Mono Nanofluid Research Articles

An experimental study on dynamic viscosity and thermal conductivity of water-Cu-SiO2-MWCNT ternary hybrid nanofluid and the development of practical correlations

In the present work, an experimental study has been carried out to investigate dynamic viscosity (μnf) and thermal conductivity (knf) of Cu-SiO2-MWCNT/water ternary hybrid nanofluid (THNF). The shear stress, dynamic viscosity and thermal conductivity have been measured within a temperature range of T = 15 °C to 65 °C and volume concentration range of ϕ = 1% to 3%. Furthermore, two linear mathematical correlations have been proposed to estimate dynamic viscosity and thermal conductivity of THNF. The combination of metal and metal oxide nanoparticles alongside ternary polymers nanoparticles was an innovative approach to fabricate a novel nanofluid. The nanofluid was prepared by a two-step method and the nanoparticles were dispersed into the base fluid with the help of ultrasonic waves and a three-dimensional mixer. To examine nanoparticles' surface and structure, XRD and FESEM analyses have been employed. Based on the results, both thermal conductivity and dynamic viscosity were dependent on ϕ and temperature. Also, the studied THNF exhibited Newtonian behavior throughout the experiments. Comparing the results with those of Mono nanofluid (MNF) and Binary hybrid nanofluid (BHNF), it has been observed that ternary nanoparticles, in THNF, leads to far greater thermal conductivity and dynamic viscosity than mono and binary nanoparticles, in MNFs and BHNFs. Finally, the maximum errors of the proposed mathematical models from the experimental results were 1.167% and 1.327% for thermal conductivity and dynamic viscosity correlations, respectively, with R-square values of 99.9361% and 99.8698%.

Numerical investigation on optimization of thermal analysis due to immersion of hybrid nanostructures in a fluid of shear dependent viscosity using the finite element method

AbstractThis article considers the dispersion of hybrid and mono nanoparticles in a fluid with viscosity (Williamson) dependent on shear rate, over a heated surface moving with nonuniform velocity and exposed to a magnetic field in the presence of an applied current. Extensive modeling leads to complex coupled mathematical models that are solved numerically via the finite element method (FEM). Convergent simulations are run to investigate the role of parameters on the dynamics of flow fields. The magnetic field intensity plays a role in controlling the magnetohydrodynamic boundary layer thickness (BLT) and thermal radiation controls the thickness of thermal boundary layers (TBL). However, the magnetic field intensity is responsible for an increase in BLT. In contrast to this, thermal radiation plays a role in controlling the thickness of the TBL. The impact of shear rate dependent viscosity on velocity is remarkable for both fluids. The motion of both of the fluids slows down when viscosity varies as a function of shear rate. Viscosity depending on the shear rate has a significant impact on wall shear stress. It is observed from simulations that wall shear increases when the parameters appearing in the model for shear rate dependent viscosity are increased. However, this increase in wall shear stress associated with a hybrid nanofluid is greater than the increase in wall shear stress associated with a mono nanofluid.

High-performance nanofluid synthesis and DFT-TDDFT study of graphene nanosheets along bent surface for enhanced oil-recovery implementations

Thermal characteristics over a slippage permeable curved surface of mono and hybrid nanofluid convective flows. The surface is assumed to be convoluted with radius R in circle part. The salt-water is used as a base fluid to model the flow with graphene and silica nanoparticles. The magnetic effect is taken into consideration with a heat source (sink) and thermal radiative flow impact. The mathematical model is solved by Chebyshev spectral collocation method after transformed into a nondimensional form. The nanostructure thin films of [SH2O/GO]m nanofluid and [SH2O/GO+SiO2]h are synthesized by using a spin-coating technique process with a thickness of 100 ± 3 nm/25 °C. The structure characterization (FT-IR spectrum and XRD) results from experimental and DFT-TDDFT (DMOl3) data are studied for mono and hybrid nanofluids. The outcomes show that the temperature is declined with a curvature of the surface, while the flow velocity is boosted. Rate of heat transmit is enhanced with the radiative and suction flow. The results specifically determine that ΔEgOpt values decrease from 2.293 eV for [SH2O/GO]m mono nanofluid to 1.196 eV for [SH2O/GO+SiO2]h hybrid nanofluid using the DFT computations EHOMO and ELUMO calculations. This result concluded that the [SH2O/GO]m transformed from semiconductor to [SH2O/GO+SiO2]h as a super-conductor hybrid nanofluid by adding (SiO2 nanoparticles).

