THERMOPHYSICAL PROPERTIES OF MATE LEAVES: EXPERIMENTAL DETERMINATION AND THEORETICAL EFFECT OF MOISTURE CONTENT

An experimental investigation to determine the specific heat, thermal conductivity and apparent density of mate leaves (Ilex paraguariensis) was carried out. The experimental method of mixtures and a quasi-adiabatic calorimeter were used to obtain a specific heat of dry leaves close to 1780 ± 450 J/kg/K. A thermal conductivity of 0.17 ± 0.01/W/m/K was tuned on transient experimental measurements of temperature in a dry bar of mate leaves. A dynamic one-dimensional heat transfer model was involved in this procedure of tuning. An apparent density equal to 750 ± 40 kg/m was experimentally found. The effect of moisture content on these thermophysical properties was also theoretically investigated by involving simplified models based on properties of only dry matter and water. Analogous results available in the literature support the reliability of all experimental data and equations presented in this investigation. PRACTICAL APPLICATIONS Mate manufacturing basically involves a stage of enzymatic deactivation and a process of drying that are together responsible for almost the full energy consumed in the mate industry. A detailed description of both these processes with mathematical models is a cheap and safe way to process optimization and energy saving. However, the knowledge of the specific heat, thermal conductivity and density of the processed material whose availability is limited in the literature is required for model solution.