Sorting Aggregates

[AmishFighterPilot]

It seems like you can only physically filter things by allowing the smaller parts to pass through the filter while refusing passage to the larger objects. This is true of gravel, but it is also true of waves of sound. A bandpass filter lets the smaller waves escape by use of a channel too small for the target wave.

 

Other than intelligent filtering, aka picking intelligently and discriminately, I can't think of a way to do filtering any other way.

 

It reminds me of a lame magic trick I read about once, where the magician had two assistants that look alike other than one being heavier than the other. One walks in to a box and then the other walks out the other side "transformed". The box can only stop the larger "twin" from passing through it, but never the other way around.

 

What other types of filtering can you think of? Am I missing something?

[exchemist]

It seems like you can only physically filter things by allowing the smaller parts to pass through the filter while refusing passage to the larger objects. This is true of gravel, but it is also true of waves of sound. A bandpass filter lets the smaller waves escape by use of a channel too small for the target wave.

 

Other than intelligent filtering, aka picking intelligently and discriminately, I can't think of a way to do filtering any other way.

 

It reminds me of a lame magic trick I read about once, where the magician had two assistants that look alike other than one being heavier than the other. One walks in to a box and then the other walks out the other side "transformed". The box can only stop the larger "twin" from passing through it, but never the other way around.

 

What other types of filtering can you think of? Am I missing something?

What about mass spectrometry?

 

Or a cyclone filter?

Edited May 29, 2017 by exchemist

[Turtle]

Shake it. Shake it good.

Granular convection

[AmishFighterPilot]

Shake it. Shake it good. Granular convection

Interesting how the larger particles form a screen for the smaller. Still removes smallest parts first.

[Turtle]

Interesting how the larger particles form a screen for the smaller. Still removes smallest parts first.

I wouldn't describe the process in those terms, but it is an interesting effect. Since the larger particles move to the top of a container I would think they would be the first to be removed if one was using the process to make a separation. In geology, granular convection results in what is called inverse grading, where normal grading has the larger particles at the bottom.

 

Graded bedding @ Wiki

[AmishFighterPilot]

What about mass spectrometry?Or a cyclone filter?

Mass spec is an interesting approach. I'm not sure exactly how you can make them "reverse" and remove largest particles first. Mass spec might fall under "selective" filtering by use of discriminating logic.

[AmishFighterPilot]

I wouldn't describe the process in those terms, but it is an interesting effect. Since the larger particles move to the top of a container I would think they would be the first to be removed if one was using the process to make a separation. In geology, granular convection results in what is called inverse grading, where normal grading has the larger particles at the bottom.Graded bedding @ Wiki

Great post. This kind of reminds me of the debate between hole flow and electron flow perspectives. Which sorts which?

[Turtle]

Here's another idea for sorting aggregates. While it seems it would primarily sort by mass, size likely would also play a roll if the range of sizes is relatively wide.

 

So, drop the aggregate so it falls roughly in a narrow plane and use an air jet perpendicular to the falling aggregate to eject lighter particles. Further subsequent separations could be done in a similar manner.

[OceanBreeze]

Here is a method of sorting by shape, using a centrifuge and atomic plane-selective-surfacant!

 

 

To date, research efforts have focused on achieving monodisperse shape by synthetic control or postsynthetic processing that relies on centrifugal sedimentation-based sorting schemes where differences in the particle mass and aspect ratios (e.g., rods and spheres) provide a driving force for separation. Here, we present a technique to reversibly modify the sedimentation coefficients of AuNPs possessing different shapes that would otherwise be virtually indistinguishable during centrifugal sedimentation due to their similar densities, masses, and aspect ratios by exploiting the preferential affinity of the surfactant cetyltrimethylammonium bromide (CTAB) for the Au(100) facet. The resulting tailored sedimentation coefficients enable AuNP shape sorting via density gradient centrifugation (DGC). DGC-refined populations of faceted AuNPs are shown to significantly enhance the growth rate of InAs nanowires when used as seed particles, emphasizing the importance of shape control for nanomaterials growth applications.

 

 

[Turtle]

Speaking of Au, agitation, and fluid, sluices and gold pans do a fine job of sorting aggregates.  

[CraigD]

Assuming all the particles to be filtered have similar densities, you can make a sort of filter that doesn’t truly refuse, but slows, passage of the smaller particles, by having them fall or rise through a container of gas or liquid of lesser or greater density than the particles.

 

For example, drop an aggregate of small and large stones into a pool of water, and the large stones reach the bottom first. The drawback to such a filtering (or sorting) scheme is that you’d have to work fast to remove the big stones from the bottom of the pool before the small ones caught up, and the aggregate was back to being an aggregate.

 

If you can impart the same initial velocity, with a non-zero horizontal component, to the aggregate, you can sort by size without the need to work fast. For example, throw the aggregate horizontally through the air (ie with a catapult, cannon, or similar machine) over a soft field (where they stick where they hit, rather than bouncing) and the smaller stones, more slowed by air resistance than the larger ones, will land sooner and closer to the launcher than the large ones.

 

An etymology (word origin) purist would take issue with such schemes being called filters, because coming from the same source word as “felt”, a filter arguably must be made of or resemble fabric. Since we’ve already accepted mass spectrometers (which are arrangements of charge-particle deflecting magnets), I think we’re past such purism.

[Turtle]

Assuming all the particles to be filtered have similar densities, you can make a sort of filter that doesn’t truly refuse, but slows, passage of the smaller particles, by having them fall or rise through a container of gas or liquid of lesser or greater density than the particles.

 

For example, drop an aggregate of small and large stones into a pool of water, and the large stones reach the bottom first. The drawback to such a filtering (or sorting) scheme is that you’d have to work fast to remove the big stones from the bottom of the pool before the small ones caught up, and the aggregate was back to being an aggregate.

 

If you can impart the same initial velocity, with a non-zero horizontal component, to the aggregate, you can sort by size without the need to work fast. For example, throw the aggregate horizontally through the air (ie with a catapult, cannon, or similar machine) over a soft field (where they stick where they hit, rather than bouncing) and the smaller stones, more slowed by air resistance than the larger ones, will land sooner and closer to the launcher than the large ones.

 

An etymology (word origin) purist would take issue with such schemes being called filters, because coming from the same source word as “felt”, a filter arguably must be made of or resemble fabric. Since we’ve already accepted mass spectrometers (which are arrangements of charge-particle deflecting magnets), I think we’re past such purism.

Given that language is plastic and we talk about search filters and band-pass filters and such, I won't take issue with 'filter' here solely on etymological grounds. Since you bring up the issue however, I might quibble that the title uses 'sort' while the OP uses 'filter'. :hammer:

 

On the throwing machines, what a great excuse to use a canon! :clapping: