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Proceedings Papers
Proc. ASME. AJKFluids2019, Volume 5: Multiphase Flow, V005T05A083, July 28–August 1, 2019
Paper No: AJKFluids2019-4943
Abstract
In recent years, Lattice Boltzmann Methods (LBM’s) have emerged as a popular class of paradigms for the simulation of multiphase flows. These methods rely on discretized Boltzmann equations to represent the individual multiphase species. Among LBM’s advantages is its ability to explicitly account for interfacial physics and its local streaming/collision operations which make it ideally suited for parallelization. However, one drawback of LBM is in the simulation of incompressible multiphase flow, whereby the density should remain constant along material characteristics. Because LBM uses a state equation to relate pressure and density, incompressibility cannot be enforced directly. This is true even for incompressible single-phase LBM calculations, in which a finite density drop is needed to drive through the flow. This is also the case for compressible Navier-Stokes algorithms when applied to low Mach number flow. To mitigate compressibility effects, LBM can be used in low Mach regimes which should keep material density variation small. In this work, we demonstrate that the assumption of low Mach number is not sufficient in multiphase internal flows. In such flows, in the absence of a Pressure Poisson constraint to enforce incompressibility, LBM predicts a compressible solution whereby a density gradient must develop to conserve mass. Imposition of inflow/outflow boundary conditions or a mean body force can ensure that mass is conserved globally, thereby quelling density variation. The primary numerical problem we study is the deformation of a liquid droplet immersed in another fluid. Though LBM is not typically conducted with a pressure Poisson equation, we incorporate one in this work and demonstrate that its inclusion can significantly lower the density variation in view of maintaining an incompressible flow.
Journal Articles
Journal:
Journal of Fluids Engineering
Article Type: Research-Article
J. Fluids Eng. July 2018, 140(7): 071103.
Paper No: FE-17-1465
Published Online: March 16, 2018
Abstract
Studies were made to understand the flow features around an open cavity at Mach 2.0 corresponding to Re = 0.55 × 10 6 based on the cavity depth. Experiments were carried out using a blowdown type supersonic wind tunnel having a test section size of 50 mm × 100 mm. Oil flow and schlieren flow visualization were made to understand the steady flow features inside the cavity. Unsteady pressures were measured at several locations to obtain the fluctuating flow field details and the pressure spectrum. Impinging wall modifications of the cavity were made with an objective to reduce the Rossiter's mode frequencies and its amplitude. Partial ramping of the impinging wall with variations in height and angles were made. With adoption of a specific combination of the impinging wall height and angle, the first two modes of the multiple tonal characteristics could be reduced significantly. The present adopted method could result in 74% reduction of root-mean-square (RMS) pressure and a noise reduction of 11 dB.
Journal Articles
Article Type: Technical Briefs
J. Dyn. Sys., Meas., Control. March 2015, 137(3): 034504.
Paper No: DS-14-1058
Published Online: October 21, 2014
Abstract
This technical brief summarizes and extends our recently introduced control framework for stochastically allocating a swarm of robots among boundaries of circular regions. As in the previous work, a macroscopic model of the swarm population dynamics is used to synthesize robot control policies that establish and maintain stable predictable team sizes around region boundaries. However, this extension shows that the control strategy can be implemented with no robot-to-robot communication. Moreover, target team sizes can vary across different types of regions, where a region's type is a subjective characteristic that only needs to be detectable by each individual robot. Thus, regions of one type may have a higher equilibrium team size than regions of another type. In other work that predicts and controls stochastic swarm behaviors using macroscopic models, the equilibrium allocations of the swarm are sensitive to changes in the mean robot encounter rates with objects in the environment. Thus, in those works, as the swarm density or number of objects changes, the control policies on each robot must be retuned to achieve the desired allocations. However, our approach is insensitive to changes in encounter rate and therefore requires no retuning as the environment changes. In this extension, we validate these claims and show how the convergence rate to the target equilibrium allocations can be controlled in swarms with a sufficiently large free-robot population. Furthermore, we demonstrate how our framework can be used to experimentally measure the rates of robot encounters with occupied and unoccupied sections of region boundaries. Thus, our method can be viewed both as an encounter-rate-independent allocation strategy as well as a tool for accurately measuring encounter rates when using other swarm control strategies that depend on them.
