Nakhon Pathom, Thailand
Nakhon Pathom, Thailand

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Janjai S.,Solar Energy Research Laboratory | Mahayothee B.,Silpakorn University | Lamlert N.,Solar Energy Research Laboratory | Bala B.K.,Bangladesh Agricultural University | And 3 more authors.
Journal of Food Engineering | Year: 2010

Litchi (Litchi Chinensis Sonn.) is an important commercial fruit in Thailand and Vietnam. Litchi fruit is consumed both as fresh and dried products. Also most of the export of litchi is in the form of dried whole litchi fruit. Thermo-physical properties and drying model of litchi fruit is important for optimum design of litchi dryer. This paper presents moisture diffusivity, shrinkage and finite element simulated drying of litchi fruit. The moisture diffusivities of litchi were determined by minimizing the sum of square of deviations between the predicted and experimental values of moisture content of thin layer drying under controlled conditions of air temperature and relative humidity. The components in the form of cylinder for seed and seed stalk and slab for seed coat, shell and flesh were dried in thin layers at the air temperatures of 50, 60, 70 and 80 °C and relative humidity in the range of 10-25%. The mean diffusivity of flesh, seed and shell of litchi fruit increased with temperature and was expressed by the Arrhenius-type equation, but the diffusivities of seed coat and seed stalk were independent of temperature. The moisture diffusivities of seed coat and seed stalk were much lower than those of the other parts of the litchi. The shrinkage of litchi fruit has also been determined experimentally and it was expressed as a function of moisture reduction. A two-dimensional finite element model has been developed to simulate moisture diffusion in litchi fruit during drying. Shrinkage of the flesh and different component diffusivities of litchi during drying were also taken into account. The finite element model was programmed in Compaq Visual FORTRAN version 6.5. This finite element model satisfactorily predicts the moisture diffusion during drying. Moisture contents in the different components in the litchi fruit during drying were also simulated. This study provides an understanding of the transport processes in the different components of the litchi fruit. © 2009 Elsevier Ltd. All rights reserved.


Janjai S.,Solar Energy Research Laboratory | Lamlert N.,Solar Energy Research Laboratory | Hee B.M.,Silpakorn University | Bala B.K.,Bangladesh Agricultural University | And 2 more authors.
Food Science and Technology Research | Year: 2011

In this paper, thin layer drying of peeled longan is presented. Thin layer drying of peeled longan was conducted under controlled conditions of temperature and relative humidity. Drying air temperature has great influence on the drying rates of peeled longan and drying time decreases with the increase in drying air temperature. Eight different thin layer drying models were fitted to the experimental data of peeled longan. The drying parameters of peeled longan were function of air temperature and relative humidity. Page model was found to be the best and Two-term model was found to be next to the best. The agreement between the predicted and experimental values for Page model is excellent. The predictions of Page model, Two-term model and modified Henderson and Pabis model were very close. Either one of these three can be used to provide design data and for simulation and optimization of the dryer for efficient operation. The colour of the peeled dried longan is golden brown for the temperature levels of 50, 60 and 70°C and there is no difference in colour for dried longan for drying at 50 to 70°C.

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