Hello from Carrboro

Status
Not open for further replies.

thebruce

New User
Andy
Quick new member intro......thebruce...retired (not dead yet).
I joined this group in hopes of finding others who might be interested in building a small Radio Frequency/Vacuum (RF/V) kiln for locally sawn materials. I am preparing to build a portable dryer which, at this stage, means assembling electronic components for a low frequency, open wire dipole exciter. Very interested in blunting the RF homebrew learning curve so anyone interested in knowledge sharing/transfer in the EE segment can expect transparent knowledge sharing/transfer and shop building services.
Absolutely not looking for business partners but, as any casual observer will soon recognize, I am seduced by the advantages/capabilities such a dryer would allow (primarily interested in heavy timber conditioning).
Anyone having similar interest please PM me for a chat.
Thanks
Andy
 

Raymond

Raymond
Staff member
Corporate Member
Welcome aboard, Andy. I haven't heard of this type of kiln drying before so it will be interesting to see what comes up on this topic.
 

thebruce

New User
Andy
Welcome aboard, Andy. I haven't heard of this type of kiln drying before so it will be interesting to see what comes up on this topic.

Thanks Raymond,
If you are interested in more than the wisdom of the crowds please see a pretty interesting/well written article freely available on the web"
“High-Frequency Electrical Current for Drying of Wood – Historical Perspectives”
While several years old, this article might help frame the discussion.
I began using RF/V dried hard maple several years ago. Being the curious type, I followed up.
Enjoy,
Andy
 

CDPeters

Master of None
Chris
Welcome to the group Andy.

I must admit that I know next to nothing about RF/V drying, but my "other" hobby being Amateur Radio, any mention of RF tends to get my attention!

Just a couple of points of curiosity. (1) Can you quantify "low frequency"? (2) How much output power is required?

My assumption is that the "dipole exciter" would be a 2 plate arrangement with a "ground" plate on the bottom and a "hot" plate on the top, lumber load sandwiched between. If this is the case, that arrangement would offer a very high capacitive reactance load to the amplifier, complicating the design.
 

thebruce

New User
Andy
Thanks for the welcome CDPeters, hereinafter CDP with your permission.

Yes...I too have been fascinated by HAM operations as well.

Absolutely right on all fronts...effectively a big capacitor. For my purposes, I'm shooting for a range below 100Mhz and around 10Kw...which would respect experimental/scientific frequencies and roughly match some of my existing equipment.

I suspected there would be radio guys in this forum...thanks for the reply.

Andy
 

Michael Mathews

Michael
Corporate Member
Hey Andy, I'm close by off Eubanks Rd. I'd love to see your tinkering some time, but alas, I still have to do the nasty 4 letter work...W.O.R.K.!!! I also happen to be a BSEE, but mostly industrial controls.
 

thebruce

New User
Andy
Hey Michael,
I've been immersed in reading on the fundamental concepts of amplification.
As a get-it-done kind of guy, the circuitry I am trying to assemble should be substantially simpler than radio from a signal quality standpoint...more brute force than finesse...if you will.
The origins of RF/V drying are quite old... around WWII. I was captivated by the referenced article...plenty more where that came from.
The next logical step in this (my) journey is to consolidate learnings into tinkering...so all suggestions appreciated/heeded.
I'm hoping this will be an adventure and I'm prepared to absorb trial and error.
But it is also a bit of a mission...having been actively involved in the forest products industry most of my life, I have learned the pace of the industry's now much needed evolution has been unnecessarily slow and poorly focused...not to mention down-right wasteful. I could digress here but suffice to say gaping holes have developed in our sustainable supply chain. So I admit I have an adz to grind as well.
And there are problems with radiation shielding...like a microwave. Any sources of information in this arena would also be appreciated...don't want to cook anyone.
The initial goal is to site saw/de-water (not dry) a couple of m3 of green timbers (a medium large tree) to just beyond FSP (think 20-25% MC) in a very short timeframe (think 5-7 days) as a pre-processing step to reduce weight (and phyto-sanitize) prior to shipping to final use/processing destination.
On the EE front...
As I appreciate it, it is common such low frequency oscillations sustain a feedback loop as a part of their amplification schema. I am following a breadcrumb trail and if you are interested I can lay it out for you...if that's what you mean by seeing tinkering. Otherwise, my shop space is in Carrboro and I would welcome your visit when you can get loose.
Thanks again,
Andy
 

golfdad

Co-director of Outreach
Dirk
Corporate Member
welcome to thesawdust pile Andy. Sounds like an interesting project. Please do keep us updated
 

danmart77

Dan
Corporate Member
Andy this sounds very interesting. I would love to hear more from you as you chip away on this endeavor.

Dan
 

CDPeters

Master of None
Chris
And there are problems with radiation shielding...like a microwave. Any sources of information in this arena would also be appreciated...don't want to cook anyone.

Andy - I assume (from skimming the paper you linked) that by "low frequency" you will be operating at an RF frequency below 100 MHz. If this is the case, yes, you will need to conduct an RF safety evaluation, which basically calculates field power densities at various distances - but the possible negative effects are not as worrisome as would be at microwave frequencies.

More importantly, unless you hold an FCC experimental license, you will be operating under Part 15 rules (I think). Without be-laboring the regulations, it boils down to - you cannot cause harmful interference to licensed radio services. There is ALOT of licensed radio service between 1 and 100 MHz, and RF generated (radiated) in this range can propagate over great distances, even worldwide below about 30 MHz. So - you need to be aware of this and take great pains to be sure your "dipole exciter" (basically an antenna!) is shielded so that it does not radiate beyond the confines of the device.

