Particle Technology Laboratory
Prof. Sotiris E. Pratsinis
Sonneggstrasse 3, ML F13, ETH Zentrum
Tel.: +41-44-632 25 10
http://www.ptl.ethz.ch
151-0917-00 U Stoffaustausch HS 2016
Exercise 7: Mass Transfer Coefficients and Correlations I
Problem 1: Chapter 8, Problem 6
Problem 2: Chapter 8, Problem 2
Problem 3
A bubble of oxygen originally 0.1 cm in diameter is injected into excess stirred water at standard
conditions (STP). After 7 min, the bubble is 0.054 cm in diameter. Assume that the saturation
concentration of oxygen in water at STP is 1.5·10-3 mol/L. What is the mass transfer coefficient?
Problem 4
A 500-gallon tank 8 ft deep is to be saturated with air using a small sparger 2 in. in diameter with a
flow of 1 ft3/min. The sparger produces 0.3-centimeter bubbles that rise through the tank at 10
cm/sec; other properties of the fluid in the tank are essentially those of water. How long does it
take to reach 50% saturation? Mass transfer in the gas-phase within the bubbles is much faster
than on the liquid side and can be neglected. Mass transfer is dominated by the liquid-side
resistance.
Outside the bubbles, one good correlation is given by P.H. Calderbank [In: Mixing, ed. V. Uhl. New
York: Academic Press (1967)]:
  

k 

D


2/3
1/ 3
   g 

 0.31
2




Additional data:
in air: y(O2) = 0.21;
in water at given conditions: csat(O2) = 2.675x10-7 mol/cm3
Unit Conversion:
1 ft (foot) = 30.48 cm
1 in (inch) = 2.54 cm
1 gal (gallon) = 3.7854 L (american)
1 lb (pound) = 453.59 g
1