Assessments of thermal performance of hybrid and mono nanofluid U-tube solar collector system

Solar energy systems are of great importance for water heating, where we spend most of the energy. U-tube solar collectors have a very important place in water heating among solar energy systems. Compensation of the intense energy used for water heating by this type of environmentally friendly solar energy system, will reduce CO2 and SO2 emissions for a cleaner nature. Therefore; the thermal performance of a U-tube complete system from evacuated tube solar collector (ETSC) systems was assessed. The heat transfer capability of the system, which contains 10 U-tubes, has been examined by considering the fact that it has different work fluids and different heat fluxes and flow rates. The finite volume method is used for this analysis. The model has been verified by many experimental and numerical studies. In the system under consideration has been used 10 vacuum U-tubes inclined at 30°, and water and nanofluid (SiO2 - Cu) which were used as working fluid in the manifolds connected to these tubes. Nanoparticles modeled in the work fluid are considered as hybrid and mono at different volume fractions. The thermal and hydrodynamic behaviors of the system have been examined by taking into account the Boussinesq approach, and the system outlet temperatures have been calculated. As a result of analyzes and comparisons made, it has been seen that the use of nanofluid improves the thermal capability of the system under consideration. It has been determined that this improvement reaches up to 15% compared to water. The thermal effects of using SiO2 nanoparticles, which are lighter than Cu nanoparticles, were observed in terms of the precipitation problem encountered in many systems when using hybrid nanofluids. Thus, instead of using more Cu nanoparticles in volume, using smaller amounts together with SiO2 nanoparticles as a hybrid both eliminates the problem of precipitation and improves the heat capability of the work fluid.

Develop artificial neural network numerical modeling to study fluid flow and heat transfer of dispersed nanoparticles through base liquid

PurposeThis paper aims to disperse the silicon dioxide in water (as the mono nanofluid [MN]) and then, carbon nanotube (CNT)-silica composite in water (as the hybrid nanofluid [HN]).Design/methodology/approachNanofluids have gained lots of attention through the recent years. Due to their usage in the industries and also medical applications, they have high protentional to be studied in different aspects. The most common study for the nanofluids is to understand the heat transfer capacity for each material in each fluid. These material(s) or fluid(s) can be one (mono nanofluid) or more than one (hybrid nanofluid).FindingsThe mixture of two solids is to assess the unique properties of each material and also to decrease the cost of experiments. The heat transfers for both MN and HN were measured at volume fractions up to 1.0%, and temperatures up to 50°C. Also, the heat transfers were compared. By more CNT, thermal conductivity was enhanced about 17.39% (from 12.42% of MN to 29.81% of HN).Originality/valueX-Ray diffraction and field emission scanning electron microscope (FESEM) were examined for mono solids and the composite. After the experimental study, for MN and HN, four novel correlations calculated.

Establishing artificial neural network to investigate thermal properties of carbon nanotube/zinc oxide composite dispersed in water

Nanofluid refers to the mixture of fluid and solid nanoparticles (NPs). If this mixture contains one NP or fluid, it is called ‘mono nanofluid’ (MN). Further, if this mixture contains more than one NPs or fluid, it is called ‘hybrid nanofluid’ (HN). In this research, first, zinc oxide NP was dispersed in the water base fluid and formed an MN. Then, thermal conductivity (TC) of MN was measured. After that, multiwalled carbon nanotube (MWCNT) NP was added to the MN and formed an HN. Further, TC of HN was measured. Both MN and HN TCs were compared, and the results revealed that by adding MWCNT, TC enhanced by about 18.79% (from 25.12% of MN to 43.91% of HN). On the other hand, to analyze the phase structure and to observe the microstructure, X‐ray diffraction analysis was examined. The measured TC for both samples was at volume fractions up to 1.0% and temperatures up to 50°C. After an experimental study, two novel correlations were calculated by the curve fitting method for MN and HN individually. In the end, to predict the other Vf and temperature, the artificial neural network approach has been developed.

Mixed Convection of Silica–Molybdenum Disulphide/Water Hybrid Nanoliquid over a Rough Sphere

