Surface trickle

Surface trickle. Water is applied through small bore perforated pipes on or near to the soil surface. They give a much more efficient use of water than sprinklers or rain guns and are often used in pereimial horticultural crops or vineyards. 

Sub-surface trickle. Often used in orchards or vineyards in hot, dry climates like California where water is becoming a scarce resource. The pipes are buried below ground to reduce evaporation waste and make water use even more efficient. 

Where there are large volumes of contaminated water under a small site, it is sometimes most convenient to treat the contaminant in a biological reactor at the surface. Considerable research has gone into reactor optimization for different situations and a variety of stirred reactors, fluidized-bed reactors, and trickling filters have been developed. Such reactors are usually much more efficient than in situ treatments, although correspondingly more expensive. 

Cascade coolers are a series of standard pipes, usually manifolded in parallel, and connected in series by vertically or horizontally oriented U-bends. Process fluid flows inside the pipe entering at the bottom and water trickles from the top downward over the external pipe surface. The water is collected from a trough under the pipe sections, cooled, and recirculated over the pipe sections. The pipe material can be any of the metallic and also glass, impeiMous graphite, and ceramics. The tubeside coefficient and pressure drop is as in any circular duct. The water coefficient (with Re number less than 2100) is calculated from the following equation by W.H. McAdams, TB. Drew, and G.S. Bays Jr., from the ASME trans. 62, 627-631 (1940). 

Distributor The rotating mechanism that distributes the wastewater evenly over the surface of a trickling filter or other process unit. 

In the first class, the particles form a fixed bed, and the fluid phases may be in either cocurrent or countercurrent flow. Two different flow patterns are of interest, trickle flow and bubble flow. In trickle-flow reactors, the liquid flows as a film over the particle surface, and the gas forms a continuous phase. In bubble-flow reactors, the liquid holdup is higher, and the gas forms a discontinuous, bubbling phase. 

Speed-up of mixing is known not only for mixing of miscible liquids, but also for multi-phase systems the mass-transfer efficiency can be improved. As an example, for a gas/liquid micro reactor, a mini packed-bed, values of the mass-transfer coefficient K a were determined to be 5-15 s [2]. This is two orders of magnitude larger than for typical conventional reactors having K a of 0.01-0.08 s . Using the same reactor filled with 50 pm catalyst particles for gas/Hquid/solid reactions, a 100-fold increase in the surface-to-volume ratio compared with the dimensions of laboratory trickle-bed catalyst particles (4-8 mm) is foimd. 

When hydrogenation is carried out in a continuous process often so-called trickle-ttow reactors are used. Mass-tran.sfer limitations often occur. An elegant improvement is the application of extrudates with a noncircular cross section, which increa.ses the external surface without increasing the pressure drop. Trilohe and Quadrilohe shapes are generally used in oil-refinery processes and they might also be useful in fine chemicals production. 

Fig. 5.2.3 Identification of rivulets and surface wetting in a packing of 5-mm diameter glass spheres contained within a column of inner diameter 40 mm. The data were acquired in a 3D array with an isotropic voxel resolution of 328 xm x 328 pm x 328 [im. (a) The original image of trickle flow is first binary gated, so that only the liquid distribution within the image is seen (white) gas-filled pixels and pixels containing glass spheres show up as zero intensity (black), (b) The liquid distribu-...

A useful application of the model is to examine the S02 and 02 concentration profiles in the trickle bed. These are shown for the steady-state conditions used by Haure et al. (1989) in Fig. 25. The equilibrium S02 concentration drops through the bed, but the 02 concentration is constant. In Haure s experiments 02 partial pressure is 16 times the S02 partial pressure. At the catalyst particle surface, however, 02 concentration is much smaller and is only about one-third of the S02 concentration. This explains why 02 transport is rate limiting and why experimentally oxidation appears to be zero-order in S02. 

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