Calculate Surface Charge Decay - Chemical Engineer

Click For Summary

Discussion Overview

The discussion revolves around calculating the rate of surface charge decay of charged particles when they come into contact with an oppositely charged electrode. The context includes practical applications in particle separation using charge, particularly in the field of chemical engineering.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant seeks a method to calculate the charge dissipation of a negatively charged polypropylene particle when it contacts a positively charged aluminum plate.
  • Another participant suggests that due to numerous variables, conducting experiments may be the most effective approach.
  • A participant mentions knowing several variables such as voltage and charge density, and expresses the need for a relationship to estimate charge loss upon impact.
  • One reply references research on the electrical conductivity of polypropylene as potentially relevant to the discussion.
  • Another participant describes an experiment measuring the charge of an electron, suggesting that if a particle has only one electron, its discharge would be instantaneous.
  • A participant explains their goal of separating particles based on charge, noting that larger particles should become positively charged while smaller ones become negatively charged, but they lose charge before reaching the electrodes.
  • One participant theorizes that oppositely charged particles attract each other, potentially neutralizing before reaching the bottom of the setup.
  • Another participant mentions observing clumping of particles before they are sent down the electrodes, indicating that they are taking measures to prevent significant electrical attraction.
  • A participant inquires about the material of the other particles involved in the separation process, seeking clarification on whether the setup is intended for a specific material or a generic application.
  • One participant notes that the setup could have applications in the pharmaceutical industry.
  • A suggestion is made to consider making all particles small to avoid the need for separation, proposing an alternative method using air drafts to separate particles based on size.

Areas of Agreement / Disagreement

The discussion features multiple competing views regarding the effectiveness of charge-based separation and the factors influencing charge decay. Participants express uncertainty about the best approach and the underlying mechanisms at play.

Contextual Notes

Participants acknowledge various assumptions, such as the influence of particle size, shape, and material properties on charge behavior, but these remain unresolved. The discussion also highlights the complexity of the interactions between charged particles and electrodes.

Disserate
Messages
6
Reaction score
0
I am a chemical engineer and have little experience with complicated electrical properties. I was wondering if there was a way to calculate the rate at which the surface charge of a particle will dissipate when it comes in contact with an electrode of the opposite charge. For example a small particle of polypropylene that has a negative charge on the surface contacting an aluminum plate that has a high positive voltage on it with respect to ground. Thanks.
 
Engineering news on Phys.org
There are so many variables in this example, that it may be easiest to just perform tests.
 
  • Like
Likes   Reactions: 1 person
Well I wouldn't even know where to begin to perform tests, but I do know most of these variables. I know the voltage on the plate, the charge density of the particle along with the size, and the shape can be approximated as spherical. I can find most material properties online, but what I really need is to have a relationship that can give me the approximate amount of charge that is lost during an impact of the particle on the plate.
 
Disserate said:
I am a chemical engineer and have little experience with complicated electrical properties. I was wondering if there was a way to calculate the rate at which the surface charge of a particle will dissipate when it comes in contact with an electrode of the opposite charge. For example a small particle of polypropylene that has a negative charge on the surface contacting an aluminum plate that has a high positive voltage on it with respect to ground. Thanks.

This sounds like something to be researched. e.g. http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=1387828&url=http%3A%2F%2Fieeexplore.ieee.org%2Fxpls%2Fabs_all.jsp%3Farnumber%3D1387828

I think you'll need to know the material's (polypropylene) electrical conductivity and it appears that this is being researched also. i.e. Electrical conductivity of polypropylene
 
  • Like
Likes   Reactions: 1 person
There were some experiments where they were trying to measure the charge of one electron.
They would charge a small particle and keep it at a constant height between two plates that were at different voltages.
They then calculated the weight of the particle and the force required and the force of the electric field. From this they could calculate the charge of one electron.

If your particle only has one electron, then the rate of discharge would be instantaneous.

If it's not a secret, what are you attempting to do.
 
  • Like
Likes   Reactions: 1 person
Basically I am trying to separate particles using charge. The particles are forced to interact with one another beforehand causing static charge to build up on them. In theory the bigger particles should charge positive and the small negative. The particles are then let to fall down between 2 high voltage electrodes, one positive and the other negative. By looking at the size of the particles underneath the electrodes, we can see if this can work. The problem is that even though we can see obvious separation at the top of the electrodes, by the time they reach the bottom they are no longer separated and are all mixed up. I was thinking that when the particles come in contact with the electrode it loses some of its charge, and by the time it gets down to the bottom, all is gone and it no longer moves towards the electrodes that it should.
 
My thinking is that the opposite charged particles attract each other and by the time they get to the bottom, they have neutralized each other.
 
That was on thing that we took into account earlier, but when this happens we can see clumps forming in the mixture before we send it down between the electrodes. To counter this we don't let the particle charge enough so that the electrical force of attraction between them is significant at all.
 
Disserate said:
Basically I am trying to separate particles using charge. The particles are forced to interact with one another beforehand causing static charge to build up on them. In theory the bigger particles should charge positive and the small negative. The particles are then let to fall down between 2 high voltage electrodes, one positive and the other negative. By looking at the size of the particles underneath the electrodes, we can see if this can work. The problem is that even though we can see obvious separation at the top of the electrodes, by the time they reach the bottom they are no longer separated and are all mixed up. I was thinking that when the particles come in contact with the electrode it loses some of its charge, and by the time it gets down to the bottom, all is gone and it no longer moves towards the electrodes that it should.

I'm curious. You mentioned polypropylene particles, so what might the other particle's material be? Or are you trying to develop a generic machine?
 
  • #10
The particles are of the same material, but different sizes. This set up should also work with other materials, but they still should be the same material in different sizes.
 
  • #11
Thanks. Very interesting idea that could apply to the pharmaceutical industry.
 
  • #12
Why don't you just make all the particles small, then you wouldn't have to separate them?

Why not forget using charge to separate the large and small particles and just slowly put particles is a vertical shaft with a small cross draft of air. The cross draft of air will cause the small particles to drift to one side of the shaft.
 

Similar threads

  • · Replies 13 ·
Replies
13
Views
2K
  • · Replies 16 ·
Replies
16
Views
5K
Replies
11
Views
3K
Replies
21
Views
2K
Replies
1
Views
1K
  • · Replies 58 ·
2
Replies
58
Views
5K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 8 ·
Replies
8
Views
2K
  • · Replies 7 ·
Replies
7
Views
3K
Replies
3
Views
2K