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Venturi effect 
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#1
Dec2908, 10:52 AM

P: 84

In the Venturi effect, in the reduction in pressure and increase velocity on the inside of the convergent cone, does the exit of the liquid on the divergent side mean the pressure that is increased (velocity decreased) can only increase to the maximum pressure that was achieved on the inside (before the convergent)? Can the pressure be increased more if somehow there is a drop in velocity?



#2
Dec2908, 11:17 AM

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P: 2,510

Yes; if the exit (after the convergence) is larger than entrance) before the convergence), velocity will be decreased, and pressure will be increased.



#3
Dec2908, 12:33 PM

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P: 7,131

The pressure returns to ambient only when the velocity (both linear and angular related (turbulent flow)) returns to back to ambient. However, water based venturi pumps, direct water from a faucet through the cone and out the nozzle output into a chamber that has a hose connection on side, and an exit hole at the far end. This allows the existing flow to remain at it's current velocity and low pressure while also allowing air and/or water to be drawn into the chamber and then travel along with the faucet water, and it makes a pretty good pump.
http://andysworld.org.uk/aquablog/?postid=247 If you click on the Candian patent, you can view the images to see the internal workings. The USA patent also works but requires you install a tiff viewer addon to your browser. 


#4
Dec2908, 02:32 PM

P: 84

Venturi effect



#5
Dec2908, 08:52 PM

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P: 7,131




#6
Dec3008, 01:56 PM

Sci Advisor
P: 2,510

Right; I was not thinking of the fluid coming from a "container," like a pressurized can, but rather I was assuming a pump moving fluid through a pipe, up to a venturi tube, then out to another pipe. If the second pipe is larger in diameter than the first, then the pressure against the walls of the second pipe will be greater, and the velocity of the fluid will be slower. Of course the rate of flow, in terms of volume/time will remain nearly constant, but the greater volume inside the second pipe will mean that the fluid travels at a slower speed, causing greater pressure against the sides. 


#7
Jan709, 03:35 PM

P: 84

1. What kind of "sufficient velocity" are we talking about? Isn't the velocity in the closed container of water at rest and equal to zero? So how do we choose at what point the velocity is going to be sufficient? Is that a function of the force/pressure applied into the water in the container; i also assume how big the nozzle throat is will affect the velocity at which the fluid leaves the container through the convergence zone? I am wrapping my idea around a piston type set up where a force will applied to the container top. 2. What if the convergence zone is long and tappers off sharply. Won't it mean the velocity starts to increase (and pressure decrease) as it approaches the apex (exit). In other words, the longer convergence zone will give the water more running time to acclerate towards the apex. 3. If the exit and the resulting medium where the venture effect occurs (i.e decrease in speed and increase in pressure) is water as well  does that affect the outcome. What I am wondering is can i ever have a lower pressure (PSI) in the container and have it come out into a higher pressure water medium because it (the exit pressure) is magnified by the venturi effect (by shaping the nozzlen (i.e longer and sharper). . 


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