Law of substance separation on cross-flow filtration in turbulent flow

Cross-flow filtration is a filtration process for separation of a disperse phase from liquids. Suspension flows tangentially to a membrane and the filtrate is drawn off perpendicular to the direction of flow. Formation of a filter cake on the membrane is thus prevented, reduced, or its composition, modified. The principle of the separation is based on tow opposing effects: on the one hand, the particles are transported by the filtration flux to the membrane where they cause and increase in concentration; on the other hand, concentration differences are again reduced by the turbulence of the cross-flow and by Brownian motion of the particles. The two mechanisms compete with each other and depend upon particle size in different ways. An energetic comparison of the two effects yields the separation law of cross-flow filtration as a steady state solution of the Fokker-Planck equation. The separation law has an exponential form and assigns each particle size a separation probability with which it reaches the membrane. Once on the membrane the particles may form a filter cake, flow through the pores or return to the bulk flow. If the particles remain on the membrane the ranges of layer-free and cake-forming filtration can be calculated from the hydro-dynamic and geometric conditions of the cross-flow filter. Conventional cake filtration is regarded as limiting case. In continuous cross-flow filtration process a low separation probability through the filtration pressure on selection of the filter medium resistance.     

Statische Mischer und ihre Anwendung

Static mixers and their applications . Static mixers are generally made up of similar, fixed mixing units installed at right angles to each other in series along a tube or a channel. The energy of mixing is extracted from the flow. Twelve different units are presented. The mixing effect in static mixers under conditions of laminar flow is accomplished either by specially designed feed systems, by cutting and twisting, by displacement and distortion, or by separation and expansion. Depending upon the mixer, very different lengths are required to achieve the same degree of homogeneity. Compared with an empty tube, the pressure drop in static mixers is some 7-to 200-fold greater for laminar flow and 100- to 600-fold greater for turbulent flow. Static mixers are employed in all areas of chemical engineering for homogenization, for reduction of the resisdence-time spectrum, and for heat exchange. Since maintenance and wear are negligible, since incorporation frequently requires no extra space, and since they can be used over wide ranges of viscosity, static mixers are being increasingly employed in continuous processes.     

Heterotrophic growth and nutritional aspects of the diatom Cyclotella cryptica (Bacillariophyceae): Effect of some environmental factors

To investigate the nutritional value of the diatom Cyclotella cryptica (Reimann, Lewin, and Guillard) as an alternative feed for use in the aquaculture industry, the heterotrophic growth characteristics and resultant fatty acid profile of the microalga were studied when cultivated under a variety of controlled salinity and temperature conditions. In addition, the effects of pH on the growth characteristics were also studied. The maximum specific growth rate was affected by initial pH and cultivation temperature, but not by salinity. The optimal pH and temperature ranges for growth were 7.2 to 8.1 and 22.5 to 25.0 °C, respectively. Lipid accumulation and the fatty acid composition were also affected by cultivation temperature and salinity. The optimal temperature range and salinity level for lipid accumulation were 18.0 to 25.0 °C and 11.2 psu, respectively. In all cases the fatty acid distribution was similar, with the most abundant fatty acids being palmitic acid (16:0), palmitoleic acid (16:1 n-7), stearidonic acid (18:4 n-3, SDA), eicosapentaenoic acid (20:5 n-3, EPA), and decosahexaenoic acid (22:6 n-3, DHA).     

Clinical anatomy of the interosseous arteries of the forearm

In recent years, several local flaps have been developed, based on the anterior and posterior interosseous arteries and their anastomoses at the wrist (e.g. posterior interosseous flap, pronator quadratus flap etc.). The anatomy of the arterial network supplying the flap is well established in both clinical and anatomical literature. Most authors agree in the constancy of the anastomoses between the interosseous arteries at the wrist and the absence of major anatomical variations excluding the use of the flap. In the present study, which is based on cadaver dissections of 60 preserved specimens, several gross vascular variations of the interosseous arteries have been found. The most frequent types were an additional anastomosis between the posterior interosseous artery and a perforating branch of the anterior interosseous artery in the middle third of the forearm, which was found in 20%. Ring-formations of the palmar and the dorsal branch of the anterior interosseous artery occurred in 5%. The point of perforation of the interosseous membrane by the dorsal branch of the anterior interosseous artery was found to vary in a larger extent, as described previously.     

A model for interference studies relating to multisatellite non-geostationary systems in the mobile satellite service

An option being considered by current and prospective mobile satellite service (MSS) operators is the use of constellations of non-geostationary orbit (NGSO) satellites to provide global personal communications. The scarcity of free spectrum, together with the bandwidth typically required, means that any new MSS system must consider sharing spectrum with other systems and services. Spectrum sharing must be based on defined interference criteria being satisfied. When multiple NGSO satellites are considered there is no accepted method for assessing interference. This paper describes a model used as the basis for a computer simulation of interference scenarios involving MSS, fixed service (FS) and fixed satellite service (FSS) systems. The simulation includes NGSO dynamics, constellations of MSS satellites with multi-spot antennas, multiple geostationary FSS satellites and multiple hop FS links. Interference events are based on C/I calculations, and statistics, such as the percentage of time that the C/I falls below a required protection ratio, are calculated. More generally C/I cumulative distribution functions are produced.