Engine Dehumidifier DIY

Discussion in 'Technical Corner' started by Huckster79, Dec 19, 2018.

  1. Stephen Poole

    Stephen Poole Pre-takeoff checklist PoA Supporter

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    Nah, think about it. The air conditioned hanger has already removed some of the moisture, so the cooling type will actually work better. ACs do remove humidity, but only a certain percentage.

    In a pinch, I've operated my transmitter sites without the desiccant. The building air conditioner removes a lot of moisture, and a compressor with a big tank will condense a lot of the moisture itself. (Just have to remember to drain it regularly.)

    Again: I'm no engine expert, but thinking out loud ... I'm not sure you need air at a sub-zero dewpoint. I just don't know.
     
  2. Huckster79

    Huckster79 Line Up and Wait

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    Oh I agree if you are in a air condidioned hanger... or heated hanger. But for me I’m not.. the AC type dehuey that cools the air then heats it to dehumidify it wouldn’t work in a hanger that’s cold as those units will freeze up if they are in the cold is what I was thinking...
     
  3. Stephen Poole

    Stephen Poole Pre-takeoff checklist PoA Supporter

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    The refrigerated types don't have a compressor; they're basically just a long tube that goes through a cooling chamber. If it's cold in the room, the refrigeration doesn't cut on. They're designed for LOTS of CFM, though ... you could do something simpler with a little portable refrigerator. Drill holes in the sides and pass your own copper coil through it.

    (The Revenooers are likely to think you're making your own wildcat whiskey, so hide it!)

    Yeah, for what you're doing, either desiccant with a filter or membrane is the way to go. I'd say desiccant with a really good particulate filter before it hits the engine -- in other words, what you've already built. Just add a good microfilter cartridge. You can use a water filter from Lowes or Home Depot. Just get the plain-jane fiber cartridge (the one that looks like a molded spool of twine).

    You're a man after my own heart, McGuyver. :)
     
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  4. Huckster79

    Huckster79 Line Up and Wait

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    I really appreciate your contributions to this thread as you brought up technology we weren't discussing... I think to add a better filter I need to get a bigger pump... right now I have a loose fibrous filter going into the pump tub and the air pump does have a felt material as a filter... However when I added an additional filter in line on the pumped air it cut the flow down to where I couldn't detect it. So I think a larger pump/compressor is necessary.

    The membrane is intriguing but the high cfm requirement I think may be disqualifying??? your thoughts? as I don't think we want rushing high volume air through it 24/7. Idk why but it just doesn't seem "right"...

    what are your thoughts on a more powerful pump vs using an oilless compressor throttled back post compressor to minimize compressor cycling? I'm torn what would be the better route...
     
  5. Stephen Poole

    Stephen Poole Pre-takeoff checklist PoA Supporter

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    Be careful about using me as a "technical X-Purt" on anything to do with aviation. I'll have your plane flying backwards, upside down, and the strobes will all be a nice shade of purple.

    An oilless compressor with a storage tank is ideal. Most of these have a little regulator that you can use to set it to, say, 10-20 lbs (though it's difficult to set really low values). Putting the filter in line will slow the CFM (i.e., the flow), but that may not be a bad thing.

    I doubt you'll be able to have a pump directly driving the desiccant, then straight into the engine through the filter. That pump is going to wear out in short order.

    Be prepared to replace the compressor from time to time. I've tried about every brand that there is, and every oilless unit that I've bought has eventually failed. This (of course) is dependent on how much it has to run. If you set the regulator just high enough to bubble dry air into the crankcase, the size of the tank will determine how often it cycles and how long it has to run to refill the tanks.

    (Sorry, that's common sense. I need more coffee.)
     
  6. flyingcheesehead

    flyingcheesehead Touchdown! Greaser!

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    Won't the air we put into the engine be quite cool then, though? It'll be heated by compression, and that heat will be lost to ambient while it sits in the storage tank, and then it'll cool down as it's released into the engine?
     
  7. Stephen Poole

    Stephen Poole Pre-takeoff checklist PoA Supporter

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    Well, duh. Yeah, I missed that in the rest of the thread. Heh.

    You want the compressor tank to be cool so that the moisture will condense there. Yes, you'll need a way to warm the air up. I can see that you wouldn't want to pump ice-cold air into your engine.

