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


Baker Products

ECHO-Bearcat

iDRY Wood Lumber Vacuum Drying for everyon

Baltic Abrasives Technologies Nyle Kiln Dry Systems




Author Topic: Jim Fuller's ideas  (Read 7753 times)

0 Members and 1 Guest are viewing this topic.

Offline Den Socling

  • Senior Member x2
  • *****
  • Posts: 4217
  • Age: 68
  • Location: Jersey Shore, Pennsylvania
  • Gender: Male
  • just wondering
    • Share Post
Jim Fuller's ideas
« on: March 25, 2004, 04:50:36 PM »
I'm trying to start a new thread from what was posted in the thread about banding.

Den

Hey Jim,

You have an audience. And at this forum, no know-it-all is going to shoot you down. I may play the devil's advocate at times but there is no guru here.

Den

Unless you are using vacume drying you can not avoid casehardening.  It occurs whether you dry slow or fast - air-drying, dh, solar or conventional.  Wood only dries from the outside-in..  When you dry slowly,air-drying, solar-drying and poorly controlled kiln drying, you risk more damage and warpage than if you  dry fast with good control.  Naturally, drying fast with poor control you are demanding a disaster

Interesting JimF. What you are saying seems to go against conventional wisdom but makes sense.

Welcome to the forum and please continue to give us your insight!

Actually it is not against conventional wisdom.  With the advent of the energy crisis the solar kiln came into fashion.  And to sell that idea the conventional wisdom was pushed out the door.  Now we hear the altered wisdom.
To support the idea of drying fast, I have a patent for monitoring/control of wood drying that reduces the drying time by more than 35%.  While do so the drying stresses are actually reduced in the end. And you end up with brighter and more defect free lumber.

JimF
Do you have a resource (publication of results) that supports the "altered wisdom" ?
 

You are presenting some interesting (teasing?) ideas, that could use some additional support. Is the patent idea available on the market? Did you do vacuum drying testing?

Thanks for filling out the bio.  

Maybe too many questions!
 

Offline Den Socling

  • Senior Member x2
  • *****
  • Posts: 4217
  • Age: 68
  • Location: Jersey Shore, Pennsylvania
  • Gender: Male
  • just wondering
    • Share Post
Re: Jim Fuller's ideas
« Reply #1 on: March 25, 2004, 04:53:22 PM »
JimF.
Please tell us more.
Can your patented idea be used in vacuum drying?

Hey Jim,

You have an audience. And at this forum, no know-it-all is going to shoot you down. I may play the devil's advocate at times but there is no guru here.

Den

Thanks for the interests in my ideas.
Beenthere,
no it is not on the market yet.  It is easy to have a great idea.  It is another thing to get financial backing.  Venture capitlaists only come on the scene when the inventor is filing for bankrupcy, after all the hard work of development is done.  And regional economic development committees are only interested in flashy high tech stuff like biotechs because it looks good on their records, not improvement of  communities .
I'm told to find a doctor or airline pilot.  They have lots of money and will go for anything a good salesman puts in front of them.  Anyone know of any doctors or airline pilots looking to invest?
Den,
I like devil's advocates.  They help bring out the fine details of a discussion

you are controlling properly and are drying fast you can not over dry the shell.  That is controled by the EMC in the kiln and is what equalization is partially for.
The "altered wisdom" is air-drying is gentle to the wood - Myth 1.  Solar-drying is different from conventional drying - Myth 2. To name some.
 If you air dry white pine or maple, for example, the center of the stack is likely to get blue stain or sticker stain.  If you air-dry oak, you are sure to get large surface checks because of the up and down trends of the EMC.  The up and down trends of the EMC only makes the surface checks worse, that have developed from the lumber being exposed to the sun or breeze on the green chain.
Solar drying is claimed to be diferent than conventional and is gentle because of the EMC rises at night.  However, in conventional kilns the airflow is switched about avery 6 hours; causing the entering air side to become the exiting air side.  The causes the EMC to go up and down at the sides of the stacks.  The cyclic gain and loss of moisture in the wood at these points can be measured and the shrinkage and swelling can be measure as a result.  Because in a conventional kiln this can be controlled to some extent but is not in a solar kiln, the wood is exposed to more sever conditions in the solar kiln.  The surface checks will be extended further into the board than in a conventional kiln.  The some of the same people that promote solar-drying say never to start the kiln drying by adding steam to bring the EMC to set point because of the surface check problem.  


