Experimental Measurements of Thermophysical Properties of $$\mathrm{Al}_{2}\mathrm{O}_{3}$$ Al 2 O 3 – and $$\mathrm{TiO}_{2}$$ TiO 2 –Ethylene Glycol Nanofluids

Abstract

This paper presents measurements of the thermal conductivity and the dynamic viscosity of $$\mathrm{Al}_{2}\mathrm{O}_{3}$$ –ethylene glycol and $$\mathrm{TiO}_{2}$$ –ethylene glycol (1 % to 3 % particle volume fraction) nanofluids carried out in the temperature range from $$0\,^{\circ }$$ C to $$50\,^{\circ }$$ C. The thermal-conductivity measurements were 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 measurements and the rheological analysis were carried out by a rotating disk type rheometer Haake Mars II instrumented with a single-cone probe (60 mm in diameter and $$1^{\circ }$$ ) having a maximum uncertainty $$(k=2)$$ lower than 5.0 % of the reading. The thermal-conductivity measurements of the tested nanofluids show a great sensitivity to particle volume fraction and a lower sensitivity to temperature: $$\mathrm{TiO}_{2}$$ –ethylene glycol and $$\mathrm{Al}_{2}\mathrm{O}_{3}$$ –ethylene glycol nanofluids show a thermal-conductivity enhancement (with respect to pure ethylene glycol) from 1 % to 19.5 % and from 9 % to 29 %, respectively. $$\mathrm{TiO}_{2}$$ –ethylene glycol and $$\mathrm{Al}_{2}\mathrm{O}_{3}$$ –ethylene glycol nanofluids exhibit Newtonian behavior in all the investigated temperature and particle volume fraction ranges. The relative viscosity shows a great sensitivity to the particle volume fraction and weak or no sensitivity to temperature: $$\mathrm{TiO}_{2}$$ –ethylene glycol and $$\mathrm{Al}_{2}\mathrm{O}_{3}$$ –ethylene glycol nanofluids show a dynamic viscosity increase with respect to ethylene glycol from (4 to 5) % to 30 % and from 14 % to 50 %, respectively. Present experimental measurements were compared both with available measurements carried out by different researchers and computational models for thermophysical properties of nanofluids.