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posted by janrinok on Monday March 03 2014, @03:00AM   Printer-friendly
from the if-you-could-see-me-now dept.

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?]

 
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  • (Score: 2, Interesting) by anubi on Monday March 03 2014, @08:27AM

    by anubi (2828) on Monday March 03 2014, @08:27AM (#9949) Journal

    Yes... I do not think I would get many sparks from a dirigible several hundred feet up; as its far higher up than power lines. Anything getting near it would charge up to the local gradient anyway just as crows do when they roost on overhead power distribution cables.

    However its the field gradient you illustrated may be insufficient to do the job.

    I do not know how well this would scale up either. That's why I throw this out here for others which may have a better feel for this to comment on.

    I was hoping the turbulence would mix the ionization with the city air sufficiently to charge a wide swath of atmosphere, causing its particulate load to be attracted to the ground. I was considering keeping the dirigible charged via an electron flow in its tether, which would be connected into the DC power grid. If this DC were negative with respect to earth, then it looks to me like this might work.

    I wonder if the dirigible were positive, it would then attract the airborne crap, but how long could it stay aloft as I consider the Chinese problem as having tons of airborne soots of various types.

    My stuff was powered by a television flyback transformer with rectification. I could get either polarity by reversing the diode and the drive to the transformer. Being I worked as a TV repairman in my earlier days, I was quite aware of how high positive voltages would attract all sorts of things out of the air. A TV repair for someone who smoked was not a fun job; the HV cage would be full of tarry dust.

    I guess what I am trying to do is inject electrons into the air only to have them charge any airborne particle they encounter... once charged, the particles are attracted to ground.

    --
    "Prove all things; hold fast that which is good." [KJV: I Thessalonians 5:21]
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  • (Score: 3, Informative) by hankwang on Monday March 03 2014, @10:39AM

    by hankwang (100) on Monday March 03 2014, @10:39AM (#9970) Homepage

    I was hoping the turbulence would mix the ionization with the city air sufficiently to charge a wide swath of atmosphere, causing its particulate load to be attracted to the ground.

    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.

    • (Score: 1) by anubi on Tuesday March 04 2014, @02:39AM

      by anubi (2828) on Tuesday March 04 2014, @02:39AM (#10406) Journal

      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

        by hankwang (100) on Tuesday March 04 2014, @08:53AM (#10519) Homepage

        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.

        • (Score: 1) by anubi on Wednesday March 05 2014, @01:56AM

          by anubi (2828) on Wednesday March 05 2014, @01:56AM (#11115) Journal

          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]
  • (Score: 4, Informative) by hankwang on Monday March 03 2014, @10:49AM

    by hankwang (100) on Monday March 03 2014, @10:49AM (#9972) Homepage

    P.S. FYI Electrostatic precitipator [wikipedia.org]. Apparently, they are commonly used at the exhaust of coal plants. Given that coal plants are suspected to be a large contributor to China's smog problem, it would be better to install them there rather than floating above the city...

  • (Score: 1) by ls671 on Monday March 03 2014, @10:56AM

    by ls671 (891) Subscriber Badge on Monday March 03 2014, @10:56AM (#9974) Homepage

    "I guess what I am trying to do is inject electrons into the air only to have them charge any airborne particle they encounter... once charged, the particles are attracted to ground."

    That's what I understood the first time ;-)

    Lets pretend your idea could work perfectly: You would have to carefully estimate the impact of those concentrated pollutants, now in a solid form, around big cities where there are more grounded structures to catch the pollutants. For example, think of the rain diluting those now solid pollutants and distributing them deep in the ground.

    Right now, since the particles do not fall to the ground as fast as they would, they tend to distribute on a wider area, some going around the planet. The cities would end up with a higher concentration share than what they have right now.

     

    --
    Everything I write is lies, including this sentence.
    • (Score: 1) by anubi on Tuesday March 04 2014, @02:25AM

      by anubi (2828) on Tuesday March 04 2014, @02:25AM (#10397) Journal

      Thanks. Exactly why I posted here. I am of the belief I do not have a solution to the problem; rather I can mutate one mess into another. The question is: Do I gain anything by trading mess#1 for mess#2?

      And that's assuming this method will work, which I am dubious of.

      HankWang has been posting some very insightful and informative replies to the technical aspects of this.

      I feel for the Chinese and wish them the best with dealing with the mess. They are caught up in a socioeconomic situation where they are being led into trading off their environment for economic matters - matters that seem to make a few individuals filthy rich while leaving the rest simply filthy.

      --
      "Prove all things; hold fast that which is good." [KJV: I Thessalonians 5:21]
      • (Score: 0) by Anonymous Coward on Tuesday March 04 2014, @03:12AM

        by Anonymous Coward on Tuesday March 04 2014, @03:12AM (#10419)

        It's a matter of doing things in order. What I suggested you to look at comes before any prototyping or any physical implementation thus, technical details about said implementation.

        What I suggested you to look at could be fairly simulated with software. IMHO, this is where you should start.

        Intuitively, if this is ever going to work, I feel like the positively charged ones would make it much easier to pick up and control the mess but that's just intuition.

        Peace.

        • (Score: 1) by anubi on Tuesday March 04 2014, @06:11AM

          by anubi (2828) on Tuesday March 04 2014, @06:11AM (#10470) Journal

          Often intuition and past experience is most of what I have to go on.

          I love to simulate, but all too often my models, hence anything I get from simulation, is not up to snuff.
           
          God knows how many Spice simulations of mine have given me misleading results due to bad models.

          So I often try empirical approaches to see how well reality matches my models.

          --
          "Prove all things; hold fast that which is good." [KJV: I Thessalonians 5:21]
        • (Score: 2) by hankwang on Tuesday March 04 2014, @09:38AM

          by hankwang (100) on Tuesday March 04 2014, @09:38AM (#10532) Homepage

          What I suggested you to look at could be fairly simulated with software. IMHO, this is where you should start.

          The question is: which software? And then: which settings? Typically, computational fluid dynamics software has many model parameters that need to be set in order to capture the relevant physical effects for the problem at hand, without wasting processing time on effects that do not make a difference. Doing so correctly requires that you have a good grasp of the underlying physics, otherwise it will be garbage in, garbage out. Moreover, once you have this good grasp, it is likely that you can do back-of-the-envelope estimates to see whether what you want to achieve is at all plausible, or likely to be orders of magnitude off.

          Part of my job is doing, outsourcing, and reviewing simulations (gas flow, diffusion, thermal, deformation, particle-gas transport, and others) for engineering purposes (not electrostatic gas filtering, though), and have seen many times that simulations produced nonsense results because the elephant in the room was missed, i.e., some dominant physical effect that was not accounted for.