters. In addition, any change in boundary conditions such as temperature can be readily reflected without incurring the entire recalculation.
Crack Tip Stress Fields and Creep Crack Growth of Interface Cracks in Functionally Graded/Layered Materials
Authors: Biner S. B.
Published: March 2022

In this study, the growth behavior of interface cracks in bimaterials and in graded/layered materials resulting from the creep cavitation was studied. The growth model includes the effects of material deposition resulting from the growth of creep cavities on the crack tip stress fields. The results indicate that in graded/layered materials under identical applied loading, the location of the interface crack strongly influence the amplitude of the stress field (C*) at steady-state. Due to large variation in the distribution of the stresses ahead of the interface cracks at creep regime, depending upon the crack location, the creep crack growth rates will be significantly different from each other under identical loading for a given graded/layered material.
Plasma Spraying of Functionally Graded NiCoCrAlY/Yttria Stabilized ZrO2 Coatings Using Composite Powders
Authors: Khor K. A. , Gu Y. W. , Dong Z. L. , Srivatsan T. S.
Published: March 2022

Pre-alloyed, plasma spheroidized powders were used as feedstock in the plasma spraying of functionally graded ZrO2/NiCoCrAlY coatings. The advantage of using pre-alloyed powders was to ensure chemical homogeneity and promote uniform density along the graded layers, and these pre-alloyed powders could be successfully used to prepare the different inter-layers of functionally graded coatings. The microstructure, density and microhardness changed gradiently in the ZrO2/NiCoCrAlY coatings. The bond strength of ZrO2/NiCoCrAlY coatings with different graded layers was measured. Results showed that for as-sprayed coatings with the same thickness, the bond strength increased with the number of graded layers. The bond strength of the coatings with five graded layers was about twice as high as that of the duplex coatings because of the significant reduction of the residual stress in the coatings. Experimental results also showed that the bond strength of as-sprayed coating increased significantly after hot isostatic press (HIP) and vacuum heat treatments, and the reason can be attributed to the densification of the microstructure, the decrease of defects in the coatings, inter-diffusion between layers and further reduction in the residual thermal stress.
Damage Development, Toughening, and the Design and Performance of Ceramic Composite Systems
Authors: Kerans Ronald J.
Published: March 2022

The remarkable toughening effect resulting from proper combination of three brittle phases in the form of fiber, coating and matrix is a consequence of a particular sequence in the development of damage It is understood that there are both beneficial and detrimental ways for damage to develop; hence, successful design of composites requires the management of the progression of such damage. The conception and design of alternative crack deflecting coating systems is greatly facilitated by, if not dependent upon, understanding such details. In addition, the same damage that is beneficial to toughness in one type of loading may be detrimental to other properties. The development of sufficient understanding of the benefits and penalties is necessary to design such materials with well chosen engineering compromises.
Self-Healing Composites Using Embedded Microspheres
Authors: Jung D. , Hegeman A. , Sottos N. R. , Geubelle P. H. , White S. R.
Published: March 2022

A self-repairing polyester matrix composite material is described which utilizes embedded polyoxymethylene urea (PMU) microspheres to store a crack filling agent to be released into the crack and rebond the crack faces. The developed repair mechanism uses naturally occurring functional sites in the polyester matrix network to trigger the repair action. The repair agent is mostly composed of styrene monomers and high molecular weight polystyrene. Microscopic observations of the microsphere/crack interaction are presented. Of particular interest is the process with which the microspheres break and release their content when encountered by a crack. The effects of the microspheres on the stiffness and toughness of the polyester resin are also studied. Using standard tensile samples, the composite elastic modulus has been found to decrease with the volume fraction of microspheres, while the fracture toughness of tapered double cantilever beam (TDCB) specimens is shown to reach a maximum value at approximately 10% volume fraction. Examinations of the fracture surfaces show tails extending from the microspheres, indicating crack pinning and crack front bowing as the primary toughening mechanisms. An enhanced level of adhesion between the microsphere and matrix has been found to decrease the composite fracture toughness and increase the incidence of sphere breakage on the fracture surface.
Effect of Sandblasting on Adhesion Strength of Diamond Coatings
Authors: Zhang Bi , Zhou Lanying
Published: March 2022

