In my last blog I went on a rant about how canola could start dripping if the canola is more than 4 C warmer than the air. And this would be the case when the fan is initially turned on, but after a few minutes — after a few bin air exchanges; there are mitigating factors.
- The roof, although it is a good conductor of heat, it might warm a bit. It isn’t necessarily the same temperature as the outside air. It could warm up a deg or so.
- The canola will be dried down just a bit, but not much, and this would also give us a small advantage in getting a bigger spread than 4 C. But we know that it dries slowly, so in a few minutes, we can’t count on much, but in several hours we would get some benefit.
- The canola will be cooled a bit, and this will also help as it will lower the EMC absolute humidity. This would be more important in the long run rather than in the short term of the first hour.
- When the fan is off the RH of the air in the bin will be that of what the EMC equations dictate for canola at that temp and MC. I call it the RHemc. However when we start the fan, we don’t have equalized air we have air that is coming into the bin with a much smaller absolute humidity. It takes time for the air and moisture to equalize, and the air passing through the grain is only in contact with the grain for a minute or so. We can’t expect the air to reach the value of absolute humidity or RHthres. This is a non linear process, as the absolute humidity approaches the EMC absolute humidity asymtoticly. Typically we describe these processes with something called a time constant. One time constant is the time it takes to reach 63% of the EMC absolute humidity. I am thinking that in our case it is probably one time constant. I am devising a means to measure just what this is from our data and that will be a discussion for another blog. In any event the absolute humidity of the air will be less than the EMC absolute humidity and this will have significant mitigating factor in dripping and increase the temp difference to perhaps 6 or 7 deg C for our canola example.