MOISTURE SORPTION THERMODYNAMIC PROPERTIES OF BERMUDA GRASS

Abstract

Thermodynamic properties such as differential enthalpy and differential entropy are important tools for analyzing postharvest handling and drying of grasses such as Bermuda grass. This particular grass is widely used as a feedstock or as pellets for energy production. Thus, this study was initiated with the aim of modeling moisture sorption thermodynamic properties of Bermuda grass with potential benefits of minimizing energy costs and optimizing drying kinetics. Moisture sorption thermodynamic properties of Bermuda grass were studied using gravimetric methods under three temperature levels, namely, 20, 30 and 40°C. Based on findings of related previous studies, the Modified Halsey model was used to obtain the thermodynamic properties of the grass. It was found that, within the ranges considered here, both properties were strong functions of equilibrium moisture content and decreased substantially (by about 97%) with equilibrium moisture content. Specifically, differential enthalpy of the grass decreased exponentially with increase in moisture content from 1912 kJ/kg at 0.03 equilibrium moisture content (decimal w.b.) to 62.8 kJ/kg at an equilibrium moisture content of 0.27. Similarly, differential entropy decreased also exponentially from 7.93 kJ/kg.K to 0.26 kJ/kg.K at the same respective levels of equilibrium moisture content. Enthalpyentropy compensation was validated by the linear relationship between the two. Finally, it was found that the moisture sorption process for Bermuda grass is enthalpy-driven.