Experimental and numerical analysis of heat transfer enhancement and flow characteristics in grooved channel for pulsatile flow.

• Difference between experimental and setting oscillatory fraction are discussed. • The flow structure under moderate Reynolds number are clarified. • Heat transfer can be better enhanced at high frequency and low oscillatory fraction. Heat transfer enhancement and flow characteristics in grooved channel for pulsatile flow are investigated experimentally and numerically in the present work. The amplitude of the pulsatile flow is focused at different Reynolds numbers and oscillatory fractions by measuring time-varying flow rate through the electromagnetic flowmeter. In addition, the pulsatile flow patterns are visualized through aluminum dust method. The experimental results showed that the oscillatory fraction decreases with frequency of pulsatile flow, which is also proved by the flow visualization results. It is further shown that the amplitude of pulsatile flow can approach the setting value only when the frequency is lower than the critical frequency f c. It is found that the steady and unstable flow states exist in a pulsatile period. The unstable flow enhances fluid mixing between mainstream and recirculation vortex, and the flow mixing increases with the frequency increment, which is the main reason of heat transfer enhancement. Two-dimensional numerical simulations are further carried out to study this problem. The numerical results showed that heat transfer performance is better at high frequency. Moreover, the heat transfer efficiency decreases with oscillatory fraction when frequency is low. Phase shift is found to exist between the pulsatile flow rate, the outlet temperature and the area-averaged wall Nusselt number. Based on the experimental and numerical results, it is found that higher frequency and small oscillatory fraction could cause a better heat transfer performance in the grooved channel. [ABSTRACT FROM AUTHOR]