bluuebunny/crossref_metadata_2025 huggingface dataset:
Stress Dependency of the Thermoelastic and Piezoelectric Coefficients
Authors: Bert Charles W. , Birman Victor
Published: March 2022

An analysis based on fundamental mechanics and thermodynamics is presented for a solid in which the elastic and piezoelectric coefficients are temperature dependent. It is proven that as a consequence of the temperature dependency, the thermal expansion and piezoelectric coefficients must be stress dependent.
Dynamics for Large Deflections of a Sandwich Plate With Thin Piezoelectric Face Layers
Authors: Yu Y. Y.
Published: March 2022

The frequency range for structural dynamics and vibration is first discussed. Nonlinear dynamics for large deflections of a sandwich plate is then reviewed. Finally, large deflections of a sandwich plate with two thin piezoelectric PVDF face layers are treated, and governing equations of motion are derived.
Analysis of Curved Sandwich Panels With Cutouts Subjected to Combined Temperature Gradient and Mechanical Loads
Authors: Noor Ahmed K. , Peters Jeanne M.
Published: March 2022

The results of a detailed study of the effect of the cutout on the response of curved sandwich panels are presented. The panels have honeycomb core composite face sheets. The loading consists of a temperature gradient through-the-thickness combined with pressure loading and edge shortening or edge shear. The analysis is based on a first-order shear-deformation Sanders-Budiansky type theory with the effects of large displacements, moderate rotations, transverse shear deformation and laminated anisotropic material behavior included. A mixed formulation is used with the fundamental unknowns consisting of the generalized displacements and the stress resultants of the panel. The nonlinear displacements, strain energy, principal strains, transverse shear stresses, transverse shear strain energy density, and their hierarchical sensitivity coefficients are evaluated. The hierarchical sensitivity coefficients measure the sensitivity of the nonlinear response to variations in the panel parameters, the effective properties of the face sheet layers and the core, and the micromechanical parameters. Numerical results are presented for cylindrical sandwich panels and show the effects of variations in the loading and the size of the cutout on the global and local response quantities and their sensitivity to changes in the various panel, effective layer and micromechanical parameters.
The Application of Sandwich Components in Hybrid Structures
Authors: Starlinger Alois
Published: March 2022

A hybrid design concept for body shells has been developed in order to achieve light and stiff structures for state of the art railway and bus vehicles. It uses longitudinal hollow aluminum extrusions combined with foam core sandwich panels of aluminum face layers. In addition to the reduction of mass, hybrid design helps to save production costs. These savings are based on the simplified assembling technique in a modular concept (via corner bolt systems, viscoelastic adhesives, riveting and laser welding), the integration of insulation (by the foam core), and the outstanding impact behavior. The direct joining of the sandwich composite elements to the aluminum extrusions is, however, one of the most challenging steps when designing a hybrid structure. For this reason the hybrid design concept requires a more sophisticated structural analysis approach. In the case of the composite components reduced shear stiffness of the core and local failure mechanisms have to be taken into account. In order to meet all the structural criteria detailed finite element models and analyses have been derived.

Several examples of railway structures built in the hybrid design are given to show the development steps and the advantages of this new design concept.
Strain Rate Compression Performance for a Linear Core Sandwich Beam, I
Authors: Weissman-Berman Deborah
Published: March 2022

One of the principal manifestations of history dependence in a linear type foam core is rate dependence. This paper details the response in compression to increased strain rate; the test response for a linear core material; the dynamic characteristics of foams; the equation of state for cored sandwich material, including the derivation of the elasto-plastic modulus and the derivation of the dilatational portion of plastic response. Compressive predictive equations are derived and correlated to test data. Finally it is concluded that the damping and modulus of resilience characteristics of the linear core material change within a narrow bandwidth of strain rate which may be a factor in determining the natural frequency of response for linear core sandwich constructions.
Forced Response Analysis of Gas Turbine Rotor Blades Using CFD-Based Aeroelastic Tools
Authors: Kruse Marlin J. , Liu Jong S. , Marenghi Yves G. , Eick Christopher D.
Published: March 2022

Integration of computational fluid dynamics (CFD) and structural dynamics codes is critical to the advancement of turbomachinery designs. This paper describes the successful integration of the CFD code UNSFLO with the structural dynamics code ANSYS® for a case study rotor. To evaluate the software combination, AlliedSignal Engines (AE) intiated a program to compare experimental observations from a set of high-pressure turbine tests to analytical predictions from UNSFLO and ANSYS®. The rotor under investigation exhibited significant blade vibratory response due to pressure wakes from upstream stator vanes. Experimental data, collected on two stator-rotor configurations, indicates dramatic strain reductions when the axial space between the stator and rotor blades is increased. Forced response analyses, which compare favorably to the experimental data, indicate a 90 percent reduction in vibratory strain levels.
Aerodynamic Response of Turbomachinery Blade Rows to Convecting Density Wakes
Authors: Ramer Becky E. , Wijesinghe Sanith , Tan Choon , Covert Eugene E.
Published: March 2022

