No abstract

Qualitative experiments were carried out to investigate the stability of Al2O3-SiO2 hybrid water-based nanofluids. The main nanoparticles used in this work were Al2O3 and SiO2 since these types of nanoparticles has been widely used and proposed in many applications and information on their hybrid dispersion stability characteristic are still elusive. The present work demonstrated the stability of Al2O3-SiO2 hybrid nanofluids using various preparation techniques and successively elucidating the optimum preparation method for hybrid nanofluid. The hybrid water-based nanofluid were prepared by dispersing a 50:50 ratio of Al2O3-SiO2 nanoparticles into distilled water to achieve total volume concentration of C=0.001, 0.01 and 0.1 vol%. Successively, the hybrid nanofluids were prepared using magnetic stirrer and ultrasonic bath. The samples are categorised into five preparation method which are: (i) 1 hour sonication, (ii) 1 hour magnetic stirrer, (iii) 0.25 hour magnetic stirrer and 1 hour sonication, and (iv) 0.5 hour magnetic stirrer and 1 hour sonication and (v) without magnetic stirring and sonication. The height of sedimentation and colloidal stability of each preparation methods were observed in the duration of 2 weeks. In the present work, it was observed that the dispersion stability of hybrid nanofluids prepared by applying magnetic stirrer for 15 minutes with prior to 1 hour of sonication had demonstrated the highest stability indicated by the lowest height of sedimentation and high colloidal stability.

Experiment were carried out to clarify the steady state condition of heat transfer coefficient (HTC) for single and hybrid Al2O3-SiO2 water-based nanofluids in low concentration of nucleate pool boiling. Al2O3 and SiO2 were chosen and ultra-sonification for 1 hour after being diluted in distilled water. The total of 0.001 vol.% concentration was divided into composition ratio of 0:100, 25:72, 50:50, 75:25, 100:0 for hybrid nanofluids. Successively, all the HTC values were collected through experimental works. In the present work, it was found that the steady stated for single and hybrid nanofluids were achieved except for single SiO2 nanofluid where even after 5 hours, the value of its ΔTW keep on decreasing. The nanoparticles deposited on the surface heater were suspected as the main factor for the current experimental results.