Generalized single-layer model for drying kinetics of unpeeled-longan

Dried longan fruit has become an important export product of Thailand.Knowledge about drying kinetics is essential to optimize the drying process.In this study,drying kinetics of unpeeled longan fruits was investigated by varying the parameters as follows:air temperature 50~90℃,relative humidity 4%~20%,air velocity 0.2~0.5 m/s,and size of the fruits.The drying curves of longan fruit,dried in a single layer,were strongly affected by the temperature of the drying air and fruit size but less dependent on relative humidity and velocity of the drying air.Eight single-layer drying models were selected from literature to identify suitable ones for fitting moisture ratio curves to data obtained from the drying experiments.Both,the proportional and exponential coefficient of drying time in the‘Page’model could be given in a generalized function for each of the investigated drying parameters.Moreover,the two coefficients could be correlated to all drying parameters simultaneously.This allowed establishing a generalized‘Page’model for estimating drying curves for any value of temperature,fruit size,relative humidity and air velocity within the range of performed experiments.The analysis also revealed an inner correlation between the two‘Page’coefficients,which opens new doors for further research on the application of the‘Page’model for describing drying processes.