Ignazio Becchi

Permoporometric study on ultrafiltration membranes

Abstract Skin layer porosity of ultrafiltration membranes was evaluated by an instrument based on the combined bubble pressure and solvent permeability methods. Nuclepore membranes were first tested for calibration and reproducibility purposes. Measurements were then carried out both on membranes prepared in our labs and an commercial ones. Porosity results are discussed in relation to membrane preparation variables as well as to phenomena controlling membrane performance during ultrafiltration application.

The use of membrane processes in the clarification of orange and lemon juices

Abstract The ultrafiltration of orange and lemon juices has been investigated on a pilot-plant scale at constant concentration using tubular configuration polymeric and ceramic membranes. The permeate fluxes were found to be strongly dependent on the tangential feed velocity at the membrane but almost independent of the driving force at average pressures over the membrane greater than ≈0.2 MPa. These results are due to the formation of a pectin-pulp deposit on the membrane, which effectively controls the ultrafiltration. Because of their different surface structures and roughness this deposit has different properties for the ceramic and polymeric membranes. This causes the latter to behave as rough tubes. The ceramic membranes give higher permeate fluxes at a lower Reynolds number than the polymeric membranes. This and their smooth tube behaviour indicate the possibility of greater energy efficiency for the industrial application of the ceramic than of the polymeric membranes.

Hydrological control of flooding: Tuscany, October 1992

In the study of flash-flood occurrence in small catchments the lack of flow measurements is often one of the main limiting factors. Prior to estimating the forecasting potentialities and techniques for such events, an accurate reconstruction of past event flood dynamics is first required. This issue is here addressed by analyzing, with the use of a distributed hydrological model, the hydrometeorological conditions in which a severe flash-flood occurred, on October 1992, on a 48 square kilometers catchment in the Arno basin. Such an event was caused by the persistence of intense convective clusters on the background of widespread rain bands of frontal origin. The distributed hydrological model here adopted is devoted to simulate the evolution and the variability of the primary processes involved in the runoff cycle. Together with the hydrological model structure, other particular aspects of the event reconstruction procedure are discussed: the managing and processing of the information coming from different sensors, with different temporal and spatial resolutions; the identification of local precipitation dynamics (frontal or convective) within small areas of integrated radar and rain gauges data fields; the interpolation of rain gauge data on the basis of the radar-estimated spatial correlation. The results of the distributed modeling, concerning the estimate of the flood wave at various sites, are compared with analogous results obtained with simpler lumped models.

Hydrological Response to Radar Rainfall Maps through a Distributed Model

Weather radars in investigating physical characteristics of precipitation are becoming essential instruments in the field of short term meteorological investigation and forecasting. To analyze the radar signal impact in hydrological forecasting, precipitation input fields, generated through a statistical mathematical model, are supplied to a distributed hydrological model. Such a model would allow the control of the basin response to precipitation measurements obtained by a meteorological radar and, in the meanwhile, to evaluate the influence of distributed input. The distributed model describes the basin hydrological behavior, subdividing it into distinct geometrical cells and increasing the physical significance by reproducing the distributed hydrographic basins characteristics, such as infiltration capacity, runoff concentration time, network propagation speed, soil moisture influence. Each basin cell is characterized by its geological, pedological and morphological status, and may be considered a unitary hydrological system, linked to the others by geomorphological and hydraulic relationships. To evaluate the dynamics of the flood event a synthetic representation of the channel network is introduced, where each stream branch is modeled as a linear reservoir. Finally, the discharge in the outlet section is derived, taking into account the hydraulic characteristics of the upstream branches.

Field analysis of the water film dynamics on a road pavement

The analysis of water film dynamics on road pavement during high intensity rainfall events is fundamental in the study of problems of different nature, from road safety to urban drainage. The influence of precipitation time-variability and road pavement geometry on the water film dynamics is investigated using an experimental monitoring station installed on a mountain road which is prone to heavy storms. The monitoring station is composed by a road portion, a rain gauge and a video-camera automatically activated during intense rainfall. The investigation is based on the digital analysis of the recorded images between summer and autumn 1999. The water film surface irregularities, due to the raindrop impact with the surface and to the presence of roll waves, are studied. The first results are relative to the analysis of the roll-waves dynamics, as they are prevalent in terms of visible effects during the periods of intense rainfall. The digital analysis of the image sequences allows estimating direction and speed of the wave propagation with variable precision due to different light conditions. Using empirical relationships derived from laboratory experiments (Caporali et al., 2000b), and a high-resolution Digital Terrain Model (DTM) of the road surface, depth and discharge of the water film in the maximum local slope direction are investigated.