Premature failure of a diamond coated tool often results from a poor adhesion of the coating to and shortens the lifetime of the tool. This study presents the results of increasing the adhesion strength of diamond coatings on cutting tool inserts by pretreating the inserts with sandblasting technique to obtain a desirable surface morphology of the inserts. A geometric model representing the ideal surface morphology is established to enhance the nucleation density and adhesion strength of diamond coatings. Diamond coating experiment is conducted on the substrates of four different sample groups. Indentation and wear tests are performed on diamond coated inserts to evaluate the effect of sandblasting on the adhesion strength of the coatings. A theoretical analysis is provided on the formation and growth of atom clusters in terms of the contact angle and the thermodynamic barrier of a substrate to predict diamond nucleation. The theoretical prediction has a good agreement with the experimental results obtained in this study and by Dennig et al. [1, 2].
Process Modeling and Interfacial Behavior in the VSPA Package
Authors: Harries Richard , Sitaraman Suresh
Published: March 2022

Interfacial delamination is a cause for concern in electronic packages consisting of several dissimilar material systems. Even if current designs do not experience delamination as a failure mode, it is necessary to understand the effect of material and geometry properties on interfacial stresses to lower the potential of interfacial delamination in future designs. The objectives of this work are to model current and future versions of a novel peripheral array package and examine the possibilities for interfacial delamination.

This paper employs 2D plane-strain parametric finite-element models to study interfacial stresses. Element birth and death features have been used to simulate the complete manufacturing process of the package. The effect of encapsulant material properties and die-attach properties on interfacial stresses is discussed. These results will serve to aid in the selection of appropriate die attach and encapsulant materials for enhanced future designs. Delamination is also studied from a fracture mechanics perspective. A separate 2D model is constructed with a crack inserted between the encapsulation/backplate interface. Principal stress vectors are plotted along the interface to qualitatively determine the potential for crack extension. Crack growth is simulated by incrementally extending the length of the crack in the mesh.
Failure Mechanism of Metallization Layer of a Multichip Module Substrate
Authors: Rastani Mansur
Published: March 2022

The work described in this paper concentrates primarily on the multichip module type D. In MCM-D technologies, the interlayer vias have been identified as potential failure sites due to fatigue caused by temperature cycling and the CTE mismatch between the dielectric and metal layers. The selected model for this study uses an MCM-D structure, implementing aluminum-silicon (Al-Si) metallization layers separated by a silicon dioxide (SiO2) interlayer dielectric.

A 3-D finite element analysis has performed on the model to determine the effect of accelerated temperature cycling and thermal shock. The resulting non-linear, elasto-plastic stress-strain response was obtained, under the von-Mises yield criterion, using PATRAN code. The fatigue life of the via was then estimated and compared with the experimental results.
Thermal Stresses in a Layer due to a Train of Laser Pulses
Authors: Hetnarski Richard B. , Hector Louis G. , Kim Woo-Seung
Published: March 2022

A solution of a thermoelastic problem dealing with the effects of the radiation generated by a repetitively pulsing laser directed toward a thin thermoelastic layer bonded to an inert semi-space is presented. Both the thermoelastic potential method and the Love stress function are employed. The temporal variation of each pulse is modeled mathematically as a function with three constants, while the radial intensity distribution of each pulse is taken as a Gaussian distribution. Results are presented in the form of graphs.
Singular Solutions of Multi-Material Wedges Under Thermomechanical Loading
Authors: Yin Wan-Lee , Jane Kuo-chang , Lin Chien-Chang
Published: March 2022

Multi-material wedges associated with free edges, matrix and interface cracks, adhesive joints, skin-stiffener attachments and other types of discontinuities in composite structures generally incur singular stress fields at the vertex of the wedge. Accurate elasticity solutions of the wedge under thermo-mechanical loads may be obtained by combining eigensolutions with appropriate coefficients and a particular solution associate with the loading. When the wedge is under a temperature load, or when the two exterior edges of the wedge are subjected to non-vanishing traction loads, the elasticity solution may differ significantly from the asymptotic solution as given by the dominant singular term. In such cases, a failure criterion in terms of the asymptotic solution or the stress intensity factors may not be appropriate.
Properties of Sandwich Structures With Reinforced Core
Authors: Sun C. T. , Hasebe R. S. , Hua Y.
Published: March 2022

Sandwich panels with a Rohacell core reinforced with composite laminates were constructed. The effective properties of the reinforced core were derived and verified by three point bending tests of a sandwich beam. The equilibrium equations for the sandwich plate with the composite reinforced core were derived. Impact experiment was also conducted by use of a drop tower. Damage modes and levels of damage in sandwich panels containing bare and reinforced Rohacell cores were investigated and compared. Several NDI methods were employed to inspect the damage in the sandwich panel and their merits were compared.
Bending of Curved Sandwich Panels With Transversely Flexible Cores: Closed-Form High-Order Theory
Authors: Frostig Y.
Published: March 2022

