bluuebunny/crossref_metadata_2025 huggingface dataset:
An Accuracy Evaluation for the Madejski Splat-Quench Solidification Model
Authors: Aceves Salvador M. , Shapiro Arthur B. , Sahai Vivek
Published: December 2021

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

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

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

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

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

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

A three-dimensional, unsteady heat transfer model has been developed for predicting the temperature field in partially stabilized zirconia (PSZ) undergoing laser-assisted machining (LAM). PSZ is a semi-transparent ceramic which volumetrically absorbs, emits and scatters radiation across a spectral region extending from approximately 0.5 to 8 μm. As a first approximation, it is treated as optically thick within this spectral band, and the high density of scattering centers, as well as the random orientation of grain boundaries, permits the assumption of isotropic scattering. Accordingly, the Rosseland diffusion approximation is used to model internal radiative transfer. Since most of the CO2 laser radiation (λ = 10.6 μm) is absorbed in the first layer of control volumes adjacent to the surface, incident laser radiation is treated as a surface phenomenon.

The equivalent radiation conductivity of PSZ is strongly temperature dependent and enhances thermal energy transfer within regions of the workpiece which are close to the location of laser irradiation. However, the effective thermal conductivity of PSZ remains relatively low, even at the highest temperatures achieved during LAM, and is responsible for large temperature gradients near the irradiated surface of the workpiece. For representative operating conditions, comparative calculations are performed with and without the radiation model to assess the influence of volumetric radiation effects on the temperature field. Numerical simulations are also performed to consider the effect of operating conditions, such as the laser power, laser/tool feed and depth-of-cut, on thermal conditions in close proximity to the material removal zone. The results are contrasted with those for silicon nitride, which is an opaque ceramic that exhibits quasi-plastic deformation when its temperature is raised above a threshold value at the depth-of-cut and can therefore be machined with a cutting tool.
Emission and Laser-Induced Fluorescence Spectroscopy of Laser-Ablated Titanium Plume
Authors: Chu Schubert S. , Grigoropoulos Costas P.
Published: December 2021

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

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

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

In the present study we apply an artificial neural network to predict the operation of a humid air-water fin-tube compact heat exchanger. The network configuration is of the feedforward type with a sigmoid activation function and a backpropagation algorithm. Published experimental data, corresponding to humid air flowing over the heat exchanger tubes and water flowing inside them, are used to train the neural network. After training with known experimental values of the humid-air flow rates, dry-bulb and wet-bulb inlet temperatures for various geometrical configurations, the j-factor and heat transfer rate predictions of the network were tested against the experimental values. Comparisons were made with published predictions of power-law correlations which were obtained from the same data. The results demonstrate that the neural network is able to predict the performance of this heat exchanger much better than the correlations.
Application of the Discrete Ordinates Method to a Continuous Glass Furnace Model
Authors: Rodicio Sandra Coutín , Chapman Kirby S.
Published: December 2021

The radiative behavior of the glass as it flows through a continuous glass furnace is studied by applying the Discrete Ordinates Method (DOM). Through the application of the DOM the radiant intensity is calculated at each of the control volumes inside the glass tank domain. Consequently, the heat fluxes of the emitted and irradiated energy in the glass are obtained. The results are presented in terms of the radiant heat fluxes distribution and temperature profile of the glass. In addition, the variation of the glass surface emissivity is studied in order to provide further understanding of the impact of this property in the glass overall thermal behavior.
Modeling and Visualization of Plasma Spray Process for Depositing Functionally Graded Materials
Authors: Wan Y. P. , Gupta V. , Zhang H. , Varshney A. , Sampath S. , Prasad V. , Fincke J. R.
Published: December 2021

