The Forestry Forum is sponsored in part by:

iDRY Vacuum Kilns


Forestry Forum
Sponsored by:


TimberKing Sawmills



Toll Free 1-800-582-0470

LogRite Tools



Norwood Industries Inc.




Your source for Portable Sawmills, Edgers, Resaws, Sharpeners, Setters, Bandsaw Blades and Sawmill Parts

EZ Boardwalk Sawmills. More Saw For Less Money!

STIHLDealers.com sponsored by Northeast STIHL


Woodland Sawmills

Peterson Swingmills

 KASCO SharpTech WoodMaxx Blades

Turbosawmill

Sawmill Exchange

Michigan Firewood, your BRUTE FORCE Authorized Dealer

FARMA


Council Tool

Baker Products

ECHO-Bearcat

iDRY Wood Lumber Vacuum Drying for everyon

Baltic Abrasives Technologies Nyle Kiln Dry Systems




Author Topic: Vacuum Drying in a Bag  (Read 19095 times)

0 Members and 1 Guest are viewing this topic.

Offline Glen Evans

  • member
  • *
  • Posts: 16
    • Share Post
Vacuum Drying in a Bag
« on: February 09, 2005, 12:53:00 PM »
It seems like the major inhibiting factor for the home hobbyist is the vacuum chamber.  Am I crazy or could a person place wet lumber in vacuum bags place the vacuum bag in a heated enclosure and then draw a vacuum on the bag?  A simple electrical moisture sensor could tell you when you've reached your desired MC.  Seems to me you could actually have several bags attached to one pump, stacked with a generous air space to allow heat to move around the bags in the heated enclosure.  I know air isn't a great conductor but still.  My question is how large a vacuum pump would the home hobbyist who wanted to do maybe 300 bd ft at a time need?  Comments anyone?

Offline Den Socling

  • Senior Member x2
  • *****
  • Posts: 4217
  • Age: 68
  • Location: Jersey Shore, Pennsylvania
  • Gender: Male
  • just wondering
    • Share Post
Re: Vacuum Drying in a Bag
« Reply #1 on: February 09, 2005, 03:06:54 PM »
What you do is put the wood in a bag and then put the bag in a tub of hot water. It can work for one piece at a time.

Offline Glen Evans

  • member
  • *
  • Posts: 16
    • Share Post
Re: Vacuum Drying in a Bag
« Reply #2 on: February 09, 2005, 03:21:55 PM »
Thanks for the reply Den.  I've read a ton of your posts and learned alot from them.  Back to the bag idea for a minute--any reason you couldn't place multiple boards side by side in the bag?  If yes, any reason why you couldn't place multiple bags in the water fed off of the same pump?  If yes what other mediums other than air could be considered--how about sand with heating cables imbedded??  Why not hot air as a medium--too inefficient.

I guess I'm just trying to dumb down the whole thing by eliminating the pressure vessel and I'd rather not replace it with a watertight tub if a knock-down insulated box could do the job.

Offline Ianab

  • Administrator
  • *****
  • Posts: 12996
  • Age: 56
  • Location: Stratford , New Zealand
  • Gender: Male
  • Marmite on toast is a real breakfast
    • Share Post
Re: Vacuum Drying in a Bag
« Reply #3 on: February 09, 2005, 04:19:15 PM »
Hi Glen

Interesting questions
I think the one piece at a time is because the heat has to be conducted thru the bag from the water to the wood. If several pieces are in the bag the middle ones would not be heated properly. Side by side could work I guess so long as they can be kept flat. Several bags from one pump should not be a problem, just need a bigger pump I guess.

I'm not sure about pump size, if the pump is too small it wont be able to pull enough vacuum and drying will take longer, but it should work.

I think the water is probably the most efficient way of getting the heat into the wood, sand and air are reasonably good insulators. The commercial kilns seem to use metal plates to transfer heat to the wood so that may be an option too.
 
If you do some experiments let us know what happens. Lots of interest in this sort of technology.

Cheers

Ian
Weekend warrior, Peterson JP test pilot, Dolmar 7900 and Stihl MS310 saws and  the usual collection of power tools :)

Offline Larry

  • Senior Member x2
  • *****
  • Posts: 5859
  • Age: 70
  • Location: NW Arkansas
  • Gender: Male
    • Share Post
Re: Vacuum Drying in a Bag
« Reply #4 on: February 09, 2005, 05:41:11 PM »
Ok you guys...I have been sperminting with this vacuum drying stuff on the sly with another guy.  Few successes but mostly dead ends and nothing to write home about.  Were trying to come up with a way to dry walnut crotches with minimum degrade.  About ready to think it is not possible due to the convoluted grain...but were going to chase it a while more.

