The heat-transfer characteristics of this system i.e. a CLOHP/CV, depend on the ratio of check valves (R-CV), aspect ratio (L-e/d(i)) and the dimensionless parameters of the heat transfer. The CLOHP/ CV used employed a copper tube with inner diameters of 1.77 and 2.03 mm. The evaporator, adiabatic and condenser lengths were equal to 50, 100 and 150 mm. The selected working fluids were water (H2O), ethanol (C2H5OH) and R123 (CHCl2CF3) with a filling ratio of 50% of total volume. The number of turns was 40. The R-CV values were 20, 8, 5 and 4. The evaporator was heated by hot water, while the condenser section was cooled by distilled water. The inclination of the CLOHP/CV used in the experiments was 90 degrees to the horizontal, with a controlled working-temperature of 50 degrees C. When the system reached the steady state, the temperature and the flow rate of the cooling water were measured in order to calculate the heat-transfer rate of the CLOHP/CV. The experimental results showed that the heat-flux increases with an increase of R-CV and decreases with an increased aspect ratio. A correlation for predicting the heat-transfer rate for the heat-pipe in the vertical position has been established. (c) 2006 Elsevier Ltd. All rights reserved.