Recently, several models have been developed to simulate the plasma spraying process. The present paper extends our previous model (Wan et al., 1999a) to the plasma spray system of two-component materials with two different feed nozzles. It accounts for plasma-particle interaction, particle heating/melting/evaporation and solidification on the substrate. A special visualization algorithm has been developed to demonstrate the effects of various parameters on particle conditions while in flight, growth of functionally graded materials and distribution of the two components in the coating. Visualization of thermal processes is a challenging task if it has to be used for materials design and system development. It requires special schemes for data management in a multivariate system that includes at least velocity, temperature and species in four co-ordinates (space and time). Our effort is focused on developing a visualization scheme which goes far beyond the process animation and can be ultimately used for virtual prototyping of the processes, an area that needs special research efforts. Simulation and visualization have been performed for spraying of zirconia and NiCrAlY powders, with many combinations of powder injection features, e.g., number of nozzles, nozzle location and injection velocity. The fluctuation of the voltage is also simulated and animated to show its effect on both plasma gas and particle behavior. The optimized operating parameters are deduced from the distribution of these two materials in the coating layer. Issues related to visualization are also discussed.
Numerical Study of Thermal Modeling of Resistance Spot Welding Utilizing Coupled Thermal-Electrical-Mechanical Analysis
Authors: Xu Lijun , Khan Jamil A. , Chao Yuh-Jin , Broach Kirkland
Published: December 2021

This paper successfully proposes a novel model to predict nugget development during resistance spot welding (RSW) of binary Al-alloys. The model employs a coupled thermal-electrical-mechanical analysis, and also accounts for phase change and convective transport in weld pool. Faying surface contact area and its pressure distribution are simulated from coupled thermal-mechanical model using a finite element method. Temperature dependent thermal, electrical and mechanical properties are used. The proposed model can successfully calculate most of the RSW response in term of nugget diameter and thickness, the extent of heat affected zone, etc. The calculated nugget shape based on the thermal model agrees well with the experimental data. Convection effect due to the interactions between phases in the porous mushy zone and the buoyancy force arising from the temperature difference is determined to be not significant for the weld-nugget formation. The proposed model can be used to optimize RSW process parameters for industrial welding.
Resonance Based Force Measurement: Prelude to High-Resolution Anemometry for Liquid Metal Flows
Authors: Phan Son , Keanini Russell , Smith Stuart , Hocken Robert
Published: December 2021

This paper describes the first phase of a two-part project designed to develop a new anemometry method for use in high temperature liquid metal flows. The device will incorporate a dual-cantilever, PZT-driven touch sensor housed within a sealed, temperature resistant ceramic Pitot tube. Due to differing cantilever lengths, the device’s unloaded spectral response exhibits two distinct peaks, each corresponding to the cantilevers’ resonant frequencies. The principal of operation is based on the fact that pressure-induced forces on each cantilever produce resonant frequency shifts which can then be correlated with applied pressures. The first project phase has focused on development and testing of the dual cantilever touch-sensor and its supporting electronics. Two new concepts have been introduced in designing the touch sensor — use of a dual cantilever for simultaneous force measurement, and simultaneous detection of associated pressure-induced resonant frequency shifts. Here, we describe design of the Pitot tube, design and fabrication of the dual-cantilever sensor and electronics, and system modeling of the sensor. We also outline two pressure measurement schemes; in the first, pressure is correlated with resonant frequency shifts at constant phase while in the second, pressure is related to phase shifts (between forcing and response signals) at constant frequency. Device driving and sensing electronics have been fabricated as has the dual-cantilever touch sensor; preliminary experimental measurements of single and dual forces are presented.
Proposed Experimental Technique for Measuring Heat Transfer Coefficients Using a Pulsed Periodic Surface Heat Flux
Authors: Turnbull Wayne N. O. , Carscallen William E.
Published: December 2021

