Selecting bigger alder seeds by their falling speed in air

I wonder if anybody on this group can help me with this?
I want to find bigger alder seeds and breed from them to produce even
bigger alder sees. You can get huge numbers from a tree, The Forestry commission breeds from the best 1 in 400 000 trees and that's the sort of numbers I want to go through. I want a mechanised way of doing at least some of that sorting. The seeds are all the same colour and very difficult to sort by eye, and they vary in thickness. I want seeds which are heavier = thicker, so it seems best to sort by falling speed in air.
In a room 3 M high I have put alder seeds into a teaspoon and tipped it. This removes the doubt as to whether the seeds fell immediately I opened my grip or whether they were stuck onto my finger. I had a big sheet of paper on floor and the seeds make a tap noise when they hit that paper. I time the time from tipping the teaspoon to the sound of the seeds hitting the paper. It was just over 1 second, so a falling speed of 3M/second. Obviously not a very exact measurement, but it can't be too far out.
(I have bought fans from RS Components which, as rated, can produce airspeeds of 10M/sec though a crossesection of 7 cm x 7 cm, but I am not sure R S Components's ratings are correct)
These are "standard" seeds. I want to search for bigger seeds with a faster falling speed.
I want this winnower to be portable, so that if I find a tree which has bigger seeds, I can look for more from that tree and not waste time on trees which produce small seeds. The idea that I am toying with at the moment is this:-
There will be a fan at the top, pulling air up and OUT. The small discards will be blown through it.
Below that will be square-sided upside-down pyramid of perspex so that I can see what is going on inside. There will also be a chute for putting the seeds to be tested in. Airflow will be inwards, so no problem about that.
The pyramid will taper down to the sorting zone, where falling speed will be tested. This will be parallel-sided. This is the point that I want advice about.
Can the airflow be laminar? The depends on the width of the sorting section and Reynold's number. I am not used to calculations involving Reynold's number and I couldn't trust my answer. How wide does it have to be for an airflow of 3M/sec to be laminar? Help please!
The answer must be either that the width is reasonable (it is something I can carry round with me) or it is not.
* The flow can be laminar at a reasonable width. But is this desirable? Doesn't it mean that a seed with a falling speed of about 3M/sec will be blown up if it falls at the centre, drift to the side and fall down the side where the air speed is lower? That's the sort of sophistication that I want advice on.
But to take the simplest view, I will have a short length of sorting section, with a taper leading into it, and well below it a catching bowl to catch the bigger seeds that have fallen through. (I can go out seed-collecting in moderate winds). Or else I can use 1mm wire mesh (cut from the bottom of a kitchen strainer) to catch the seeds at the bottom of the sorting section. Like this :-
Cone and Fan \ / \ / | | | Sorting | | section | | | | | | | | | / \ / \ / \ / \ Air-smoothing entry cone.
| | |_________________| Catching bowl
* The flow cannot be laminar at a reasonable width. This does at least mean that the airspeed will be constant, though turbulent, right across the width. But how can I get a reasonably sharp cut-off? (I say "REASONABLY sharp cut-off" because in practice, to be sure I am not eliminating seeds that would be useful to me, I will adjust the airspeed to allow through a small number of the upper end of the "normal distribution". Does it help to make the sorting section longer so that seeds are bounced up and down and tested many times?
So, help, comments, answers, redirection to a site where they KNOW about these things - all would be welcome.
Michael Bell
--


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Michael.
I don't want to spoil your dreams, but have you proved the basic premise behind your machine that heavier seeds fall faster than smaller ones? 500 years ago a man called Galileo Galilei reputedly dropped different size iron balls from the leaning Tower of Pisa and demonstrated to the world that they fell at the same rate. Admittedly air resistance will play a bigger part in the descent of seeds than iron balls, but I doubt the difference is so marked that it could be used for grading, so I ask again: have you proved that thicker seeds fall faster than thin seeds? I'd hate to see you waste time and money on a machine that does not work.
Cliff Coggin.

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Cliff
All praise to you for your scepticism, but :-
1) Without air resistance an object will fall 5 Metres = 16 feet in the first second.
2) I just quoted the FIRST tap on the paper on the floor. It takes another 2 seconds for all of them to come down.
3) Winnowing is a well-known process for separating wheat from chaff.
Michael

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OK, as long as you appreciate the sometimes non-intuitive concept that heavy bodies do not necessarily fall faster then similar lighter bodies.
As an aside, the acceleration due to gravity is twice the figure you quoted i.e. 32 feet/second/second.
Cliff.

