Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: SteveFish on 04/10/2010 01:22:58
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Hi physicists. In beer brewing, the wort resulting from the mash step is boiled with hops for bitterness and flavoring. At the end of the boil the wort contains coagulated proteins and hop flower particles that are not desirable for fermentation that comes next. To remove these solids, which would normally just settle out on the bottom of the boil vessel, the wort is swirled so that it is rotating. This causes the solids to settle in the center of the boil kettle bottom and the clean wort can then be drained from the periphery.
Inducing a swirling motion (a vortex? I don't know the appropriate terminology) is often used for removing solids from air in, for example, bagless vacuum cleaners, from air cleaners in heavy equipment designed for dusty conditions, and from water in industrial processes. This is a puzzle because in these processes the heavy solids are pushed to the outside of the whirlpool by centrifugal force where they are collected.
I would very much like to know what the physical forces are that cause solids to pile up in a cone in the center of a beer liquid whirlpool instead of around the periphery. Steve
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http://www.lenntech.com/library/clarification/clarification/centrifugation.htm
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Nice one Tommya, downloaded that one.
Steve I don't see how the heavier particles can be collected at the center either?
If we think of it as a spiraling force, like a tumbler, then those particles heavier will be the ones to get forced out furthest from the center as they will be the ones heaviest, ahh that is wrong :) the lighter ones should be thrown furthest, but in form of energy a larger mass, I think? Should be the one possible to move furthest.. Dam* :)
What one might think is that if the force is applied with great care then the lighter particles will be the one leaving the center first and the heaviest, with the largest inertia, will be the last to move?
What you might see is that they will hit the walls and from there glide down to a center at the bottom, possibly? but if you have a flat surface at the bottom, why would they collect in the center of it? As it is that I assume you mean here?
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And a vortex is exactly that spiraling form, maybe it have to do with the way you can see it form in water. There it will take a form of a cone if I'm correct with the sharp end being situated under it, but then the 'force' creating the swirling motion comes from down under too?
(ahem, down under as in 'down under' that is, not Australia.. Just to clear that up, no, not the beer.)
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Thanks Tommya300 for the link. Among several I have read, your link is a good one for describing centrifugal separation in which solids are spun to the outside of a spinning mass of water or air. My puzzle is a situation in which the solids are drawn to the center of the whirlpool.
Tommya and Yor_on, you might get some insight by watching this phenomenon. In your kitchen take a pot or small kettle (round, straight sides and flat bottom), fill partway with water, add a pinch of uncooked instant oatmeal and/or rice (or whatever, as long as it sinks), and stir it with a spoon and then watch. As the swirling water slows down, the heavier than water particles move to the center and remain there when the swirl stops instead of spinning to the outside edges of the pot as might be expected.
Compared to the big questions asked on this forum my question is pretty mundane. I am hoping someone will come up with the unexciting forces at work in my beer pot. Steve
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There is a difference between things being thrown to the walls in a vortex and sediment piling up in the middle of a glass that has been stirred. When it falls to the bottom the particles will tend to congregate where the liquid is moving slowest and that is the centre. Also as the particles reach the side of he glass they are slowed down in a surface layer of stationary fluid and fall towards the bottom of the glass. If things are falling down the side of the glass they will drag some of the fluid with them and this will set up an inwards flow at the bottom of the glass and a rising flow at the centre which then cause a small mountain of bits to form in the middle of a glass.
The observations come from drinking a lot of sludgy beer in the past :-)
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:)
Nice one Soulsurfer..
I think I got it now, you have the 'cone' in the middle whirling throwing out particles to the sides. The force creating it comes from the bottom and works its way up through the 'vortex'. That introduces a convection that works from the vortex out to the walls, then down to the bottom, into the center.. How about it?
Is it worth a Nobel?
500 years to late?
Wha'da'ya'mean 500 years??
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And who said they were mundane Steve?
I'm sure some Chinese scholar explained it long before this, probably using the principles of yin and yang to exemplify them :) No way they're mundane.. After all, a really good beer can very well be divine, right?
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Soul Surfer, I hope your sludgy beer was real ale and not something poorly made. I have heard your description before, but in fiddling with my pot with a little oatmeal and rice (brown Basmati) this does not seem to be what is happening. The particulates don't spin to the outside and fall down, they move toward the center. The particulates seem to collect where water movement is fastest. For example, I chucked up a 60mm X 6.5mm hexagonal bar in my drill and spun it vertically in the pot to cause very local whirlpools. Moving this around picked up and moved particulates, and held them spinning until the whirlpool stopped by itself. This worked for both clockwise and anticlockwise directions of the drill. This worked when the overall rotation in the pot was very slow or undetectable.
