Faculty of Applied Science and Engineering Office of the Dean

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Dynamical flow characterization of transitional and chaotic regimes in converging-diverging channels
(Cambridge University Press, 1996-03) Guzmán, A. M. ; Amon, C. H.
Numerical investigation of laminar, transitional and chaotic flows in convergingdiverging channels are performed by direct numerical simulations in the Reynolds number range 10 < Re < 850. The temporal flow evolution and the onset of turbulence are investigated by combining classical fluid dynamics representations with dynamical system flow characterizations. Modern dynamical system techniques such as timedelay reconstructions of pseudophase spaces, autocorrelation functions, fractal dimensions and Eulerian Lyapunov exponents are used for the dynamical flow characterization of laminar, transitional and chaotic flow regimes. As a consequence of these flow characterizations, it is verified that the transitional flow evolves through intermediate states of periodicity, two-frequency quasi-periodicity, frequency-locking periodicity, and multiple-frequency quasi-periodicity before reaching a non-periodic unpredictable behaviour corresponding to low-dimensional deterministic chaos. Qualitative and quantitative differences in Eulerian dynamical flow parameters are identified to determine the predictability of transitional flows and to characterize chaotic, weak turbulent flows in converging-diverging channels. Autocorrelation functions, pseudophase space representations and Poincare maps are used for the qualitative identification of chaotic flows, assertion of their unpredictable nature, and recognition of the topological structure of the attractors for different flow regimes. The predictability of transitional flows is determined by analysing the autocorrelation functions and by representing their attractors in the reconstructed pseudophase spaces. The transitional flow behaviour is examined by the geometric visualization of the evolution of the attractors and Poincare maps until the appearance of a strange attractor at the onset of chaos. Eulerian Lyapunov exponents and fractal dimensions are quantitative parameters to establish the onset of chaos, the persistence of chaotic flow behaviour, and the long-term persistent unpredictability of chaotic Eulerian flow regimes. Lastly, three-dimensional simulations for converging-diverging channel flow are performed to determine the effect of the spanwise direction on the route of transition to chaos.
Lagrangian chaos, Eulerian chaos, and mixing enhancement in converging–diverging channel flows
(American Institute of Physics, 1996-01) Amon, Cristina H. ; Guzmán, Amador M. ; Morel, Benoit
A study of Lagrangian chaos, Eulerian chaos, and mixing enhancement in converging–diverging channel flows, using spectral element direct numerical simulations, is presented. The time‐dependent, incompressible Navier–Stokes and continuity equations are solved for laminar, transitional, and chaotic flow regimes for 100≤Re≤850. Classical fluid dynamics representations and dynamical system techniques characterize Eulerian flows, whereas Lagrangian trajectories and finite‐time Lagrangian Lyapunov exponents identify Lagrangian chaotic flow regimes and quantify mixing enhancement. Classical representations demonstrate that the flow evolution to an aperiodic chaotic regime occurs through a sequence of instabilities, leading to three successive supercritical Hopf bifurcations. Poincaré sections and Eulerian Lyapunov exponent evaluations verify the first Hopf bifurcation at 125
Transition to chaos in converging–diverging channel flows: Ruelle–Takens–Newhouse scenario
(American Institute of Physics, 1994-02) Guzmán, A. M. ; Amon, C. H.
Direct numerical simulations of the transition process from laminar to chaotic flow in converging–diverging channels are presented. The chaotic flow regime is reached after a sequence of successive supercritical Hopf bifurcations to periodic, quasiperiodic, and chaotic self‐sustained flow regimes. The numerical experiments reveal three distinct bifurcations as the Reynolds number is increased, each adding a new fundamental frequency to the velocity spectrum. In addition, frequency‐locked periodic solutions with independent but synchronized periodic functions are obtained. A scenario similar to the Ruelle–Takens–Newhouse scenario of the onset of chaos is verified in this forced convective open system flow. The results are illustrated for different Reynolds numbers using time‐velocity histories, Fourier power spectra, and phase space trajectories. The global structure of the self‐sustained oscillatory flow for a periodic regime is also discussed.
A novel heat transfer model and its application to information storage systems
(American Institute of Physics, 2005-05) Ghai, Sartaj S. ; Kim, Woo Tae ; Escobar, Rodrigo A. ; Amon, Cristina H. ; Jhon, Myung S.
