SOLUTION

Assumptions

1. Thermal conductivity is assumed to be independent of temperature.
2. Inside wall temperature of the furnace is equal to furnace temperature.
3. Oil price can change. Oil price is taken just to appreciate the fuel economy concept.

a)
Heat loss through the wall

 

By solving we get

     i)   Heat loss

     ii)  Fuel oil consumption  .                                                                                                              operates for 24 hrs.

      iii)   Thickness of the brick exposed to  

              .

                  inches.
 
b)    (i) Furnace is lined with an insulating brick in addition to silica brick. As a result  will change to  .Heat balance

.

Not the advantage of insulating brick; there is a reduction in wall temperature.

Heat loss  

% reduction in heal loss 

(ii) Fuel consumption  litres/ day 

Fuel saving  per day

(iii)   Thickness of brick 3.04 inches
It is important to understand that addition of insulating brick will increase the thickness of the brick is exposed to   .