FOULING MECHANISMS BY AB INITIO CALCULATIONS CONDENSATION REACTIONS ON THE RUTILE (101) SURFACE AND ADSORPTION OF IONS ON THE Cr2O3 SURFACES

Molecular modelling approach was utilized to describe detailed fouling mechanism caused by crystallization. The interest was on the heat transfer surfaces, which were manufactured from titanium and stainless steel. With ab initio calculations, the role of the surface oxide layer structure of titanium and stainless steel on fouling was investigated. The surface structure of titanium and stainless steel were assumed to consist of rutile (TiO2) and dichromium trioxide (Cr2O3), respectively. It was found that the inorganic fouling depends strongly on the oxide layer structure and the existence of hydroxyl groups on the surface. Based on the results, two mechanistically different fouling categories were found. When the surface hydroxyl groups exist, the fouling can take place via condensation reactions with species containing hydroxyl groups. On surfaces without the surface hydroxyl groups, fouling takes place preferably via adsorption of ions

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

Adsorption of as(V), Cd(II) and Pb(II), in multicomponent aqueous systems using activated carbons

The project CIMO North-South-South‘‘PROENV2’’, theAdMAtU–project (AKVA Program) financed by the Academy ofFinland, and HYMEPRO financed by the Finnish FundingAgency for Innovation (Tekes) are acknowledged for the financial support. The National University of Tumbes (ProyectoCanon – Resoluci ́on N80722-2014/UNT-R) and the PeruvianNational Council for Science and Technology (CONCYTEC)(Proyecto. No. 002/PE/2012) are gratefully recognized for theirsupport. The authors also want to thank their home universities for their support.Consejo Nacional de Ciencia, Tecnología e Innovación Tecnológica - Concyte

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

Microporous activation carbon made of sawdust from two forestry species for adsorption of methylene blue and heavy metals in aqueous system:case of real polluted water

Abstract Activated carbon samples were prepared and characterized from two novel forestry precursors by one-step chemical activation with ZnCl₂. The adsorption capacities of the adsorbents were tested with methylene blue in monocomponent synthetic solution and with heavy metals from polluted river water. The specific surface areas (S BET ) of the produced activated carbons were 1278 and 1404 m²/g. Further characterization was carried out by FTIR, RAMAN spectroscopy, XRD and FESEM analysis. The pore structure of both activated carbons was predominantly microporous with presence of mesopores. The maximum methylene blue (MB) adsorption capacities for both activated carbons were 250 mg/g and 357 mg/g. MB kinetic experiments were carried out and the influence of the initial MB concentration and the activated carbon dosage was evaluated. The samples reached removal levels close to 100% during the first 5 min of experiments with dissolved As(V) and Pb(II) in the polluted river water, reducing the concentration of these elements until levels below the local water quality standards.Resumen Se prepararon carbones activados a partir de dos precursores de la actividad forestal utilizando activación química en un solo paso con ZnCl₂. Las capacidades de adsorción se determinaron con azul de metileno en soluciones sintéticas y con metales pesados de agua de un río contaminado. Las áreas superficiales específicas de los carbones activados se calcularon entre 1278 y 1404 m²/g. Una caracterización de los materiales se realizó mediante FTIR, espectroscopía RAMAN, difracción de rayos X y microscopía electrónica de barrido. La estructura porosa de ambos carbones activados fue predominantemente microporosa con presencia de mesoporos. La máxima adsorción de azul de metileno por ambos carbones fue de entre 250 mg/g y 357 mg/g. La cinética de adsorción de azul de metileno con diferentes concentraciones iniciales del colorante y diferentes dosis de carbón activado, también fue evaluada. Las muestras alcanzaron una capacidad de remoción de As(V) y Pb(II) disueltos en agua de un río contaminado cercanas 100 % durante los primeros 5 min, reduciendo los valores de estos contaminantes a niveles por debajo de los estándares de calidad de agua locales