The Forestry Forum

General Forestry => Drying and Processing => Topic started by: Crusarius on March 25, 2019, 12:35:50 PM

Title: Random thought for a solar kiln
Post by: Crusarius on March 25, 2019, 12:35:50 PM
So I had a very random thought on my way to work this morning. 

I want to build a solar kiln. 

I started wondering what would happen if I found a 6' diameter culvert pipe, painted it black and put vents and fans on each end of it. Then place it in a very sunny area.

Anybody have any thoughts how that may work? I would expect to be able to get some pretty high temperatures inside

If it doesn't work for drying wood maybe it will work for sterilizing?
Title: Re: Random thought for a solar kiln
Post by: GeneWengert-WoodDoc on March 26, 2019, 04:30:10 AM
You will get some heating, but the 50% of the pipe not exposed to sunlight will lose a lot of heat and so you will not have much heat for evaporation.  Also, the solar input will be the shadow that the pipe casts.  So the areas that are not getting perpendicularly close to perpendicular sunlight will also have a net lose of energy.
Title: Re: Random thought for a solar kiln
Post by: Southside on March 26, 2019, 07:41:39 AM
I think it will work great, for catching snakes.. :D
Title: Re: Random thought for a solar kiln
Post by: doc henderson on March 26, 2019, 07:52:31 AM
could make and underground shooting range/storm shelter.  So if I understand gene correctly, you have to be able to put heat in, and insulate or trap the heat inside.  to sterilize you could use a outdoor wood furnace but would need to insulate.  then the question is, is this the size you want and is it easy to load and unload.  do you have the pipe already?  I respect and relate to wanting to use things you have access too.  Creative Idea.
Title: Re: Random thought for a solar kiln
Post by: Crusarius on March 26, 2019, 07:59:08 AM
It was more of a curiosity question. I do not have the pipe but I started thinking I could probably get an old decommissioned pipe from the highway garage and fit small loads in it.

I mostly was thinking sterilization tube because of all the horror stories I hear about ppl buying bug infested wood.

This morning I was thinking about it a little more. (I need a shorter drive to work) :). But I could put the pipe up in the air and build a firebox and just run the exhaust from the fire box under the main pipe for supplemental heat.

The primary goal was sterilization, but then I got to thinking if I am going to sterilize it why wouldn't I also be able to use it to dry. I do wonder what kind of temperatures I could get in that pipe. Without supplemental heat.

What Gene says makes a ton of sense. anything that is not gaining in direct sun will be losing. That would definitely mess up the efficiency. I guess the trick would be proper orientation so the sun shoots down the length of the pipe.
Title: Re: Random thought for a solar kiln
Post by: doc henderson on March 26, 2019, 08:11:11 AM
You did say random thoughts.   :).  I think it could work. in fact you could orient it at a 45 angle sticking up out of the ground.  the back half could be insulated, the front ( facing the sun)  could be flat black.  If it is galvanized, it would slow the degrade. It would naturally draft like a chimney. but how would you load and unload that bad boy.  If you get free pipe, and have the equipment to handle and move the pipe, then your COO may nix it cause it does not look nice in the yard.   :(  could use sawdust as insulation if you can keep it dry.  I do not think the zinc oxide will get hot enough to give you "fume fever". 8)
Title: Re: Random thought for a solar kiln
Post by: WDH on March 26, 2019, 08:14:06 AM
If you go the firebox route, and it does not do what you want it to do drying wood, you could always cook a hog in it, or several ;D. 
Title: Re: Random thought for a solar kiln
Post by: Crusarius on March 26, 2019, 08:19:07 AM
If you go the firebox route, and it does not do what you want it to do drying wood, you could always cook a hog in it, or several ;D.  

