No abstract

In a local exhaust ventilation system, where the pollutant or the emitted flows are captured near the generated source, the knowledge of the capture efficiency is necessary to evaluate performance. This article reports a study of the influence of the exhaust hood slot height on the capture efficiency. For this study, the emission of gases and vapors from open surface tanks used in industrial treatments has been simulated in an installation fitted with two ventilation systems: lateral exhaust and push-pull. Several configurations were possible by varying the geometrical and operational conditions. Both qualitative and quantitative evaluations have been performed, the former through observations of the flows using smoke and the latter by using sulfur hexafluoride as tracer gas. The results obtained on capture efficiency for both ventilation systems tested with several exhaust slot height and as a function of the operating flows rates, are presented. It was found that varying the exhaust slot height between 15 and 45 cm had no effect on capture efficiency. The results show that there are no significant differences between the exhaust slots heights tested, although, in the case of 60 cm for lateral exhaust ventilation, the efficiency was slightly lower.

High and increasing rates of isolates resistant to TMP-SMZ and erythromycin were observed, as well as a decreasing percentage of isolates resistant to chloramphenicol. These trends highlight differences among the countries studied.

Los 32 metros superiores de un corazón de 200 metros, principalmente sedimentos de laguna de edad pleistocena y holocena de la Sabana de Bogotá, se analizaron sobre su contenido de polen, con una distancia entre muestras de 10 a 15 cms. El resto del corazón se está analizando, y el diagrama de esa parte se publicará más tarde. A base de polen se pudieron reconocer aproximadamente setenta especies, géneros o familias, muchas de ellas por primera vez. Se puede deducir del diagrama qué períodos glaciales e interglaciales afectaron al trópico, lo mismo que a Europa y Norte-América. También se colige del diagrama que los períodos glaciales fueron al mismo tiempo pluviales, y los interglaciales interpluviales. Se calcularon curvas para las fluctuaciones del límite altitudinal del bosque, para los cambios de precipitación anual y para los cambios de la temperatura. Las temperaturas medias durante las principales fases de la glaciación Würm eran más o menos 8 ºC más bajas que las de hoy día; el límite altitudinal del bosque se bajó hasta 1300 metros, y el límite de las nieves todavía más. Las fechas obtenidas por medio de los análisis del radiocarbono, comprobaron que las partes del diagrama consideradas respectivamente como Holoceno y última parte de la glaciación Würm, efectivamente correspondieron a estas edades. Con estos conocimientos parece completamente justificado correlacionar también las fases más antiguas con las glaciaciones e interglaciales de Europa y Norte-América, utilizando la nomenclatura alpina. La parte inferior del diagrama parece corresponder al final de Riss I, seguido por el interstadial Riss 1-11, y el Riss 11 (Warthe-stadial). Siguen entonces el interglacial Riss-Würm, el glacial Würm (subdividido por dos interstadiales largas, juntos llamados Interpleniglacial, y varios interstadiales de menor importancia), y el Holoceno. Las conclusiones más importantes de este estudio están resumidas en las conclusiones.

A pilot installation was designed that simulates a surface treatment tank fitted with a push-pull ventilation system. The installation contained elements for measuring and controlling the operational variables (flow rate and tank temperature) and smoke generating equipment for injecting smoke through the holes of the push unit and from the tank surface. Visual observation and video recording of the flows involved meant it was possible to follow the qualitative behavior of the push flow rate along the tank surface and to identify any emissions not captured by the exhaust system. It was possible to differentiate the initial semifree push curtain, its impact with the tank surface, the wall jet that moved toward the exhaust, and its entrance into the exhaust. The methodology proposed is complemented by a quantitative technique for measuring the efficiency, using sulfur hexafluoride as tracer, which permits the causes and location of losses in the ventilation system to be determined.