Convecting density wakes have not been considered as a source of unsteady aerodynamic loading on turbomachinery blade rows. These unsteady loads could influence high cycle fatigue failure of blades and vanes in gas turbine engines. The goals of this study are to understand the temporal evolution of density wakes and to determine key controlling parametric trends on blade loading. Inviscid numerical calculations are conducted to illustrate the basic flowfield in the absence of boundary layer interactions. The profile and scaling of the unsteady loads is given here for two density gradient distributions.
The Role of Threshold Fatigue Crack Growth in Life Prediction of the Alloy Ti-6Al-2Sn-4Zr-6Mo Under High Cycle Fatigue Spectra
Authors: Larsen James M. , Russ Stephan M. , Maxwell David C. , Worth Brian D.
Published: March 2022

Damage tolerance methods are widely used to assure reliability of fracture critical components in advanced gas turbine engines. Although low cycle fatigue often determines component lifetime, high cycle fatigue of airfoils and airfoil attachment regions is a growing concern. Crack-growth-rate behavior tends to dominate life under low cycle fatigue, but crack formation and the threshold crack growth condition, ΔKth, are crucial under high cycle fatigue. In addition to material-dependent effects, key factors controlling fatigue crack growth thresholds in titanium alloys used in turbine engines include effects of load spectra, crack geometry, crack size, and residual stress. The utility of ΔKth as a life prediction criterion is examined under load histories that contain both low and high cycle fatigue. These results are discussed with respect to life management methods used for titanium-alloy fan and compressor components in high performance turbine engines.
Micromechanics Study of Plastic Zone at Crack Tip in Steel Under Cyclic Load
Authors: Wang Qing , Du Ming-Liang , Chiang Fu-Pen
Published: March 2022

A novel experimental micromechanics technique SIEM (Speckle Interferometry with Electron Microscopy) is employed to examine the plastic deformation field at crack tip during fatigue process. A fatigue cracked specimen made of AISI-SAE 1035 carbon steel was tested under a three-point bend load. Both displacement and strain fields were mapped over an area of 50μm by 40μm at the crack tip. Accumulation of the local damage due to fatigue was revealed by showing the evolution of the plastic zone at the crack tip. Crack growth was found in mixed mode at small scale. The variation of plastic crack opening displacement with the number of fatigue cycles in both mode I and mode II were determined. Two mechanism of crack propagation, crack branching and crack-wake ligament bridging, were observed and clearly demonstrated on the deformation map.
Micromechanics of High Cycle Fatigue in Single and Polycrystals
Authors: Lin T. H. , Wong K. , Teng N. J.
Published: March 2022

The micromechanic analysis of a fatigue band in the most favorably oriented crystal at the free surface of a polycrystal is reviewed. The localization of plastic strain in thin slip bands under monotonic loadings and the ratchet mechanism of fatigue bands provided by the stress fields of two closely located parallel thin slices sliding in opposite directions are shown. Each of these two thin slices slides monotonically. The alternate sliding of the two thin slices results in the macroscopic forward and backward plastic strain in cyclic loading.

Single crystals are used in turbine engine parts. The fatigue band analysis of polycrystals is extended to analyze the fatigue band in single crystals. Hysteresis loops of a single crystal under constant stress amplitudes and under constant plastic strain amplitudes are shown. Two sets of these hysteresis loops, one with small initial stress and one with large initial stress, are presented. These calculated hysteresis loops explains the two diagonal sharp corners in each loop to be due to reversals of loadings.
Two-Phase Gas-Liquid Slug Flow in the Transient and Steady States
Authors: Hewitt G. F.
Published: March 2022

A review is presented of recent results obtained at Imperial College, London on two-phase gas-liquid slug flow in horizontal pipes. The survey begins by reviewing work on the mechanism for transition between stratified flow and slug flow. Correlations for slug frequency are then discussed. Next, models for prediction of slug creation and evolution are reviewed; it is shown that slug formation is a complex process, occurring at various distances from the entrance. The application of one-dimensional two-fluid models to the prediction of slug formation and evolution is discussed and their limitations reviewed. Experimental and CFD studies of slug tail and slug front behaviour are then described and Ute inclusion of the results of this work into an overall slug evolution model is discussed. Finally, transients involving slug flow are reviewed and exemplified by a transient in which the gas flow is reduced (a “down-gas” transient). Predictions of such a transient using a commercial two-fluid model code are used to illustrate the difficulties that can be encountered in such predictions.
Snake and Corkscrew Waves in Core-Annular Flow
Authors: Renardy Yuriko Y.
Published: March 2022

Core-annular flow of two fluids in down-flow is examined at the onset of a n = ±1 non-axisymmetric instability. This leads to a pattern selection problem; the bifurcating solutions are traveling waves and standing waves. The former travel in the azimuthal direction as well as the axial direction and would be observed as corkscrew waves. The standing waves travel in the axial direction but not in the azimuthal direction and appear as snakes. Weakly nonlinear interactions are studied to see whether one of these waves will be stable to small amplitude perturbations. The corkscrews are found to be preferred when the armulus is narrow and snakes are preferred when the annulus is wide.
Flow Characteristics of Condensing Two-Phase Flow in Horizontal Microfin Tubes
Authors: Nozu Shigeru , Honda Hiroshi
Published: March 2022

