Page 237 - Modelling in Transport Phenomena A Conceptual Approach

7.6. DESIGN OF A SPRAY TOWER 217

Hence, the average heat transfer coejjicient is

= (19.5) (":: Tz-3) 246 W/ m2. K
=
The time required for cooling and solidification can be calculated from Eqs. (7.6-1 0)
and (7.6-13), respectively: ~[(Tm)in - ("'1

tl = ~ P P In ~ P ~
6 (h) T, - (Ta)
- (2 x 10-3)(1700)(1460) In 110 - 15
-
(6) (246) ( 70 - 15 ) = 1*8s

t2 = PmDP
6 (h) (Ts - Pa) 1
- (186,000)(1700)(2 x = 7.8s
-
(6)(246)(70 - 15)
Therefore, the tower height is

H = (6.5)(1.8 + 7.8) = 62.4m

NOTATION

A area, m2
AM mass transfer area, m2
G heat capacity at constant volume, kJ/ kg. K
eP heat capacity at constant pressure, kJ/ kg. K
C concentration, kmol/ m3
DAB diffusion coefficient for system d-B, m2/ s
EK kinetic energy, J
EP potential energy, J
E rate of energy, J/s
& activation energy, J/ mol
f friction factor
9 acceleration of gravity, m/ s2
H enthalpy, J
K
h elevation, m; heat transfer coefficient, W/ m2,
k thermal conductivity, W/ m. K
kc mass transfer coefficient, m/s