# Chapter 12 : Heat transfer by the combined effect of conduction, convection and radiation¶

## Example 12.1 page : 240¶

In :
import math

# Variables
D = 4.5/12;                                     # Outer diameter of pipe in ft
D2 = 6.5/12;                                    # Outer diameter of insulation in ft
k = 0.035;                                      # Thermal conductivity in Btu/hr-ft-degF
T1 = 400.;                                       # Temperature of pipe in degF
T3 = 70.;                                        # Temperature of air in degF
T2 = 120.;                                       # Assumed temperature in degF

# Calculations and Results
h = 2*k*(T1-T2)/(D2*(T2-T3)*math.log(D2/D));         # Sum of coefficient of convection and radiation
delT = T2-T3;                                   # Temperature differnce in degF
T2 = 120.;                                       # Assumed temperature in degF
print "The assumption of T2 = 120 comes out to be satisfactory and hc+hr = %.2f  "%(h);
q = h*math.pi*D2*delT;                              # Heat loss in Btu/hr
print "The heat loss per unit foot of pipe is %d Btu/hr-ft"%(q);


The assumption of T2 = 120 comes out to be satisfactory and hc+hr = 1.97
The heat loss per unit foot of pipe is 167 Btu/hr-ft


## Example 12.2 page : 241¶

In :
# Variables
D = 2.375/12;                                     # Outer diameter of pipe in ft
k = 0.035;                                      # Thermal conductivity in Btu/hr-ft-degF
T1 = 400.;                                       # Temperature of pipe in degF
T2 = 70.;                                        # Temperature of air in degF

# Calculations
delT = T1-T2;                                   # Temperature differnce in degF
T2 = 120;                                       # Assumed temperature in degF
h = 3.67;
# As seen from the table , for delT = 330. the value of hc+hr = 3.67
q = h*delT;                                     # Heat loss in Btu/hr

# Results
print "The heat loss per square foot of pipe is %d Btu/hr-ft"%(round(q,-1));

The heat loss per square foot of pipe is 1210 Btu/hr-ft