Lattice Boltzmann method (LBM) based on Boltzmann transport equation is developed to simulate the nanoscale heat transport in solids. The LBM can simulate both the metals and semiconductors by properly incorporating the energy carriers. We found that boundary scattering of phonons results in an anisotropic thermal transport in nanoscale solids. The electron-phonon coupling is introduced to accurately describe the thermal behavior of nanoscale confined solids. Our numerical tool will be suitable for simulating complex multiscale systems involving multiple energy carriers with different length and time scales, and is useful in magnetic recording technology when the thermal response plays a crucial role such as for reliability of the head-disk interface and the heat assisted magnetic recording systems.
Transient thermal modeling of a nanoscale hot spot in multilayered film
(American Institute of Physics, 2006-04) Ghai, Sartaj S. ; Kim, Woo Tae ; Amon, Cristina H. ; Jhon, Myung S.
A subcontinuum based lattice Boltzmann method is used to accurately model the transient thermal response of a nanoscale hot spot in solids. We developed the numerical scheme for the hot spot in a thin uniform material and extended the approach to study the multilayered materials. We observed that subcontinuum effects of high temperature rise become more prominent as the size of the film reduces to the scale of carrier mean free path. The thermal transport through a double layer is also considered, both for constant temperature difference across the double layer and hot-spot generation in one of the layers, using the diffusive mismatch scattering model at the interface. A finite temperature jump is observed at the interface whose magnitude depends upon the dimensions and properties of the material on the either side of the interface. The insight into the nanoscale thermal modeling, acquired in this work via a relatively simple model, will be critical for the design and operation of complex data storage and electronic systems, dealing with subcontinuum systems.
Drawing suspended polymer micro-/nanofibers using glass micropipettes
(American Institute of Physics, 2006-09) Nain, A. S. ; Wong, J. C. ; Amon, C. H. ; Sitti, M.
This letter proposes a method for fabricating suspended micro-/nanoscale polymer fibers continuously, in which polymeric micro-/nanofibers are formed by drawing and solidification of a viscous liquid polymer solution which is pumped through a glass micropipette. By controlling the drawing parameters, this method is demonstrated to form networks of suspended fibers having amorphous internal structure and uniform diameters from micrometers down to sub-50-nm for different molecular weights of polystyrene dissolved in xylene.
Proximal Probes Based Nanorobotic Drawing of Polymer Micro/Nanofibers
(IEEE, 2006-09) Nain, A. S. ; Amon, C. ; Sitti, M.
This paper proposes a nanorobotic fiber fabrication method which uses proximal probes to draw polymer fibers down to few hundred nanometers in diameter and several hundred micrometers in length. Using proximal probes such as Atomic Force Microscope (AFM) and Scanning Tunneling Microscope (STM) or glass micropipettes, liquid polymers dissolved in a solvent are drawn. During drawing, the solvent evaporates in real-time which solidifies the fiber. Controlling the drawn fibers trajectory and solidification in three-dimensions (3-D), suspended fibers, fiber cantilevers, custom 3-D fibers, and fiber networks, are proposed to be fabricated. Poly(methyl methacrylate) (PMMA) polymer dissolved in chlorobenzene is used to form a variety of suspended polymer fibers with diameters from few microns to 200nm. Fabrication of crossed and linear networks of fibers is also demonstrated. Viscoelastic modeling of polymer fiber drawing is realized using a finite element method to test the significance of the drawing speed and velocity profile on the extensional behavior of the drawn fiber. Since the mechanical properties of the drawn micro/nanofibers could vary from the bulk polymer material significantly, mechanical characterization of suspended fibers using an AFM and a Nanoindenter setup is proposed. Extending this technique to a variety of nonconductive and electroactive polymer fibers, many novel applications in micro/nanoscale sensors, actuators, fibrillar structures, and optical and electronic devices would become possible
Concurrent Design and Analysis of the Navigator Wearable Computer System: The Thermal Perspective
(IEEE, 1995-09) Amon, C. H. ; Nigen, J. S. ; Siewiorek, D. P. ; Smailagic, A. ; Stivoric, J.
