35,882 research outputs found
Relaxation and breakup of an initially extended drop in an otherwise quiescent fluid
In this paper we examine some general features of the time-dependent dynamics of drop deformation and breakup at low Reynolds numbers. The first aspect of our study is a detailed numerical investigation of the âend-pinchingâ behaviour reported in a previous experimental study. The numerics illustrate the effects of viscosity ratio and initial drop shape on the relaxation and/or breakup of highly elongated droplets in an otherwise quiescent fluid. In addition, the numerical procedure is used to study the simultaneous development of capillary-wave instabilities at the fluid-fluid interface of a very long, cylindrically shaped droplet with bulbous ends. Initially small disturbances evolve to finite amplitude and produce very regular drop breakup. The formation of satellite droplets, a nonlinear phenomenon, is also observed
Microfluidic immunomagnetic multi-target sorting â a model for controlling deflection of paramagnetic beads
We describe a microfluidic system that uses a magnetic field to sort paramagnetic beads by deflecting them in the direction normal to the flow. Our experiments systematically study the dependence of the beadsâ deflection on: bead size and susceptibility, magnet strength, fluid speed and viscosity, and device geometry. We also develop a design parameter that can aid in the design of microfluidic devices for immunomagnetic multi-target sorting
Stokes flow in a drop evaporating from a liquid subphase
The evaporation of a drop from a liquid subphase is investigated. The two
liquids are immiscible, and the contact angles between them are given by the
Neumann construction. The evaporation of the drop gives rise to flows in both
liquids, which are coupled by the continuity of velocity and shear-stress
conditions. We derive self-similar solutions to the velocity fields in both
liquids close to the three-phase contact line, where the drop geometry can be
approximated by a wedge. We focus on the case where Marangoni stresses are
negligible, for which the flow field consists of three contributions: flow
driven by the evaporative flux from the drop surface, flow induced by the
receding motion of the contact line, and an eigenmode flow that satisfies the
homogeneous boundary conditions. The eigenmode flow is asymptotically
subdominant for all contact angles. The moving contact-line flow dominates when
the angle between the liquid drop and the horizontal surface of the liquid
subphase is smaller than , while the evaporative-flux driven flow
dominates for larger angles. A parametric study is performed to show how the
velocity fields in the two liquids depend on the contact angles between the
liquids and their viscosity ratio.Comment: submitted to Physics of Fluid
A describing function for resonantly commutated H-bridge inverters
AbstractâThe paper presents the derivation of a describing function to model the dynamic behavior of a metal oxide semiconductor field effect transistor-based, capacitively commutated H-bridge, including a comprehensive explanation of the various stages in the switching cycle. Expressions to model the resulting input current, are also given. The derived model allows the inverter to be accurately modeled within a control system simulation over a number of utility input voltage cycles, without resorting to computationally
intensive switching-cycle level, time-domain SPICE simulations. Experimental measurements from a prototype H-bridge inverter employed in an induction heating application, are used to demonstrate a high degree of prediction accuracy over a large variation of load conditions is possible using the simplified model
Techniques for the realization of ultrareliable spaceborne computers Interim scientific report
Reliability tests on spaceborne digital computer
An experimental and theoretical investigation of particleâwall impacts in a T-junction
Understanding the behaviour of particles entrained in a fluid flow upon changes in flow direction is crucial in problems where particle inertia is important, such as the erosion process in pipe bends.We present results on the impact of particles in a T-shaped channel in the laminar-turbulent transitional regime. The impacting event for a given system is described in terms of the Reynolds number and the particle Stokes number. Experimental results for the impact are compared with the trajectories predicted by theoretical particle tracing models for a range of configurations to determine the role of the viscous boundary layer in retarding the particles and reducing the rate of collision with the substrate. In particular a 2D model based on a stagnation point flow is used together with 3D numerical simulations. We show how the simple 2D model provides a tractable way of understanding the general collision behaviour, while more advanced 3D simulation can be helpful in understanding the details of the flow
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