5TH INTERNATIONAL CONFERENCE ON ADVANCES IN MECHANICAL ENGINEERING, İstanbul, Turkey, 17 December 2019 - 19 January 2020, pp.1466-1472
Drying is simultaneous heat and mass transfer energy intensive operation, widely used as a food preservation technique. In the present study, applicability of cabinet dryer was investigated at air temperature of 50, 60 and 70°C for drying of pear slices. Drying characteristics and kinetics of pear slices were evaluated as well as study the applicability of some empirical models for modelling. Nonlinear regression was used to fit Lewis, Henderson & Pabis, Page and Midilli & Kucuk models to the drying data. The goodness of fit between experimental and predicted moisture ratio was tested using regression coefficient (R2) and reduced chi-square (c2) and root means square error (RMSE). Highest R2 and least c2 and RMSE indicate the suitability of the model to experimental data. The effects of hot air drying temperature of 2.0 m/s on the drying kinetics of pear slices were determined. Prior to the drying experiments, the samples were divided into two groups. Samples in the first group were treated with citric acid + ascorbic acid (SA+AA) solution for 1 minute. Control samples were dried naturally without any pretreatment. During the drying experiment, the moisture content of pear slices decreased from 81.45% to 10% (w.b.). The results showed that pretreatment solution and air temperature affected the drying behaviours of pear slices. Drying rate of the pear slices increased markedly air temperature increased from 50 to 70°C. The results of regression analysis indicated that the Midilli & Kucuk model is the best to describe the drying behaviour with the lowest c2 and RMSE values and highest R2 value. The effective moisture diffusivity at each air temperature was determined by Fick’s second law of diffusion, an increase in the temperature led to increase in the effective moisture diffusivity between 3.64×10−10 and 8.36×10−10 m2/s. The dependence of effective moisture diffusivity on temperature was expressed by an Arrhenius type equation. The values as activation energy of SA+AA and Control samples were estimated as 28.13 and 34.60 kJ/mol, respectively.