Page 78 - Modelling in Transport Phenomena A Conceptual Approach

3.5. TRANSPORT ANALOGIES 59

Solution
Physical properties

For water at 35 "C (308 K) : Pat = 0.0562 bar
f p = 1.1460 kg/ m3
v = 16.47 x io-6 m2/s
For air at 35 "C (308 K) :
Cp = 1.005 kJ/ kg. K
,-
( Pr = 0.711
Digusion coeficient of water (A) in air (23) at 35°C (308K) :

3/2
= (2.88 x 10-5) (g) 2.81 x lo-' m2/s
=
The Schmidt number .is
v
sc = -
DAB
-
- 16.47 x = 0.586
2.81 x 10-5
Assumption

1. Ideal gas behavior.

Analysis

The use of the Chilton-Colburn analogy, j, = jM, gives

Substitution of the values into Eq. (I) gives the avemge mass transfer coefficient
as

(21)(15)0.6 ( 0.711)213 = 0.105 m/ s
(kc) = (1.1460)(1005) 0.586
Saturation concentration of water is
psat
--
'A
c& - RT
-
- 0.0562 = 2.19 x kmol/ m3
(8.314 x 10-2)(35 + 273)