Influence of ultrasonication energy on the dispersion consistency of Al₂O₃–glycerol nanofluid based on viscosity data, and model development for the required ultrasonication energy density

Figures & data

Table 1. Physical properties of alumina nanoparticles.

Name	Crystallographic structure	Size (nm)	Shape^a	Density^a (g/cm^3) at 20 ^oC	Manufacturer
γ-Al2O3	Rhombohedral^b	20–30	Nearly spherical	3.7	Nano Amorphous Inc.
α-Al2O3	Hexagonal	80	Nearly spherical	3.5–3.9	US Nanomaterials Inc.
α-Al2O3	Rhombohedral	100	Nearly spherical	3.7	MK Nano

^aAs stated by the manufacturer.

^bCubic by manufacturer's estimation.

Figure 1. Experimental set-up (a) constant temperature thermal bath with ultrasonication device in use and (b) viscometer set-up.

Figure 2. TEM image of Al₂O₃: (a) 20–30 nm, (b) 80 nm, (c) 100 nm.

Figure 3. Size distribution of Al₂O₃ nanoparticles: (a) 20–30 nm, (b) 80 nm, (c) 100 nm.

Figure 4. X-ray diffraction pattern for Al₂O₃ nanoparticles: (a) 20–30 nm, (b) 80 nm, (c) 100 nm. The black font represents corundum and the blue font represents millosevichite.

Figure 5. UV–visible spectra analysis of Al₂O₃–glycerol nanofluid (a, b and c) spectra pattern at different volume fractions and wavelengths for 20–30, 80 and 100 nm, respectively, and (d, e and f) absorbance of Al₂O₃ in glycerol at different concentrations and 230 nm wavelength for 20–30, 80 and 100 nm, respectively.

Figure 6. In situ nanoparticle size distribution in glycerol base fluid using DLS technique: (a) 20–30 nm, (b) 80 nm, (c) 100 nm.

Table 2. pH and zeta potential values for the Al₂O₃–glycerol nanofluids at 20 °C.

Nanofluids	pH	Zeta potential (mV)	DLS average size (nm)	DLS peak (nm)
20–30 nm Al2O3–glycerol	6.44	−504.33	59.61	49.63
80 nm Al2O3–glycerol	6.26	−243.67	128.70	72.45
100 nm Al2O3–glycerol	4.09	−79.43	118.00	72.93

Figure 7. Comparison of measured viscosity values of glycerol with available data. The horizontal bar shown on the experimental data point represents the standard deviation of the experimental values.

Figure 8. Effect of ultrasonication time on effective viscosity: (a) 2% volume fraction, (b) 3% volume fraction.

Figure 9. Effect of temperature on viscosity of Al₂O₃–glycerol nanofluids: (a) 20–30 nm, (b) 80 nm, (c) 100 nm. Results represent the viscosity value at 3-hour ultrasonication.

Figure 10. Relative viscosity plots showing the combined effect of particle size and increase in volume fraction at different ultrasonication periods.

Figure 11. Sedimentation rate of Al₂O₃–glycerol nanofluids for 5% Al₂O₃ concentration (a) prepared with 4.99 × 10⁶ kJ/m³, after 3 months of preparation; (b) and (c) prepared with 1.5 × 10⁷ and 3.0 × 10⁷ kJ/m³, respectively, after 12 months of preparation: (A) 20–30 nm, (B) 80 nm, (C) 100 nm.

Figure 12. Model performance for prediction of the required energy density for Al₂O₃–glycerol nanofluids.

Figure 13. Performance of the model at different volume fractions for 20–30 nm Al₂O₃–glycerol nanofluid.