Mechanism analysis of heat transfer and flow structure of periodic pulsating nanofluids slot-jet impingement with different waveforms

Heat transfer and flow structure of Al ₂ O ₃ -H ₂ O nanofluids periodic pulsating slot-jet impingement with rectangular wave (R-wave) and triangular wave (T-wave) are investigated. The effects of jet wave form, pulsation frequency f = 10–50 Hz, nanoparticles volume fraction ϕ = 0–3.5% and Reynolds number Re = 10,000–20,000, are analyzed. The results indicate that T-wave is more conducive to heat transfer enhancement. And, ϕ and Re exhibit good mutual promotion relation on heat transfer performance. The frequency-induced trend indicates that the effect of f on the heat transfer enhancement is weakened at larger f, showing a non-linear trend. f = 20 Hz is a limit where the increment rate of Nu _ave is reduced. Moreover, the application of nanofluids, as well as large f, improves local and average heat transfer, but deteriorates temperature uniformity of target surface. Furthermore, the required pumping power (PP) increases with the increase of Re and decrease of ϕ. PP at case f = 20 Hz is much less than that of f = 50 Hz. Overall, comprehensive results reveal that large ϕ and Re with medium f of T-wave can achieve high-efficient heat transfer enhancement.