Thermal performance enhancement in an indirect solar greenhouse dryer using helical fin under variable solar irradiation

In this study, the effect of helical fins on the thermal performance of the greenhouse solar dryer with solar air heater under non-uniform thermal radiation has been analyzed. This article is written with the aim of investi-gating various parameters, including the type of helical fin (CASE A to CASE D), pitch of the helical fin (170 mm to 320 mm), mass flow rate (0.01, 0.013, 0.015 kg/s) and variable solar irradiation (10:00 AM to 14:20 PM). The 3D simulation was performed using the finite volume method (FVM) in ANSYS-Fluent software under k-epsilon RNG turbulent modeling. The results demonstrate that using four helical fins inside the tube increases the outlet temperature by 5.22 % at 10:00 AM. Compared to the simple model. Increasing the flow rate cause less op-portunity for heat transfer rate from the solid surface to the airflow, so the outlet temperature decline by 19 % when the air flow rate rise to 0.015 kg/s. In the flow rate of 0.01 kg/s, by decreasing the pitch of the helical fin from 320 mm to 170 mm, the greenhouse outlet temperature rises by 3.01 %. Unexpectedly, changes in solar irradiation at different flow rates do not exhibit a linear correlation with thermal efficiency. Nevertheless, the highest achievable thermal efficiency of 61.30 % occurs at 13:00 with an airflow rate of 0.015 kg/s.