Modeling heat and mass transfer in the heat treatment step of yerba maté processing

Abstract

The aim of this research was to estimate the leaf and twig temperature and moisture content of yerba maté branches (Ilex paraguariensis Saint Hilaire) during heat treatment, carried out in a rotary kiln dryer. These variables had to be estimated (modeling the heat and mass transfer) due to the difficulty of experimental measurement in the dryer. For modeling, the equipment was divided into two zones: the flame or heat treatment zone and the drying zone. The model developed fit well with the experimental data when water loss took place only in leaves. In the first zone, leaf temperature increased until it reached 135°C and then it slowly decreased to 88°C at the exit, despite the gas temperature, which varied in this zone from 460°C to 120°C. Twig temperature increased in the two zones from its inlet temperature (25°C) up to 75°C. A model error of about 3% was estimated based on theoretical and experimental data on leaf moisture content

Thermophysical Properties of Mate Leaves: Experimental Determination and Theoretical Effect of Moisture Content

“…2–4 present results of thermal conductivity and apparent density. Again, a good agreement between the currently determined properties and analogous results for leaves (Peralta and Schmalko 2007) and twigs (Schmalko et al. 1997) of mate shown in the literature is revealed.…”

“…2. Basically, it reveals a negligible difference between the specific heat obtained in this investigation and the same property available in the literature for leaves (Peralta and Schmalko 2007) and twigs of mate (Schmalko et al. 1997).…”

“…All the procedures to experimentally obtain C ps , k s , ρ s and to theoretically calculate the effect of moisture content on these properties were validated by a comparison between the results obtained in this investigation and the few analogous data available in the literature (Yin 1985; Yoshitomi 1987; Schmalko et al. 1997; Peralta and Schmalko 2007). …”

“…Based on the large consumption of energy in these stages, any reliable strategy for reducing manufacturing costs of the mate industry involves optimization of both these operations with mathematical models. However, as already mentioned, thermophysical properties of mate leaves are important variables required for model solution (Peralta and Schmalko 2007; Zanoelo 2007) whose availability is limited in the literature (Schmalko et al. 1997; Peralta and Schmalko 2007).…”

Thermal inactivation of peroxidase and polyphenoloxidase enzymes in mate leaves (Ilex paraguariensis) in a conveyor belt oven

“…There is no consensus on the ideal temperature for the sapeco process, and the temperatures reported in literature are between 400 and 620°C (Peralta & Schmalko, 2007;Schmalko, Ramallo, Ferreira, & Berlingheri, 2002;Vieira et al, 2008). Mate leaves vary greatly in area and thickness; therefore, the heat transfer is uneven, and such fact hampers a quality control of the final product (Coelho, Mariath, & Schenkel, 2002).…”