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