Mathematical modelling of thin layer solar drying of whole okra (Abelmoschus esculentus (L.) Moench) pods

A flat plate type natural convective solar dryer was designed and constructed for conducting thin layer drying experiments of whole okra pods. Determination of the air-drying characteristics of thin layer solar drying process of whole okra pods and simulation of thin layer solar drying process of whole okra pods by two drying models, namely; Newton (Lewis) model and Page model were investigated. The drying process of whole okra pods was carried out during three successive days interrupted by two night periods. The drying air is heated by the solar dryer satisfactory and the maximum attained difference between air temperature inside the solar collector and the ambient temperatures was 41.9°C. The dramatic moisture reduction of okra pods took place during the first day of the drying process. Okra pods were dried from a decimal initial moisture content of about 5.51 d.b. (84.64% w.b.) to a decimal final moisture content of about 0.16 d.b. (13.61% w.b.). The drying process occurs in falling rate period and moisture diffusion was the dominant physical mechanism governing moisture movement within the okra pods. The probability of being wrong if the null hypothesis is rejected for Newton (Lewis) model was 0.88, while for Page model it was 1.0 (P ˂ 0.05). The two tested drying models predicted whole okra pods drying process adequately but Page predictions were more accurate.