Análise do coeficiente global de transferência de massa via simulação da secagem de cevada (Hordeum Vulgare L.) em leito fixo de camada delgada

Abstract

Barley (Hordeum vulgare L.) is a grain of great economic interest due to its application in the production of malt for beer industries, animal feed, and flours. It’s considered the best grain for the malting process due to its high starch content, high enzyme content, and appropriate protein composition, as well as its natural disease resistance and its protective shell which envelops the grain. In Brazil the main economic use is for the production of malt and the country does not yet produce enough to satisfy the national demand. The humidity in barley immediately after Harvest can vary anywhere from 12% to more than 20%. Grains stored with humidity higher than 12% lose their germinative capacity, producing low-quality malts, thus, the drying of barley previous to its storage is crucial. The understanding, analysis, modeling, and simulation of the drying of grains is complex due to the simultaneous occurrence of heat and mass transfer in a fragile biological material. Heat is necessary to transfer water from a liquid to a gas and the concentration gradient created leads to the mass transfer, which occurs both from the inside of the grain to its surface and from the grain surface to the air. The ideal drying process is one which maintains the equilibrium between those two processes while preserving the quality of malting barley, especially its germinative ability and physical integrity and prevents the development of fungi, bacteria, and insects. With that in mind, the objective of this work is to collect, analyze, and simulate barley drying data in a fixed bed and thin layer with drying air temperatures ranging from 40 °C to 60°C, air velocities of 1,0 m/s to 2,0 m/s and initial humidity ranging from 13,90±7,70 to 15,95±9,00 % (wet basis). For this, a simulation using a global theoretical drying model for fixed bed drying in a thin layer was used to obtain the global mass transfer coefficient and its effect in the germinative power of the grain with different drying conditions, and a parametric sensitivity analysis of the global mass transfer coefficients and the specific heat of the solid was made. The increase in temperature and velocity of the drying air led to a reduction of the final humidity of the seeds, and, in terms of germination, the results were in the range of 88 to 84%. The model used presented appropriate fitting for the conditions used and demonstrated that the greatest influence on the value of the global mass transfer coefficient was the drying air temperature. The values obtained are in the range of 9,0 x10-5 a 6,7 x10-4 kg/m²s. In the parametric sensibility analysis, it was found that the Kp found were the best possible fitting for the conditions studied, and the value of Cps used was appropriate and didn’t noticeably affect the simulation used.