The trick is getting my co-workers to come down.... :) wait what kind of hogs are you talking about? :)
Title: Re: Random thought for a solar kiln
Post by: Crusarius on March 26, 2019, 08:21:59 AM
Doc, thats not a bad idea. would not be hard to put it on a swivel stand. Would almost look like a giant cannon. :)

have it like a teeter totter. hinged in the center, flip it flat to load then rotate it up and allow convection to do its thing. The water would drop to the bottom and warm moist air out the top.
Title: Re: Random thought for a solar kiln
Post by: doc henderson on March 26, 2019, 08:22:25 AM
could insulate with straw or even sand if you can keep it dry.  A reflector on the back side could warm the back.  If it could move with the sun could be efficient.  so the problem becomes making free stuff work may cost more and not work as well as just building a solar kiln with traditional frame construction.  It is fun to think about, and maybe the next new thing.  I eat bacon. digin_2
Title: Re: Random thought for a solar kiln
Post by: Crusarius on March 26, 2019, 08:22:40 AM
When all else fails I could launch pumpkins out of it in the fall :)
Title: Re: Random thought for a solar kiln
Post by: Crusarius on March 26, 2019, 08:24:03 AM
I wonder if ii does not work how much vacuum I could put into a pipe like that and not have it collapse. Would not be hard to turn it into a vacuum kiln.
Title: Re: Random thought for a solar kiln
Post by: WDH on March 26, 2019, 08:25:22 AM
When all else fails I could launch pumpkins out of it in the fall :)
Or one of your co-workers :D. 
Title: Re: Random thought for a solar kiln
Post by: doc henderson on March 26, 2019, 08:30:11 AM
I am not sure if you have been watching too many, or have not watched enough old James Bond Movies.  The problem with vacuum is getting a pump big enough and sealing leaks in a container that can open and close.  vacuum effectively lowers the boiling point (evaporation) of liquids like water.  so a combo of heat and vacuum would be great.  and maybe a rotating disc on the back side could slice bread.   :D
Title: Re: Random thought for a solar kiln
Post by: Don P on March 26, 2019, 08:34:53 AM
Vacuum and a decommissioned pipe, uh-huh :D
Flue wrapped... hmm this is sounding more like a charcoal retort, which will sterilize the wood.
Title: Re: Random thought for a solar kiln
Post by: doc henderson on March 26, 2019, 08:39:07 AM
ok, so you need two diameters of pipe to create and inner and outer core (sounds like Austin powers baby) and insulate the gap between with saw dust.  stand it on end and have a rod attached to a round plate on the bottom and wood can be loaded in the top.  use a forced air outside wood furnace to heat the inside and can vent moisture form the circulating air.  when done use a skid steer to pull out the plate or a basket with the wood.  If this works you will have to find a smaller person to imitate your every move and laugh when ever you do.   smiley_sun 
Title: Re: Random thought for a solar kiln
Post by: Crusarius on March 26, 2019, 08:45:47 AM
doc, you crack me up :) I already have a mini me. bet I can get him to copy me. He is in that stage.

Don, it'll be fine. What could really go wrong? :)

By decommissioned pipe I was thinking one that got damaged from the excavator while being moved. not old rotten one.

And from what I understand you would only need 7" of vacuum to lower the boiling point to an effective level.

Title: Re: Random thought for a solar kiln
Post by: doc henderson on March 26, 2019, 08:58:55 AM
Hey Cru.  (like gru from despicable me)  any vacuum will lower the bp or increase evaporation.  Vacuum just like air pressure can result in violent catastrophic failure.  Also the strength and integrity of the spiral corrugated pipe would be decreased by any bend or deformation of the structure.  Now I just sucked the air out of the room.   :D  I assume you have an old ac refridge vacuum pump to try.  HF sell a vacuum pump that runs on compressed air.  Prob. not 100% duty cycle.  The trouble as eluded to is creating a door that will seal and not collapse under the vacuum if you can generate it.
Title: Re: Random thought for a solar kiln
Post by: Crusarius on March 26, 2019, 09:18:39 AM
never thought about an old refrigerator for a vacuum pump. Figured I would test the waters with the HF pump. Unless I could find a good price on a different one.