Proceedings Papers
Proc. ASME. InterPACK2013, Volume 1: Advanced Packaging; Emerging Technologies; Modeling and Simulation; Multi-Physics Based Reliability; MEMS and NEMS; Materials and Processes, V001T07A005, July 16–18, 2013
Paper No: IPACK2013-73137
Abstract
During service and/or storage, Sn-Ag-Cu (SAC) solder alloys are subjected to temperatures ranging from 0.4 to 0.8 Tm (where Tm is the melting temperature of SAC alloys), making them highly prone to significant microstructural coarsening. The microstructures of these low melting point alloys continuously evolve during service. This results in evolution of creep properties of the joint over time, thereby influencing the long-term reliability of microelectronic packages. Here, we study microstructure evolution and creep behavior of two Sn-Ag-Cu (SAC) alloys, namely Sn-3.0Ag-0.5Cu and Sn-1.0Cu-0.5Cu, isothermally aged at 150°C for various lengths of time. Creep behavior of the two SAC solders after different aging durations was systematically studied using impression creep technique. The key microstructural features that evolve during aging are Ag 3 Sn particle size and inter-particle spacing. Creep results indicate that the creep rate increases considerably with increasing inter-particle spacing although the creep stress exponent and creep activation energy are independent of the aging history.
Journal Articles
Journal:
Journal of Heat Transfer
Article Type: Technical Briefs
J. Heat Transfer. December 2013, 135(12): 124501.
Paper No: HT-08-1030
Published Online: September 27, 2013
Abstract
A method to solve the radiative transfer equation (RTE) for absorbing-emitting and/or scattering media for 2-D and axisymmetric geometries using a general 3-D solver with a special treatment of the boundary condition in the third direction is presented. It allows a choice of first- or second- order schemes and can be used with non-orthogonal hexahedral grids for complex domains. Two-dimensional or axisymmetric problems are treated as different special cases of a three-dimensional problem. The method is tested on axisymmetric problems with absorbing-emitting and/or scattering media and on a 2D planar problem with a transparent medium and validated by comparisons with benchmark solutions.
Journal Articles
Journal:
Journal of Solar Energy Engineering
Article Type: Research-Article
J. Sol. Energy Eng. August 2013, 135(3): 031009.
Paper No: SOL-11-1254
Published Online: April 29, 2013
Abstract
This paper presents a mathematical model for drying agricultural produce using a solar dryer capable of oscillating its bed while kept at an inclined position with respect to vertical. A model of the solar dryer with double-pass flat plate collector and an oscillating-bed has been fabricated and tested for drying agricultural produce (sunflower seeds). The model can predict the change in the absolute humidity of air across the bed, the temperature of the air, the moisture content, and the dryer thermal efficiency. Sunflower seeds were dried on a physical model of the solar dryer with its bed tilted at different angles and oscillated at different frequencies. The predicted and the experimental results are in good agreement. The average error and standard deviation for the absolute humidity of air across the bed is 1.74 and 1.55%, the exit temperature of air leaving the bed is 1.11and 1.21%, and the dryer thermal efficiency is 0.78 and 1.33%, respectively.
Journal Articles
Article Type: Research Papers
J. Thermal Sci. Eng. Appl. March 2012, 4(1): 011006.
Published Online: March 19, 2012
Abstract
In many industrial casting processes, knowledge of the solid fraction evolution during the solidification process is a key factor in determining the process design parameters such as cooling rate and stirring intensity, and in estimating the total solidification time. In the present work, a new method for estimating solid fraction is presented, which is based on calorimetric principles. In this method, the cooling curve data at each point in the melt, along with the thermal boundary conditions, are used to perform energy balance in the mould, from which solid fraction generation during any time interval can be estimated. This method is applied to the case of a rheocasting process, in which Al–Si alloy (A356 alloy) is solidified by stirring in a cylindrical mould placed in the annulus of a linear electromagnetic stirrer. The metal in the mould is simultaneously cooled and stirred to produce a cylindrical billet with nondendritic globular microstructure. Temperature is measured at key locations in the mould to assess the various heat exchange processes prevalent in the mould and to monitor the solidification rate. The results obtained by energy balance method are compared with those by the conventional procedure of calculating solid fraction using the Scheil’s equation.
