Natural vortex length

As illustrated in Fig. 5, the outer downwardly spiralling gas velocity decays as gas peels off into the inner upwardly spiralling exiting vortex. The length of this inner vortex, the natural vortex length, L, (Alexander, 1949) then represents the distance below the edge of the gas outlet tube below which no feed gas remains to peel off into the inner vortex. If the... 

Dp Particle diameter Dth Smallest particle able to cross width Lw El Collection efficiency at actual inlet loading E0 Collection efficiency at <1 gr/ft3 inlet loading H Cyclone height as defined in Fig. 6 L Natural Vortex Length... 

Hoffman AC, de Jonge R, Arends H, Hanrats C. Evidence of the natural vortex length and its effect on the separation efficiency of gas cyclones. FUt Sep 32 799, 1995. 

The position of the vortex end is difficult to model. The first and, by far, the best known relation for the natural vortex length i.e. the length from the lip of the vortex finder to the position of the end of the vortex) was proposed by Alexander (1949) ... 

If the body tube length is increased so that it is greater than the natural vortex length , the vortex end or tail will pop up into the tube body, and take up a position on the wall at some distance from the solids (or liquid) discharge opening. It is likely that a drop in efficiency and a rise in pressure drop will be observed at the length at which this first takes place, since the effective tube length will decrease quite considerably at this point. 

---