    If I was MacGuyverin' it, I'd just use a spaceheater and some copper coil to warm the air back up. I doubt that would heat the engine block very much, but it would at least keep the air from cooling the block off. (Maybe.)

    I done exhausted my thoughts on this one, I s'pect.
     
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  8. EdFred

    EdFred Touchdown! Greaser! PoA Supporter

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    "Hi, I'm a solution. Is there a problem around here someone could point me to?"
     
  9. Huckster79

    Huckster79 Line Up and Wait

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    I’m thinking I could toss the coil under my cowl as it stays in the 80s in there, and mines super accessible with two piano hinged sides...

    But if we kept it to a trickle of air would it really make a difference? If it wasn’t enough to cool off the intervals which once they are running in the low 100s a wisp of air I would doubt would do that... and going from cold to warm shouldn’t cause a condensation issue as the cold air can hold even less moisture than warm so even though absolute humidity would remain the same the relative humidity of the piped in air would drop as it heats up.

    Just thinking out loud...
     
  10. kyleb

    kyleb En-Route PoA Supporter

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    Why not a theromostatically controlled heater that keeps your engine at 70F (or your temp of choice) permanantly with a 24 hour nitrogen purge after each flight. During the purge, feed 10 CFH of 0% humidity nitrogen for 24 hours. That ought to dry the sucker out and the warmth will prevent condensation once the nitrogen bath ends.

    Seems a lot simpler than the dehydration schemes.
     
  11. Huckster79

    Huckster79 Line Up and Wait

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    You may have a very valid point... even with or without the heat that nitrogen bath may be the ticket... certainly worth the discussion...
     
  12. Stephen Poole

    Stephen Poole Pre-takeoff checklist PoA Supporter

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    Very good idea. Nitrogen is preferred, as I said. We don't use it because of the expense, and because of the difficulty in getting the canisters delivered to remote transmitter sites.
     
  13. flyingcheesehead

    flyingcheesehead Touchdown! Greaser!

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    Yes, but because cold air holds less moisture, it also won't help draw moisture out of the engine as quickly. So, if going with a compressor setup, it'd be a matter of reheating the air between the tank and the engine.

    Not a bad idea at all. I was talking with an experimental owner yesterday who suggested the same thing, and said that a winter's worth of nitrogen costs him less than 100 bucks.

    Anyone know of a good (accurate) oxygen sensor that can be used with an Arduino? Maybe I'll go with my oil-cap-with-tube idea, and put sensors for temp, humidity, pressure and O2 a few inches inside, and a display outside.
     
  14. Huckster79

    Huckster79 Line Up and Wait

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    Is tanked nitrogen that cheap? I couldn’t find price online. Was gunna call a plave tomorrow. If ur interested in really investing up front a nitrogen generator can be had for $1000 on up- just pump it to it 24/7...
     
  15. flyingcheesehead

    flyingcheesehead Touchdown! Greaser!

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    Airgas lists it as $59 for a 300 cu ft cylinder - Sounds like that's an exchange or fill price maybe? But I also found new cylinders for $425. So, yeah, cheaper than any of the GA engine dehydrators that I've seen. ;)
     
  16. Stephen Poole

    Stephen Poole Pre-takeoff checklist PoA Supporter

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    My lack of experience with aircraft engines means that I have no way to estimate how much nitrogen you'd need. The idea of just using it to fill the crankcase after a flight, with a block heater, seems workable. But that's just a guess.

    If you need to fill a coax with nitrogen, I gots all sorts of formulas. The aforementioned 6" line at 101.1 FM is 1300' long, so you're talking tens of THOUSANDS of cubic feet. Using the biggest cylinders available, I went through several of them just to purge the line one time.(!)

    Edit: remember, too, that my coax lines are pressurized -- more than one atmosphere. Roughly speaking, you have to multiply the volume by the number of atmospheres that you want in the line. I typically run between 3-15 lbs PSI. That multiplies the amount of gas needed. There's no nitrogen generator available that I can justify on the cost basis.

    The nitrogen generator might work, and might be cost-effective in the long run. But then again, I'm so stingy, the desiccant-with-particulate-filter is still the most appealing to me.

    Again: speaking from total ignorance ... I wonder if the best solution isn't just to crank the engine and let it run a while at frequent intervals? It's an excuse to fly .. .. ..:D
     
  17. flyingcheesehead

    flyingcheesehead Touchdown! Greaser!

