Purchased tank to make into vacuum kiln

[boardwalker]

Den

Should the heating cycle shut off when the condenser is on or should it just be controled by a thermostat or an rtd in the wood?

[boardwalker]

Den

I have a pressure transducer and a humidity transmitter located that should work good. Looks like I will need 3 loop controllers. 1 for the heating, 1 for the condensing(humidity)control, and 1 for the pressure control.

So my cycle is turn the heating circuit on, turn the vacuum circuit on. Run the vacuum pump till the pressure transducer reaches its set point(which is ?) ,run the heating till it reaches its set point which will be controled by rtd's in the wood, and run the condensing cycle which will be controlled by the Rh transmitter(100% rh turns on the condenser ?% turns the condenser off).

Does this look right? Now all we need to figure out is where all the set points should be).

With this type of a system I don't think I should need a cooling tower since the vacuum pump will not be running very much.

Anymore input before I finish buying the rest of the parts?

Thank you
Craig

[Den Socling]

With discontinuous vac, you heat with atmospheric pressure. This means there will be plenty of air to circulate and carry the heat from your fin pipe. I would control vacuum from wood temperature. Heat with no vacuum until the wood is warm then pull vac until the wood is cool. I would leave humidity run high.

With Sergey's method, you have lower pressure in the chamber but there is still enough air to circulate heat. If I remember correctly, I translated around 200 -250 torr from one of his post. Then you would need the condenser is assist airflow.

Yep. Three loop controllers and you should be able to use either process.

[boardwalker]

Den

What is the boiling point of water at 250 torr?

[Den Socling]

Around 160'F but you don't have to boil water to dry wood.

[boardwalker]

Den

I know this drawing is small I couldn't get things to work right, but if you can see my arrows does the air move through the kiln like it is drawn on the left where the cool air drops through the center and is pulled through the stack to the heating coils as it drops and then back up the outside to the fanwall under the condenser drain, or does it move like the right side of the drawing with the cool air dropping down the center and coming up the outside and then through the stack to the center and up?



I'm still thinking of using some tubing runs along the outside of the tank for extra btu's plus the added benefit of not having condesate on the tank walls. Do you think this is a good idea?

Can you tell the moisture content of the wood by how high the maximum humidity is inside the chamber or how do you know when the charge is dry? I guess I was thinking that since lumber will equalize at a certain moisture content depending on temp./ humidity that you might be able to tell the moisture content of the charge by how high you can push the humidity inside the chamber.

[Den Socling]

I think the air flow is as shown on the left. That would make it depend on a drop in humidity. That's why I think some fans blowing down would assist. What do you think, Sergey?

I think that, if you add extra tubing, you should put it inside. If you keep the steel of the chamber warm, it will stay dry.

When the wood is dry or has reached EMC, humidity will drop. At the same time, you will stop dumping condensed water.

[serg]

Den.
I against the fan. I build drying chambers without fans. Fans a problem as drying a wood.
I learn(teach) to dry a wood - humidity 6 +/-0.2 % a stack, thickness, length of a board. All exotic breeds of a wood.
The fan to apply in drying result gives badly. Speed of the agent of drying vacuum a dryer and DH a dryer 0.3 m / second.
Such speed of the agent of drying allows me to not cover an end face a board a paint mastic!
Den advice(council) I can not give.
Sergey.

[boardwalker]

Den

Will I still need the shell & tube heat exchanger for a condenser in the vacuum line if I'm going to use the cold water pipe and chute it the top of the chamber for the condenser?

[Den Socling]

Yes. If you are drying something that is easily cracked, you will want to leave humidity in the chamber high. That's when the pump condenser is needed.