Numerical investigation of an indirect solar dryer equipped with two solar air collectors using computational fluid dynamics

Generally, in most conventional solar dryers, there is one solar air heater, which means that the air enters the drying chamber from one side. The problem with a single inlet solar dryer, especially in natural convection, is that the air is not well distributed along the trays, resulting in the non-uniform moisture content of the final product. So, instead of using a large solar air heater, we divided it into two small solar air heaters facing the sun, each of which is connected to the drying chamber by pipes, leading to two inlets facing each other and supplying hot air from both sides. The CFD method was applied to study the airflow distribution in the proposed case. To be more realistic, we used a UDF (user-defined function) subroutine written in C++ to integrate the unsteady evolution of the climatic data for one day in the Oujda region (Eastern Morocco). A comparison between a solar dryer with one and two solar air heaters is presented. The effect of outlet position on air distribution is used as a criterion parameter for the study. All tests were performed using 2D modeling. The results showed that the optimum position of the outlet was in the right (North direction) and center corner for one and two solar air heaters, respectively. By comparing these two cases in terms of mass flow rate, temperature along the trays and inside the drying chamber it was found that the two solar air heaters dryer was more efficient, such as the drying efficiency reaches 97.36%.