Originally Posted by
Richard Coers
For some reason, someone always brings up the sun and earth when a discussion of vacuum kilns starts. I'll let a professor rebut your comment;
From Professor Gene Wengert, forum technical advisor:
The sun heats due to emitted radiation, but in outer space it only heats the surface of what the energy hits. Without air, there would not be heating within the stack.You will find over-drying and under-drying from piece to piece and within an individual piece. Contributor D's dryer addresses this issue, but others I have seen and used did not except for Vacuum-Therm.
The oscillation between vacuum and atmospheric must be done carefully indeed. Humidity at atmospheric is important.
https://www.woodweb.com/knowledge_ba...rinciples.html
Not trying to start a debate, but this professor agrees that radiant heating does work in a vacuum.
And he does raise an interesting point. Without a medium to move heat through convection (and conduction) radiant heating would not work well with a snack of lumber, as the pieces within the pile would essentially shielded by the outer layer and not heated.
But for a slab this would be different, since the surface of the slab would be heated, and the slab itself would heat to the center by conduction, similar to the way stacks of boards are heated in a normal kiln.
This may be the reason the person referred to initially may be finding the vacuum kiln very useful for drying slabs, which might not be the same with stacks of boards.
Too much to do...Not enough time...life is too short!