Jorge Andrey Wilhelms Gut

Modeling of plate heat exchangers with generalized configurations

A mathematical model is developed in algorithmic form for the steady-state simulation of gasketed plate heat exchangers with generalized configurations. The configuration is defined by the number of channels, number of passes at each side, fluid locations, feed connection locations and type of channel-flow. The main purposes of this model are to study the configuration influence on the exchanger performance and to further develop a method for configuration optimization. The main simulation results are: temperature profiles in all channels, thermal effectiveness, distribution of the overall heat transfer coefficient and pressure drops. Moreover, the assumption of constant overall heat transfer coefficient is analyzed.

Using ultrasound technology for the inactivation and thermal sensitization of peroxidase in green coconut water

Green coconut water has unique nutritional and sensorial qualities. Despite the different technologies already studied, its enzymatic stability is still challenging. This study evaluated the use of ultrasound technology (US) for inactivating/sensitizing coconut water peroxidase (POD). The effect of both US application alone and as a pre-treatment to thermal processing was evaluated. The enzyme activity during US processing was reduced 27% after 30min (286W/L, 20kHz), demonstrating its high resistance. The thermal inactivation was described by the Weibull model under non-isothermal conditions. The enzyme became sensitized to heat after US pre-treatment. Further, the use of US resulted in more uniform heat resistance. The results suggest that US is a good technology for sensitizing enzymes before thermal processing (even for an enzyme with high thermal resistance). Therefore, the use of this technology could decrease the undesirable effects of long times and/or the high temperatures of the conventional thermal processing.

Predicting the dielectric behavior of orange and other citrus fruit juices at 915 and 2450 MHz

ABSTRACT Dielectric properties (DP: relative permittivity and loss factor) and electrical conductivity are important parameters for evaluating the microwave penetration depth and designing applicators for pasteurization processes. In this context, generalized equations that can predict the DP of a group of food products as a function of their characteristics are useful. The dielectric behaviours of eight citrus fruit juices (Pera, Lima, and Navel oranges, Ponkan tangerine, Murcott tangor, Mediterranean mandarin, Sicilian lemon, and Persian lime) and three Pera/Lima blends (25, 50, 75%) for temperatures between 0 and 90 °C and frequency between 500 and 3000 MHz were studied. The results were correlated with temperature at frequencies of 915 and 2450 MHz. It was possible to quantify the ionic and dipolar contributions. DPs were modelled based on the behaviour of pure water in a semiempirical approach using correction factors, which were correlated with temperature and juice physicochemical characteristics (pH, Brix, conductivity). Polynomial regressions can successfully predict relative permittivity with mean absolute errors of 0.49±0.35% and 0.58±0.48% and the loss factor with errors of 4.1±3.9% and 2.8±2.3% at 915 and 2450 MHz, respectively, for juices with Brix/acid ratio between 1.26 and 29.9.

Optimial design of continuous sterilization processes with plate heat exchangers

An optimization procedure is presented for configuration design of the plate heat exchanger sections of a plate pasteurizer subject to constraints on the equipment performance and operational limitations. The process mathematical model is presented for evaluating the unit thermo-hydraulic performance. Moreover, the extent of thermal processing inside the exchanger is determined. Both pasteurization costs and product thermal degradation are minimized using a structured search procedure that overcomes the limitations of representing the problem as a MINLP model. An example is presented for the design of a beer pasteurization unit.