Desenvolvimento de um secador por micro-ondas para secagem de grãos em camada espessa.

Abstract

Heating is one of the several possibilities of application of microwaves. The process of conversion of the electromagnetic energy in to heat, directly inside the product, besides other advantages, facilitates its use in the processing of products, specifically in the drying processes. This work has the purpose of using a dryer based on microwaves in the drying of corn grains in layers of 2 cm, 5 cm and 10 cm of height. The equipament is based on a microwave oven, modified for the experiment, with the substitution of the control panel, the addition of a field scatter, an exaustor, a metallic wedge, a filament transformer, a meter of anode current and insulators et the base of the transformer of high voltage. The distribution of electric field in the corn layers using the prototype of the dryer is shown to be uniform, due the modifications. The power absorbed by the layers were indirectly measured for the adjustment of the anode current. Four levels of power were chosen by means of the characteristic plots to irradiate each layer. The power curves are not linear, because the product is not homogeneous. The layers of corn of 2 cm, 5 cm and 10 cm of height were dehydrated from approximately 53% for 13% in dryness basis, using two drying methods: the exposition of the layer to microwave does not suffer interruption and the second drying method, for which the exposition to microwaves suffers interruption. It is verified, for this second method, that the drying temperature for each layer varied, on the average from 70 °C up to 130 °C and that the interval of drying decreases with the increase of the method used, independent of the applied power.