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Author Topic: Calculations for upward current classifier  (Read 629 times)

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Offline DharmaSoldat

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Calculations for upward current classifier
« on: December 28, 2018, 06:22:07 AM »
Hi guys... I'm working generally on modelling an upward current classifier and specifically sizing a pump for it.

I wanted to share my calculations in case anyone can see something I'm doing wrong.

Generally I've been modelling the pebble or whatever substance as a sphere with the general downward force being (weight - buoyancy) and the general upward force being drag.

My weight and buoyancy formulae look like (density * volume * force_of_gravity).

My drag formula looks like (drag_coefficient * face_area * ((fluid_density * (fluid_velocity^2)) / 2)).

To figure out my pump size (or at least the pump size required to keep a particle of the given properties stationary in the fluid), I find the general downward force, make it positive, then plug that in as the answer to the drag formula and solve for the fluid_velocity. I used a drag coefficient of 0.7 and calculated the area from the volume of the pebble roughly as (area ^ 2/3).

I then convert the velocity to flow rate for a 15cm diameter pipe using the formula ((velocity * (PI * diameter^2)) / 4) and convert from cm^3/s to GPH using a 1.052 conversion factor.

The data I got from all this jalopy was as follow:

Pebble Size (cm^3)GPH for Gold (density 19.3)GPH for Lead (density 11.0)GPH for Copper (density 8.0)GPH for Magnetite (density 5.0)
0.216 (1/4")10603.267838.156557.874957.28
0.108 (3/16")5950.884399.023680.482782.18
0.032 (1/8")2159.51596.351335.61009.62

This kinda makes sense to me but thought some physics-inclined folks here might have some more input :)

Cheers!


Steven

Offline mcbain

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Re: Calculations for upward current classifier
« Reply #1 on: December 28, 2018, 07:11:36 PM »
Hi.Steven way over my head.I will stick with what I got.luck on your project.Mcbain.
I started out with nothing Istill have most of it.

Offline DharmaSoldat

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Re: Calculations for upward current classifier
« Reply #2 on: December 28, 2018, 09:17:30 PM »
Hay Mark way over my head too!  <-laugh->

According to some more reading i've been doing the forces I've been using have been good but somehow I feel my numbers are off... I'll keep updating as I learn more.

Science rules.

Offline jobinyt

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Re: Calculations for upward current classifier
« Reply #3 on: January 06, 2019, 02:12:01 PM »
I think you can't classify that way. Well... of coursed you can ... but what are you classifying/separating for? At some point dissimilar size pieces of gold and rock will be placed in the same class.

 Elutriation tubes are used for separation not classifying.

Offline DharmaSoldat

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Re: Calculations for upward current classifier
« Reply #4 on: January 09, 2019, 09:41:26 PM »
I'm working on it. More later...

Offline jobinyt

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Re: Calculations for upward current classifier
« Reply #5 on: January 13, 2019, 01:23:06 PM »
You don't say why you're interested in this. Classification is usually based on physical size - and then like size material is separated by density.  The 'machine' you develop may not do well as a classifier but may be excellent as a separator. As you work on your project, keep that in mind and maybe try coming at your material/desired results from both ends to get to your desired outcome.

Offline DharmaSoldat

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Re: Calculations for upward current classifier
« Reply #6 on: January 20, 2019, 10:15:25 AM »
Sooooo... I have done some more work on this and will be effectively classifying to a certain size range and then separating by density, repeating this process with the output as necessary with smaller classifiers and lower water velocities until I have all the heavies out... then just pan the slime afterwards.

Currently immersed in understanding the design procedure for axial flow pumps.

Offline JOE S (INDY)

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Re: Calculations for upward current classifier
« Reply #7 on: January 20, 2019, 10:13:04 PM »
Just remember the "Rule of 4"

Elutriation separation by SG (weight) needs to have the particles to within 4 diameters. 

Approximately same sized particles will make the Gold (SG ~19) sink while Black Sands (SG ~5.2) and quartz (SG ~ 3.1) ascend  in the water column flow. 

The Coriolis Effect due to shape figures in there too, of course.

 <~ShOcK~> <-shock_> <~ShOcK~> <-shock_>
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Offline DharmaSoldat

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Re: Calculations for upward current classifier
« Reply #8 on: January 21, 2019, 07:52:05 AM »
Joe, coolio! :)

I ended up figuring that out analyzing my velocity graph against the various sizes and specific gravities of gravel.

I've been working with a 'hovering specific gravity' of around 8 from reading this guide: http://rruff.info/doclib/cm/vol6/CM6_273.

I still have to figure out where I want my starting point to be in terms of initial classification but I figure it'll be around 1/8".

I noted as well that there are many different ways to calculate the settling velocities and settled (pun!) on the ferguson-church method which analytically blends the stokes and turbulent methods of calculating settling velocity.

Now to look up coriolis effect.

Offline tonofsteel

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Re: Calculations for upward current classifier
« Reply #9 on: January 21, 2019, 08:54:00 AM »
This idea sounds similar to the Gold Cyclone from Gold Hog?  There are 4 or 5 videos on their Youtube channel that show the operation and how it works.

Remember watching this years ago and tried to look up the product on their site but it looks like it is no longer offered.

Quote
The Gold Cyclone has been dropped from our product lineup since we have released the MULTI SLUICE concentrator. It works faster and with less classifying

Also curious about what you are aiming to achieve?  An experiment or faster separation/better recovery than other methods?  Looks interesting either way.

 


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