I am trying to figure out this problem - maybe it is simple for someone of you but I can't figure it out.

I have known variables of outside air temperature and relative humidity (RH), I am taking that air into the heater and have two fans that pump 640,000 m$^3$ per hour. The air is being heated up to 80 degrees Celsius.

My question is how can I calculate the RH of the heated air and is there any corelations between how much air is being pumped and how much can that air take RH from grain that I am trying to dry?

In short two fans with capacity of 640,000 m$^3$ per hour, 100 tons of grain, how to calculate best way and how much air does it need to dry it?

  • $\begingroup$ Are these grains suspended in a stream of air or piled on a floor and blown from above? $\endgroup$ Commented Jul 31, 2019 at 14:21
  • $\begingroup$ Grains are piled on the floor ( to be precise on sieves and air is blown from below them and trough them, layer is thick around 1.1 meter) @AlexTrounev $\endgroup$ Commented Jul 31, 2019 at 14:55
  • $\begingroup$ Is it organic grains? $\endgroup$ Commented Jul 31, 2019 at 16:05
  • $\begingroup$ Yes they are, barley grains @AlexTrounev $\endgroup$ Commented Jul 31, 2019 at 19:06
  • $\begingroup$ For barley grains, there is a temperature limit during drying. If the grains are supposed to be used for seeds, then 40C, and if not, then 60C. $\endgroup$ Commented Aug 1, 2019 at 2:11

1 Answer 1


The relative humidity of outside air heated to 80 C will always be very low. Worst case (beginning at 100 % and 35 C) would be 17 % or so, eyeballing the vapor pressure graph below.

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  • $\begingroup$ Thank you for this, and what do you think about other part - how much can 640,000 m3 per hour take humidity and is it beter to be blown faster or slower. Does slower air stream take more humidity? @pieter $\endgroup$ Commented Jul 31, 2019 at 14:56
  • $\begingroup$ @IvanĆalušić At 80 C, saturated air would contain 290 grams of water per cubic meter. But evaporation would cool the air, so one needs a psychrometric chart with adiabatic cooling lines, I will see if I can find one later tonight that goes up to 80 C. $\endgroup$
    – user137289
    Commented Jul 31, 2019 at 16:15

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