Experimental and numerical investigations of moisture diffusion in pistachio nuts during drying with high temperature and low relative humidity
2007
Rafiee, S. (Tehran Univ., Karaj (Iran). Faculty of Biosystem Engineering) | Jafari, A. (Tehran Univ., Karaj (Iran). Faculty of Biosystem Engineering) | Kashaninejad, M. (Gorgan Univ. of Agricultural Sciences and Natural Resources (Iran)) | Omid, M.
In this study, a numerical solution based on finite element (FE) is adopted to simulate the mass distribution inside a pistachio nut (cv. Ohadi). It was found that the FE solution of the diffusive moisture transfer equation could improve nut-drying simulation of axisymmetric bodies. An axisymmetric linear triangular element with two degree of freedom per node was used to discretize the pistachio nuts in the model. A thin layer pistachio nut was dried at two drying air temperatures of 55 and 70 degree C under constant air velocity and relative humidity and moisture content was measured every minute. The simulation data were tested using values obtained from thin layer drying experiments. Comparison showed that the simulation program gave good prediction for moisture content variations during the drying process. Results showed that there was no constant-rate-drying period and the whole drying process occurs during the falling rate period. The mo isture distribution inside the individual pistachio nuts was predicted using the model at five selected periods of 5, 10, 20, 50 and 100 min with drying air temperatures of 55 and 70 degree C. The results showed that distribution of the moisture content inside kernels was non-uniform. The moisture content at the center and surface of kernels reduced slowly and very rapidly respectively.
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