Flow observation study along with local heat transfer and pressure drop measurements were conducted during condensation of CFC11 in horizontal microfin tubes. A smooth tube and two microfin tubes with different fin geometry were tested. Flow observation study with use of industrial borescopes revealed that two major flow patterns exist during complete condensation of a vapor. A correlation equation for the local frictional pressure gradient was derived, in which the effect of refrigerant mass velocity was introduced on the basis of the flow regime consideration. The condensing two-phase frictional pressure drop data for the microfin tubes were correlated by the present method to have a mean absolute deviation of 8.3 percent.
Fluids Engineering Division Conferences
Authors: Morrow Thomas B.
Published: March 2022

The ASME Fluids Engineering Division (FED) sponsors technical sessions at the FED Summer Meeting (FEDSM) and at the International Mechanical Engineering Conference and Exhibition (IMECE). This paper describes the FED’s role in the way in which these conferences are planned, organized, publicized and presented, and provides information on FEDSM attendance, registration fees and conference publications.
Collision Behavior of a Water Droplet With a Hot Surface
Authors: Fujimoto Hitoshi , Hatta Natsuo , Takuda Hirohiko
Published: March 2022

This paper treats the deformation process of a water droplet impinging on a hot surface above the Leidenfrost temperature. Emphasis is placed on the effects of the kind of surface material and the surface temperature on the deformation process. The surface material used are stainless-steel and silicon. The surface temperature is fixed at 673K and at 773K. It has been found that the time histories of droplet diameter as well as height on two kinds of surfaces are very similar in low Weber numbers such that the droplet rebounds from the surface without disintegration. However, the critical Weber number whether or not the droplet breaks up into some pieces on the surface during deformation has been confirmed to be changeable depending upon the kind of surface material. Furthermore, it has been confirmed that the effect of surface temperature on the droplet deformation process is remarkable in the later deformation period for the case of the low Weber number.
Collision Dynamics of Two Droplets
Authors: Fujimoto Hitoshi , Hatta Natsuo , Takuda Hirohiko
Published: March 2022

This paper treats the numerical analysis of the deformation behavior of liquid after head-on collision of two droplets. The simulation of the liquid deformation process has been performed using the MAC-type solution method to solve a finite differencing approximation of the Navier-Stokes equations governing an axisymmetric incompressible fluid flow. When a water droplet collides head-on into another one with small initial Weber numbers, two droplets coalesce and remain permanently united. For larger Weber numbers, two droplets merge temporarily and subsequently separate into two or more drops. The calculated free surface configurations have been in qualitative agreement with the experimental results observed by other researchers. Also, the critical Weber number to predict coalescence/separation of liquid after head-on collision has agreed with the experimental data. The details of droplet deformation mechanism have been discussed from a qualitative as well as quantitative point of view.
Detailed Characterization of Fuel Droplets in a Spray Flame Using an Integrated Phase Doppler/Rainbow Refractometer System
Authors: Sankar Subramanian V. , Robart Didier M. , Bachalo William D.
Published: March 2022

The characteristics of fuel droplets burning in an unconfined, non-swirling spray flame have been experimentally studied in great detail using an integrated phase Doppler/Rainbow Refractometer system. This newly developed non-intrusive diagnostic instrument allows for the measurement of individual fuel droplet temperatures in addition to their diameter and velocity. The fuel used for this study is hexadecane (C16H34) which has a boiling point of about 287°C. A solid cone Hago pressure atomizer with a flow rate of 0.5 gph was used to atomize the liquid fuel, and a spray flame was established by firing the atomizer vertically upward. Droplet temperature, size, and velocity data were obtained at several radial and axial locations within the spray flame. The study revealed that at the center of the spray, the droplets were well below their boiling point. Within the flame zone, the droplets had higher mean temperatures. A strong dependence of temperature on droplet size was also observed within the flame zone. The largest drops were close to room temperature whereas the temperature increased asymptotically to temperatures close to the boiling point with decreasing droplet diameters.
Measurement of Sphere Drag in High Turbulent Intensity Flows
Authors: Sankagiri Narayanaswamy , Ruff Gary A.
Published: March 2022