Been trying a electric blanket for our heat source...think we need a electric blanket running on 220 though.  :D

The links are all geared towards veneering...but should be the same process for drying.

For parts and simple tutorial go here  http://www.joewoodworker.com/veneering/welcome.htm

For more parts and stuff go here  http://www.vacupress.com/
Larry, making useful and beautiful things out of the most environmental friendly material on the planet.

We need to insure our customers understand the importance of our craft.

Offline Den Socling

  • Senior Member x2
  • *****
  • Posts: 4217
  • Age: 68
  • Location: Jersey Shore, Pennsylvania
  • Gender: Male
  • just wondering
    • Share Post
Re: Vacuum Drying in a Bag
« Reply #5 on: February 09, 2005, 05:43:13 PM »
Ian is right about the heat transfer through multiple layers. There are ways to move heat in a low pressure atmosphere (vacuum) but they involve complex and expensive methods.

Water would be the best medium for heat transfer (for the hobbyist). I helped a guy do this a couple years ago and, if I remember correctly, he built a wood box and lined it with plastic. He wanted to dry a big flitch for a bar top, if I remember correctly.

A compressor from a refrigerator could pull the vacuum but it wouldn't last long. It wouldn't take much of a pump.

Offline Buzz-sawyer

  • Senior Member x2
  • *****
  • Posts: 2210
  • Location: Brighton (S/W) Illinois
  • Gender: Male
  • To see it is to saw it....
    • Share Post
Re: Vacuum Drying in a Bag
« Reply #6 on: February 09, 2005, 06:16:24 PM »
I use refrigerator compressors for both vac and compressed air.......I use the vac to produce refined vegitable oil under vacuum and have a friend that has used one several times a week several hours at a time, for 2 years.....it really depends on how the thing lubricates itself, and how ya care for it ;) :)
    HEAR THAT BLADE SING!

Offline Den Socling

  • Senior Member x2
  • *****
  • Posts: 4217
  • Age: 68
  • Location: Jersey Shore, Pennsylvania
  • Gender: Male
  • just wondering
    • Share Post
Re: Vacuum Drying in a Bag
« Reply #7 on: February 09, 2005, 08:29:35 PM »
The problem when drying wood is that it will pull water vapor.

Offline GaS

  • member
  • *
  • Posts: 32
  • Age: 118
  • Location: Pennsylvania
  • Gender: Male
  • this space for rent
    • Share Post
    • PC Specialties
Re: Vacuum Drying in a Bag
« Reply #8 on: February 09, 2005, 10:01:21 PM »
To clarify :

The compressor will suck water vapor into its innards...typically water contaminated with junk from the wood you are drying (as if regular water wasn't bad enough for its inner workings).




Offline Buzz-sawyer

  • Senior Member x2
  • *****
  • Posts: 2210
  • Location: Brighton (S/W) Illinois
  • Gender: Male
  • To see it is to saw it....
    • Share Post
Re: Vacuum Drying in a Bag
« Reply #9 on: February 09, 2005, 10:03:57 PM »
We use them to remove water and methanol. For biodiesel production.

You are right Den as a rule they dont last long and take a while to draw down

These pumps only last a few months (@ 200 litres per week of biodiesel production)But if you arent drawing vapor/chemicals over them they last a bit :)
    HEAR THAT BLADE SING!

Offline Glen Evans

  • member
  • *
  • Posts: 16
    • Share Post
Re: Vacuum Drying in a Bag
« Reply #10 on: February 10, 2005, 09:19:05 AM »
Thanks for all the great comments guys.  I hadn't thought of making the tub with a liner.  That would allow me to stick with the knock down idea.  With respect to the pump and water degrade is it a stupid question to ask if you can't filter out the the water vapour, in-line, a head of the pump?  I know the volume of water is much greater but I'm thinking along compressed air line terminology...

Offline Den Socling

  • Senior Member x2
  • *****
  • Posts: 4217
  • Age: 68
  • Location: Jersey Shore, Pennsylvania
  • Gender: Male
  • just wondering
    • Share Post
Re: Vacuum Drying in a Bag
« Reply #11 on: February 10, 2005, 10:53:31 AM »
You should take out the water before it gets to the pump. Set up a condenser. We use shell & tube, single pass heat exchangers mounted vertically with the pump connected to the top and the kiln (or bag) connected to the bottom.

