Sandra M. Couto

Three-Dimensional Simulation of the Temperature Variation in Corn Stored in Metallic Bin

This work presents the modeling of the heat transfer process in a cylindrical bin with 3.6 m of diameter and 2.2 m of height filled with corn. The model is a threedimensional and does a transient analysis of the process. The developed model simulated well the temperature variation across the corn bin. The mean relative error of the simulated product temperature was 2.2%.

Modelagem de máquina pneumática recolhedora de frutos de café em terreiro usando análise por elementos finitos

The objective of this work was the development of a mathematical model by finite element analysis, using the software ANSYS®, version 5.7, to optimize the design of a machine which collects coffee fruits on a yard. The machine modeling was based on the aerodynamic characteristics of coffee fruits and on the air flow necessary to pneumatically transport the coffee fruits. The static pressures on the machine ducts was obtained experimentally and these values were compared with the results obtained by the software ANSYS to validate the modeling. Based on the results, it was concluded that the modeling using the software ANSYS had similar results to the ones obtained experimentally, with a relative mean error of 9.2% for the simulated pressure values. Through the modeling, it was identified pressure ranges that would make the coffee fruits pneumatic transport more difficult, at some parts inside the machine. These problems were corrected and the air flow supplied by the fan was sufficient to collect coffee fruits on the ground by suction. The developed modeling fulfilled the requirements of this work which was to collect coffee fruits on the yard using pneumatic transport efficiently.

Unity and bulk densities and porosity of coffee as affected by moisture content

This research presents values for some physical characteristics of coffee necessary for development of aerodynamic separation units and for design of driers and silos. The effect of moisture content on the values of unity and bulk density and porosity of coffee varieties Catuaí and Timor, was investigated. The coffee was harvested in two stages of maturation (green and cherry). The grains from cultivar Catuaí were harvested in two different periods. The harvesting period did not cause differences on the values of the densities. The behaviors of unity and bulk densities of coffee were different from those observed for most of the agricultural grains. The unity density of coffee increased with increases in moisture content, whereas the bulk density decreased. The unity and bulk density values for coffee are lower than those for others grains, but the values for porosity were found to be in the same range.

Airflow distribution in aerated silos: finite element analysis

In this work the finite element technique was used to obtain the air distribution in a mass of corn kernels submitted to an aeration process. The product (13% w.b.) was stored in metallic bin provided with a circular duct aeration system. The mass of grains was considered as being composed of regions (distributed resistances) that offer different resistances to the airflow in the horizontal and vertical directions. The model for air distribution in the bin was validated through experiments under similar conditions to the simulated ones with 0.0157 m3 s-1 m-2 airflow. The simulated air distribution indicated the existence of zones of low air velocities in the mass of grains located at the base of the bin (close to the center and to the wall of the bin). The simulated and experimental air velocities on the surface of the mass of grains showed a uniform tendency. The use of the finite element technique for the prediction of the airflow distribution in bins with aeration system was satisfactory and it involved a mean relative error of 6.9%..

Determinação de propriedades térmicas de grãos de milho

Realizou-se este trabalho com o objetivo de determinar a massa especifica, condutividade termica, difusividade termica e calor especifico de graos de milho, em funcao do teor de agua do produto. Na determinacao da condutividade e da difusividade termicas, foi usado o metodo do cilindro infinito dotado de uma fonte de calor linear central. Para tal, foi construido um equipamento que consistiu de um tubo de aluminio (0,1 m de diâmetro e 0,5 m de altura) isolado nas extremidades superior e inferior. Para funcionar como fonte linear de calor, instalou-se no centro do cilindro (na direcao longitudinal) um fio resistor de niquel-cromo envernizado (resistencia, aproximada, 4,16 W.m-1), com diâmetro de 0,0006438 m. Durante cada determinacao, o fio resistor foi submetido a uma diferenca de potencial de 2,08V (fonte alimentadora de tensao e voltagem), que proporcionou uma corrente eletrica de 1A. O teor de agua das amostras testadas variou de 8,6 a 17,1% b.u. O comportamento dos valores de condutividade termica, difusividade termica e calor especifico em funcao do teor de agua no produto pode ser representados por relacoes lineares. A condutividade termica e o calor especifico dos graos aumentaram com o teor de agua do produto, enquanto a difusividade termica diminuiu. Erros envolvidos nas determinacoes das propriedades termicas sao tambem discutidos neste trabalho.

