Experiments with Al2O3 nanofluid in a single-phase natural circulation mini-loop: Preliminary results

Natural circulation (NC) is a heat transfer mechanism which occurs in case of density gradients inside a fluid. Even if the heat transfer coefficients are lower than in case of forced convection, NC guarantees a good reliability and low costs of maintenance as it does not need any mechanical part. Therefore the main industrial applications of NC systems are in the field of nuclear power plants, solar heaters and passive cooling systems of engines, turbines and electronic components. Most researchers focused their attention on large size systems, with particular care to performance optimization and stability analysis, while there are few studies about natural circulation inside small size devices. In this paper an experimental study focused on the macroscopic effects on the thermal performance of a mini-loop is presented. In particular, two working fluids were used during the tests: distilled water and a nanofluid (distilled water and Al2O3) characterized by two different concentrations (0.5% and 3.0% by volume). The analised parameters were: power transferred to the fluid, mini-loop inclination and temperature at the cooler. Experimental results of the two fluids were compared to the Vijayan’s correlation, developed for large scale natural circulation loop, showing good agreement.