# Chapter 11 : Boiling and Condensation¶

## Example 11.1 Page No : 480¶

In [7]:
import math

# Variables
Tsat = 100.;			#Saturation temperature of water in degree C
p1 = 957.9;			#Density of liquid in kg/m**3
Cpl = 4217.;			#Specific heat in J/kg.K
u = (279.*10**-6);			#Dynamic viscosity in N.s/m**2
Pr = 1.76;			#Prantl number
hjg = 2257.;			#Enthalpy in kJ/kg
s = (58.9*10**-3);			#Surface tension in N/m
pv = 0.5955;			#Density of vapour in kg/m**3
m = 30.;			#Rate of water in kg/h
D = 0.3;			#Diameter in m

# Calculations
q = round((m*hjg*1000)/(3600*math.pi*D**2/4));			#Heat transfer in W/m**2
Ts = Tsat+(((q/(u*hjg*1000))*math.sqrt(s/(9.81*(p1-pv)))))**0.33

# Results
print 'Temperature of the bottom surface of the pan is %3.2f degree C'%(Ts)

# NOte: answer in book is wrong.

Temperature of the bottom surface of the pan is 101.02 degree C


## Example 11.2 Page No : 481¶

In [2]:
# Variables
Tsat = 100;			#Saturation temperature of water in degree C
p1 = 957.9;			#Density of liquid in kg/m**3
Cpl = 4217;			#Specific heat in J/kg.K
u = (279*10**-6);			#Dynamic vismath.cosity in N.s/m**2
Pr = 1.76;			#Prantl number
hjg = 2257;			#Enthalpy in kJ/kg
s = (58.9*10**-3);			#Surface tension in N/m
pv = 0.5955;			#Density of vapour in kg/m**3
m = 30;			#Rate of water in kg/h
D = 0.3;			#Diameter in m

# Calculations
q = (0.18*hjg*1000*pv*((s*9.81*(p1-pv))/pv**2)**0.25)/10**6;			#Burnout heat flux in MW/m**2

# Results
print 'Burnout heat flux is %3.3f MW/m**2'%(q)

Burnout heat flux is 1.520 MW/m**2


## Example 11.3 Page No : 481¶

In [3]:
# Variables
D = 0.0016;			#Diameter of the wire in m
T = 255;			#Temperature difference in degree C
p1 = 957.9;			#Density of liquid in kg/m**3
Cpl = 4640;			#Specific heat in J/kg.K
u = (18.6*10**-6);			#Dynamic viscosity in N.s/m**2
hjg = 2257;			#Enthalpy in kJ/kg
k = (58.3*10**-3);			#Thermal conductivity in W/m.K
pv = 31.54;			#Density of vapour in kg/m**3
Ts = 628;			#Surface temperature in K
Tsat = 373;			#Saturation temperature in K

# Calculations
hc = (0.62*((k**3*pv*(p1-pv)*9.81*((hjg*1000)+(0.4*Cpl*T)))/(u*D*T))**0.25);			#Convective heat transfer coefficient in W/m**2.K
hr = ((5.67*10**-8)*(Ts**4-Tsat**4))/(Ts-Tsat);			#Radiative heat transfer coefficient in W/m**2.K
hm = (hc+(0.75*hr));			#Mean heat transfer coefficient in W/m**2.K
Q = (hm*3.14*D*T)/1000;			#Power dissipation rate per unit length of the heater in kW/m

# Results
print 'Mean heat transfer coefficient is %3.1f W/m**2.K \n \
Power dissipation rate per unit length of the heater is %3.3f kW/m'%(hm,Q)

Mean heat transfer coefficient is 1340.9 W/m**2.K
Power dissipation rate per unit length of the heater is 1.718 kW/m


## Example 11.4 Page No : 485¶

In [3]:
# Variables
Ts = 10.;			#Surface temperature in degree C
p1 = 10.;			#Pressure of water in atm

# Calculations
hp = (5.56*Ts**0.4);			#Heat transfer coefficient in kW/m**2.K
hp1 = (5.56*(2*Ts)**3*p1**0.4);			#Heat transfer coefficient in kW/m**2.K
hp2 = (5.56*Ts**3*(2*p1)**0.4);			#Heat transfer coefficient in kW/m**2.K
x1 = (hp1/hp)/1000;			#Ratio of heat transfer coefficients
x2 = (hp2/hp)*100;			#Ratio of heat transfer coefficients

# Results
print 'Heat transfer coefficient becomes %.f times the original value in the first case\n \
Heat transfer coefficient is increased only by 32 percent in the second case'%(x1)

Heat transfer coefficient becomes 8 times the original value in the first case
Heat transfer coefficient is increased only by 32 percent in the second case


## Example 11.5 Page No : 485¶

In [13]:
import math

# Variables
p = 6.;			#Pressure of water in atm
D = 0.02;			#Diameter of the tube in m
Ts = 10.;			#Wall temperature in degree C
L = 1.;			#Length of the tube in m

# Calculations
p1 = (p*1.0132*10**5)/10**6;			#Pressure in MN/m**2
h = (2.54*Ts**3*math.exp(p1/1.551));			#Heat transfer coefficient in W/m**2.K
Q = (h*math.pi*D*L*Ts);			#Heat transfer rate in W/m

# Results
print 'Heat transfer rate is %3.1f W/m'%(Q)

# note : rounding off error.

Heat transfer rate is 2361.8 W/m


## Example 11.6 Page No : 489¶

In [17]:
# Variables
p = 2.45;			#Pressure of dry saturated steam in bar
h = 1;			#Height of vertical tube in m
Ts = 117;			#Tube surface temperature in degree C
d = 0.2;			#Distance from upper end of the tube in m

