Numerical Study of a Trapezoidal Tunnel as a Drying Cabin

The drying of fishery products is a critical issue for the valorization of local resources. The most commonly used devices are greenhouse or tunnel dryers, due to their ability to process large quantities of products. In this context, we designed and evaluated a mixed trapezoidal tunnel dryer operating with forced convection, equipped with a solar collector and a drying chamber. This system relies exclusively on solar energy, utilizing both direct solar radiation and the thermal contribution of the collector. To ensure the continuity of the drying process, a stable and constant energy source is required, either through exclusive use of solar energy during the day or with supplementary energy input at night. With this in mind, we investigated the thermal behavior of the drying chamber under steady-state conditions. The objective of this study is to analyze the influence of drying parameters on the heat transfer fluid and the product within a trapezoidal greenhouse dryer. Specifically, we examined the impact of key parameters, such as solar irradiance and air velocity, on the temperature of the heat transfer fluid and the dried product (fish). To this end, a numerical simulation approach was employed to model the thermal behavior of the dryer. The energy conservation equations, derived from the thermal balance of the walls, and the mass conservation equations, based on a polynomial model of the fish drying kinetics, were utilized. The results indicate that the optimal air velocity for effective drying is 1 m/s for low irradiance and 2 m/s for an irradiance of 900 W/m<sup>2</sup>. For products with a thickness of approximately 1 mm, the air velocity inside the dryer should not exceed 1 m/s. However, for products with thicknesses ranging from 5 to 20 mm, the air velocity can vary between 1 m/s and 2 m/s. Additionally, for a low irradiance of 300 W/m<sup>2</sup>, an air velocity of 0.2 m/s maintains an optimal drying temperature of around 60°C. Conversely, for an irradiance of 900 W/m<sup>2</sup>, an air velocity of 2.5 m/s is recommended.