Conditional statistics of nonreacting and reacting sprays in turbulent flows by direct numerical simulation

Conditional statistics concerning evaporation and combustion of a spray are investigated in homogeneous, isotropic, and decaying two-dimensional (2D) turbulence. Randomly distributed, polydisperse droplets of n-heptane go through single-step combustion chemistry. Attention is focused on parametric effects of initial Sauter mean radius (SMR), turbulence level and droplet velocity in both reacting and nonreacting cases. A simple linear model for the conditional evaporation rate is proposed and validated against DNS data. A conventional β-probability density function (pdf) is shown to be valid with no peak occurring on the fuel side. The amplitude mapping closure (AMC) model works well for the conditional scalar dissipation rate with evaporating and reacting sprays. Parametric study shows that initial SMR and droplet velocity are major factors affecting conditional flame structures, whereas the effect of reaction is not significant except during autoignition.     

The effect of reactor geometry on frontal polymerization spin modes

Using reactors of different sizes and geometries the dynamics of the frontal polymerization of 1,6-hexanediol diacrylate (HDDA) and pentaerythritol tetraacrylate (PETAC), with ammonium persulfate as the initiator were studied. For this system, the frontal polymerization exhibits complex behavior that depends on the ratio of the monomers. For a particular range of monomers concentration, the polymerization front becomes nonplanar, and spin modes appear. By varying the reactor diameter, we experimentally confirmed the expected shift of the system to a greater number of "hot spots" for larger diameters. For square test tubes a "zig-zag" mode was observed for the first time in frontal polymerization. We confirmed the viscosity-dependence of the spin mode instabilities. We also observed novel modes in cylinder-inside-cylinder reactors. Lastly, using a conical reactor with a continuously varying diameter, we observed what may be evidence for bistability depending on the direction of propagation. We discuss these finding in terms of the standard linear stability analysis for propagating fronts. (c) 2002 American Institute of Physics.     

Template‐Assisted Synthesis of Self‐Doped Polyaniline: Morphological Effects of Templates on the Conductivity

Self‐doped sulfonated polyaniline (PSA) has been synthesized on the surface of micellar nanoparticles made from positively charged surfactants by biocatalysis. The conformation forced by the electrostatic charge interactions between the positively charged micelle and the negatively charged PSA increases the conductivity of the PSA by three orders of magnitude. The pure PSA recovered from ion exchange, however, shows quite similar electrical properties compared with sulfonated polyanilines reported earlier. The increased conductivity of PSA complexes is as a result of the increased charge carrier concentration caused by a certain conformational locking.

     

Exploring Multidimensional Data with the Flipped Empirical Distribution Function

Abstract

This article introduces a new form of empirical distribution function (EDF) called the flipped empirical distribution function (FEDF), to represent univariate data graphically. Because the plot shows the location of individual points, it may be useful when we need to manipulate specific data points as with dynamic graphics. The article introduces several methods to explore multidimensional data using the FEDF. They are called a parallel FEDF, an FEDF scatterplot matrix, and an FEDF starplot. Usefulness of these plots in exploring multidimensional data becomes more prominent when they are implemented with the methods of dynamic graphics such as selecting, deleting, linking, locating, and identifying a group of data points.     

An experimental investigation of flow boiling in an asymmetrically heated rectangular microchannel

By using unique experimental techniques and carefully constructed experimental apparatus, the characteristics of flow boiling of water in microscale were investigated using a single horizontal rectangular microchannel. A polydimethylsiloxane rectangular microchannel (D_h = 103.5 and 133 μm) was fabricated by using the replica molding technique, a kind of soft lithography. A piecewise serpentine platinum microheater array on a Pyrex substrate was fabricated with the surface micromachining MEMS technique. Real time flow visualization of the phase change phenomena inside the microchannel was performed using a high speed CCD camera with microscope. The experimental local boiling heat transfer coefficients were studied, and single bubble inception, growth, and departure, as well as elongated bubble behavior were analyzed to elucidate the microscale heat transfer mechanisms. Tests were performed for mass fluxes of 77.5, 154.9, and 309.8 kg/m² s and heat fluxes of 180–500 kW/m². The effects of mass flux, heat flux, and vapor qualities on flow boiling heat transfer in a microchannel were studied.     

On the number of equivalence classes arising from partition involutions II

In this paper, we consider the pseudo-conjugation and its variations on the sets of partitions with restricted cranks and involutions on Frobenius symbols. We give several partition identities revealing relations between the number of equivalence classes in the set of partitions arising from an involution and the number of partitions satisfying a certain parity condition.     

Analysis of combustion regimes and conditional statistics of autoigniting turbulent n-heptane sprays

DNS is performed for a statistically one dimensional layer of a spray region resembling diesel engine conditions. The group and collective combustion regimes are identified according to the ratio of the chemical and transport time scales for a single droplet. The statistics in group combustion are similar with those in gas phase combustion. The collective combustion regime involves interspersed rich regions with different dissipation characteristics. Reasonable agreements are shown with the scaled AMC model and the linear evaporation model in the ranges of meaningful probability. Initially the evaporation terms are dominant in the budgets of the conditional enthalpy equation. After ignition the chemical reaction term becomes dominant to be balanced by the time rate of change term. For modeling turbulent spray combustion it may not be essential to consider detailed micro structures around each droplet, unless in the droplet combustion regime.     

Dynamic stability and bifurcation in a bundle flow

In roll draft operation mechanisms, the behavior of floating fibers is known to cause the thickness variation in output fiber bundles. Despite the significance of this phenomenon, few studies have sought to explain the underlying mechanism theoretically. We analyzed the dynamic characteristics of bundle flow in roll draft systems, based on a model of bundle flow. By applying both linear stability and phase plane analyses, we investigated an occurrence of draft waves. Our results suggest that the principles of linear stability can be applied to analyze bundle flow dynamics. The nonlinearity of bundle flow, however, reveals that the stable fixed point disappears when draft ratio changes, which in turn implies that the topological structure of the phase portrait changes as the process parameter is varied: a bifurcation property. As the process parameter increases above certain critical values, fixed points are destroyed and oscillations within the limit cycle occur. Also the system oscillates at a critical draw ratio harmonically, indicating the onset of a Hopf bifurcation, which corresponds to the draft wave. The phase portrait converges to a shell-shaped curve if the process parameter increases further. The results of this study also show that there is a specific draft ratio below which flow is always stable.