Chapter 14: Radiation Heat Transfer

Exa 14.2

In [1]:
#If a blackbody is maintained at 116C, determine (a) the wavelength at which 
#the maximum monochromatic emissive power occurs and (b) the maximum 
#monochromatic emissive power
import math
#initialisation of variables
T= 116. 														#C
C1= 3.74*math.pow(10,-16)
C2= 1.44*math.pow(10,-2)
#CALCULATIONS
WLmax= (2893*math.pow(10,-6))/(T+273) 							#Maximum Wavelength 
Wb= (C1*math.pow((WLmax),(-5)))/(math.exp(C2/2893*1000000.)-1)	#Coffecient of performnance
#RESULTS
print '%s %.2e' % ('Wavelength at which the maximum monochromatic emissive power (m) = ',WLmax)
print '%s %.2e' % (' \n Coffecient of performnance (W/m^3) = ',Wb)
raw_input('press enter key to exit')

Wavelength at which the maximum monochromatic emissive power (m) =  7.44e-06
 
 Coffecient of performnance (W/m^3) =  1.14e+08
press enter key to exit
Out[1]:
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Exa 14.3

In [2]:
#Determine the total emissive power for the black body of solved problem 2
import math
#initialisation of variables
T= 389 						#K
s= 5.7*math.pow(10,-8) 		#K^4
#CALCULATIONS
Wb= s*T*T*T*T 				#Emissive power for the blackbody
#RESULTS
print '%s %.2f' % ('Emissive power for the blackbody (W/m^2) = ',Wb)
raw_input('press enter key to exit')

Emissive power for the blackbody (W/m^2) =  1305.19
press enter key to exit
Out[2]:
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Exa 14.4

In [3]:
#A gray body at 100F receives radiant energy from a wall at 2000 F at a rate
#of 3.2x 10^4. Simultaneously, the body emits energy at the rate of 140. What
#is the average absorptivity of the body at (a) 100 F and (b) 2000 F
import math
#initialisation of variables
T= 100 								#F
T1= 2000 							#F
W= 3.2*10000. 						#Btu/hr ft^2
W1= 140. 							#Btu/hr ft^2
s= 0.17*math.pow(10,-8) 			#Btu/hr ft^2 R^4
#CALCULATIONS
alpha= W/(s*math.pow((T1+460),4)) 	#Average absorptivity at 100
b= W1/(s*math.pow((T+460),4)) 		#Average absorptivity at 2000
#RESULTS
print '%s %.2f' % ('Average absorptivity of the body at 100 F = ',alpha)
print '%s %.2f' % (' \n Average absorptivity of the body at 2000 F= ',b)
raw_input('press enter key to exit')

Average absorptivity of the body at 100 F =  0.51
 
 Average absorptivity of the body at 2000 F=  0.84
press enter key to exit
Out[3]:
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Exa 14.5

In [4]:
#A red brick conduit 10 in square has a surface temperature of 300F and is 
#mounted inside a large earthen chamber whose walls are at 50 F. estimate
#the heat loss from the conduit by radiation
import math
#initialisation of variables
T= 300. 												#F
T1= 50. 												#F
s= 0.17*math.pow(10,-8) 								#Btu/hr ft^2 R^4
e1= 0.93
A= 10. 													#in
F= 1.
#CALCULATIONS
A1= 10*(40./(12.*10.)) 									#Area
q= A1*F*e1*s*(math.pow((T+460),4)-math.pow((T1+460),4)) #heat loss
#RESULTS
print '%s %.2f' % ('Heat loss from the conduit by radiation (Btu/hr per ft) = ',q)
raw_input('press enter key to exit')

Heat loss from the conduit by radiation (Btu/hr per ft) =  1401.66
press enter key to exit
Out[4]:
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Exa 14.6

In [5]:
#Estimate the radiation heat transfer coefficient for solved problem 5
import math
#initialisation of variables
T= 300. 														#F
T1= 50. 														#F
s= 0.17*math.pow(10,-8) 										#Btu/hr ft^2 R^4
e1= 0.93
F= 1.
#CALCULATIONS
hr= F*e1*s*(math.pow((T+460),4)-math.pow((T1+460),4))/(T-T1)	#Radiation heat transfer coefficient 
#RESULTS
print '%s %.2f' % ('Radiation heat transfer coefficient (Btu/hr ft^2 R) = ',hr)
raw_input('press enter key to exit')

Radiation heat transfer coefficient (Btu/hr ft^2 R) =  1.68
press enter key to exit
Out[5]:
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Exa 14.7

In [8]:
import math
#initialisation of variables
P= 1. #atm
T= 11. #C
Csf= 0.006
Tsat = 170.03
r= 1./3.
s= 1.
dt = Tsat - T
cl= 4.218 #J/gm K
hfg= 2257 #J/gm
Pr= 1.75
ul= 283.1/1000. #gm/m s
s= 57.78/1000. #N/m
pl= 958*1000. #gm/m^3
pv= 598. #gm/m^3
gc= 1000. #gm m/N s^2
g= 9.8 #m/s^2
#CALCULATIONS
p= pl-pv
q= ((math.pow(((cl*dt)/(hfg*Csf*math.pow(Pr,s))),(1/r)))*(ul*hfg))/math.pow(gc/(g*p),(1./2.))
h= q/T
#RESULTS
print '%s %.2e' % ('Heat transfer coefficient for nucleate boiling (W/m^2 C) = ',h)
raw_input('press enter key to exit')

Heat transfer coefficient for nucleate boiling (W/m^2 C) =  6.21e+08
press enter key to exit
Out[8]:
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