Secagem de fatias de caju (Anacardium occidentale L.) em secador de bandejas.

Abstract

The drying of cashew slices in common tray or solar dryers are alternatives to serve small farmers, who can aggregate value to their product and minimize losses, using this technique. During the development of dryers, it’s necessary to know the thermal-physical properties of the material to be dried, the hygroscopic equilibrium relation, as well as to be aware about drying kinetics. According to that, this work had the objective to offer a viable technological alternative in order to optimize the development of the equipment and product quality. The thermal and physics properties of cashew apple were determined in function of moisture content, regarding the hygroscopic equilibrium, it was verified that, among three mathematic models, the GAB best represents the cashew moisture equilibrium. It was studied the cashew drying kinetic, in different operational conditions, with temperature of 60 to 80ºC, air drying velocity of 1 to 1.8m s-1 and bed height varying between 1 to 3cm. For the mathematic modeling it was used the diffusional model based on Fick’s 2nd law, which is suitable to predict the cashew drying kinetics. In order to analyze the development of tray dryer it was studied the mean global energetic efficiency, the air saturation index, and the final moisture content of the product after operating during 300 minutes. It was prepared a factorial planning 23 with three experiments in central point, involving temperature, air drying velocity and bed thickness as independent variables, and global energetic efficiency, air saturation index, and final content moisture as response variables. The obtained results showed that the energetic efficiency varied from 5.12 to 18.86%, whereas the variation for the air saturation index was from 5.35 to 38.38%. The generated response surface show that these results can be improved by increasing the loading into the dryer trays and by decreasing the drying air velocity. It was implemented some changes in the “Secador” program developed in FORTRAN language to simulate the cashew slices drying in the dryer trays. Sub-routines were added in order to implement, in the model, cashew physics and thermal properties variations as a function of moisture content, variable diffusion coefficient, equilibrium moisture content in function of tools for large scale units, suitable to attend small farmers.