Moisture Sorption Thermodynamic Properties of Bermuda Grass

MAJDI AL-MAHASNEH¹; MOHAMAD I. AL-WDYAN²; TAHA RABABAH³; MUHAMMAD ALU’DATT^3
1 Jordan University of Science and Technology, Department of Chemical Engineering, Irbid 22110, Jordan
² Jordan University of Science and Technology, Department of Mechanical Engineering, Irbid 22110, Jordan
³ Jordan University of Science and Technology, Departmet of Nutrition and Food Technology, Irbid 22110, Jordan

Abstract

Al-Mahasneh, M., M. I. Al-Wdyan, T. Rababah and M. Alu’datt, 2017. Moisture sorption thermodynamic properties of Bermuda grass. Bulg. J. Agric. Sci., 23 (4): 682–687

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 benefi ts 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 fi ndings of related previous studies, the Modifi ed 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. Specifi cally, 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.
Key words: Bermuda grass; equilibrium relative humidity; moisture sorption isotherms; postharvest; thermodynamic properties

List of Abbreviations: ΔH_d – differential heat of sorption (also known as net isosteric heat of sorption); ΔS_d – differential entropy; T_β – isokinetic temperature; w.b. – wet basis; T_hm – harmonic mean temperature; ERH – equilibrium relative humidity; T – temperature; EMC – equilibrium moisture content; ΔG – Gibb’s free energy change; Q_s – isosteric heat of sorption; R² – correlation coeffi cient; MSE – mean square error

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