novel design of natural double-pass solar air heater for higher thermal performance using vortex generator

In this paper, the effects of flapping flexible vortex generators in a two dimensional turbulent free convection airflow in a double-pass solar air heater are discussed. two thin elastic winglets, used here as vortex generators, are attached on two absorber walls near the inlet section with the attack angle of 65o. this novel concept is demonstrated using transient numerical simulation of the flow field by the finite element method with considering the fluid-solid interaction. in this work, an extensive comparison is made between four different configurations. the absorber and outlet temperatures, as well as flow rate and velocity field, are discussed in detail and the numerical findings reveal considerable thermal performance enhancement in comparison with conventional parallel double pass heater. the improvement up to 54% in the ∆t ̅=t ̅_out-t_in , from 13 to 20 o c, while reducing 33.6% flow rate. the present numerical results are validated against the experimental and numerical data reported in the literature.