have never had the oportunity to try the new method out on vacuum drying.  As has been mentioned here there are numerous methods to vacuum dry.  They all produce important differences in terms of control and stress development.  In a past post I generalized vacuum drying as not producing casehardening.  It depends on the method.  If you use conductive heat source, like heat blankets or hot water pipes,  you still produce cashardening.  After the initial pull of a vacuum, the water still only evaporates from a liquid boundary line.  The heat can only travel through the surface of the wood to the water; heating up the water nearest to the surface first.
 Radio frequency while enters the dry portion of the wood and heats up the water inside it mostly only heats up the water nearest the surafce of the wood.  Therefore it produces casehardening.  However, there is one company that claims the frequency that there equipment uses penetrates the wet wood more evenly and heats up the water more evenly. I have not seen the data for that to know enough about it to comment on it.
The intermitantly heated method that has been mention here alot is another species all together and is much more complitcated.  I have not sat down to study how things occur within it yet.
Speaking on vacuum drying.  There is one method that intrigues me for very small operators.  It encloses the wood in a plastic bag, in essences and immerses it in hot water.  Then a vacuum is pull on the bag.  This is a inexpensive way to provide continuous heating.  Admittedly in practice it is for small chunks or a small number of boards, but it is a method most people can fabricate and operate.  It is patented and a company is working on getting it on the market.

Offline Den Socling

  • Senior Member x2
  • *****
  • Posts: 4217
  • Age: 68
  • Location: Jersey Shore, Pennsylvania
  • Gender: Male
  • just wondering
    • Share Post
Re: Jim Fuller's ideas
« Reply #2 on: March 25, 2004, 04:57:08 PM »
jimF.
What if one was to pre-heat in a vac kiln before he pulls a vacuume?Would this not bring the whole piece of wood up to the same temp?

yes, and the whole piece should loss water some what evenly.  But not all the water.  So the concern is after the initial vacuum pull, how is it heated?  With intermittant heating system mentioned here, it seems like this would happen each time, but with repeated occurances things can become complicated quickly.  Which is why I hold back my opinion in this ins

To stir the pot some, what are the concerns during drying - in all systems of drying?

jimF.
With square drying in a vac kiln the concern was honey comb and surface cracks.In flooring blanks and lumber the concern is with stress and un even moisture content.
Also in vac drying some people complain about the sap wood being to bright and the MC being to low.
There was a problem with bow in vac dried squares but that is an easy problem to fix.

I may also add that in the last 2 weeks I found that stress is not that big of a deal in vac dried lumber.

A lot of copy and paste. hope it works and please continue questions to jim from here.
Den

Offline DanG

  • Senior Member x2
  • *****
  • Posts: 13489
  • Age: 72
  • Location: Chattahoochee, Florida USA
  • Gender: Male
  • DanG, The Official ForestryForum Cussword
    • Share Post
Re: Jim Fuller's ideas
« Reply #3 on: March 25, 2004, 07:31:30 PM »
JimF, I just want to welcome you to the ForestryForum, and encourage you to continue sharing your ideas and expertise with us. Maybe, someday, I will learn enough to ask an intelligent question. :D   Seriously, though, there are a lot of us who handle lumber on a regular basis, guided only by what we read here, and what we learn through our own experimentation. I just want you to know that the input from folks like you, Den, Don Lewis, and all the others that are operating kilns, is appreciated. Sometimes these posts don't get much response, but they are read by many who just don't have anything to add to the discourse.

Thanks for being here.
"I don't feel like an old man.  I feel like a young man who has something wrong with him."  Dick Cavett
"Beat not thy sword into a plowshare, rather beat the sword of thine enemy into a plowshare."

Offline old3dogg

  • Senior Member
  • ****
  • Posts: 646
  • Age: 52
  • Location: Falls Creek PA.
  • Gender: Male
  • You can twist perception but reality won't budge.
    • Share Post
Re: Jim Fuller's ideas
« Reply #4 on: March 26, 2004, 02:05:02 AM »
DanG.
I have been reading a lot of post on all of the forums here and have not run across a question yet that was not intelligent.
I have been over in the sawmilling forum getting a ton of info.
Im thinking of setting up my own little mill and a kiln or two.
Who knows?Maybe even my very own vacuum kiln ;)
The really cool thing about this forum is no matter what the question everyone offers their insite,gives good information and doesnt treat anyone like they are dumb.

