PIPE SIZE CALCULATION 2

[seatrendgokhan]

Could anyone help me about calculating the size of the discharge pipe, WITHOUT creating any back pressure or restriction in the system?

Pump details : 200 cbm @ 2.5 BAR
Tank to be circulated : 7.5m heigh from the filling cone

What we are going to do is ; to enlarge the de-aeration pipe and just before the de-aeration cap, fitting a branch line for overboard discharge. Current size of the de-aeration pipe is 4" (DN 100). So could you help me to find out the proper pipe size, without causing any other problem(s).

Many thanks

GOKHAN
Naval Arc.& Marine Eng.

 

[CRG]

WITHOUT creating any back pressure or restriction in the system?????


Not sure what you are saying; however, the only way to do this is to have the discharge pipe slope down where the change of elevation (in feet) equals the friction loss of the line (in feet).

 

[seatrendgokhan]

The tank is already filled up to the de-aeration cap. It is a normal precedure and sometimes water overflows from the de-aeration cap already. So there is no problem with the height as i presume.

GOKHAN
Naval Arc.& Marine Eng.

 

[WebWizz]

For normal line sizing the following site helps:

http://www.engineeringpage.com

Choose > Line sizing for a list of the calculators

It also has some good pressure drop / pump conditions calculation routines that can help you.

Regards, Wim

 

[Cooky]

whenever fluid travels along a pipe, there will always be some pressure drop, albeit very low if the pipe is large enough.

Here's a pressure drop calculator I developed a couple of years ago, you may find it helpful.

http://mysite.wanadoo-members.co.uk/pressure_drop2/index.html

Good luck

Cooky

 

[Ashereng]

If the pipe is not filled, there may also be a chance for close to zero back pressure. It would be similar to weir flow.

I like CRG's solution of using gravity to make up for lost pressure. Star for you.

 

[Maury]

CRG is exactly right. Use manning's equation to design the pipe as an open channel. For a closed conduit, this can still mean flowing full, but the hydraulic gradient can't be any higher than the top of the pipe.

 

[MortenA]

if any of you guys really gets this question then im really impressed.

Best regards

Morten

 

[seatrendgokhan]

Morten

Could you be more clear? Is it me ? or the people ?



Regards

GOKHAN
Naval Arc.& Marine Eng.

 

[seatrendgokhan]

Cooky:

The program doesnt work. But thanks anyway.

GOKHAN
Naval Arc.& Marine Eng.

 

[MortenA]

maybe its just me - but i just can picture what you are trying to describe (the system that is)..

Best regards

Morten

 

[seatrendgokhan]

That is what?

Let me clarify Morten;

In 10 years there will be a new rule for the ships (10 year is nothing for shipbuilding indutry). Rules says; in 3 years you have to provisions to change your all ballast tank water (sea water), %95 percent (at least 3 times) during your voyage. The reason of the rule is not to convey some destructive species to clean seas. And In 10 years time your vessel has to have provisions to filter the ballast water (load + discharge) against 10 destructive species which you can find the names on IMO.ORG. Anyway we are now going for the cheapest option that we just want to have a single ballast line which will be all the time running till our the water is changed 3 times. So for that purpose, i m thinking of using one of the de-aeration pipes as also overboard discharge pipe (onto the open deck to the sea) so i only need to know the basic calculations to obtain the proper pipe size. I used to do this a few years ago but i forgot.

For your information, our ballast tanks are in L shape and has 7 meters head plus each of them is 200 cbm. The loading and unloading are done through the same pipe 6" (DN 150) Which is located at the bottom of the tank. So when this tanks are filled up we already have 0.7 Bar backpressure automatically. And as usual our de-aeration cap is at the top of the tank ( @7 meters).

Hope this is more clear.

Kind regards / Gokhan

GOKHAN
Naval Arc.& Marine Eng.

 

[katmar]

Gokhan,

There are two critical bits of information that you have left out.

Firstly, at what rate do you want to pump this water? You have said that your tank is 200 cbm (presume you mean cubic metres) and that you want to exchange this water three times during a voyage, but you have not put this in time terms. At what rate must the water be pumped into (and therfore overflow from) the tank.

Secondly, we have no indication of the length or slope of the overflow pipe. You have said "I'm thinking of using one of the de-aeration pipes as also overboard discharge pipe (onto the open deck to the sea)". I am afraid that I share Morten's confusion on this and I cannot picture what you are doing. I am not a naval architect, and neither are most of the members here. I have no idea what an "open deck to the sea" is. I cannot imagine that you would be discharging your ballast water onto the ship's decks. Try to imagine us as fairly knowledgable piping people who have no knowledge of ships or of your particular application when you describe what you want to achieve.

regards
Harvey



Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com