A steady combined convective motion over a rough sphere with hybrid nanoparticles is analyzed. We have considered silica (SiO2) and molybdenum disulphide (MoS2) nanoadditives which are added in H2O to form MoS2–SiO2/H2O hybrid nanoliquid. The partial differential equations describing the boundary layer flow characteristics are reduced into non-dimensional form with appropriate non-similar reduction. It should be noted that the governing equations have been written using the conservation laws of mass, momentum and energy. These considered equations allow simulating the analyzed phenomenon using numerical techniques. Implicit finite difference approximation and technique of Quasilinearization are utilized to work out the dimensionless control equations. The influence of various physical characteristics included in this challenge, such as the velocity fields and temperature patterns, is investigated. The study of border gradients is performed, which deals with the skin friction and energy transport strength. The plots of computational outcomes are considered, which ascertain that velocity distribution reduces, whilst coefficient of friction at the surface, energy transport strength and temperature distribution augment for enhancing values of hybrid nanofluid. For enhancing magnitude of combined convection parameter, dimensionless velocity distribution, surface drag coefficient and energy transport strength enhance, while temperature distribution diminishes. High impact of hybrid nanofluid on energy transport strength and the surface friction compared to the host liquid and mono nanofluid in presence/absence of surface roughness is shown. Velocity distribution enhances for rising values of velocity ratio parameter. Enhancing values of frequency parameter rise the friction at the surface and energy transport strength. It is also examined that the hybrid nanofluid has a maximum temperature for the blade-shaped nanoparticles and has a low temperature for the spherical-shaped nanoparticles.

A review on the application of hybrid nanofluids for parabolic trough collector: Recent progress and outlook

By far, the Parabolic trough collector (PTC) is the most established solar concentrating technology worldwide. This paper draws a comparison among various studies done earlier in the domain to bring forth different models and mediums used to evaluate the effect of nanofluids on thermal parameters for PTC providing an optimum output, resultantly. The study also reveals that by using nanofluid and hybrid nanofluids as heat transfer fluid (HTF) inside the absorber tube of solar collector, the thermal and optical characteristics can be enhanced. Reported papers in literature mention stability, effect on PTC’s performance by implementing various novel designs, collector efficiency enhancement by using various inserts, and selecting proper hybrid nanomaterial into the base fluid. Varied experimental studies report that using hybrid nanofluid results in a more significant enhancement in thermal properties viz-a-viz than the mono fluids. A close look at the results of some of the notable works of the domain explicitly implies that for enhancing the thermal conductivity of nanofluid, metal oxide hybrid nanofluids are more promising than the oxide ones in a rather ‘pecking order’. The study also verges on the proposition that the thermal properties of nanofluid can be accelerated by the usage of hybrid nanofluid instead of mono nanofluid, as a medium, into a more efficient hybrid structure. Conclusively, this review advances the understanding of optimizing alteration parameters for obtaining maximum increase in outcomes and offers substantially adequate understanding for choosing specific techniques to enhance the overall efficiency of PTC, which can be used as a guideline for future trends. • Current and past studies of parabolic trough collectors have been reviewed. • Nanofluid techniques are delineated in performance enhancement. • The implementation of inserts has resulted in Brownian motion enhancement. • The efficiency of the collector using nanofluids is higher than that of the base fluid. • This review provides research gaps for researchers to investigate further.

Numerical investigation of heat transfer and pressure drop for cooling of microchannel heat sink using MWCNT-CuO-Water hybrid nanofluid with different mixture ratio

Micro-channel heat sinks are gaining prominent importance in cooling of micro-electronic devices due to their high rate of heat dissipation and very high surface area. Also during the recent times, hybrid nanofluids have appeared as a innovative group of working fluids for many heat transfer applications owing to special heat carrying characteristics. In view of the importance, a numerical study is carried out to examine the heat transfer and pressure drop characteristics for laminar flow of hybrid nanofluid as a coolant in a circular micro-channel heat sink (MCHS) under forced convection conditions in the present work. The performance of heat sink is evaluated using Multi-Walled Carbon Nano Tubes (MWCNT)-CuO/water based hybrid nanofluid for different mass flow rates, with the volume fractions ranging from 1% to 3%. The law of mixtures and correlations existing in the literature are used to find the properties of hybrid nanofluids. The influence of Reynolds number on pumping power and the heat transport rate is studied for different mixture ratios of MWCNT-CuO/water based hybrid nanofluids and similar studies were carried out for MWCNT-water and CuO-water mono fluids. The results show a step up in heat transfer with hybrid nanofluids over mono nanofluids and the enhancement of heat transfer is observed with raise in volume fraction. The maximum enhancement in Nusselt number was found at 3% of hybrid MWCNT-CuO/water nanofluid. An enhancement of 4.68% and 12.64% was found, when compared with CuO/water and MWCNT/water mono nonofluids respectively. The pressure drop results indicate that hybrid MWCNT-CuO/water nanofluid possess less pressure drop when compared to CuO/water nanofluids and when compared to water an increase of pressure drop of 300 Pa was found. This indicates that there is no significant increase in pumping power with hybrid nanofluids compared to mono-nanofluids and water. The present model is validated by comparing the numerical results got for mono nanofluid with the data available in literature.

