Can a Y-joint at high flow velocity create negative pressure?

[Timmertjuhh]

Hello,

I was wondering, for the understanding of my research, the following.
I try to create a negative pressure using the venturi effect.
There is a problem a.t.m. with the understanding (theoretical) of negative pressure.

Let me qestion this:
If i have a straight pipe. there is halfway in the pipe an y-joint. if i have a flowvelocity of apr. 34 m/s will this create underpressure in the y-joint? so that is will create a suction area? and if so, what creates the underpressure?

I have attached a preview of the problem.

 

[BvU]

Hallo Timmer, !

Bird, Sewart and Lightfoot work out your case in two slightly different forms (liquid and gas -- in the index under: ejector pump - which is a good search term in google).

Momentum from your main stream is transferred to the side stream, thus creating some suction. (suction is not negative pressure, just negative pressure difference).

 

[Timmertjuhh]

hello,

Thankyou for the respond. What do mean with the principle of negative pressure difference? I thought suction was created by a pressure under the atmospheric pressure. Like with a venturi, you create a restriction, where the flowvelocity rises and the pressure CAN (not always will) drop under 1 atm. It depends on de pressure at first, and the area of restriction. But if you have a straight pipe without restriction and the air just flows straight. I can only imagine the air will go out at the sideline and end of the pipe. So it basically splits.

Maybe you have a link of an explanation about the momentum? I actually can't find the right theory behind it.

 

[BvU]

What do mean with the principle of negative pressure difference?

Ha, I'm allergic to the terms 'negative pressure' and 'negative temperature', that's all.

explanation about the momentum

textbook about fluid dynamics ? No hits with google at all ? (else try 'venturi suction pump')

 

[Chestermiller]

In my judgment, the diagram is over specified, and the total flow is not compatible with the pressures indicated. In any case, most of the flow would go from the 2 bar region out the side tube to the 1 bar region.

 

[A.T.]

What do mean with the principle of negative pressure difference? I thought suction was created by a pressure under the atmospheric pressure.

That's exactly what "negative pressure difference" means: pressure - atmospheric pressure < 0

 

[russ_watters]

textbook about fluid dynamics ? No hits with google at all ? (else try 'venturi suction pump')

Also try "educator pump".

The diagram shows no flow restriction, so there's no venturi effect and no reason I can see why the flow wouldn't just exit through the low pressure branch pipe.

 

[russ_watters]

In my judgment, the diagram is over specified, and the total flow is not compatible with the pressures indicated.

Can it be over and under specified at the same time?!

 

[Tom.G]

Also try "educator pump".

Also known as "eductor pump" or "jet pump". They are used in water wells that are more than about 32ft, 10M, deep, that's where it is impossible to draw enough vacuum (suction) to raise the water that high.

 

[russ_watters]

Also known as "eductor pump" or "jet pump". They are used in water wells that are more than about 32ft, 10M, deep, that's where it is impossible to draw enough vacuum (suction) to raise the water that high.

Oops, mine was a typo or autocorrect.