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hankwang writes:
"For the past couple of days, China's capital has been suffering under severe smog, leaving the sun and skyscrapers barely visible. The highest concentration of small airborne particles (PM2.5) was 0.50 mg per cubic meter, a factor 20 above the Word Health Organization's safe limit. Scientists went as far as comparing this to a nuclear winter. The worst seems to be over for now: today, the monitors are reading 0.180 mg/m3, only a factor 7 above the WHO limit.
The Chinese smog seems to behave differently from the smog in Europe and the US. Existing scientific models developed in the West do not work well. To improve the models and understanding, plans are underway to build a 600 cubic-meter (that's 21,000 cubic ft or 160,000 US gallon) transparent dome as a smog chamber."
[NOTE TO EDITOR: I can't get slashcode to display the mu symbol, so I converted to milligrams] [Ed's Note: Thankyou - but what is it in firkins?]
(Score: 3, Informative) by hankwang on Monday March 03 2014, @10:39AM
I see two issues here.
1. Assuming that the home electrostatic filter needs about 1 kV over 1 cm (E=100 kV/m field strength) to catch small particles within the 50 ms travel time along the electrode plates, it appears that the drift velocity at that field strength is about 0.2 m/s. Atmospheric turbulence involves air velocities that are much higher than that.
2. Moreover, if you scale up this concept to atmospheric dimensions, then having a 500 kV potential over 100 m distance is actually only 5 kV/m of field strength - i.e. only 0.01 m/s of particle drift velocity. So, this is not going to work. If you did increase the voltage, the risk of causing lightning bolts would go up considerably.
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(Score: 1) by anubi on Tuesday March 04 2014, @02:39AM
Thanks, Hank.
I appreciate the feedback on the technical aspects. I am trying to structure this as an electrostatic precipitator with the earth itself as the positive plate and the dirigible as the negative ion emitter. I was hoping maybe it would not be so windy at ground level that the precipitate could drop out at ground level. If it were blowing over the ground, the particle drift velocity, like you say, would be so great that the kinetic energy of its motion would exceed the forces attracting it to the plate and the deposition would not happen.
I sure hope they try to precipitate at the coal plants themselves as you indicated in another post. When I worked at the Chevron Oil Refinery in Pascagoula, Mississippi, I remember walking into huge "buildings" with electrical plates hung from the ceiling whose function was to charge emissions from the refining process and drop them out before they reached the atmosphere.
I know you already know all about this, but I will link it for the casual readers of this thread what this is all about...its known as a "Cottrell precipitator". [google.com].
"Prove all things; hold fast that which is good." [KJV: I Thessalonians 5:21]
(Score: 2) by hankwang on Tuesday March 04 2014, @08:53AM
I found some lecture notes on electrostatic precipitators with harder numbers: http://ce.udel.edu/~dentel/434/Lecture6-ESP.pdf [udel.edu] . My hand-waving estimate based on what I think a home-ESP looks like (100 kV/m, 20 cm/s drift velocity) were a bit off; on page 7 it shows an example calculation: 300 kV/m and 3 cm/s drift velocity for typical 1 micron particles.
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(Score: 1) by anubi on Wednesday March 05 2014, @01:56AM
Thanks. Hank!
I find these precipitators an interesting thing to study, being its so very much easier to clean up a mess before its made ;) .
"Prove all things; hold fast that which is good." [KJV: I Thessalonians 5:21]