Percorrer por autor "Silva, Teresa R."
A mostrar 1 - 3 de 3
Resultados por página
Opções de ordenação
- Development of a non-isothermal method for determination of diffusional parametersPublication . Moreira, Lília A.; Oliveira, Fernanda A. R.; Silva, Teresa R.; Oliveira, Jorge C.A non-isothermal method for determination of diffusional parameters was developed. The dependence of diffusivity on temperature was described by an Arrhenius type equation, 'with the pre-exponential factor and the,activation energy as parameters. These parameters were obtained by optimization of the fit between experimental and theoretical values, using the Simplex method of minimization. Equilibrium conditions were described with a constant unit partition coefficient. This model was applied to the diffusion of acetic acid into turnips. Results compared well with values obtained with the conventional method, using a set of experiments at isothermal conditions. The non-isothermal method has significant advantages, nameiy the need for much less experimental data and better insight into the statistical significance of the results.
- On the theoretical determination of optimal times for biomass production in batch cultures of aggregate-forming cellsPublication . Silva, Teresa R.; Malcata, F. XavierA model based on transient substrate and population balances coupled with Monod kinetics for growth has been formulated using several simplifying assumptions for batch cultures of cells which form biomass aggregates. The functional form of the analytical solution of this system of equations in its most generic aspect has been obtained and applied in the calculation of the time period corresponding to the maximum average rate of biomass increase.
- Prediction of pH Change in Processed Acidified TurnipsPublication . Moreira, Lília A.; Oliveira, Fernanda A. R.; Silva, Teresa R.The acetic acid uptake by turnips was studied during an acidification process in containers. The process was successfully described by a Fickian diffusion, using a correlation for the buffer effect. Diffusion coefficients (0.629 to 3.99 × 10-9 m2/sec) and partition coefficients (0.8 to 1.1) were obtained by optimization of the fit between experimental and theoretical values, using the simplex method. The partition coefficient did not show an evident dependence on temperature, while diffusivity followed an Arrhenius type behavior. The relationship between acid concentration and pH was described using a cubic model with parameters independent of temperature. Results showed that the combination of these models describing the acid diffusion into the food and the buffering effects of the food allowed accurate prediction of pH evolution in the acidification process.