An analytical and numerical investigation has been carried out to ascertain the possibility of using a pulsed periodic surface heat flux to measure local surface heat transfer coefficients. The proposed technique is an extension of a previously proven experimental method. It is based upon the premise that the harmonics of a surface temperature response to an imposed periodic pulse will display phase shifting behavior that is a function of the thermophysical properties of the surface, the local heat transfer coefficient and the harmonic frequency. The phase behavior is not a function of the magnitude of the energy deposited by the pulse. Since phase behavior is being investigated there is no requirement to calibrate the surface temperature-sensing device. The numerical solution confirms the analytical results, which were obtained using a non-rigorous mathematical assumption. Results indicate that in order to maximize the sensitivity of the proposed experimental technique the pulse frequency should be kept low, the surface layer thin and the substrate thermal conductivity and diffusivity as low as possible.
A New Experimental Technique for Measuring Surface Heat Transfer Coefficients Using Uncalibrated Liquid Crystals
Authors: Turnbull Wayne N. O. , Oosthuizen Patrick H.
Published: December 2021

A new experimental technique has been developed that permits the determination of local surface heat transfer coefficients on surfaces without requirement for calibration of the temperature-sensing device. The technique uses the phase delay that develops between the surface temperature response and an imposed periodic surface heat flux. This phase delay is dependent upon the thermophysical properties of the model, the heat flux driving frequency and the local heat transfer coefficient. It is not a function of magnitude of the local heat flux. Since only phase differences are being measured there is no requirement to calibrate the temperature sensor, in this instance a thermochromic liquid crystal. Application of a periodic surface heat flux to a flat plate resulted in a surface colour response that was a function of time. This response was captured using a standard colour CCD camera and the phase delay angles were determined using Fourier analysis. Only the 8 bit G component of the captured RGB signal was required, there being no need to determine a Hue value. From these experimentally obtained phase delay angles it was possible to determine heat transfer coefficients that compared well with those predicted using a standard correlation.
Combined Pulsating and Capillary Heat Pipe Mechanism for Cooling of High Heat Flux Electronics
Authors: Zuo Z. Jon , North Mark T. , Ray Lee
Published: December 2021

This paper discusses an advanced heat pipe mechanism for cooling of high heat flux electronics. The mechanism combines the capillary effect of sintered metal powder wicks with a pulsating motion of the working fluid to maintain sufficient liquid supply to high heat flux regions. The pulsating motion is driven by thermal conditions in the heat pipe evaporator and condenser and can be sustained with proper internal flow channel design. A theoretical model was developed to describe the pulsating motion of the working fluid. Proof-of-concept copper/water heat pipes were tested to verify the heat flux capability of this advanced mechanism. The test results demonstrated over 220W/cm2 heat flux capability, a fourfold improvement over present state of the art heat pipe performance. Comparisons between the test results and the model predictions validated the theoretical model.
Experimental Study of the Transient Turbulence Generated by a Bubble Using PIV
Authors: Ortiz-Villafuerte Javier , Schmidl William D. , Hassan Yassin A.
Published: December 2021

The particle image velocimetry measurement technique was used to measure the whole-volume, three-dimensional, transient velocity field generated by a single air bubble rising in stagnant water in a small diameter pipe. The three-dimensional flow field was reconstructed using a stereoscopic technique. Conditional averages of the velocity fields for the situations when the bubble rises close to the center of the pipe, and close to the pipe wall were determined, and the turbulent motion generated in the continuous liquid phase for both situations was studied.
Artificial Neural Network Control of an Experimental Heat Exchanger Facility
Authors: Díaz Gerardo , Sen Mihir , Yang K. T. , McClain Rodney L.
Published: December 2021

The artificial neural networks technique is applied to control the dynamic behavior of a fin-tube single-row compact heat exchanger. The experimental setup consists of a variable-speed wind-tunnel facility built specifically for heat exchanger analysis. Two different control methodologies were studied. The first one corresponds to adaptive control in which the weights and biases of the artificial neural network that acts as a controller are modified depending on the error obtained between the desired outlet air temperature and its measured value. Experimental results show that the stability of the system varies depending on the different ways of performing the adaptation of the controller. The second control strategy tested corresponds to internal model control. We added a filter and an integral control structure to obtain an offset-free steady state prediction. The control methodology was extensively tested and the results compared to those of conventional PID control. The results were very favorable for the neural controller.
Results of Implementing an Introductory Course: Foundations of Thermal-Fluid Sciences
Authors: Ochterbeck J. M. , Gaddis J. L.
Published: December 2021