The bending behavior of a curved sandwich panel with a transversely flexible core, i.e. “soft” in the out of plane direction, is derived. It is formulated using a rigorous systematic closed-form approach based on variational principles. The effects of the transversely flexible core are incorporated resulting in non-linear patterns, denoted also as high-order effects, for the inplane and the transverse deformations through the height of the core. The governing equations along with the associated boundary and continuity conditions for a general type of sandwich panels, i.e. unidentical skins, composite laminated or metallic and a “soft” core are derived. General type of boundary conditions, including spring conditions, as well as different conditions at the upper and the lower skins at the same section are implemented and the effects of “stiff edge inserts, denoted as global boundary conditions, along with the induced localized effects are considered. Localized effects at support regions with or without edge stiffeners, with movable and immovable supports, and in the vicinity of concentrated loads are studied. The effects are described in terms of the internal resultants and displacements of each skin, peeling (transversely normal) stresses and shear stresses at the skin-core interfaces, and stress and displacement fields in the core through its height. Numerical results of a typical curved panel used in a test set-up and comparisons with experimental data are presented. A comparison, that is in very good agreement, between the analytical results and the experimental ones is conducted. The effects of a global boundary conditions, such as a “stiff” edge beam, and similar local boundary conditions on the localized effects are presented and discussed. The stress concentration involved in case of a concentrated load especially in its near vicinity is described.
A Refined Theory for the Analysis of Sandwich Beams and its Application to Local and Global Stability Investigations
Authors: Meyer-Piening Hans-R.
Published: March 2022

An analytical method is proposed to study the local and global instability of three-layered assymmetric sandwich beams with arbitrary relative face thicknesses ranging from very thin faces to a vanishing core height. The method accounts for extensional orthotropy, shear elasticity, Poisson’s ratio effects and lateral compressibility within each layer. As each layer is modelled in an identical manner and all stress and displacement related interface conditions are satisfied, there is no limitation with regard to geometry relations, except for numerical instabilities or convergence criteria. The displacement functions are represented by Fourier series which leads to a set of 12 linear equations for each value of the harmonic m The eigenfunction associated with the minimum load will then represent the (local or global) design buckling (or wrinkling) mode.

The results can be compared with buckling formulas like that proposed by Hoff [1] or the formula related to a beam on elastic foundation [2], as well as the approximation for Euler columns accounting for shear elasticity. It becomes evident that modifications to the aproximate methods may be suitable for some geometric relations and material properties.
Formation of Large Disturbances in Separated Fluid-Fluid Flows
Authors: McCready M. J. , Uphold D. D.
Published: March 2022

If flow regime transitions to slugging or annular flow occur from an initially stratified state, growth of long wavelength waves to large amplitude has been implicated by previous researchers (e. g., Barnea, 1991) as an important mechanism. Thus it is not surprising that various linear stability theories have been used to predict when such waves will grow and therefore the onset of such transitions. However there is much evidence that longwave disturbances do not grow directly from infinitesimal amplitude by linear processes (e.g., Fan et al., 1993) and thus the use of linear stability theory to predict flow regime transitions may not be reliable. This paper compares experiments into wave formation with predictions of linear theory. It is seen that linear theory provides only part of the story of wave formation. Waves must be linearly unstable to grow to significant amplitude, but observed subharmonic and low mode formation or even saturation of the linearly growing peak, are not predicted by linear theory. Weakly nonlinear theories can predict wave mode interactions and stabilization, but experiments with paddle-induced waves suggest that there is no dramatic destabilization for wavenumbers below the peak as suggested from the positive value of the Landau coefficient in this range.
Computational Flow Simulation and Interfacial Shear for Annular/Stratified Condensing Flows
Authors: Yu G. , Narain A.
Published: March 2022

External and internal flows of pure vapor experiencing film condensation on an appropriately cooled wall are computationally simulated. The stratified/annular flow regimes considered here are such that the vapor flow is either laminar or turbulent while the liquid condensate flow is always laminar. For negligible droplet entrainment into the vapor phase, both smooth and wavy interface situations are considered. A full two dimensional numerical solution strategy is presented. This strategy is then implemented for smooth interface laminar/laminar flows. The simulations for the classical problem of film condensation on a tilted (horizontal to vertical) plate are in very good agreement with established classical solutions. For wavy interface turbulent/laminar flows, only a one dimensional approach is implemented. This approach employs suitable semi-empirical interfacial shear models for wavy flows which yield predictions in reasonable agreement with experiments.
Two-Phase Flow Regime Maps for Straight and Coiled Spirally Fluted Tubes
Authors: Ewing Mark E. , Priedeman Douglas K. , Wynn Bruce E. , Bohon Richard N. , Christensen Richard N.
Published: March 2022

