The mass transfer coefficient in covered, right-cylindrical tanks full of liquid, turbulently agitated at various speeds by turbines with six flat blades, was measured by the rate of solution of suspended solids in water and in 45% sucrose solutions.
Screened crystals in the following U. S. mesh sizes were used: boric acid: 18/20, 16/18, 16/20, 14/16, 12/14, 10/12, 8/10, 6/8; rock salt: 6/8, 4/6. Pellets were benzoic acid: 0.126 in. long by 0.218-in. diam.; salt: 0.565-in. diam. by 0.531-in. long (over rounded ends).
Tanks and and in. in diameter, centrally located. Four full-length baffles 10% of the tank diameter wide were spaced at 90 deg. A few runs were made without baffles.
The coefficient of mass transfer was found to be independent of particle size and Schmidt number (Ns, = 735 to 62,000) and could be correlated with turbine Reynolds number in each tank, with larger tanks yielding smaller coefficients at the same N R ~. An empirical equation which fits all the data from the baffled tanks within about 4% (in the range 0.1 < k < 2) is
In (10 k ) = /2 + 0.85 P O m 5 In (NRJ10') where /2 = 0.8235 -1.544 V'/' + 0.115 P'
The variance of estimate for this expression is 0.0383, in units of [ln(10 &)I2.
For extrapolation outside the experimental range of vessel sizes it is recommended that h = 0.676 -1.266 V'" be used in place of Iz. Nz0 = JC Tzn/v. The results indicate that power per unit volume for a given k goes through a maximum, with the following relative values for the 6-, 12-, 18-and 30-in. tanks: 1, 1.73, 1.78, 0.62.
A treatment of the data according to dimensionless groups provides another correlation:
t is shown that for the systems used 1 / D is essentially proportional to Ns,".", and so the effect of diffusivity here is only apparent.
6 12 18
Height, inside wall, in.
5.95 12 18.1
Diameter, inside, in.