Horizontal transport

In a horizontal pipeline the distribution of the solids over the cross-section becomes progressively less uniform as the velocity is reduced. The following flow patterns which are commonly encountered in sequence at decreasing gas velocities have been observed in pipelines of small diameter. 

The particles are evenly distributed over the cross-section over the whole length of 

The flow is similar to that described above but there is a tendency for particles to flow preferentially in the lower portion of the pipe. If there is an appreciable size dishibution, the larger particles are found predominantly at the bottom. 

As the particles enter the conveying line, they tend to settle out before they are fully accelerated. They form dunes which are then swept bodily downstream giving an uneven longitudinal distnbution of particles along the pipeline. 

The particles settle out as in slug flow but the dunes remain stationary with particles being conveyed above the dunes and also being swept from one dune to the next. 

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High-pressure systems are characteristicaly the opposite of lows. Since the winds flow outward from the high-pressure center, subsiding air from higher in the atmosphere compensates for the horizontal transport of mass. 

But how can we estimate the pressure-loss coefficient A Stegmaier - has summarized horizontal transport for several fine-granular solids by a correla tion which contains some characteristics of the material. The same idea has been used by Weber, who has found a correlation of the pressure-loss coefficient for vertical pneumatic conveyance based on data measured by Flatow. In order to express these models, we first introduce two dimensiitnless numbers... 

The mathematical model developed by Stegmaier for horizontal transport... 

FIGURE M.I3 Pressure-loss coefficient for horizontal transport according to Stegmaier. ... 

Toigerson T, Tnrekian KK, Turekian VC, Tanaka N, DeAngelo E, O Donnell J (1996) ""Ra distribution in surface and deep water of Long Island Sound Sources and horizontal transport rates. Cont Shelf Res 16 1545-1559... 

And the ratio of the nuclides in the net horizontally transported portion is assumed to equal that observed in the water column ... 

Thus, for particles with a similar density and shape, sinking rates increase with increasing diameter because of the decrease in surface area to volume ratio. As shown in Table 13-5, sand-sized grains reach the sediments in a few days, whereas clays can take centuries. If entrained in a current, sinking particles can also experience significant horizontal transport. 

Since there is no effective mechanism for transporting molecules from a buried source to the surface when the soil is very dry (see Section 4.3.1.3) when faced with such conditions, the system operator may need to become innovative. In addition, unless there is some mechanism for horizontal transport of molecules in moist soil, the operator should expect the strongest surface concentration to appear directly above the buried source. 

Note Horizontal transport mainly by advection (wind)... 

As mentioned earlier, turbulent motion is usually more intensive along the horizontal than the vertical axis. Turbulent structures (eddies) can be horizontally very large. For instance, the eddies or gyres produced by the Gulf Stream are more than 100 km wide. Thus, for horizontal transport the separation between random and directed motion plays a more crucial role than for the case of vertical diffusion. 

The drag coefficient. Cjx. for a horizontally transported particle is defined by Brodkcy (4] ... 

Vertical profiles of long lived trace gases can be used as a basis for the analysis of stratospheric dynamics. The structure of these profiles gives indications for vertical and horizontal transport processes, i.e. descent inside and filamentation of the vortex. An attempt of a vortex climatology describing seasonal subsidence and the position of the measured air parcels relative to the vortex centre is made by comparing the correlation of N20 mixing ratios versus PV values for different years. 

It is the aim of this contribution to contrast the effect of vertical fluxes of material in the open ocean with horizontal transport which is likely to be important in shallow-water systems. The models described below are based on a number of simplifying assumptions, therefore the results must be treated with caution. In particular the magnitude of predictions may not always be realistic, although the relative proportions and sequence of events modelled are believed to reflect the real situations. 

Both of the models presented here are based on the flow of nitrogen through ecosystems in one case a nearshore kelp-bed system and in the other a general offshore plankton community. The klep bed model was developed to explore the hypothesis that nitrogen flow is affected by horizontal water transport in shallow water marine systems here wave action or mixing associated with horizontal transport are likely to retain nitrogen in the photic zone and the benthic community is of fixed location so that boundaries of the system can be easily defined. In pelagic systems, on the other hand, the community tends to move horizontally with water in the mixed layer, and vertical transport into and out of the mixed layer is an important feature of the system dynamics. 

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