Two-phase flow patterns in spirally fluted tubes were investigated through visual observation. Both straight (horizontal) and coiled fluted tubes were studied using adiabatic flow of air and water in transparent castings. The same types of patterns which occur in smooth tubes (i.e. annular, stratified, wave, plug, slug, and bubble) were observed in both the straight and coiled fluted tubes. For these tubes, experimental data support the use of a flow regime map of the type proposed by Breber et al. (1980), which was developed for condensation in smooth tubes. Based on results of the testing of two straight and three coiled fluted tubes, a generalized, modified Breber-style map is proposed for the prediction of flow regimes in spirally fluted tubes.
Effect of Apparent Solid’s Viscosity on the Hydrodynamics of Fluidized Beds
Authors: Gera Dinesh , Tsuji Yutaka
Published: March 2022

The dynamics of bubbles, the flow of gas and solids through the emulsion phase, and interchange of flowing gas between these two phases play a dominant role in heat transfer, mass transfer and solid-catalyzed chemical reactions. The pattern of gas flow through the bubbles has an effect on the degree of gas-solids contacting and under certain conditions a high degree of by-passing can occur. This research is aimed at understanding the aspects of bed hydrodynamics, especially to investigate the gas flow patterns inside the bubbles and solids’ mixing in a fluidized bed.
Numerical Study of Two-Phase Flow Field in a Simplified Swirl Cup Combustor
Authors: Park Tae W. , Roquemore William M. , Katta Viswanath R. , Aggarwal Suresh K.
Published: March 2022

A numerical study was performed to investigate the two-phase flow field in a geometrically simplified swirl cup in a gas turbine combustor. The actual combustor has a hybrid-atomization feature with pressure atomization from the nozzle and airblast reatomization for the liquid film at the tip of venturi wall. The amount of fuel formed in venturi tube could play an important role in characterizing the flow field of this combustor. The present study first investigates the effects of the swirl mode and temperature of the primary and secondary air on the gas-phase flow field and then the effect of droplet injection characteristics in terms of velocity and location on the droplet transport and vaporization behavior. The detailed plots of droplet trajectory are used to identify the size ranges of the droplets which can form a liquid film by their impaction on the venturi tube wall. In general, the results indicate that the droplet injection characteristics have the dominant effect on the cut-off droplet diameter for droplet impaction on the venturi wall.
Medical Atomization Design for Inhalation Therapy
Authors: Corcoran T. , Mansour A. , Chigier N.
Published: March 2022

The medical community has lately shown increased interest in drug administration via the internal surfaces of the lung. Administration of medication to the lungs is typically performed using either an aerosol or a spray, that is inhaled by the patient. Spray droplet size distribution is a primary determinant of whether medication will deposit effectively within the lungs. Spray liquid flow rates will determine required treatment time. Examination of three typical atomizer (nebulizer) designs used to generate inhalation sprays is presented. The separate stages in the design of these nebulizers include entrainment (jet pump), atomization, and conveyance stages. Mass flow rate of liquid in the sprays delivered from all examined designs was at least two orders of magnitude less than the mass flow rates of liquid pumped through the atomization stages. This indicated that liquid typically circulated through the atomization stages many times before being completely administered. Visualization was performed on the atomization stages showing less than ideal mechanisms for break up. Final outlet droplet cumulative number distributions obtained via Phase Doppler Particle Analyzer (PDPA) demonstrate that approximately 80% of the droplets generated by each design are within the range of sizes generally considered desirable for inhaled administration. (1–5 μm).
Recent Developments in Spray Technology: Agricultural Applications
Authors: Hitchman Alec Keith
Published: March 2022

The use of high efficiency water spray systems for outdoor climate control has become more popular of late; the 1996 Olympic Games in Atlanta being a well-publicized recent example. The increase in popularity has initiated the consideration of these inexpensive systems for use in other applications as well. The application of these water spray systems inside buildings has as their primary function the delivery of humid air to large indoor areas at a minimum of cost. Such water spray systems have proven their effectiveness in the bulk storage of both potatoes and wine. If used as the sole means of humidity control, or in conjunction with more traditional means of environment management, high efficiency water spray systems can reduce the product losses associated with the long term storage of potatoes and wine.
Effect of Initial Conditions on Turbulent Pipe Mixing
Authors: Hansen Lisa J. , Klewicki Joseph C.
Published: March 2022

