Luca Saraceno

Heat transfer in water-based SiC and TiO2 nanofluids

The article reports the results of heat transfer experimental tests on water-based TiO2 (9 wt%) and SiC (3, 6, 9 wt%) nanofluids. Measurements were performed in a two-loop test rig for immediate comparison of the thermal performances of the nanofluid with the base fluid. The convective heat transfer is evaluated in a circular pipe heated with uniform heat flux (from 20 to 240 kW/m2) and flow regimes from laminar to turbulent. Tests have been performed to compare the heat transfer of nanofluids and water at the same velocity (from 0.7 to 1.6 m/s) or Reynolds number (from 300 to 6000), and they have also been compared with values calculated from some of the most widely used correlations. The analysis of the experimental data shows a strong dependence on the parameter used, while both the nanofluid and water data have the same agreement with the calculated values. Nanofluids were manufactured through a two-step procedure: laser synthesis of nanoparticles followed by dispersion in water.

Visual analysis of flow boiling at different gravity levels in 4.0 mm tube

The aim of the present paper is to describe the results of flow boiling heat transfer at low gravity and compare them with those obtained at earth gravity, evaluating possible differences. The experimental campaigns at low gravity have been performed during the parabolic flight campaign of October-November 2013. The paper will show the analysis of differences between the heat transfer coefficients and vapour bubble parameters at normal and at zero gravity. The results of 4.0 mm tube are presented and discussed. With respect to terrestrial gravity, heat transfer is systematically lower at microgravity in the range of the experimental conditions. Heat transfer differences for the two gravity conditions are related to the different bubble size in each of them. The size of a bubble in flow boiling is affected by the gravity level, being larger at low gravity, unless inertial forces are largely predominant over buoyancy and other forces acting on the bubble itself when detaching from a heated wall. Vapour bubble parameters (bubble diameter, bubble length, width, and nose velocity) have been measured.