Desenvolvimento de secador solar autônomo: utilização na secagem de feijão-caupi.

Abstract

Because solar radiation is abundant in Brazil for most of the year, and as it is a source of renewable and non-polluting energy, solar drying of agricultural products becomes a promising alternative. The use solar radiation for drying presents a basic difficulty, which is the periodic nature of the radiation and the consequent interruption of drying process at night, which leads to the idea of storing some of the thermal energy for night or cloudy days use. Taking this into consideration, the objective of this work was to develop a solar dryer that stores heat (ACSN dryer), using vacuum collectors with forced circulation for night use, fed with an autonomous system of electric energy generation based on photovoltaic panels; this system was used in the drying of cowpea samples. For comparative analysis, several dryings were performed: conventional drying (drying (oven) at various temperatures; direct solar drying by natural convection; drying by direct exposure to the sun; and a combined drying using the ACSN drier both with solar drier and with direct exposure to the sun. The drying of cowpea in the ACSN was efficient, reaching high levels of reduction of water contents, even at night; higher drying rates and high values of average temperatures within the heat accumulator drier (ACSN) were observed. Some of the main mathematical models used in the literature were applied and all presented satisfactory adjustments to the drying kinetic curves of cowpea, where the Page model presented the best fittings. The values of the effective diffusion coefficient obtained corroborate the values of the literature for other grains.