Offline Ga_Boy

  • Senior Member x2
  • *****
  • Posts: 1014
  • Age: 57
  • Location: Purlear, NC
  • Gender: Male
  • Been rode hard and hung up wet; more than once.
    • Share Post
Re: Jim Fuller's ideas
« Reply #5 on: March 26, 2004, 05:03:48 AM »
Good move Den.
 
By the way, did thar feller with the questions about the WM vac 1K ever give you a call?

Jim,

I am starting up a Kiln operation and agree with the other postes here that your insights and ideas are valued.  Thank you for putting your thoughts to the banding stirng which created this one.  I'm looking forward to reading and contrubuting where/when I can.
10 Acers in the Blue Ridge Mountains

Offline jimF

  • Full Member x2
  • ***
  • Posts: 188
  • Location: VA
  • Gender: Male
  • Go for it!
    • Share Post
Re: Jim Fuller's ideas
« Reply #6 on: March 26, 2004, 05:21:19 AM »
Old3dogg,
As I have said I have not used a vacuum kiln, how do you avoid bow?  What do you do to avoid honeycomb?
The stanardl test for stress is the prong test.  It is a critical how you cut the test.  The KOM by USFS gives no details on how to do it.  It shows but does not say to cut a 1/3 out in the center and it does not specify what the result should be.  Just the difference of cutting the prongs 1/3 or 1/4 of the board thickness will given completely different results.  The KOM also does not mention the length of the prongs.  This is also important.  It takes very accurate methods to compare two different boards.Usually stressed boards can be used in most cases and not show any problems.  It is when the boards are used in critical situations that problems show up.

Offline jimF

  • Full Member x2
  • ***
  • Posts: 188
  • Location: VA
  • Gender: Male
  • Go for it!
    • Share Post
references
« Reply #7 on: March 26, 2004, 05:34:41 AM »
The three papers that directly support the patent are in Drying Technology: 18(4&5):1023-1031, 18(6):1349-1359, and and and (don't have the numbers for the third now, I think 18(10)).  The work started from three other papers in the same journal in some of the same issues.  These were on drying stresses and the test.  The first patent was 5,873,182 which can be down loaded from the patent office at www.uspto.gov.

Offline jimF

  • Full Member x2
  • ***
  • Posts: 188
  • Location: VA
  • Gender: Male
  • Go for it!
    • Share Post
question
« Reply #8 on: March 26, 2004, 05:40:03 AM »
If you follow the IMPRESSIONS given in books and conversation and seminars your answer will be off.  The key to the question is "during drying".  The answer: honeycomb, surface checks, stain, mold,etc, but not moisture content.  I'll let this boil some and I'll get to work here at the office.

Offline jimF

  • Full Member x2
  • ***
  • Posts: 188
  • Location: VA
  • Gender: Male
  • Go for it!
    • Share Post
Re: Jim Fuller's ideas
« Reply #9 on: March 26, 2004, 07:37:20 AM »
When MC is not a concern during drying and is not directly related to the other concerns why do we monitor it during drying?

Offline old3dogg

  • Senior Member
  • ****
  • Posts: 646
  • Age: 52
  • Location: Falls Creek PA.
  • Gender: Male
  • You can twist perception but reality won't budge.
    • Share Post
Re: Jim Fuller's ideas
« Reply #10 on: March 26, 2004, 10:46:39 AM »
JimF.
I control both bow and honey comb with schedules.
DB,WB,and chamber pressure.
Not all bow is avoidable.We still get some but I havent seen a piece of honycombed wood in over 12 years.
I dont watch MC's while Im drying.I stick meter 10 samples from 10 different areas of the load when it "looks" dry.
All of my schedules are based on time.
Now Im talking about drying squares here not lumber.
Thanks for the info on the stress test.I have never had to worry about it before with squares but I will have to learn with vac drying lumber.