Despite its use in numerous industrial applications, the specific mechanisms governing mixing in pipe flow are not fully understood. Recent experiments by Guilkey et al. (1997) indicate that simple changes in the geometry of the inlet at which the scalar is introduced can lead to substantial differences in the rate of scalar variance decay downstream. In an effort to better understand this phenomenon, the effects of two different initial conditions on mixing in turbulent pipe flow were investigated. The present results are compared with three earlier turbulent mixing experiments. Overall, the results of these experiments demonstrate that the method used to introduce two constituents to be mixed in pipe flow can profoundly affect the downstream mixing rate.
Models of Fracture-Matrix Interactions During Multiphase Heat and Mass Flow in Unsaturated Fractured Porous Media
Authors: Ho Clifford K.
Published: March 2022

Models of liquid, gas, and heat flow between fractures and matrix elements in dual-permeability models are presented in this paper. Heterogeneities necessitate scaling the liquid geometric conductance between fracture and matrix elements to account for a reduction in the wetted area available for liquid flow while maintaining reasonable conductances for gas and heat flows. The models in this study consisted of conductance multipliers that were either constant, a function of upstream saturation, or a function of upstream relative permeability. Numerical analyses were performed using TOUGH2 to determine hydrologic and thermal parameters that are sensitive to the various fracture-matrix models. Results showed that for thermohydrologic simulations of the potential repository at Yucca Mountain, the ambient hydrology (e.g., matrix liquid saturations and fracture liquid flow) was strongly dependent on the fracture-matrix interaction model. The thermal response of the system was less sensitive to the different fracture-matrix models in the dual-permeability systems.
NAPL Dissolution in Saturated Porous Media: Model Experiments and Pore-Scale Interpretation
Authors: Radilla Giovanni , Quintard Michel , Bertin Henri
Published: March 2022

Predicting the rate of mass transfer in liquid-liquid systems is of crucial importance for the study of ground water contamination by hydrocarbons. Proposed correlations assume that mass transfer is strongly related to the interfacial area between the two immiscible fluids. In this paper, we present results of column experiments on the dissolution of pure hydrocarbons as well as a 1D model. Experiments were conducted for small values of the Peclet number (Pe < 1). The model involves a classical convection-dispersion-mass transfer equation. Mass transfer coefficient was calculated for various periodical simplified porous systems on the basis of theoretical results from the volume averaging theory. Results show that the transport model simulates correctly the shape and dynamics of the dissolution front. It is shown that an average value of the distance between two NAPL blobs can be a key parameter for the estimation of the mass transfer coefficient rather than the interfacial area.
Numerical Analysis of Discrete Phase Influence on Gas Flow in a Two-Phase Turbulent Free Jet
Authors: Stakić Milan B. , Živković Goran S. , Sijerčić Miroslav A.
Published: March 2022

The influence of discrete phase (particles and/or droplets) on gas flow in a two-phase turbulent flow is of particular importance in many fields of chemical engineering. Results of numerical simulation of the two-phase turbulent flow inside a long vertical pipe as well as in a two-phase turbulent free jet formed at the pipe outlet, compared to the previously obtained experimental results, are the scope of this paper. Experimental investigation of gas and particle interaction in a two-phase turbulent free jet formed from a long vertical injection pipe were presented earlier [1].

In all numerical calculations, as well as in the experiments performed, air has been used as a gas phase (mass flow rate ma = 1.25–4.0 g/s), and sand particles of two different size ranges (0.25–0.3 mm, and 0.8–1.0 mm) as a discrete phase, with particles to gas mass flow ratio from 0.72 to 4.08. The cases of vertical downward two-phase flow inside the pipe as well as in a turbulent free jet was studied. Gas-particle interaction has been analyzed on the basis of gas velocity obtained in the particle laden two-phase flow and the clean gas flow at various distances along both the injection pipe and jet axis and radius.

Mathematical model for the continuous phase was based on the models developed for a single phase flows, with corrections due to presence of particles. The simulation model treats the flow as two-phase mixture with Eulerian description of the gas phase and Lagrangian description of the particles movements. In order to close the system of time-averaged equations, as the most reliable, k-ε turbulent model has been used. Phase coupling was achieved on the basis of so-called PSI-CELL concept. Results obtained on the basis of numerical simulation have shown a good agreement with experimental results.
Structural Integrity of Optical Fibers in Connectors
Authors: King Wilton W. , LeFevre Bruce G. , Hardee A. Guy
Published: March 2022

Fracture of fiber in a connector occurs when induced tensile stress exceeds local strength, usually governed by a stripping-related flaw. Stress analyses based upon elementary models from structural mechanics are presented to explore the significance of differential thermal expansion of ferrule and backbone. Results of finite-element analyses are used to suggest an epoxy-driven mechanism for fractures observed after thermal cycling. Implications for reliability are discussed.
Modeling and Stability Analysis of Polymer Sheet Extrusion
Authors: Nizami Javeed , Batur Celal
Published: March 2022

