Thermal performance of Al2O3/water nanofluid in a natural circulation loop with a mini-channel heat sink and heat source

•Heat transfer of a natural circulation loop was investigated experimentally.•The loop has mini-channel heat sink and source and contains Al2O3–water nanofluid.•Al2O3–water nanofluid can enhance the heat-transfer performance of the loop.•Heat-transfer effectiveness were 3.5–22% (in heating) and 9.5–62% (in cooling). In this study, the heat transfer characteristics of Al2O3–water nanofluid were investigated experimentally in a rectangular natural circulation loop of 402mm in height and 205mm in width. The 120-mm-long heated section and 155-mm-long cooling section in the loop were constructed with mini-channel heat exchangers. The nanometer-sized particles of alumina (Al2O3) were dispersed in pure water (the base fluid) to form the alumina–water nanofluid with mass fractions in the range of 0.1–1wt.%. The results clearly indicate that Al2O3–water nanofluid can markedly enhance the heat-transfer performance of the natural circulation loop considered. The average heat-transfer effectiveness at the heating and cooling sections were approximately 3.5–22% and 9.5–62% respectively.