Instructions: enter "Extra heat" value from previous dryer run or use 0% as a starting point. If airflow is not known, enter parameters from previous dryer run and use "Compute airflow". The computed airflow can then be used to predict a feedrate for different situations (different starting moisture, different ambient conditions).

The airflow value can be determined if fuel usage is measured for a previous drying run. Compute the fuel usage rate based on the amount of used fuel (in L/hr or gal/hr). Enter the conditions for the run (moistures, temperatures, feedrate), adjust the "extra heat" value and use "Compute airflow" until the computed fuel rate matches the measured value.

"Cold grain" is the temperature of the wet grain entering the dryer. "Hot grain" is the temperature of the grain before it enters any cooling sections. "Exit air" is the average temperature of the air exiting the heated section of the dryer (default value is 30 °C). The airflow rate is the airflow for only the heated section of the dryer. The "feedrate" value is the dry feedrate, based on the discharge rate of dry grain from the dryer. Typical conversion efficiency for a LPG burner is 85% (percent of energy density of fuel converted to heated air). Typical energy density for LPG is 25.6 MJ/L.

Theory of operation: This calculator is designed for mixed-flow grain dryers using LPG as the fuel. The basic theory is an energy balance. The thermal energy added to the air in the plenum is compared with the energy used for the following: heating the air to the exit air temperature, heating the cold grain to the hot grain temperature, and to evaporate the water removed from the grain. The "extra heat" value is computed as (energy_added / energy_removed - 1) * 100. I.e. percent of energy added to the air in excess of the computed energy used. It is expected to be greater than 0% given correct input parameters.

The following is a link to an excellent guide to grain drying systems from UW-Madison.

Comments to the webmaster.