Dimensional stability of thin extruded sheets is analyzed as a function of draw ratio. It is assumed that the sheet keeps its rectangular cross section between the flat die and the chill roll and the flow is Newtonian. Through the analysis of linearized equations it is shown that the system is linearly unstable beyond a critical draw ratio similar to the one observed in experimental studies. The nonlinear model is then analyzed using singular perturbation analysis and simulations to confirm the existence of a stable limit cycle.
Natural Convection Heat Transfer to Ice Spheres Melting in Air
Authors: Janna William S. , Jakubowski Gerald S.
Published: March 2022

Three different diameter ice spheres were formed and allowed to melt in air. Each sphere was suspended by a string from a cantilevered beam, which had strain gages attached. A four active element Wheatstone Bridge was used to measure the output of the strain gages. The output signal was calibrated to measure weight of the sphere at any time during the phase change process. Data on weight versus time were thus obtained using a recorder, and used to calculate values of Nusselt and Rayleigh numbers at various instants in time. The geometry of each sphere changed during the melting process as did surface area and volume. A satisfactory determination of characteristic length was proposed which yielded excellent results. An equation relating Nusselt number to Rayleigh number was derived with a correlation coefficient of 0.975. Rayleigh numbers ranged 1.0 × 104 to 1.2 × 107, while Nusselt number ranged from 4 to 10.2. It was found that the Nusselt number could be predicted with

Nu = 1.45 Ra0.126
Influence of Flow Regime, Heat Flux, and Mass Flux on Electrohydrodynamically Enhanced Convective Boiling
Authors: Bryan James E. , Seyed-Yagoobi Jamal
Published: March 2022

The influence of quality, flow regime, heat flux, and mass flux on the EHD enhancement of convective boiling of R-134a in a horizontal smooth tube was fundamentally investigated. The EHD forces generated significant enhancements in the heat transfer coefficient, but the enhancements were highly dependent on the quality, flow regime, heat flux, and mass flux. The experimental data provided evidence that an optimum EHD enhancement exists for a given set of these variables for a specific electrode design. However, experimental data also provided evidence that the EHD forces can drastically reduce the rate of heat transfer at certain conditions.
Chaos Analysis and Contact Dynamics of Heat Transfer in a Gas-Fluidized Bed
Authors: Pence Deborah V. , Beasley Donald E.
Published: March 2022

The present study examines fundamental aspects of the heat transfer and hydrodynamics in pulse-stabilized fluidization from a chaos perspective. The pulsed atmospheric fluidized bed combustor (PAFBC), a pulsed combustor coupled with an atmospheric bubbling fluidized bed, has technical advantages in energy efficiency and emissions. The flow in the tailpipe of the pulsed combustor was modeled in a laboratory scale fluidized bed by superimposing an oscillating component on a steady mean component. Time-varying local heat transfer was measured from a heated horizontal cylinder to the cold bed.

Contact dynamics and spectral analysis of instantaneous heat flux signals clearly indicate that the bed hydrodynamics were significantly altered by the opposing secondary flow. The purpose of the present paper is to quantify these changes using chaos analysis and fractal measures. Specifically, the effect of the secondary flow on the chaotic dynamics and fractal characteristics of heat transfer were assessed by evaluating the Kolmogorov entropy and Hurst exponents, respectively, at several positions around the cylinder. The relation between chaos measures and contact dynamics was examined.
Scanning Laser Thermoelectric Microscope for Thin Film Thermophysical Property Measurement
Authors: Tasciuc Theodorian Borca , Chen Gang
Published: March 2022

This work presents a new thermal diffusivity measurement technique for thin films as well as bulk materials. In this technique, a modulated laser beam is focused through a transparent substrate onto the film-substrate interface. The generated thermal wave is detected using a fast responding thermocouple formed between the sample surface and the tip of a sharp probe. By scanning the laser beam around the thermocouple, the amplitude and phase distributions of the thermal wave are obtained with micrometer resolution. Thermal diffusivity of the film is determined by fitting the obtained phase signal with a three dimensional heat conduction model. Experimental results are presented for a 150 nm gold film evaporated on a glass substrate.
Optical Properties in the Visible of Soot Emitted From Turbulent Pool Fires
Authors: Krishnan S. S. , Lin K.-C. , Wu J.-S. , Faeth G. M.
Published: March 2022

