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Gravity flow from an atmospheric tank

Posted Jul 4, 2014, 4:56 p.m. EDT Fluid & Heat, Modeling Tools & Definitions, Parameters, Variables, & Functions Version 4.4 5 Replies

Eloy Ruiz
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Hello community!!

I'm in a license trial of COMSOL to verify its capabilities to our simulation requirements.

We have an open roof tank at the top of a hill; it is filled by a pipeline with constant flow.

The tank nozzle is connected to a gravity pipeline that discharges to a pond. The stationary state water height in the tank is closely related to the discharge coefficient of the nozzle that was calculated through a manual of small dams but the real height differed a lot.

I plan to simulate the tank and see if the stationary height of the tank is closer than the dam-exit aproximation.

I'd appreciate some recommendation about the appropriate (transient - stationary??) simulation and the input and gravity pipeline characteristics.

Kind regards.
Eloy Ruiz
Lima, Peru
5 Replies Last Post Jul 9, 2014, 3:58 a.m. EDT
Pieter Westerik
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Posted: 1 decade ago Jul 8, 2014, 3:31 a.m. EDT
Since you are only interested in the stationary situation you can use a stationary study I think.

What do you mean by
- discharge coefficient
- a manual of small dams
- dam-exit approximation
?

The real height differed a lot from what?

Since you are only interested in the stationary situation you can use a stationary study I think. What do you mean by - discharge coefficient - a manual of small dams - dam-exit approximation ? The real height differed a lot from what?
Pieter Westerik
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Posted: 1 decade ago Jul 8, 2014, 3:34 a.m. EDT
I think you would have to know the flow resistance of the nozzle and the pipe, which will relate the flow speed through both elements to the pressure drop over them.
I think you would have to know the flow resistance of the nozzle and the pipe, which will relate the flow speed through both elements to the pressure drop over them.
Eloy Ruiz
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Posted: 1 decade ago Jul 8, 2014, 9:28 a.m. EDT
Hello Mr. Westerik,

Thanks for answering. To your questions:

- The discharge coefficient is a factor in the calculation of the discharge flow from a tank, related to the water height in it.
- The manual of small dams is the reference we used to obtain the discharge coefficient in the original calculation of the tank it is "Design of Small Dams - Bureau of Reclamation - US Department of Interior"
- Dam-exit approximation is the simplification where it is advisable to use the discharge coefficient of the Dams Manual.

Kind regards.
Eloy Ruiz
Hello Mr. Westerik, Thanks for answering. To your questions: - The discharge coefficient is a factor in the calculation of the discharge flow from a tank, related to the water height in it. - The manual of small dams is the reference we used to obtain the discharge coefficient in the original calculation of the tank it is "Design of Small Dams - Bureau of Reclamation - US Department of Interior" - Dam-exit approximation is the simplification where it is advisable to use the discharge coefficient of the Dams Manual. Kind regards. Eloy Ruiz
Eloy Ruiz
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Posted: 1 decade ago Jul 8, 2014, 9:31 a.m. EDT
You're right Mr. Westerik,

But the flow resistance for the nozzle isn't related to simple equation. There're tables for some situations but they're reliable only if your design is close enough to their asumptions.

Kind regards.
Eloy Ruiz
You're right Mr. Westerik, But the flow resistance for the nozzle isn't related to simple equation. There're tables for some situations but they're reliable only if your design is close enough to their asumptions. Kind regards. Eloy Ruiz
Pieter Westerik
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Posted: 1 decade ago Jul 9, 2014, 3:58 a.m. EDT
Maybe then you have to make a model of the nozzle and calculate the throughput for different pressure drops. Or include this in your total model.
Maybe then you have to make a model of the nozzle and calculate the throughput for different pressure drops. Or include this in your total model.

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