gas hold up/gas volume fraction
 

can any one please tell me about the difference between gas hold up and gas volume fraction.
regards

Typically hold up is termed for liquids.
May be gas holdup = 1-liquid holdup.
Anyways, input GVF= Q_g/(Q_g + Q_l). It is based on the flow rates. It gives an idea on the area fraction covered by the gas, liquid if both are moving with same velocity.

But, if there is slip, the gas tends to move with higher speed than the liquid. During this time, the in-situ volume fractions for both phases will be very different. because, gas occupies less area than the liquid due to mass conservation principle.Typically, liquid holdup is calculated using emperical correlations.

Regards,
sanbhat

Thanks...
regards
CHAKER