Abstract: - This study presents an empirical investigation into the impact of surfactant's enhanced stability and

thermophysical characteristics of water-ethylene glycol (60:40) based Al2O3-TiO2 hybrid nanofluids. It aims to

shed light on the nanofluid's behavior, mainly how surfactants affect its stability and thermal performance, thus

contributing to advancements in heat transfer technology and engineering applications. The growing interest in

nanofluids, which involves blending nanoparticles with conventional base fluids, spans diverse sectors like

solar energy, heat transfer, biomedicine, and aerospace. In this study, Al2O3 and TiO2 nanoparticles are evenly

due to PVP surfactant addition compared to other conditions. However, the nanofluids with PVP still exhibit

more excellent thermal conductivity value than the base-fluid and significantly reduced viscosity (max 55%).

Hence, the enhanced thermal conductivity and reduced viscosity with improved stability due to PVP addition

significantly impact heat transfer performance. However, the maximum thermal conductivity was obtained for

surfactant-free Al2O3-TiO2/Water-EG-based hybrid nanofluids that reveal a thermal conductivity that is 17.05

% higher than the based fluid. Instead, the lower viscosity of hybrid nanofluids was obtained at 70 0C with the

addition of PVP surfactant. Therefore, adding surfactants positively impacts Al2O3-TiO2/Water-EG-based

hybrid nanofluids with higher stability, enhancing thermal conductivity and reducing viscosity compared to the

based fluids. The results show that adding surfactants at a fixed volume concentration affects thermal

conductivity at low temperatures and viscosity at high temperatures, suggesting that these fluids might be used

1 Introduction

Heat transfer devices play a role in our lives as their

efficiency is essential for minimizing energy

improved energy efficiency. However, traditional

methods of heat transfer often face difficulties in

achieving optimal heat transfer performance. The

researchers introduced metals and metal oxides with

heat transfer properties into the liquids to overcome

the difficulties. This enabled the fluids to employ

methods of heat transfer, [2]. The remarkable

thermal properties of nanofluids have attracted

attention as fluids for heat transfer purposes.

Nanofluid consists of a base fluid such as water,

applications, [4]. Scientists and researchers have

been conducting extensive research on nanofluids.

They encountered a sheared obstacle that needed to

be addressed. However, nanofluids are considered

fluids that pose challenges in their synthesis,

characterization, and applications. Models do not

adequately describe these aspects, [5], [6]. In

contrast, nanofluids have gained attention across

fields. They are extensively utilized in sectors

including cosmetics, [7], manufacturing [8], [9],

on the characteristics and sensitivity of nanofluids in

the introduction. Nanoparticles have caught the

attention of researchers because of their size, surface

area, and surface-to-volume ratio, and they exhibit

enhanced thermal conductivity. Nanoparticles are

made of metal and metal oxides [15], carbon

nanotubes [16], and graphene-based nanofluids in

the fields of heat transfer, [17]. Choosing the type of

nanoparticle base fluids and their concentration is

vital when preparing nanofluids with thermal

nanofluids' stability and performance, reducing

thermal conductivity and enhanced viscosity, [1]. It

is vital to maintain the thermal characteristics of the

base fluid to ensure long-term stability that enables

nanofluids to be consistently used in heat transfer

treated TiO2 particles with CTAB and SDS and

finally found stability for over two weeks, [25]. The

research also revealed an enhancement of 15% and

10% in thermal conductivity at a volume

concentration of 1.25%. After sufficient sonication

with SDS surfactant addition, Al2O3/distilled water

nanofluid behaved as a homogeneous nanofluid with

nearly 30 mV zeta potential value, [26]. Another

study suggested using [BMIM] PF6 ionic liquid to

prepare a stable Al2O3 nanofluid, [27]. However, the

on 60: 40 Water-EG. Hence, the present research

focuses on the impacts of various surfactants on the

2 Materials and Methods

recognized two-step synthesis technique for

preparing Al2O3- TiO2 hybrid nanofluids in water-

ethylene glycol as the base fluid. Figure 1 illustrates

a two-step technique to prepare the hybrid

nanofluids utilizing the chosen based fluid and

nanoparticles. Utilizing individual beakers, the

proportion were blended with the base fluid (DI-

water and EG) at a weighting ratio of (60:40) and

sulfonate (SDBS), and sodium dodecyl sulfate

(SDS). Information on a selection of surfactants is

presented in Table 2.

