Chapter 22 - Refrigeration

Example 1 - Pg 476

In [2]:
#calculate the refrigerator and heat pump cp values in both cases
#Initalization of variables
t1=45+460. #R
th=70+460. #R
t2=-200+460. #R
th2=100+460. #R
#calculations
cp1=t1/(th-t1)
cp2=th/(th-t1)
cp3=t2/(th2-t2)
cp4=th2/(th2-t2)
#results
print '%s %.1f' %("In case 1, Refrigerator cp = ",cp1)
print '%s %.1f' %("\n In case 1, Heat pump cp = ",cp2)
print '%s %.3f' %("\n In case 2, Refrigerator cp = ",cp3)
print '%s %.3f' %("\n In case 2, Heat pump cp = ",cp4)

In case 1, Refrigerator cp =  20.2

 In case 1, Heat pump cp =  21.2

 In case 2, Refrigerator cp =  0.867

 In case 2, Heat pump cp =  1.867

Example 2 - Pg 479

In [3]:
#calculate the coefficient of performance in wet and dry compression
#Initalization of variables
h3=85.282 #Btu/lb
s2=0.16392
sf=0.16798
#calculations
sfg=sf-0.023954
x3=-(s2-sf)/sfg
h2=78.335 - x3*67.651
h4=26.365 #Btu/lb
h1=h4
ref=h2-h1
work=h3-h2
cp1=ref/work
h2d=78.355
h1d=26.365 #Btu/lb
h3d=87.495 #Btu/lb
ref2=h2d-h1d
work2=h3d-h2d
cp2=ref2/work2
#results
print '%s %.3f' %("\n Coefficient of performance in wet compression = ",cp1)
print '%s %.3f' %("\n Coefficient of performance in dry compression = ",cp2)

 Coefficient of performance in wet compression =  5.654

 Coefficient of performance in dry compression =  5.688

Example 3 - Pg 480

In [4]:
#calculate the tonnage value in both cases
#Initalization of variables
h1=24.973 #Btu/lb
h2=81.436 #Btu/lb
cfm=200 #cfm
v2=0.77357
v3=3.8750
h4=72.913
#calculations
mass=cfm/v2
ref=h2-h1
tonnage=mass*ref/cfm
mass2=cfm/v3
ref2=h4-h1
tonnage2=mass2*ref2/cfm
#results
print '%s %.1f %s' %("In case 1,Tonnage =",tonnage," tons")
print '%s %.2f %s' %("\n In case 2,Tonnage =",tonnage2," tons")

In case 1,Tonnage = 73.0  tons

 In case 2,Tonnage = 12.37  tons

Example 4 - Pg 481

In [5]:
#calculate the refirgeration, shaft hp and cop
#Initalization of variables
h2d=93.410 #Btu/lb
h1=80.740 #Btu/lb
x=0.75
PD=160
vol=0.82
v1=1.7213
w2=80.156
w1=27.3
#calculations
twork=h2d-h1
swork=twork/x
flow=PD*vol/v1
ref=flow*(w2-w1)/200.
shp= flow*swork/42.4
cop=(w2-w1)/swork
#results
print '%s %.1f %s' %("Refrigeration =",ref," tons")
print '%s %.1f %s' %("\n Shaft hp=",shp," hp")
print '%s %.2f' %("\n Coefficient of performance = ",cop)

Refrigeration = 20.1  tons

 Shaft hp= 30.4  hp

 Coefficient of performance =  3.13

Example 5 - Pg 488

In [6]:
#calculate the cop
#Initalization of variables
mc=3000 #lb
hv=1080.2 #Btu/lb
hfe=26.06 #Btu/lb
hfp=10.05 #Btu/lb
x=0.7
#calculations
mv=(mc*hfp-mc*hfe)/(hfe-hv)
dh=145.4 #Btu/lb
chp=dh*mv/(x*42.4)
cop=mc*(hfe-hfp)/(chp*42.4)
#results
print '%s %.2f' %("Coefficient of performace = ",cop)

Coefficient of performace =  5.07

Example 6 - Pg 493

In [7]:
#calculate the power required
#Initalization of variables
loss=80000. #Btu/lb
t=560. #R
#calculations
ratio=t/68.
power=loss/(ratio*2544.)
#results
print '%s %.2f %s' %("Power = ",power," hp")

Power =  3.82  hp

Example 7 - Pg 493

In [8]:
#calculate the power required
#Initalization of variables
loss=2*80000. #Btu/lb
tb=72. #F
to=12. #F
to2=42. #F
tf=104.+460 #R
#calculations
ratio=tf/(tf-460.)
power=loss/(2544.*ratio)
#results
print '%s %.1f %s' %("Power =",power," hp")

Power = 11.6  hp