Defect and Diffusion Forum Vol. 399

Abstract: This work presents a drying study of banana fruit (cylindrical slices) using heat, mass and shrinkage lumped models, and experiments in different drying conditions. Whole bananas were peeled, sliced manually (cylindrical pieces) and dried in an oven at constant drying condition (40 and 70°C). Drying, heating and shrinkage lumped models were proposed and fitted to experimental data. Results revealed which air temperature affects significantly the moisture removal, heating and shrinkage of bananaslices. Furthermore, results revealed which air temperature affects significantly the moisture migration, heating and shrinkage rates of banana slices. The fitted results presented good agreement with experimental data.

Abstract: Cashew is a fruit with high nutritional value and great economic importance in the Northeast region of Brazil, however, due to high moisture content, it is highly perishable. Freezing is one the most efficient methods for conservationof biological products, especially, fruits and vegetables. Then, the optimizationof the freezing process by numerical simulation is crucial. In this sense, the objective of this work was to investigate the influence of the moisture content on the cooling and freezing processes of cashew appleby using thecomputational fluid dynamics technique. Results of the cooling and freezing kinetics of the cashew apple and temperature distribution inside the fruitduring these processes are presented and analyzed. It was verified that the variation inthe initial moisture content had small effect in the total time of the process, however the samples with higher moisture content presented higher heat transfer rate during the cooling period and lesser during the freezing period.

Abstract: The present work has the objective to study the water diffusion in the process of intermittent solar drying of mangabas. Osmotic dehydration (OD) pretreatment was performed in sucrose solution and the drying took place in a direct solar dryer with the fruits arranged in stainless steel screens, temperatures varying between 30 and 45°C along the day with peaks of 70°C. The period of intermittence was approximately 16 h reaching equilibrium after 6 days. The diffusional model based on the second Fick’s law was proposed for each of the daily drying periods of 360 minutes, considered that the process is controlled by internal diffusion, negligible external resistance, spherical geometry, shrinkage based on the average radius. The coefficients of effective diffusion (D_ef) obtained by using 4 terms of the infinite series, present values of D_ef ranging from 0.2 to 3.30x10^-10 m2/s with R2≥ 0.868 and average relative deviations MRD≤10^-2.

Abstract: This work presents a theoretical drying study of sisal fiber. Fibers with moisture content of around 11.2% were dried in an oven in the temperature 90°C. A transient and three-dimensional mathematical modeling to predict heat and mass transfer in a bed of fiber was proposed and numerically solved by using the finite-volume method. Results of the average moisture content and surface temperature were compared with experimental data to verify the consistence of the proposed model, and good agreement was verified.

Abstract: Drying is an essential pre-treatment step that plays a critical role in the energy balance of biomass power plants. This has motivated the search by cost-effective drying technologies. Within this context, the present work aims to investigate the application of a spouted bed dryer with inert solids for drying sugarcane bagasse, the most important biomass used for generating energy in Brazil. Effects of the biomass volume fraction, inlet air temperature and spouting gas flow rate on the drying time and thermal efficiency of the equipment were examined. Results show that drying time decreases by decreasing the biomass fraction and by increasing air temperature. Highest values of biomass percentage and air temperature allied to the lowest velocity of the spouting air greatly improve the efficiency of the biomass drying. Based on a balance between the energy that the product is capable of suppling and the total energy consumed by the dryer the optimum operating conditions recommended for making feasible the use of the bagasse dehydrated in spouted bed for energy purposes are: air temperature of 67°C, biomass volume fraction of 0.6 and air flow rate equal to the minimum stable spouting condition.