The optical properties of soot at visible wavelengths (350–800 nm) were measured for soot emitted from liquid-fueled (benzene, toluene, cyclohexane and n-heptane) buoyant turbulent pool fires burning in air in the long residence time regime where soot properties are independent of position in the overfire region and residence time. The measurements were analyzed to find soot fractal dimensions, refractive index functions, refractive indices and dimensionless extinction coefficients, assuming Rayleigh-Debye-Gans scattering for populations of polydisperse mass fractal aggregates (RDG-PFA theory). The measurements yielded results that support recent findings for soot emitted from similar gas-fueled flames (acetylene, propylene, ethylene and propane): RDG-PFA theory is effective for estimating the optical properties of soot for the present range of conditions, soot fractal dimensions are independent of the fuel type and have a mean value of 1.79, soot refractive index properties are independent of the fuel type and are in reasonably good agreement with the often criticized measurements of Dalzell and Sarofim (1969), and dimensionless extinction coefficients are relatively independent of wavelength and fuel type over the present range of conditions and yield a mean value of 5.7, averaged over findings for both gaseous and liquid fuels.
Demonstration of a Continuous Flame Process for Producing Nanosized Silica Particles
Authors: Danczyk Stephen A. , Wu Jianfan , Wooldridge Margaret S.
Published: March 2022

The current work describes a novel laboratory-scale flame process for gas-phase combustion synthesis of nanosized silica (SiO2) particles. Hydrogen (H2) and oxygen (O2) are pre-mixed with argon (Ar) in a flat flame burner to produce a primary flame. Silane (SiH4), dilute in argon, is injected through the center of the cylindrical burner. The SiH4/Ar mixture produces a secondary flame and SiO2 particles are formed in the plume region of this flame. By changing reactant stoichiometries, the particle size distribution and morphology are altered. In an effort to identify the relevant processes controlling particle growth, temperature profiles, digital images and emission spectra are used to characterize the dual flame system. Particle morphology is examined by sampling directly from the secondary flame onto transmission electron microscope (TEM) grids.
Extinguishment Characteristics of Buoyant Liquid and Gas Diffusion Flames With Physical and Chemical Agents
Authors: Babb Michael , Gollahalli Subramanyam R. , Sliepcevich Cedomir M.
Published: March 2022

A comparative study of the extinguishment characteristics of liquid heptane and gaseous propane diffusion flames in a co-flowing stream of air in an apparatus simulating the NFPA standard 2001-cup burner apparatus is presented. A physical agent, carbon dioxide, and a chemical agent Halon 1301 were used as flame extinguishing agents. Results indicate that when the agents were premixed with air, the concentrations of CO2 and Halon 1301 at extinction of propane flames were approximately the same as the corresponding values in heptane flames. Results are substantiated with the measurements of in-flame temperature profiles and exhaust gas composition/temperature measurements in the flames.
Liftoff and Blow Off Characteristics of Laminar Non-Premixed Planar Jets
Authors: Tillman S. T. , Annamalai K. , Caton J. A.
Published: March 2022

The NOx emission from gas burners is essentially due to thermal NOx occuring at temperatures above 1500 K. Lean combustion reduces the flame temperature and hence thermal NOx production. However, operation at leaner mixtures creates problems in flame stability. It is well established that the closer the standoff distance of the flame to the burner, the more stable the flame. In the current paper, the liftoff and blow off characteristics of two dimensional planar jets (width/length ≪ 1) have been analyzed. The equations of mass, momentum, energy, and species have been transformed from compressible to incompressible form, then normalized, and converted into ordinary differential equations using an appropriate similarity variable, η. Explicit mixing solutions are obtained for a range of Schmidt numbers. The mixing solutions for single jets are used to determine flame standoff distance by matching the local axial velocity on the stoichiometric contour with the laminar burning velocity. The blow off velocity is then deduced. It has been verified, but not reported here, that the results are qualitatively similar for circular jets. It is envisioned that this model will be extrapolated to include multiple planar/cluster jets and thus allow the effect of flame interaction on liftoff height and blow off velocity to be studied.
Fractal Properties of Smoke Produced From Smoldering and Flaming Fires
Authors: Litton Charles D.
Published: March 2022