Proceedings Papers
Proc. ASME. InterPACK2011, ASME 2011 Pacific Rim Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Systems, MEMS and NEMS: Volume 2, 763-771, July 6–8, 2011
Paper No: IPACK2011-52220
Abstract
During service, micro-cracks form inside solder joints, making a microelectronic package prone to failure particularly during a drop. Hence, the understanding of the fracture behavior of solder joints under drop conditions, synonymously at high strain rates and in mixed mode, is critically important. This study reports: (i) the effects of processing conditions (reflow parameters and aging) on the microstructure and fracture behavior of Sn-3.8%Ag-0.7%Cu (SAC387) solder joints attached to Cu substrates, and (ii) the effects of the loading conditions (strain rate and loading angle) on the fracture toughness of these joints, especially at high strain rates. A methodology for calculating critical energy release rate, G C , was employed to quantify the fracture toughness of the joints. Two parameters, (i) effective thickness of the interfacial intermetallic compounds (IMC) layer, which is proportional to the product of the thickness and the roughness of the IMC layer, and (ii) yield strength of the solder, which depends on the solder microstructure and the loading rate, were identified as the dominant quantities affecting the fracture behavior of the solder joints. The fracture toughness of the solder joint decreased with an increase in the effective thickness of the IMC layer and the yield strength of the solder. A 2-dimensional fracture mechanism map with the effective thickness of the IMC layer and the yield strength of the solder as two axes and the fracture toughness as well as the fraction of different fracture paths as contour-lines was prepared. Trends in the fracture toughness of the solder joints and their correlation with the fracture modes are explained using the fracture mechanism map.
Proceedings Papers
Proc. ASME. InterPACK2011, ASME 2011 Pacific Rim Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Systems, MEMS and NEMS: Volume 2, 773-780, July 6–8, 2011
Paper No: IPACK2011-52221
Abstract
In this study, a novel architecture composed of uniformly distributed high melting phase (HMP, e.g. Cu) in a low melting phase (LMP, e.g. In) matrix, which can be produced via liquid phase sintering (LPS), is proposed to produce next generation thermal interface materials (TIMs) and interconnect (IC) materials. The LMP determines the shear compliance of these composites whereas the HMP determines its thermal and electrical conductivities. The volume fraction of In was optimized to produce a Cu-In solder with suitable mechanical, electrical and thermal properties for TIM and IC applications. Since, Cu and In react to form several Cu-In intermetallic compounds (IMCs), which may deteriorate the long-term performance of these solders, interfacial-layers of Au and Al 2 O 3 were applied on Cu to further improve the performance of the Cu-In solders. The effect of interfacial-layers on the reaction between Cu and In, during sintering at 160°C and during aging at 125°C, was studied and its impact on the mechanical, thermal and electrical properties was evaluated. Au interfacial layer (50∼200nm) quickly reacted with In to form AuIn 2 IMC, which acted as a tenacious diffusion-barrier and slowed down the reactions between Cu and In. 8-monolayer thick Al 2 O 3 did not react with either Cu or In and inhibited reactions between Cu and In. During short-time sintering, the effect of interfacial layer on the thicknesses of IMCs was insignificant to affect the yield strength of the as-sintered composites. However, IMC layer thickened rapidly in the Cu-In composites without an interfacial-layer, which led to a drastic decrease in the volume fraction of unreacted In leading to an increase in the yield strength of the solder. On the other hand, the interfacial-layers effectively suppressed the growth of IMCs during aging and hence the yield strength of such composites increased at slower rates. Since, the IMCs formed at the interface radically affect the contact resistance, significant differences in the thermal and electrical conductivities were recorded for the solders with different interfacial-layers.
Proceedings Papers
Proc. ASME. InterPACK2009, ASME 2009 InterPACK Conference, Volume 1, 385-387, July 19–23, 2009
Paper No: InterPACK2009-89194
Abstract
This paper reports on a new paradigm for highly flexible solder design, proffering high electrical and thermal conductivity, in conjunction with good mechanical compliance, via a novel Liquid Phase Sintering (LPS) approach. The new LPS solders comprise a high melting point phase HMP (e.g., Cu or Sn) with a small amount of a low melting-point phase LMP (e.g., In) at grain boundaries, such that different properties can be controlled by different constituents. In general, conductivity is dominated by the majority HMP constituent, while deformation is controlled by the minority, LMP grain boundary constituent. The LPS solders are suitable for both thermal interface material (TIM) and interconnect applications. As the application space for solders shifts in the future, and requirements for new property-sets emerge, the flexibility of the LPS solder approach will allow integration of different materials into new LPS solder-systems.
