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How to include Mass Transfer Coefficient into MSX

Hi Everyone,

We're currently working on developing an MSX model for Chlorine Decay that can account for wall decay as a factor of Biofilm growth (thus removing the need to specify wall decay for specific pipes throughout the network).

Unfortunately the equation for this relies on the mass transfer coefficient, which is dependent on the type of flow, as explained here: https://docs.bentley.com/LiveContent/web/Bentley%20WaterGEMS%20SS6-v1/en/GUID-D7D70292-50F6-4066-A30E-3B98BBB2BF7B.html.

This is built into the WaterGEMS standard pipe wall reaction calculations, however I need to know whether we can reference this coefficient in MSX, does anyone know whether this is possible? My understanding is that EPANET is capable of this so I assume WaterGEMS is capable as well, I just don’t know how.

For anyone wondering, the equations for Bulk decay are very simple. Below is a copy of what we use currently (no wall decay):

The Wall Decay equations are derived as follows (A&B are constants to be determined by trial and error, kw is what we need from WaterGEMS)

Thank you,

 Ryan

Parents
  • Hello Ryan,

    You would need access to the WaterObjects.NET functionality to use the "Mass Transfer Coefficient" used in the first order wall reaction rate.

    Another approach would be to use Formula Based User Defined Extensions. From the formula provided develop an equation to calculate the mass transfer coefficient from the equations given. However, that would first require classification of flow based on Reynold's number.

    You can develop an formula based UDX for Reynold's number and classify the flow as laminar or turbulent; then develop separate equations (using formula based UDX) for both the type of flows for the Sherwood number. It is best in this case that you create two separate selection sets for both the type of flows and work on them individually.

    Once you have the Sherwood number values for both the flow use the equation to calculate mass transfer coefficient again using the formula based UDX.

    This procedure is a bit complicated, but can be achieved.

    Let me know if this helps.


    Regards,

    Yashodhan Joshi

Reply
  • Hello Ryan,

    You would need access to the WaterObjects.NET functionality to use the "Mass Transfer Coefficient" used in the first order wall reaction rate.

    Another approach would be to use Formula Based User Defined Extensions. From the formula provided develop an equation to calculate the mass transfer coefficient from the equations given. However, that would first require classification of flow based on Reynold's number.

    You can develop an formula based UDX for Reynold's number and classify the flow as laminar or turbulent; then develop separate equations (using formula based UDX) for both the type of flows for the Sherwood number. It is best in this case that you create two separate selection sets for both the type of flows and work on them individually.

    Once you have the Sherwood number values for both the flow use the equation to calculate mass transfer coefficient again using the formula based UDX.

    This procedure is a bit complicated, but can be achieved.

    Let me know if this helps.


    Regards,

    Yashodhan Joshi

Children
  • Hi Yashodhan,

    Thank you for your assistance. I have absolutely no programming knowledge so I'm afraid that first suggestion is not an option.

    Unfortunately I'm only a Civil engineer so my knowledge of the chemical reactions and their associated equations behind them is very limited. In order to be able to follow your workaround I need the following knowledge.

    • Firstly I’d need formulas to calculate Sherwood’s number for both turbulent and laminar flow as you've described (I’ve tried researching Sherwood’s number and it’s beyond the degree of information I have available to learn from)
    • Secondly I don't understand what you mean by creating selection sets for the different types of flows
    • Thirdly I need the mass transfer coefficient equations to add the Sherwood equations to based on whether it’s laminar or turbulent flow (I don’t know the correct equations for this either and again it seems to be beyond the level of information I can find online)

    This would be a lot easier if WaterGEMS could simply calculate the mass transfer coefficient for me (as I assume it does this already for first order wall decay calculations).

    Regards,

     Ryan

  • Alright, I have actually managed to find equations for Sherwood's number for both laminar and turbulent flow. As well as how this fits into into the Mass Transfer equation using information I found in the following paper  by Risala A.Mohammed and Kifah M. Khudia: http://files.engineering.com/download.aspx?folder=a63c406b-103d-43d8-85bd-cf947370fb71&file=iasj.pdf (relevant information screenshotted below)

    Yashodhan, if you could explain what you mean by 'selections sets' and how I can get the MSX code to differentiate between turbulent and laminar flow I should be onto a winner!

  • Hi Ryan,

    Did you see my earlier response?

    Regards,

    Wayne.



  • Hi Wayne,

    I did see your earlier response and I'm well aware of the user guide and it's contents. The mass transfer coefficient equation you provided has the wrong constants for Chlorine in water and doesn't allow for variations in temperature. Additionally it doesn't allow for the changes in the coefficient that occur between laminar and turbulent flows.


    Regards,

     Ryan

  • The equation I provided is just a sample equation. You can choose whatever constants you like. In fact you have complete control over the full definition of any terms that you want/need.

    With regards to "Additionally it doesn't allow for the changes in the coefficient that occur between laminar and turbulent flows." - Isn't that what Reynolds number is for? If not, can you please explain to me what is missing?

    With regards to factoring in temperature, I guess you could model that as another species, though it sounds like a pretty challenging thing to attempt. Most people would just assume a constant temperature, is my guess.

    Regards,

    Wayne.