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Author Topic: Calculations for upward current classifier  (Read 240 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.

 


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