# Chapter 8 : Heat transfer by forced convection¶

## Example 8.1 page : 139¶

In :
# Variables
D = 0.0752;                               # Outer diameter in ft
T1 = 61.4;                                # Pipe surface temperature in degF
T2 = 69.9;                                # Air temperature in degF
Tf = (T1+T2)/2;                           # Film temperature at whih physical properties is to be measured
delT = T1-T2;
rho = 1.94;                               # Density in slug/ft**3 , 62.3/32.2
u = 0.0780;                               # vismath.cosity in slug/ft-hr , 2.51/32.2
Cp = 1*32.2;                              # heat capacity in Btu/slug-ft
k = 0.340;                                # thermal conductivity in Btu/hr-ft-degF
v = 7*3600;                               # velocity in ft/sec

# Calculations
Nre = D*v*rho/u;                          # Reynolds number
Npr = u*Cp/k;                             # Prandtls number
Nnu = 0.023*Nre**.8*Npr**.4;
h = Nnu*k/D;                              # heat transfer coefficient

# Results
print "The average film coefficient of heat transfer is %.d Btu/hr-ft**2-degF"%(h);

The average film coefficient of heat transfer is 1267 Btu/hr-ft**2-degF


## Example 8.3 page : 141¶

In :
# Variables
D = 1./12;                                    # Inner diameter of pipe in ft
k = 0.0174;                                  # Thermal conductivity in btu/hr-ft-degF
Nre = 8000.;                                  # Reynolds number

# Calculations
# From table we can find out nusselt number
Nnu = 0.3*Nre**0.57;                           # Nusselt number
h = round(Nnu)*k/D;                           # Heat transfer coefficient in btu/hr-ft**2-degF

# Results
print "heat transfer coefficient for air flowing is %.1f Btu/hr-ft**2-degF"%(h);

heat transfer coefficient for air flowing is 10.4 Btu/hr-ft**2-degF