Offline jimF

  • Full Member x2
  • ***
  • Posts: 188
  • Location: VA
  • Gender: Male
  • Go for it!
    • Share Post
Re: Jim Fuller's ideas
« Reply #11 on: March 30, 2004, 05:20:56 AM »
The strategies for monitor and control of processes is to look at the limiting concern.  Since, moisture content is not a concern which of the following concerns are the limiting ones? honeycomb,  surface checks,  stain, progress, mold

Offline Den Socling

  • Senior Member x2
  • *****
  • Posts: 4217
  • Age: 68
  • Location: Jersey Shore, Pennsylvania
  • Gender: Male
  • just wondering
    • Share Post
Re: Jim Fuller's ideas
« Reply #12 on: March 30, 2004, 06:08:54 AM »
Mike,

I do believe that it has been less than 12 years since I've seen honeycomb in BWP's squares. There used to be a lot, at times. It was caused by stress in your squares.

Jim,

The limiting concern is moisture gradient. You can have too little or too much. One or the other causes all drying defects.

Den

Offline old3dogg

  • Senior Member
  • ****
  • Posts: 646
  • Age: 52
  • Location: Falls Creek PA.
  • Gender: Male
  • You can twist perception but reality won't budge.
    • Share Post
Re: Jim Fuller's ideas
« Reply #13 on: March 30, 2004, 06:13:26 AM »
You are right Den.I guess its only been 8 years.

Offline jimF

  • Full Member x2
  • ***
  • Posts: 188
  • Location: VA
  • Gender: Male
  • Go for it!
    • Share Post
Re: Jim Fuller's ideas
« Reply #14 on: March 30, 2004, 07:36:49 AM »
no, moisture gradient is in the equation but is not directly related to the limiting factor.

Offline Den Socling

  • Senior Member x2
  • *****
  • Posts: 4217
  • Age: 68
  • Location: Jersey Shore, Pennsylvania
  • Gender: Male
  • just wondering
    • Share Post
Re: Jim Fuller's ideas
« Reply #15 on: March 30, 2004, 07:55:34 AM »
I'll have to disagree  ;) and I'd like to know what you are leading to but I have to make a service call DanG it. Be back tomorrow.  8)

Offline jimF

  • Full Member x2
  • ***
  • Posts: 188
  • Location: VA
  • Gender: Male
  • Go for it!
    • Share Post
Re: Jim Fuller's ideas
« Reply #16 on: March 30, 2004, 10:01:33 AM »
Sure, as wood looses water it tries to shrink and produces stresses.  But wood reacts with visco, visco-elastic and mechano-sorptive strains.  Some research has been preformed in this country and alot in Europe on predicting stresses as it relates to water loss.  No one has achieved significant results.  You can not predict drying stresses by moisture content, moiisture loss nor moisture gradient.  But I do agree with your line of logic that drying stresses is the limiting factor (which I asume is why you pick moisture gradient as the limiting factor). and many people think that moisture gradient is directly related to it.  John Hill tried to come up with a control system of measuring the moisture gradient and did not get very far.

Offline old3dogg

  • Senior Member
  • ****
  • Posts: 646
  • Age: 52
  • Location: Falls Creek PA.
  • Gender: Male
  • You can twist perception but reality won't budge.
    • Share Post
Re: Jim Fuller's ideas
« Reply #17 on: March 30, 2004, 10:22:49 AM »
jimF.
I feel that in vac drying wood,most stress is caused by heat and how fast you evaporate water from the surface of the wood.
Drying at a lower temp and keeping the temp around the load close to the temp of the wood helps in keeping stress and other defects to a minuim.
I also feel that no matter how you dry wood you are going to see some stress and some defects.
Den.
Im not leading to nothing.When you left us I just found a different way of drying in our vac kilns.Gee man!Are you thinking Im trying to pick a fight here?
I dont beat up old guys! :D
Again im just kidding.Age is a state of mind not a state of being.
Jeff B.
PLEASE PUT A SPELL CHECKER ON THIS FORUM FOR US FOLKS THAT CANT TYPE.
Mike.