In the drill experiment the particulates were drawn in at the bottom against centrifugal force, while at the top a few, presumably the lightest were flung outward. For this to happen, it seems to me, requires that there must be inward fluid flow on the bottom and outward at the top, unless we invoke the Flying Spaghetti Monster. I will try to find a syringe with a hypodeemic nerdal and some food dye to verify these flows. The questions might be-- What powers this flow? What is it about a vortex with an axis perpendicular to gravity, that is NOT powered by flow into or out of the center (e.g. draining sink, hurricane), that the vortex by itself pumps water in at the bottom and out at the top? How is this flow organized and what mechanisms power it? Steve
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Thanks Tommya300 for the link. Among several I have read, your link is a good one for describing centrifugal separation in which solids are spun to the outside of a spinning mass of water or air. My puzzle is a situation in which the solids are drawn to the center of the whirlpool.
Tommya and Yor_on, you might get some insight by watching this phenomenon. In your kitchen take a pot or small kettle (round, straight sides and flat bottom), fill partway with water, add a pinch of uncooked instant oatmeal and/or rice (or whatever, as long as it sinks), and stir it with a spoon and then watch. As the swirling water slows down, the heavier than water particles move to the center and remain there when the swirl stops instead of spinning to the outside edges of the pot as might be expected.
Compared to the big questions asked on this forum my question is pretty mundane. I am hoping someone will come up with the unexciting forces at work in my beer pot. Steve
Yes it has clarified the the picture and the question.
I can see it in a way Soul Surfer explains it.
Does the sediment mass or is it great enough to cause a displacement to produce a fluid current flow of any magnitude?
Or has the air pocket of the vortex been displaced by an inverted fluid vortex current upon deceleration, attempting to lift and circulate at the center with a siphoning affect?
During the deceleration of the air vortex, the center bottom is being displaced with the circulating fluid vortex.
As this is being displaced, the fluid at the walls of the container is slowly circulating in a downward motion, along the floor of the cylindrical container and still revolving adjacent to the axial spin, transporting along with it the sediment.
With not enough velocity, the angular momentum of the circulating fluid attempts an upward swirl, but falls back over toward the wall of the container (cylinder).
At which time, the mass of the sediment is greater than the current draw and begins to rest at the center of the axial of the dying vortex.
The fluid current is attempting to create an upward swirl centering at the axial as a donut at the bottom of the container. This force will sustain the large diameter of the solid mess at the bottom and the upward donut circulation will develop the mountain peak.
Fluid current calculations is tricky in a container at the bottom when the vortex is decelerating...
I guess the fluid current of the almost dead vortex might look more like a shape of a end connected slinky sitting at the bottom of the cylinder, observing the fluid current flow from the bottom center to the top flopping over back to the cylinder walls at a small angular fashion.
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I think its a momentum thingy - but I need to get my head straight before I can explain it properly. I am thinking along the lines of equal angular momentum, the lighter particles go to the outside where a long track combined with the same rotational frequency means they travel faster - to have the same momentum the heavier particles either need to travel slower (but they cannot because the viscosity drags them round) so they go to the centre where the circular track length is shorter per revolution. Now why they should both have the same momentum is beyond me.
I suppose you could also think in energy terms - if you had a disc spinning on its centre axis with the heavy stuff attached to the middle; you would need to increase the overall energy of the system to continue rotating at the same frequency with the heavy stuff at the outside. If there is enough disturbance then even if the heavy stuff starts well distributed then it will eventually end up in the lowest energy atate - ie nearest the axle.
BTW Steve - I think its far from mundane; its a brilliant question, simple, everyday and yet drawing many different, possibly all wrong, answers
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I think that there is an opportunity for some kitchen science experiments here. There may be different results if the particles are much heavier or nearly equal to the density of water or even lighter. Also the results may well be different if the vortex is produced by stirring a fixed circular vessel or by a slowly accelerating turntable that avoids excessive shear and has the walls of the container rotating with the vortex.
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Ok Vortex was spot on Steve, we both thought of a centrifugal force when we should have considered a centripetal though (Well, I know I did:). The 'spin' of the water is slowest at the outside and fastest at the inside, as oposite to riding a carousel and then walking to its center. Doing so we would feel the centrifugal 'force' acting outward on us, but if you think of how that tornado in OZ carried both Dorothy, Toto and the witch inside it, never throwing them away, you get a description of the oposite idea.
