Cold Water Spray for Equalization

[Ga_Boy]

Has anyone tried to heat a "Cold Water" spray?

I am looking for a way to reduce the temp swings when the spray kicks on.

I can either pre heat the water before is enters the pump or heat the water after it is presurized.

Both offer technical challanges.

Heating before it is preausreized - can the pump take the heat?  How will this effect my pressure out put?

Heating after the pump - Finding a heat exchanger to handle the pressure (600-800 PSI) at a reasonable cost.  How to regulate the increased pressure after the pressurized water is heated, anticipate an increase in pressure.

Any thoughts?




Mark

[Don_Lewis]

Heating the water is almost a waste of time. Let's say the water is 60 degrees F and you heat it to 160 F. That reduces the heat it takes in the kiln by only about 10%. Not enough to make much difference. The important this is to make sure the amount of humidification spray you are doing does not overwhelm the heat capacity you have.

It only takes 100 BTU to heat a pound (pint) of water 100 degrees but it takes 1000 BTU to turn it from water droplets to water vapor. Heating the water eleiminates the 100 BTU part but the cooling effect of 1000 BTU per pound of water is still there.

[Den Socling]

If I have this straight, you are using a cold mist to raise RH but the evaporation is pulling the temperature down - is that correct? If so, preheating might not do much good. It's the change of state from liquid to vapor that eats up the Btu's.

Maybe a little steam generator for part time use would be better.

[Ga_Boy]

Den and Don,

You both are right about the change of state.  I forgot my Physics/Chemistry 101....changing states takes an order of magnitude more energy....putting a heat exchanger in the system is a waste of good money......


Thanks for the reminder.....





Mark

[oakiemac]

For those that run dehumidification style kilns, is conditioning with water spray (or anyother method) necessary?
I was told that with the small dehumidification kilns that it is not really required do to the slow drying and low stress put on the lumber.

[Den Socling]

Conditioning puts some water back into the over dried shell. With non-vacuum kilns, the shell is always lower than the core. You increase drying speed by increasing the moisture gradient between shell and core. Therefore, if your DH kiln dries slowly, the gradient won't be great.

[jimF]

I don't like to disagree buuuut.  If non-vacuum drying is performed properly the shell is not over dried and conditioning only adds about 1% MC.  If you dry too slow in DH kilns the stress gradient will not be great enough to allow stress relieve to take place during conditioning.

[Den Socling]

Jim,

How do you define overdried? The shell has to be lower than desired to get the core to the desired final MC.

Are you adding 1% to the shell or to the cross section?

Den

[jimF]

The shell should only go down to about 5% during drying.  During equalization, it either stays there or goes to about 6%.  During conditioning,  the average MC goes from 6-8% to 8-9%.  I would call over-dry below 4-5%.