The Effect Factors of Hygroscopic Behavior and Thermodynamic Properties of the Hybrid Pennisetum

Abstract

<b><sc>Abstract.</sc></b> To know the hygroscopic behavior is helpful to understand the law of heat and mass transfer during drying Hybrid Pennisetum. And it is essential for drying and storage. The moisture sorption behaviors of the Hybrid Pennisetum at the temperature of 10, 20, and 30 ℃ and relative humidity among 50% and 90% were obtained using the static℃ gravimetric method. The effects of the initial material temperature and the material layer‘s thickness on the hygroscopic properties were analyzed at the condition of temperature 30 ℃ and relative humidity of 70%. The results showed that the moisture sorption isotherms of the Hybrid Pennisetum coincided with the standard type III isotherm, and the adsorption equilibrium moisture content increased with the increase of water activity. The material layer‘s thickness and the initial temperature influenced a little on the sorption equilibrium moisture content. Modelling showed that the Peleg model expressed the Hybrid Pennisetum hygroscopic behavior best. At the ambient temperature of 10, 20, and 30℃, the absolute safe moisture contents (dry basis) of the Hybrid Pennisetum were 0.13, 0.15, and 0.18 g/g, respectively. And the relative safe moisture contents (dry basis) was 0.18, 0.20, and 0.19 g/g, respectively. Correspondingly, the critical relative humidity of the Hybrid Pennisetum was 79.88%, 81.23%, and 79.10%, respectively. The binding energy and net isosteric heat of sorption decreased with the increase of equilibrium moisture content. The binding energy and the net isosteric heat of sorption were low when the equilibrium water content was greater than 0.20g/g.