Mathematical modeling of withering characteristics of tea leaves

The withering characteristics of tea leaves were examined for different temperatures. Tea leaves were withered at a temperature range of 20-45 degrees C with a constant air velocity of 1.1 m/s. The experimental results illustrated the absence of constant-rate drying period and withering took place only in the falling-rate period. During the falling-rate period, at constant drying air flow rate, the drying rate increased and drying time decreased with the increase in drying air temperature. Drying models of Henderson and Pabis and Page were evaluated based on mean bias error (E-MB), root mean square error (E-RMS), correlation coefficient (R-2), and the chi square (chi(2)). The Henderson and Pabis model was found to be a better model for describing the withering characteristics of tea leaves for each of the temperatures of 20, 25, 30, and 35 degrees C. The values obtained from Page model were found to be more reasonable for temperatures of 40 and 45 degrees C than the other model. Both the models closely fitted the withering data within a certain range of temperature. The Henderson and Pabis model gave better prediction and satisfactorily described the withering characteristics of tea leaves at temperatures lower than 40 degrees C whereas the Page model fitted well at temperatures greater than 40 degrees C.