I am really grateful for this video. I am taking a course that just said, "make a venturi". So I googled it, wiki'ed it, and was still lost. A video is worth a trillion words. Well demonstrated. Thank you.
The principle is also used in old chemistry labs to provide vacuum for rotary evaporators. An adapter is connected to a faucet to create the vacuum. Wastes a good deal of water in the process.
You sir, are an artist and genius. I thoroughly enjoy your channel. Every video is a fascinating gem. Thank you for sharing your many varied creations.
It's specifically much more the venturi effect than the bernuli principle. The bernulli effect is about energy conservation, whereas this is about mixing of air streams. That's why a vernturi pump is a venturi pump, not a bernulli pump.
This is a fantastic video. I learn best with examples, and when learning a new concept, displaying several examples really paints the picture. Thank you.
A Pelican fountain pen. Bought it in Germany Nice no nonsense fountain pens, work way better than the parker fountain pens (which are mostly for status)
I know this is an old video, but could the exhaust port of a vacuum be hooked up to the intake port of a vacuum to increase the suction effect using the Venturi effect? Or is there diminishing returns?
Thank you good sir for demonstrating the venturi effect and giving a thorough explanation. It make a lot of sense now with what I am learning in the lab :)
Excellent work; I'm going to use a clip of the first example with the paper tube for part of a presentation as an example of the venturi effect and how it relates to my research. Thank you!
Pelikan, with the regular blue Pelikan ink. Pelikan makes the best fountain pens. Plain, simple and relatively inexpensive, but they write way better than expensive Parker pens.
Sir Wandel this is my correction, Venturi effect describes drop of static pressure in fluid entering a narrower tube from a wider tube, Coanda effect describes a drop of pressure in ambient fluid around a jet of fast moving fluid I'm a big fan
You know the bucket of water with the hose pipe experiment you demonstrated, if you swapped the hose pipe with an airline like you used for the saw dust, I'm guessing that's what you're explaining? Water's way more dense than air, so the energy will dissipate and not push the water out as quick as water to water would... makes sense.
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Have been looking around for a good explanation of the Venturi effect since I've heard sports cars use it...this has been the most intuitive explanation I've found so far. Thanks! :)
By your reasoning, the direction that I blow the air wouldn't matter Bernoulli's principle is about conservation of energy in one flow, whereas this is about mixing of streams of fluid. Try thinking a bit more and parroting a bit less.
In the sawdust (injection) pump, the compressed air pushes air out of the top section of the cylinder thereby reducing the pressure in the lower section, as you describe. It operates on the principle of induced current, not the Venturi effect (there is no Venturi tube). Likewise for the hose in the bucket. The flame thrower is an atomizer nozzle. While some atomizers use a Venturi tube, this one doesn't and relies solely on the Bernoulli effect.
That is also how a steam injector works for getting water pumped into a pressurized boiler (eg on a powerplant or a steam locomotive) and how a Giesl ejector creates a draft in the boiler of a steam locomotive. Airbrushes and many paint guns uses this to propel the paint.
IIRC the Bernoulli equation relates the speed of a fluid to it's drop in pressure, assuming density and temperature are unchanged. The Venturi effect is when you constrict a fluid stream, causing the fluid speed to increase so the pressure drops. A jet of air is using entrainment to transfer momentum to the ambient air mass, and may be higher or lower pressure than ambient depending on the nozzle orifice. Basically, this video is showing a whole bunch of physical effects!
FYI, this application of the Venturi effect is known as an injector, there is a neat Wikipedia article on such devices. They used to be used to pump water into the boilers of steam locomotives using high pressure steam from the boiler.
I get the venturi effect now. I've heard of it in a number of contexts all my life but, really did not know what it was exactly. What I see happening is that you're creating a relative low pressure zone in the top of the straw which creates a vacuum which draws up the liquid or gas. Very cool.
I think that's how carburetors work. The engine pulls in air by the vacuum created from the piston on the intake stroke, and then the flow of air causes the fuel to come up to be mixed with the air (like your spray gun example). :)
If you lower the pressure on that makeshift sprayer, you could probably sustain the flame without using the torch (though it would still have to be high enough pressure to make the fluid flow through the straw, so I'm not sure if that would work.)
The explanation of what happens is accurate. This name of the effect is, however, turbulent mixing, not the Venturi effect. The Venturi effect is the decrease in pressure at a restriction according to Bernoulli's law. This can also be used to create a low pressure, but it does not require turbulence nor viscosity. Thanks for the demonstration.
Since your spray gun hose (straw) is placed in front of the compressed air nozzle, I would argue that the drop in pressure is caused by the Bernoulli Effect - fluids in an area moving faster than the the surrounding area possess less pressure. Since the air moving across the top of the straw is moving so quickly, the pressure drops and causes suction through the straw. Granted, I was a music major and my knowledge of the Bernoulli Effect is limited to its effect on vocal folds! Also granted, I had never heard of the Venturi Effect until just now. Thanks for learning me so good!
