Blaise Nsom

Computation of drag reduction in fiber suspensions

We report the results of a theoretical study of the drag reduction phenomenon in dilute and semi-concentrated suspensions of stiff fibers. For this, we use the Ericksen anisotropic fluid rheological equation of state in a wide-gap Couette–Taylor configuration. The drag reduction is directly computed from its definition, in relation to the fiber aspect ratio and the cylinders radii ratio in the dilute concentration range. In the semi-concentrated range, the drag reduction is computed with respect to the cylinder radii ratio, the fiber concentration and density.

Effect of Atmospheric Pollutants on the Air Quality in Tunisia

This paper presents the evolution of Saharan dust advection when the PM10 (particles with an aerodynamic diameter below 10 μm) concentration exceeds standard limits in different Tunisian sites. Meteorological and concentration data (from 2004 to 2010) obtained from several monitoring stations and in situ measurements were used to identify African dust change in seasonal occurrence, their source origin, and their impact on surface PM10 concentrations. We pointed out that the Saharan dust contribution caused frequently the surpassing of the maximum number of days in excess of EU standard limits as well as of the maximum yearly average in the Mediterranean Tunisian coasts. The maximum daily concentration reaches 439 μg/m3 during the Saharan events. The decrease in particulate levels recorded at the end of each event is due to the injection of European air masses and rainfalls. Primary pollutants peaks were much higher in winter than in summer which can be explained on the basis of the lower ventilation and mixing.

Experimental Study of the Effect of the Spreading Buoyant Gravity Current on the Coastal Environment

The experiments of injection gravity currents were completed in a rectangular basin by release the fresh water over a salty water surface at rest. The surface flow of lighter liquids horizontally can be considered as a special case of a two dimensional gravity current, and the spreading law of the fresh water is validated by using image processing technique to record the progress of the injection current. The jet fluid was colored and the digital video can have a variation of light intensity in order to obtain the shape of the outer boundary of the gravity current and its distance from the source point with relation to time, initial, or flow parameters of the jet source.

Air Quality Monitoring in the Mediterranean Tunisian Coasts

The transfer from the liquid element (the sea) to the solid one (the land) engenderers thermal phenomena such breezes. During the day, the land heats up more rapidly than the sea. Over the land surface, the heat spreads in the low layers and gives birth to upward currents. This hot continental air rises up, and then is superseded by a colder air coming from the sea; it is the sea breeze. During the night, the phenomenon is reversed to become a land breeze. If the synoptic wind is weak, the breezes will take their true size and result in the formation of convergent zones on the land and divergent zones over the sea. Some visual signs can help observe these phenomena. The low clouds of the cumulus type are a proof of the vertical movement. They are often related to the setting of the sea breeze (Simpson, 1994). Many experimental and numerical studies have shown the impact of breeze circulations on the evolution of pollutant concentrations (Bouchlaghem et al., 2007; Srinivas et al., 2007; Baumgardner et al., 2006; Evtyugina et al., 2006; Flocas et al., 2006; Lim et al., 2006). The photochemical transformation also plays a crucial role in the production and destruction of pollutants. These transformations coupled with the dynamic circulations such as breezes represent the responsible process of the formation, transport and redistribution of reactive chemical species in the low layers of the atmosphere. The study made by (Ma and Lyons, 2003) via a 3D version of RAMS model (Regional Atmospheric Modelling System) has shown that the recirculation of pollution is a Mediterranean characteristic. They have defined the recirculation as follows: in the presence of a weak synoptic wind, the heating and cooling of the land and the sea determine the local circulation which affects the transport and diffusion of emissions. In fact, during the night, emissions can be transported over the sea via a land breeze or an offshore synoptic wind just to return onshore to the land after the launching of the sea breeze. The study of (Nester, 1995) has shown that the phenomena of photochemical Smog are generally associated with this type of meteorological conditions such as, a weak synoptic wind and a recirculation of 11