Cross-flow velocity impact

Koseogju H, Kahay N, Yiiksel M, Sarp S, Arar O, and Kitis M, Boron removal fiom seawater using high rejection SWRO memhranes— Impact of pH, feed concentration, pressure and cross-flow velocity. Journal of Membrane Science 2008, 227, 253-263. 

The collection of particles is achieved in a countercurrent flow between the water droplets and the particulates. In a cyclonic scrubber, water is injected into the cyclone chamber from sprayers located along the central axis, as shown in Fig. 7.19. The water droplets capture particles mainly in the cross-flow motion and are thrown to the wall by centrifugal force, forming a layer of slurry flow moving downward to the outlet at the bottom of the cyclone. Another type of scrubber employs a venturi, as shown in Fig. 7.20. The velocity of the gas-solid suspension flow is accelerated to a maximum value at the venturi throat. The inlet of the water spray is located just before the venturi throat so that the maximum difference in velocity between droplets and particles is obtained to achieve higher collection efficiency by inertial impaction. A venturi scrubber is usually operated with a particle collector such as a settling chamber or cyclone for slurry collection. 

Under the impact of the cross-flow, the biopoly-mers/particles are forced in the direction of the membrane. To ensure that the analytes do not pass through the membrane, different pore sizes can be used. In this way, the analytes can be selectively rejected and it is possible to remove low-molecular compounds before the separation. The analytes diffusion back from this membrane is counteracted by the cross-flow, where, after a time, a dynamic equilibrium is established. The medium equilibrium height for smaller sized analytes is located higher in the channel than for the larger analytes. The smaller sized analytes are traveling in the faster velocity lines of the laminar channel flow and will be eluted first. As a result, fractograms, which... 

In down-wash configuration, the flame is established in the wake of the burner tube. A recirculation vortex in the wake of a burner tube appears as a flame sheet. When R is further reduced, the flame tip is severely deflected by the crossflow. A small recirculation bubble was observed by Huang and Chang [16] atR = 0.04. For a value of R between 0.1 and 1, the impact of a cross-flow stream is dominant. An axisymmetric tail flame forms downstream of the recirculation vortex and the flame widens. This structure is characterized by several features such as flickering and bifurcation. In jet-dominated mode, the recirculation vortex disappears and only the tail part remains attached to the burner. The transition from crossflow-dominated to jet-dominated conditions occurs from 1 = 1 to 3. For R>3, the effect of crossflow becomes negligible the jet fluid mechanics dictate the flame characteristics. For R > 10, the flame detaches from the burner and stabilizes above the exit plane of the burner tip. Depending upon the jet exit velocity and burner diameter, the flame is either attached to the burner tip or stabilizes as a lifted flame until it blows out. 

A major advantage of the dilution principle is that CD profiles of main fiber orientation can be rectified (Fig. 5.36 ). As mentioned before local slice bar adjustment causes cross flow in the nozzle chamber and in the exiting jet. Even a small angle of the jet velocity vector against the machine direction results in a large main fiber orientation angle. The main fiber orientation angle describes the direction of the plurality of the fibers in the paper and can be measured by laser or by ultrasonic devices. It has an impact on other important paper properties. 

As part of preliminary studies, the separation model in Eq.(3) was applied for the classification of sand/split and gravel, Table 3. In Fig. 3, the measured values for the three separation experiments with the cut size dr = 2,1 4.6 and 6.7 mm are shown. Despite reduction by particle shape impact, the quasi-statlonary settling velocity of spheres v,t at this cut-point is higher than the averaged channel air flow rate u being characteristically for the predominant cross-flow separation principle. 

The crossing trajectory effect refers to the impact of the continuous change of the fluid eddy-particle interactions as the heavy particle trajectory might go through numerous eddies reflecting different flow properties. Hence it follows that the velocity history of heavy particles may differ from that of a marked fluid particle. Similar closure models for the drift velocity and the velocity co-variances have been derived from kinetic theory by Koch and co-workers [38, 39] and Reeks [62, 63]. 

Figure 1.6 Geometry of ducts, impact of cross-sectional shape (a-c) and impactofbends (d-f). (a) Relevant geometries in segmented flows, including the shape of the menisci between the channel wall and dispersed phase. The graph shows what fraction of the cross-sectional area the menisci fill for round and square channels, as a function of Co [104]. (b) Evolution of meniscus shape in square channels [97]. The shape at the frontofthe bubble is markedly different from that at the tailing end. The numerical grid and computed film shape and velocity field were...

Influence of pneumoconstriction on dust deposition. Bronchoconstriction in man can be caused by exposure to cigarette smoke as shown by Loomis (1956), Nadel and Comroe (1961), and Guyatt et al. (1970), or by exposure to inert dusts as shown by Dautrebande et al. (1948), and Dubois and Dautrebande (1958). The mechanisms involved have been discussed by Nadel et al. (1965), Nadel (1968) and Dubois (1969). Bronchoconstriction, by reducing the cross section for flow in the conductive airways, results in increased air velocities and turbulence. Increased velocity can result in greatly increased deposition by impaction at the airway bifurcations, while increased turbulence can account for an increase in deposition by eddy diffusion (Lehmann 1938, Worth and Schiller 1951). 

The parameter predicts the chance of impaction against an obstruction in the flow direction of the particle and can for instance be used to predict oropharyngeal deposition. Practically, instead of particle velocity sometimes the flow rate (4>) through an inhaler is used, but this does not enable comparative evaluations between different inhalers when the cross sections for airflow in the mouthpieces are different between the inhalers as this will result in different velocities. 

Pitot tube An instrumentused to measure the velocity ofaflowingfluidby measuring the difference between the impact pressure and static pressure in the fluid. The device normally consists of two concentric tubes arranged in parallel one with a face directed towards the flow to measure the impact pressure, the other face perpendicular to the flow to measure the static pressure. By taking a number of readings at various points in the cross section of a pipe or duct, known as a Pitot traverse, the overall rate of flow can be determined. As with all flow measurement devices, Pitot tubes should ideally be located away from disturbances such as bends. The device was devised by Italian-born French engineer Henri de Pitot (1695-1771). 

Figure 1 Deposition by impaction A schematic drawing of the respiratory tract, which can be seen as three filters in line, to protect the fragile alveoli from particles. The first two filters, mouth and throat and tracheobronchial airways, work by impaction (i.e., particles tend to continue forward and deposit when the gas flow changes direction). Impaction is the most important deposition mechanism for medical aerosols in the upper airways and in larger bronchus, and correlates well with the impaction parameter AD F. In the last filter, the bronchioles, impaction is insignificant owing to the large total cross-sectional area, leading to low velocities.

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