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An experimental and numerical study on convection heat transfer of water flowing through an alternating cross-section flattened (ACF) tube are investigated in this paper. The thermal-fluid characteristics were evaluated by numerical simulation. The test run conditions covered a mass flux of 200 to 800 kg m −2 s −1 , a heat flux of 10 kW/m 2 , and an inlettemperature of 40°C. The results showed that the Nusselt number increased with the increase in mass flux. Moreover, the heat transfer was also affected by the flow characteristics. Vortices were formed at the curved wall, and their intensities were increased along the flow direction. It was also found that the heat transfer and pressure drop were larger than that of the circular tube. However, the thermal performance was greater than the pressure loss penalty.The comparison results showed that the ACF tube had better performance than the circular tube. Further, the details of heat transfer, flow resistance, and fluid behavior were investigated and discussed in this study. K E Y W O R D S alternating flattened (AF) tube, computational fluid dynamics (CFD), flow characteristics, heat transfer enhancement, vortex generation Heat Transfer-Asian Res. 2019;48:817-834.wileyonlinelibrary.com/journal/htj

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