Percolation flow

The flow of water through soil is called percolation. The more porous the soil, the greater the rate of percolation. With excessive percolation, flowing water removes many water-soluble nutrients needed to make the soil productive. This process is known as leaching. With too little percolation, topsoil becomes waterlogged, choking off a plants supply of oxygen. Soils with optimal percolation drain water from all but the smallest air pockets. 

The various factors that influence percolation leaching were examined by Seidel (S6). The percolation flow rate through the ore bed is very dependent on the permeability or texture of the bed. It decreases with increase in air or gas bubbles present in the bed and can be increased by increasing the temperature of the leaching solution. The size distribution of the particle, the porosity, temperature, leaching solution concentration, and percolation rates influence the mass-transfer rate. 

Let us consider the problem about a porous particle of radius a in a translational fluid flow with velocity U. We assume that the flow outside the particle obeys the Stokes equations (2.1.1) with viscosity /z. We also assume that the percolation flow of an incompressible fluid inside the particle satisfies Darcy s law [97, 346,423] ... 

We will be concerned with dense porous materials wherein the percolation flow velocity is normally small and the characteristic Reynolds number is much less than... 

From the values of catholyte flow, percolation flow and the percolation velocity (see Appendix 4.7.2 for details) and the mqh- and OH- values calculated using the... 

This adverse effect occurs much less in tanks 8 m deep where air percolation flow is four or... 

In the first atmospheric freeze-drying experiments, the frozen droplets were kept on the sieve and sublimation dried by a percolating flow of nitrogen at approximately — 10 °C for 20 h. 

Therefore, the freezing and drying steps were studied separately and batches of frozen droplets were vacuum dried in a laboratory lyophilizer within less than 20 h as shown by Serim et al. [35]. In the final project phase, a modified version of atmospheric freeze-drying was implemented, where frozen droplets were collected on a fine-meshed steel sieve and dried in a percolating flow of gas at temperatures... 

The sample solution flows onto a piece of fritted glass through which argon gas flows. The flow of argon is broken down into narrow parallel streams of high linear velocity, which meet the thin film of liquid percolating into the pores of the frit. At the interfaces, an aerosol is formed and is blown from the top of the frit. 

Eor pesticides to leach to groundwater, it may be necessary for preferential flow through macropores to dominate the sorption processes that control pesticide leaching to groundwater. Several studies have demonstrated that large continuous macropores exist in soil and provide pathways for rapid movement of water solutes. Increased permeabiUty, percolation, and solute transport can result from increased porosity, especially in no-tiUage systems where pore stmcture is stiU intact at the soil surface (70). Plant roots are important in creation and stabilization of soil macropores (71). 

Further down, ca 75 cm below the electrode tips, the mix is hot enough (2200—2500°C) to allow the lime to melt. The coke does not melt and the hquid lime percolates downward through the relatively fixed bed of coke forming calcium carbide, which is Hquid at this temperature. Both Hquids erode coke particles as they flow downward. The weak carbide first formed is converted to richer material by continued contact and reaction with coke particles. The carbon monoxide gas produced in this area must be released by flowing back up through the charge. The process continues down to the taphole level. Material in this area consists of soHd coke wetted in a pool of Hquid lime and Hquid calcium carbide at the furnace bottom. 

Batch Percolators The batch tank is not unlike a big nutsche filter it is a large circiilar or rectangiilar tank with a false bottom. The solids to be leached are dumped into the tank to a uniform depth. They are sprayed with solvent until their solute content is reduced to an economic minimum and are then excavated. Countercurrent flow of the solvent through a series of tanks is common, with fresh solvent entering the tank containing most nearly exhausted material. In a typical ore-dressing operation the tanks are 53 by 20 by 5.5 m (175 by 67 by 18 ft) and extract about 8200 Mg (9000 U.S. tons) of ore on a 13-day cycle. Some tanks operate under pressure, to contain volatile solvents or increase the percolation rate. A series of pressure tanks operating with countercurrent solvent flow is called a diffusion battery. 

Percolation The movement or flow of water through soil or rocks. 

As shown in Fig. 14.2, the material conveying region is bounded by the air-only curve and the stationary-plug curve, where the air merely percolates through or flows above a packed bed of stationary particles. Dense-phase conveying occurs when v, the velocity of air, is below the so-called saltation velocity. 

Its main features are given by the use of a stream of inert carrier gas which percolates through a bed of an adsorbent covered with adsorbate and heated in a defined way. The desorbed gas is carried off to a detector under conditions of no appreciable back-diffusion. This means that the actual concentration of the desorbed species in the bed is reproduced in the detector after a time lag which depends on the flow velocity and the distance. The theory of this method has been developed for a linear heating schedule, first-order desorption kinetics, no adsorbable component in the entering carrier gas (Pa = 0), and the Langmuir concept, and has already been reviewed (48, 49) so that it will not be dealt with here. An analysis of how closely the actual experimental conditions meet the idealized model is not available. 

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