No measurable airflow through my stack in Nyle L53 kiln

[customsawyer]

Blackhawk in your picture it looks like you have some lumber that is twice as thick as the rest of the lumber. That is one thing that I try to avoid doing. Either the thicker lumber won't get dried enough or the thinner will end up a little to dry. One thing a kiln will do, is have you planning your kiln loads as you are sawing. It will also teach you how to saw better lumber if you pay it enough attention. You are where most of us have been. I very much enjoyed the learning phase of the kiln and I still am.

[blackhawk]

I installed shrouds on the intake side of all 4 fans like I showed in my sketch in Reply #13.  I cut a hole behind each one on the horizontal shelf with roughly the same square inch area as the round fan.  I also put a 45° angle on the inside to help the flow. I now have airflow through the stack!  With my borrowed wind meter I am getting between 120 fpm and 200 fpm.  I am actually getting the higher flow rate at the bottom of the stack.  As you move higher in the stack the flow goes down but I still have 120 fpm up high.  I've pulled out almost 5 gallons of water in just over 24 hours.  I really appreciate everyone's help on solving this.  I'll sleep better tonight.  I think I lost at least 2-3 pounds working inside that kiln at 120°F  :laugh:  I wore shorts and no shirt when I was in there this morning.

Yellowhammer - I did cut a hole in the bottom of the L53 with an extra filter.  I had read one of your earlier posts about this and did it from the get go.  I'm sure that is a big contributor to having good flow in the bottom of the stack.  I have my two end fans fairly close to the sides of the kiln, so I don't think the air will be too stagnant there, but I will keep an eye out for that.  

Customsawyer - Yea, this kiln charge was kind of a mashup of all kinds of lumber.  I had lumber in there from at least 3 different sawmills.  (I just got my own mill last Spring.)  I definitely agree that after this experience I will pay attention to how I saw so that it stacks in the kiln better.  All of this lumber had been air dried at least 2 years down to between 12 and 14%.  Even the thicker lumber was that dry in the core.  I have a Lignomat remote MC station, so I have pins in both the thick and thin lumber and check it at least twice a day.  

[doc henderson]

  smiley_clapping smiley_clapping smiley_clapping smiley_applause

[YellowHammer]

There ya go, success.  

[customsawyer]

Glad to hear it.

[K-Guy]

When adding circulation fans to the L53 chamber, I recommend building it as a scaled down L200 chamber.

[blackhawk]

When adding circulation fans to the L53 chamber, I recommend building it as a scaled down L200 chamber.

K-Guy - Would it help to put a 45° deflector on the wall/ceiling opposite the L53 unit to help guide the air down the wall and through the stack?  Any studies done by Nyle on this?  See sketch attached.

Also, what about if I added a small deflector over the two fans on the L53 to try and direct the air across the top of the stack better?

[K-Guy]

Blackhawk

A deflector in the corner that the fans are blowing to is recommended but not over the kiln unit(that will cause back pressure on the motors and burn them out).

[blackhawk]

Blackhawk

A deflector in the corner that the fans are blowing to is recommended but not over the kiln unit(that will cause back pressure on the motors and burn them out).

K-Guy - Thanks for the reply.  Any recommendations on the size of the deflector in the corner?  My kiln is 8 feet wide and 7 feet tall.  Would an angled piece that extended 10" along the ceiling and 10" down the wall be sufficient? 

[K-Guy]

You can use a 6" wide strip of plywood at 45° and get the affect you want.

[YellowHammer]

It sounds like you have an anemometer?  At this point you should do an airflow pattern test by scanning it across the face of your stack of wood looking for inconsistencies in air velocity.  

[blackhawk]

It sounds like you have an anemometer?  At this point you should do an airflow pattern test by scanning it across the face of your stack of wood looking for inconsistencies in air velocity.  

I did do a brief check like this after I got my shrouds installed.  (Too hot to stay in the kiln for a long time.)  I am getting around 200 FPM at the bottom middle of the stack.  It gradually goes down to 120 FPM as you get to the top of the stack in the middle.  On the ends, I am getting around 180 FPM at the bottom and it goes down to around 100 FPM as you get to the top.  (All this is assuming my borrowed anemometer has decent calibration.)
I'm trying to understand the better flow at the bottom of the stack.  My only theory is that the air travels down the wall and bounces up from the floor so the bottom of the stack is getting more air flow.  After this load is done, I thought about attaching some small 3/4" x 3/4" strips horizontally on the wall opposite the L53 about midway of the stack height.  I'm thinking that may break up the air flow down the wall to distribute it more evenly.  But, if you think about my auxiliary fans that are now pulling air through the bottom of my horizontal shelf, they are pulling air up high.  You would think that would make the airflow better in the top layers of the stack.  I need some type of smoke machine in the kiln to visualize the air flow just like a wind tunnel.

[YellowHammer]

Generally, as a rule of thumb, 150 fpm to 250 fpm is optimum for drying hardwood.  Under 150 fpm risks sticker stain.  

[doc henderson]

can you make the hole in the shelf inside the shroud, the size of the base (less restrictive)  more like the kiln unit base.  see if that helps the ends, and gets more at the top.  the center is being pulled down more due to the position of the air intakes on the unit.