Backyard Aquaponics
A place to discuss aquaponics

Well... that's easy then....

A hookah still makes bubbling noise though.

But in all seriousness lots of these equations are derived from bernoulli's principle and applying the proper boundary conditions. Time to brush up on the differential equations and integrals.

The diameter and height would be part of the boundary conditions that define the system.

So kind of like a pitot tube?

Well true to form threads always go off topic.



The reason I was looking at Vortexs is because I am not sure that Affans explanation for why his siphon works better is correct.

His explanation is that the wider mouth narrowing causing an increase in velocity and corresponding drop in pressure resulting in faster flow.

Based on the Bernoulli theorem you would get the same decrease in pressure from simply having a narrower tube. This got me thinking that the reason the Affan siphon starts faster could be because of one of two other reasons or possibly both.

The friction loss from a projecting outlet is greater (K~0. than the friction loss from an outlet flush with the tank wall (K~.5). If the diameter of a projecting outlet is increased by adding a bell then the velocity of the flow at the point of entry is decreased and causes a corresponding reduction in friction loss. As the diameter of the outlet bell approaches infinity the friction loss from the entry approaches the friction loss of a flush outlet of diameter equal to the diameter exiting the bell, ie K~.5.

So by adding a bell in the inner standpipe (projecting outlet) of a bell siphon the friction loss through the siphon will be reduced and this will cause a corresponding decrease in the resistance to flow.

The second reason that I though that an affan siphon may work better is that it aids the formation of a vortex which increases the rate at which air is entrained within the siphon once it starts to flow which would reduce the time it takes for the siphon to reach full flow.

Stuart - I came across this paper that may lead you to a PhD if you get this all straightened out.

www.nbi.dk/~lautrup/papers/bathtub.pdf

Seriously stretching my mathematical abilities there.

Also a little intimidating when you see that Einstein did some work on the problem but in order to find a solution simplified the problem considerably by ignoring a series of effects.

Stuart and Kimocal

Take a bucket, fill it full of water and then tip it upside down. Then put a top on it with a pipe and appropriate hole in the bottom do the same. I seriously doubt that a vortex would increase the flow of water, yes it would move faster but it has longer to travel to reach its destination.
Personally I am not enamored by F&D and especially by bell syphons so I don't give this a lot of thought, and anyway I have had a few beers.

It is not the vortex moving the water faster that increase the flow but the speed at which the siphon goes from flow start (trickle) to full flow. The flow that is crucial is not actually the flow of water but the flow of air from the top of the siphon.

In a standard bell siphon the turbulence at the projecting inlet entrains bubbles of air and as each bubble is removed the flow increases as turbulence increases the amount of air entrained increases which increase the rate at which air is exported from the top of the siphon. The rate at which the siphon flow therefore increases exponentially until full flow is achieved.

Inducing a vortex may increase the initial rate of air removal and the rate at which the rate of air removal increases.

So in short - he is trying to prove/disprove that the "swirling coke bottle" effect helps syphons work better, for us laymans.

I think that he is just trying to get a better understanding of why the Affnan siphons work better.

Often siphon problems require slight adjustments to flow.... which is what I understood the affnan to basically do/say... widen the flow range.... as Stuart posts...

At a glance this seems counterintuitive to me. I would think that any reduction in friction would be offset by the increased surface area so that it would even out or be very close to the same energy loss. I'm curious to see what you find.

The flare acts as a throat. Due to conservation of mass flow the velocity of the water increases as the cross sectional area gets smaller. When the velocity increases it also causes the pressure to drop.

For all you motor heads it's kind of like a Velocity Stack. It helps the fluid flow become laminar more quickly.

I don't think laminar is the right word. Since in fluid dynamics that has its own meaning.

You can have laminar, turbulent and a mix of both in fluid mechanics. It is relevant to all this.

http://www.efm.leeds.ac.uk/CIVE/CIVE140 ... bulent.htm