# Chapter 13: Boiling Heat Transfer¶

## Exa 13.1¶

In [1]:
#Water at 1 atm is boiled on a brass surface. Using the rohsenow correlation
#determine the heat transfer coefficient for nucleate boiling if the wall
#superheat is 11C?
import math
#initialisation of variables
P= 1 				#atm
dt= 11 				#C
Csf= 0.006
r= 1./3.
s= 1.
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 			#change in density
q= ((math.pow(((cl*dt)/(hfg*Csf*Pr)),(1/r))*(ul*hfg))/math.pow((gc*s/(g*p)),(0.5))) #Heat transfer rate
h= q/dt 			#Heat transfer coefficient
#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) =  1.76e+05
press enter key to exit

Out[1]:
''

## Exa 13.2¶

In [2]:
#A tube, 1/2 in OD and 5 ft long, is used to condense steam at 6 psia; the
#average temperature of the tube is maintained at 130 F. Determine the
#condensation heat transfer coefficient if the tube is mounted
#(a) vertically and (b) horizontally
import math
#initialisation of variables
k= 0.384 											#Btu/hr ft F
Tsat= 170.03 										#F
hfg= 996.2 											#Btu/lbm
T= 130 												#F
l= 5. 												#ft
P= 6. 												#psia
g= 4.17*math.pow(10,8) 								#ft/h^2
d= 0.042 											#ft
p= 61.2 											#lbm/ft^3
u= 1.05 											#lbm/ft h
#CALCULATIONS
dt= Tsat-T 											#Change in temp.
Tf= (Tsat+T)/2. 									#Average temp.
hc= 0.943*math.pow(((k*k*k*p*p*g*hfg)/(l*u*dt)),(1./4.))
hc1= 0.725*math.pow(((k*k*k*p*p*g*hfg)/(d*u*dt)),(1./4.))
#RESULTS
print '%s %.2f' % ('Condensation heat tranfer coefficient if the tube is vertical (Btu/h ft^2 F) = ',hc)
print '%s %.2f' % (' \n Condensation heat tranfer coefficient if the tube is horizontally (Btu/h ft^2 F) = ',hc1)
raw_input('press enter key to exit')

Condensation heat tranfer coefficient if the tube is vertical (Btu/h ft^2 F) =  758.79

Condensation heat tranfer coefficient if the tube is horizontally (Btu/h ft^2 F) =  1926.98
press enter key to exit

Out[2]:
''