Alex C. Hoffmann

  • Citations Per Year
Learn 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)
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)
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)
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)
The pressure-driven gas flow through micro- and nano-porous structures is particularly interesting for innovative technologies such as microelectromechanical and nano-mechanical-electrical systems. The classical continuum assumption breaks down for rarefied flow through channels with a characteristic dimension comparable to the mean free path of the gas.(More)
Why is it so hard to lift a wet glass from a table? Is it easier when there is whiskey between the glass and the table? Macroscopically, the picture is quite simple: two surfaces have to be disrupted that are connected indirectly through hydrogen bonds and/or van der Waals forces. In the beginning, a surface has to be created leading to surface tension, and(More)
In two earlier papers the present authors modified a standard hard-sphere particle-wall and particle-particle collision model to account for the presence of adhesive or cohesive interaction between the colliding particles: the problem is of importance for modeling particle-fluid flow using the Lagrangian approach. This technique, which involves a direct(More)
In this article Eulerian-Lagrangian 2D computer simulations of consequences of primary dust explosions in two vessels connected by a duct are described. After an explosion in the primary vessel a propagation of hot pressurised gases to the secondary vessel, initially uniformly filled with dust particles, is simulated. The gas phase is described by the(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)