Pursuant to implementation of a new mechanical engineering curriculum at Clemson University, results of the new introductory course in thermal-fluid science are presented. This course is situated in the second semester of the sophomore year for mechanical engineering majors, and is a prerequisite for the subsequent courses in thermodynamics and fluid mechanics. In addition to introducing thermodynamic property analysis, the course develops conservation laws for mass, momentum, and energy and provides an emphasis in design. Discussion is presented of the motivation, placement in the overall curriculum, interaction with other curriculum elements, and the selection of textbooks.
A Partnership Between University’s Engineering Services Departments and Academic Departments for Energy Systems Education
Authors: Somerton Craig W. , Genik Laura J. , Schroeder Joseph , Thelen Wayne A. , Crouch Mike , Hudson Michael , Ellerhorst Robert , Gies Roy
Published: December 2021

Incorporation of plant tours into a laboratory course is discussed. The unique feature of these plant tours is that they are facilities on the university campus and utilize the expertise of the practicing engineers on campus to enhance the students educational experience. Examples of course materials used in these activities are provided.
Teaching Heat Transfer in a Studio Mode
Authors: Ribando Robert J. , Scott Timothy C. , O’Leary Gerald W.
Published: December 2021

Over the past four years we have transformed our undergraduate heat transfer course from a lecture format into what we call a “partial studio model.” Two lecture hours per week are supplemented with a two-hour “hands-on” session in a classroom equipped with a computer for each pair of students. Much of the studio work revolves around a suite of teaching modules that we have developed for use in our undergraduate and graduate heat-and-mass-transfer courses. Most modules include research-based numerical algorithms which solve the governing ordinary and partial-differential equations in real time. Several of the modules may be considered “virtual laboratories,” that is, they allow students to take data from the computer screen for post-processing — much as if they were working in a real, extremely well-equipped, laboratory. Others give the option of performing dozens of “what if” calculations rapidly, thus inviting use in the design process. Each module has been custom tailored for the particular topic; inputs and outputs are limited to only those essential to that problem. Thus, unlike most industry-grade computation fluid dynamics packages, there is virtually no “learning curve” associated with software operations. For a number of these modules we have developed an accompanying desktop experiment to enhance still further the hands-on nature of the studio.
NASA Ames Integrated Risk Assessment
Authors: Mendoza D. R. , Navarro R. J. , Flippen A. A.
Published: December 2021

NASA’s shift towards streamlined business practices depends on innovative management processes and tools. One such innovation, Risk Management (RM), has been levied as an Agency-wide requirement with corresponding policies which define the RM process. However, these policies are top level and do not necessarily ensure the institutionalization and transfer of the process’s best practices. Thus to implement the Agency’s philosophy while ensuring consistency and quality of risk assessments, the NASA Ames System Safety and Mission Assurance Office developed the Integrated Risk Assessment (IRA) process. IRA is the systematic use of both inductive and deductive assessment methods applied such that a risk is assessed for its potential harm to any resource and is tailored to the activity’s overall technical and programmatic constraints. Independently these methods are not unique; but their ensemble, which IRA represents, provides a powerful yet practical RM tool. This paper presents an overview and case study of the IRA process.
The Use of Performance Criteria in Developing Standard Methods for Land-Use Planning
Authors: Ale B. J. M. , Laheij G. M. H. , Post J. G.
Published: December 2021

The assessment and management of risk has been a matter of public and political interest for some decades.

The growing industry and the growing number of industrial products and services and the associated transport of goods have presented more and more partly unfamiliar hazards with which industry itself, but also the population and governments have had to cope. The Netherlands is one of the countries that struggled most explicitly with this problem. In the Netherlands risk is controlled by setting quantitative performance standards for the industry and for the spatial planners. These standards are expressed in limiting values for individual and societal risk.

