Numerical analysis and validation of a natural convection mix-mode solar dryer for drying red chilli under variable conditions

The objective of this paper is to model a natural convection mix-mode solar dryer (NCMMSD) for drying agricultural products in an environment with short sunshine duration. The solar dryer was used to dry red chilli and was operating under the climate of the coastal area of South Eastern Nigeria characterized by low solar radiation intensity with a short duration of sunshine hours. The model took into consideration the thermophysical properties of the drying air and dried red chilli. The simultaneous heat and mass transfer equations were solved using the fourth-order Runge-Kutha method. The numerical solution allows for the determination of temperature and relative humidity of drying air at different points within the dryer as well as the moisture profile of the dried product. The experimental values of moisture ratios, temperature, and relative humidity during the mix-mode solar drying process with and without NaCl were used to validate the proposed model. Numerical simulation results were in close agreement with experimental results. The present model can serve as good reference bases to explain the drying phenomenon of mix-mode solar drying of other agricultural products when necessary thermophysical properties of these products are known. Using this model, the potential of mitigating gross fossil (coal) CO2 in Africa is annually estimated to 1280148 tons of CO2.