group3-ps number 9
TRANSCRIPT
5Che-BGroup 3
A condenser for a distillation unit must be designed to
condense2000 kg/h of vapor. The effective condensation
temperature for the vapor is 132oC.The heat of condensation for
the vapor is 350000 J/kg. Cooling water is available at 15oC.The cost
of cooling water is $25/1000m3.The optimum Heat Transfer
Coefficient is 300 W/m2K.The cost of the installed heat exchanger is
$400/m2 and life of the equipment is 10 years with interest rate of
8%. The heat capacity of water is 4184 J/kgK. Determine the
cooling water flow rate in kg/hr and exit temperature for optimum
economic conditions.
tsteam 132 273 tsteam 405 t1 15 273 t1 288
U 300 Cw25
1000 Cp 4.184 Lsteam 350000 CA 400
wsteam 2000 Hy 8760 Kf0.08
1.08( )10 1 Kf 0.069
U Hy Cw 3.6Kf CA Cp 1000
2.047
Assume t2opt 390
Using Fig. 11-6/370
Giventsteam t2opttsteam t1
0.225
Find t2opt( ) 378.675 K
t2optC 378.675 273 t2optC 105.675 deg C
Using Equation 56
Given
tsteam t1tsteam t2opt
1 lntsteam t2opttsteam t1
U Hy Cw 3.6
Kf CA Cp 1000
Find t2opt( ) 379.375 K
T2379.375 378.675
2 T2 379.025 K
Given w 3500
wsteam Lsteam w Cp 1000 T2 t1( )
Find w( ) 1838.001 kg/hr