# Homework Help: Queries about an electrostatic precipitator

1. Jun 20, 2012

### sgstudent

1. The problem statement, all variables and given/known data

In a precipitator, at the bottom is a negatively charged wire mesh while at the top is a set of rods at the two sides that are either earthen or positively charged. The purpose of the negative wire mesh is to charge the flue ash negatively by conduction then it is attracted to the positive rods at the side. But how can the ash get the charge? Isn't it an insulator of electricity? And even if it is water present, how can it gain the charge? In a electrolysis setup, the two reactions at the cathode and anode must occur at the same time so how can the cations be reduced there?

2. Relevant equations

None
3. The attempt at a solution
My physics tutor said that it can transfer electron by I just don't see how. Thanks for the help!

2. Jun 22, 2012

### BruceW

hmm. Well hair-combs and balloons are insulators. And from doing physics practicals with them, you can see that they gain charge. So is it so surprising that ash can get charged as well?

3. Jun 24, 2012

### sgstudent

Oh but ash gets charged by direct touching (neutral touches charged redistribution then it becomes charged). But this method is a conductor mean of charging and not a insulators mean. So I don't get how it can simply be charged this way. As fair the water explanation, the process is like the electrolysis case, but anyhow a solution must be electrically neutral so the oxidation of the anion and reduction of cations must happen together but in this case it is not. So I'm pretty confused about this... Thanks for the help?

4. Jun 28, 2012

### BruceW

Ok, I wasn't sure how this equipment specifically works, so I looked it up and apparently there is a corona (i.e. ionisation) created around the negative electrodes, and it is by this method that the dust particles acquire electrons. Does this make sense to you? I'm not certain which bit you are concerned with.

5. Jun 28, 2012

### sgstudent

Hi that another type that I learnt too. But the one I'm talking about is http://www.school-for-champions.com/science/static_uses.htm

I'm not sure how the ash can get a negative charge since its an insulator of electricity so the negative charges shouldn't be able to flow into it. Thanks for the help!