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Bubble column - Inlet boundary conditions

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Old   June 19, 2012, 20:56
Default Bubble column - Inlet boundary conditions
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I was wondering what is best way to specify the inlet boundary condition for bubble columns with ring sparger.

The options are:
  1. 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)

  2. 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

  3. 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?

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Old   October 17, 2012, 03:49
Default bubble column
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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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bubble column, inlet boundary condition

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