Offline jimF

  • Full Member x2
  • ***
  • Posts: 188
  • Location: VA
  • Gender: Male
  • Go for it!
    • Share Post
Re: Jim Fuller's ideas
« Reply #18 on: March 30, 2004, 11:11:28 AM »
"how fast you evaporate water from the surface of the wood".  Now is not the theory of vacuum drying that all the wood through out is under vacuum at the same time and that the water evaporates all at once?  If it is evaporated in the center how can it evaporate again on the surface?
"keeping the temp around the load close to the temp of the wood "The wood surfaceis at or above the WB.  For heat to be transfered the DB has to be greater than the WB.  The greater the difference the more heat transfered.  (This assumes no true vacuum. Otherwise no heat is tranfered by conduction from air.)
"in vac drying wood,most stress is caused by heat "  Heat softens the wood if the EMC is kept constant otherwise when it does reduces the EMC too much you increase the MC loss rate and/or too low of MC on the surface..
I've only seen a vacuum kiln once and never used one, but wood does not change behavior just because the energy source is different. :
By the way I like your quote Old3dogg

Offline Tom

  • In Memoriam
  • *
  • Posts: 25839
  • Age: 76
  • Location: Jacksonville, Florida
  • Gender: Male
    • Share Post
    • Toms Saw
Re: Jim Fuller's ideas
« Reply #19 on: March 30, 2004, 11:27:53 AM »
Mike,
Most of us use iespell for a spell checker.  It's better'n we ever had on the forum and it's free.  When you can get something this good for free why bother shopping for some more software.  :D

Go to www.iespell.com and install the checker.  

It works in any update window on IE (maybe more?)  and is actuated by putting your cursor in the window and right clicking.

......and it's free......it's free!...it's free! :D


they're coming to take me away, hey hey, hee hee
extinct

Offline old3dogg

  • Senior Member
  • ****
  • Posts: 646
  • Age: 52
  • Location: Falls Creek PA.
  • Gender: Male
  • You can twist perception but reality won't budge.
    • Share Post
Re: Jim Fuller's ideas
« Reply #20 on: March 30, 2004, 11:30:10 AM »
In a vacuum the water is moved from the center of wood to the surface.How fast you evaporate from the surface dictates how fast you can move water from the surface.
So in vac drying:Slow at the begining,a little faster toward the middle and after the MC is under 20% it really doesnt matter.

Offline old3dogg

  • Senior Member
  • ****
  • Posts: 646
  • Age: 52
  • Location: Falls Creek PA.
  • Gender: Male
  • You can twist perception but reality won't budge.
    • Share Post
Re: Jim Fuller's ideas
« Reply #21 on: March 30, 2004, 11:32:27 AM »
Thanks Tom.
I ill ceeck it ouy! :D

Offline Den Socling

  • Senior Member x2
  • *****
  • Posts: 4217
  • Age: 68
  • Location: Jersey Shore, Pennsylvania
  • Gender: Male
  • just wondering
    • Share Post
Re: Jim Fuller's ideas
« Reply #22 on: March 30, 2004, 04:20:02 PM »
I'm home again.

In vacuum drying, evaporation is not limited to the surface. The better the heat transfer technique, the deeper into the wood the drying goes. If you use too much heat in an effort to force heat transfer, you create the stress that Mike is talking about.

Mike,

If you apply what I taught you years ago (I know it's hard with the control systems you have), your old kilns could dry as almost as fast as my new kilns. The answer is pressure control.

Jim,

The pressure control consist of water vapor pressure as set by water temperature and the gradient to chamber pressure. With the method we use (patent pending), we use the gradient to minimize moisture gradient. It's very effective.

Den

Offline jimF

  • Full Member x2
  • ***
  • Posts: 188
  • Location: VA
  • Gender: Male
  • Go for it!
    • Share Post
Re: Jim Fuller's ideas
« Reply #23 on: March 31, 2004, 09:30:48 AM »
Den,
whats your patent application number?

Offline Den Socling

  • Senior Member x2
  • *****
  • Posts: 4217
  • Age: 68
  • Location: Jersey Shore, Pennsylvania
  • Gender: Male
  • just wondering
    • Share Post
Re: Jim Fuller's ideas
« Reply #24 on: March 31, 2004, 09:55:32 AM »
Jim,
Our Do-all girl (Kelley) is doing the paper work from where I left off some time ago. I'll let you know when I know. There's been an exchange with the patent office but I'm not involved.  :D
Den

Offline jimF

  • Full Member x2
  • ***
  • Posts: 188
  • Location: VA
  • Gender: Male
  • Go for it!
    • Share Post
Re: Jim Fuller's ideas
« Reply #25 on: April 02, 2004, 01:08:39 PM »
Den,
Are you  saying there is a pressure gradient in the void of the chamber? or pressure gradient  in the wood?  How are you measuring it?
If you are applying heat continuously by platens,you are only evaporating water from the liqiud boundary  surface, not from the surface of the wood nor throughout the whole peice of wood.  It is just like at atmospheric pressure just at a different pressure.  Heat transfer is the same not matter what the pressure is..

