Study of flow and heat transfer characteristics of heated asymmetrical concave surfaces under multi-piezoelectric fans actuation

Abstract

A transient numerical simulation was carried out to investigate the convection heat transfer enhancement of heated asymmetrical concave surfaces using multi piezoelectric fans. And the numerical methodology has been validated through the comparison with the results of validation tests. The effects of the relative curvature (RK), dimensionless fan-to-fan pitch (P/WPF), vibration phase difference between adjacent piezoelectric fans (φ) and the dimensionless offset distance of multi-fans (Δy/APP) on flow and heat transfer performance were reported. RK was varied from 6 to 2. P/WPF was varied from 0.25 to 1.0. The value of φ was 0° and 180°. Δy/APP was varied from 0 to 1.0. The heat transfer of the heated surface was characterized by evaluating a time-averaged convection heat transfer coefficient over a complete vibration cycle of the multi-piezoelectric fans after the flow and thermal fields reached a quasi-steady state. In addition, transient and time-averaged flow fields were captured to study the underlying mechanism of the heat transfer enhancement. It was found that higher heat transfer coefficients were observed in stagnation zone with small P/WPF at smaller RK value of asymmetrical concave surfaces whereas the P/WPF is observed to affect the data only marginally at larger RK values. The influence of φ on the heat transfer coefficients was primarily reflected in the clearance region of adjacent fans, where operating in-phase could produce stronger flow in clearances than out-of-phase. Finally, it was also observed that proper adjustment of the fan position can reduce its equivalent relative curvature, resulting in improvement in the heat performance of the asymmetrical concave surface with large RK value.