Inverted "U" Vent Criteria, Air pockets

[DNitzsche]

Hi my friends.
I am looking for some bibliography or texts from where I can exctract some criteria. I need to know in which situations I need to use a vent for normal runing and sistem starting, depending on diameter ,flow rate, pressure and temperature.
Mostly I am searching for norms or bibliography to suport a valid argument depending the case of air acumulation.


Thanks a lot!

Diego Andrés Nitzsche

 

[bimr]

You need to provide some information on what you are doing.

 

[DNitzsche]

Well I am studing mechanics engineering and I am working for a power generation nuclear reactor design, currently on a sistem called "Heat up an cold down starting and stoping system" for regulating temperatures during stoping and starting phases for the primary circuit . The rooms where the system is placed are really tight, so there are some inverted U in the piping design. I am looking foward to justify the need or not of air vents .

Roughly simplifying the pipes could be resumed like this:

Between 2" and 4" 20 000 Kg/h 9.4 mPa

Between 4" and 6" 150 000 Kg/h 0.5 mPa


Between 1.5" and 3" 5000 Kg/h 11 mPa


Any ideas where I can get some criteria reflected on text, norm or paper?


Thanks!!

 

[DNitzsche]

Note I am only ganing experience on the field and this issue will be revised by experienced people, but I want to make a valid and constructive point

Thanks a lot!

 

[LittleInch]

Ok, what I think you're talking about is whether air pockets will be swept out of piping or not.

You need to look up "Froude number" or search for things like "air pipe flow".

Froude number is, in metric, = v / (g x d)^0.5 v, g and d in metres.

The numbers seem to chnge a bit, but all are agreed that for a vertical down pipe, this needs to be > 0.35 in order for bubbles /air to be forced downwards. For a horizontal pipe, to obtain a full pipe, you need a number greater than 1.

In any event whether you actually need air vents depends on your design. If the pipes are all fed with liquid under pressure, then it shouldn't make any difference. It is only if there is a condition where you need to get a syphon going is there a big issue with air vents. However if you are at Froude numbers where there isn't sufficient flow to blow any air bubbles or pockets out on re-start, then you could get two phase or surging flow.

for liquids anything more than about 1m/sec is normally more than enough to sweep air through the pipe.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way