Offline Glen Evans

  • member
  • *
  • Posts: 16
    • Share Post
Re: Vacuum Drying in a Bag
« Reply #12 on: February 10, 2005, 01:07:38 PM »
Thanks Den, I'm doing some digging on the web now to see how to plumb that.  As an alternative would I be able to pull enough of a vacuum with a venturi valve connected to my air compressor, (5 hp 6 cfm @ 90 psi) and effectively blow the water out with the evacuated air??

Offline Glen Evans

  • member
  • *
  • Posts: 16
    • Share Post
Re: Vacuum Drying in a Bag
« Reply #13 on: February 10, 2005, 01:32:51 PM »
Den,

Can you elaborate on the set up for condensor and heat exchanger you recommend please.  I'm not familiar with "shell and tube" and so on.

Glen

Offline Ironwood

  • Senior Member x2
  • *****
  • Posts: 4551
  • Age: 51
  • Location: Near Pittsburgh,Pa
  • Gender: Male
  • I need to edit my profile!
    • Share Post
    • http://www.branchandburl.com
Re: Vacuum Drying in a Bag
« Reply #14 on: February 10, 2005, 02:04:34 PM »
Well, as am sure Den will tell you it is a rather complex process. I have a 9000lb wood oven, vaccum, and steam chamber. It was constructed with the thought of using it to dry round stock with the bark on. Envision Old Hickory funiture, the problem in the rustic furniture industry is how to dry the wood before the bugs get to it. I have never been a volume rustic builder but the idea was berthed many years ago before my busness evolved into custom one off creations. The "pig" as we affectionately refer to the beast was constructed by a friend with several 12' "drop" pieces or heavy walled 36" and 30" pipe from huge cantilievered outdoor advertising signs. I have yet to hook up the water jacket to a boiler, which is the entire outside of the tube.
I simply use the water jacket as a flue to heat the chamber as a wood oven.
from a wood burner below.

   I researched quite a bit and the authorities seem to be PC Specialties and several other custom vaccum kiln guys around the country, including Fred Lamb down at Virginia Tech. Fred tends to know all the ins and outs an actually encouraged me to seek Gov. grants avalible at the time. Sounds like some great projects for you retired  guys. Anyway the devil is in the heat tranfer issue and "cycling" the thing with vaccum. The wood web drying archive has some fairly invovled discussions on the science.  :P :P Reid
There is no scarcity of opportunity to make a living at what you love to do, there is only scarcity of resolve to make it happen.- Wayne Dyer

Offline Den Socling

  • Senior Member x2
  • *****
  • Posts: 4217
  • Age: 68
  • Location: Jersey Shore, Pennsylvania
  • Gender: Male
  • just wondering
    • Share Post
Re: Vacuum Drying in a Bag
« Reply #15 on: February 10, 2005, 05:10:46 PM »
Glen,

I don't think a venturi will move the volume unless it's big and uses a large volume of air. I use little venturis on suction cups to lift our heating plates. They use only 0.74CFM but, even at that low volume, .74 x 60 minutes x 24 hours = a lot of air.

Shell and tubes have a bundle of tubes surrounded by a shell. The shell side, in my case, has cold water circulating through it. The vapor is pulled into the tube side where it is condensed and drops into a tank. One of the guys I've helped with a DIY sloped a pair of long copper pipes up the side of his chamber. One pipe is inside the other. Cold water is pumped through the outer pipe and warm vapor is pulled into the inner pipe.

Den

Offline Larry

  • Senior Member x2
  • *****
  • Posts: 5859
  • Age: 70
  • Location: NW Arkansas
  • Gender: Male
    • Share Post
Re: Vacuum Drying in a Bag
« Reply #16 on: February 10, 2005, 05:42:04 PM »
Glen,
We are working with the venturi valve from joewoodworker...5 hp compressor.  Not ideal but does work for a bag.

Reid has the right idea when he said

"Anyway the devil is in the heat tranfer issue and "cycling" the thing with vaccum."



Larry, making useful and beautiful things out of the most environmental friendly material on the planet.

We need to insure our customers understand the importance of our craft.