Multiphase flows composed of dispersed phase elements interacting with a turbulent continuous phase are encountered in many engineering applications. In analyses of these systems, the sphere drag coefficient is frequently used to determine not only the rate of momentum transfer from these elements but also the rates of mass and energy transport. Considerable research has demonstrated that the drag coefficient is dependent on the turbulence intensity of the free stream but experimental studies have been limited to relatively low levels of turbulence intensities, and have been obtained over limited ranges of particle Reynolds numbers. The objective of this research is to obtain data at low levels of turbulence where existing data is sparse or inconsistent, extend the measurements to higher levels of relative turbulence intensity, and cover the range of particle Reynolds numbers found in typical multiphase flows (50 < Rep < 1500, 0.08 < Ir < 0.6). Current drag measurements at turbulence intensities of approximately 0.1 show good agreement with the results of previous researchers. Results at an intensity of 0.3 have indicated how the drag coefficient transitions between high and low Reynolds number data from different researchers. Measurements at other turbulence intensities are continuing.
Numerical Modeling of Flow Over Dunes in Ice-Covered Channels
Authors: Tan Cheng-Ann
Published: March 2022

This paper presents a recently undertaken study of flow over dunes in an ice-covered channel. A fully three-dimensional numerical model was selected to simulate the flow physics. The model solves the complete Reynolds-averaged Navier-Stokes (RANS) equations, closed with the standard k-ε turbulence model. Small-scale bed roughness at the river bed and ice cover, is accounted for by using two-point wall-functions. A comparative study of ice-covered and open channel flow is presented to illustrate the differences in flow physics due to ice cover. Effects of varying roughness of ice on the flow physics is also investigated. Comparisons with measurements reveal the ability of the model to capture experimental trends with remarkable accuracy.
Quantitative Radiography for Transient Multidimensional, Multiphase Flows
Authors: Theofanous Theo G. , Angelini Sergio , Chen Xiaoming , Luo Rui , Yuen Walter W.
Published: March 2022

As computations of transient, multidimensional, multiphase flows are becoming increasingly more realistic, so increases the demand for their detailed experimental validation. Key in this task is the evolution of flow patterns, and the usual approaches of local measurements are inherently limited in meeting this demand. In this paper, we demonstrate the particular suitability of flash X-ray radiography, and the feasibility of reliably quantifying the radiographs of flow regions of various sizes, from microscopic to rather large scale.
Imaging of Particle Shear Migration With Electrical Impedance Tomography
Authors: Butler Jason E. , Bonnecaze Roger T.
Published: March 2022

Electrical impedance tomography is used to investigate the net migration of particles in a suspension undergoing pressure-driven flow through a tube at low Reynolds number. A low frequency electrical current is applied to the flowing suspension by two flush-mounted electrodes on the pipe wall to create a potential field which is sampled by other pairs of flush-mounted electrodes. A numerical inversion of the data, which takes into account the geometry and symmetry of the problem, gives the conductivity variation within the flow. An image of the suspension particle volume fraction in the tube is then formed using a relationship between the local conductivity and local suspension concentration. Consistent with particle shear migration of a concentrated suspension, the images from experimental data show a net migration of particles toward the centerline of the tube. The images favorably compare to an existing continuum theory of particle shear migration.
An Electrical Impedance Method for Measurements of Attached Cavitation
Authors: Ceccio Steven L. , George Darin L.
Published: March 2022

An electrical impedance probe is described which will be used to study the properties of attached cavitation. The method uses a series of electrodes mounted flush to the surface of a cavitating hydrofoil, and detects the presence of liquid or vapor through changes in the impedance of the local fluid medium. Characteristics of steady and unsteady attached cavitation, including cloud shedding and re-entrant jets, are reviewed. The impedance technique is shown to have the potential to measure advection velocities of bubble clouds, velocities of re-entrant jets, and frequencies associated with unsteady cavitation.
Instrumentation and Measurement Techniques for Multiphase Flow: The State-of-the-Art
Authors: Hussein Esam M. A. , Ingham Paul J.
Published: March 2022

This papers reviews recent progress in multiphase flow measurement methods and assesses the capabilities and limitations of developed or proposed techniques. Instrumentation for measuring global and local phase volume-fraction, phase-distribution, flow-pattern visualization and identification, interfacial area, phase-velocity and other parameters are examined. The paper concludes by identifying some of the most promising techniques and defining the remaining challenges.
Phase Discrimination Techniques for Phase Doppler Measurements in Dispersed, Bubbly Flows
Authors: Stanley K. N. , Nikitopoulos D. E.
Published: March 2022

A combined Phase-Doppler Anemometry (PDA) and video imaging measurement technique for non-intrusive measurements in dispersed bubbly flows is presented. A one-component Phase-Doppler Velocimetry system has been employed to measure liquid seeding particle size and velocity as well as bubble size and velocity non-intrusively. Measurable flow quantities include: (1) mean velocities and RMS velocity fluctuations for bubbles and liquid; (2) local bubble diameter, and (3) local bubble passage frequency. Non-intrusive local measurement of seeding particle and bubble size is an advantage over techniques used previously (Laser-Doppler Velocimetry, Hot-Film Anemometry). Visual data collected simultaneously with the light-scattering measurements and analyzed with the aid of image processing are used to verify the trends portrayed by the light-scattering measurements. A multi-level phase discrimination technique based on velocity, diameter, and relative data rates between the carrier and dispersed phases is employed to minimize bias from bubble signals when measuring liquid phase data in dilute flows. An amplitude discrimination technique for the Phase-Doppler system is proposed for higher volume fraction flows. The proposed method enables local non-intrusive measurement of liquid phase velocity as well as local bubble size characteristics, velocity, and concentration.
Wall Heat Transfer Measurements in Saturated Pool Boiling of FC-72 on a Small Heated Area
Authors: Rule Toby D. , Kim Jungho
Published: March 2022

