Experimental measurement of thermophysical properties of oxide–water nano-fluids down to ice-point

Abstract

This paper presents the measurement of the thermal conductivity and the dynamic viscosity of Al 2O 3–water (1–4% particle volume fraction) and TiO 2–water (1–6% particle volume fraction) nano-fluids carried out at atmospheric pressure in the temperature range from 1 to 40 °C, which is particularly interesting for the application of nano-fluids as thermal medium in refrigeration and air-conditioning. The thermal conductivity measurement was performed by using a Transient Hot Disk TPS 2500S apparatus instrumented with a 7577 probe (2.001 mm in radius) having a maximum uncertainty ( k = 2) lower than ±5.0% of the reading. The dynamic viscosity measurement and the rheological analysis were carried out by a rotating disc type rheometer Haake Mars II instrumented with a single cone probe (60 mm in diameter and 1° angle) having a maximum uncertainty ( k = 2) lower than ±5.0% of the reading. The thermal conductivity measurements of the tested nano-fluids show a great sensitivity to particle volume fraction and temperature and a weak sensitivity to cluster average size: TiO 2–water and Al 2O 3–water nano-fluids show a thermal conductivity enhancement (with reference to pure water) from −2 to 16% and from −2 to 23% respectively. TiO 2–water and Al 2O 3–water nano-fluids exhibit a Newtonian behaviour in all the investigated ranges of temperature and nano-particle volume fraction. The relative viscosity shows a great sensitivity to particle volume fraction and cluster average size and no sensitivity to temperature: TiO 2–water and Al 2O 3–water nano-fluids show a dynamic viscosity increase with respect to pure water from 17 to 210% and from 15 to 150% respectively. Al 2O 3–water nano-fluid seems to be more promising as thermal medium than TiO 2–water nano-fluid, particularly at low thermal level (between ambient temperature and ice point) where TiO 2–water is not suitable showing worse performance than pure water. Present experimental measurements were compared both with available measurements carried out by different researchers and computational models for thermophysical properties of suspensions.