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    And it's more involved than that. Part of the problem is that the only easy entrance to the engine is the oil filler tube, so there isn't any way to pass air through the whole thing. There's going to be some mixing and some diffusion. I'm relying solely on diffusion at a very small port right now, so it would be a big improvement just to put a few cubic feet of nitrogen through it. Using a tube with a hole in one side and the end plugged would probably help stir things up in there - I don't have enough room to actually curve the tube.

    I think the whole reason that we're even talking about this is that we can't always do that. :( There have been times where I've had to go 6-10 weeks in between flights in the winter due to weather and surface conditions. It really sucks not being able to fly for that long, but what sucks even more is hurting your airplane in the process. :(
     
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  18. kyleb

    kyleb En-Route PoA Supporter

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    The crankcase breather gives you a second access point.
     
  19. flyingcheesehead

    flyingcheesehead Touchdown! Greaser!

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    Nope. It comes off the side of the filler neck.
     
  20. kyleb

    kyleb En-Route PoA Supporter

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    Curses! Foiled again.
     
  21. flyingcheesehead

    flyingcheesehead Touchdown! Greaser!

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    Yeah, it's kind of annoying that everything goes to one spot! See post 61 - That's the view down the filler, and the black hose on the right (just above the dipstick in the picture) is the breather.
     
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  22. Huckster79

    Huckster79 Line Up and Wait

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    I’m thinking I’m going to go desiccant and air compressor... I’m thinking of not going overly high tech- especially with ez access to breather- just hook it open for a bit then close it... in summer I could probably put a menards dehuey in a box and pump air from there... wouldn’t work in winter tho in unheated hanger. I’m almost done w my custom insulated cowl cover, all sewn just have to sew in Velcro and one strap and it’s good to go. Then my tinkering time can go to this though may take my time now we are coming into flying season and likely not going to be grounded for weeks on end... if my plane didn’t have a good sized want list I would consider the generator and just blast it open loop with nitrogen 24/7... but that much cash could be airplane upgrades..
     
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  23. Cap'n Jack

    Cap'n Jack Final Approach

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    Probably an exchange or fill price. The tanks usually have a rental cost; when we run out, they take the empty and leave us a filled one. I go though enough nitrogen that I buy a liquid nitrogen tank. $180 buys me 230 liters, and it lasts me a month. I draw off gas to a number of instruments at 60 PSI. It's cheaper than a nitrogen generator for the volumes we need. I'm not counting tank rental in the cost.
     
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  24. Huckster79

    Huckster79 Line Up and Wait

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    Any idea how many cubic feet that 230L amounts to? So you can use the liquid in gas form?
     
  25. Cap'n Jack

    Cap'n Jack Final Approach

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    In reverse order, yes, they have a take-off for the gas. It is the same fitting as for a cylinder. I use the same regulator as for the cylinder- the high-pressure gauge doesn't register, but I regulate the low pressure side to 65 PSI.

    230 L gets us about 5600 cubic feet at 1 atm : http://www.airproducts.com/Products...s/weight-and-volume-equivalents/nitrogen.aspx

    Note that the 230 L Dewar lasts me about a month whether I use it or not, since the gas is always boiling off and venting. If you don't draw it off fast enough, the safety valve will pop and make a loud hissing noise, it makes everyone jump until you get used to it. A lot of companies with "house nitrogen" piped through the facility use large tanks of LN2 and draw off the gas, just on a larger scale. If I use a cylinder, I can run one mass spectrometer for 2 days if I turn the gas off at night. With the Dewar, I can run a mixture of 5 instruments at once if I needed to so.
     
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  26. Huckster79

    Huckster79 Line Up and Wait

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    Well here is my old cowl cover...
    IMG_4453.JPG

    Here is my new one, that took some hours to sew! It ended up just a bit shorter than I wanted it to, I wanted it to come just shy of the windsheild... IMG_4458.JPG
    IMG_4456.JPG
    IMG_4455.JPG

    Being the Continental it is and always having a little puddle under the vent tube which would be covered by the cowl cover, I sewed in about a 1 foot chunk of old air compressor hose that happens to fit perfectly inside the vent tube, so when I put the cover on I can slide that in there and keep the cover from getting all that oil in it..
    IMG_4459.JPG

    If I do a lot of cold weather flying next year away from home base I may sew on a 4-6" extension so it can be cinched tighter and "seal" off this open area.
     
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