# Calculations
Tsat = 127;			#Saturation temperature of water in degree C
p1 = 941.6;			#Density of liquid in kg/m**3
k1 = 0.687;			#Thermal conductivity in W/m.K
u = (227*10**-6);			#Dynamic vismath.cosity in N.s/m**2
hfg = 2183;			#Enthalpy in kJ/kg
pv = 1.368;			#Density of vapour in kg/m**3
q = round((((4*k1*u*10*d)/(9.81*p1*(p1-pv)*hfg*1000))**0.25)*1000,2);			#Thickness of condensate film in mm
h = (k1/(q/1000));			#Local heat transfer coefficient at x = 0.2 in W/m**2.K

# Results
print 'Thickness of condensate film is %3.2f mm \n \
Local heat transfer coefficient at x = 0.2 is %3.0f W/m**2.K'%(q,h)

Thickness of condensate film is 0.09 mm
Local heat transfer coefficient at x = 0.2 is 7633 W/m**2.K


## Example 11.7 Page No : 491¶

In [21]:
import math

# Variables
D = 0.05;			#Diameter of the tube in m
L = 2;			#Length of the tube in m
Ts = 84;			#Outer surface temperature in degree C
Tsat = 100;			#Saturation temperature of water in degree C
Tf = (Tsat+Ts)/2;			#Film temperature in degree C
p1 = 963.4;			#Density of liquid in kg/m**3
u = (306*10**-6);			#Dynamic vismath.cosity in N.s/m**2
hfg = 2257;			#Enthalpy in kJ/kg
pv = 0.596;			#Density of vapour in kg/m**3
k1 = 0.677;			#Thermal conductivity in W/m.K

# Calculations
hL = (1.13*((9.81*p1*(p1-pv)*k1**3*hfg*1000)/(u*16*L))**0.25);			#Heat transfer coefficient in W/m**2.K
Ref = ((4*hL*L*2)/(hfg*1000*u));			#Reynolds nmber
Q = (hL*math.pi*D*L*10);			#Heat transfer rate in W
m = (Q/(hfg*1000))*3600;			#Condensate mass flow rate in kg/h

# Results
print 'Heat transfer rate is %3.0f W  \n \
Condensate mass flow rate is %3.1f kg/h'%(Q,m)

# note : rounding off error.

Heat transfer rate is 17930 W
Condensate mass flow rate is 28.6 kg/h


## Example 11.8 Page No : 492¶

In [26]:
# Variables
h = 2.8;			#Height of the plate in m
T = 54.;			#Temperature of the plate in degree C
Tsat = 100.;			#Saturation temperature of water in degree C
Tf = (Tsat+T)/2;			#Film temperature in degree C
p1 = 973.7;			#Density of liquid in kg/m**3
u = (365.*10**-6);			#Dynamic viscosity in N.s/m**2
hfg = 2257.;			#Enthalpy in kJ/kg
pv = 0.596;			#Density of vapour in kg/m**3
k1 = 0.668;			#Thermal conductivity in W/m.K

# Calculations
Re = (0.00296*((p1*9.81*(p1-pv)*k1**3*(Tsat-T)**3*h**3)/(u**5*(hfg*1000)**3))**(5./9));			#Reynolds number
hL = (0.0077*((9.81*p1*(p1-pv)*k1**3)/u**2)**(1./3)*Re**0.4);			#Heat transfer coefficient in W/m**2.K
Q = (hL*h*(Tsat-T))/1000;			#Heat transfer rate per unit width in kW/m

# Results
print 'Heat transfer rate per unit width is %3.2f kW/m'%(Q)

# note : rounding error.

Heat transfer rate per unit width is 702.33 kW/m


## Example 11.9 Page No : 494¶

In [13]:
# Variables
T = 100;			#Temperature of dry steam in degree C
Do = 0.025;			#Outer diameter of the pipe in m
Ts = 84;			#Surface temmperature of pipe in degree C
Tf = (T+Ts)/2;		#Film temperature in degree C
p1 = 963.4;			#Density of liquid in kg/m**3
u = (306*10**-6);	#Dynamic viscosity in N.s/m**2
hfg = 2257;			#Enthalpy in kJ/kg
pv = 0.596;			#Density of vapour in kg/m**3
k1 = 0.677;			#Thermal conductivity in W/m.K

# Calculations
h = (0.725*((9.81*p1*(p1-pv)*k1**3*hfg*1000)/(u*(T-Ts)*Do))**0.25);			#Heat transfer coefficient in W/m**2.K
q = (h*3.14*Do*(T-Ts))/1000;			#Heat transfer per unit length in kW/m
m = (q/hfg)*3600;			            #Total mass flow of condensate per unit length in kg/h

# Results
print 'Rate of formation of condensate per unit length is %3.2f kg/h'%(m)

Rate of formation of condensate per unit length is 21.94 kg/h


## Example 11.10 Page No : 494¶

In [14]:
# Variables
m = 50;			#Mass of vapour per hour
n = 100;			#Number of tubes
D = 0.01;			#Diameter of the tube in m
L = 1;			#Length of the tube in m
n1 = 10;			#Array of 10*10

# Calculations
mr = ((0.725/1.13)*(L/(n1*D))**0.25);			#Ratio of horizontal and vertical position
mv = (m/mr);			#Mass flow rate in the vertical position in kg/h

# Results
print 'Mass flow rate in the vertical position is %3.2f kg/h'%(mv)

Mass flow rate in the vertical position is 43.82 kg/h