This paper describes the concurrent design of a wearable computer, called the Navigator, developed and built at Carnegie Mellon University in a multidesigner, multidomain environment. The design effort for the Navigator involved nineteen designers, representing the disciplines of electrical engineering, industrial design, mechanical engineering, software engineering, and human-computer interaction. The concurrent design framework developed by the Navigator design team is outlined and the parallel activities within each design phase are described, including the synchronization and interactions among all design disciplines at the phase boundaries. The evolution of the interdisciplinary design of the Navigator wearable computer is presented, with particular emphasis placed upon the role of the thermal design group in the overall design process. Furthermore, the particular challenges associated with the concurrent thermal management of wearable computer systems are outlined
Bayesian surrogates for integrating numerical, analytical and experimental data: application to inverse heat transfer in wearable computers
(IEEE, 2000-03) Leoni, N. ; Amon, C.
Wearable computers are portable electronics worn on the body. The increasing thermal challenges facing these compact electronics systems have motivated new cooling strategies such as transient thermal management with thermal storage materials. The ability of building models to assess quickly the effect of different design parameters is critical for effectively incorporating innovative thermal strategies into new products. System models that enable design space exploration are built from different information sources such as numerical simulations, physical experiments, analytical solutions and heuristics. These models, called surrogates, are nonlinear, adaptive, and suitable for system responses where limited information is available and few realizations of experiments or numerical simulations are feasible. This paper applies a Bayesian surrogate framework to estimate values for unknown physical parameters of an embedded electronics system. Physical experiments and numerical simulations are performed on an embedded electronics prototype system of a wearable computer. Numerical models for the experimental prototype, which involve five and three unknown parameters, are implemented with and without thermal contact resistances. Through the use of orthogonal arrays and optimal sampling, an efficient exploration of the parameter space is performed to determine thermal conductivities, thermal contact resistances and heat transfer coefficients. Surrogate models are built that combine information obtained from numerical simulations, experimental model measurements and a thermal resistance network. The integration of several information sources reduces the number of large-scale numerical simulations needed to find reliable estimates of the system parameters. For the embedded electronics case, the use of prior information from the thermal resistance network model reduces significantly the computational effort required to investigate the solution space
Special Section on Components and Packaging Technologies With Contributions From ITherm 2002 Thermal Management Track
(IEEE, 2003-03) Amon, C. H. ; Ramakrishna, K. ; Sammakia, B. G. ; Joshi, Y. K.
ITHERM 2002, the 8th Intersociety Conference on Thermal, Mechanical and Thermomechanical Phenomena in Electronic Systems, hosted approximately 500 international experts in the areas of thermal management, thermomechanical and mechanics issues, and emerging technologies in electronic packaging and systems in San Diego, CA, May 30–June 1, 2002. The Technical Program included nearly 150 peer-reviewed papers presented in 35 sessions arranged into three Tracks: Thermal Management, Applied Mechanics, and Emerging Technologies. Twenty-five of these sessions were in the area of Thermal Management. This represented an increase in the number of presented papers and attendance compared with ITherm 2000, in spite of an economic downturn in the intervening period. Three special issues of the CPMT IEEE TRANSACTIONS ON COMPONENTS AND PACKAGING TECHNOLOGIES have been planned, one for each Track. The papers appearing in this Special Issue are in the area of thermal management and have been nominated by session chairs for consideration for the ITherm 2002 Best Paper in the Thermal Management Track. In addition, three of the six Keynote Speeches have also been included in this Special Issue. These papers reflect a broad range of current interest topics covered in the area of thermal management at ITherm 2002. Of the sixteen papers selected for this Special Issue, eleven have been accepted for publication after peer review.
Computation of Natural Convection in Channels With Pin Fins
(IEEE, 2004-03) Boyalakuntla, D. S. ; Murthy, J. Y. ; Amon, C. H.