Proceedings Papers
Proc. ASME. InterPACK2009, ASME 2009 InterPACK Conference, Volume 1, 389-396, July 19–23, 2009
Paper No: InterPACK2009-89205
Abstract
Electronic packages in mobile devices are often subjected to drops, leading to impact loading. Since solder joints, which serve as mechanical and electrical interconnects in a package, are particularly prone to failure during a drop, the fracture behavior of solders at high strain rates is a critical design parameter for building robust packages. Here we report on a methodology for measuring mixed-mode fracture toughness of Sn3.5Ag0.7Ag (SAC387) solder joints under dynamic loading conditions (at strain rates up to 100s −1 ), and use this method to investigate the role of solder microstructure and interfacial intermetallic compound (IMC) layer thickness on the joint fracture toughness at different mode-mixities and strain rates. Modified compact mixed mode (CMM) samples with adhesive solder joints between Cu plates and a thin film interfacial starter crack were used for the measurements. The interfacial IMC layer thickness was adjusted by controlling the dwell time during reflow, while the solder microstructure was controlled via the post-reflow cooling rate and subsequent thermal aging. The critical strain energy release rate (G c ) was measured as a function of these microstructural and loading variables, and these data were correlated with the associated crack path, details of which were elicited through fractography as well as crack-profile observations. The crack profile studies were based on samples with double interfacial starter cracks, one of which propagated only partially. Associated with the alteration of the joint microstructure, transitions in the fracture behavior were noted. In all cases, the cracks remained confined to the interfacial region, although the details of the crack propagation path and its interaction with interfacial IMCs, the adjacent solder and the pad surface finish varied significantly. Fracture toughness decreased with an increase in the strain rate and decreased with increasing mode-mixity. A thicker/coarser interfacial IMC layer (due to high dwell times) decreased toughness, while coarser solder microstructures (due to slow cooling during reflow or post-reflow aging) increased toughness. Correlations between joint microstructure and the observed deformation and fracture mechanisms will be highlighted, and a qualitative model based explanation for the inter-play between solder and IMC, and the associated interfaces will be presented.
Proceedings Papers
R. Vijayashree, R. Veerasamy, Sudheer Patri, S. Suresh Kumar, S. C. S. P. Kumar Krovvidi, S. K. Dash, T. Logaiyan, N. Ravichandran, S. Chandramouli, K. K. Rajan, Indranil Banerjee, R. Dhanasekaran
Proc. ASME. ICONE17, Volume 3: Thermal Hydraulics; Current Advanced Reactors: Plant Design, Construction, Workforce and Public Acceptance, 979-986, July 12–16, 2009
Paper No: ICONE17-75853
Abstract
PFBR, India’s first commercial fast breeder reactor employing fast fission is a challenging project from technological point of view to meet the energy security of the country. It is currently under advanced stage of construction at Kalpakkam, India. PFBR is equipped with two independent, fast acting and diverse shutdown systems. A shutdown system comprises of sensors, logic circuits, drive mechanisms and neutron absorbing rods. The absorber rods of the second shutdown system of PFBR are called as Diverse Safety rods (DSR) and their drive mechanisms are called as Diverse Safety Rod Drive Mechanisms (DSRDM). DSR are normally parked above active core by DSRDM. On receiving scram signal, Electromagnet of DSRDM is de-energised and it facilitates fast shutdown of the reactor by dropping the DSR in to the active core. For the prototype development of DSR and DSRDM, three phases of testing namely individual component testing, integrated functional testing in room temperature and endurance testing at high temperature sodium were planned and are being done. The electromagnet of DSRDM operates at high temperature sodium environment continuously. It has been separately tested at room temperature, in furnace and in sodium. Specimens simulating the contact conditions between Electromagnet and armature of DSR have been tested to rule out self welding possibility. The Dashpot provided to decelerate the DSR at the end of its free fall has been initially tested in water and then in sodium. The prototype of DSR has been tested in flowing water to determine the pressure drop and drop time. The functional testing of the integrated prototype DSRDM and DSR in aligned and misaligned conditions in air/water has been completed. The performance testing of the integrated system in sodium has been done in three campaigns. Based on the performance testing in the first two campaigns of sodium testing, design modifications and manufacturing quality improvement were done. Methods of drop time measurement based on ultrasonics and acoustics were also developed along with the first two campaigns. During the third campaign of sodium testing, the performance of the system has been verified with 30 mm misalignment at various temperatures. The third campaign has qualified the system for 10 years of operation in reactor. This paper describes the test setup for all the above mentioned testing and also gives typical test results.
