Vacuum drier

[NeighborJ]

I am curious if anyone here has tried to use a vacuum to dry stars or chemicals. I live in western Pennsylvania where the humidity is usually quite high. It is difficult to get certain stars dry enough to seal up for storage. This became painfuly evident the other day when I opened up a large batch of D1 made about 2 months ago and smelled strong ammonia. They still work but have degraded.

I have a drying rack with lights inside but it gives no guarantees of dryness. So I was thinking if I make a vacuum chamber and finish drying the stars in there I can be sure that I won't loose any more batches of stars to moisture.

I have several concerns about doing this. First is, as moisture evaporates it absorbs energy(latent heat of vaporization, approx 970 btus per lb)which could end up turning the stars into Popsicle's. This isn't terrible but would lengthen the drying time significantly. The second concern, would the stars have any chance of puffing up or turning to mush as the water boils out of them?

I just don't want to waste my time welding up a vacuum chamber if it isn't going to work.

[Fulmen]

I would rather make a simple condenser-arrangement. I dried some organic material a while ago, to speed things up I used some ice packs and a fan to circulate inside a sealed box. Worked like a charm.

 

For a more permanent setup I would try a couple of peltiers and a recuperator (heat exchanger). Air flow should be: cold side - recuperator - hot side - drying area - recuperator - cold side.

[NeighborJ]

I didn't elaborate about it's uses, the idea behind the vacuum chamber is to also dry chemicals. Certain chemicals don't readily give up their moisture to air. Drying chems in the oven does not sit rite with me. While a condenser works removing moisture from the air it needs to be forced from the chems to get into the air.

Another use of the chamber would be to make rocket motors with oxidizers which are normally considered too hygroscopic for pyrotechnic use.

Edited August 18, 2016 by NeighborJ

[dagabu]

I use an old NEMA 12 box for pulling a vacuum, its 6x6x18 so there is lots of volume and a good size. The top and bottom do bow somewhat but I have a couple 2x2's I set in the box to hold them off in case I want the full 29".

 

Works great for wood preservation, epoxy and drying out desiccant as well. Bulkhead fittings (1/4" NPT) and a refrigeration gauge set to the vacuum pump is all I need. The seal that comes with the NEMA 12 box holds well and I can pump it down every 5 minutes for a complete dry in an hour or so.

 

A heating pad under the box works well to speed the process up as ice will form if pulling too deep too fast. I stop at 15" and wait for the pressure to rise to 5" before pulling again.

[Fulmen]

A vacuum chamber can be quite useful, but it's overkill for normal stars and pyro stuff. None of the comps and chems in common use are hygroscopic, nobody want's that hassle if they can avoid it. So your stars should dry just fine if you reduce the humidity a bit. Both freezing and expansion due to boiling or trapped air can happen with vacuum, but I can't say for sure as I haven't tried it. I'd be surprised if this hasn't been discussed in the past, so a search in the archives would be my first stop.

 

As for drying chems in the oven I see your point. Not all chemicals should ever be present in a kitchen, so unless you have a dedicated dryer it can be tricky. But I still thing something like a dehumidifier with a radiant heat source would be more useful for drying than a vacuum chamber. just my 2 cents.

[dagabu]

A vacuum chamber can be quite useful, but it's overkill for normal stars and pyro stuff. None of the comps and chems in common use are hygroscopic, nobody want's that hassle if they can avoid it. So your stars should dry just fine if you reduce the humidity a bit. Both freezing and expansion due to boiling or trapped air can happen with vacuum, but I can't say for sure as I haven't tried it. I'd be surprised if this hasn't been discussed in the past, so a search in the archives would be my first stop.

 

As for drying chems in the oven I see your point. Not all chemicals should ever be present in a kitchen, so unless you have a dedicated dryer it can be tricky. But I still thing something like a dehumidifier with a radiant heat source would be more useful for drying than a vacuum chamber. just my 2 cents.

