For evaluating the efficiency of gas stirring, an alternative approach is to calculate energy input W in watt. The energy input can be calculated by

(3)

Here W is stirring energy in watt, Q is flow rate in Nl/min, t is bath temperature in K,  is pressure at the bottom surface of the bath ( where is density of molten steel, H is bath height and  is atmospheric pressure). For gas injection rate 200 Nl/min into a bath of 2m height the stirring energy would be 390W/m³ when the bath diameter is 2.5 m.

Electromagnetic induction induces stirring energy about 100 W/m³. RH degassing gives about 800 W/m³stirring energy at a circulating rate of 40 tons/minute.

Mixing time i.e. time to homogenize the bath indicates the conditions for stirring. Good mixing promotes the rate of slag/metal reaction as indicated by smaller mixing time. The following results are to be noted:

i)    Scrap enhances the mixing time. Homogenization is possible within a definite time only       up to a certain maximum scrap ratio.

ii)    The mixing time decreases with increase in bottom gas rate

iii)    Mixing time decreases with increasing the aspect ratio of bath.

iv)    Mixing time() in seconds can be correlated with the energy input in W/m³, volume of        scrap ():

(4)

where  in %.and  expresses aspect ratio.