Exercise- 4

A pipe is insulated by asbestos cement . The pipe is exposed to room temperature at   with

Calculate the critical radius of insulation for asbestos cement.

 
Decrease in  will decrease the critical thickness of insulation.

Calculate the heat loss from a  dia pipe when

1. covered with the critical radius of insulation
2.  and without insulation.

 

Without insulation the convection from the outer surface of the pipe is

 

  
So addition of insulation increases the heat transfer
Suppose we use now asbestos
 

The critical radius of the insulation is less than the radius of the pipe, so addition of fiberglass will decrease the heat transfer.