Heat transfer under composite arrangement of pulsed and steady turbulent submerged multiple jets impinging on a flat surface

• Combination of pulsed-steady jets can improve the Nusselt number distribution.
• Intermittent jets show the much higher impingement heat transfer rate.
• Decrease of frequency below 25 Hz leads to a reasonably uniform distribution.
• Pulse amplitude of sinusoidal jets has a significant role in heat transfer uniformity.

A numerical study has been conducted to seek an optimized arrangement of steady and pulsating impinging multiple submerged slot jets. A composite design consisting of steady as well as intermittent (on/off) or sinusoidal jets in different combinations of four slot jets was simulated. Effect of large temperature differences between jets and the impingement surface was examined by considering fluid properties to be dependent on temperature. In addition, the effect of frequency, phase angle for both types of pulsation as well as amplitude of the sinusoidal pulsing jets was examined on the time-averaged local Nusselt number distribution on an isothermal planar target surface. Results indicate that the combination of pulsed jets with steady jets provide the most uniform and enhanced Nusselt number distribution for the array of four jets. Furthermore, due to the alternating pulsating flow patterns, an increase in the convective heat transfer is observed around a secondary stagnation point. Significantly higher heat transfer can be obtained by the combinations of intermittent-steady jets rather than the sinusoidal-steady ones.