Water film on the wall,
(d)
(5 Marks) the log-mean driving force (in mol m?³), and
(5 Marks) the average mass-transfer coefficient (in m s?¹).
Question #4 (20 Marks)
A cylindrical tube with an inside diameter of 2.54 cm is cast from benzoic acid. Water, having a
temperature of 14 °C and a bulk velocity of 3 m/s, flows through the tube.
(a)
(10 Marks) Estimate the length of the tube required such that the solution exiting from
the tube is 1 percent saturated with benzoic acid?
(b) (10 Marks) Calculate the mass-transfer coefficient for this system?
The saturation concentration of benzoic acid in water at 14 °C is 2.36 g/L, and the value of the
Schmidt number is 1870. The density of water is 1 g/cm³ and the viscosity of water at 14 °C is
1.17 g s?¹m?¹. The diffusivity of benzoic acid in water at 25 °C is 1.21 x 10?? cm²/s. The mass
transfer coefficient can be estimated by means of the following generalized correlation for the
Sherwood number for turbulent flow in smooth circular pipe:
$N_{Sh} = \frac{k_c D}{D_{AB}} = 0.023 \, Re^{0.8} Sc^{1/3}$