Numerical Study on Heat Transfer Characteristics of Different Rectangular Impinging Jets

A numerical study has been made to examine the thermal fields of rectangular impinging jets with different duty cycle(DC), which is defined as the ratio of pulse cycle on-time to off cycle time in one period, inlet Reynolds number and frequency. The Nusselt numbers show best enhancement with DC=1:3, Re=22000 and f=40Hz. The possible reason for this is that the instantaneous velocity change in this case from off to on and on to off, especially when the velocity changes from onto off, is more severe than other cases.