In this paper, we numerically analyze the possibility of using buoyant flow in the display panel of a laptop for electronics cooling. Three-dimensional (3-D) channels with embedded pin fin arrays are analyzed using an unstructured finite volume method. Studies have been performed with a uniform heat flux boundary condition applied on the inner wall as well as for a constant inner wall temperature condition; the outer wall in all cases is exposed to the ambient. A single periodic module is selected in the lateral direction. In the axial mean flow direction, however, the entire height of the display channel is considered. Buoyancy has been modeled using Boussinesq approximation. A range of Rayleigh numbers, panel inclinations, and pin fin arrangements are considered. Local and global flow and heat transfer results are obtained including Nusselt numbers as well as local temperature and velocity fields. The results are useful in designing augmented cooling schemes in portable electronics.
Three-Dimensional Nanoscale Manipulation and Manufacturing using Proximal Probes: Controlled Pulling of Polymer Micro/Nanofibers
(IEEE, 2004-12-13) Nain, A. S. ; Amon, C. ; Sitti, M.
Besides imaging and characterization, proximal probes are proposed to be used as three-dimensional (3D) nanoscale manipulation and manufacturing tools in this paper. We propose 3D nanoscale pulling of liquid polymer micro/nanofibers by precise positioning of atomic force microscope (AFM) nanoprobes and control of polymer solidification. An AFM probe is used to pull or extrude thermoset and thermoplastic polymers precisely to fabricate 3D polymer nano-fiber structures. A liquid polymer fiber bridge between the probe tip and a substrate is maintained when pulling the probe from the surface with controlled speed and position. We present results of our pulling experiments in vertical, horizontal and arbitrary 3D pulling directions for poly(methyl methacrylate): PMMA polymer fibers. Force-distance curves obtained using AFM for PMMA samples at different scan rates are presented. A preliminary study showing the effect of velocity profile on pulling liquid bridges using POLYFLOW® is presented.
Polymer Micro/Nanofiber Fabrication using Micro/Nanopipettes
(IEEE, 2005-09-06) Nain, A. S. ; Amon, C. ; Sitti, M.
One of the most significant barriers for enabling the breakthroughs promised by nanotechnology is mass production of nanoscale structures, devices, and systems. One of the main challenges of nanomanufacturing systems is three dimensional customized manufacturing of micro/nanofibers. In this article we present a specialized tool developed for reproducible and controlled fabrication of micro/nano polymer fibers using micro/nanopipettes. Development of this tool will facilitate controlled deposition and shaping of polymer materials at the sub-micron scale in precisely determined locations. We present experimental results obtained using concentrated solutions of high molecular weight poly(methyl methacrylate) dissolved in chlorobenzene. Results indicate that it is feasible fabricating high aspect ratio (length to diameter ratio) polymer fibers having diameters approaching less than 200 nanometers using this approach.
Thermal Management of Die Stacking Architecture That Includes Memory and Logic Processor
(IEEE, 2006-07-05) Dewan-Sandur, B. P. ; Kaisare, A. ; Agonafer, De. ; Agonafer, Da. ; Amon, C. ; Pekin, S. ; Dishongh, T.
The convergence of computing and communications dictates building up rather than out. As consumers demand more functions in their hand-held devices, the need for more memory in a limited space is increasing, and integrating various functions into the same package is becoming more crucial. Over the past few years, die stacking has emerged as a powerful tool for satisfying these challenging integrated circuit (IC) packaging requirements. Previously, present authors reported on the thermal challenges of various die stacking architectures that included memory (volatile and non-volatile) only. In this paper, the focus is on stacking memory and the logic processor on the same substrate. In present technologies, logic processor and memory packages are located side-by-side on the board or they are packaged separately and then stacked on top of each other (package-on-package [PoP]). Mixing memory and logic processor in the same stack has advantage and challenges, but requires the integration ability of economies-of-scale. Geometries needed were generated by using Pro/Engineerreg Wildfiretrade 2.0 as a computer-aided-design (CAD) tool and were transferred to ANSYSreg Workbenchtrade10.0, where meshed analysis was conducted. Package architectures evaluated were rotated stack, staggered stack utilizing redistributed pads, and stacking with spacers, while all other parameters were held constant. The values of these parameters were determined to give a junction temperature of 100degC, which is an unacceptable value due to wafer level electromigration. A discussion is presented in what parameters need to be adjusted in order to meet the required thermal design specification. In that light, a list of solutions consisting of increasing the heat transfer co-efficient on top of the package, the use of underfill, improved thermal conductivity of the PCB, and the use of a copper heat spreader were evaluated. Results were evaluated in the light of market segment requirements
Foreword - Special Issue on Emerging Technologies
(IEEE, 2003-06) Amon, C. H. ; Goodson, K. ; Luo, G.