Not trying to throw a wet blanket, but you do need to be aware so you don't wind up with some very irate neighbors, or worse with an FCC pink slip!
 

scsmith42

New User
Scott Smith
Hi Andy, welcome to NCWW and best of success to your with your project.

Of the four kiln types used for drying lumber (conventional, dehumidification solar and vacuum), RF Vacuum kilns (and vacuum kilns in general) are the least common. Vacuum kilns are primarily used for specialty application such as baseball bat blanks, thick lumber or lumber prone to stain such as holly. As I'm sure that you are aware, vacuum is what does the actual drying of the lumber; RF provides a heat source within the lumber in lieu of the heat blankets or plates that are commonly used in vacuum kilns.

I still kick myself for not buying a large RF Vacuum kiln setup out of Washington State back in 2009. It was auctioned off as part of a bankrupty sale and was sold for scrap! It would have cost me close to 100K to dismantle, transport and reassemble it in NC (it was a VERY LARGE kiln), and at the time I was not comfortable enough with the direction of the economy to commit the funds. In 20/20 hindsight, I should have made the investment...

From a fabrication perspective, did you have a targeted size kiln chamber in terms of width, height and length?

Den Socling at PC Specialties in PA is one of the resident vacuum kiln experts on the east coast. Den manufacturers several models of vacuum kilns, but to my knowledge none of them utilize RF as the heat source. He has been quite generous with his time before in advising hobbiests with vacuum kiln building; you might want to reach out to him and introduce yourself.

A forum that Den frequents is the Forestry Forum (www.forestryforum.com). They have a very active participation on their drying forum and both Den and well known kiln expert Gene Wengert are usually active daily in answering questions and providing advice.

What's your fabrication background and what did you retire from? Are you planning to fabricate your own kiln chamber or obtain something already built?

Regards,

Scott
 

thebruce

New User
Andy
Right Again CDP,

Among the earliest references I sought out were those related to safety. As it happens, a standing ungrounded human adult absorbs RF energy at a maximum rate when the frequency of the RF radiation is in the range of about 70 MHz. I am most actively considering 14 to 41 Mhz because of the depth of literature in that range...so little difference from maximum in the "Specific Absorption Rate" or "SAR at those frequencies. The published allowable SAR value for the whole body is 4 watts per kilogram (partial body exposures vary accordingly) but owing to this"resonance" phenomenon exposure rates are given a 10x safety factor at the published allowable. I suppose every accident is preceded with intention to take as little risk as possible...I am no different.

Most predecessor RF/V kilns have been monolithic pressure vessels replete with thick metal walls and rated openings for manipulation of atmospheric pressures at great capital cost. The proposed kiln utilizes bagging for negative pressures only and the enclosure is designed to be portable (rather than site specific). Among the many advantages of smaller scale is that effective, grounded copper enclosures can be economically fabricated for wavelengths in the 7 – 12 meter range on a small scale.
At this point I’m pretty sure this kiln will pose no more of a threat to the electromagnetic peace than medical equipment.
That being said, I am not as familiar with Part 5 rules as I could be...so thanks for the reference.

Andy
 

thebruce

New User
Andy
Hey Scott,

Ohhh...The one that got away...I bought into the oil patch downturn in the late 80’s...it was a scary ride for a while but it came out all right. I reckon a monolithic kiln would be about the same as drilling rigs and equipment.

I appreciate the link. I’m pretty sure the capital cost of a pressure vessel would cause me to turn tail on this idea. My primary interest in this phase is de-watering green timbers whose dimensions resist conventional drying economics. I have air-dried timbers most of my life and I can tell you that inventory cycle costs will make a fellow question his sanity in the 2[SUP]nd[/SUP] half of the turnaround every time. I also know that the incredible cost of structural timbers never really seemed enough to me from either side of the transaction.
To be absolutely accurate, timbers are dried as a result of both of the inputs. The vacuum input lowers the boiling point of the moisture and the dipole heating effect (the plates) ensure mass transfer, certainly above the fibre saturation point (FSP). In timbers, there is no substitute for homogeneity of moisture content as internal stress is your number 1 enemy...useful timbers are presumed straight. A lot of research has been conducted on how moisture moves through wood and the stresses induced...but all you really need to do is cut a few green timbers and stack them up for posterity to see it in action. I am seduced with the time frames and oddly, the whole phyto-sanitation thing. I think the industry needs to pay a lot more careful attention to “bugs and fungi”...another lesson learned from carrying wood inventory.
I loosely throw around the “couple of m3” when I describe this kiln because I have not gotten a good feel for how effective a 10Kw-40Mhz RF field might be. Like I said...it’s a time thing. I’m still loving on the whole preposterous notion of operating a kiln and never again having to handle another sticker...now in my mind...that is SEXY...if you will pardon the expression.

Thanks for the welcome extended.
 

thebruce

New User
Andy
CDP, Frank and all others interested...call to consult.
I have to admit that it got my attention that this kiln might be considered/classified as an antenna...but as best I can tell from the literature it is unlikely I will need a license to build it. On the other hand, the silver lining is that I had not adequately planned for the lead time for Special Temporary Authority (STA) or Experimental Licensing System (ELS). I'm guessing I'm a long way from the 90-120 day trigger but things tend to snowball toward the end of hard fought projects.
So the consult is whether anyone can think of any more regulatory got-chas.
and...thanks to CDP for the heads-up.
Andy
 
Status
Not open for further replies.

Our Sponsors

LATEST FOR SALE LISTINGS

Top