Building a Vacuum Kiln: The Challenge of Applying Heat to Wood

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SUMMARY

The discussion centers on the challenges of applying heat to wood in a vacuum kiln, specifically at a pressure of 29.9 Hg. Users suggest that heat mats should be used between layers of wood, as traditional methods like light bulbs and fans may not effectively convey heat in a near-perfect vacuum. The consensus is that heat radiation from bulbs is essential, and a powerful bulb is necessary to counteract the cooling effect of evaporating water in the wood. Additionally, maintaining low pressure requires a robust vacuum pump to manage steam buildup within the chamber.

PREREQUISITES
  • Understanding of vacuum technology and pressure measurements
  • Knowledge of heat transfer principles, specifically heat radiation
  • Familiarity with vacuum pumps and their operation
  • Basic concepts of wood drying processes in low-pressure environments
NEXT STEPS
  • Research the operation and specifications of heat mats for vacuum kilns
  • Learn about the design and functionality of vacuum pumps suitable for wood drying
  • Explore the principles of heat radiation and its application in vacuum environments
  • Investigate the mechanics of freeze drying and its relevance to vacuum kiln processes
USEFUL FOR

Woodworkers, kiln operators, and engineers interested in optimizing wood drying techniques using vacuum technology.

Jupiter'sTwin
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I'm building a vacuum kiln to dry wood and have some questions that may be rhetoric, since I am fairly certain I know the answers. I don't see a need to describe the project in great detail so I'll stick with the basics.

The biggest challenge is applying heat to the wood. I believe I will have to use heat matts between each layer of wood because in a near perfect vacuum of 29.9 Hg a light bulb and fan will not work will it? I only ask because within the wood community some people have built a vacuum kiln and suggest that this works. But with no atmospheric pressure to speak of, how can heat from a bulb be conveyed within the chamber?

The bulb will burn of course, and the heat has to go somewhere I suppose, so does it convect to be equally distributed within the chamber? And if it does, is the minute amount of air left in the chamber (I am at 600' MSL) enough to be a carrier of heat when a fan is running?
 
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Jupiter'sTwin said:
within the wood community some people have built a vacuum kiln and suggest that this works. But with no atmospheric pressure to speak of, how can heat from a bulb be conveyed within the chamber?
The heat from the bulb will be conveyed by heat radiation. So the wood must be exposed.

When the water in the wood evaporates ( boils at low pressure ) the wood will be cooled, so a powerful bulb is needed to keep up temperature.

Also the chamber will be filled by steam, so you must have a powerful vacuum pump to maintain a low pressure.

Mayby you should read how a "freeze dryer" works. ( Not sure about the name in english ).
 
Hesch said:
The heat from the bulb will be conveyed by heat radiation. So the wood must be exposed.

When the water in the wood evaporates ( boils at low pressure ) the wood will be cooled, so a powerful bulb is needed to keep up temperature.

Also the chamber will be filled by steam, so you must have a powerful vacuum pump to maintain a low pressure.

Mayby you should read how a "freeze dryer" works. ( Not sure about the name in english ).

Thank you for your . . . . . rhetorical answer? (Not sure if if we are speaking english)