ABSTRACT The homogeneity and efficiency of moisture removal from coffee beans depend on the airflow patterns inside the drying chambers used for drying. This study aimed to implement a porous medium model to simulate the airflow through mesh trays containing parchment and ripe fruit coffee ( Coffea arabica L.) using computational fluid dynamics (CFD). The geometry of the ripe fruit and parchment coffee beans was simplified as spherical and semi-ellipsoidal, respectively. The pressure drop in the normal direction to the monolayer was calculated as the average pressure of the normal planes located 1 mm before and after the bean layer for different air velocities. The viscous and inertial terms were adjusted by nonlinear regression for each case and incorporated into the Navier–Stokes equations as subdomains. The pressure drops calculated by the porous medium model and those calculated using the bean layers presented a good fit. The modeling of the trays as porous media can help reduce the computational resources required for CFD simulations while maintaining an acceptable accuracy.

ABSTRACT This study aimed to fit mathematical models to whey foam drying processes in different air temperature conditions, to determine the effective diffusion coefficient and to obtain the activation energy. For foam formation, 5.0% Emustab® was added to the serum in mass and subjected to stirring in a domestic shaker for 15 min. After, it was spread onto trays to form a thin layer of about 1 cm in which the drying conditions were: 40, 45, 50, 55 and 60 °C, 5.6 m s-1 and 60%. The Logarithm and Midilli models describe the kinetics of serum foam drying; the effective diffusion coefficient increased with the elevation of drying temperature and activation energy of 50.84 kJ mol-1.

ABSTRACT: Development of efficient and specific equipment to dry microalgae is essential for commercial use of these microorganisms that show high growth rates and biotechnological potential. Drying costs of microalgae biomass are still high and they should be reduced for the production of compounds with low added value. Therefore, we evaluated the drying process of the microalga Scenedesmus obliquus BR003 using low temperatures. S. obliquus BR003 is a robust microalga that shows high lipid productivity. At laboratory scale, it was observed that the biomass of S. obliquus BR003 was rapidly dried at low temperatures between 50 and 60 ° C. A gas dryer was used to evaluate the drying of the biomass of S. obliquus BR003 on a pilot-scale. The biomass was dried in less than 24 h using the gas dryer; however, the high moisture of the microalga biomass required a higher air renovation in the drying chamber. Computational fluid dynamics analysis of the gas dryer showed two important parameters to achieve greater effectiveness of heat and mass transfer rates during the drying process of the microalga biomass. It was concluded that a gas dryer suitable for the microalgae biomass should have multiple air injection points, and an efficient circulation and renovation system of air inside the drying chamber.

RESUMO: O desenvolvimento de equipamentos eficientes e específicos para a secagem de microalgas é essencial para a exploração comercial destes microrganismos que apresentam alta taxa de crescimento e grande potencial biotecnológico. Os custos de secagem da biomassa de microalgas ainda são elevados e precisam ser reduzidos para a produção de compostos com baixo valor agregado. Portanto, realizou-se o estudo da secagem da microalga Scenedesmus obliquus BR003 utilizando baixas temperaturas. S. obliquus BR003 é uma microalga robusta que apresenta alta produtividade de lipídeos. Em escala laboratorial, observou-se que a biomassa de S. obliquus BR003 foi rapidamente seca em baixas temperaturas entre 50 e 60 ºC. Um secador a gás foi utilizado para avaliar a secagem da biomassa de S. obliquus BR003 em escala piloto. A biomassa foi seca em menos de 24 h utilizando o secador a gás, entretanto, a elevada umidade da biomassa da microalga requereu uma maior renovação de ar na câmara do secador. A análise de fluidodinâmica computacional do secador a gás mostrou dois parâmetros importantes para se obter uma maior efetividade de transferência de calor e massa durante o processo de secagem da biomassa de microalga. Concluiu-se que um secador a gás adequado, para a biomassa de microalgas, deve possuir múltiplos pontos de injeção de ar, e um eficiente sistema de circulação e renovação de ar no interior da câmara de secagem.