Offline Den Socling

  • Senior Member x2
  • *****
  • Posts: 4217
  • Age: 68
  • Location: Jersey Shore, Pennsylvania
  • Gender: Male
  • just wondering
    • Share Post
Re: Jim Fuller's ideas
« Reply #26 on: April 02, 2004, 01:35:58 PM »
Jim,

The gradient is between the vapor pressure of the water (that is set by the temperature of the water) and the chamber pressure.

We're applying heat continuously but there's more than one way to skin the cat.

I can set the boiling point with the chamber pressure. I can put an RTD in the core and verify that the change in boiling point occurs at the core.

Den

Offline old3dogg

  • Senior Member
  • ****
  • Posts: 646
  • Age: 52
  • Location: Falls Creek PA.
  • Gender: Male
  • You can twist perception but reality won't budge.
    • Share Post
Re: Jim Fuller's ideas
« Reply #27 on: April 02, 2004, 02:36:08 PM »
I would have to agree with Den on this one.I have seen the core temp of squares dried in a vacuum the same as the shell temp.I feel that if you can get the core and shell temp even during drying then you can dry without honeycomb and stress.
Heck!I have even seen this done in an old RF/V kiln!

Offline jimF

  • Full Member x2
  • ***
  • Posts: 188
  • Location: VA
  • Gender: Male
  • Go for it!
    • Share Post
Re: Jim Fuller's ideas
« Reply #28 on: April 02, 2004, 05:34:28 PM »
Den,
It sounds like what you are calling pressure gradient is the partial vapor pressure in the chamber compared to the total pressure of the chamber.  Is that what you are talking about?  This would tell you the percent vapor in the total vapor/gas composite.  This is a measure of humidity, though not relative humidity.
By applying heat to the surface the heat has no other way to get into the wood other than going through it.  For this to happen there must be a temperature gradient thrugh the wood.  Heat energy only travels from high temperature to low temperature.  No matter how small of a temperture difference there is, it still has to be there for heat to be transfered.

How are you measureing the temperature?  How do you put the RTD in the wood?  How do you seal it up?  If you drill a hole in the wood, the bottom of the hole is the outside of the wood.  No matter how deep the hole is.  It has direct exposure to the chamber pressure.  The hole would have to be absolutely completely sealed up with the RTD in it for the RTD to accurately record temperature. That is almost impossible to do.  Wax is too brittle or is not able to adhere to wood well enough.  Most polymeric material will not adhere to wet wood well enough to seal.
It's like when my wife checks her baking with a thermometer, continues to bake it and then rechecks it in the same hole.  That hole had become the surface of the cake becuase it is exposed to the oven air.  It always "seems " to cook faster than when she rechecks in a different spot.  Because that new spot was not exposed to the oven air between the two times.  Or consider ...the inside of a balloon becomes the outside of the balloon when you pop it.  The internal pressure becomes the same as the external pressure and collpases.
Old3doff,
If the frequency of the RF in a RF?VAC kiln is just right, the energy seems not to totally absorbed at the water boundary layer, but some of it is able to penetrate deeper.  This enables some RF/VAC kilns to heat more evenly.  However, the energy is still going from a high energy state to a low energy state,  RF tube to the interior of the wood.  Since the dry outside portion of the wood does not have water in it to absorb the energy, it does not heat up.
Boy, this discussion gets the old noodle going. jim

Offline Den Socling

  • Senior Member x2
  • *****
  • Posts: 4217
  • Age: 68
  • Location: Jersey Shore, Pennsylvania
  • Gender: Male
  • just wondering
    • Share Post
Re: Jim Fuller's ideas
« Reply #29 on: April 02, 2004, 07:17:32 PM »
Yep. if you obey the gas laws, it partial vapor pressure.

If you press in an RTD with a plastic sleeve, you get a tight fit. Especially when the wood begins to shrink. And vapor is the conveyance.

The frequency of an RF oscillator is rarely 'just right' because the kiln charge is part of the circuit and it changes as MC goes down.