I am hoping with my fab and engineering skills I could make it stay round. 7" of vacuum is not that much. however the surface area it will be acting on is a concern. anywhere there are deformities in the pipe will definitely have to be addressed with additional support. It would be very easy to reinforce.
Title: Re: Random thought for a solar kiln
Post by: Southside on March 26, 2019, 09:43:45 AM
I think by the time you did all of that you could cobble up a solar kiln and not worry about if it's going to work and just how well it works.

Not to mention eliminating the chance that you end up on a no-fly list along with a line of black SUV's following you everywhere as some satellite picked up a WMD / ICBM being built in your backyard.   :D
Title: Re: Random thought for a solar kiln
Post by: Crusarius on March 26, 2019, 09:48:51 AM
southside your probably right. But I did get a good laugh out of that :) I will paint it like a p-51 mustang with the teeth on the front :)

Of course we go back to the primary goal. Sanitized lumber, so I do not have bugs when I sell it. But side product being able to use it to also dry lumber.
Title: Re: Random thought for a solar kiln
Post by: GeneWengert-WoodDoc on March 26, 2019, 01:04:58 PM
I think part of the issue here is trying to make a kiln and a solar collector out of the same material at the same time. Try making each unit separately.  

It is easy to build an insulated, vapor-proof box for the kiln.  Include vents, fans, etc.  maybe include a control system.  Make sure that the insulation and all other material can withstand 160 F or so.

Then, take a pipe, or other shape or materials, and make the solar collector...black absorber with two layers of clear material to trap the heat with insulated back side...and then duct the heat into a kiln.  

Once this is done, you could consider putting the two units together as I did with the VT kiln...the south-facing roof of the kiln is the collector.
Title: Re: Random thought for a solar kiln
Post by: Crusarius on March 26, 2019, 01:36:19 PM
That is definitely a good idea. Wonder how efficient I could make it. Living in upstate NY I have a hard time believing I will be able to get 150f for 24 hours in a solar kiln.
Title: Re: Random thought for a solar kiln
Post by: doc henderson on March 26, 2019, 08:51:26 PM
You cannot do high heat for 24 hours in a solar kiln, i guess alaska in the summer?  but you can dry it in the kiln.  As it dries, the wood can increase temp more easily.  The heat treat is usually at the end of drying.  after it is dry, you're only heating wood mostly, when wet, you also have to heat the water.  i think the goal is to get the wood up to 136 by having the kiln at 150/160.  so thinner wood may not take 24 hours.  nice thread, I think we all had fun and discussed some theoretical ideas.  Thanks Gents.
Title: Re: Random thought for a solar kiln
Post by: GeneWengert-WoodDoc on March 26, 2019, 09:59:26 PM
When you combine collector and kiln, you will lose heat at night and reach 100% RH which will relieve stress or casehardening.  The kiln cools because the collector loses a lot of heat at night.  You could  get 150 F at night if you used a small auxiliary heater and covered the collector with insulation.

When you have two separate units...kiln and same size collector...you can get a little hotter as heat losses can be lower, overall, but fail to get 100% RH at night to relieve stress.  Plus the separate units cost more.  With a separate  collector, you can easily make the collector larger than the roof size of the kiln...10 BF per sq. Ft. of collector.
Title: Re: Random thought for a solar kiln
Post by: tacks Y on March 27, 2019, 03:45:27 AM
This talk of vacuum? There is a you tube with a tanker unloading that forgot to open a hatch. Did not last long.
Title: Re: Random thought for a solar kiln
Post by: Crusarius on March 27, 2019, 07:43:54 AM
That be pretty kool to see.

Well I do think we have all learned a little about my crazy random thought. Be nice to actually try it out and see how it works. What really sux is I have all sorts of data acquisition stuff here at work. all stuff that would work great for monitoring and learning but I can;t take it home :(

And in order to buy all of it I am looking at about 30k. So maybe now is a good time to learn arduino or raspberry pi. And start setting stuff up and doing real data acquisition. I like testing.