David Gerson- Dust Filtrationb 4/30/2010

Hey everyone, sorry I haven't been posting, I hadn't realized I was supposed to until today. So I will try to do the last three weeks justice without writing so much that I bore all of you!

Basically my project is to test different filters and types of filters for information on filtration efficiencies at varying sizes of particles for varying flow rates. Ok, thats a lot of weird stuff if you aren't used to the topic, so let me try to break it down:

First off, why does this matter?

In space there isn't an atmosphere for us to breathe, so we have to bring all the air with us, which means that the air within a spacecraft must constantly be recycled to keep costs at a practical level. This means that the clean air must flow into the cabin, but that the “dirtied” air must then flow out of the cabin into a filtration system that purifies the air and removes all contaminants, thus providing clean air that astronauts can breathe and stay healthy. My particular project is turned more towards a lunar base. Lunar dust turns out to be made of very tiny particles (varying in size from hundreds of nanometers to a few tens of microns) and are very jagged due to the constant heating and cooling of the moon's surface as it is hit by asteroids. This is very dangerous to human respiratory systems, but at the same time is very hard to filter, so part of my job is to test different ways of filtering these particles to figure out the best way to go about creating a filtration system. So I am working on real stuff whose information will be used over the next year or so to create a filtration system for the ISS and hopefully at some point for a planetary base.

Next question, what am I actually trying to figure out?

So different filters accomplish different things based off what they are made of and how they perform the filtration. The main measures of efficiency are a) what sizes of particles the filters can filter effectively and b) what the pressure drop across the filter is. a) is important because it determines whether the filter accomplishes what it is supposed to and b) is important because the higher the pressure drop, the more power is required to drive the system, and in space, the lower power required the better. The three types of filters I am looking at right now are normal filters, sintered metal filters, and cyclone filters. Normal filters just pass air through them and the particle penetrates into the filter and eventually stops; depending on the pore size, these filters can be manufactured as screens (for very large objects like lint or hair), prefilters (medium sized, so about a few hundred microns), and filters (for everything too small for the prefilter). And generally, the smaller the pore size, the higher the pressure drop. The sintered metal filter is similar, except that for it the dust particles accumulate just on the surface and form more of a dust cake (which is very important for our project, but I will explain that later). The cyclone (see above) works by running a higher flow rate in (they are rated at 10-30 cubic feet per minute (cfm)), running the air in a tight spiral down a tube so that the dust particles fall out and then can be collected at the bottom, and the air can then be recycled out the top and continue in the system.

Now what actually matters, what am I working on?

I am helping to design a system for “dust cake removal.” Basically the sintered metal is used as a prefilter and collects particles of roughly the same size that the cyclone can remove. As the system runs, the dust particles collect on the surface of the sintered metal, and at a certain point, it becomes clogged enough that it requires too much power to push the air through that it is terribly inefficient. My mentors came up with the idea of at some point using a very high speed blower to back flow the air through the prefilter momentarily (so as not to have to stop the overall system itself), which would hopefully remove the dust cake, and that air could then be sent through a cyclone filter which would remove the particles and the air could then be sent on its way to the main filter. This blower-cyclone system would only be run when needed, and wouldn't run for that long, but if implemented correctly, it should help increase the time for which the filter system lasts without the parts needing to be switched out giving astronauts time to spend elsewhere.

Right now I am basically saying ok, I have this sintered metal filter and this cyclone, what are the pressure drops across them in different flow configurations to figure out which design would work best. This means I basically look around the lab and if something looks like fun to use, I throw it in, take my measurements and see what happens. The fundamental lesson I have learned about engineering goes as follows: when in doubt, try it out. You can never really predict what is going to happen unless you try, so if its there, try, because it could easily save you a lot of time and effort. The other important lessons are really test different things and figure it all out before you start building, and keep things as simple as possible. It really goes a long way as I have learned in only 3 weeks.

So yea, in essence, thats what I have been doing. Things are starting to pick up as we figure out what we need to do and are getting better at knowing what to actually do. I am working on stuff no one has ever done, so my mentors don't know much more than me which makes things very exciting. Sometimes they have actually trusted my judgment and decisions! They don't know how bad an idea that is yet, and hopefully it will stay that way. Soon I will try to take pictures of some of the test rigs I have set up and some of my drawings so that this makes more sense, I just hadn't realized I was supposed to be blogging. Good luck to all of you on your projects and I hope you all have a ton of fun!And I apologize for all my grammar and spelling and whatever mistakes as I am writing this in the 10 minutes it took for my mentor to cut some stuff on the super duper saw machine downstairs. Adios por ahora!