pipe with slots: flowrate & pressure drop 2

[Gorostidi]

Hi to All,

we are trying to develop an air flow system where:

1) we have a pipe of certain diameter, let's say 50mm
2) we insert air in it at certain flowrate
3) we put slots along the pipe let's say about 0.4mm width and certain length

our idea is to keep certain pressure between the internal part of the pipe and the external so that all the slotswill more or less send the same amount of air. but there are some additions to be included in bernouilli equation such as coeficcients because of the flow of the air through the slots

does any one have any experience about this?

thanks to all in advance

 

[zdas04]

You know, the first time I saw "of a certain ..." in your post it annoyed me. By the third time I was pretty sure that either this was a homework problem or you are just being cute. Either way I'm not playing.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"

 

[Latexman]

Certainly.

Good luck,
Latexman

Need help writing a question or understanding a reply? forum1529

 

[MikeHalloran]

Star to Latexman for answering the question asked.



Mike Halloran
Pembroke Pines, FL, USA

 

[Gorostidi]

We will try to explain the problem again just in case some can have clue of solving it.

in any case for anyone that is interested and might be able to help us:

we are an industrial group working together with a research center and making some simulations of air flow in pipes. that is not something new at all.
The aim is to develop a system that sends bubbles in the bottom of different tanks (different sizes) using piping systems (the pipes will have slots to push the air out) . Since in real life the tanks will not be copletelly levelled some internal pressure is required inside the pipes so that it will possible to send bubbles in all the slots.
If we focus on a single pipe with slots, Bernouilli covers this case with some corrections. the first one is to find the coefficient of a pressure drop in a slot of a pipe.
there are many cases solved with small holes but we cannot find something with slots. Our simple question if someone has been involved in a similar project.

We have some experimental data and trying to make some computer simulation in the department, but any help will be much appreciated.

 

[MikeHalloran]

The customary word for injecting gas bubbles in the bottom of a tank of liquid is "sparging". The equipment is called a "sparger". You may find some parts commercially available.

I have used porous plastic air mufflers as spargers with decent success. They are pretty cheap relative to custom machining of slots in pipe.

Either way, your best option is to arrange a test of a representative sample of what you will actually get, instead of attempting to work out the Cv of a slot from first principles. For liquid orifices, and I think also for gas orifices, the exact edge radius has a profound effect on the orifice coefficient. So much so that you generally get more consistent performance from a hole finish like "no burrs/ no chamfer/ no radius", than from trying to specify any particular chamfer or radius. Your worst enemy in fabrication of controlled flow apertures is the machinist who will "do you a favor and just knock the edges off to improve the flow a bit".



Mike Halloran
Pembroke Pines, FL, USA

 

[Gorostidi]

Hi Mike

thanks a lot for your answer.

we have also used porous plastic as spargers also with success but in some applications where the tarjet is to create bubbles in order to "add" some gas in the water. In our case what we want is to move (and mix) 1.5 meters of sand in order to wash it afterwards in a sand filter. we have some previous solutions such as the ones you mentioned before but just looking for something cheaper. to be honest we have not tried the porous plastic pipes in this application. we will try it also.
We have though in slots in the bottom part of the pipes because they tend to balance the flow when the tanks are not leveled. if the area of the slots is not so big we can keep a pressure in the pipe so that air will come out from all the slots.
We are working in parallel in some solutions. We will take into account your suggestion about the porous pipes, and also go on with bernouilli calculations for slots in the pipes

thanks again for your suggestions

Gorostidi
PHd mechanical engineer