Modelling of Thin Layer Solar Drying of Okra (Abelmoschus Esculentus L.) Pods

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Idriss, Ebtihal Mohammed Ibn
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Experiments of okra pods solar drying in thin layer were conducted at the Workshop of the Department of Agriculture Engineering, Faculty of Agriculture, University of Khartoum, Sudan. The objectives of the study were testing the performance of a natural convective solar dryer, determination of the drying characteristics of okra pods, simulation of the drying process of okra pods. A natural convective solar dryer previously constructed for M.Sc. research work was used in conducting the experimental work. Fresh okra pods were brought from local market for carrying out the drying trials. A data logger with thermocouples were used for recording temperatures at intervals of one hour at inlet of the solar collector, inside absorber, outlet of the solar collector and ambient air. Two hygrometers were used to record air relative humidities at intervals of one hour at inlet of the solar collector and outlet of the solar collector. The drying process of okra pods was carried out for three successive days interrupted by two overnights. Results indicate that, the solar dryer heated the drying air satisfactory. This was depicted by the maximum attained temperature difference between inside absorber and ambient temperature which was 41.90C, and the maximum attained relative humidity difference between inlet and outlet of the solar collector air relative humidities which was 19%. Okra pods drying took place in the falling rate period i.e. okra initial moisture content is less than its critical moisture content. The effective drying process for okra pods occurred in the first day while equilibrium state was attained during the second and the third days of the drying process. Two drying models namely, Lewis and Page were tested to simulate okra pods drying process. Consequently two mathematical models were written in Turbo Pascal for windows, version 1.5. Results showed that the two tested drying models predicted okra pods drying moisture contents accurately but Page model gave close agreement between measured and predicted data. For validating the tested two drying models statistical analysis showed that, average model error (AME), average absolute difference (AAD) and standard error of estimate (SEE) were 0.127, 0.225 and 0.324, respectively for Lewis model. While for Page model, the parameters are -0.001, 0.125 and 0.160, respectively.
Okra (Abelmoschus Esculentus L.)
University of khartoum