Submitted in fulfilment of the academic requirements for the Degree of Masters in Technology: Chemical Engineering, M.L. Sultan Technikon, 2002. / Crossflow microfiltration (CFMF) using a fabric support has been successfully used to treat a range of problematic waters. Experimental evidence indicates that the formation of a dynamic membrane or precoat on a woven-fibre microfilter can significantly increase the performance of the filter, that is, the production rate and rejection. The use of precoats in filtration applications is based on the precoat's unique microstructure that is able to trap sub-micron particles while maintaining a permeable filter cake. However, to date the precoating step has been more of an art than a science. Very little knowledge exists on the best type of precoat to use, or the the optimal velocity, pressure and concentration to form a stable precoat. Further, although various models have been proposed for CFMF, their still exists a lack of knowledge of the mechanisms by which precoats improve performance. / M

As the world population approaches seven billion, a greater strain is put on the resources necessary to sustain life. One of the most basic and essential resources is water and while two thirds of the earth is covered by water, the majority is either salt water (oceans and seas) or it is too contaminated to drink. The purpose of this project is to develop a portable device capable of testing whether a specific source of water (i.e. lake, river, well…) is potable. There are numerous filtration techniques that can remove contaminants and make even the dirtiest water clean enough for consumption but they are for the most part, very time consuming and immobile processes. The device is not a means of water purification but rather focuses on determining the content of the water and whether it is safe. Particles within the water are separated and trapped using a combination of a Taylor Couette fluid flow system and Dielectrophoretic electrodes. This paper explores Taylor Couette flow in a large gap and low aspect ratio system through theory and experimentation with early stage prototypes. Different inner cylinder radii, 2.12cm, 1.665cm and 1.075cm, were tested at different speeds approaching, at and passing the critical Taylor number, 3825, 4713 and 6923 respectively for each cylinder. Dielectrophoretic (DEP) electrodes were designed, fabricated, coated and tested using latex beads to determine the method of integrating them within the fluid flow system. Taylor Couette theory, in terms of the formation of vortices within the large gap, small aspect ratio system, was not validated during testing. The flow pattern generated was more akin to a chaotic circular Couette flow but still served to move the particles toward the outer wall. Fully integrated tests were run with limited success. Recommendations were made to pursue both circular Couette flow as the basis for iv particle separation and dimensional changes in the setup to allow for the formation of Taylor vortices by increasing the radius ratio but still allowing for a larger volume of fluid.

A general, non-iterative design technique for low shapefactor, transversal filters is presented. This design approach uses two cosine series to specify appropriate eigenfunctions. An infinite set of such eigenfunctions are defined and the method for choosing the coefficients is discussed. The total filter response is specified as the product of two individual frequency responses. The impulse response of each is then determined by applying the superposition of appropriate eigenfunctions. The criteria for choosing the appropriate eigenfunctions is discussed. A synthesis procedure for designing surface acoustic wave filters is presented. The effects of truncating the impulse response are also explored. A design example is shown for a filter with 10 percent fractional bandwidth and a shapefactor of 1.15.

Fast Recursive Least-Squares Transversal Filters (FTF), an important class of algorithms for adaptive filtering, have the well known problem of numerical instability. Several recent papers have suggested methods to modify the algorithm presented by Cioffi [3] to improve the algorithm’s stability. This paper explores the relationship between precision and stability of the adaptive filter. The effect of changing the adaptive time constant and the filter order are also investigated. These effects are studied for a floating point implementation of the FTF filter that allows for limiting the number of bits used in the mantissa of the results of all additions and multiplications. / Master of Science

Ceramic candle filters were subjected to 500 hour high temperature/ high pressure (HTHP) exposure tests to examine their extended durability in simulated coal pressurized-fluidized bed combustion (PFBC) environments. The candle filter materials analyzed included two SiC filters, one with clay binder and one with a minimal amount of clay binder, a cordierite filter, a mullite candle filter and an aluminosilicate refractory concrete filter. Exposure testing conditions included a range of temperature from 700-850°C and a pressure ranging from 1.7-1.8 MPa. The HTHP tests included exposing the ceramic filter materials to steam and steam-alkali environments. The presence of alkali significantly accelerated the deterioration of the filters. The results of the analysis show that significant crushing strength losses were exhibited by the SiC filters after exposure to HTHP alkali-steam conditions at temperatures as low as 700°C. The expansive and destructive cristobalite phase developed in the SiC filters after most of the treatments. The cordierite candle filter showed a decrease in crushing strength associated with grain growth after each high temperature exposure but few other signs of deterioration were detected. The mullite candle filter and the refractory concrete candle filter showed the least amount of change in crushing strength and overall the most candle stability. / Master of Science

No description available.

No description available.

