Diameter Considerations

For random packings there are many reports (3,56,98,136,140a,162-167) of an increase in HETP with column diameter, fewer in which column diameter had little effect on HETP (3,56,162,163), and an odd case in which increasing column diameter led to a deorease in HETP (56). Billet emd Mackowiak s (3,62,166) scaleup chart for Pall rings implies that efficiency decreases as column diameter increases. 

For structured pa ngs, tests with the Kodi-Sulzer BX and CY wire-mesh packings and with Mellapak 250Y showed no diam r rf-fect on HETP (3,19,32,83). Wu and Chen (167) state that the same plies to Gempak pac gs. On the other hand, tests with Hyperffl showed an increase in HETP with column diameter (168). 

The inoease in HETP with column diameter appears to be most pronoimced for small column diameters ( 1 ft Refs. 56,164) and with smaller packings ( 1 in Refs. 66,136). It has therefore been recommended tiiat for scaleup purposes, a column at least 1 ft in diameter, and prefmably larger, ould he used (164). 

Practically all sources explain the increase of HETP with column diameter in terms of enhanced maldistribution (3,56,62,136,148,162-164). Pilot colwnns seldom operate at column to packing diametmrs ratios (Dt/Dp) lai r than 20 under these conditions, lateral mixii effective counteracts loss of effidenty due to maldistribution pindi (Sec. 9.2.3). On the othmr hand, industrial-scale columns usually operate at DjiDp ratios of 30 to 100 under these conditions, latmal mixiiig is ineffective for counteracting maldistribution pinch. 

In small columns, the wett contributes to mass transfer. This problem can be overcome by keeping the ratio of column to packing diameter above 10 (Sec. 9.2.4), For cases where wall effects are significant, Wu and Chen (167) recommend applying the following safety factor. 

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Catheter angiography provides exquisite image detail and can visualize vessels as small as 0.1 mm in diameter, considerably smaller than those seen by CT- and MR-based vascular imaging techniques. Catheter angiography also provides high temporal resolution, which can help to distinguish arteries from veins and to detect prolonged intravascular stasis of blood. 

Powder for rockets is usually in the form of perforated grains with a large diameter, considerably larger than that of the tubes used for cannon charges. This makes the production process for extruding the powder mass very complicated. 

From Figs. 3a and 3b, it is deduced that structure sensitivity should appear only for particles with d less than about 5 nm. It is convenient to call systems that actually exhibit this behavior systems with limited structure sensitivity. On the other hand, if geometric effects are governed by ensembles of several atoms, then structure sensitivity should extend to diameters considerably greater than 5 nm. This behavior we call extended structure sensitivity. In other words, with limited structure sensitivity, the system is structure insensitive for d > 5 nm. A glance at the figures in the rest of this review shows that many actual systems present extended structure sensitivity. 

Even with the collimator lenses, light from the centre and from the edge of the fibre bundle passes the filter at a different angles. The difference can be kept small only by using lenses of a focal length and a diameter considerably larger than the diameter of the fibre bundle. 

A membrane is a heterogeneous barrier between otherwise two homogeneous systems. It consists of a complicated network of pores which may be connected to each other in a complex manner. The mechanism of transport depends on (i) the size and shape of the pores, and (ii) nature of the permeant. The phenomenon of thermo-osmosis can occur only when the diameter of pores is comparable to mean free path of the permeating species. For gaseous systems, the mean free path can be controlled by controlling the mean pressure. In view of the membrane being made up of a complex network of pores, some pores may have diameters considerably less than the mean free path while some others may have pore diameters considerably larger than the mean free path. In the latter case, viscous flow can occur and the net flow is a composite flow made up of... 

Purthermore, the presence of some impurities on the surface of the okra fibre can also be seen, and the fibres are cemented in non-cellulosic compounds. In particular, the cross-sectional shape of okra fibre shows a polygonal shape that varies notably from irregular shape to reasonably circular, as depicted in Pig. 1.15. Their diameter considerably vary in the range of about 40-180 pm. Purthermore, each ultimate cell is roughly polygonal in shape, with a central hole, or lumen like other natural plant fibres, as shown in Pig. 1.15. The cell wall thickness and lumen diameter vary typically between 1-10 pm and 0.1-20 pm, respectively. As a consequence of it. 

Rollers on conveyor chains normally have diameters considerably larger than the widths of their adjacent sidebars, as shown in Figure 2-4. This is done for two reasons. First, and most obvious, the large rollers, called carrier rollers, carry the sidebars well above the conveyor tracks... 

Critics described the proposed structure as a vast pile of masonry that they feared would never be removed and would become a permanent mutilation of Hyde Park. Indeed, the committee s malproportioned behemoth would have required the laying of fifteen million bricks and the construction of a dome two hundred feet in diameter, considerably larger than that of St. Paul s Cathedral. The mortar would not have been expected to be dry in time for the opening of the exhibition, then less than a year away. 

Greif performed measurements on an experimental cyclone at various solids loadings and distributions and vortex tube immersion depths and diameters. Considerable attention was devoted to improving the limiting load at low to moderate levels of sohds loadings. For illustration purposes, one data set was selected for simulation herein. Its geometry and dimension are shown in Fig. 6.A.7. Physical property and flow data at test conditions follow. 

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