Experimental validation of enhancement in thermal conductivity of titania/water nanofluid by the addition of silver nanoparticles

The paper presents the experimental investigation of thermal conductivity enhancement of a newly developed nanocompositefluid (TiO2-Ag/water) and compares the enhancement with mono nanofluid (TiO2/water). The experiments are carried out for 0.1, 0.2, 0.3 and 0.4 volumetric concentrations and at fluid temperatures 35, 40, 50 and 60 °C. The results show that the thermal conductivity enhancement of the nanocompositefluid is higher than the mono nanofluid. The maximum enhancement is 18.47% for 0.4 vol% at 60 °C relative to the TiO2/water nanofluid. From the results, it is understood that 0.1 vol% of TiO2-Ag/water has almost the same thermal conductivity as that of 0.4 vol% TiO2/water nanofluid. Thus, for the same enhancement, a lower vol% of TiO2-Ag nanocomposite particles is required as compared to the TiO2 nanoparticle only in water. Based on the experimental data, regression analysis, thermal conductivity ratio models are developed for the two nanofluids and the best model is selected based on maximum R2 values.

MHD Hybrid Cu-Al<sub>2</sub>O<sub>3</sub>/ Water Nanofluid Flow with Thermal Radiation and Partial Slip Past a Permeable Stretching Surface: Analytical Solution

The influence of velocity slip and thermal radiation effects on the magnetohydrodynamic hybrid Cu-Al2O3/water nanofluid flow over a permeable stretching sheet is reported in this paper. The similarity transformation is adopted to reduce the partial differential equations to the ordinary differential equations. Exact analytical method is implemented to solve the problem. Maple program is used to facilitate the calculation process. The new additional effects which are the velocity slip and thermal radiation effects are considered towards the model to scrutinize the impacts. The effects of various parameters towards the velocity and temperature profiles are demonstrated through graphs, meanwhile the skin friction coefficient and the local Nusselt number are exhibited through the tabulation of data. The existence of velocity slip reduced the velocity profile but enhanced the temperature profile. The thermal radiation effect has increased the temperature profile. The heat transfer rate are enhanced for the case of hybrid nanofluid compared to the mono nanofluid.

Compuational study on transport of thermal energy and mass species in power law rheological fluid with hybrid nanostructures in the presence of chemical reaction

Power law rheological model is used for mathematical modeling of simultaneous transport of heat and energy via hybrid nanoparticles distributed in heat generating fluid exposed to magnetic field. Governing conservation laws, correlation between thermos-physical properties fluid, solid particles, suitable no-slip momentum and temperature boundary conditions are provided system of boundary value problems which are solved numerically using finite element method (FEM). The FEM simulations are used in capturing the dynamics of physical parameters on the momentum transport and heat energy transfer under the influence of non-uniformly moving surface which is being heated in non-uniform manner. Power law fluid flow experiences retardation as intensity of magnetic field is increased. Hybrid nanofluid is more heat generative than mono nanofluid and power law index causes a decrease in flow. Consequently, convective transport of heat is compromised. Generative and destructive chemical reactions have opposite trend on transport of species in power law fluid.

Influence of hybrid nano-structures on thermal performance of shear rate dependent viscosity fluid over a heated rotating cone with Hall and ion slip currents

The fluid of shear rate dependent viscosity has totally different rheology and exhibits dynamics which play a key role in heat transfer rate and friction experienced by surface over which this type of fluid is considered in this study as this type of fluids are extensively used in thermal processes. The governing laws and constitutive equations for hyperbolic tangent fluid and thermo-physical relation correlation for hybridity of nano-structures are simultaneously solved via finite element method (FEM). The predictions are recorded, and outcomes are explained. It is found from outcomes that suspension of hybrid nano-structures is the most approximate technique for the enhancement of thermal performance of coolant (hyperbolic tangent fluid). The process of diffusion of wall momentum into fluid speeds down as viscosity decreases as a function of shear rate. It is predicted from simulations that mono nanofluid is less shear thinning than hybrid nanofluid. Hence, if it is desired to reduce shear thinning phenomenon, enhance the thermal performance and suspension of hybrid nano-structures are recommended. The results are validated by comparing them with already published benchmarks. The parameters are varied, and simulations are recorded in term of numerical values and graphical data. The rotation of micro-structures has shown significant reduction in angular velocity of mono and hybrid nanofluids. Angular field has depicted an increasing trend when vortex viscosity parameter is varied through increasing values. Temperature decreases as a result of an increase in thermal relaxation time. Hence, thermal memory effects play a significant role in controlling the thermal boundary layer thickness.