Offline Glen Evans

  • member
  • *
  • Posts: 16
    • Share Post
Re: Vacuum Drying in a Bag
« Reply #17 on: February 11, 2005, 10:09:49 AM »
Thanks Guys,

The lights are starting to go on!  Given that I live in Ottawa, Canada keeping that chilling water cold shouldn't be a problem for at least half of the year!  I'm assuming that the condensate exits through some kind of valve after the heat exchanger/ before the vacuum pump.  Do you have to worry about any kind of additional filter infront of the pump?

Offline GaS

  • member
  • *
  • Posts: 32
  • Age: 118
  • Location: Pennsylvania
  • Gender: Male
  • this space for rent
    • Share Post
    • PC Specialties
Re: Vacuum Drying in a Bag
« Reply #18 on: February 11, 2005, 08:00:34 PM »
You can do some manual condensate dump with two three valves and a tank.  Put the tank low so that water drains down.  When it fills, close the valve which leads back to the vacuum.  Open two other valves, one on top to bleed vacuum and on one bottom to drain the water.

Offline isimitibiti

  • member
  • *
  • Posts: 12
  • Age: 50
  • Location: new york
  • Gender: Male
    • Share Post
Re: Vacuum Drying in a Bag
« Reply #19 on: February 11, 2005, 08:30:09 PM »
hi
special thanks to denis and garret at pc specialties.
your help is unexpected and appreciated.
i have been experimenting with drying in bag.
im am half way through the first real life and size prototype of kiln.

ive gone through the heated tank idea and while this is probabbly the best heat transfer,
it is also tough to keep an even and constant temperature in a giant tank.
ive done the electric blanket with some results, but it was kind of ugly and just seemed llike a fire
hazard. im right now using a simple heated 2" insulation board box with an electric heater inside.
i have a thermo coupler in the core, on the surface and in the box. heated is controlled by the
core temp. also ive a probe for monitoring MC. im pulling about 29"hg.
im getting water!!!!! so this is the start. i was worried the heated air chamber would not transfer well.
it really is working fine. i dont think there is need for the water tank, ive also keeping some buckets of water
in the box to keep it humid to help tranfer heat to the vinyl. all three temps will fluctuate, but there seems to be no problem keeping the core and surface of the slab at a reasonablely stable temp. im running at 105-110F for the core, 100-115 for the surface and 100-140F for the chamber. temperatures vary as the thermostat is controlled
by the core temp whic has a lag time to reheat (its set for 110) the other temps stay within these ranges as the system runs itself. this seems reasonble, seem to be working. yesterday it seemed to stop working as well.
i shut it off and let it acclimate, then it seemed to spew more water. im installing a timer to run discontinuous.
this shoudl help to even the drying. im drying 12/4 lumber. walnut. biggest problem im haveing is the water through the pump. 1/2 horse kinney kc8, ive been changing the oil daily, its a mess but of course i have no collection chamber. tomorrow im running the pre pump out-pipe through a chest freezer in a flexibel copper coil then putting
a 2" copper pipe "tank" that i can install a motorized valve to empty when the pump stops for the down cycle.
this should work, itll hold more than ill produce in a seveeral hour pump cycle. and the chest freezer should be an adequate cool down through 50' of copper. then ill run the out put of the pump into the freeqer to capture any
other vapors i migh miss for measurments sake of exactly how much water im removing.
im convinced this is a reasonble DIY method. of course itll take some experimenting. but i believe
i have enough control over the variables that seem to be crucial. next is developing some sort of schedule.
but im most impresed that the heated box seems to keep the wood temp where its needed to work.
(by the chart i have water vaporizes in 29"hg at 80 degrees, if so this system should work.) i havent tried it that low, maybe im jusst excited to see the water come out. ill try that next, its in an overnight down cycle right now for 100F. well see what it does in the am.

T




making furniture


Share via delicious Share via digg Share via facebook Share via linkedin Share via pinterest Share via reddit Share via stumble Share via tumblr Share via twitter

xx
Vacuum Drying Shortcourse

Started by VTwood on Drying and Processing

6 Replies
1112 Views
Last post December 06, 2014, 09:23:22 AM
by boardmaker
xx
vacuum drying lumber

Started by c44u on Drying and Processing

9 Replies
2097 Views
Last post July 02, 2005, 02:07:00 PM
by c44u
xx
vacuum drying a single crotch?

Started by Dan_Shade on Drying and Processing

27 Replies
5040 Views
Last post September 10, 2008, 09:03:27 PM
by Dan_Shade
xx
Contact method of vacuum drying?

Started by serg on Drying and Processing

2 Replies
992 Views
Last post September 11, 2005, 12:24:10 PM
by serg
 


Powered by EzPortal