An alternative procedure for modeling of Knudsen flow and surface diffusion

An alternative procedure for the calculation of impingement rate distribution and simultaneously the transmission probability in pores under Knudsen diffusion conditions is introduced. It is based on a combination of the finite difference method and a projection approach. Pore entrance and exit effects, and the influence of the pore length on diffusive fluxes are investigated. Later on, it is applied for a simultaneous Knudsen and surface flow system. In the model, the equation system is built without the independent flow and adsorption-desorption equilibrium assumptions. For the conditions investigated, the results indicate that if the surface flow rate is substantial, the independent flow and adsorption equilibrium assumptions become improper estimates for the behaviour of the system. The surface and gas flow rates, the impingement rate distribution and the surface coverage behave much more complex than the characteristics found with such assumptions

MONTE CARLO CALCULATIONS: DIFFUSION IN ZEOLITES

The objective of this study is to estimate the diffusivities of single and multicomponent systems as a function of temperature, concentration and parameters of the zeolite frame- work

NUMERICAL CALCULATION OF PRESSURE FIELDS IN SONOCHEMICAL REACTORS - LINEAR EFFECTS IN HOMOGENEOUS PHASE

During the last 50 years sonochemistry was under active investigation. Nevertheless, there is still a lack of a sound theoretical basis for the design of sonochemical reactors. Furthermore, sonochemical reactions are not understood in detail on a molecular level. In order to calculate the yield of chemical reactions in reactors of different shapes one needs to know the number of cavitation bubbles in the reactor. These bubbles are generated by oscillating pressures in the liquid. Therefore, as a first step of the design of sonochemical reactors pressure fields in homogeneous media in reactors of different geometric shapes are calculated .

MULTICOMPONENT DIFFUSION AND REACTION IN COMPOSITE CATALYSTS - A MONTE-CARLO AND DUSTY-GAS MODEL APPROACH APPLIED TO THE METHANOL-TO-OLEFIN SYNTHESIS IN ZEOLITES

A model of the description of reaction and mass transport within composite catalysts by Ruckenstein was improved by taking a volume change during the reaction into account, and by describing the internal fluxes by the Dusty-Gas Model. A new numerically improved notation of the Dusty-Gas-Model equations was investigated. The new model is used for describing the Methanol-To-Olefin synthesis in zeolite catalysts. The diffusivities in zeolite particles were obtained by a Monte-Carlo approach. The new model offers an improved description of experimental data

MODELING OF SUPPORTED-LIQUID-PHASE CATALYSTS BY PERCOLATION THEORY

The program developed is a useful tool for detailed examination of different influences on the behavior of SLP-catalysts. Up to now, not all of the possible parameter variations have been studied. The program can be a useful support of modeling SLP-catalysts by comparing measurable values to computed results effected by particular parameters

Understanding the loading dependence of self-diffusion in carbon nanotubes: Understanding the loading dependence of self-diffusion in carbonnanotubes

The influence of loading on the self-diffusion in an isolated single walled carbon nanotube is studied by molecular dynamics simulations. By simulating the carbon nanotube as a flexible framework we demonstrate that the flexibility has a crucial influence on self-diffusion at low loadings [1]. While simulating the nanotube as rigid a remarkable increase of the diffusion coefficient at low loadings is observed [2]. Molecular dynamics simulations of a fully flexible nanotube result in a far less pronounced increase, by a further reduction of the loading the diffusion becomes constant again. To incorporate the influence of the flexible walls in a simulation of a rigid nanotube, we have introduced a Lowe-Andersen thermostat which works on interface-fluid collisions [1]. The reproduction of the results of a flexible carbon nanotube by a rigid nanotube simulation is excellent. With this approach we simulate the loading dependent self-diffusion in carbon nanotubes. The influence of pore width and temperature on self-diffusion is studied. Furthermore, the influence of adsorption strength is investigated by comparing the self-diffusivities of different components. For small pores, in which the molecules cannot pass each other, single-file diffusion is observed under certain conditions