Modeling and Simulation of Dewatering of Particulate Suspensions by Batch Pressure Filtration

A Darcy law based approach for simulation of batch const-ant pressure filtration of particulate suspensions when the feed solids concentration changes, is developed. Using filtration data obtained using a feed suspension with a not-very-low solids concentration, we propose procedures to predict changes in (0 kinetics of dewatering in the cake formation stage, and (ii)transition point between the cake formation and consolidation stages, as the initial solid concentration changes. The evolution of dewatering can be predicted using these two model parameters. The approach is simpler to implement in comparison to avail-able pressure filtration models which require several char acterization experiments

Synchronization Based Approach for Estimating All Model Parameters of Chaotic Systems

The problem of dynamic estimation of all parameters of a model representing chaotic and hyperchaotic systems using information from a scalar measured output is solved. The variational calculus based method is robust in the presence of noise, enables online estimation of the parameters and is also able to rapidly track changes in operating parameters of the experimental system. The method is demonstrated using the Lorenz, Rossler chaos and hyperchaos models. Its possible application in decoding communications using chaos is discussed.Comment: 13 pages, 4 figure

Spontaneous dewetting and ordered patterns in evaporating thin liquid films on homogeneous and heterogeneous substrates

The growth of instabilities and the initial stages of dewetting of volatile thin aqueous films on partially wettable solid substrates are investigated based on 2D nonlinear simulations. Dewetting by the formation of holes occurs by a spinodal mechanism due to the hydrophobic attraction on chemically homogeneous surfaces. The number density of holes and, consequently, the rate of dewetting can be enhanced by as much as an order of magnitude by evaporation on a homogeneous surface. At moderate to high rates of evaporation, all the holes do not form at the same time uniformly over the surface but form gradually in a rather ordered way around the earliest holes which act as "seeds". On a chemically heterogeneous substrate, spatial gradients of the interaction potential and the rate of evaporation engender the surface instability. A chemical heterogeneity can induce faster rupture at a higher mean thickness and, thus, control the hole size distribution and the pattern of drying very significantly. A locally ordered, complex pattern often forms that consists of a central giant "nucleated" hole surrounded by a few concentric rings of smaller spinodally created satellite holes. An increase in the rate of evaporation encourages the formation of a larger number of ringlike structures containing the satellite holes but reduces the size difference between the spinodal satellite holes and the heterogeneously nucleated holes. The results obtained are in accord with recent experimental observations

Instability and pattern formation in thin liquid films on chemically heterogeneous substrates

The surface instability, dynamics, morphology, and spontaneous dewetting of a thin liquid film on chemically heterogeneous substrates are studied on the basis of 3D nonlinear simulations. A new mechanism of dewetting in the presence of heterogeneity is proposed where the instability is engendered by the gradient of intermolecular interactions that lead to a microscale wettability contrast. The time scale of instability, which can be several orders smaller than the spinodal dewetting time scale on homogeneous surfaces, varies inversely with the potential difference induced by the heterogeneity. Heterogeneity can even destabilize spinodally stable films, reduce the time of rupture substantially for thicker films, and decrease the dependence of rupture time on the film thickness. The presence of heterogeneity produces complex and locally ordered morphological features that are not predicted by the spinodal dewetting, for example "ripples" and "castle-moat" structures, radially symmetric structures, and a lack of undulations before the birth of a hole. The precise morphological pattern selection depends on the size of the heterogeneity, the potential difference caused by the heterogeneity, the film thickness, and also the spinodal characteristics of the substrate. The resulting morphologies can be understood on the basis of simple arguments that consider interplay among these factors

Instability and morphology of thin liquid films on chemically heterogeneous substrates

A new mechanism for the surface instability and dewetting of thin films on chemically heterogeneous substrates is identified and simulated. The time scale for instability varies inversely with the potential difference due to the heterogeneity. Heterogeneities can even destabilize spinodally stable films, reduce the time of rupture substantially for thicker films, and produce complex and locally ordered morphological features (e.g., ripples and castle-moat structures, lack of undulations before hole formation) that are not predicted by the spinodal mechanism

Modeling the size-density partition surface of dense-medium separators

A stochastic model is proposed for describing the size-density partition surface in dense-medium (DSM) gravity/centrifugal separators. The model is obtained by super-imposing a random walk on a simplified particle flow behavior inside the separator. The novel feature of the model is that it permits a description of the partition surface without incorporating the pivot phenomenon, i.e., without considering the partition number at the pivot point. The model also yields analytical expressions for the cut size, cut density and the ecart probable. The computed separation indices are in agreement with existing empirical relationships. Data from the published literature have been used to test the validity of the model in representing the partition surface

Data analysis and modeling of constant pressure batch dewatering of fine particle suspensions

The problems of data analysis and modeling of experimental constant pressure batch dewatering of materials forming compressible cakes are considered. Dewatering in these materials is typically completed in two stages, viz. cake formation and cake consolidation. A data representation method especially useful for determining the transition point between the filtration and consolidation stages, as well as for comparing accuracy of model predictions, is illustrated. It is shown that dewatering occurs via one of three qualitatively different pathways. A simplified model for engineering analysis of the process is presented. A time-invariant spatially uniform volume fraction of solids approximation is invoked in the cake formation stage. A time-dependent spatially uniform volume fraction of solids assumption is made in the cake consolidation stage. The two models contain four model parameters and have a common physical basis in Darcy's law. Interrelationships between key process parameters are determined and employed to predict the temporal evolution of dewatering in the cake consolidation stage as well as the end point of dewatering