Will you change??

[Tucker]

fjlip, I think Tom is closer to correct on this matter. Cooling the grain
down to safer storage temps is how aeration helps with grain storage the
most. Grain will have to give up moisture as it's cooled just because as it
cools, the RH of the air surrounding the kernels in the bin has to rise.
Any time you can push air into a bin that has lower RH than the air in it,
you're doing some amount of drying with the air exchange. Once the grain is
cooled to the ambient night time temps, blowing more air through it is
probably just wasting energy.

Any supplemental heat you can give the air that doesn't also raise the
water content of it is going to lower the RH of that air and speed drying.

[grrrr]

I am rigging up a system that will bring cold night air into my wifes clothes dryer. The plan is to dry everything with cold outside air Monday night. I can hardly wait to jump into my jeans Tuesday morning, straight out of the dryer!!!!!!!!!!!!

[Hopperbin]

Yep looks like us farmers have done many experiments threw the years. I remember waking up in the morning many times to a blinding fog, go running out to turn the fans off and wonder well how long and how much h2o did I just add to them bins???? Upon unloading it was a lot I just don't have numbers. Raining outside is better than the fog cause fog gets sucked in more than rain and I ain't going to run fans in the rain. Pami has done airation experiments also so could ask them. August if of course typically much better than sept.
Tom I like you like to cool the grain down for winter, spring is a good time to dry grain with air but then again this guy says you take moisture out of the grain better when it is cooling. So then why do us farmers with a lot of experience know that we can air a dry our grain in the spring effictiently.

[Hopperbin]

When you said wife's cloths dryer I thought you said all the wife's cloths.
Then she can come back to bed for some warming up.

[farmaholic]

I think it is fair to say that grain will release alot of moisture during the initial cooling period.
The article states that air(volume not stated) at a temperature of 27*C at and 0%(assumed) RH holds 4.3 kg of water and at 50% RH holds half as much at 2.15 kg. Therefore, it is fair to say that it is half full and can take on more water if conditions are favorable to do so. As RH drops, regardless of temp, shouldn't the air be able to hold more water, since it isn't as full? If RH drops to 30% the air should be able to absorb alot of water, up to the point an equilibrium is reached and the air is no longer able to hold any more water and net drying is no longer occuring(or rate of drying reduced).
What the article doesn't tell us is how much water does cool air hold at about 10*C and 80% RH vs 40% RH(use what ever numbers you want, the important thing here is there is no mention of it). Or is it that air temp doesn't mean as much as %RH. Does air at 30% RH hold the same amount of water at 27*C and 10*C?
Then there is "dew point", which means, at what temp does the air have to cool down to, at a given %RH, for the water vapor in the air to cool and cause condensation. And why would you run fans when the temp is near the dew point.
What about static pressure? Does a high static pressure reduce the airs ability to hold water? Does it in effect squeeze it and reduce its carrying capacity? Or isn't it high enough to make any difference?
I was told to run the fans continuously because the "drying front" continues to move and "rewetting" of the grain happens slowly. The grains we've dried in aeration usually are over dry at the bottom and not dry at the top and near right in the middle. So how long would you have to run the fans to re-wet the bottom to the allowed moisture content?
Can someone who understands this explain it because it seems completely contadictory to what we've been doing!!

[Hopperbin]

Farmaholic lets go with what we know. At harvest time when temps are 30 our grain going in the bin can be upwards of 40. so yes some drying can occure on cool down, hot air dryers work on putting heated dry air into the grain and then also the grain drys uppon cool down. That is a fact. Cool down in a grain dryer is only 1 to 2 hours max. Could be longer but there is no point. And typically when grain is 40 degrees going into the bin then night time temps are also warmer but no one is going to dry grain down better than running the fan all day. That we know.

[rbrunel]

Anytime we put tough/damp grain in the bin, no
matter the temp of relative humidity we leave fans
running. I have dried down 19-20%mc wheat
down with this method. It might take a couple
months. Theory goes keep moisture font moving.
Sf3 s right though. Grain dryer is quickest and
most reliable to know how dry grain is.

[Burbert]

Interesting, very interesting. This is
probably the Comedian Wheatie Bored,
trying ta du a number on Comedian framers.
Why couldn't they have released these
findings on April 1st? Then it wooda been
way more confusing.......

[craig]

No one has talked about grain kernel
temperature. I was always told the grain
needed to warm up to give off moisture. In
our area( central alberta) aeration is
usually only good for cooling unless your
in August, early September.

[cottonpicken]

From my brother


If you cool air, then you increase the Relative
Humidity (the RH is the ratio of the total amount of
moisture that is in the air (moisture content)
compared to how much it can hold total before some
must condense-out (dew point moisture content)
...cooler air can hold less moisture before some must
condense-out than hot air....think: it takes a bunch of
kinetic energy at the molecular level to keep water
from coalescing ... the more energy (higher temp) the
faster the particles in the air are moving and colliding
to keep the moisture in suspension).

So as the warmer air enters the bin it may have a
lower RH, however it has a significant amount of total
moisture in it (the total amount of moisture that air
can carry vs temperature is a non-linear
relationship....
http://upload.wikimediaorg/wikipedia/commons/4/4
1/Relative_Humidity.png ). The grain acts as a huge
heat-sink and cools the air thereby raising it's RH (not
it's total moisture content) so there is a tendency for
water to condense-out and be deposited in the bin.

Not sure why pre-heating the air is counterproductive
... perhaps you aren't really removing moisture from
the air, just reducing the RH? This would reduce the
tendency for water to condense-out as it gets worked
by the fan (before entering the bin). It has been a
while, but I think I remember moisture pouring off
the fans when they run at night? It could be that the
act of running the air through the fans (increasing the
velocity of the air) increases the tendency of the
moisture to drop out of suspension...? It is important
to note that there is a difference between increasing
the velocity of the air (with a fan) and increasing the
kinetic energy at a molecular level (heating) the air. A
fan will inevitably heat the air, however an efficient
fan heats the air less than inefficient fan.

Air temperature and RH are related to the kinetic
energy at a molecular level and I believe it is not
related to the velocity of the body of air.

Running at night when the air is cooler gives air with
a lower total moisture content and higher RH. If the
grain is warmer than the air (due to daytime heating),
then it should transfer heat and moisture to the air.

It would be interesting to see what would happen if
you first cooled the air, then ran it the through a
dessicant (i.e. an enthalpy wheel
http://cipco.apogee.net/ces/library/tdew.asp ), then
heated the air before sending it into the bin...the trick
would be: what do you exchange the moisture from
the enthalpy wheel with?

[TOM4CWB]

"It would be interesting to see what would happen if you first cooled the air, then ran it the through a
dessicant"

In the 'cooling process' this is EXACTLY what happens.

The bottom of the full grain bin has NEVER gotten too wet... has almost always been 'dry' grain by CGC standards.

This is a system of averages... and exactly why the fan should run night and day... except perhaps on peas/beans when warm high RH air (25-35C 80RH) can rewet the pea/bean (and reck bin bottoms) as peas/beans ability to reabsorb moisture is much greater than the other small grains.

The absorbtion rate of the grain is important on RH controls for natural air drying.