Abstract
Mechanical intervention in each stage of post-harvest processing of paddy is the demand of the time due to shortage and increased cost of labor, and higher losses incured in traditional processing. Post-harvest loss reduction by introducing appropriate drying technology may play a vital role in enhancing national food security. Overall objective of the study was to find out appropriate dryer for farmers and small traders. At this end, survey, laboratory and field experiments, neural network modeling, energy and exergy analysis were conducted. A survey was conducted to identify present status and future potential of drying technologies in Bangladesh using a semi-structured questionnaire. Laboratory and field experiments were conducted to evaluate BAU-STR and Solar Bubble (SB) dryer at different drying capacities and paddy varieties in terms of drying rate, drying efficiency, drying loss and quality of dried product in different paddy seasons. An independent multilayer neural network approach was used to predict the performance of BAU-STR dryer for drying of paddy and to demonstrate the ability of neural network modeling in predicting drying behavior of paddy. Ten sets of experimental data were used for training using back propagation algorithm and another ten sets of data were used for testing the artificial neural network model. In addition, energy and exergy analysis of BAU-STR dryer for drying of paddy was conducted using experimental data to find out energy and exergy efficiency of the dryer. It was observed from survey that traditional open sun drying is a common practice in Bangladesh. The average cost of drying paddy in yard was found higher compared to field drying. The survey also revealed that the loss of drying both in field and in yard was found around 1- 3%. Experimental results showed that BAU-STR dryer was found better thanthe SB dryer in terms of uniformity of drying, drying rate, drying efficiency and drying cost. The average drying efficiency was found 45.9% in BAU-STR dryer whereas 18.8% in SB dryer. In addition, temperature inside the SB dryer was very much dependent on solar radiation. The maximum paddy drying efficiency of BAU-STR dryer was found at 500 kg capacity. The lowest drying rates was obtained for short paddy variety compared to medium and long variety in BAU-STR dryer due to more internal resistance to moisture transport of paddy variety. Average drying loss of paddy in BAU-STR dryer was found 0.43% at laboratory and 0.39% at farmer's field. On the other hand, drying loss of paddy in open sun drying method was found in the range of 2.41 - 3.95% at farmers' field. The germination rate of BAU-STR dried samples was found satisfactory 87% in Boro and Aman season, respectively. Rice qualitiesof BAU-STR dried paddy were found above satisfactory levels in terms of whole grain, broken grain, damaged grain, whiteness and hardness. In ANN model, the prediction of the performance of the dryer was found excellent after it was adequately trained. The statistical analysis showed that the errors (MSE, RMSE and SE) were within the acceptable range of ±5% with a coefficient of determination (R2) of 99%. The overall energy efficiency to dry 500 kg of rice was obtained 48.5% during drying operation. In addition, exergy efficiency of paddy drying in BAU-STR dryer was found 44.8% which clearly indicated that large amount of exergy was wasted during paddy drying. Sustainability index (SI) of drying process of paddy ranged from 1.5 to 2.2 in BAU-STR dryer. BAU-STR dryer would be an alternative low cost effective drying technology forfarmers and small traders in Bangladesh.