Journal Articles
Journal:
Journal of Heat Transfer
Article Type: Research Papers
J. Heat Transfer. February 2010, 132(2): 023501.
Published Online: November 30, 2009
Abstract
This article presents a numerical simulation of combined radiation and natural convection in a three-dimensional differentially heated rectangular cavity with two opposite side walls kept at a temperature ratio T h / T c = 2.0 and T c = 500 K , with others walls insulated. A non-Boussinesq variable density approach is used to incorporate density changes due to temperature variation. The Navier–Stokes (NSE), temperature, as well as the radiative transfer (RTE) equations are solved numerically by a finite volume method, with constant thermophysical fluid properties (except density) for Rayleigh number Ra = 10 5 and Prandtl number Pr = 0.71 . The convective, radiative, and total heat transfer on the isothermal and adiabatic walls is studied along with the flow phenomena. The results reveal an extraordinarily complex flow field, wherein, along with the main flow, many secondary flow regions and singular points exist at the different planes and are affected by the optical properties of the fluid. The heat transfer decreases with increase in optical thickness and the pure convection Nusselt number is approached as the optical thickness τ > 100 , but with substantially different velocity field. The wall emissivity has a strong influence on the heat transfer but the scattering albedo does not.
Proceedings Papers
Proc. ASME. IJTC2008, STLE/ASME 2008 International Joint Tribology Conference, 275-279, October 20–22, 2008
Paper No: IJTC2008-71107
Abstract
The prediction of elastohydrodynamic lubrication (EHL) film thickness requires knowledge of the lubricant properties. Today, in many instances, the properties have been obtained from a measurement of the central film thickness in an optical EHL point contact simulator and the assumption of a classical Newtonian film thickness formula. This technique has the practical advantage of using an effective pressure-viscosity coefficient which compensates for shear-thinning. We have shown by a perturbation analysis and by a full EHL numerical solution that the practice of extrapolating from a laboratory scale measurement of film thickness to the film thickness of an operating contact within a real machine may substantially overestimate the film thickness in the real machine if the machine scale is smaller and the lubricant is shear-thinning in the inlet zone.
Journal Articles
Journal:
Journal of Tribology
Article Type: Research Papers
J. Tribol. October 2008, 130(4): 041504.
Published Online: August 5, 2008
Abstract
The estimation or prediction of elastohydrodynamic lubrication (EHL) film thickness requires knowledge of the lubricant properties. Today, in many instances, the lubricant properties have been obtained from a measurement of the central film thickness and the assumption of a classical Newtonian film-thickness formula. This technique has the practical advantage of using an effective pressure-viscosity coefficient, which compensates for shear-thinning. We have shown by a perturbation analysis of limiting cases for fluid with Carreau rheology (represented by Newtonian and power fluid) and by a full EHL numerical solution for Carreau fluid that the practice of extrapolating from a laboratory scale measurement of film thickness to the film thickness of an operating contact may substantially overestimate the film thickness in the real machine if the machine scale is smaller and the lubricant is shear-thinning within the inlet zone. The intention here is to show that errors result from extrapolation of Newtonian formulas to different scale and not to provide advice regarding quantitative engineering calculations.
Proceedings Papers
Proc. ASME. IMECE2002, Heat Transfer, Volume 3, 163-169, November 17–22, 2002
Paper No: IMECE2002-33496
Abstract
In this paper, we investigate the effects of laminar double-diffusive natural convection on directional solidification of binary fluids when cooled and solidified from the top. The study is performed using aqueous ammonium chloride solution as the model fluid. The experiments are performed with an initial concentration of ammonium chloride is less than the eutectic composition, leading to an aiding double-diffusive convection. In this case, solidification leads to the formation of a diffused matrix of dendritic crystals (mushy region) separating the pure solid and liquid regions. Below the two-phase mushy region, Rayleigh-Benard type of cellular convective motions are observed. The cellular motions, which are caused by thermal buoyancy, die once the thickness of the liquid layer falls below a critical value. The features of convective transport are visualised using a sheet of laser light scattered through neutrally buoyant glass particles seeded in the solution. Numerical simulations are also performed, and the agreement with experimental results is found to be good.
Journal Articles
Article Type: Technical Briefs
J. Manuf. Sci. Eng. May 1990, 112(2): 194–197.
Published Online: May 1, 1990
Abstract
Reports have indicated the poor performance of the conventional type of cutting tools during machining of composites. In this paper electrochemical spark machining (ECSM) for the cutting and drilling of holes in the composites is being proposed. The feasibility of using ECSM for composites was first ascertained. Then, kevlar-fiber-epoxy and glass-fiber-epoxy composites as work material, copper as tool material, and an aqueous solution of NaCl as electrolyte were used. It has been concluded that the ECSM is a viable solution for cutting of Fiber Reinforced Plastics (FRP). For achieving desired accuracy, surface finish, and economics of the process, the machining parameters should be optimized.
Journal Articles
Journal:
Journal of Fluids Engineering
Article Type: Discussions
J. Fluids Eng. June 1969, 91(2): 238.
Published Online: June 1, 1969