In a fluid you also get this centripetal force acting inward, towards the center, which I should have remembered if I only had taken the moment to visualize how it looked when I played in my bathtub, so long ago :) The way I think it works is by pressure-gradients, as I sees it, like invisible layers of different pressure where the water wants to get to the the least pressure, which then will be at the center, and as it also rotates it have to take the long path around, swirling. In a way you could say that the force 'sucks you in' to its center or, if you like, 'pushes' you away from its periphery, but I'm pretty sure it will feel more like a suction. I think that is how it does it, but if someone have a better description, preferably simple, I will be pleased to take part of it.
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Let see here… see if I am seeing the correct picture. Scenario:
We have a beaker of water half full.
As the water is stirred, a vortex is being formed.
The open area of the vortex is displacing the water up the side of the beaker.
As it is observed from the top opening of the vortex, viewing the center lower point, closest to the of the vortex axial, the rotational velocity is more rapid with respect to the upper wider opening, observing a spiral lag in the vortex fluid wall.
No on the second thought the velocity looks to be homogenous at the vortex wall just a lagging spiral affect.
The energy of stirring is displacing fluid and the sediment towards the wall of the beaker.
Stopping the stir the vortex begins to slow.
The top outer wall of the spiral fluid begins to lower as the center lower point begins to rise to fill the void of the vortex this must be a fluid displacement.
This displacement carries a current towards the center of the dying vortex or the center of the beaker. The current follows the screw type swirl of the vortex and as the vortex is losing the swirl energy the fluid is also following the downward motion at the outer beaker wall and across the bottom toward the center of the beaker where the axial of the vortex was and is subsiding. And begins to attempts to follow the path of the weakening vortex but falls back on itself at the degrading vortex spiral angle, creating a donut shape current revolving on the vortex axial at the bottom of the beaker.
While these currents are being created the sediment follows the current flow, eventually resting at the center of the donut current core.
That is the way I see it occurring.
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Tommya, that's how I thought of it too :)
You wrote "The energy of stirring is displacing fluid and the sediment towards the wall of the beaker." And why I did so, I expect to have to do with that, when we normally meet a spiraling force while growing up, we feel how it transfers our mass outwards, just like that carousel does. But the centripetal spiral don't, and that's kind of weird? It's more like the suction created as you let the water out of your bathtub, not so much 'pushing' as 'sucking', it seems to me? And if you do, you will see that centripetal force looking at the drain, just like a tornado.
As for how that cone is created I don't know, well, I might guess that the further down 'into' a 'Jello', or a fluid, you come the stronger the pressure will be. Higher at all points surrounding this 'cone', forcing it to shrink inwards to its center with depth and pressure? But I'm not sure at that? The rotational force created must have an importance for it too I guess, like the angle of the force creating it? Fluid dynamics are nonlinear, at that I'm reasonably sure at least, making them very hard to predict.
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If one try to make the same experiment you described in space Steve, being in a 'free fall'. Would it behave the same?
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You could look at it the same way a black hole 'sucks in' matter, presumably? If you imagine no event horizon, just a 'infinite point' in SpaceTime, but you won't get the 'spiraling pattern' though. To get that you need 'pressure' acting at it at a right angle to its overall direction 'downward' to that pint of infinity.
So maybe you could look at the rotation as an try for constant escape at a right tangent, constantly broken by the 'force' of the 'suction', diminishing in strength relative the 'suction' as it comes closer to the center of the 'force/point' although accelerating as it's radii becomes narrower and the downward force stronger?
Does that make sense?
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Weird one :)
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A BH without frame-dragging that is :)
A Schwarswald?
Or is that a cake?
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And the reason why I assume we would see a spiral, instead of a swinging motion I assume to be that it's a non-linear system. In a perfectly linear world the 'force' acting at an angle would describe a straight line, although bent downward to the 'geodesics' formed by th fabric of space getting bent by the BH mass. But as we are in a 'instable' non-linear SpaceTime that won't happen, and the force acting at a right angle will have a certain unpredictability, maybe? But why would we see a spiral? and repeatedly so? Ahh, the constants again huh?
Or, I'm just bicycling through the blackery of space?
Ahem?
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I don't need any non-linearity do I?
It will still form a spiral as observed by someone outside the gravitation.
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http://en.wikipedia.org/wiki/Tea_leaf_paradox - I think this is the best explanation I can find.
