Comparison of stability and thermophysical properties of CNT–GNP hybrid nanofluids using different surface modification techniques

Figures & data

Table 1. Basefluid properties.

	EG–water (80:20)	EG–water (90:10)	EG (100)
Boiling point, °C	122.22	133.8	194.6
Freezing point, °C	−12.22	−28.88	−43.33
Specific heat, kJ/kg/K (25 °C)	3.15	2.95	2.73
Thermal conductivity (W/m/K) (25 °C)	0.326	0.258	0.224
Viscosity, cP (25 °C)	4.601	6.421	9.092
Density, kg/m^3 (25 °C)	1082	1091	1103

Figure 1. HRTEM pictograph of (a) pristine CNTs, (b) treated CNTs, c) GNPs.

Table 2. Basefluid compositions.

S. No	Blend
1	100% EG
2	EG–water (80:20)

Figure 2. Zeta Potential of pure ethylene glycol dispersed with a) pristine 0.5% CNT–GNP on the first day and b) pristine CNT–GNP on the 5th day.

Figure 3. Zeta Potential of pure ethylene glycol dispersed with a) oxidized 0.5% CNT–GNP on the first day and b) oxidized CNT–GNP on the 60th day.

Table 3. Pristine CNT–GNP zeta potential values.

Base fluid composition	Nanoparticles wt% (CNT–GNP)	Zeta potential, mV
		First day	After 5 d
100% EG	0.0625	21.4	−8.6
100% EG	0.125	20.3	11.6
100% EG	0.25	−23.8	8.8
100% EG	0.5	−22.4	−10.2
EG–water (80:20)	0.0625	21.5	−12.9
EG–water (80:20)	0.125	21.2	8.4
EG–water (80:20)	0.25	22.7	9.1
EG–water (80:20)	0.5	20.1	−10.8

Table 4. Oxidized CNT–GNP zeta potential values.

Base fluid composition	Nanoparticles wt% (CNT–GNP)	Zeta potential, mV
		First day	After 60 d
100% EG	0.0625	−48.3	−40.9
100% EG	0.125	−47.9	−41.2
100% EG	0.25	54.2	45.9
100% EG	0.5	−57.7	47.9
EG–water (80:20)	0.0625	51.5	−42.7
EG–water (80:20)	0.125	−44.3	40.1
EG–water (80:20)	0.25	48.4	41.3
EG–water (80:20)	0.5	−48.3	−39.8

Figure 4. Zeta Potential of pure ethylene glycol dispersed with 0.5% CNT–GNP surface modified with CTAB with a ratio of (2:1) on a) the first day and b) the 60th day.

Figure 5. Zeta Potential of pure ethylene glycol dispersed with 0.5% CNT–GNP surface modified with SDS with a ratio of (3:1) on a) the first day and b) the 60th day.

Figure 6. Zeta potential variation across 60 days using SDS and CTAB for a) 0.5% EG–water (80:20) and b) 0.5% pure EG.

Figure 7. Variation of thermal conductivity for pristine CNT–GNP for a) EG–water (80:20) and b) Pure EG.

Figure 8. Dynamic viscosity variation of pristine CNT–GNP dispersed in a) EG–water (80:20) and b) Pure EG.

Figure 9. Thermal conductivity variation across pristine, SDS, CTAB, and Oxidized CNT–GNP dispersed in EG–water (80:20) for a) 0.0625% b) 0.0125% c) 0.25% d) 0.5%.

Figure 10. Thermal conductivity variation across pristine, SDS, CTAB, and oxidized CNT–GNP dispersed in pure EG for a) 0.0625%, b) 0.0125%, c) 0.25%, d) 0.5%.

Figure 11. Thermal conductivity variation with temperature for nanofluids dispersed with surfactants for a) EG–water (80:20) and b EG 100%.

Figure 12. Variation of viscosity with temperature for nanofluids dispersed with surfactants for a) EG–water (80:20) and b) Pure EG.

Figure 13. Validation of correlation formulas for a) thermal conductivity and b) dynamic viscosity.

Data availability statement

The data that support the findings of this study are available from the corresponding author, V. Srinivas, upon reasonable request.