Strategi Pengendalian pada Pengeringan Jagung Pipilan yang Memanfaatkan Udara lingkungan

Abstract

In artificial drying, consumption of thermal energy is about 90%-95% of requirement total energy (Manalu, 1999; Nelwan, 1997). Ambient air drying is a drying method that use unheated air, thus its thermal energy consumption is very low. Indonesia is a tropical country that ambient air condition generally has high relative humidity, however the mean temperature is more than 30oC and the relative humidity is lower than 70%. This condition is potential to dry the corn up to it’s equilibrium moisture content (Me) i.e. 14%. Because of the fluctuative condition, the ambient air doesn’t have potential ability to dry at all. In deep bed dryer, there are various moistures in layers. Therefore, control system based on differences of moisture content in corn layers is needed to flow the potential ambient air -high of air temperature and low relative humidity- and to control the velocity of ambient air flow. The control system consists of detector of temperature and RH by SHT11 and SHT75 sensor, LCD, power supply and zero crossing circuits. The controlling system program was written ‘C language’, and written by Uc51 software 3.48 version, and also has function as compiler to convert ‘C language’’ to file.hex. The controlling strategy compare equilibrium moisture content in layer with the ambient as a hint of round of blower. If ambient Me < Me of the lower layer, the blower flows the maximum flow rate (0.455 m2/s). Contraryly, if Me >Me of the upper layer, the blower won’t flows . And if Me of the lower layer < ambient Me < Me of the upper layer, the blower flows the ambient air with five different levels of flow rate ( 0.398m2/s, 0.347 m2/s, 0.272 m2/s, 0.169 m2/s ,and 0.136 m2/s ) based on the comparation of the third Me. The experiment without control system showed that when the ambient temperature is about 25.7oC - 36oC and average ambient RH is about 55.25% - 97.65%, can dry the corn from average moisture content 20.48% b.k to 16.08% bk in 46.5 hours and consumed electrical energy as much as 4.288 MJ/kg of water evaporated. But, In the experiment with control system with average ambient temperature is about 27.9oC – 40.6oC, and average ambient RH is about 39.47% - 93.43%, the drying process start from average moisture content 20.89% b.k to 16.20% b.k due 10.517 hours and consume electric energy as much as 1.553 MJ/kg of water evaporated. Control Strategy Program worked properly and consumed less electrical energy and drying time process than the experiment without control system.