Local wall heat flux measurements of saturated pool boiling of FC-72 on a small heated area held at constant wall temperature were made. An array of 96 temperature controlled heaters was used to measure the heat flux distribution on this surface. Array-averaged heat flux, RMS variations in heat flux, and local heat flux information is presented. Local heat flux variations are shown to be three to six times larger than variations in the spatially averaged heat flux.
Simulation of 3-D Mold-Filling and Solidification Processes on Distributed Memory Parallel Architectures
Authors: Ilinca Florin , Hétu Jean-François , Audet Martin , Bramley Randall
Published: March 2022

This work presents industrial mold-filling applications of a three-dimensional stabilized finite element solver on distributed memory parallel architectures. The paper focuses on the solution algorithm and parallel implementation for complex multiphasics problems involving high Reynolds number flows with free surfaces, turbulence modeling and heat transfer. Standard domain decomposition methods (Chaco, Metis) are applied to the graph of nodes obtained from the finite element mesh, and a distributed-memory MPI programming model is used. An implicit time integration scheme and a segregated iterative algorithm are used to solve the momentum, energy, turbulence variables and front tracking equations. The equations are dis-cretized using a stabilized SUPG finite element method on linear elements. The resulting sparse system of linear equations is solved using parallel preconditioned iterative methods.
Moisture Induced Failures of Plastic Packages of IC Devices: State-of-the-Art and Crucial Needs
Authors: Feng Y. , Raju V. R. , Suhir E.
Published: March 2022

This review addresses the current status of understanding of the mechanical behavior of plastic microelectronics packages and the ability to predict and prevent moisture induced failures in them. While significant progress has been made during the last decade to improve the reliability of plastic packages, moisture related failures are still a major concern to both the manufacturing and user communities. The current procedures used in the industry to alleviate this problem are identified and discussed. These include controlling moisture content in the packages, improving geometrical designs, developing new molding compounds with higher strength and/or lower thermal stresses and treating material surfaces for better interfacial adhesion, etc. Understanding derived from theoretical modeling based on structural and fracture mechanics is also discussed. Some unsolved problems crucial in helping to find an ultimate solution to eliminate moisture induced failures in plastic packages are also addressed.
A Mechanical Reliability Evaluation of Several Electrically Conductive Epoxies: Part III — Fracture Properties
Authors: Rafanelli Anthony J.
Published: March 2022

Electrically conductive epoxies have become attractive alternatives to traditional tin-lead solder as bonding media for electronic interconnections. However, these materials, being of a different nature than solder, have not undergone as extensive material and mechanical characterization as the latter. Subsequently, a comprehensive, multi-phase evaluation is warranted prior to approving a direct substitution. Such an evaluation would include several key mechanical studies such as basic material properties, fatigue, creep, and fracture. This paper reports on results of fracture property studies, namely determination of the J-Integral on samples of conductive adhesive epoxies. In addition, testing was also performed on eutectic or near eutectic solder, to provide a benchmark for comparison.
A Study on Reliability of Pb40/Sn60 Solder Joints Under Dynamic Loading
Authors: Basaran Cemal , Chandaroy Rumpa
Published: March 2022

Solder interconnects are commonly used in surface mount technology microelectronics packaging. It is well known that the dominant failure mode for solder joints is thermal fatigue. When semiconductor devices are used in vibrating environment such as in automotive and military applications, dynamic stresses contribute to the failure mechanism of the solder joint and in certain circumstances they can become the dominant failure cause. In this paper a unified constitutive model for Pb40/Sn60 solder joints is developed and then implemented in a finite element dynamic analysis procedure. The purpose of the material model and the implementation is to study the contribution of vibration induced strains to the fatigue life of solder interconnects in low-cycle and high cycle fatigue. The proposed material model, which is based on the Disturbed State Concept (DSC), is used for dynamic analysis of a solder joint.
In Situ Sensing System for Rapidly Spreading Microdroplets During Droplet-Based Manufacturing
Authors: Kim Ho-Young , Qiu Taiqing , Chun Jung-Hoon
Published: March 2022

Deposition of microdroplets is fundamental to many emerging technologies. The strongly coupled droplet spreading and cooling processes have profound impact on the quality of droplet-formed structures. This work developed a microsensor for characterizing rapidly spreading microdroplets on a substrate after the impact. The sensor consists of fine conducting lines made of Au and Ti two-layered structure with both width and spacing 2 μm. Transient droplet contact diameters were measured with the sensors of 8 μm spatial and 1 μs temporal resolutions. Two different regimes of spreading were discovered: an extremely fast initial spreading process followed by slow spreading. The results are important for achieving a better understanding of rapid solidification and formation of novel microstructures in droplet-based manufacturing processes.
Numerical Modeling for Rotational Molding of Thermoplastics
Authors: Olson Lorraine G. , Gogos George , Pasham Venkataramana , Liu Xuejun
Published: March 2022

