Optimizing Airflow in a Solar Kiln

Ideal airflow in a kiln varies by wood species. Here are some rules of thumb. December 31, 2012

I'm planning to build a 600 BF solar kiln. I would like to know how much air flow I will need. Is there a rule for CFM per BF?

Forum Responses
(Sawing and Drying Forum)
From Professor Gene Wengert, forum technical advisor:
What species, thickness and initial MC? This will determine the best fpm.

If 200 fpm is desired, then the cfm is 200 fpm x (sticker thickness in inches / 12) x length of lumber x number of sticker openings or layers. Then add 50% more to account for leaks and inefficiency.

From the original questioner:
I will be drying 4/4 cherry, red oak, poplar and walnut mostly. The moisture content may vary from load to load from 20% to 50%. I may even start from green on occasion. How will air flow needs differ from specie to specie and from low MC to higher MC? What conditions would require the 200 fpm that was used in the formula as far as specie and MC?

From Professor Gene Wengert, forum technical advisor:
Species that dry quickly or that need fast drying for best, white color need higher air flow at higher MCs to achieve that color. Under 40% MC, all of the ones listed will be okay at 100 fpm. The poplar will need 200 fpm at higher MCs and even a few more fpm would be good.

From contributor C:
So is the discoloring on lighter woods solely the presence of bacteria or mildew stain that the higher air flow inhibits?

From Professor Gene Wengert, forum technical advisor:
No. Loss of color in drying can be fungal or chemical oxidation.

From contributor C:
When wood changes color from exposure to the sun, what is the correct term to associate with that? Or is this still oxidation?

From Professor Gene Wengert, forum technical advisor:
Yes, oxidation enhanced by UV light. In fact, if you use a strong oxidizer, like ammonia, on the wood, it will age instantly.