Gravity separations terminal velocity

For very small particles or low density solids, the terminal velocity may be too low to enable separation by gravity settling in a reasonably sized tank. However, the separation can possibly be carried out in a centrifuge, which operates on the same principle as the gravity settler but employs the (radial) acceleration in a rotating system (o r) in place of the vertical gravitational... 

In the first, droplets separate from the earner vapor when the gravity force overcomes the Ruid drag force. The minimum requirement for separation occurs when the gravitv force balances the drag force, at which point the droplets fall at a constant terminal velocity. U,. 

Gravity separations depend essentially on rite density differences of rite gas, solid, or liquids present in the mix. The particle size of the dispersed phase and the properties of die continuous phase are also factors with rite separation motivated by die acceleration of gravity. The simplest representation of this involves rite assumption of a rigid spherical panicle dispersed in a fluid with rite terminal or free-settling velocity represented by... 

Gravity separation occurs try merely reducing die velocity of a stream an that terminal particle settling or rise velocities due to gravity exceed die velocity of the bulk Row. The terminal particle or bubble velocities can be estimated try die methods described in Section 3.1. 

A cyclone separator is used to remove sand grains from an airstream at ISO C. If the cyclone body is 0.6 m in diameter and the average tangential velocity is 16 m/s, what is the radial velocity near the wall of particles 20 and 40 pm in size How much greater are these values than the terminal velocity in gravity settling ... 

For an example of 10 fun particles of specific gravity = 3, Are terminal velocity is 0.033 ft/s. To separate these particles and all larger particles from a water stream of 1(X) fl /min (833 gal/min), the basin dimensions... 

Dilute This is a fully expanded condition in which the solids particles are so widely separated that they exert essentially no influence upon each other. Specifically, the solids phase is so fuUy dispersed in the gas that the den sity of the suspension is essentially that of the gas phase alone (Fig. 12-29). Commonly, this situation exists when the gas velocity at all points in the system exceeds the terminal setthng velocity of the solids and the particles can be lifted and continuously conveyed by the gas however, this is not always true. Gravity settling chambers such as prilling towers and countercurrent-flow spray diy-ers are two exceptions in which gas velocity is insufficient to entrain the sohds completely. 

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