This report presents the initial results of experiments to determine the fractal-like properties of aggregate smoke particles produced from both smoldering and flaming fires. In the experiments, angular intensity data were acquired in order to determine the fractal dimension, Df, radius of gyration, Rg, and albedo, ω, for smoke produced from smoldering coal and wood, flaming coal and wood, a pool fire of No. 2 diesel fuel, and the smoke produced at the exhaust of a diesel engine. This data was combined with simultaneous measurements of current reduction in a calibrated ionization chamber detector and independent measurements of specific extinction for the different types of smoke in order to determine the primary particle diameters for the aggregate smoke particles. Both types of smoldering fires yielded similar fractal properties, and the three types of flaming fires also possessed similar fractal properties, but significant differences exist between the smoldering and flaming properties. The characteristics of smoke from the diesel engine were similar to those of smoke from the flaming fires, yet distinct Smoldering aggregates appear to be composed of a small number (≃ 100) of large primary particles (dp ≃ 0.07 μm), while flaming aggregates are composed of a large number (≃ 1000) of small primary particles (dp ≃ 0.025–0.035 μm). The average ω’s of smoldering aggregates are a factor of 2 to 3 larger than those of the flaming aggregates. In addition, further analysis indicates that the complex component of the index of refraction, i.e., the extinction coefficient, k, is a factor of 2 to 3 lower for the smoldering aggregates compared to the flaming aggregates. The implications of these results are also discussed.
Active Control of Thermoacoustic Instability Using a Model-Based Approach
Authors: Hathout J. P. , Annaswamy A. M. , Fleifil M. , Ghonlem A. F.
Published: March 2022

Recently, active control has been pursued vigorously for combating thermoacoustic instabilities in the combustion process. While many of the reported experiments, with controllers that include filter components determined by trial and error, have demonstrated that the dominant thermoacoustic instability can be suppressed, often the response contains secondary peaks at other frequencies which were not excited in the uncontrolled combustor. In this paper, a physical systematic model-based design of an active controller for suppressing thermoacoustic instability which overcomes many of the drawbacks of the experimental controllers is presented. This model takes into account laminar flame kinematics and linear acoustic dynamics with coupling between the acoustic modes and actuation using an end-mounted loudspeaker. With this model, a model-based controller which results in a distinctly improved performance over the experimental controllers is designed. This controller is based on an optimization strategy and leads to significantly faster settling time of the pressure oscillations, exhibits no secondary peaks, and uses smaller control effort.
Clean Coal Slurries, Their Processing for Burning
Authors: Barsky L. A. , Timnat Y. M.
Published: March 2022

Clean coal slurry is a possible alternative to liquid fuel. The mine problems in use of coal in engines (ash content and particles size) are solved via a novel slurry processing technique consisting in superfine grinding of the coal, selective separation of the coal particles and other inorganic ingredients, and finally combustion of the fine fraction coal in slurry droplets. An experimental rig for column flotation and selective flocculation has been built. A vibroinertial grinding facility reduces the coal particles to 40 microns or less. After addition of appropriate amounts of a suitable oil and water an emulsion flotation step produces coal-water slurry with ash content under 4%, which in turn coal under 20 microns in size with ash content 0.4% by film-flotation.
Turbulent Natural Convection in Enclosures: 1992 Workshop Revisited
Authors: Londino Joseph M. , Yang K. T.
Published: March 2022

The objective of this paper is to provide an improved finite-volume numerical method for turbulent natural convection in a vertical differentially-heated square enclosure for the benchmark problem in the 1992 Workshop (Eurotherm Seminar n° 22). The specific purpose here is to identify difficulties associated with the use of the QUICK scheme in solving all the governing equations, including those for k and ∈, and to demonstrate that our algorithm provides accurate calculations without the observed difficulties. A computational logic has been developed to insure the presence of positive source terms, resulting in very stable results with the use of the QUICK scheme. The present results at Ra = 5(10)10 are directly compared with those from the 1992 Workshop contributors.
Mechanisms of Heat Transfer Enhancement in a Turbulent Boundary Layer Downstream of a Cylinder-Wall Junction
Authors: Wroblewski Donald E. , Xie Qi
Published: March 2022

The wall heat transfer enhancement behind a circular cylinder-wall junction was investigated experimentally for Reynolds numbers ranging from ReD = 21,000 to 54,000 for locations up to 12 diameters downstream of the cylinder leading edge. Surface heat transfer was studied using a fully-heated surface downstream of the cylinder to provide traditional heat transfer coefficients, and thin-film surface sensors flush-mounted on an unheated surface to provide adiabatic heat transfer coefficients. Flow field transport measurements were obtained with a triple-wire Reynolds heat flux probe. The enhancement could be attributed to two effects: (1) a local fluid dynamic effect attributed to increased eddy diffusivity and subsequent increased turbulent transport and (2) an upstream heating effect, caused by reduced wall temperatures in the region directly behind the obstacle, and their effect on the subsequent redevelopment of the boundary layer downstream. The adiabatic heat transfer coefficients obtained from the surface sensors provided misleading results, because of the breakdown in the analogy between heat and momentum transport.