3 replies to this topic

[c.addle]

Hello,

 

how do I calculate a size of a vessel if I need 1 m3/s air flow at 13 barg for 30 seconds from the vessel?I dont have dynamic simulation SW, only the steady state. Thank you

[Saml]

The main issue you have is that you have three variables to define:

- Initial volume.

- Initial pressure.

- Final pressure

And from that infinite number of combinations you have to select the vessel based on a criteria you have to define.

 

Soy you have to remove 30 m3 from the vessel and end up with a pressure above 13 barg.

So, roughly (assuming isothermal, what is not true because the temperature will be decreasing as you remove gas and you have to calculate it), you can have:

 

- a 30 m3 vessel at 14.5 barg that ends at 13.5 barg

- a 15 m3 vessel at 15.5 barg that ends at 13.5 barg

- a 7.5 m3 vessel at 25 barg that ends at 21 barg

- a 3.75 m3 vessel at 25 barg that ends at 17 barg

 

And you can go on and on and on....

 

So the problem is not calculating (that is basic thermodynamic) but defining the selection criteria.

[c.addle]

I dont know the initial volume. I only know I need to remove 1 m3 every second for 30 seconds from the vessel. How did you calculate the volumes please? Is it true I need 10.5 m3 vessel at 15 barg that ends at 11 barg?

[Saml]

I dont know the initial volume. I only know I need to remove 1 m3 every second for 30 seconds from the vessel. How did you calculate the volumes please? Is it true I need 10.5 m3 vessel at 15 barg that ends at 11 barg?

 

No, if it ends at 11 barg you cannot remove air at 13 barg

As I said, you have to assume or define a vessel volume and that will give you the pressure needed.

Of you can define the initial vessel pressure and calculate the volume needed.

There is no single criterion.

In fact, you can also use a battery of air cylinders at 150 barg from a compressed gas supplier too, but those will go quite cold if you depressurize in 30 seconds.

 

All the examples are that you need 30 m3/s at normal conditions. If they are actual 30 m3/s at 13 barg, then you have to adjust the volumes accordingly.