Offline jimF

  • Full Member x2
  • ***
  • Posts: 188
  • Location: VA
  • Gender: Male
  • Go for it!
    • Share Post
Re: Jim Fuller's ideas
« Reply #30 on: April 03, 2004, 06:27:26 AM »
I agree with your assertion that the wood is part of the circuit and rarely is the frequency right.  That is why I part "seems" in my post.  This is what a campany claims and I have no way of proving or disporving it.  It is common to get burned araes just below the surface.  This is where and when the liquid boundary layer is slightly below the surface and all the energy is absorbed there.  The heat can not be transfered quick enough to the center or surface, even in a vacuum system that is conntrolled by vapor is the conveyance.
Have you tested your plastic sleeve with a pressure probe inserted?  I have a hard time getting a consistant seal with compression fittings on tubes let alone in wood.

Offline old3dogg

  • Senior Member
  • ****
  • Posts: 646
  • Age: 52
  • Location: Falls Creek PA.
  • Gender: Male
  • You can twist perception but reality won't budge.
    • Share Post
Re: Jim Fuller's ideas
« Reply #31 on: April 03, 2004, 10:56:53 AM »
jimF.
Lets say I put a load of wood in a vac kiln.I set the heat at 100 and the WB at 100 and then I pull the CP.I get down to lets say 40torr.The water at the surface of the wood cant go anywhere because of the WB being at the same temp as the temp of the wood wont let it evaporate.
This I feel will bring the whole load to the same temp.Core and shell.
Just a thought.

Offline jimF

  • Full Member x2
  • ***
  • Posts: 188
  • Location: VA
  • Gender: Male
  • Go for it!
    • Share Post
Re: Jim Fuller's ideas
« Reply #32 on: April 05, 2004, 07:15:07 AM »
At 40 torr and 100/100 how much water are you producing /BDFT/hr?

Offline jimF

  • Full Member x2
  • ***
  • Posts: 188
  • Location: VA
  • Gender: Male
  • Go for it!
    • Share Post
Re: Jim Fuller's ideas
« Reply #33 on: April 06, 2004, 06:12:04 AM »
old3dogg,
Where do you measure the wetbulb temp and what temperature are the heating platens?

Offline jimF

  • Full Member x2
  • ***
  • Posts: 188
  • Location: VA
  • Gender: Male
  • Go for it!
    • Share Post
Re: Jim Fuller's ideas
« Reply #34 on: April 09, 2004, 12:58:17 PM »
I never did get to the conclusion I was pointing to.  Being drying stresses are the limiting factor in drying, which causes surface checks and honeycomb, and moisture content nor gradient is a good measure of drying stresses, why measure moisture content?  (Stain and mold all dictate to dry very quickly)  What should be monitored is something that indicates drying stress - strain fits the bill.  Strain is directly related to stress.  But what stress are you looking for?  Often what is called stress reversal is mentioned when discussing drying stresses and is one reason in standard schedules a change in settings is dictated.   But what you really are looking for is a reduction in stress, not a complete reversal.  This point I call peak stress and the idea was first mentioned by a person called Reitz.  He said it occurs approximately when an 1/8 of the original MC is loss but an axact figure can not be given because it is not directly related to moisture content.  This is the point in the standard schedules that the first change in settings is dictated.  If one measures strain you can determine when peak stress occurs and increase the drying rate at that point and safely avoid and degrade.

Offline Den Socling

  • Senior Member x2
  • *****
  • Posts: 4217
  • Age: 68
  • Location: Jersey Shore, Pennsylvania
  • Gender: Male
  • just wondering
    • Share Post
Re: Jim Fuller's ideas
« Reply #35 on: April 09, 2004, 03:14:17 PM »
Jim,

I see what you're saying but I think the stress is caused by the moisture gradient. Maybe I'm oversimplyfying but, with a change in water volume, cells shrink. If all cells don't change volume at about the same rate, some shrink more than others. If too many shrink too much, stress is created. Too much stress and you end up with kiln degrade.

In conventional drying, the surface has to be dryer than the core to get the water out of the core. Therefore, you have to create some stress. So, as you say, you can measure the stress to control drying. But isn't the stress caused by MC gradient?

