Douglas MillerGetting started on the temperature and humidity control. I ordered a temperature and humidity sensor from Adafruit, and as soon as it gets here I'll get the temperature taken care of. Adafruit normally ships stuff pretty quickly, so it shouldn't take long. Hopefully first of next week that's over and done with.
Humidity is another thing. I'm still tossing around ways to control the humidity, and haven't settled on anything yet. Driving the humidity down could be as simple as cranking up the exhaust fan. Or maybe not. I really can't see needing to ADD humidity during a run, but who knows, maybe I'll have too. So I'm not counting that out. So while I do my google-foo to see what the options are, I figured I'd ask you guys for suggestions. How would you go about controlling humidity in a semi-closed chamber?
Come to think of it, I may have to have the ability to raise or lower it. Because repeatable runs are something I want to be able to do, what if you run something with a given set of parameters all summer long in humid conditions, get it dialed in, then need to run the same thing in the winter, where humidity will be much lower? Do we do change the parameters and take a few runs to get it dialed back in, or do we just bring the humidity back up to where it was under the old parameters? Good question. Guess I'll have to think about it a bit...
Any suggestions?
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Wow. Thank you. You've certainly laid it all out better than I did in my own mind. :P
I had considered ultrasonics, but had just about eliminated it because of cost. Now I think I'll just rule that out entirely because of the drawbacks you mentioned. What direction I think I'll tinker with now is a heating coil. Just so happens I have a E-sig laying around I never use, and it's coil should work nicely. :)
That would work for getting MORE humidity if needed. For the most part I'm thinking we'll want it drier, and for that a Peltier should do. I have a couple of large ones on a shelf here somewhere, but I think they may be much bigger than needed. Time to EBay, I'd guess.
As for your project, I had seen that, and I thought I was following it. No wonder I never got word of any updates. That situation is now taken care of.
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I'm still working on the Haber thing, but haven't found time to post any blog entries.
By and large, high humidity allows electric charge to leak off, which is why we get static in the winter and not so much in the summer.
From this, I would guess that you want low humidity for your project for that reason.
If you get a peltier, a standard digital temperature controller should work. You probably want a PWM controller instead of a bang-bang (ie - relay) controller, but these are cheap on eBay.
Something like this should be what you need for the near term for experimenting:
http://www.ebay.com/itm/Dual-Digital-F-C-PID-Temperature-Controller-Control-TA4-SNR-with-K-thermocouple-/131823099517?hash=item1eb144de7d:m:mqqzHZ84eBwP2BIBcV0p4hA
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As you might have guessed, I'm into the physical side of chemistry.
I think your project is awesome, and was considering asking to join.
Here's my ongoing project:
https://hackaday.io/project/4689-improve-the-haber-process
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And to followup, adding moisture to air is relatively simple.
Modern humidifiers have a wheel - sort of like a ferris wheel - with a high-surface area mat on the outside. As the wheel spins, the mat dips into a water reservoir and out again. A blower passes air over the moist mat, drying it and putting the moisture into the air.
Ultrasonic humidifiers have a transducer at the bottom of a reservoir, and the action of the ultrasoound vaporizes small globules of water. If the globules are small enough, the output can be fog or moist air.
The drawback of the ultrasonics is that since the water is small globs (and not evaporated water), it takes any dissolved minerals with it. Using one of these will deposit a fine white powder over your surfaces, more if you have hard water.
And of course you can heat some water and blow air over it. A wick of fiberglass with a heating coil wrapped around sticking in a container of water, for instance. The fiberglass wicks up the water from capillary action, and the coil vaporizes the water as needed.
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Traditionally you lower the air temperature, let the moisture condense, then raise it back up again.
If you have a closed air supply, a peltier would work. Find a CPU heat sink with embedded copper tubing, cut the tubing and run water through it from a bucket of ice water. Put the heat sink on one side of the peltier, and have the other side contact your air supply. Put a catch-basin under the peltier.
The ice will keep the water at 0 degrees and have a lot of thermal mass, so the peltier will have a nice cold reference to pump to.
Peltiers are straightforward to control, you would be able to adjust its working face to any desired temperature.
For experimental purposes it might be easier just to start with dry air and add humidity as needed. Any compressor generates relatively dry air. During the expansion process (as air comes out of the tank) the temperature drops and water condenses - this is why compressors have condensation traps.
(Also, any scuba supply store will fill your tank with "dry" air. Probably welding gas supply shops will fill be able to a bottle with dry air as well.)
For chemistry, gas apparatus experiments typically pass the gas through Calcium Sulfate (image below). CaSO4 has little capacity, but it scrubs almost all the moisture out of the air. You can also reuse it (the Calcium Sulfate) by heating or putting it in a vacuum.
Hope this helps!
http://www.chem.ucla.edu/~bacher/Specialtopics/Drying%20Agents.html
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