The standards are used in the policy to reduce the number of people exposed to the effects of an accident. In principle, the societal risk for each new land-use plan should be re-calculated. Since this is proving increasingly cumbersome for planning agencies, several methods have been developed to determine the effects of new land-use plans on the societal risk. These methods give the uniform population density from a certain distance around the establishment at which the indicative limit for the societal risk is not exceeded. Correction factors are determined for non-uniform population distributions around the establishment, non-continuous residence times and alternative societal risk limits. Using these methods allows decision-making without the necessity of repeating quantified risk analyses for each alternative proposal.
Rheology and Bulk Flow Characteristics of a Thixotropic Fluid in Turbulent Pipe Flow
Authors: Pereira Américo S. , Pinho Fernando T.
Published: December 2021

In this work, aqueous suspensions of 1% and 1.5% by weight Laponite and a blend of 0.5%/ 0.07% Laponite/ CMC are investigated in terms of their rheology and their hydrodynamic behaviour in a pipe flow.

The viscometric viscosity was measured for all fluids, but due to the fluid thixotropy a flow-equilibrium procedure was adopted. All fluids were viscoplastic and the measurement of the yield stress was carried out by direct and indirect methods. The yield stress values were of 0.93, 2.13 and 3.4 Pa for the 1% Laponite, 0.5/0.07% Laponite/CMC blend and 1.5% Laponite suspensions, respectively. The oscillatory tests shows that the 1% Laponite suspension is inelastic but the other two suspensions exhibit some elasticity.

All solutions exhibited drag reduction with the difference between the total and shear-thinning drag reductions (DR – DRv) of the order of 10% to 20% for both pure laponite suspensions but increasing to 25 to 30% for the laponite-polymer blend. For the pure clay suspensions, and based also on evidence from the literature, it was speculated that DR – DRv, could be due to a strong decrease of the viscosity associated with a turbulence-induced destruction of the internal structure plus a second mechanism more akin to that found with drag reducing polymer solutions.
PRECO: A Novel Means of Determining the Pressure Coefficient of Viscosity Using a Modified Capillary Extrusion Rheometer
Authors: Carter Roy E. , Privett Grant J. , Allen Crispin R. G. , Brown Chris S. , Chakravorty Sekhar , Rides Martin
Published: December 2021

The viscosity of some polymeric fluids increases significantly when measured at pressures above atmospheric pressure. If this phenomenon is not taken into account for example when using CAD programmes to design injection moulding tools, then consequences such as short mouldings and inferior mechanical properties may be obtained, resulting in a high scrap rate and the need for expensive tool modifications.

A simple new method of measuring the pressure coefficient of viscosity using a tandem-die technique with a modified capillary extrusion rheometer is described.
Quasi-Static Capillary Impregnation of a Porous Fiber Bed
Authors: He J. , Altan M. C.
Published: December 2021

The impregnation of a fiber bed by capillary forces in a gravity field is analyzed. Fiber bed is modeled as infinitely long, parallel cylinders arranged in a hexagonal pattern. Quasi-static creeping flow equation is used to obtain the fluid front location and shape during impregnation of the fiber bed. The fluid front motion during impregnation are presented for different Bond numbers, contact angles and fiber volume fractions. It is found that impregnation velocity is significantly affected by contact angle and fiber volume fraction at the initial stages of impregnation. The influence of the Bond number becomes more significant when the fluid front approaches its final position where gravity balances capillary forces. The permeability of the fiber bed is also obtained from the time-dependent motion of the fluid front. The permeability predictions agree with the published experimental result and with those obtained by using lubrication theory.
Dilute Polymers and Coherent Structures in Wall Turbulence
Authors: De Angelis Elisabetta , Casciola Carlo M. , Piva Renzo
Published: December 2021

Both numerical and experimental data confirm that the introduction of dilute polymers in a turbulent flow changes some mean characteristics of the flow: the wall drag can decrease up to 40% while the average spacing among streaks can even double. Actually a link exists between streaks spacing and mean velocity gradient at the wall.

