The aim of this study was present a Phenomenological Based Semi-physical Model (PBSM) for the milk evaporation process. The evaporation is the elimination of solvent in form of water steam from a solution. In the dairy industry, the evaporation is a pretreatment for the powder milk processes that reduce the cost of the drying process, storage and transport. Thus, an appropriated mathematical model is necessary in order to get a good control and optimized process of milk evaporation, which allows obtaining a high-quality product. Previous studies have presented mathematical models for the evaporation process. However, the majority of these models are based on maintaining constant values such as the thermal properties of fluids, latent heat of vaporization and global coefficient of heat transfer, among others and this means that there will be high errors of predictions. The aim of this model was to predict the temperature, concentration and milk level in the evaporator. The model obtained was solved using the Runge-Kutta method with the software "LABVIEW 2011" and it was quantitatively validated with experimental data from a real process using the absolute mean error. The experimental data of temperature, concentration and milk level in the evaporator were obtained applying step-like disturbances in the process variables: vacuum pressure in the evaporation chamber, steam flow and milk feeding flow. The quantitative validation showed that the obtained model can predict satisfactorily the dynamic behavior of the target variables of the milk evaporation process because the error was less than 5%.
The aim of this research was to measure the effect of maltodextrin and gum Arabic on the rheological behavior of the sapote pulp. The rheological behavior of fruit pulp is modified with the addition of encapsulants which in turn influences the energetic performance of spray drying. In such processes, both maltodextrin and gum arabic are used as encapsulants of fruit pulp and acting as sugars protectors and thus reducing caramelization reactions. The experiment was conducted under a completely randomized design with 2×4 factorial arrangements (Factors: encapsulants and concentration). A Rheometer (AR 1500ex) was used for conducting the flow trials on continuous ramp on the pulp with encapsulants concentrations of 15, 20, 25 and 30% (w/w). Ostwald de Waele's model was adjusted to apparent viscosity data with determination coefficients greater than 0.994, apart from that, the consistency index (k) and the flow behavior index (n) showed significant differences (p≤0.05) between encapsulants and concentrations used. Those n values lower than one characterize the encapsulated pulp as pseudoplastic flow and the presence of hysteresis among the ascending and descending curves indicate that this is time-dependent fluid with thixotropic nature. The apparent viscosity of the pulp increased with the rise in the encapsulants concentration for the same shear rate, being the gum arabic the one with the greater values. Results will contribute to the improvement of the pump systems design of spray dryers.
Green and roasted coffee oil was extracted using supercritical CO2 at temperatures of (333, 343, 353 and 363) K and pressures from (235 to 380) bar, providing a CO2 densities range from (680 to 880) kg.m-3. The mathematical models of Del Valle-Aguilera and Chrastil were applied to predict the oil solubility. The Del Valle-Aguilera led to elevated deviations between the predict solubility values and those observed experimentally. The Chrastil model provided better results, with better fitting being observed. With this procedure, the mean percentage deviation was 0.16 and 0.19, respectively, for green and roasted coffee oil, showing a good correlation between the observed and predicted values.
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