-Neural networks and hybrid models were used to study substrate and product inhibition observed in the enzymatic hydrolysis of cellobiose at 40ºC, 50ºC and 55ºC, pH 4.8, using cellobiose solutions with or without the addition of exogenous glucose. Firstly, the initial velocity method and nonlinear fitting with Statistica ® were used to determine the kinetic parameters for either the uncompetitive or the competitive substrate inhibition model at a negligible product concentration and cellobiose from 0.4 to 2.0 g/L. Secondly, for six different models of substrate and product inhibitions and data for low to high cellobiose conversions in a batch reactor, neural networks were used for fitting the product inhibition parameter to the mass balance equations derived for each model. The two models found to be best were: 1) noncompetitive inhibition by substrate and competitive by product and 2) uncompetitive inhibition by substrate and competitive by product; however, these models' correlation coefficients were quite close. To distinguish between them, hybrid models consisting of neural networks and first principle equations were used to select the best inhibition model based on the smallest norm observed, and the model with noncompetitive inhibition by substrate and competitive inhibition by product was shown to be the best predictor of cellobiose hydrolysis reactor behavior.
Microcomputers introduced process control to a new era. A simple and didactic experiment, used to control the temperature of an equipment, is described. Features of this experiment include the use of two computers connected by serial ports and allowing students to build the controller and to disturb the process. ß
In one of the stages of the gelatin production process, a highly concentrated solution of gel is cooled and extruded to form gelatin noodles, which are then laid on a drying belt. Gelatin is a molecular colloid that is not porous under these drying conditions, and as a consequence, water migration occurs solely by diffusive processes. To achieve a commercial standard of dryness, the dependence of the diffusion coefficient as a function of temperature is used. This set of circumstances favors the appearance of sharp concentration gradients inside the gel. In a numerical simulation of the drying process these characteristics create difficult conditions for use of the traditional methods for solution of time-dependent partial differential equation models. This paper evaluates an implementation of the boundary element method to determine surface conditions of the gelatin particle
RESUMO. Neste trabalho, um modelo transiente para um secador do tipo esteira, utilizado na secagem de gelatina, foi obtido através de balanços de massa e energia, sendo inicialmente consideradas três hipóteses para a isoterma de equilíbrio e duas para a taxa de secagem. A definição dessas expressões foi realizada pelo ajuste do modelo aos dados de uma situação típica de operação com as principais variáveis do processo medidas pelo acompanhamento de um lote de gelatina ao longo do secador. Um ensaio, em laboratório, foi realizado para se obter a curva de secagem, indicando que a secagem da gelatina ocorre essencialmente em uma fase. Assim, o modelo utiliza a isoterma de Henderson e uma expressão para a taxa de secagem de apenas uma fase. Os resultados da simulação do modelo nas condições do processo demonstram que esse é capaz de representar as principais tendências do processo.Palavras-chave: secagem, modelo, gelatina, secador industrial. ABSTRACT. Modeling of a conveyor dryer: an industrial application.In this work, a transient model for a conveyor dryer used in gelatin drying is made through mass and energy balances, being initially considered three hypotheses for the equilibrium isotherm and two for the drying rate. The option about these equations was done through the model's fitness to typical operation values with the main process variables measured coming with a small portion of gelatin. An experiment done to get the drying curve suggests the gelatin drying happens in only one phase. As a result, the model uses the Henderson's isotherm and a single phase expression for the drying rate. Model simulation's results at process conditions show it is able to represent the main trends of process.
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