I got an interesting email from Tom in Ohio, wandering how he could dry his cold tough corn. It went something like this:
Hello Ron Palmer, hoping you can offer suggestion. South West Ohio U.S.A. 5000 bu. bin with 5 hp fan, 2500 bu of corn harvested Feb with air temp 20 f. and mc of 20.5. a cooking thermometer was inserted from top of corn today that read 50 f, probably colder farther down. Spring temps are fluctuating into 70’s f. with off and on rain in the 10 day forecast. Your trials involved grain that was much warmer than this corn, should it be warmed up with daytime air before starting the night time drying and to run or not during nights with rain?? Thanks you for any help/strategy to dry down corn.
And my reply:
Tom: You have some pretty tough corn at 20.5 % MC; however, the good news is that it is not heating at 50 deg. F. So, the question is: how are we going to get some of that moisture out. And you are right in thinking that we need to get some heat into the corn, so that it has some energy to push the moisture out. Actually most of the energy is used to change the water in the grain from liquid state to a gas state. We have found that it takes about a 15 deg C (27 deg F) reduction in temperature to evaporate the water to get a one point reduction in moisture content. For example, let’s say that we have corn at 70 deg F @ 20% MC, and we run the aeration fan to get the corn down in temperature of 43 deg F (70 – 27). We should have reduced the MC by one point, 19%. But how do we get energy into the corn?? Yes you can use the outside temp of the air to heat the corn; but, as you heat the grain this way, there is a good chance that you will be wetting the corn down. So, yes use the heat of the day to get your your corn warmer, and then use the cool night air to cool it down and for every 27 deg F that you drag the corn down, you should be able to take the grain down one point. We want to get this cycle going of getting energy into the corn during the day, and then cooling it at night to remove the water. My first reaction would be for you to run the fan continuously; heat the corn during the day, and cool it down at night. If you can get a 27 deg swing you could take out as much as a point a day. However when the corn get closer to being dry, you might find that you are adding as much water during the day when you are heating the grain as you take out at night. How will you know? I suggest you use my Grain Drying Calculator. You can find it at planetcalc/4959/ and it will tell you when the conditions are OK for drying. I ported this website calculator to my cell phone, and I can use it anywhere. Unfortunately the temperature entries are in Celsius, and I know you like F, so you have to convert. To convert F to C, subtract 32, and then divide by 1.8. So 32 F is 0 C. 70 F is 21 C, 50 F is 10 C. I entered the following into my calculator.
Grain Moisture Content % 20.5
Grain Temperature C 10 (this is 50 deg F, — this is what you told me the temperature of your corn was)Air Temperature C 20 (this would be 70 F, the daytime high)
Now push calculate and scroll down to shelled corn, and you will see that you get a threshold relative humidity of 48.4%. In other words if the relative humidity of the air outside is below this you will be drying. I doubt this is the case for you, when you said there were showers around. It is probably more like 70 or 80%, in which case you will be wetting you corn down.
OK let’s run the fan when it is 10 C or 50 F outside — what does the calculator give us — it says the threshold relative humidity is 93%. So even though the air temp outside is the same as your corn temp; as long as the RH outside is less than 93%, you will be doing some decent drying. Not bad.
If
we run the fan when the outside temp is just above the corn temp. say
15 C (59 F), and we run that through the calculator we get a threshold
RH of 66.6%. You might get this on a dryer day — but certainly if it
is not raining.So, roughly speaking, it looks like we can run
the fan without wetting down too much provided the temperature of the
air does not exceed the temperature of the corn by more than 5 C or
about 9 deg F. But if you want to be more precise, use the
calculator. As the corn gets drier, you will find that the
temperature difference will get less and less, and it will be more
difficult to get some heat into the corn.I hope this helps//Ron