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 t (  t )
q  1 n 1
l n 1 d 1 (1. 10)
 ln i
 i 1 2 d i

Sample Problem Statement

Determine the heat transfer rate per unit area, by means of

conduction for a furnace wall made of fire clay. Furnace wall

thickness is 0.3 m. Thermal conductivity of the furnace wall clay

is 0.3 W/m·K. The furnace wall temperature can be taken to be

0
same as furnace operating temperature which is 650 C and
0
temperature of the outer wall of the furnace is 150 C.

Heat transfer rate per unit area of the wall is calculated as,

q = λ × (T 1 – T 2)/L

q= 0.3×(650-150)/0.3 = 492.1 W/m 2

Sample Problem Statement

Determine the minimum insulation thickness required for a pipe
0
carrying steam at 180 C. The pipe size is 203 mm and the

maximum allowable temperature of outer wall of insulation is
0
50 C. Thermal conductivity of the insulation material for the

temperature range of the pipe can be taken as 0.04 W/m·K. The

heat loss from steam per meter of pipe length has to be limited

to 80 W/m.

Solution*

For radial heat transfer by conduction across a cylindrical wall, the heat transfer rate is

expressed by following equation,

11