In such viscoelastic flows the wall turbulence regeneration is still influenced by the mean shear and by the interaction of the coherent structures even if they appear more ordered and larger with respect to Newtonian flows. These phenomena, which have been repeatedly observed since the findings of Toms, would require a better understanding of the mechanisms that locally induce this behaviour. The analysis of data from direct numerical simulation with FENE-P model for the polymers, seems to suggest, as the main effect of the viscoelastic reaction, a stabilizing action on the low speed streaks and a related decrease in the population of the wall layer coherent structures. The decreased level of activity induces relevant changes in the scales of the turbulence and originates the observed drag reduction.
Forced Convection in Channels With Viscous Dissipation for the Simplified Phan-Thien–Tanner Fluid
Authors: Pinho Fernando T. , Oliveira Paulo J.
Published: December 2021

The temperature distribution and the heat transfer coefficient for forced convection in laminar channel flow with viscous dissipation are derived for the simplified Phan-Thien–Tanner fluid with a linear stress coefficient. Fully-developed thermal and hydrodynamic conditions are assumed with a constant wall heat flux imposed on both walls. As a simplifying assumption the effect of temperature variations on the material parameters is neglected.

The results show that, in all circumstances, ie for wall heating and cooling and regardless of the magnitude of viscous dissipation, an increase of fluid elasticity and/or an increase of ε results in enhanced heat transfer. As a beneficial consequence the range of temperatures inside the duct is reduced. There is also a coupling effect of viscous dissipation and fluid elasticity: heat transfer enhancement by fluid elasticity is stronger in the presence of a more intense viscous dissipation. For positive wall heat fluxes, ie wall cooling, whenever the Brinkman number exceeds a threshold value, the viscous dissipation overcomes the wall cooling effect and the fluid heats up longitudinally. Fluid elasticity delays this critical Brinkman number to higher values.
Non-Reflective Boundary Conditions for a Consistent Model of Axisymmetric Electro-Magneto-Hydrodynamic Flows
Authors: Ko Hyung-Jong , Dulikravich George S.
Published: December 2021

In this paper, the non-reflective boundary conditions for the axisymmetric electro-magneto-hydrodynamic (EMHD) flows have been derived. The electro-magneto-hydrodynamics (EMHD) deals with the motion of electrically conducting incompressible fluids under the combined influence of externally applied and internally generated electric and magnetic fields. A consistent axisymmetric EMHD flow model with linear constitutive relations and artificial compressibility was expressed in cylindrical coordinates. After some simplifications, the resulting EMHD system comprised of modified Maxwell equations for the electro-magnetic fields and modified Navier-Stokes equations for the flow-field, was transformed to a characteristic form, and the non-reflective boundary conditions were derived. The results show the strong mutual interactions between the axisymmetric flow-field and the electro-magnetic fields. The limiting cases, including the conventional axisymmetric flow-field model and the electro-magnetic field model in vacuum, are recoverable from these results.
Effect of Particle Size and Distribution on the Viscosity of a Model Electrorheological (ER) Fluid
Authors: Chen Ying , Conrad Hans
Published: December 2021

The zero-field viscosity of model ER fluids consisting of glass beads in silicone oil was determined as a function of average particles size (D¯ = 3–75 μm), volume fraction (ϕ = 0.1–0.3) and bimodal mixtures of two sizes. The viscosity increased with ϕ and decreased with D¯. The viscosity of the suspensions ηs in all cases was described reasonably well by the following relation:ηs=ηs,o(ϕ)+b(ϕ)D¯2/D¯3 where ηs,o(ϕ) and b(ϕ) are constants which increase with ϕ. Reasonable agreement with the Mooney crowding equation occurred for the single size particles, giving for the crowding factor k = 1.3 + 1.5/D¯. For ϕ < 0.2 the viscosity of the bimodal mixtures could be described by a modification of the Mooney equationηsηo=exp(2.76ϕ11-k1ϕ1)exp(2.76ϕ21-k2ϕ2) where ηo is the viscosity of the silicone oil, ϕi the volume fraction of each particle size Di and ki the normal crowding factor for that size. At ϕ = 0.3 the measured values of ηs for the bimodal mixtures became appreciably larger than those calculated from the modified equation. The decrease in particle size leads to both an increase in surface area of the particles per unit volume of the suspension and to a decrease in spacing (crowding); both factors probably contributed to the increase in ηs.
Velocity, Potential, and Temperature Distributions in Molten Metals During Electromagnetic Stirring: Part I — Experimental Measurements
Authors: Bakhtiyarov Sayavur I. , Overfelt Ruel A. , Meir Amnon J. , Schmidt Paul G.
Published: December 2021

