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Experiments were carried out to study the heat transfer characteristics of a thermosyphon when modifying the evaporator and condenser sections to be oriented at 0, 60 and 90 degrees with respect to the 70 degree inclination of the adiabatic section (Z shaped). The thermosyphon was made of copper tube with an outer diameter of 15.87 mm and 300, 450 and 600 mm total lengths. The evaporator, adiabatic and condenser sections were equal in length. R-134a, ethanol and distilled water were employed as the working fl uids with a 50% fi lling ratio by evaporator volume. The evaporator section was heated by hot water at 60, 70 and 80 o C, whereas 20 o C cool water was supplied to the condenser section. The test was conducted at various inclination angles, i.e., 0, 20, 40, 60, 70, 80, 90, 110, 130, 150, 170 and 180 degrees. The results show that the heat fl ux signifi cantly depends on the working temperature. R-134a had the best performance followed by ethanol and distilled water. The heat fl ux decreased with an increase in the total length. When increasing the orientation angles of the evaporator and condenser sections, the heat fl ux rose due to the assistance of gravity. The maximum heat fl ux was 26.85 kW/m2 with the lowest thermal resistance of 0.065 o C/W. In addition, the optimal tested orientation angle was in the range of 40-110 degrees with respect to the horizontal plane.
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