 

There are a few that dry their stars this way, I use it on comets and chems, most of the stars I make are too numerous to drop into a vacuum chamber but with some that were "driven in", the vacuum dried out with little trouble.

 

I do challenge you on your view of no common chems being hygroscopic, my ruby red and metallic red both use Strontium Nitrate as do my AP red falling leaves, they become a real mess unless dried in an air-conditioned box or a vacuum. Sodium Nitrate as well as Sodium Benzoate are hygroscopic as well.

 

Also, keep in mind that pulling a vacuum can be just pulling 1/4", you dont have to pull a full vacuum and have expanding stars, a little will do well to draw out the water. Ice? Only if you pull heavy, keep it under 5" and you will not get ice to form in water laden comps. BUT! Evaporation will not happen quick enough when cold so get the temps up to 70°F or higher (100°F is about as high as I go) to speed it up.

 

Not good nor bad, just another tool in your expanding kit. Good luck and post your results.

[OldMarine]

Here's a thread on the subject:

http://www.amateurpyro.com/forums/topic/11050-vacuum-drying-chamber/?hl=vacuum

[NeighborJ]

Wow it wouldn'tp matter if I over wet my glitters if it only takes an hour to dry.

I was planning on using 12" .375 wall X65 steel pipe with a 150# flange and blind. I could make it as long as I'd need, perhaps 4'and make slide out hardware cloth trays. It would probably be a good idea to epoxy coat the inside. I could set up a timer for my pump and if I do that I could install a solenoid valve to break the vacuum. If I really want to get OCD about moisture I can rig up a nitrogen gauge to the solenoid.

Calcium nitrate, sodium nitrate and ammonpulver are some of the oxidisers I'd like to explore as fuels.

[dagabu]

Here's a thread on the subject:

http://www.amateurpyro.com/forums/topic/11050-vacuum-drying-chamber/?hl=vacuum

 

I stayed complete out of that one due to the postulating done by some that in the real world is udder nonsense. One thing I would like to point out is the price of a HVACR vacuum pump. $50.00 shipped from ebay. I bid on them sometimes to get them down to $35.00 or so for other hobbyists (layup projects) and find that IF you keep up on the oil changes, the motors will last about 200-300 hours.

[NeighborJ]

I've got two vacuum pumps from when I worked in hvac. After skimming thru OMs linc it occurred to me that the best method of controlling the pump would be the use of a thermister embedded in the stars connected to a PID controller. This controller would work a three way solenoid valve hooked in series to my pump. When the stars get too cold the vacuum line closes and breaks the vacuum in the chamber. The pump can run while the line is closed without hurting anything and when the stars come back up to temp the solenoid will cycle, pulling the vacuum back down.

[dagabu]

Sounds like a good plan. No need for a PID if you dont want to program it, a Stc-1000 will do the trick as well with a SCR.

[Fulmen]

Sure there are some hygroscopic chems around, but not that many that require extreme measures like vacuum. But if you need or want one either way then go for it.

As for control, I think it's wise to start with something simple until you know what you really need. You should be able to regulate the vacuum with two valves (one between bump and chamber and one venting the chamber to atmosphere), then try measuring the temp to see if the idea actually works. I would think that a pressure regulator would be more useful.

[NeighborJ]

The whole idea of regulating the vacuum stems from the need to control the temp. So why not just control the temp to begin with? I understand the relationship between pressure and temperature but due to the lagtime, temp would be far more accurate and faster, after all if I am able to pull a 5 micron vacuum without it freezing then I will. I do intend on using my refrigeration guages to hook up the pump any metering needed can be done there. And the PID controllers main function is to anticipate reaching the setpoint then take action before hand. I have a few spare PIDs, the only thing I'll still need to buy is the solenoid. I don't have a vacuum regulator.

I'm curious if the vacuum will be effective on sulfates.

[Fulmen]

If you already have the PID regulator then by all means go for it. If you choke the vacuum line you could perhaps just control the pump, that will eliminate the need for a solenoid.