The four miniature heat pipes filled with DI water and SiO2-water nanofluids containing different volume concentrations (0.2%, 0.6% and 1.0%) are experimentally measured on the condition of air and water cooling. The wall temperature and the thermal resistance are investigated for three inclination angles. At the same of inlet heat water temperature in the heat system, it is observed that the total wall temperatures on the evaporator section are almost retaining constant by air cooling and the wall temperatures at the front end of the evaporator section are slightly reduced by water cooling. However, the wall temperatures at the condenser section using SiO2-water nanofluids are all higher than that for DI water on the two cooling conditions. As compared with the heat pipe using DI water, the decreasing of the thermal resistance in heat pipe using nanofluids is about 43.10%-74.46% by air cooling and 51.43%-72.22% by water cooling. These indicate that the utilization of SiO2-water nanofluids as working fluids enhances the performance of the miniature heat pipe. When the four miniature heat pipes are cut to examine at the end of the experiment, a thin coating on the surface of the screen mesh of the heat pipe using SiO2-water nanofluids is found. This may be one reason for reinforcing the heat transfer performance of the miniature heat pipe.

The experimental results regarding the surface tension and contact angle of Al 2 O 3-oil and SiO 2-oil nanofluids with 0.1%~1.0% volume fraction at the temperature of 25°C~65°C are presented. The measurements illustrate that the surface tension is improved and the contact angle is reduced compared with oil based liquid. At the temperature of 25°C, for 0.5% volume fraction with 60 nm nanoparticles size, the enhancement of the surface tension is about 4.11% for Al 2 O 3-oil nanofluids and 6.79% for SiO 2-oil nanofluids. Corresponding, the weakening of the contact angle is 37.93% and 27.59%. In addition, the experimental profiles of the surface tension of Al 2 O 3-oil and SiO 2-oil nanofluids indicate that they fall with temperature, and inversely rise with the increasing of volume fraction and nanoparticles size. And the contact angle of the two kinds of nanofluids increase with nanoparticles size, whereas decrease with the increase in volume fraction. All demonstrate that the wetting properties are modified when Al 2 O 3 and SiO 2 nanoparticles are added into oil based liquid. Furthermore, the experimental phenomena are thoroughly analysed.