Chapter 5 : Thermodynamic Potentials and Maxwell Relation

Example 5.1 Page No : 119

In [2]:
import math 

#Given
T = 293.0;#Consmath.tant temperature in K
w_NH3 = 20/100.0;#weight of NH3 in an aqueous solution in Kg
w_H2O = 80/100.0;#weight of H2O in an aqueous solution in Kg
V = 40.0;#feed rate in Kg/min
M_NH3 = 17.0;#Molecular weight of NH3
M_H2O = 18.0;#Molecular weight of H20
R = 1.98;#gas consmath.tant in Kcl/Kg mole K
V_s = 62.0;#Rate of heating steam in Kg/min
P1_H2O = 11.6;#Vapour pressure of water in feed in  mm Hg
P2_H2O = 17.5;#Vapour pressure of pure water in mm Hg
P1_NH3 = 227.0;#Vapour pressure of NH3 in feed in mm Hg
P2_NH3 = 6350.0;#Vapor pressure of  pure NH3 in mm Hg
#From steam tables:
Hs = 666.4;#Enthalpy of steam at 160 deg celsius & 2Kgf/cm**2 in Kcal /Kg 
Ss = 1.75;#Entropy of steam at 160 deg celsius & 2Kgf/cm**2V in Kcal/Kg K
Hl = 20.03;#Enthalpy of liquid water at 20 deg celsius in Kcal/Kg
Sl = 0.0612;#Entropy of liquid water at 20 deg celsius in Kcal/Kg K

#To Calculate the efficiency of the separation process 
#Material Balance:
n_NH3 = (V*w_NH3)/M_NH3;#Kg moles of NH3 in feed(tops)
n_H2O = (V*w_H2O)/M_H2O;#Kg moles of H20 in feed(bottoms)
#del_F = del_F_NH3 +del_F_H2O;
del_F = (R*T*n_NH3*math.log(P2_NH3/P1_NH3))+(R*T*n_H2O*math.log(P2_H2O/P1_H2O));#Theoretical minimum work done in Kcal
#The available energy of the steam can be calculated from equation 4.14(page no 110)
del_B = -V_s*((Hl-Hs)-T*(Sl-Ss));#Available energy of the steam in Kcal
E = (del_F/del_B)*100;
print "The efficiency of the separation process is %f percent"%(E);
#end
The efficiency of the separation process is 14.192424 percent