Thermal performance of an oscillating heat pipe with Al2O3–water nanofluids

An experimental investigation was performed on the thermal performance of an oscillating heat pipe (OHP) charged with base water and spherical Al2O3 particles of 56 nm in diameter. The effects of filling ratios, mass fractions of alumina particles, and power inputs on the total thermal resistance of the OHP were investigated. Experimental results showed that the alumina nanofluids significantly improved the thermal performance of the OHP, with an optimal mass fraction of 0.9 wt.% for maximal heat transfer enhancement. Compared with pure water, the maximal thermal resistance was decreased by 0.14 °C/W (or 32.5%) when the power input was 58.8 W at 70% filling ratio and 0.9% mass fraction. By examining the inner wall samples, it was found that the nanoparticle settlement mainly took place at the evaporator. The change of surface condition at the evaporator due to nanoparticle settlement was found to be the major reason for the enhanced thermal performance of the alumina nanofluid-charged OHP.