A thermal model for rotational molding is presented which includes heat transfer from the oven to the mold, through both the mold and gradually depositing plastic layer, and to the unmelted but well-mixed powder. The problem is addressed numerically for the first time using Arbitrary Lagrangian Eulerian finite element methods. One dimensional results (spherically symmetric) show excellent agreement when compared with more limited numerical models, and when compared with experimental results from the literature and with the trends observed in practice. Extending these finite element techniques to axisymmetric cases may make accurate wall-thickness predictions possible.
Study on Propagative Collapse of a Vapor Film of Film Boiling: Effects of Liquid Subcoolings on Characteristics of Propagative Collapse
Authors: Sakamoto Yasuyoshi , Ohtake Hiroyasu , Koizumi Yasuo
Published: March 2022

Using a platinum wire of 1 mm in diameter and 160 mm in length, pool film-boiling experiments were performed for saturated and subcooled water at atmospheric pressure and the propagative collapse of the vapor film was examined. The temperature of a local-cooled spot which was suspected to have a large effect on the collapse of the water film was varied systematically in the experiments.

The experimental results showed that the propagation velocity of the vapor film collapse decreased and the surface temperature at the collapse increased with decreasing the cold-spot temperature. In particular, when the cold-spot temperature was below the thermodynamic limit of superheat of water, the surface temperature at the collapse increased remarkably. The propagation velocities of the collapse of the vapor film were similar to the rewetting velocities by a falling-film.
Effect of Fluid Properties on Electrohydrodynamically Enhanced Heat Transfer in Pool Boiling
Authors: Hardesty John T. , Raghupathi Priya , Seyed-Yagoobi Jamal , Bryan James E. , Wawzyniak Markus
Published: March 2022

The effect of fluid properties on electrohydrodynamically enhanced heat transfer in pool boiling was studied using R-123, R-134a, and R-407c as the working fluids at various pool temperatures. Two experimental boiling apparatuses were used, one electrically heated and suitable for high pressure refrigerants, and the other water heated, suitable only for low pressure refrigerants. In both cases, the pool boiling consisted of a single horizontal copper tube with the same surface finish, heated length, and outer diameter. The electrode design consisted of eight straight wires spaced radially at equal angles around the tube. The electrical properties of working fluids as a function of temperature were measured using a unique test cell.

Results show that of the three refrigerants, R-123 and R-134a both demonstrate significant EHD enhancement at 4 °C and 20 °C pool temperatures. Enhancements at 4 °C are larger than those at 20 °C for both refrigerants. Measured electric charge relaxation time and estimated bubble departure time indicate that negligible enhancement should be realized with R-407c at 4 °C pool temperature, while some enhancement should be achieved at 20 °C and 35 °C pool temperatures. Experimental results confirm this and clarify the relationship between bubble departure time and electric charge relaxation time.
Electrohydrodynamic (EHD) Enhancement of Boiling Heat Transfer With a Lo-Fin Tube
Authors: Han Sang-Houn , Na Min-Kyun , Oh Si-Doek , Kwak Ho-Young
Published: March 2022

The effect of D.C electric field on nucleate boiling heat transfer for refrigerants of R-11, HCFC-123 and FC-72 was investigated experimentally by using a single lo-fin tube shell/tube heat exchanger. The lo-fin tube which brings two times increase in the heat transfer area provided about 150% of boiling heat transfer enhancement compared to that of smooth surface. Experimental study has revealed that the electrical charge relaxation time is an important parameter for the boiling heat transfer enhancement under electric field. Boiling heat transfer enhancement was obtained up to 40% for R-11 which has moderate relaxation time of 1.3 s. However remarked boiling heat transfer enhancement has been obtained up to three fold increase (300%) for HCFC-123 which has the electrical charge relaxation time of 0.89 × 10−3 s. For FC-72 having longer relaxation time than the bubble detachment one, no appreciable effect on the nucleate boiling heat transfer was observed.
Wavelet and Fractal Analyses of Fluidized Bed Heat Transfer
Authors: Ross Kristen A. , Pence Deborah V.
Published: March 2022

The present study examines hydrodynamics and heat transfer in a gas-fluidized bed using wavelet and fractal analyses. Wavelet analysis provided the opportunity to investigate time-varying heat transfer simultaneously from both a time and frequency (scale) perspective. As a result, intermittent periods of local bubble formation were discovered to occur at the stagnation point on the cylinder for fluidization ratios 50 percent greater than those required for minimum fluidization. In addition to physical insight, the time-frequency plots (scalograms) revealed what is believed to be fractal characteristics of these time-varying data. The fractal nature of these signals was confirmed using Hurst’s rescaled range analysis, which was employed to estimate the fractal dimension of each time series. For the present investigation, time-varying local heat transfer from a heated horizontal cylinder to a cold bubbling bed of 345 μm particles was measured as a function of angular position and flow rate.
Numerical Solution of the Effect of Vibration on Melting of Unfixed Rectangular Phase-Change Material Under Low-Gravity Environment
Authors: Shirvanian A. , Faghri M. , Zhang Z. , Asako Y.
Published: March 2022

