Gabriel Henrique Horta de Oliveira

Modelagem matemática e determinação das propriedades termodinâmicas do café (Coffea arabica L.) durante o processo de secagem

The aim of the present work was to model the drying process and to obtain the thermodynamic parameters of coffee beans (Coffea arabica L.), cultivar Catuai Amarelo, for three different conditions of temperature and relative humidity (35 oC and 32.1 %; 45 oC and 15.7 %; 55 oC and 10.2 %). Coffee beans were hand picked with an initial moisture content of 1.25 (d.b.) and dried to a mean moisture content of 0.13 (d.b.). Six mathematical models commonly used to represent the drying process of agricultural products were fit to the experimental data. Fick’s second law was used to obtain the diffusion coefficients of coffee beans using the drying kinetics. The activation energy for the drying process of coffee beans, as well as the entropy, enthalpy and Gibbs free energy were determined. The modified Midili model best represented the drying phenomenon of coffee beans. The calculated diffusion coefficients were 2.99 x 10 -11 , 2.39 x 10 11 and 5.98 x 10 -11 m 2 s -1 , to the temperatures of 35, 45 and 55 oC, respectively. Enthalpy decreased with the increase in

Tomato Infrared Drying: Modeling and some Coefficients of the Dehydration Process

La deshidratacion por infrarrojo es mas ventajosa que el sistema convectivo, en condiciones similares, y el estudio de este proceso es importante para el desarrollo de equipos y procedimientos. Por tanto, el presente trabajo tuvo como objetivo el estudio del proceso de deshidratacion en tres diferentes estados de maduracion de rebanadas de tomate (Solanum lycopersicum L.) por medio del secado por infrarrojo, usando dos metodos: aproximacion del periodo constante de deshidratacion a la teoria de la transferencia de calor y masa para el termometro de bulbo humedo; y al periodo decreciente de la deshidratacion a la teoria de difusion de liquidos. Se utilizaron frutos de tomate cv. Santa Cruz. Tres estados de maduracion fueron obtenidos: verde (estado 1), naranja (estado 2) y rojo (estado 3). Modelos matematicos usualmente utilizados para representar el secado de productos agricolas fueron ajustados a los datos experimentales del secado de tomate. El coeficiente de difusion efectivo fue obtenido por medio del ajuste del modelo matematico de difusion liquida a los datos experimentales del periodo decreciente de deshidratacion. El modelo Dos Terminos represento mejor el proceso del secado de rebanadas de tomate. La humedad critica para la deshidratacion de tomate fue 2.97 kgw kgdm-1. Existe un periodo inicial de deshidratacion en que la tasa de secado alcanzo el maximo (aproximadamente 1.05 kgw kgdm-1, alrededor de 3 min). Tres diferentes metodos fueron utilizados para obtener los valores del coeficiente efectivo de difusion, incluyendo el metodo de elementos finitos, en que presento los menores valores de la suma de desviaciones minimas al cuadrado, 1.00 x 10-7 m2 s-1. El coeficiente global de transferencia de calor fue 12.45 W m-2 K-1, y el coeficiente global de transferencia de masa fue 0.0105 m s-1.

Effects of the mechanical damage on the water absorption process by corn kernel

The purpose of this study was to investigate and model the water absorption process by corn kernels with different levels of mechanical damage Corn kernels of AG 1510 variety with moisture content of 14.2 (% d.b.) were used. Different mechanical damage levels were indirectly evaluated by electrical conductivity measurements. The absorption process was based on the industrial corn wet milling process, in which the product was soaked with a 0.2% sulfur dioxide (SO2) solution and 0.55% lactic acid (C3H6O3) in distilled water, under controlled temperatures of 40, 50, 60, and 70 oC and different mechanical damage levels. The Peleg model was used for the analysis and modeling of water absorption process. The conclusion is that the structural changes caused by the mechanical damage to the corn kernels influenced the initial rates of water absorption, which were higher for the most damaged kernels, and they also changed the equilibrium moisture contents of the kernels. The Peleg model was well adjusted to the experimental data presenting satisfactory values for the analyzed statistic parameters for all temperatures regardless of the damage level of the corn kernels.

Thermodynamic properties of drying process and water absorption of rice grains

ABSTRACT This study aimed to obtain the drying and water absorption curves of husk rice grain (Oryza sativa L.), cv. Urucuia, as well as the thermodynamic properties. Five temperatures (35°C, 45°C, 55°C, 65°C and 75°C) were used. Two terms, logarithmic, modified Midilli, Page and Verma models were used to model the drying process, and the Peleg model was used to model the soaking process. The modified Midilli and Peleg models satisfactorily accounted for the processes of drying and absorption of water, respectively. The activation energy for the drying and soaking was 51.03 and 37.06 kJ mol−1, respectively. The enthalpy and entropy decreased with increasing temperature, regardless of the process. Their values ranged between −6.60 and 48.47 kJ mol−1 and between −0.1084 and −0.2464 kJ mol−1 K−1 for enthalpy and entropy, respectively. The Gibbs free energy increased with increasing temperature, with values between 69.36 and 86.22 kJ mol−1.

Modelagem e propriedades termodinâmicas na secagem de morangos

The drying of agricultural products is widely used throughout the world to diminish the moisture content of the product, making microbial growth and chemical and biochemical reactions difficult, enabling safe storage for longer periods and also reducing the volume and mass to be transported. The aim of the present work was to evaluate and model the drying process of strawberries (Fragaria L.) and obtain the thermodynamic parameters at three different temperatures (40, 50 and 60°C). Fruits purchased at CEASA-DF with an initial moisture content of 93% (w.b.) were used. The experimental data were fitted to six mathematical models commonly employed to represent the drying step. The activation energy for the drying of strawberries and also the entropy, enthalpy and Gibbs free energy were determined. The Logarithmic model was the one that best fitted the drying phenomenon of strawberry fruits, presenting values for the mean relative error between 7.59 and 8.48%, with an estimated standard error between 0.03 and 0.06 and determination coefficient between 99.93 and 99.95%. The enthalpy of the drying process decreased with increase in drying temperature, with values of –481.21, –564.35 and –647.49 J mol–1 for temperatures of 40, 50 and 60°C, respectively. The same trend occurred for entropy, with values of –238.35, –238.61 and –238.86 J mol–1K–1 for the temperatures of 40, 50 and 60°C, respectively. Gibbs free energy increased with increase in temperature, attaining values of 74,159.75, 76,544.54 and 78,931.90 J mol–1 for the temperatures of 40, 50 and 60°C, respectively.

LINSEC: the software for modeling and simulation of grain drying systems

Considering the importance of mathematical models in the development and analysis of grain drying systems, and understanding the need to develop interfaces that will improve the accessibility of these models, this work aimed to: a) implement the Thompson model to simulate grain drying at high temperatures; b) develop an appropriate language to generate drying models; and c) develop a graphical interface with the goal of facilitating user understanding. Thus the computational program LINSEC that was created using the programming language Visual Basic 6.0. LINSEC was highly effective for the modeling and simulation of drying systems and in providing simulated values close to reality. LINSEC is highly flexible and user-friendly during the modeling of several types of dryers.