Biofouling in tubes: some trends and perspectives

A significant increase in the literature concerning the formation of biological deposits in tubes has been noticed in the last few years. Yet, the scope of the majority of the reports is limited to the study of a single operating parameter. Besides, the operating conditions differ significantly from case to case, renderino difficult the absortion of the available information. In this work, a survey of the most recent publications on the subject of tube biofouling is undertaken, as a means of clarifying further research proprams. Emphasis is placed on the systems used, experimental equipments adopted and, essentially on the parameters studied. Of these, specially attention is qiven to the influence of tube material and roughness, foulant type and concentration, fluid velocity and temperature field

Fractal Conductance Fluctuations of Classical Origin

In mesoscopic systems conductance fluctuations are a sensitive probe of electron dynamics and chaotic phenomena. We show that the conductance of a purely classical chaotic system with either fully chaotic or mixed phase space generically exhibits fractal conductance fluctuations unrelated to quantum interference. This might explain the unexpected dependence of the fractal dimension of the conductance curves on the (quantum) phase breaking length observed in experiments on semiconductor quantum dots.Comment: 5 pages, 4 figures, to appear in PR

Photonic Hall effect in cold atomic clouds

On the basis of exact numerical simulations and analytical calculations, we describe qualitatively and quantitatively the interference processes at the origin of the photonic Hall effect for resonant Rayleigh (point-dipole) scatterers in a magnetic field. For resonant incoming light, the induced giant magneto-optical effects result in relative Hall currents in the percent range, three orders of magnitude larger than with classical scatterers. This suggests that the observation of the photonic Hall effect in cold atomic vapors is within experimental reach.Comment: 4 pages 4 figure

Etiologia, fatores de risco e aspectos clínicos da mastite ovina.

bitstream/CNPC-2010/22751/1/doc87.pd

Linfadenite caseosa: o estado da arte.

bitstream/CNPC/20869/1/doc74.pd

A model for the interpretation of biofouling

The formation of biofilms on heat exchange surfaces was studied using water with Pseudomonas fluorescens as a contaminant and also a mixture of these bacteria and kaolin particles. In every case increasing the fluid velocity resulted in a decrease in the final amount of deposit and in the deposition rate . The effect of the fluid velocity was interpreted using a mathematical model and it was found that cell adhesion and reproduction were the fundamental processes controlling the deposition rate . The presence of inorganic particles in the deposit enhanced the biofilm growth rate . This result was explained by the differences in the structure of the fouling layers

Fouling in heat exchangers: a study of the mechanisms of formation of kaolin deposits

Fouling caused by a water-kaolin suspension in an annular heat exchanger was studied. Deposition seemed to be controlled by ma!!s transfer for lower Reynolds numbers and by adhesion for higher Re. The data was satisfactorily described by the generalized model of Pinheiro. The relative cohesion of the deposits was measured using a concentric cylinders apparatus, which also helped in confirming the existence of a loose and a hard layer in the kaolin deposits

Particulate fouling: controlling processes and deposit structure

Fouling caused by a water-kaolin suspension in an annular heat exchanger was studied. Deposition seemed to be controlled by mass transfer for lower Reynolds numbers and by adhesion for higher Re. The data was satisfactorily described by the generalized model of Pinheiro. The relative cohesion of the deposits was measured using a rotating cylinder apparatus, which also helped in confirming the existence of a loose and a hard layer in the kaolin deposits.(undefined

Estimating friction factors in a fouled annulus

Fouling of heat transfer surfaces modifies the associated conductive thermal resistance and convective heat transfer coefficient. Often, the latter varies as a result of changes in the roughness of the deposition surface. If fouling is being studied in an annular heat exchanger, deposits may form on both surfaces of the annular cross section, and an estimation of the friction factors of each fouled surface is needed. In order to evaluate these factors a simple method can be used as described in this paper, based on pressure drop measurements and current equations. Experimental results are reported and appear to support the method.L'encrassement des surfaces de transfert de chaleur modifie leur résistance thermique conductive et leur coefficient de transfert de chaleur par convection. Celui-ci change, souvent, comme résultat de variations de la rugosité de la surface causées par des dépôts. Dans un échangeur de section annulaire, les dépôts peuvent se former sur les deux surfaces de l'espace annulaire. Il est donc nécessaire de calculer les coefficients de frottement de chacune de ces surfaces, ce qui peut être accompli en appliquant la méthode décrite ici, basée sur des équations simples et des mesures de la perte de charge. Les résultats expérimentaux semblent confirmer la validité de cette méthode