Bubble column - Inlet boundary conditions

oj.bulmer · June 19, 2012, 20:56

Hello

I was wondering what is best way to specify the inlet boundary condition for bubble columns with ring sparger.

The options are:

Determine superficial air velocity by experimental measurement, assume a suitable volume fraction at sparger inlet (generally 0.3) and use this to calculate inlet gas velocity by following relation.

$V_{gas-inlet}A_{inlet}* \epsilon_{gas}=V_{gas-superficial} A_{column}$ ...........( $\epsilon_{gas}$ being inlet gas volume fraction)
Calculate ellispsoidal regime settling velocity $w_\infty=\sqrt{ \frac {2\sqrt{g \Delta \rho \sigma} } {\rho_{liquid}}}$ and use it as a superficial velocity, to calculate the inlet velocity as mentioned in point #1. This avoids the tedious and more-than-often impractical measurement of gas superficial velocity
Specify inlet volume fraction (~0.3) and mass flow rate that is known. This seems a lot easier, especially when it comes to mass imbalance calculations at degassing outlet at top.

In literature I have reviewed so far, option 1 seems mostly ( rather universally) popular, though difficult to implement in my case due to lack of availability of data. Option 2 is theoretical simplification and discards any geometrical influence and there is no evidence of this being appropriate in the literature. Option 3 seems so obvious choice, but I am yet to find a publication that mentions the use of mass flow rate at inlet. Quite surprising.

Any ideas about which may be the best way?

Regards
OJ

mohamad3564 · October 17, 2012, 03:49

I am using inlet same condition for bubble column and with try and error I found that 0.3 is suitable for my case.can we share our information?

June 19, 2012, 20:56	Bubble column - Inlet boundary conditions	#1
oj.bulmer Senior Member OJ Join Date: Apr 2012 Location: United Kindom Posts: 292 Rep Power: 7	Hello I was wondering what is best way to specify the inlet boundary condition for bubble columns with ring sparger. The options are: Determine superficial air velocity by experimental measurement, assume a suitable volume fraction at sparger inlet (generally 0.3) and use this to calculate inlet gas velocity by following relation. $V_{gas-inlet}A_{inlet}* \epsilon_{gas}=V_{gas-superficial} A_{column}$ ...........( $\epsilon_{gas}$ being inlet gas volume fraction) Calculate ellispsoidal regime settling velocity $w_\infty=\sqrt{ \frac {2\sqrt{g \Delta \rho \sigma} } {\rho_{liquid}}}$ and use it as a superficial velocity, to calculate the inlet velocity as mentioned in point #1. This avoids the tedious and more-than-often impractical measurement of gas superficial velocity Specify inlet volume fraction (~0.3) and mass flow rate that is known. This seems a lot easier, especially when it comes to mass imbalance calculations at degassing outlet at top. In literature I have reviewed so far, option 1 seems mostly ( rather universally) popular, though difficult to implement in my case due to lack of availability of data. Option 2 is theoretical simplification and discards any geometrical influence and there is no evidence of this being appropriate in the literature. Option 3 seems so obvious choice, but I am yet to find a publication that mentions the use of mass flow rate at inlet. Quite surprising. Any ideas about which may be the best way? Regards OJ

October 17, 2012, 03:49	bubble column	#2
mohamad3564 New Member mohamad Join Date: Jun 2012 Posts: 7 Rep Power: 2	I am using inlet same condition for bubble column and with try and error I found that 0.3 is suitable for my case.can we share our information?

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