Seed Energy: How much moisture can the energy in the grain remove?

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.

 

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