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How to calculate Volumetric Mass transfer coefficient using CFX?

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Old   July 20, 2010, 02:18
Question How to calculate Volumetric Mass transfer coefficient using CFX?
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tukaram
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Hi,
We have measured mass transfer coefficient from experiments and we want to validate it using CFX. The process is absorption of CO2 from Air to liquid solvent NH3. We plan to use inter-phase mass transfer model to simulate mass transfer between gas & liquid phases.



Following are some questions:
  1. Can we calculate overall volumetric mass transfer coefficient of CO2 (say K_L*a)? If yes, what is the procedure?
  2. Can we calculate volumetric mass transfer coefficient in individual phases (in liquid, k_l*a and in gas, k_g*a)? If yes, what is the procedure?
Please reply. Its urgent.
Thanks
Tuks
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Old   July 21, 2010, 04:43
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Tommy
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I'm not clear of your problem, just a suggestion. Hope it may help.

If the dissolved gas in liquid will not enlarge volume of liquid, can you calculate the decreasement of gas volume from outlet and inlet?
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Old   July 22, 2010, 01:15
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tukaram
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My objective is to evaluate overall volumetric mass transfer coefficient for CO2 absorption from Air (gas) to Amine (liquid) with no reactions.

Using basic definition "N*a = K_L*a*(C_L_eq - C_L)". Where N is molar flux, K_L*a is volumetric coefficient and C_L_eq and C_L are concetration at interface (in equlibrium with gas phase conc) and bulk concentration. All values pertaining to CO2 in liquid ammonia/amine.

Can we evaluate K_L*a from hydrodynamics and concentration profiles in CFX?
My approach could be
  1. Define diffusivity of CO2 in Air (gas) and amine (liquid).
  2. Define gas-liquid interphase mass transfer using a model where only Henry's constant for CO2 needs to be specified.
  3. Solve the momentum, mass transfer equations for gas, liquid phases and get concentrations pofiles.
  4. Use concentration profiles to calculate molar flux (N) and then calculate K_L*a.
As I dont know details of interphase mass transfer models in CFX. Also I am not sure if approach is correct?
Experts views are welcome.

Thanks
Tuks
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