This paper presents a numerical method for simulating the melting process in a cavity in the presence of wall vibration. An enthalpy method is employed to solve the governing equations associated with melting of an unfixed solid Phase Change Material (PCM) in a low gravitational environment. In this method, the problem is solved in one domain. The PCM, initially at its melting temperature, is placed inside a rectangular enclosure. The enclosure walls are then exposed to a uniform temperature under a specified amplitude and frequency of vibration. Melting begins from all sides, and due to natural convection, the PCM would not retain its initial shape. The governing equations are discretized by using a control-volume based finite difference method and are solved in together with solid PCM’s equation of motion. The results are presented in the form of a parametric study of the effects of aspect ratio, Stefan number, Strouhal number and dimensionless frequency or period of vibration, on the melt thickness, the solid PCM velocity and the volume of solid PCM. The melt thickness and solid PCM velocity are found to vibrate at the same frequency as of the exciting vibration. The melting rate increases with increase in Strouhal number while decreases with increase in dimensionless frequency of vibration. As seen from the results, for very high frequencies of vibration the melt thickness and molten volume fraction essentially approach those for without vibration. The results show that for the range of parameters investigated, vibration can enhance the melting rate up to 15%.
Guidelines for Preliminary Thermal Design of Convectively Cooled Printed Circuit Boards
Authors: Park Hyunjae , Nigro Nicholas , Elkouh Abdel , Gollhardt Neil , Lee Ping
Published: March 2022

This paper discusses the development and use of an approximate analysis model for predicting the temperature distribution on a Printed Circuit Board (PCB) containing imbedded heat dissipating electronic components which are being cooled by laminar air flow induced by a fan. The direction of the air flow is parallel to the PCB. Temperature results obtained from the model are presented in dimensionless curves as a function of the PCB design parameters including the board dimensions, air velocity (or flowrate), and number, position and heat dissipation of the components. These curves enable the engineer to quickly select the optimal values of the design parameters which meet the design specification imposed on the maximum allowable board wall temperature. Information gained from these curves is employed to establish a set of guidelines (steps) for the preliminary thermal design and layout of the PCB and components.
Inflow and Outflow Effects on Natural Convection in Partially Heated Vertical Parallel Plate Channels
Authors: Campo Antonio , Manca Oronzio , Morrone Biagio
Published: March 2022

In a vertical uniform wall heat flux channel in natural convective flow, the adiabatic. extensions can ameliorate or worsen the chimney effect and the corresponding heat transfer characteristics. The investigation set up in this paper is devoted to the detailed analysis of the aforementioned problem, by numerically solving the elliptic equations in an enlarged I-shaped computaional domain. The results presented herein have the aim to ascertain the discrepancies between the two investigated configurations, i.e. heated inlet and unheated inlet. The results are reported in terms of maximum wall temperatures and nondimensional induced flow rates. Further, some thermal and flow fields are shown. The channel Rayleigh number ranged between 102 and 105 and the adiabatic extension between 0.0 and 19.0. The I-shaped domain allowed to evaluate the discrepancies in terms of stream function and thermal fields, particularly at the exit section. Moreover, it is shown the less the channel Rayleigh number the greater the influence of the adiabatic extensions. This influence is relevant up to four times the adiabatic extension respect to the heated section.
Diagnosis of Gas Species Concentrations and Temperatures in Laminar Flames
Authors: Zhu Yingjie , Sivathanu Yudaya R. , Gore Jay P.
Published: March 2022

The structure of premixed laminar methane/air flames at atmospheric pressure was studied in this paper. In the post-flame region of these flat flames, the emission specctroscopy was used to obtain the temperature and gas species concentrations information which are very important in the study of combustion. Based on the thermal emission by gas molecules in lean flames, the emission data obtained by using the multiwavelength infrared detection method were operated in an iterative algorithm to get the gas species moles fractions and temperatures. At the same positions in the flames, temperature measurements were also obtained from thermocouple and H2O and CO2 concentrations were obtained from gas chromatography. The emission spectroscopy provided accurate temperature and mole fractions data compared to the theoretical value with the consideration of reasonable heat loss.
Simultaneous Measurement of Velocity, Size and Temperature of Burning Coal Particles in Swirl-Stabilised Vitiated Air Flames
Authors: Prassas Ilias , Taylor Alex M. K. P. , Whitelaw J. H.
Published: March 2022