An experimental technique has been developed to measure the local velocity in molten metals. Couette flow of liquid aluminum, lead, tin and low melting alloy in cylindrical container was chosen for calibration of the experimental technique and the magnetic probe. Velocity and temperature profiles for liquid aluminum rotating in cylindrical container at different angular velocities are obtained for two different values of the depth. We determined that the velocity values increase with magnetic induction, and the relationship between the normalized azimuthal velocity and the magnetic induction can be expressed by quadratic function.
Flow in a Hele-Shaw Cell With Restrictions Above and Below the Entrance
Authors: Clark Peter E. , Zhu Qinsheng
Published: December 2021

The question of how slurries are transported and placed during hydraulic fracturing treatments was first broached by Kern et al. (Kern, Perkins et al., 1959), in 1959. In the early 90’s, Cleary and Fonseca (Cleary and Fonseca Jr., 1992) suggested that gravity acting on the slurry as a whole would cause the heavier slurry to fall through the fluid in the fracture and that this would dominate individual particle settling in determining the final distribution of proppant. This sparked a healthy debate concerning the nature of flow into a fracture and brought about a renewed interest in fracture fluid flow. A fracture is analogous to a Hele-Shaw flow cell. However, most experimental studies that deal with flow in fractures assume that the fracture is globally uniform with constant height and width. This is hardly the case in real fractures. Downhole cameras have revealed that fractures are anything but uniform. There are wide and narrow regions coupled with abrupt changes in uniformity. In addition, pressure analysis indicates that, in many cases, the height of the fracture changes during most of the treatment. These all serve to disturb not only bulk slurry flow but also the settling behavior of the particles that make up the slurry. While it is difficult to simulate the growth of a fracture experimentally, width non-uniformities can be simulated and their effect on slurry flow determined. A method that can be used to predict the behavior of the slurry in the presence of a non-uniformity will be presented. These techniques can be incorporated into computer models to improve predictive capabilities.
Temperature Distribution in a VLSI Chip due to Dynamic Power Density
Authors: Jahanian Shahriar , Delalic Z. J.
Published: December 2021

High speed computation is driving VLSI custom chips into smaller micron sizes and scale down power supplies. To accomplish very high speed, industry is developing shut down methods and short channel devices. Going below 0.5 micron technology speed is accomplished but hot spots, power density, and die failure are increased. Failure accumulated knowledge has not yet established a classic theory. In this paper, the STEPS method is used to determine the power dissipation in a CMOS circuit The experiment demonstrates dynamic power dissipation and assumes that static power dissipation is negligible in the CMOS devices. Each node is examined individually as signals are propagated through the chip. At each node the power distribution in the form of heat is determined.
Stress Analysis and Strength Evaluation of Single-Lap Adhesive Joints Combining Rivets Subjected to External Bending Moments
Authors: Liu Jiemin , Sawa Toshiyuki
Published: December 2021