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(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fupload.wikimedia.org%2Fwikipedia%2Fcommons%2Fthumb%2F7%2F77%2FTea_leaf_Paradox_Illustration.svg%2F200px-Tea_leaf_Paradox_Illustration.svg.png&hash=2b39f0ff24841246fefae9b427546c79)
Yep, that would create a similar effect, assuming that the 'blue' convection is evenly distributed around the teacups rim as it have to work at all 'points' of the blacks rotation, I think?:) But how does the 'blue one' manage to be so 'ideally' localized around the black rotation? And also, how does it explain the 'cone geometry', as well as the higher rotation in the center?
And in a real model, wouldn't the blue one also become a spiraling pattern following the cups geometry around the black 'circulation' or 'centrifugal force' as I assume that it would have to be without that friction created by the cups boundaries?
Nice one imatfaal.
This one was good for describing it too. Enstein's Tealeaves. (http://www-paoc.mit.edu/paoc/papers/Einstein%27sTeaLeavesTPT.pdf)
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Still, i have trouble translating this ideal system to a real one, it seems like that blue convection should break down fairly quickly as you have two forces meeting at all points, or vectors, all slightly different? Or is it me thinking wrongly here? Is it that it gets reinforced by the 'friction' at all times?
Otherwise I think it's the best description I've seen too :)
But confusing all the same :)
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Much thanks Imatfaal and Yor_on, these links are exactly what I was looking for! Tea leaves, whooda thunkit? I now understand this phenomenon perfectly.
Spinning water, whether in a teacup or a large container, indents in the middle because centrifugal force pushes the water outward against the centripetal force of gravity (water pressure). Rapidly spinning water indents deeply into a funnel that is narrow at the bottom because the centripetal force (pressure) is greater there, and wider at the top because water pressure approaches zero. Friction of the spinning water with the bottom of the teacup slows water rotation there so centrifugal force is reduced, and this allows water pressure to force water into the bottom of the funnel causing a periphery to center current along the bottom. To balance this, water leaves the top of the funnel where water pressure is near zero. A vortex attached to a bottom in a gravity field is a sort of vertical water pump that leaves the heavier than water tea leaves and beer sludge behind in the center, and it doesn't have to be spinning so rapidly that the surface indents very much for the pump to work.
The question about whether this would work in zero gravity in answerable. Starting a vortex in air, far away from the ground, or below the surface in water happens all the time, they are just invisible. As a child I had a vortex gun, and if you don't know about air vortices you are in for a treat. I have never found a good replacement for the gun, but what it did is propagate an invisible vortex across a room that was strong enough that it would give someone a soft bap or cause curtains to flap. This type of vortex is what would happen in zero gravity. They are usually sealed by connecting to themselves to make a toroid. Once you understand them you can better understand complex phenomena like tornadoes and how airfoils work. Google vortex gun to see some really big ones and look at videos on the Zero toys site. Steve
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Hi, all. All I can say is that you guys are dealing with a different kind of centrifugal force than any I have encountered. When I think of this kind of force, I think of a cream separator where the heavier liquid goes to the outer part of the separator and the cream(which is lighter) goes to the center and is drained off from there. Thanks for comments. Joe L. Ogan
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http://en.wikipedia.org/wiki/Tea_leaf_paradox - I think this is the best explanation I can find.
WOW I visualized the currents of the fluid, but for the life of me could not find anything on the net that would support my minds eye.
I am more impressed on the find, more than the contents of it.
Associating tea leaf paradox... I am still trying to Google associated phrases and still can not come up with the link.
Of course "Tea Leaf paradox" works, how did you come up with that site Mat?
Yor_on I had difficulty discribing what I was visualizing, I was rereading and revising.
Like I said the find is more impressive.
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Hi Joe. The forces aren't really that different, it is just a different application of a whirlpool. If you put whole milk in my 15 gallon home brew pot and stirred it vigorously with a large spoon you could skim the heavy cream at the top of the whirlpool near the center, but it wouldn't be very efficient at all. Similarly, if you put a bunch of large lead shot in a tank of whole milk (not recommended), they would probably collect on the bottom near the inlet of the cream separator. Different kinds of separators are designed for specific purposes, and a cream separator would be similar to those in the link provided by Tommya300 in the second post of this thread. The tea leaves/brew pot situation we have been talking about is more a natural phenomenon similar to a tornado or hurricane, but with a spoon as the driver instead of hot air. Steve