ITherm 2002, the 8th Intersociety Conference on Thermal, Mechanical and Thermomechanical Phenomena in Electronic Systems, hosted about 500 international experts in the areas of thermal management, thermomechanical and mechanics issues, and emerging technologies in electronic packaging and systems, from May 30 to June 1, 2002, in San Diego, CA. The Technical Program included nearly 150 peer-reviewed papers presented in 35 sessions arranged into three Tracks: Thermal Management, Applied Mechanics, and Emerging Technologies. The area of Emerging Technologies brought together engineers and scientists from industry, academia and government research organizations for exploration of emerging technology issues on electronic systems. There were 4 sessions in the Emerging Technologies area and each session had a nomination for the ITherm 02 Emerging Tech. track best paper. Of the nine papers selected for this Special Issue, four have been accepted for publication after peer review. These papers deal with wide ranging issues on emerging technologies; from thermosciences, heat transfer in Bio-MEMS, analysis and simulation of anode heating, to investigations of thermal responses of MEMS components.
Thermal Management and Concurrent System Design of a Wearable Multicomputer
(IEEE, 1997-06) Amon, C. H. ; Egan, E. R. ; Smailagic, A. ; Siewiorek, D. P.
This paper describes the concurrent system design and thermal management of the Navigator2 which is used as a computerized maintenance manual for aircraft inspection with speech recognition capabilities. The Navigator2 is a wearable computer that includes a novel dual architecture, spread spectrum radio, and variable gain amplifier (VGA) head-mounted display. The semi-custom electronic design includes two electronic boards-a custom designed system board and a 486-based processor board. The system board captures glue logic functions and provides support for two PCMCIA slots, a power management microcontroller, memory backup batteries, and a power supply. The thermal design of the Navigator2 develops concurrently with the overall design in a series of stages. A framework of concurrent thermal engineering consisting of three basic stages is used to maintain interdisciplinary interaction while satisfying thermal design goals. In the first stage of the thermal design, a cooling arrangement that meets the needs of other disciplines is proposed, and an enhanced-conduction thermal design with aluminum heat spreaders and active power-saving is explored. In the second stage, the thermal contact between heat spreaders and electronic components is optimized, and physical experimentation is performed with liquid heat sinks and conductive elastomers as thermal contact interfaces. In the third stage, numerical simulations are performed to ascertain the effectiveness of the thermal design, giving the thermal designer flexibility to change critical parameters and perform sensitivity analyses. A simplified computational model is used to investigate the performance of thermal interface devices and the effect of the heat spreader design on the maximum electronic component temperatures. Although the simplified model proves adequate for thermal design purposes, a detailed geometrically-accurate computational model assesses the adequacy of the exposed heat spreader surface area and predicts temperature distributions with better agreement to the experimental measurements on the Navigator2
PCM Thermal Control Unit for Portable Electronic Devices: Experimental and Sumerical Studies
(IEEE, 2003-03) Amon, C. H. ; Alawadhi, E. M.
This paper investigates the effectiveness of a thermal control unit (TCU) for portable electronic devices by performing experimental and numerical analyses. The TCU objective is to improve thermal management of electronic devices when their operating time is limited to a few hours. It is composed of an organic phase change material (PCM) and a thermal conductivity enhancer (TCE). To overcome the relatively low thermal conductivity of the PCM, a TCE is incorporated into the PCM to boost its conductivity. The TCU structure is complex, and modeling an electronic device with it requires time and effort. Hence, this research develops approximate, yet effective, solutions for modeling the TCU, which employ effective thermo-physical properties. The TCU component properties are averaged and a single TCU material is considered. This approach is evaluated by comparing the numerical predictions with the experimental results. The numerical model is then used to study the effect of important parameters that are experimentally expensive to examine, such as the PCM latent heat, Stefan number, and heat source power. It is shown that the TCU can provide a reliable solution to portable electronic devices, which avoids overheating and thermally-induced fatigue, as well as a solution which satisfies the ergonomic requirement.

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