Moisture sorption equilibrium and thermodynamic properties of palm kernel
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Department of Agricultural Engineering, Obafemi Awolowo University, Ile-Ife, Nigeria
Department of Agricultural Engineering, University of Maiduguri, Maiduguri, Nigeria
Int. Agrophys. 2005, 19(4): 273–283
Equilibrium relative humidity – moisture content data for palm kernel at five different temperatures (40, 50, 60, 70, and 80°C) and moisture content values ranging from 8.6 to 19.1% (dry basis) were determined using the vapour pressure manometric method. A non-linear least squares regression programme was used to evaluate four moisture sorption models. The models were compared using the standard error of estimate, the mean relative percent deviation, the fraction-explained variation, and residual plots. Modified Henderson model was found to be the best model for predicting both the equilibrium moisture content and equilibrium relative humidity of palm kernel. The experimental data and the model that best predicted the equilibrium relative humidity were used to determine the thermodynamic characteristics of palm kernel. The heat of vapourization of moisture in the kernel decreased with increase in moisture content and approached the latent heat of pure water at a moisture content between 28 and 32% dry basis. The spreading pressure increased with increase in relative humidity and was not significantly affected by temperature. Net integral enthalpy decreased with increase in moisture content and became asymptotic in trend as the moisture content of 24% (db) was attained. Net integral entropy had positive values in the moisture range from 8.6 to 15% (db) and negative values from the moisture content of 15.3% (db) till 20% (db) was approached.