This study examines the heat and mass transfer coefficient, thermal effusivity, and other thermal properties of solar-dried cocoyam chips, as well as the drying kinetics. The research also assessed the economics of the solar dryer. For these reasons, a solar dryer with a partitioned collector was developed that creates a double airflow travel distance to delay the airflow inside the collector. The partitioning of the collector delays the airflow and helps to create more turbulence for the airflow with increased energy. The solar dryer was locally developed at the Michael Okpara University of Agriculture and tested during the humid crop harvesting period of September for the worst-case scenario. The obtained drying curves and kinetics for cocoyam drying are subjected to the vagaries of weather conditions. The drying rate showed declining sinusoidal characteristics and took about 25 h to attain equilibrium. Analysis of the airflow velocity showed gravitation between laminar and turbulent flow, ranging from 171.69 to 5152.77. Specific heat capacity, thermal conductivity, and effusivity declined with moisture content while the thermal diffusivity increased. However, the values of thermal effusivity ranged from 12.2 to 47.94 W·s^1/2·m⁻²·K⁻¹, which is within the range of values for insulators. The heat and mass transfer coefficient varied as a function of the airflow velocity. Fitting the drying curve into semi-empirical models showed that the two-term model was the best-fitted model for the experimental data from drying cocoyam. Using the solar dryer in Nigeria can save $188.63–$1886.13 in running costs with a payback period of 0.059–0.59 years (21.54–215.35 days) at a rate of 10–100% of usage.

This study presented the behavior of a laboratory scale solar dryer, which was designed with the objective of meeting the needs of low income carpenters of the tropical region of Africa. The following materials were used to build the solar dryer: aluminum sheets painted in black, a wooden support, and a plastic polyethylene used as a cover. Drying was carried out in the city of Yaoundé in Cameroon, and the tested boards were ebony (Diospyros crassiflora). Drying must be performed with the following conditions: slow process at a low temperature in order to maintain the proper air relative humidity. Since, no apparatus was used to force the circulation of the air, natural convection was the mode used by the dryer. The solar dryer was mathematically modeled by applying heat and mass transfer balance to the different components of the solar dryer. It is important to mention that the used heat and mass coefficients were proposed as variable with the operating conditions. The mathematical model was a reasonable description of the physical phenomena taking place in the dryer. The results show that the average relative error between numerical and experimental moisture contents was equal to 2.102%. Heat transfer convective coefficients and global mass transfer coefficients varied with drying time from 0.25 to 5.5 W/(m²K) and from 1 × 10⁻⁸ to 5.5 × 10⁻⁸ m/s, respectively. The proposed model allowed designing and dimensioning the solar dryer, to the industrial scale. It allowed following the evolution of the different temperatures and moisture content of the tested material and then optimizing the design of the dryer and the drying process conditions. Based on the model, proposing the opening of the drying chamber during the night time and the use of substances capable of retaining heat in the chamber were some proposed solutions in order to have more efficient drying process. The modeling results showed also that an improvement can be obtained at the addition of a solar collector.