This study investigated the effectiveness of vegetative filter strips (VFS) in removing phosphorus from surface runoff. Dissolved and particulate nutrients were treated separately due to differing transport and removal mechanisms. Nutrient transport in VFS appears to be a function of runoff rate, concentration and size distribution of suspended solids, and biological factors that influence hydrologic and chemical processes in filter strips. Three sets of experimental field plots were constructed to simulate VFS. Each set consisted of three plots containing sediment and nutrient source areas and 0.0, 4.6, or 9.1 m grass filter strips. Artificial rainfall was applied to the plots, and surface runoff, soil, and plant material samples were collected and physically and chemically analyzed. The VFS reduced surface runoff, suspended solids, and phosphorus losses. Most removal of sediment and phosphorus was accomplished in the first few meters of the VFS. The filter strips did not remove phosphorus as effectively as sediment, due to their ineffectiveness for filtering dissolved phosphorus and sediment-bound phosphorus associated with fine particles. The VFS often increased orthophosphorus losses in surface runoff. Laboratory batch experiments of phosph~rus desorption reaction suggested that plant residues, living plant canopy, and soil components of the strips could release dissolved phosphorus to surface runoff. A modified Elovich equation and a diffusion-control model were used to describe the phosphorus release from the plant and soil materials. A computer model, GRAPH, was developed to simulate phosphorus transport in VFS by incorporating phosphorus transport submodels into the VFS model in SEDIMOT II, a stormwater and sediment transport model. The model considers the effects of advection processes, infiltration, biological uptake, phosphorus desorption from the soil surface to runoff, the adsorption of dissolved phosphorus to suspended solids in runoff, and the effects of dynamic changes in the sediment size distribution on chemical transport. GRAPH was verified using the results of the physical plot simulations. The model's predictions and observed phosphorus transport compared favorably. Sensitivity analysis suggested that sediment and phosphorus removal was sensitive to the input parameters in the order: filter length and width, grass spacing, and filter slope and surface roughness. Increased filter width and length and aboveground biomass increased orthophosphorus loss from VFS. / Ph. D.

Commercial pure terephthalic acid (PTA) manufacturing generates process streams mainly containing acetic acid (HAc) and water. A large financial incentive exists to replace the costly and energy intensive distillation column used to recycle HAc-water mixtures. This work focuses on the development of pervaporation technology to separate HAc-water mixtures using a hollow fiber-based membrane unit. Currently a 250 m outer diameter Matrimid® hollow fiber is used in industry for gas separation. Due to the difference between gas and liquid separations, the fiber performance associated with high flux in pervaporation is limited by a pressure change inside the bore along the axial direction of the fiber. A mathematical model was developed to describe the bore pressure change in pervaporation in this work, which demonstrated that spinning a large bore size fiber was a good solution to minimize the bore pressure change. Spinning technology has been adapted to obtain a large bore size defect-free Matrimid® hollow fiber. In addition to a large bore size, the asymmetric fiber exhibits an intrinsically defect-free selective layer supported on an open porous substrate. This eliminates the post-treatment with a caulking layer and has a special advantage for aggressive liquid separation. A proof of concept was provided by testing both small and large bore size defect-free fibers with a model 20% wt HAc feed in a pervaporation system at 101.5oC. The membrane selectivity (~ 25) and water flux (~ 4.5 kg/m2hr) were increased by about 150% with a diameter (O.D. ~ 500 m) twice as large as the regular fiber. Further, a decrease in the HAc flux was observed with the increased bore size due to the reduction in HAc-induced plasticization. Sub-Tg thermal annealing was used to stabilize the fiber by suppressing HAc-induced plasticization. This improves the polymer discrimination of shape and size for penetrants although no chemical reaction occurs with thermal annealing. The resulting membrane selectivity was increased from 10 to about 95 using a large bore size defect-free annealed fiber with acceptable water flux (~ 1.5 kg/m2hr) for 20% wt HAc concentration feed streams. These improvements make Matrimid® hollow fiber membranes very attractive for future scale-up and commercial development.

A mathematical model has been developed which describes the fluid exchange from a capillary network of realistic topology, and calculates the spatial distribution of extravascular pressure. In this model, the capillaries are represented by a superposition of sources and sinks, resulting from a D'Arcy's Law description of flow in tissue of uniform fluid conductivity. The combination of this representation and Starling's Hypothesis, which relates the forces influencing transmural fluid exchange, yields an integral equation of the second kind which is solved numerically for the source strength distribution. Two important features of this approach are that: (i) it allows for interaction between the local tissue pressure field and fluid exchange (the model is called, therefore, the tissue pressure interaction model); and (ii) complex network morphologies are easily modeled. In single capillaries, this interaction, which decreases the predicted fluid exchange, increases with the magnitude of the ratio of capillary wall to extravascular fluid conductivities. For multiple capillaries, in addition to the "self" interaction of a capillary with the local extravascular pressure field, there is the possibility of interaction between capillaries ("capillary-capillary" interaction). The ratio of conductivities, and the additional factors of intercapillary distance and the number of capillaries, also affect interaction in capillary networks. Although interaction is only a weak function of intercapillary distance, it depends strongly on the number of capillaries. The major result from this work is that for the entire physiological range of conductivity ratios, interaction cannot be neglected in predicting fluid exchange. Although tissue pressure interaction affects the magnitude of fluid exchange, it does not greatly alter the pattern of extravascular flow. Therefore, previous models which neglected interaction are not invalidated by the present findings. The effect of interaction on planar capillary networks within a semi-infinite tissue space was also investigated. Flow boundary conditions were imposed at opposed planar boundaries, parallel with the capillary network. Interaction was found to decrease with decreasing distance between the boundary and plane of the capillaries. It still exerted a large effect, however, for distances greater than one-fourth the reference capillary length.