For this exercise we will use one cubic meter of barley at 30 C. And we know that it takes energy to evaporate water; this is called latent heat of evaporation, which is 2257 kJ/kg. Let’s assume that all the energy in the barley in going from 30 C to 5 C is used in evaporating water from the barley. How much water (in %MC) can be removed?
1 bu = 1.2446 cubic feet 35.31 cubic feet = 1 cubic meter 2.204 lbs/kg
One cubic meter of barley weighs 35.31 ft3/1.2446 = 28.57 bu x 48 lb/bu = 1361 lbs, 618 kg
One percent moisture, 1% MC would then be 6.18 kg. If barley was 15% MC then 92.6 kg would be water.
The barley in going from 30 C to 5 C has how much energy to give. What is the specific heat? It can vary, but I found one source: 1.36 kJ/kgC
1.36 x 618 kg x 25 C = 21012 kJ and divide by how much energy is needed to evaporate
21012 kJ /2257 kJ/kg = 9.3 kg of water can be evaporated with the energy in the barley.
But 1%MC was 6.18 kg/%MC , 9.3 kg/6.18 = 1.5% reduction in MC. If the barley was 15% and all the energy went into evaporating water in going from 30 to 5 C, then the MC would be reduced by 1.5% and be dried from 15% MC to 13.5%.
Our data showed just about the same thing. Cooling the grain with aeration, we found that reducing the temperature by 15 C would remove 1% moisture. In the case above, 1.5% resulted from a 25 C. A 1% reduction would require 16.66 deg reduction. This demonstrates that aeration (at least with our experimental trials) is very efficient at using the energy in the grain. I thought we might be losing more of the energy to conduction, but it appears that almost all the energy in the grain goes into drying.