Labyrinths

Impingement demister systems are designed to intercept liquid particles before the gas outlet. They are usually constructed from wire mesh or metal plates and liquid droplets impinge on the internal surfaces of the mist mats or plate labyrinth as the gas weaves through the system. The intercepted droplets coalesce and move downward under gravity into the liquid phase. The plate type devices or vane packs are used where the inlet stream is dirty as they are much less vulnerable to clogging than the mist mat. 

Other modifications have special but more limited apphcations. A centrifugal bowl may contain, instead of disks, several aimular baffles that take the hquid through a labyrinth path before discharge. The multiple cylinders increase cake capacity to as much as 70 L for easily sedimented sohds. This centrifuge is used for clarification of food symps and antibiotics (qv), and for recovery of heavy metallic salts and catalysts (see Fig. 14c). 

Fig. 10. The Groth ZG 5 centrifuge. R, rotor R, stationary shaft T, Teflon seal K, K, chambers for gas scoops S, S2, scoops V, gas supply M, manometer Z, Z2, tapping points for enriched and depleted gas P, P2, vacuum chambers E, electromagnet for eddy current heating Tb, Tb2, temperature measuring devices K, cooling coil and D, D2, labyrinth seals.

Labyrinth Seals The labyrinth is one of the simplest of the many sealing devices. It consists of a series of circumferential strips of met extending from the shaft or from the bore of the shaft housing to form a cascade of annular orifices. Labyrinth seal leakage is greater than that of clearance bushings, contact seals, or filmriding se s. 

Labyrinth seals are simple to manufacture and can be made from conventional materials. Early designs of labyrinth seals used knife-edge seals and relatively large chambers or pockets between the knives. These relatively long knives are easily sibject to damage. The modern, more functional, and more reliable labyrinth seals consist of sturdy, closely spaced lands. Some labyrinth seals are shown in Fig. 10-107. Figure 10-107 7 is the simplest form of the seal. Figure... 

Leakage past these labyrinths is approximately inversely propor-... 

P = absolute pressure before the labyrinth P = absolute pressure after the last labyrinth = specific volume before the labyrinth n = number of lauds... 

The labyrinth sleeve can be flexibly mounted to permit radial motion for self-ahguiug effects. In practice, a radial clearance of under 0.008 is difficiilt to achieve. 

Labyrinth type seal where rubbing contact is to be avoided. 

Valve bags usually rely on a labyrinth of paper or plastic film to seal off the valve. The automatic internal valve, while adequately protecting the contents of the bag, does allow a small amount of sifting of fine powders. 

Wear and increased leakage from the glands are common. Carbon rings may need replacement after I or 2 years of operation. A unit with labyrinth packing may never need packing replacement. This depends upon operation. If a unit is started quickly with a temperature bow in the shaft, the result is a rub in the labyrinth, and then all packing may need replacement. 

Rotor Seals To balance the thrust on the rotor, usually there are one or two labyrinth-type seals on the rotor. These seals often are damaged if there is dust in the incoming fluid or gas, and wear on the backside seal causes serious upsets in thrust-bearing loads. Provisions are available for coUecting and disposing of the dust which tends to accumulate in the seal so as to protect the seal from serious erosion. 

The shaft seal (see subsection Shaft Seals ) generally is a close-clearance labyrinth-type seal. It is desirable that there be available a suitable pressurized buffer gas for injection into the intermediate point in the seal, such gas to be available at an absolute pressure well above the highest shaft pressure to be sealed. Then the seal-gas system may consist of only a filter, a flow-indicating device, and a throttle... 

These are an itnprovised version of a totally enclosed motor to protect its live parts from ingress of water, rain, snow or airborne particles etc. This is achieved by providing them with additional protection such as labyrinths at joints such as bearing end covers, centrifugal discs, end shields and terminal box and giving the outer... 

Labyrinth seals work best when the pump is running. Centrifugal force favors the labyrinth seal s action. Earlier models were only specified for horizontal pump shafts. Later models are designed for both horizontal and vertical pump shafts and effectively perform their function whether the pump is running or off... 

The RR developed by the author at UCC was the only one that had a high recycle rate with a reasonably known internal flow (Berty, 1969). This original reactor was named later after the author as the Berty Reactor . Over five hundred of these have been in use around the world over the last 30 years. The use of Berty reactors for ethylene oxide process improvement alone has resulted in 300 million pounds per year increase in production, without addition of new facilities (Mason, 1966). Similar improvements are possible with many other catalytic processes. In recent years a new blower design, a labyrinth seal between the blower and catalyst basket, and a better drive resulted in an even better reactor that has the registered trade name of ROTOBERTY . ... 

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