Stress analysis and strength evaluation of single-lap adhesive joints combining rivets subjected to external bending moments are conducted by three-dimensional finite element analysis (FEA). In this analysis, the effects of the ratio of Young’s moduli of the rivets to that of the adherends, the initial tightening force produced in the rivets, the adhesive layers between the rivet heads and the adherends, and the positions of the rivets on the stress distributions at the interfaces between the adherends and the adhesives are examined. The rupture process of the single-lap adhesive joint combining rivets is demonstrated. The strength of single-lap adhesive joints combining rivets is evaluated by the maximum principal strain criterion using the maximum principal strain at the adhesive interfaces. The FEA results show that the failure of single-lap adhesive joints and single-lap adhesive joints combining rivets with thinner adherends are due to large elasto-plastic deformation of the adherends. For single-lap adhesive joints of thick adherends, the rupture is initiated from the edge of the adhesive interface. Experiments to measure the strength of single-lap adhesive joints, single-lap riveted joint and single-lap adhesive joints combining rivets were carried out. The failure types of single-lap adhesive joints and single-lap adhesive joints combining rivets obtained from the experiments coincide with the FEA results. The experimental results also show that the failure of single-lap riveted joints with thinner adherends is due to large plastic deformation of the adherends. However, for single-lap riveted joints with thick adherends it is shown that their failure is caused by the rupture of the rivets. Finally, it is found that fitted rivets in single-lap adhesive joints of thick adherends can enhance the joint strength.
The Strength of Joints Combining Adhesives With Bolts (Case Where Adherends Are Pipe Flanges of Which the Interfaces Are Bonded Partially)
Authors: Yoneno Masahiro , Sawa Toshiyuki , Ishihara Tomoya , Kawamura Hiroshi
Published: December 2021

The stresses of joints combining the bonding force of adhesives with the clamping force of bolts is analyzed using axisymmetrical theory of elasticity and FEM, when an internal pressure is applied to the combination joint in which two pipe flanges are clamped together by bolts and nuts with an initial clamping force after being joined by anaerobic sealant. The anaerobic sealant is applied at the interfaces partially instead of formed gaskets in pipe flange connections. In the numerical calculations, the effect of the bonding area and position and Young’s modulus of sealant (epoxy adhesive) on the contact stress at the interfaces are clarified. In addition, using the interface stress distribution, the strength of the combination joint is predicted. Experiments are performed and the analytical results are consistent with the experimental results concerning the variation in axial bolt force and the strength of combination joints. It is found that the joint strength changes as the bolt pitch circle diameter, the bonding position and the area, the initial clamping force and the adhesive material properties change. Furthermore, it is seen that the sealing performance of such combination joints in which the interfaces are bonded partially is improved over that of pipe flange connection with metallic gaskets.
Selective Use of Rubber Toughening to Optimize Lap-Joint Strength
Authors: Sancaktar Erol , Kumar Sumeet
Published: December 2021

This paper introduces a novel approach to increasing the lap joint strength, different than the traditional methods of either increasing the lap joint area or changing the joint geometry. This is accomplished by the selective use of rubber toughening in epoxy to optimize lap joint strength. This was accomplished in three stages, in the first stage an adduct was prepared, this was used to make bulk tensile specimens to calculate the bulk properties for various concentrations of rubber, i.e. 0, 10 & 20 parts per hundred parts of resin (epoxy). In the second stage finite element models were developed using the bulk properties previously obtained. Interfacial stresses were used to access the trends obtained by the selective use of rubber toughening at different location of the overlap in different configurations. The modeling of adhesive joints was done using ALGOR 2-D, linear and nonlinear Finite Element Analyses (FEA). In the third stage, conducting tensile shear tests on the lap joints validated the trends from the finite element models.

Finite element modeling and meshing of the lap joints having 25.4 mm and 50.8 mm adhesive overlap lengths were completed. Different configurations of rubber toughened and untoughened adhesive were tried in these two overlaps. The validation was done by tensile lap joint tests conducted on an Instron mechanical tester coupled with an extensometer.

Comparable strengths were obtained for completely toughened overlap and the configuration where only the edges of the adhesive overlap were toughened and the region in-between was untoughened. Also, the nonlinear FEA was shown to represent the experimental results more closely than the linear approach.