Escola Superior de Biotecnologia
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- Heat removal from heat-sensitive foods: an economic approach to the transient behaviour of finned surfacesPublication . Malcata, F. XavierThe transient behaviour of a fin used to remove heat from the surface of a rectangular-shaped liquid food container is studied in dimensionless form leading to a single-term equation for the heat transferred in relation to time. For heat-sensitive foods the rate of heat removal is important so an economic value can be ascribed to such removal to balance the captial investment on finning the container. An optimal solution can be found in order to maximize the net profit involved using the fin length as the independent variable.
- Computer aided design of pellets for fixed-bed reactors performing Michaelis—Menten reactionsPublication . Malcata, F. XavierThe problem of designing the pellet characteristics for existing fixed-bed reactors has been studied. The reactor is assumed to be a unidimensional, plug-flow, heterogeneous type. Three particle shapes, two intraparticle mass transfer mechanisms, two lands of film resistance to mass transfer and two poisoning patterns have been considered. An economic balance to both product market price and pellet market cost was taken into account. An interactive program (HIMER) containing all these contributions was thus developed, enabling the investigator to follow the reactor performance along the flow coordinate.
- HERSIM: a microcomputer program designed to compute the limits of conversion for real homogeneous isothermal enzymic reactorsPublication . Malcata, F. XavierHERSIM is a program written in BASIC designed to aid the investigator interested in determining the substrate conversion in a real homogeneous isothermal enzymic reactor, for various kinetic equations. The program runs after tracer data relative to a Dirac impulse to the reactor have been entered, and computes the two limits of real conversion: total segregation and maximum mixedness. The kinetic constants of the reacting system are input as data, and the variation of conversion with reactor temperature between given limits is computed as accurately as requested.
- Optimal design on an economic basis for continuous stirred tank reactors in series using michaelis-menten kinetics for ping-pong reactionsPublication . Malcata, F. XavierA theoretical analysis of the reactant concentration profile along a given number of CSTR's in series for ping-pong type reactions following Michaelis-Menten kinetics (with equal initial concentrations for both substrates) has been developed. Minimising the total holding time was taken as the intermediate objective function whereas minimising the total capital investment was assumed to be the main objective function.
- Double surface-renewal model for the prediction of mass transfer rates during bubble formation with instantaneous reaction on the liquid sidePublication . Malcata, F. XavierDesorption of a component from a gas mixture being injected through a submerged nozzle, during the bubble formation stage, is theoretically studied. The solute is assumed to suffer an instantaneous reaction on the liquid side, the reaction plane being on the liquid/gas interface. The volume elements on the gas bubble are assumed to result from a forced surface renewal coupled with a natural surface renewal, both achieved via gas elements with fresh composition. A surface residence time distribution is thus obtained, and desorption rates are calculated from the relevant variables, assuming non-steady state, unidimensional diffusion in a semi-infinite medium as the main mass transfer mechanism. Comparison of the model with experimental data is reported, physical evidence being predicted better than with previous models.
- A note on the optimal volumetric flow rate during start up of a BSTR performing a Michaelis-Menten reactionPublication . Malcata, F. X.Theoretical background for the calculation of the optimum constant volumetric flow rate for an isothermal BSTR performing a Michaelis-Menten reaction under transient behaviour arising from start up conditions is reported. The asymptotic kinetlic behaviours of zeroth and first order were used in order to derive derive analytical criteria, quite useful for the predesign steps in some situations where the filling up and the overall operating time are of the same order of magnitude.
- A heuristic approach for the economic optimization of a series of CSTR's performing michaelis–menten reactionsPublication . Malcata, F. XavierThe estimation of the size of each reactor of a series of CSTR's performing a Michaelis–Menten reaction in the liquid phase can be obtained to advantage via an optimization technique leading to the minimum overall capital cost. The cost scaleup is assumed to be described by a power rule on the equipment capacity. Various contributions are lumped into the exponent, thus leading to values above unity. The analytical development leading to the optimal intermediate concentrations of substrate according to the foregoing criterion is presented. A short-cut method based on an empirical expression that approximates the numerical solution is reported. This correlation is found to be exact at the asymptotic behaviors, and to give accurate results within an acceptable error level for the range with physical interest. Therefore, it is particularly useful during the predesign steps of equipment for the biochemical industry.
- Starter culture production in fluidized bed reactor with a flocculent strain ofL. plantarumPublication . Barreto, M. T. O.; Melo, E. P.; Carrondo, M. J. T.A lactic starter culture of a flocculentLactobacillus plantarum was produced in a fluidized bed reactor with higher cell volumetric productivities than in a continuous stirred tank reactor. The fluidized bed reactor was operated at optimised parameters obtained in batch reactor performed with and without pH control.
- Chloride pseudotitration in wines by FIA with a Ag2S/Ag tubular electrode as detectorPublication . Lima, José L. F. C.; Rangel, António O. S. S.The determination of chloride in wines by potentiometric titration with silver cation in a nonsegmented flow system (FIA) using a tubular electrode of silver/silver sulfide detector is described. There was good agreement between the results obtained using the FIA titration and those obtained using the reference procedure. The methodology developed is adequate for the determination of chloride in various types of wines with chloride contents between 5 and 600 mg/liter, at sampling rates of 60 and 120 samples per hour.
- A note on the optimization of batch distillation times for binary systemsPublication . Malcata, F. Xavier