Characterization of the evolution of crystallization fouling in membranes

National Science and Engineering Research Council of Canada (NSERC)Peer Reviewe

EVALUATION OF HEAT TRANSFER BOUNDARY CONDITIONS FOR CFD MODELING OF A 3D PLATE HEAT EXCHANGER GEOMETRY

In this paper fluid flow and heat transfer are modeled in a corrugated 3D plate heat exchanger geometry with a commercial computational fluid dynamics (CFD) program, Fluent 6.1.22 (Fluent Inc., Lebanon), in order to find out the most realistic heat transfer boundary conditions for a plate heat exchanger. The built-in boundary conditions of Fluent available for this case are Heat flux, Convection and Constant wall temperature. The CFD models are verified with correlations and experimental data obtained by a flat plate test equipment of which parameters can be calculated analytically. Deficiencies are found in all the built-in heat transfer boundary conditions. Heat transfer modeling with CFD in a corrugated plate heat exchanger is problematic because of the assumptions that have to be made when defining the boundary conditions in the complex geometry. The values of the computational parameters have spatial variations and can not be defined explicitly. However, when compared to the experimental correlations in the literature, the Convection boundary condition gives the most realistic results in the case of corrugated plate heat exchanger

Surface patterning of stainless steel in prevention of fouling in heat transfer equipment

Fouling of surfaces is a major challenge in design and operation of many industrial heat transfer equipment. Fouling causes significant energy, material and production losses, which increase the environmental impact and decrease economic profitability of processes. Even small improvements in prevention of fouling would lead to significant savings in a wide range of heat transfer applications. In this study, crystallization fouling of aqueous calcium carbonate solutions on a heated stainless steel surface is used to investigate the prevention of fouling in heat transfer equipment by physical surface modifications. Fouling behaviour of different surface patterns are studied experimentally in a laboratory scale fouling test apparatus. CFD modelling is used to study hydrodynamic and thermal conditions near surfaces with different patterns. In addition, the effect of surface pattern on the removal of particles is studied numerically. Surface patterning is found to affect the hydrodynamic and thermal conditions near the wall, and therefore to change the conditions for fouling layer build-up and removal, when compared to a flat heat transfer surface. The most promising surface pattern includes curved shapes, and it seems to create flow conditions in which improved convective heat transfer decreases the driving force for crystallization fouling. In addition, curved surfaces increase the shear forces at the wall, which prevents adhesion of the foulants to the surface and increases resuspension.</jats:p

Sedimentology of cherts in the Early Proterozoic Wishart Formation, Quebec–Newfoundland, Canada

The siliciclastic Wishart Formation of the Early Proterozic Labrador trough is high-energy shelf deposit. Wishart sandstones contain both interstitial chert with textures of void-filling cement and thin chert intercalations contaminated with siliciclastic mud. Although volumetrically minor, these cherts occur in several thin, areally extensive stratigraphic mud. Although volumetrically minor, these cherts occur in several thin, areally extensive stratigraphic intervals. The Wishart contains intraclasts of both the chertcemented sandstone and the impure chert layers (as well as several other types of chert sand and gravel). This suggests the cherts formed penecontemporaneously, which is consistent with the absence of any signs of replacement in all but one of the chert types and the clear-cut distinctions between chert types, even where they are side by side in a single thin section. The origin which appears to be most compatible with available evidence is that the cherts represent silica precipitated from thermal waters that rose through the sediments of the Wishart shelf and discharged precipitated from thermal waters that rose through the sediments of the Wishart shelf and discharged into suprajacent seawater. A biogenic origin is unlikely in view of the lack of appropriate organisms during the Early Proterozic and the rapidity with which the cements formed. A volcanogenic origin is likely because volcaniclastic tezxtures are plentiful in associated formations but absent from the Wishart. Precipitation induced by evaporative concentration in unlikely in view of the widespread evidence of tidal currents and the lack of evidence of desiccation in the Wishart. Finally, the cherts are not restricted to the lowest-energy faces, and therefore they presumably did not accumulate as a background sediment. Deposition of silica above the sediment/water interface was probably made possible by ambient concentrations of silica that were significantly higher than those of Phancrozoic seawater. Cherts with similar textures occur in other Early Proterozoic sediments, most notably arenitic or granular iron-formations