Counter-down

Fluidized leaching and washing is a countercurrent operation with downflow of solids, called counter-down. The following equation for generalized fluidization... 

Equation (3) is plotted in the upper diagram of Fig. 2 as A versus with TV as a parameter. It shows that corresponding to any value of TV, there exists a minimum value of A at which the fluidized leacher/washer possesses the least cross-sectional area or the maximum throughput. This minimum A corresponds to theflooding point characteristic of all counter-down systems and can be calculated by setting the derivative d4 /d = 0, thus yielding... 

Composite IIAB possible for u 0 between zero and point F. Region I1IA Counter-down, restrained, area AGHCB, voidage change +/+ ... 

Region IIIB Counter-down, free, area GEC, voidage change — same application as for IIIA. 

For the counter-down moving bed, such as shaft furnaces, and shown by the AB segment of the e0 = 0.4 line in Fig. 11, fluid velocity can be assigned any value from zero to the point of incipient fluidization, B. The counter-down moving bed can be operated at fluid velocity less than that specified by Eq. (3.5m), resulting, however, in a pressure gradient less than that for incipient fluidization, L0 Ap(l — e0). This reduced pressure gradient can be prorated in accordance with the theory for idealized fluidization ... 

Area AOB in Fig. 12 shows the counter-down moving-bed operation described above, with the value of Q0 = 0 for no fluid flow to Q0 = 1 at incipient fluidization. 

Fluidized leaching and washing belong to counter-down, or mode III, operation for simultaneous particle-fluid motion. A basic case for uniform particle size will be established, and it will then be extended to mixed particle sizes. 

Region BOC Negative pressure difference, countercurrent-cogravity operation (abbreviated designation - Ap counter-down)... 

MOH —Ap counter-down, particles fall by gravity with drag acting upward (shaft furnace) ... 

For either the in-line or hybrid analyzers, the ions injected into the TOF section must all begin their flight down the TOF tube at the same instant if arrival times of ions at a detector are to be used to measure m/z values (see Chapter 26, TOF Ion Optics ). For the hybrid TOF instruments, the ion detector is usually a microchannel plate ion counter (see Chapter 30, Comparison of Multipoint Collectors (Detectors) of Ions Arrays and MicroChannel Plates ). 

When the dryer is seen as a heat exchanger, the obvious perspective is to cut down on the enthalpy of the air purged with the evaporated water. Minimum enthalpy is achieved by using the minimum amount of air and cooling as low as possible. A simple heat balance shows that for a given heat input, minimum air means a high inlet temperature. However, this often presents problems with heat-sensitive material and sometimes with materials of constmction, heat source, or other process needs. AH can be countered somewhat by exhaust-air recirculation. 

Several factors were utilized in bringing formaldehyde release down. In particular, resin manufacturer executed more careful control of variables such as pH, formaldehyde content, and control of methylolation. There has also been a progressive decrease in the resin content of pad baths. The common practice of applying the same level of resin to a 50% cotton—50% polyester fabric as to a 100% cotton fabric was demonstrated to be unnecessary and counter productive (89). Smooth-dry performance can be enhanced by using additives such as polyacrylates, polyurethanes, or siUcones without affecting formaldehyde release. 

DP systems can be shut down when not in use to conserve energy. If a Hquid-nitrogen trap is incorporated, the manner in which this trap is warmed up and the DP is cooled down should be deterniined by the presence or absence of a valve between the chamber and the Hquid-nitrogen trap. In critical systems, this head valve can be included in order to permit rapid shutdown and rapid return to operation. The assertion that dry nitrogen gas can be used to sweep contamination from traps and pumps in such manner that oil contamination is prevented from mnning counter to the nitrogen-sweeping flow direction is questionable. Proper placement of valves can eliminate the need of a sweep gas. 

In the steady-state operation of the OXITOX reactor, pelletized solid of catalytieally aetivated sodium earbonate slides down a Silo type reaetor. Counter-current to the solid flow, the polluted air rises through the sliding bed of solids. At reaction temperature the following reaetion oecurs ... 

The drying of the curd is completed by passing through a rotary drier such as the Pillet-Bordeaux. In this machine the curd passes down a chute with hot air running counter to the direction of flow of material. Strict temperature control is essential, the maximum discharge temperature being below 65°C. If such control is not made then the resin will be dark in colour. 

Packed Towers (also known as wet-scrubbers) A packed tower is a vessel that is filled with some suitable packing material. The liquid is introduced at the top of the tower and flows down through the packing to the bottom, and in so doing, exposes a large surface area to contact with the gas. The gas may be introduced at either end of the tower since the gas and liquid flows may be either co-current or counter-current. The counter-current operation is most commonly used. 

A stone dropped in a pond pushes the water downward, which is countered by elastic forces in the water that tend to restore the water to its initial condition. The movement of the water is up and down, but the crest of the wai c produced moves along the surface of the water. This type of wave is said to be transverse because the displacement of the water is perpendicular to the direction the wave moves. When the oscillations of the wave die out, there has been no net movement of water the pond is just as it was before the stone was dropped. Yet the wave has energy associated with it. A person has only to get in the path of a water wave crashing onto a beach to know that energy is involved. The stadium wave is a transverse wave, as is a wave in a guitar string. 

Propeller Turning Counter-Clockwise Looking Down on Shaft... 

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