Calculate water level with conditions open to environment (static head)

[Arve S]

TL;DR Summary

Understanding the physics of head pressure generated in an open system, and how it affects liquid building in horizontal pipeline

Hi all, I have a challenge with solving a simple question: Will water exit the flare

I have a vertical pipe (40 meter with diameter of 1100mm) with the following connetions:
- At the bottom: bend reducer to 514mm and approx. 100 meter length
- At the top: 750mm pipe that goes up another 30 meter, some bends and some horizontal lines as well - AKA flare
- At approx. 10 meter from the top my inlet: diameter 400mm

Through my inlet I run water (1000m3/h)
The goal is to ensure that the bottom pipes are configured sufficiently to make sure that all water are directed downwards, meaning no water in flare.

I've calculated the backpressure from the outlet at my bottom and the pipes that goes from there to be 0.1 barg.

In my head, I would expect that approx. 1 meter water head would be required above my bottom part (where i've calculated the backpressure) - Note that this section is way below my injection point.

When talking to one of my collegue, he stated that the required head to push the water beyond the 0.1 barg, would be 1 meter above my injection point, and not 1 meter above my bottom area where I have my reducer. I struggle to understand why it would be so high up on my vertical pipe..

Anyone got any ideas? - I also have several images, but I cant figure out how to post them. Copy / paste does not seem to be working.

Best regards,
Arve

 

[sophiecentaur]

Hmm. A diagram of this is essential. I have no idea what the set up could be.
```try again.

 

[BvU]

!

Well, it works for me

Howwever, it doesn't work when 'toggle BB code'is on (

), or -- of course -- when you preview,


What is an AKA flare ?

I've calculated the backpressure from the outlet at my bottom and the pipes that goes from there to be 0.1 barg.

Can help but smile at that, Can you post the calculation so we get an idea what's going on ?

$\$

 

[Lnewqban]

Welcome, Arve!
We need you to be more specific about what you call bottom and injection point.
Click on the little picture next to the happy face above, and you will be able to attach pictures.

 

[sophiecentaur]

Well, it works for me

You know exactly what a 'Flare' is. Lucky man. It's a style for trouser legs (=pants) for me or an explosion on the Sun or landing an aircraft etc. etc.

Many images can just be pasted directly into a post and the 'link' symbol is good for pasting links (EDIT PASTE works too.)

 

[Arve S]

Here we go, thanks Lnewqban for sharing how I can insert an image.

So, a Flare offshore is the pipe network where all the gas is exiting, I have included a photo of a typical Flare.

I have also included an image of the pipe network im curious to where i will have water- The snipp image is from my simulation, where the coloring indicates that I will have some water creeping up in my "Flare-pipe". My inlet pipe is located on the side of the "main seawater caisson" (The large vertical pipe).

Hope this can provide a more clear idea of the challenge - to calculate where the "level of water" will in the large vertical pipe, and if the water will creep up in my flare pipe as indicated in my simulation.

​

 

[Dullard]

Elevations / Sea level are required to evaluate this problem.

 

[BvU]

You know exactly what a 'Flare' is. Lucky man. It's a style for trouser legs (=pants) for me or an explosion on the Sun or landing an aircraft etc. etc.

I suppose so. But was disoriented by the liquid context and the AKA epitheton.

@Arve S colorful picture isn't alll too far from what I sketched on the basis of post #1, but there's still a lot to be explained.

Inlet 10 m below top of 1100 mm pipe. Inlet seems to come from lower right, hundreds of meters away, close to outlet open to environment . A pump ? 1000 m3/h 'with water' (and what else?)

One (750 mm) outlet 5 m below top ? The 30 m is what ? Looks more like 100 m to the flare

Outlet to environment ? Air? Water ? Atmospheric pressure ? As @Dullard asks: where is sea level ?

Color denotes mass fraction of liquid water ? What else ? water vapour ? First section (how many m ?? ) of 750 mm pipe is 50% liquid water ?

I suppose pressure drop calculations can be done based on main flow pure water 2.2 m/s in inlet pipe, 0.29 m/s in main pipe (1100mm) and 1.34 m/s in outlet pipe ?

Roughness ?

What is your simulation program called and what is it doing ? You mention t=500 s after what ? start from empty ?

$\$

 

[Arve S]

Hi BvU, ineed its as you sketched it.
I guess first of all im trying to understand some simple physics on how the water will react in this open system. I believe we have two options on where the water will "stabilise" in some way when the system is running with 1000m³/h.

Option A: We will achieve a water level (air above) that is above my injection point, some distance, and might even creep in the flare pipe. The distance will depend on the backpressure produced in my system.

Option B: We will achieve a water level some distance over the reducer piece. Where the distance depends on the backpressure produced in my system.

I always believe that the waterlevel would be under my injection point as long as the backpressure generated from my outlet pipe is considered low, however one of my collegue informed me that regardless of the backpressure produced, the waterlevel will always be some distance above my injection point, this as a result of an open system (open to environment both in the top and in the bottom).

So, any idea if this will be true?

 

[Dullard]

Referring to your original question:
Get a smarter colleague (you're right).

 

[BvU]

With this calculator I get a pressure drop of 6.5 kPa over the 100 m, 514 mm pipe

Since you have an additional head of 11 m after the reducer, there seems to be no problem.

I also don't understand why your colleague thinks much more is needed.

(provided my questions in #8 don't have surprise answers... )

$\$