The Effect of Geometric Adjustments in an Indirect Forced Convection Solar Tunnel Dryer: A Study Based on CFD Simulations and Experimental Investigations

The quality of dried agri-food products depends on the uniformity of their moisture content at the end of the drying process. Controlling parameters such as temperature, air velocity, and relative humidity within the dryer is essential to ensure optimal drying. This study presents the design of a tunnel-type indirect solar dryer intended for drying agri-food products. The main scientific challenge lies in the numerical evaluation and proposal of solutions to improve the dryer's performance. With this in mind, a numerical simulation was carried out using computational fluid dynamics (CFD) to analyse the distribution of air flow and temperatures inside the dryer. Three simulation models were developed, with variable input values: air speed (1 m/s, 2 m/s and 3 m/s) and the temperature of the wall exposed to solar radiation (40°C, 50°C and 60°C). To validate the numerical results, an experimental study was conducted. Comparisons revealed high coefficients of determination between the simulated and experimental data: R² = 0.9951 for temperature and R² = 0.9217 for air velocity. Geometric adjustments were then made to the CFD model. The right angles (90°) at the upper ends of the drying chamber were changed to flat angles (0°), while those at the lower ends were replaced by 45° angles. These modifications led to an optimisation of the dryer's thermal performance, as well as a significant improvement in the efficiency of the drying process.