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Cliff Coggin wrote:

In fairness he quoted a Distance 16ft I think. when I was in school some 55yrs agoI learned that S= ut + 1/2 a t squared
Don

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You must have gone to the same school as did I, or else also sat the London University 'A' Level maths.
Also off the top of my head 40 years later ...
v = u + a t v^2 = u^2 + 2 a s
But you are both right
a = 32'/s^2
s after one second = 16'
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invalid wrote:

'O' level physics?

I only remember the S = ut + 1/2 at^2 one - but it's about all you need to remember, you can work out the others (or even just the numbers) from it.
-- Peter Fairbrother
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Mea culpa. The distance travelled in one second would indeed be 16 feet. The result seemed so obvious to me that I didn't bother to actually calculate it. My apologies.
Incidentally, when I did O level physics some 43 years ago in London I seem to remember the abbreviation for acceleration was f, so the above equation would have been s = ut + 1/2f(t squared). Is my memory failing or was it just one of those conventions that changed over time? Just to stir up memories for the older generation, I also recall force as a result of weight being expressed in poundals.
Cliff.
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Cliff Coggin wrote:

Yes the FPS system if I remember rightly (Foot-Poundal-Second), I started with the symbol "a" for acceleration which changed to "f" some years after. Don
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invalid wrote:

How do you manage to insert the square symbol (little 2 after and above the v and u) It dissapears when I reply. Don
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Donwill wrote:

It depends on your newsreader, but the normal way is to use the caret ^ character to denote a superscript. So it's s ^ 2 without the spaces, s^2.
Some newsreaders also allow the use of the underscore _ to denote subscripts, but not many.
Both of these conventions were popularised by TeX, though the caret was used earlier in Algol.
How nerdy that I know that!
-- Peter Fairbrother
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Peter Fairbrother wrote:

Even nerdier. For an example of multiple sub- and super- scripts, it's probably about as complex as it gets. This is the final version, as a .png:
http://www.zenadsl6186.zen.co.uk/rect1875.png
And this is the LaTeX required to create it:
http://www.zenadsl6186.zen.co.uk/ICURmath
-- Peter Fairbrother
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It's an up-arrow, Shift 6 on the UK keyboard
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Cliff
At the end of its first second's fall in a vacuum, an object will be falling at 10 Metres/sec, and at that time it will actually have fallen 5 Metres. But we are both on the same side, so I don't want to start a flame war.
Michael

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No war or criticism intended Michael. Fortunately this newsgroup is open to discussion and even argument without getting offensive, though it does mean that threads often drift off topic.
Have you considered a centrifugal separator for your seeds? http://process-equipment.globalspec.com/datasheets/2901/HosokawaMicronPowderSystems/810BAA60-0540-4E5D-8EEC-2126D3D5E286 is an industrial machine, but it shows the concept.If you could make something suitable it would probably be more compact than the machine you envisage, though somewhat more expensive.
Cliff.

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Thank you for this link.
It has to be a portable machine, powered by a little 12 volt lead-acid battery. I want to be able to do a full day over ground which will not always be even
Michael Bell

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Michael Bell wrote:

I googled for a few secs and came up with :- http://www.hannafords.com/seed-grading-history.php as a start. This has surely been done before, no point in reinventing the wheel . In a place where I worked for many years we had masses of machinery for sorting seeds of many different grasses, clovers and cereals using blowers, screens, even iron filings and magnets (surface roughness). Cheers Don
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Donwill wrote:

Have a look here : http://science-in-farming.library4farming.org/Seeds_2/THE-PROCESSING-OF-SEEDS/Equipment-for-Cleaning-Seeds-1.html Don
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I've looked at this link. It doesn't explain their processes, and I couldn't get their CAPTCHA ("TYPE IN WHAT YOU SEE") to accept my input.
You once did seed sorting yourself? I hear they have rather tough standards of purity for sale to the public, like "no more than ONE rat per tonne of wheat!"
Michael Bell
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Michael Bell wrote:

I wasn't personally involved in seed sorting, but it went on in our plant breeding research establishment. Our physics dep wksp was called on to design and make small bench type sorters in perspex to facilitate precise separation of various seed types. I think that you will see in my second link some of the basic principles in seed cleaning and separation. Hope this helps. Don

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