Alex C. Hoffmann

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Numerical simulations of flows of fluids with granular materials using the Eulerian-Lagrangian approach involve the problem of modeling of collisions: both between the particles and particles with walls. One of the most popular techniques is the hard-sphere model. This model, however, has a major drawback in that it does not take into account cohesive or(More)
We have studied mixtures of alcohol and water in an extensive series of 465 molecular-dynamics simulations with an aggregate length of 713 ns, in order to study excess properties of mixing, in particular the relation between mobility and viscosity. Methanol/water, ethanol/water, and 1-propanol/water mixtures were simulated using an alcohol content of 0–100(More)
In this paper we study stochastic models for the transport of particles in a uidized bed reactor, and compute the associated residence time distribution (RTD). Our main model is basically a diiusion process in 0; A] with reeecting/absorbing boundary conditions, modiied by allowing jumps to the origin as a result of transport of particles in the wake of(More)
Some aspects of the use of order parameter fields in molecular dynamics simulations to delimit solid phases containing water, namely ice and hydrate, in both hydrophilic and hydrophobic fluids are examined; this includes the influences of rectangular meshes and of filtering on the quality of these parameters. Three order parameters are studied: the mass(More)
Applied Mathematics and Computation The present work is a study of the gas-flow phenomenon known as the ?end of the vortex? (EoV), which spontaneously occurs at the lower end, or under, reverse-flow centrifugal separators such as cyclones or swirl tubes. Different CFD models of swirl tubes have been built to study and analyse this phenomenon in detail. The(More)
Different CFD models of reverse-flow centrifugal separators namely swirl tubes have been built in order to study and detail analysis of the phenomenon of the "end of the vortex". The present work based on previous experience and experimental activities in the field of this phenomenon. The models was built in absolutely agree with geometrical characteristics(More)
Hydrates in some crude oils have a smaller tendency to form plugs than in others, and lately this is becoming a focus of research. To study this and the action of hydrate antiagglomerants in general, hydrate surface properties must be known. To help in characterizing the surface properties by simulation, the capillary waves of clathrate hydrate surfaces in(More)
This article introduces a type of stochastic model, which we call a multiphase stochastic model, for the particle transport in bubbling fluidized beds, making it possible to take into account the finite velocity of fluidization bubbles and also extra particle transport due to "gulf streaming." An extended analysis of experimental results for particle(More)
This paper shows that Danckwerts' law for mean residence time in a vessel with continuous and steady throughflow holds for a stochastic model based on a Markov chain for the particle spatial position, under a set of three very general conditions on the transfer probabilities. These are natural conditions and represent mass balance conditions on the transfer(More)
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