A model considering evaporator wettability in terms of the contact angle is developed in this study. In addition, experiments are conducted using a copper thermosyphon with a length of 240 mm and internal and external diameters of 22.2 mm and 25.4 mm. The influences of the inclination angle and evaporator wettability on the heat performance of a thermosyphon charged with water are investigated. It is observed that simulated temperatures agree well with experimental data with a relative error of 0.12% for a modified thermosyphon. The results show that bubbles attaching to the wall of the evaporator decrease as the inclination angle increases from 15 degrees to 90 degrees, which decreases thermal resistance by 59.5%. As the heating power increases from 10 W to 14 W, thermal resistance reduces more significantly (44.1% decrease) for an evaporator with a hydrophilic surface than for an evaporator with a hydrophobic surface (20.6% decrease) because the bubble emission frequency of a hydrophilic surface rises more sharply (265% increase) than that of a hydrophobic surface (100% increase) at an inclination angle of 90 degrees. (C) 2017 Elsevier Ltd. All rights reserved.