Module 1 : Conduction
Lecture 7 : 1D unsteady conduction (contd.)
 
1D unsteady conduction - constant k
no heat generation-26
  • Let the temperature of the end of the slab be always 95 % of the centerline value. Then:
   
  • Using equn (7.1):
  • Thus a Biot number of 0.1 results  in a temperature difference of 5 % between the center and one end of the slab.
1D unsteady conduction - constant k
no heat generation-27
  • If this 5 % variation is ignored then the temperature between the center and the boundary can be assumed to be the same which is the lumped approach (zero dimension). Therefore if the
    Bi < 0.1 the lumped approach can be used and this approximation yields quick and reasonably accurate results. We have not proved anything only demonstrated the ‘thumb rule’.