Den

Offline jimF

  • Full Member x2
  • ***
  • Posts: 188
  • Location: VA
  • Gender: Male
  • Go for it!
    • Share Post
Re: Jim Fuller's ideas
« Reply #36 on: April 10, 2004, 01:06:40 PM »
Yes, the stress is caused by any moisture gradient and with TOO much stress you end up with kiln degrade (surface checks, honeycomb and collpase).  But but, drying wood does not act as a simple mildly stretched steel spring where it returns to the original position when the force is released.  That is called elastic strain, think rubberband. Similar to a steel spring when it is stretched  too far, the spring remains stretched, as does wood during drying.  Other types of strain occur during drying.  Viscous strain and visco-elastic strain occur over time during drying - drying takes time.  Another strain called mechano-sorptive strain occurs when a material loses moisture and becomes stretched.  I know these are big technical terms but the point is that wood does not behave simply like a new car spring during drying.  It is because of these different types of strains that occur during drying that you can not use moisture gradient.  We  do not know the values of these strains to be able to predict stress level when a so and so moisture gradient occurs.  More than a few people have performed many experiments to try to get these values and have not succeeded yet.  A few people have tried to use moisture gradient for control and have not gotten very far. Neither moisture content nor moisture gradient tells you enough to accurately control drying.  Current drying practices are just a guesstimate of what is going on.
It is because of these various types of strains that you end up with less stress after conditioning if you push the wood to the limit but not damage it by producing surface checks.  Many people say that kiln dried wood is cooked and cuts differently than air-dried wood.  Don't confuse this concern with pushing the wood to the limit.  Realize a commercial kiln is very large. They can be 20 feet high.  The top portions of the kiln receive air that is hotter than the wood on the bottom and where the temperature sensors are.  The difference can be as much as 8F.  When the EMC at the bottom is 4%, an increase in temperature at the top by 8F can reduce the EMC down to 1-1.5%  This is one of the sources of kiln dried wood being of possible lower quality than air-dried wood.
jimF



Offline jimF

  • Full Member x2
  • ***
  • Posts: 188
  • Location: VA
  • Gender: Male
  • Go for it!
    • Share Post
Re: Jim Fuller's ideas
« Reply #37 on: April 10, 2004, 01:18:39 PM »
Den,
You say "In conventional drying..." and that "you can skin a cat more than one way" to get heat into the wood.in vacuum kilns.  I'm still not convinced vacuum drying is totally different than conventional.  Yes, it occurs faster but.  All energy and mass transfer requires a temperature or pressure difference.  It's been stated here that the chamber temperature, wood surface temperture, and center of the wood are all the same temperature.  That the pressure in the chamber and in the center of the wood are all the same pressure.  Can you explain how you can skin the cat differently? ie getting energy into the center of the wood.
jimF
PS Is everyone that visits this board vacuum driers or is this just a good drying board?

Offline Den Socling

  • Senior Member x2
  • *****
  • Posts: 4217
  • Age: 68
  • Location: Jersey Shore, Pennsylvania
  • Gender: Male
  • just wondering
    • Share Post
Re: Jim Fuller's ideas
« Reply #38 on: April 10, 2004, 02:25:48 PM »
Jim,

I don't think that anybody who participates in this forum uses a vac kiln except Mike and I.

I don't know if my explanation of other ways to skin the ol' cat would have any effect on me trying to patent cat skinnin' or not but I think I'll keep it private, for now. It's the same stuff I've been expounding for years.

Den

Offline stevareno

  • member
  • *
  • Posts: 41
    • Share Post
Re: Jim Fuller's ideas
« Reply #39 on: April 11, 2004, 10:12:56 AM »
Jim,
I've been reading this thread with interest.  We just ordered a vacuum kiln from Dennis so I'm trying to absorb everything I can get my eyes on.   Thanks for sharing some good information!

Steve


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
Jim Fuller

Started by Den Socling on Drying and Processing

32 Replies
3914 Views
Last post November 25, 2012, 02:11:35 PM
by jimF
xx
I am in need of ideas

Started by Ernie on General Board

9 Replies
1161 Views
Last post September 14, 2007, 07:58:01 PM
by stonebroke
xx
Looking for ideas

Started by Hydroax on Forestry and Logging

16 Replies
3590 Views
Last post January 03, 2010, 01:27:18 PM
by Hydroax
xx
Any Ideas ?

Started by Autocar on Ask The Forester

2 Replies
765 Views
Last post April 14, 2012, 07:58:55 PM
by Autocar
 


Powered by EzPortal