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 Post subject: Fluid flow?
PostPosted: March 26, 2016, 8:19 pm 
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Thinking crazy thoughts about airflow. It struck me that air flows faster through multiple smaller tubes rather than a single larger tube of the same area. Therefore my thought was if I ran 4 intake tubes from the the air filter to the throttle body the air would travel faster and be less restricted then through a single tube.

I decided to do a simple experiment. I got a large soda drinks cup and cut a hole in the bottom. The first test was using a 1/4" ID 24" long hose and I timed how long it took for a full cup of water to drain, 18 seconds. I then repeated the experiment using 2 x 3/16" ID by 24" tubes they only took 12 seconds.

The cross sectional area of the 1/4" tube is 0.049" and the 2 x 3/8" are 0.0552. So while the area of one 1/4" is about 10% smaller than two 3/16" tubes. The rate of flow was still much faster. Obviously my experiment was not perfect but gives a good idea to start from.

The faster flowing air will be cooler/denser too allowing more air into the engine. Can anyone think of a reason not to use multiple tubes. Obviously 4 tubes compared to 1 would be almost 4 x cost and weight but I think the benefits would be worth it. After all engines are basically air pumps. Any thoughts, before I Patent MY idea and become a millionaire?

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 Post subject: Re: Fluid flow?
PostPosted: March 26, 2016, 9:44 pm 
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Bernoulli pretty much figured that out. In short: no, a single large tube is better. Mass flow and velocity are two different things

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 Post subject: Re: Fluid flow?
PostPosted: March 27, 2016, 11:34 am 
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Thinking crazy thoughts about airflow. It struck me that air flows faster through multiple smaller tubes rather than a single larger tube of the same area.


I don't think this is true, it doesn't seem to make sense. I don't know why you measured such a difference with your test rig. That's the right thing to do, but I think somehow you have a bad result.

If you connect tubes to an engine and do these measurements you would see more velocity in a smaller tube than alarger one. That would be because your vacuum is coming from an engine with a constant displacement. It's trying to pull a fixed amount of air and if you provide more restriction it will pull a higher vacuum to get that air. So the smaller tubes flow faster because they flow less and therefor there is more vacuum.

Do you get the same result if the tubes are only 6" long and then try just holes (tube very short < 1"). Maybe the large tube has turbulent flow and the small tube laminar flow. The motion of fluids in tubes is how Renold developed the Renold's Number, If you calculate the Reynold's number for these tubes it will tell you if the flow was turbulent.

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 Post subject: Re: Fluid flow?
PostPosted: March 27, 2016, 10:04 pm 
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That experiment, or at least the result is flawed in some way. Air as a fluid likes to have an un-restricted path, otherwise the flow becomes turbulent (available paths interfereing with each other) and the resistance goes up. As an example, if you put a 10"x10" square pipe next to a stack of 100 1"x1" ID square tubes, and pushed air though both at the same time, more air will go through the 10"x10" opening than through the tubes. The reason is that all those side walls cause restriction and change in direction of some of the air molecules. Those molecules in turn affect their neighbors and so on and so on, disrupting the laminar flow of air.

Even if you put the air under pressure, positive or negative, the resistance is still there.

Tom

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 Post subject: Re: Fluid flow?
PostPosted: March 27, 2016, 11:22 pm 
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The test indicates that two smaller tubes with 12% greater flow area will have a 50% greater flow rate. There is an entire field of study that would be turned on it's head if these results were accurate. So either you're about to get a Nobel, in addition to your patent and millions, or something is not being correctly accounted for in the setup or procedures. Consider that the increased total surface area of multiple pipes, in the case of your experiment 50%. That equivalently increases the drag on the fluid, in addition to increasing the rate of heat transfer into it as well.

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 Post subject: Re: Fluid flow?
PostPosted: March 28, 2016, 6:53 am 
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Interesting that you all think the results are incorrect/impossible. I guess I will try the experiment again in a more scientific manor. Maybe with a video, so you can point to the error of my ways.

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 Post subject: Re: Fluid flow?
PostPosted: March 28, 2016, 8:20 am 
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Science aside.. you would have to run the computer on a speed density tune, as four smaller intake runners would obliterate the possibility of using a mass airflow sensor.

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 Post subject: Re: Fluid flow?
PostPosted: March 28, 2016, 9:40 am 
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The reason one large tube flows faster than many small tubes is straightforward enough. The primary SDI (slowing-down influence; please pardon the scientific jargon) is interaction between the fluid and the walls of the tube(s). Four 1" tubes have the same area as one 2" tube, but twice the wall surface, hence (roughly) twice the drag.