Matt Wallace Well, since all the air around me isn't moving either, I should then experience a tremendous vacuum from all the air that is not moving, according to your explanation.
Matthias Wandel Matt Wallace The Venturi effect is a subset/example of the Bernoulli Principal. Either can be explained by particle replacement or the pressure/speed-of-flow relationship. Matthias, going off of Matt's explanation, we do experience pressure (not vacumm) from the air that is not moving ~1 atm of pressure. That applied pressure is actually quite important for biological functions! Some people can actually feel pressure differences caused by storm systems because the pressure inside their body is not equalized properly and then the pressure differential is then felt as a force on their joints, for example.
Matthias Wandel Bernoulli's equation is a relation between speed and pressure along a single streamline, that is, a path taken by particles through the fluid. It's not valid in this case because Andrew is trying to compare different streamlines, and because the flow is unsteady. (In fact, the pressure in the jet is more or less atmospheric!) The suction is (as you stated) due to the deceleration of the jet due to turbulence, which causes a rising pressure gradient. Since the air at the far end of the tube is atmospheric, the air at the jet end is must be below atmospheric pressure, hence suction. Your friendly neighbourhood engineering student
+Matt Wallace Bernoulli: Fluid pressure is inverse to velocity. Venturi: Fluid pressure in a pipe reduces in a constriction. Since we are talking in very oversimplified terms (compared to actually modeling this with CFD and being realistic about what is happening here), the process would be: #1. The ID of the pipe is expanded when it exits the nozzle into the paper towel roll - most directly relevant to the Venturi principle which relates fluid pressure to pipe ID. #2. The high velocity fluid pushes out the air inside the paper towel roll, and this high velocity compared to the static atmospheric air creates a pocket of low pressure (Bernoulli- ish), which creates a pressure differential that moves air up to fill behind it. That relationship is also the result of the conservation of mass (mass flux in needs to equal mass flux out, the high velocity air going out x the cross sectional area needs to be equal to the velocity of the air entering x the same cross section). It is probably best to phrase this system in the context of the conservation of mass because applying Bernoullis has a lot of requirements, which they would not discuss in music. For example, Bernoullis only applies to inviscid flow, but all fluid is viscous so it will have viscous forces along the inner walls of the paper towel (in the boundary layer). So Bernoullis could only apply outside the boundary layer, and in a pipe this small the boundary layer is significant. Source: Fluid mechanics is a subset of mech engr, I have BSME, MSME
+CoolRiffz Not sure if i understand (english is not my native language...), but Bernoulli principle can be related with limitations in flow, derived from pressure drop (that comes from viscous limitations) and pressure gains (inputs, pumps, for example). So you can apply in every system, taking in account the real limitations on a system.
Matthias: I need to move about 18 inches of blow-in insulation from one part of my attic (approx 400 sqft) to another, and doing it by lifting & carrying would not work (the spaces are separated). Do you think I could aim a hose attached to the outlet side of my shop vac into the side of a larger hose (4"?) then suck the insulation from the "back" end of the 4" hose and blow it out the "front" end in the new location? Or a leaf blower instead of shop vac?
Thanks for this - studying for a pilot’s license and this helped to (finally) conceptualize this. Got a video for aerodynamic lift / Bernoulli’s Principle?
What would happen if you did this in a vacuum where there is no air for it to mix with?? Would it still fan out or just be a laser like beam coming out the nozzle
zakkyummms No need to be sarcastic, but then again you didn't say much either, I was making fun, and if you don't like it don't click that reply button.
it doesnt create a negative pressure, it creates a low pressure zone in the fast moving air.. the ambient pressure in the straw is what pushes out to meet the lower pressure zone
just trying to help you keep it real. you created a lower pressure zone. vacuum does nothing, pressure does the work. dont you remember this from school?? in physics its good to get the terminology correct.
It's not pedantry to say your video is factually inaccurate. It might not seem important once you understand the principle but for kids or beginners coming into fluid dynamics the wrong terminology can really set them back in understanding the basics. They need to realise that it isn't 'negative' pressure, it is merely a lower pressure than the surrounding fluid.
There are airplanes that have pumps with no moving parts called ejector pumps (or eductor pumps, or jet pumps) that operate on the principle shown in the video. Some fuel is diverted from the engine-driven high pressure pump, plumbed all the way to the tank where a small volume is ejected inside the tank through a narrow nozzle at high speed. A larger volume of fuel is drawn out of the tank and taken back to the engine - where it ends up going through the engine pump again. Any given parcel of fuel may actually circulate a few times around this loop before finally being pumped into the engine.