The velocity, size and volume flux of individual burning and non-burning particles were measured simultaneously in the near-burner region of a natural-gas supported 8 kW swirl burner for swirl number 0.68, using in the secondary stream unheated air as well as preheated vitiated air as oxidant, with oxygen mole fraction of 0.165 and 0.177, at 400 and 350 °C preheat temperatures respectively. An optical instrument based on a combined shadow Doppler velocimeter instrument (for sizing particles of arbitrary shape) and spatially-precise two-colour pyrometry was developed for the measurements. The results at axial distance z/D = 2.6 which lay within the recirculation zone showed that the fraction of burning particles (defined as the ratio of detected burning particles and the total measured) decreased with increasing radial distance in all flow conditions. The maximum fraction of burning particles decreased as a function of decreasing oxygen mole fraction from about 94% at a 0.21 mole fraction to 28% and 12% at oxygen mole fractions of 0.177 and 0.165 respectively and, as a consequence, the volume flux of burning particles was an order-of-magnitude smaller than the volume flux of the ensemble.
Fuel Preheat Effects on Soot Formation in Soot-Emitting Laminar Microgravity Jet Diffusion Flames
Authors: Konsur Bogdan , Megaridis Constantine M. , Griffin DeVon W.
Published: March 2022

An experimental investigation conducted at the 2.2s drop tower of the NASA Lewis Research Center is presented to quantify the influence of moderate fuel preheat on soot formation within 0-g laminar gas jet diffusion flames. The experimental methodology implements jet diffusion flames of nitrogen-diluted acetylene fuel burning in quiescent air at atmospheric pressure. Fuel preheat in the 0-g laminar jet diffusion flames is found to reduce soot loadings on the annular region but causes an increase in soot volume fractions on the centerline. In addition, fuel preheat reduces the spatial extent of the soot field in 0-g. The results also show that the soot growth stage is shortened when elevated fuel temperatures are used. Finally, an attempt is made to provide an explanation for the pronounced annular character of the soot field in 0-g.
Ignition Analysis of SHS Processes Subjected to a Constant Heat Flux
Authors: Escobar-Vargas Sergio , Hernandez-Guerrero Abel , Baltazar-Cervantes Juan C.
Published: March 2022

The research presented here deals with the minimum ignition times for a Ti+C (graphite) powder mixture. A family of curves from the simulation of the ignition process involves the application of radiant heat to a cylindrical sample. Some non-dimensional parameters of the process are varied such as the Damköhler number (Da), as well as Zeldovich (A) and Stefan (H) numbers. The initial composition of the mixture was varied from the non-stoichiometric to the stoichiometric case. The minimum ignition time was used to develop an ignitability curve which directly relates the applied radiant heat flux with the Da number. These curves define the ignition/non-ignition zone for the reactants considered.
Influence of Fuel-Air Ratio on Horizontal Flame Spread Rates
Authors: Litton Charles D. , Hwang Charles C.
Published: March 2022

Flame spread along horizontal surfaces in the presence of a forced convective airflow depends primarily upon the transfer of radiant energy to downstream surfaces from a flame front that is tilted in the direction of flow. The soot in the flame serves as the primary source of radiation but the soot that emerges from the flame and mixes with the forced airflow also serves to attenuate the radiation thereby decreasing the radiant flux at the downstream surfaces. There is, then, a complex interaction between the quantity of soot produced and the radiative heat transferred to the downstream surfaces. It has also been shown that when flames transition from over-ventilated to under-ventilated conditions, the soot yield increases while both the total combustion efficiency and the convective fraction of the combustion efficiency begin to decrease. This transition occurs when the flame is unable to entrain sufficient air to burn either at the stoichiometric fuel-air ratio or on the over-ventilated side of stoichiometric. When the total and convective combustion efficiencies do not decrease at the same rate, the radiative fraction tends to increase at equivalence ratios in the range of 1 to 1.3. This results in an increase in radiative heat transfer to the downstream surfaces that causes the flame spread rate to accelerate. A flame spread model was developed to quantify these processes. Predictions from the model are in excellent agreement with experimental data for flame spread along surfaces of styrene-butadiene rubber conveyor belts in a largescale fire gallery where the transition to under-ventilated combustion occurs when the flames begin to impact the roof of the gallery.
On the Thermal Runaway in Solid Foams
Authors: Goldfarb Igor , Goldshtein Vladimir , Kuzmenko Grigory
Published: March 2022

The phenomenon of the spontaneous insulation fires is investigated. An original physical model is based on the classical cell approach of multiphase media. The real complex media is modelled by a set of the identical parallel capillaries containing the thin film of the combustible fluid spread over their inner surface. The dynamics of the thermal explosion in this multiphase medium is studied. An advanced mathematical technique (integral manifold method) is used for qualitative analysis of the system dynamics. The classification of the possible scenarios of the thermal runaway is obtained analytically. Peculiarities of the dynamical regimes are investigated and their dependence on physical system parameters is analyzed. The research is focused on the regime with delay. Lower and upper analytical estimates for the delay time have been gained. The theoretical delay times estimations were verified when compared to those found experimentally. This comparison demonstrates sufficient qualitative and quantitative agreement.