Performance Augmentation of Solar Air Heater for Space Heating Using a Flexible Flapping Guide Winglet

A new idea is presented in this paper for improving the performance of solar air heater (SAH) designed for space heating by employing a thin flexible guide winglet. In addition to the role of winglet in pushing the convective airflow toward the heated surface, it behaves as a vortex generator (VG) due to its vibration by fluid-solid interaction (FSI) that causes flow mixing and breaking thermal boundary layer. In flow simulation, the finite element method (FEM) is employed with considering a two-way strongly-coupled FSI approach at transient condition. Numerical solution of the governing equations, including the continuity, momentum and energy for convective flow and the equation of motion for VG are obtained by COMSOL multi-physics. The well-known  model is employed for computation of turbulent stress and heat flux. The present numerical results are validated against the most recent relevant literature. To provide a clear and deep understanding of the proposed concept, extensive comparisons are made between different test cases. Results reveal considerable performance enhancement of SAH with elastic guide winglet compared with clean solar air heater (CSAH), such that 56% increase in the natural airflow rate and 9% decrease in the average absorber temperature is seen because of the flapping winglet. But, the air outlet temperature decreases about 14% due to flapping VG.  This study aims to make the proposed SAH as an essential renewable thermal-solar system more efficient and attractive so that this improvement pushes the industrial society toward more sustainable infrastructure.