A question for you if I may. I'm wondering if you're riding a small carbureted vehicle up a hill that it cannot accelerate on, is it counter productive to hold the throttle wide open versus just open enough that the engine can fully use? I've always wondered if the airflow would draw the correct amount of gasoline naturally or if it's better to have the jet needle slightly blocking the main jet and restricting gasoline so the mixture is not too rich. I'm talking about the point where the throttle is equal to engine output versus wide open where you can definitely hear the vacuum. My understanding of the theory is the fuel will correctly mix with air based on air speed alone regardless of throttle position above current engine demand. Hopefully I'm clear enough. The furnace seems to support my thoughts though it's a bit reversed.
As Matt Wallace pointed out, you have confounded Bernoulli's principle with the Venturi effect. Bernoulli's principle is that pressure decreases when velocity of a fluid increases. The Venturi effect is a consequence of Bernoulli's principle in the special case of a fluid flowing through a constricted pipe. It states that a fluid that does not compress will lose fluid pressure at the constriction. It results because the fluid must move faster in a narrow pipe than a wide pipe to move an equivalent volume which leads to a lower pressure by Bernoulli's principle. You provided some very neat demonstrations of Bernoulli's principle, and a couple of them may incidentally also involve the Venturi effect, but Matt Wallace is correct, this video should be titled "Bernoulli's Principle."
I'm about to make up a new exhaust system for the car and I wondered if the angle of the very end of the tube, plays much of a part in better moving the exhaust gasses? Ie. a 45 degree angle (or less), coming out on one side with sliced section facing the 'wind' or with it facing away from the 'wind'. Just curious about how each might affect things. 2:10
Matt, I'm trying to understand the maximum force that can be exerted through the straw on your spraygun, do you know of an equation? I'm interested in using the venturi effect to spray aggregate free concrete, but would like to run the math to make sure it's possible to move that much weight, and if it is possible how much PSI I would need coming through the hose.
The Venturi effect is shown here. You have to have a high moving air stream for the Venturi effect to even take place hence the air compressor. Take the paper towel roll in the first part of video as the restriction or the narrow part in a closed tube system and the surrounding air around it as the larger tube that you described. The same principle is applied here.
Your a really smart and inspiring guy when I graduate from high school in gonna go for a degree in things like this thank you for all your knowledge and your videos are inspireing keep up the great work I hope to be like you someday p.s. your dad must have been very proud of the great work you do and all your accomplishments....take care and make a wooden fidget spinner plzzz i started a business making these things....
I like your video very much. Do you have something I can use as a gas burner for a brick oven. I bake bread and I would like to know what I can use. thanks
This is the same method used in those diesel "cannon" style space heaters, there is no high pressure fuel pump - at least for the cheap ones. Just a small air pump, sucking up fuel from the tank by ventury effect and mixing it with air. Just recently found this out after servicing one...
Scott, This is better known as Bernoulli's principle which your teacher might recognize. It's the principle that makes aircraft fly (heavier than air craft anyway) cauburetors work, and atomizers such as the "Flame Thrower" that Mr. Wandel demonstrated very well. Also deep water wells with a surface pump use the same principle. N
Hello, awesome video. I am trying to calculate the air intake flow rate related to the pressure drop. Should I just calculate the pressure drop inside the blower and then relate the pressure from the vena contracta with the atm pressure to calculate the intake? Thank you
You refreshed a memory of a modified Preval sprayer someone showed me how to make in my 1st yrs. of work. Same premise as the airhose mod., just attach tube to a screw on replaceable glass lidded container. When your broke, they work awesome. You gave me some good ideas for paint sprayers though, with your excellent drawings. I have to see stuff happen or you might as well talk Wookie? Thanks.
A real venturi action is helped a lot by a narrowing passage.. like all the carburators have. The tube narrows and when it enlarges again there is a drop of air pressure and an increase of air speed.. The Homelite Shop Service Manual says: "Carburator design is based on the venturi principle which is that a gas or a liquid flowing through a neckde-down section ( venturi) in a passage undergoes an increased in speed and a decrease in pressure as compared to its speed and pressure in the full section of the passage. "
The missing key is a narrowing tube. Without that it is not utilizing the Venturi Effect. However, I can see how one could consider the outside as an infinitely large tube. In any case, the Venturi tube is specialized application of Bernoulli's principle.
Thank you Matthias for such a simple presentation of a complex scientific phenomena. Do you know if the Dyson bladeless fan, which is using the Venturi effect, is more efficient by thrust to power?
Man I wish I was as smart as Matthias ... I could do fun crazy things like this without either burning myself, or burning the house down... I love watching you fun videos like this
What you would have to do is downsize the size of the suction hose going to the insulation to create more vacuum force. You could make a venturi out of PVC pipe, and try the air from reversing a large vacuum, but I think you would most likely need compressed air to do it correctly.
