Chapter 10: Refrigeration

Example 10.1, page no. 193

In [6]:
#initialization
capacity = 5.0                 #tons
hp = 10.0                       #hp

#calculation
beta = (778*3.33*capacity)/(hp*550)

#result
print "Coefficient of performance  = ", round(beta, 2)

Coefficient of performance  =  2.36

Example 10.2, page no. 197

In [13]:
#initialization
P1 = 30.0                   #lb/in^2
P2 = 200.0                  #lb/in^2
capacity = 3.0              #tons

#calculation
#From the pressure enthalpy chart
Tt1 =  -1                   #F
st1 = 1.34
ht1 = 612.0
ht2 = 733.0
ht3 = 141.0
ht4 = 141.0
WbyJ = ht2-ht1
Q = ht1-ht3
beta = Q/WbyJ
Qdot = capacity*3.33
wdot = Qdot/Q
Power = wdot*778*WbyJ
Power = Power/550.0

#result
print "Coefficient of performance  =  ", round(beta, 2)
print "Evarator temperature  =  %d F" %Tt1
print "Power required  =  %.2f hp" %Power

Coefficient of performance  =   3.89
Evarator temperature  =  -1 F
Power required  =  3.63 hp

Example 10.3, page no. 200

In [24]:
#initialization
P1 = 14.0                   #lb/in^2
P2 = 60.0                   #lb/in^2
Tt1 = 80+460.0              #R
Tt4 = -20+460.0             #R
m = 30.0                    #lbm/sec
cp = 0.24

#calculation
Tt2 = round(Tt1*(P2/P1)**(0.286))
Tt3 = round(Tt4*(P2/P1)**(0.286))
WbyJ1 = cp*(Tt2-Tt1)
WbyJ2 = cp*(Tt3-Tt4)
Q = cp*(Tt1-Tt4)
beta = Q/(WbyJ1-WbyJ2)
Power = (m*778)*(WbyJ1-WbyJ2)
Wdot = Power/550.0

#result
print "Coefficient of performance  =  %.3f" %beta
print "Net power  =  %d hp" %Wdot

#difference in answer due to rounding of in Python

Coefficient of performance  =  1.923
Net power  =  529 hp