The alternating cross-section flattened (ACF) tube is employed to comprise the test tube bundle in this study. This test tube is placed in a crossflow to evaluate the air-side thermal-hydraulic performance. Two test tube bundles are inline tube arrangements with two tube rows. One is made from the circular tube with a diameter of 6.35 mm, and another is made from the ACF tube with a hydraulic diameter of 4.75 mm. The test sections are made from copper tubes. The test conditions were the water mass flow rate of 0.13 kg/s, the inlet water temperature of 50-60 °C, the dry air inlet bulb temperature of 30-40 °C, and the frontal velocity of 1-5 m/s. The experimental results revealed that the tube geometry significantly affects thermal-hydraulic performance. The experiment will compare the circular tube bundle and the ACF tube bundle on heat transfer and pressure drop characteristics. On the other hand, the pressure drop of the circular tube bundle is higher than that of the ACF tube bundle. The result of the experiment concluded that the ACF tube bundle is a better performance than the circular tube bundle by about 1.08-1.17 times and 1.13-1.46 times by the heat transfer coefficient ratio and goodness factor ratio, respectively.