# Chapter 9 : Refrigerator And Liquifaction¶

## Example 9.1 page no : 128¶

In :
import math

# Variables
T1 = 261.15;			#[K] Temgeratureof refrigerated space
T2 = 294.15;			#[K] Temperature of cooling water
dT = 5.6;			#[K]    Temperature Difference
Qc = 35.2;			#[kW]  Refrigerant Capacity
eta = 0.8;			#Efficeincy(b)

# Calculations and Results
#(a) Carnot Refrigerator
Tc = T1-dT;
Th = T2+dT;
#Umath.sing Eqn(9.3)
w = round(Tc/(Th-Tc),2);
print '(a)Coefficient of Performance for Carnot Refrigerator',w

#(b)  Vapor Compression Cycle
#From Table(9.1)
#@ Tc = 255.55K
H2 = 388.13;			#[KJ/Kg]
S2 = 1.7396;			#[KJ/Kg/K]

#@ Th = 299.75K
H4 = 236.76;			#[KJ/Kg]

S3 = S2;			#Isentropic
#Hence
H3 = 420.27;			#[KJ/Kg]
#Step 2 --> 3
del_Hs = H3-H2;
#But Compressor Efficiency  =  0.80
del_Hs = del_Hs/eta
#Step 1 --> 4
H1 = H4;			#isenthalpic
w = round((H2-H4)/del_Hs,2);
print '(b)Coefficient of Performance for Vapor Compression Cycle',w
rm = round(Qc/(H2-H4),4);			#[Kg/s]
print 'Circulation rate',rm,'kg/s'

(a)Coefficient of Performance for Carnot Refrigerator 5.78
(b)Coefficient of Performance for Vapor Compression Cycle 3.77
Circulation rate 0.2325 kg/s


## Example 9.2 page no : 128¶

In :
import math

# Variables
Qh_Winter = 30.;			#[KW]
Qc_Summer = 60.;			#[KW]
Tc_Winter = 283.15;			#[K]
Th_Winter = 303.15;			#[K]
Tc_Summer = 278.15;			#[K]
Th_Summer = 298.15;			#[K]

# Calculations and Results
#For WINTER's
#Using Eqn(5.7)
Qc_Winter = Qh_Winter*(Tc_Winter/Th_Winter);
#Umath.sing Eqn(9.1)
W_Winter = round((Qh_Winter-Qc_Winter),2);			#[KW]
print "Power Requirement for WINTER''s",W_Winter,'KW'

#For SUMMER's
#Combining Eqn(9.2) And Eqn(9.3)
W_Summer = round((Qc_Summer*((Th_Summer-Tc_Summer)/Tc_Summer)),2);
print "Power Requirement for SUMMER''s",W_Summer,'KW'

Power Requirement for WINTER''s 1.98 KW
Power Requirement for SUMMER''s 4.31 KW


## Example 9.3 page no : 129¶

In :
import math

# Variables
x = 0.25;
#For Superheated Methane
#By Perry and Green  by linear interpolation
H4 = 1140.;			    #[KJ/Kg]  @ 300K and 60 Bar
H15 = 1188.9;			#[KJ/Kg]  @ 295K and 1 Bar
#By interpolation based on lnP
T_sat = 111.5;			#[K]
H9 = 285.4;		    	#[KJ/Kg]  Saturated Liquid
H12 = 769.9;			#[KJ/Kg] Saturated Vapor
S12 = 9.521;			#[KJ/Kg/K] Saturated vapor

T5 = 253.6;			    #[K]
H5 = 1009.8;			#[KJ/Kg]  @ 60 Bar

#From Eqn(9.7)
z = ((x*(H12-H5))+H4-H15)/(H9-H15);
H14 = ((H5-H4)/(1-z))+H15;			#[KJ/Kg]
#Whence
T14 = 227.2;			#[K]  @ 1Bar
H7 = H5-((1-z)/(1-x)*(H14-H12));			#[KJ/Kg]
T7 = 197.6;			#[K]  @ 60Bar
#From Eqn(9.8)
z = round((H4-H15)/(H9-H15),4);
H7 = H4-((1-z)*(H15-H12));
T7 = 206.6;			#[K]

# Results
print 'Fraction of methane liquefied',z*100,'%'
print 'Temperature of High Pressure steam entering the throttle valve',T7,'K'

Fraction of methane liquefied 5.41 %
Temperature of High Pressure steam entering the throttle valve 206.6 K