Experimental study on the surface tension of Al₂O₃-H₂O nanofluid

Due to the good performance of thermal conductivity, nanofluids are regarded as a new type of heat transfer working medium, which have huge potential value. The addition of nanoparticles makes nanofluids exhibit different thermal properties from the base fluids. In this experiment, the maximum bubble pressure method was adopted to measure the surface tension of Al2O₃-H₂O nanofluids whose nanoparticle sizes are 10 nm and 20 nm with four different volume fractions (1%, 1.5%, 2% and 1.5%), and 50 nm and 100 nm with the volume fraction of 2.5%. The temperatures of nanofluids are within the scope of 18 ℃ to 30 ℃. The surface tension ratio (the ratio of surface tension value of nanofluids to its base fluids) is also calculated at different temperature points. Results show that the surface tension of nanofluids decreases with the elevation of temperature and decreases with the increase of volume fraction. For different temperatures and particle sizes of nanofluids, there exists a corresponding critical concentration value. Only reaching the value, the addition of nanoparticles can reduce the surface tension of the base fluids.