Evaluating isotherms and isosteric heat utilization during sorption characteristics of feed barley

Abstract

A well-formulated sorption model defines the grain moisture and also the energy expenses associated with drying and/or rehydration. Though literature contains adsorption and desorption models that are used to identify the hysteresis, they are not efficient to implement in sensors simultaneously when monitoring stored grain transient conditions. This study modifies the existing sorption model to fit transient monitoring criteria based on harvest moisture conditions between 11.3 and 85.9% RH at three temperatures (15, 25 and 35 °C). Feed barley was taken for the sorption study and fitted with equilibrium moisture content (EMC) and equilibrium relative humidity (ERH) equations of five widely used isotherm models, respectively. Model was fitted with EMC's attained at individual temperatures and the transfer phases between them.Sorption isotherms showed a non-smooth Type II sigmoidal trend with positive correlation between RH and EMC. The time taken to reach EMC irrespective of RH was inversely proportional to the temperature difference noted from the transfer phase. The Modified-Oswin equation (EMC) was found to be appropriate to represent the sorption isotherm of feed barley. For the transfer phases, EMC at higher temperature showed negligible difference with initial EMC phase except at 15 °C with higher RH (adsorption). Heat of sorption showed a decreasing trend with moisture and was 27% (average) higher than the latent heat of vaporization. Sorption heats for transfer phases were higher than initial EMC phases but not significantly different. Energy difference went up to 250 kJ kg−1 between 9 and 14% db moisture showing a normal distribution below and above the moisture range, respectively. Thus, future storage models should consider sorption heats for proper estimation of energy expenses during drying and rehydration.