Distribuição da pressão estática em uma coluna de canola: análise por elementos finitos

The flow of a fluid through a porous medium occurs during the aeration and drying stages of a mass of grains, used for the product quality conservation. In this work, using the finite element technique, the variation of the static pressure in a bed of rapeseed Iciola-41 (Brassica napus L. var. olifera) submitted to different airflows was modeled. Through an optimization process, the permeability of the bed to the different airflows was also determined. The results of the finite element analysis, when compared with those obtained from some classical models, presented the best performance. The relative error using the finite element technique varied in the range 0.7 - 24.3% while the relative error for all simulations was approximately equal to 5.3%.

Resistência de café em coco e despolpado ao fluxo de ar

In this study expressions to describe (1) variations of unit and bulk density and porosity of the coffee (dried cherry and pulped) as a function of the product moisture content and (2) the behavior of the values of airflow resistance in coffee columns (dried cherry and pulped) as a function of the product moisture content, airflow intensity and depth in the coffee column were investigated. For pulped coffee, unit and bulk density and porosity are linear functions of moisture content; densities increase with the product moisture content while the porosity decreases. For dried cherry coffee: unit and bulk densities are quadratic functions of the product moisture content that present minimum values in the moisture content range investigated. The porosity is, practically, independent of the product moisture content; for the same moisture contents: the unit bulk density values of dried cherry coffee are smaller than those for pulped coffee; the porosity values of dried cherry coffee are greater than those for the pulped coffee. In terms of the behavior of the static pressure values in the product column, it was observed that the pressure in the pulped coffee is always larger than in the dried cherry coffee for all the column depths and three moisture contents.

Determinação da força de arrasto e da velocidade terminal de frutos de café pela técnica de elementos finitos

This work presents an alternative method for terminal speed and drag force determinations for coffee fruits with different moisture contents and geometric configurations (spherical and elliptic). Specifically, the use of the finite element technique was investigated for obtaining: (a) product drag forces using experimental values of the fruit dimensions and its terminal velocity and (b) product terminal velocity using experimental values of fruit dimensions and weight. The use of finite element technique was shown to be an efficient tool to simulate terminal velocity and drag force on coffee fruits submitted to airflow. Independent of the fruit moisture content, simulated and experimental values for the terminal velocity and drag force did not differ statistically when the product was considered elliptic. For each product moisture content, the mean relative errors involved in the simulated values of terminal velocity were not superior to 7.5 and 13.6% for the fruits considered elliptic and spherical, respectively.

Variação da temperatura e umidade de grãos armazenados em silos com aeração

The temperature and moisture content variations in corn kernels stored in a bin during an aeration process are presented in this work. The aeration time requirements were determined to obtain a temperature difference of 3 oC between the mass of grains and the external environment. The temperature of the stored grains was increased by submitting the product to a forced flow of moist and pre-heated air before the aeration. Airflow of 0.0157 m3 s-1 m-2 was used in the aeration process. Temperatures were recorded at several points inside the grain mass with the aid of thermocouples connected to a data acquisition system. The points were located radially at different horizontal and vertical distances on the North, South, East and West directions. Samples of the product were collected periodically during the process for moisture content determination. The temperature reduction in the mass of grains depended on the location of the product inside the bin. The largest temperature reductions were detected for the product located at South and East, and the smallest for the product at North and West (initially with lower temperature). The largest reduction in the temperature of the mass occurred between 24 and 48 h of aeration. An aeration time of approximately, 70 h was necessary to obtain a 3 oC temperature difference between the mass of grains and the external environment.