Mass transfer coefficients for solids suspended in agitated liquids

Publisher Website
Google Scholar
Abstract
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 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 were 6, 12, 18, and 30 in. Turbines were 2, 3, 4, 6, 9, and 12 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 member (NSc = 735 to 62,000) and could be correlated with turbine Reynolds number in each tank, with larger tanks yielding smaller coefficients at the same NRe. An empirical equation which fits all the data from the baffled tanks within about 4% (in the range 0.1 < k < 2) is where l2=0.8235−1.544V1/3+0.115V2/3The variance of estimate for this expression i s 0.0383, in units of [ln(10 k)]2.For extrapolation outside the experimental range of vessel sizes it is recommended that l1 = 0.676 − 1.266 V1/3 be used in place of I2. NRe = T2n/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:kd/D=0.02NNt is shown that for the systems used 1/D is essentially proportional to N, and so the effect of diffusivity here is only apparent.