Water and ethylene glycol) and nanoparticles (Al2O3

needles. The KD2 Pro analyzer sensor, which is thin

and needle-shaped, is inserted vertically into the

sample without making contact with the container

walls. It ensures that the sample remains

undisturbed while measurements are taken. Three

different temperatures, 30, 50, and 70 degrees, are

being examined to assess their properties. Ten

readings are collected for each sample and

temperature, with a 15-minute delay between each

reading, and the average results are finally

connected to a calibrated spiral spring. The motor’s

drive shaft powers a spindle immersed in the tested

fluid. We measured the resistance of the flow

movement by observing the increasing torque

values. When the LVDV III Ultra motor rotates, we

measured the fluid's ability to resist movement by

monitoring the increasing torque values. The

experiments included the viscosity changes at 30 to

70 0C with 20 0C intervals using a designed Rheocal

Program. Similarly, we gathered ten readings for

percentage enhancement of thermal conductivity for

insights into their complex thermal behavior. Based

on the information in Figure 2(a), the thermal

conductivity of samples with and without

surfactants surpasses that of the base fluid (water;

EG) as the ASHRAE reference value. A noticeable

increase in the thermal conductivity of tested hybrid

nanofluids as temperature rises. The noticeable

increase in thermal conductivity is mainly attributed

which leads to collisions. The second factor is the

composition of the nanoparticles and the type of

surfactants employed. In addition, the increasing

kinetic energy of the nanoparticles and the repetitive

collisions of the nanoparticles with the increasing

temperature are additional factors that contribute to

improving thermal conductivity, [31], [32]. The

highest thermal conductivity is achieved for the

sample without surfactant at 70 oC, while the lowest

value is revealed for the sample with PVP at 30 oC.

Eq. (2).

Thermal Conductivity 󰇛󰇜



The thermal conductivity of nanofluid was

assessed with and without surfactant, as well as with

conductivity is observed for the sample without

surfactant at 70 oC, while a minimum of 5.33%

enhancement is derived for the Al2O3-TiO2 with

PVP at 30 oC. In addition, the thermal conductivity

is reduced by 2.92%, 1.41%, and 4.61% at 30 oC, 50

compared to the Al2O3-TiO2 hybrid nanofluid

temperature which retards the sedimentation of

particles. This is because the attraction interactions

between the nanoparticles are reduced, resulting in

wider gaps between the molecules in the fluid, [2].

As a consequence of this,

resistance to the fluid flow, decreasing its viscosity.

Furthermore, the fluid molecules increase energy

when the temperature rises. This increased energy

enables them to overcome the forces within the

Al2O3 -TiO2 hybrid nanofluid without surfactant

presented the highest viscosity enhancement at 70

33.62% was found for the sample with PVP

surfactant at 30 oC. The enhancement rate with

%. However, the hybrid nanofluid containing 0.1 %

volume concentration and a PVP surfactant

exhibited significant sensitivity regarding thermal

conductivity at a temperature of 30 0C. This implies

that after introducing a specific quantity of

nanoparticles into the nanofluid suspension, the

thermal conductivity exhibits reduced efficiency at

higher temperatures in contrast to lower

temperatures.

According to the findings in Figure 5, the

viscosity of the hybrid nanofluid, both with and

without the surfactant, exhibited the maximum level

of sensitivity at a temperature of 70 degrees Celsius

and a volume concentration of 0.1 %. On the

contrary, in case the sensitivity of viscosity of TiO2-

increases with rising temperature, and the increasing

rate of sensitivity is comparatively higher for the

sample without surfactant, which means the sample

nanofluid employing the most widely recommended

two-step technique. This study investigates hybrid

nanofluids' stability and thermophysical properties

with various temperature ranges. It has also

explored the impact of three distinct surfactants on

these properties, including SDS, SDBS, and PVP.

The sensitivity of thermophysical properties to the

volume concentration at various temperatures was

evaluated. The findings of this study are detailed as

follows: