Page 345 - APPLIED PROCESS DESIGN FOR CHEMICAL AND PETROCHEMICAL PLANTS, Volume 1, 3rd Edition

Mixing of Liquids 313

.-·Droll Tubt
Gos·fud
Manifold
··coil Bonk

Figure 5-24A. Draft tubes prevent short- Figure 5-248. Forced convection past Figure 5-24C. Gas-liquid mixing is more
circuit!ng of liquid from inlet to outlet in a heat transfer surfaces improves the overall complete when concentric draft tubes are
continuous mixing vessel. By permission, coefficient of heat transfer. By permission, used to recirculate gases. By permission,
Weber, A. P., Chem. Engr., Oct. 1953, p. Weber, A. P., Chem. Engr., Oct. 1953, p. Weber, A. P., Chem. Engr., Oct. 1953, p.
183 (23]. 183 [23]. 183 [23].

Settled Solid
Y j -, \ - :::, ,Concenlric or Layered
Draft Tubu Liquid
�----D-----l
Figure 5-240. Capacity of a draft tube Figure 5-24E. Baffles positioned in the Figure 5-24F. Settled solids or layered liq-
assembly to suck in gases ;s a function of draft tube accentuate the direct mechani- uids are quickly dispersed by the direc-
the liquid height above the rotor hub. By cal action of low speed mixing elements. tionalized flow from the draft tube. By per-
permission, Weber, A. P., Chem. Engr., By permission, Weber, A. P., Chem. Engr., mission. Weber, A. P., Chem. Engr., Oct.
Oct. 1953, p. 183 [23]. Oct. 1953, p. 'i 83 [23]. 1953, p. 183 (23].

--
---... \ - Draft Tu be
1
j I I
-- .:»: -Helix
Continuous
\\

Figure 5-24G. Direct mechanical action Figure 5-24H. Helix-in-draft-tube assem- Figure 5-241. Mechanical design problems
can be increased by the addition of a grat- blies are effective for crutching pastry or may be solved by using a draft tube to
ing piate to the draft tube. By permission, fibrous materials. By permission, Weber, amplify the action of the mixer. By permis-
Weber; A. P., Chem. Engr., Oct. 1953, p. A. P., Chem. Engr., Oct. 1953, p. 183 (23]. sion, Weber, A. P., Chem. Engr., Oct. 1953,
183 (23]. p. 183 [23].

the real problem. The important similitude concept 2. Kinematic similarity requires geometric similarity
involves the following: and requires corresponding points in the system to
have the same velocity ratios and move in the same
l. Geometric similarity requires all corresponding direction between the new system and the model.
dimensions of a new system to have the same ratio
with a test model which has proven acceptable. 3. Dynamic similarity requires geometric and kinemat-
These dimensions should include vessel diameter ic similarity in addition to force ratios at corre-
and liquid level, baffle width and number in vessel, sponding points being equal, involving properties of
impeller diameter, number of blades and width gravitation, surface tension, viscosity and inertia [8,
ratio. For example, a tank four times the diameter of 21]. With proper and careful application of this
the original model also requires a turbine ten times principle scale-up from test model to large scale sys-
the diameter of the original turbine. tems is often feasible and quite successful. Tables 5-