The concern of the present work is the convective drying of empty cocoa shells in an indirect solar dryer. Some drying experiments, using one sample, were carried out. During the experiments, the sample is introduced ...The concern of the present work is the convective drying of empty cocoa shells in an indirect solar dryer. Some drying experiments, using one sample, were carried out. During the experiments, the sample is introduced in the drying chamber. Then at steady time intervals, the sample is withdrawn from the drying chamber, for a rapid weighing. After each weighing, the sample is reintroduced in the dryer. At each time interval, the ambient temperature of the drying chamber and its relative humidity γ are measured by a thermo-hygrometer. From the experimental data, a theoretical determination of the moisture evaporated from the product was performed and a good agreement was found between the theoretical and experimental values, confirmed by the value of the RMSE. Those calculations used the constants in the Nusselt number found in literature. Then those constants were evaluated again, to get new values more suitable with the experimental data. The dimensionless numbers of Nusselt, Grashof and Prandtl were calculated. That allowed the calculation of the average value of the Nusselt number. The average convective heat transfer coefficient was determined.展开更多
An exergetic analysis of three basic types of solar drying systems is presented. The analysis is used to find the available useful energy and the quality of energy that is obtainable from the dryers. The dryers were i...An exergetic analysis of three basic types of solar drying systems is presented. The analysis is used to find the available useful energy and the quality of energy that is obtainable from the dryers. The dryers were installed side by side and tested simultaneously to eliminate influence of solar radiation and environmental changes in comparing their performances. The results obtained show that mixed mode and indirect mode solar dryers are more effective in utilizing the captured energy than direct mode dryer, and mixed mode has a slight edge in superiority over indirect mode system. 78.1% and 77% of energy collected in the mixed mode and indirect mode systems, respectively, were available as useful energy, while direct mode system could only convert 49.3% of collected energy to useful energy. The overall exergetic efficiencies of mixed mode, indirect mode and direct mode systems were found to be 55.2%, 54.5% and 33.4%, respectively.展开更多
文摘The concern of the present work is the convective drying of empty cocoa shells in an indirect solar dryer. Some drying experiments, using one sample, were carried out. During the experiments, the sample is introduced in the drying chamber. Then at steady time intervals, the sample is withdrawn from the drying chamber, for a rapid weighing. After each weighing, the sample is reintroduced in the dryer. At each time interval, the ambient temperature of the drying chamber and its relative humidity γ are measured by a thermo-hygrometer. From the experimental data, a theoretical determination of the moisture evaporated from the product was performed and a good agreement was found between the theoretical and experimental values, confirmed by the value of the RMSE. Those calculations used the constants in the Nusselt number found in literature. Then those constants were evaluated again, to get new values more suitable with the experimental data. The dimensionless numbers of Nusselt, Grashof and Prandtl were calculated. That allowed the calculation of the average value of the Nusselt number. The average convective heat transfer coefficient was determined.
文摘An exergetic analysis of three basic types of solar drying systems is presented. The analysis is used to find the available useful energy and the quality of energy that is obtainable from the dryers. The dryers were installed side by side and tested simultaneously to eliminate influence of solar radiation and environmental changes in comparing their performances. The results obtained show that mixed mode and indirect mode solar dryers are more effective in utilizing the captured energy than direct mode dryer, and mixed mode has a slight edge in superiority over indirect mode system. 78.1% and 77% of energy collected in the mixed mode and indirect mode systems, respectively, were available as useful energy, while direct mode system could only convert 49.3% of collected energy to useful energy. The overall exergetic efficiencies of mixed mode, indirect mode and direct mode systems were found to be 55.2%, 54.5% and 33.4%, respectively.
