Nucleate pool boiling heat transfer characteristics of TiO2–water nanofluids at very low concentrations

A study of nucleate pool boiling heat transfer of TiO2–water nanofluids is experimentally conducted. Nanofluids with various concentrations of 0.00005, 0.0001, 0.0005, 0.005, and 0.01 vol.% are employed. Horizontal circular plates made from copper and aluminium with different roughness values of 0.2 and 4 μm are used as heating surfaces. The experiments are performed to explore the effects of nanofluids concentration as well as heating surface material and roughness on nucleate pool boiling characteristics and the heat transfer coefficient under ambient pressure. The results show that based on the copper heated surface which is tested with a concentration of 0.0001 vol.%, higher nucleate pool boiling heat transfer coefficient is obtained when compared with the base fluid. A 15% increase is obtained for the surface roughness of 0.2 μm and a 4% increase is obtained for roughness of 4 μm. For concentrations higher than 0.0001 vol.%, however, the higher the concentration, the lower the heat transfer coefficient. In the case of aluminium heated surface, the corresponding heat transfer coefficients are larger than for the copper surface by around 30% with a roughness of 0.2 μm and around 27% with a roughness of 4 μm. Moreover, the results also indicate that the heat transfer coefficient obtained based on a roughness of 4 μm is higher than that for a roughness of 0.2 μm by around 12% for aluminium and by around 13% for copper.