Backyard Aquaponics
A place to discuss aquaponics

But laminar flow would only exist very briefly just as the siphon started.

Thereafter it would be turbulent.

Or is that an over simplification?

I guess I misunderstood your statement. Laminar flow is occurring further down the pipe and that does effect what is happening at the flare in the affnan siphon if even initially.


Found this massive PDF (200+ pages) that is used to teach a _masters_ level degree.

http://www.tfd.chalmers.se/~lada/postsc ... elling.pdf


Might found your pearl amongst those pages. I only have a BS in mechanical engineering and I'm afraid I've hit my knowledge limit in this topic. Although I am enjoying this discussion immensely

Perry's Chemical Engineers' Handbook is what I mostly learnt from.

I still think that laminar flow is only going to occur momentarily. Any situation with a reynolds numbers over 4000 is said to be in turbulent flow. For a 32mm pipe any velocity over .215m/s is going to produce turbulent flow. Below that it is going to have transitional flow until velocity is less than ~0.1ms/s.

For larger pipes the velocities are even less.

Once full flow develops then flow regime would have to be turbulent. Unless I'm missing something.

Far out that pdf is full on.

I'll take it to bed tonight

So did you find anything worthwhile?

Lot o stuff but nothing pertinent.

Yet.

Few times I've gone to with a glass of wine and I've fallen asleep instead.

The problem I had is that the level is above my understanding from reading it once. I can get the sense of what it is saying but to truly understand I will have to take the time to check all the things it refers to as excepted knowledge. Some of it is simple stuff like just using different symbols for different things like v instead of U for velocity. Others will take me longer to get my head around.

When I studied physics, u represented initial velocity and v represented final velocity. I haven't followed kimocal's link so am not in a position to comment further.

It depends on the background of the author. Its pretty common to see v1 and v2 or u1 and u2. I've never seen u and v like you have.

Also see a lot of substitution with different alphabets. Simpler texts and derived formulas often use a standard alphabet where as the closer you get to theoretical texts a lot more greek appears.

Just as a matter of curiosity and not that I am interested in bell syphons but are you really sure that the effect is caused by a high enough Reynolds number? I don't think the creation of a vortex, as we are talking about it, is dependent on turbulent flow. Opposing flows as you would get more significantly with a flared mouth as opposed to a simple straight pipe.
There again I have got in from work and had a few beers.

I'll have to be careful to make sense since I'm on to my second tumbler of elderberry port.

I think a number of points and posts have been confused.

Is the effect caused by a high reynolds number? NO.

IS the formation of a vortex dependent on turbulent flow? No.



I think that this is where either the beer or the port has kicked in cause I don't know what you mean by this.

Three possible reasons why an Affan siphon may work better:

1. wider standpipe entrance means less friction which means a faster start;
2. vortex more quickly entrains air and evacuates the bell of the siphon faster; and
3. i forget.

Either one or two or all three may contribute to the effect.

I disagree with the second differential in the viscous diffusion term



Sorry - could not help myself but I had to point out the error

Im not up on all the fancy math learnin' and all that, but it would make more sense to me that a wider top means more surface area, which means a wider area for water to flow over the top, meaning more water can flow initially.
Does this really have anything to do with friction created by flow?

i would have thought not, more a factor of - the more water that gets dumped into the standpipe initially, the quicker the siphon effect will take place.

"Quote:
Opposing flows as you would get more significantly with a flared mouth as opposed to a simple straight pipe.


I think that this is where either the beer or the port has kicked in cause I don't know what you mean by this.

Three possible reasons why an Affan siphon may work better:

1. wider standpipe entrance means less friction which means a faster start;
2. vortex more quickly entrains air and evacuates the bell of the siphon faster; and
3. i forget."

2 and 3 might be a reason but I don't understand 1. A flared mouth would allow more water to initially break surface tension but travelling down an inclined slope as opposed to a straight drop would create more friction.

I am not sure that a vortex entrains air you just don't get the large bubble formation you do dropping down a straight pipe, and if I had to guess it would be laminar flow down the incline of the wider mouth creating the vortex.
There again I have never seen an Affan syphon nor tried to make one.