Chapter 8 - Availability of Energy

Example 1 - Pg 120

In [2]:
#calculate the available energy loss
#Initialization of variables
q=1000. #Btu
th=1140. #F
tl=40. #F
ts=940. #F
#calculations
Q1=q*(th-tl)/(th+460)
Q2=q*(ts-tl)/(ts+460)
dif=Q1-Q2
#results
print '%s %d %s' %("Available energy loss =",dif,"Btu")

Available energy loss = 44 Btu

Example 2 - Pg 124

In [3]:
#calculate the untransferred, transferred, available, unavailable energy for both gas and water
#Initialization of variables
import math
ma=200000. #lb
cpa=0.26
T2g=1200. #F
T1g=300. #F
T1w=200. #F
mw=250000. #lb
cpw=1.02
Tl=560.  #R
cx=1.01
#calculations
T2w=T1w+ ma*cpa*(T2g-T1g)/(mw*cpw)
Qun=Tl*ma*cpa*math.log((T2g+460)/(T1g+460))
Qtr=ma*cpa*(T2g-T1g)
Qav=Qtr-Qun
Qun2=Tl*mw*cx*math.log((T2w+460)/(T1w+460))
Qav2=Qtr-Qun2
ht1=Qav-Qav2
#results
print '%s %d %s' %("For gas, Untransferred energy =",Qun,"Btu/hr")
print '%s %d %s' %("\n For gas, transferred energy =",Qtr,"Btu/hr")
print '%s %d %s' %("\n For gas, available energy =",Qav,"Btu/hr")
print '%s %d %s' %("\n For water, Untransferred energy =",Qun2,"Btu/hr")
print '%s %d %s' %("\n For water, available energy =",Qav2," Btu/hr")
print '%s %d %s' %("\n Loss of available energy =",ht1,"Btu/hr")
print '%s' %('The answers are a bit different due to rounding off error in textbook')

For gas, Untransferred energy = 22750129 Btu/hr

 For gas, transferred energy = 46800000 Btu/hr

 For gas, available energy = 24049870 Btu/hr

 For water, Untransferred energy = 34693187 Btu/hr

 For water, available energy = 12106812  Btu/hr

 Loss of available energy = 11943058 Btu/hr
The answers are a bit different due to rounding off error in textbook