Another way to look at it: Imagine a square tube with 2" sides. Now imagine a + shaped insert you could slide into the tube, effectively making it into four 1" square tubes nested together. Is that insert going to increase flow?*

And yet another: As Shylock queried in The Merchant of Venice, if you prick us, do we not bleed? Well yeah, we do, but we bleed a lot faster if you hit an artery than a zillion capillaries.

That said, amazing things have been discovered through experimentation, and surprising results--though generally resulting from defects in the experiments--occasionally** result in scientific advancements. But I think the mysteries of subsonic fluid flow were pretty well beat to submission in the 1800s. Stokes' Law predates the Civil War, and Reynolds Numbers were used in the sewage industry twenty years before the Bros. Wright took their first powered flight. So I, for one, will be quite amazed*** if your premise...
wrightcomputing wrote:
It struck me that air flows faster through multiple smaller tubes rather than a single larger tube of the same area.
...proves correct.
wrightcomputing wrote:
Any thoughts, before I Patent MY idea and become a millionaire?
I think the great majority of patents in that arena expired in the days when scientists wore muttonchops.

*Rhetorical question answer: nope.
**Rarely nowadays, but it happens.
***And so will the folks who build intercoolers. If there's more interaction between air and the walls of one big tube than a bunch of small tubes, they'll want to start making intercoolers with one big tube.

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 Post subject: Re: Fluid flow?
PostPosted: March 28, 2016, 10:33 am 
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I think one of the reasons Reynold did the work he did is because of trying to get power out of steam engines. They didn't understand why some boiler tubes would flow more hot combustion gas than others. When they built bigger boilers, they didn't always get the power they predicted. If your boiler flows %30 less, your steam engine will have %30 less steam.

The Wright brothers were original locosters. For some reason ( lack of internet and supportive forums like ours ), they did not understand or know about Reynold. Without Reynold's number they did not understand how to scale the results from their wind tunnel and this gave them trouble.

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 Post subject: Re: Fluid flow?
PostPosted: March 28, 2016, 10:58 am 
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Another thing to consider is that water through a couple hoses in the bottom of the cup is for the most part a constant variable equation.

An IC engine is essentially a vacuum pump, and obviously consumes different amounts of air at different RPMS. going back to your cup test, if you optimize the hose size and length for the quickest amount of water flow against gravity, you isolate the prime flow to that one specific set of variables, hoping it works well enough with other forces in mind to not severely bog the system down.

This is why variable valve timing and variable intake geometry have made such leaps and bounds lately over engines of the past. they essentially change the velocity and amount of air allowed into the cylinders.

You may get more velocity out of 4 tubes similarly sized to one larger tube, but at the cost of more turbulence, and less mass.

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 Post subject: Re: Fluid flow?
PostPosted: March 28, 2016, 1:49 pm 
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After years of covering motor sports as a journalist, it occurs to me that aero rarely seems to "look right" or "make sense" these days.

If aero was totally figured out, F1 teams wouldn't be spending, what, $20,000 per day for wind tunnel time in an era of all sorts of powerful computer programs?

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 Post subject: Re: Fluid flow?
PostPosted: March 29, 2016, 1:07 pm 
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I think the main problem with my idea is that higher velocity = less mass = less combustible air. Therefore even if the air flows faster into the engine it will be less dense so any gain would be negated. Still a great exercise in critical thinking and as always thank you all for your wealth of knowledge. I guess I am back to trying to keep intake air temperature cooler. Now where did I leave my ice.

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 Post subject: Re: Fluid flow?
PostPosted: March 29, 2016, 1:07 pm 
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I think the main problem with my idea is that higher velocity = less mass = less combustible air. Therefore even if the air flows faster into the engine it will be less dense so any gain would be negated. Still a great exercise in critical thinking and as always thank you all for your wealth of knowledge. I guess I am back to trying to keep intake air temperature cooler. Now where did I leave my ice.

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 Post subject: Re: Fluid flow?
PostPosted: March 29, 2016, 1:07 pm 
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I think the main problem with my idea is that higher velocity = less mass = less combustible air. Therefore even if the air flows faster into the engine it will be less dense so any gain would be negated. Still a great exercise in critical thinking and as always thank you all for your wealth of knowledge. I guess I am back to trying to keep intake air temperature cooler. Now where did I leave my ice.

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 Post subject: Re: Fluid flow?
PostPosted: March 29, 2016, 1:31 pm 
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wrightcomputing wrote:
Still a great exercise in critical thinking...
Absolutely! :cheers:

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