Comparative study on ethylene glycol based Ag-Al 2 O 3 and Al 2 O 3 nanofluids flow driven by electroosmotic and peristaltic pumping: a nano-coolant for radiators

This paper aims to provide a comparative analysis of hybrid (Ag- Al 2 O 3) nanofluid and Al 2 O 3 mono nanofluid in a convective heat transfer process driven by electroosmotic and peristaltic pumping. Ethylene glycol (EG) due to its strong anti-freezing properties is taken as a base fluid. The features of mixed convection, magnetohydrodynamics, and Joule heating are also comprised in this study. The slip boundary conditions for axial velocity and temperature are employed at the walls of the microchannel in a porous environment and conditions of zero normal mass flux are imposed for the passive control of nanoparticles. This model is composed by using the Buongiorno flow model along with the modified Maxwell-Garnett model for thermal conductivity of hybrid nanofluids and Poisson-Boltzmann distribution for electric potential generated within the fluid medium. The problem is simplified under the approximations of lubrication theory and Debye–Hückel linearization and the numerical computations have been made through Maple 17 code. The graphical results of flow variables for various involved quantities are prepared and presented with a requisite interpretation. Moreover, contour graphs are also plotted for stream function in order to discuss the trapping phenomenon. The addition of a volume fraction of 9% of aluminum dioxide in ethylene glycol tends to raise the thermal conductivity of working fluid up to 28.97% however further addition of a small number of silver nanoparticles increases its thermal conductivity up to 53.57%. Due to this increment in thermal conductance, it is found that the efficiency of Ag- Al 2 O 3 nanofluid in the heat transfer mechanism is better than the Al 2 O 3 nanofluid. It is further reported that EG based hybrid nanofluid (Ag- Al 2 O 3) as nano-coolant is more applicable for radiators and other cooling systems as compared EG based (Al 2 O 3) nanofluid.

Thermal Conductivity Enhancement via Synthesis Produces a New Hybrid Mixture Composed of Copper Oxide and Multi-walled Carbon Nanotube Dispersed in Water: Experimental Characterization and Artificial Neural Network Modeling

Nanofluid is a solid–fluid mixture. By using one solid nanoparticle or one fluid, mono-nanofluid (MN) forms, and by using two solid nanoparticles (NPs) or two fluids, hybrid-nanofluid (HN) forms. For this study, for MN, copper oxide (CuO) and for HN, two solids, which are CuO and multi-walled carbon nanotube (MWCNT) were dispersed in base fluid which is water. After nanofluid preparation, thermal conductivity was measured, and the achievements were numerically modeled. After that, XRD–EDX were performed for the phase-structural analysis. Then, FESEM was examined for NPs-microstructural study. Thermal conductivity (TC) of MN and HN were investigated at 0.2 % to 1.0 % volume fractions (Vf) in 25 °C to 50 °C temperature (T) ranges. Thermal conductivity enhancements of 19.16 % and 37.05 % were seen at the utmost Vf and T for mono-nanofluid and hybrid-nanofluid, respectively. New correlations have been presented with R2 = 0.9, and also Artificial Neural Network (ANN) has been done with R2 = 0.999. For the presented correlation, 0.86 %, and 0.51 % deviations, and for the trained model, 0.41 % and 0.51 % deviations were estimated for mono-nanofluid and hybrid-nanofluid, respectively. As a final result, by adding MWCNT to CuO–H2O mixture, thermal conductivity is raised by 17.89 %, and the hybrid-nanofluid has acceptable heat-transfer capability.

The impact of monocity and hybridity of nanostructures on the thermal performance of Maxwellian thin-film flow with memory and Darcy–Forchheirmer effects

This article considers viscoelastic effects on the enhancement of transportation of heat in thin-film flow when the relaxation time phenomenon is considered to be significant. Transport models characterizing momentum and thermal memory effects are solved numerically. Finite element simulations are carried out for the prediction about viscoelasticity, relaxation time memory effects and drag by nonlinear porous medium and suspension of hybrid nanostructures in the Maxwellian fluid. The predictions are recorded in the form of graphical and numerical data which are interpreted to extract significant outcomes. A notable contrast in the behavior of thermal relaxation time and suspension of nanostructures is observed. This consequence is a blessing that thermal and momentum boundary layer thicknesses may be rheostated via relaxation times. On the other hand, a substantial rise in the thermal conductivity of Maxwellian working fluid in a thin-film region is observed due to the suspension of hybrid nanoparticles. Further, it is observed that improvement in thermal efficiency of the Maxwellian thin-film flow via hybrid nanoparticles is higher than the improvement in thermal efficiency of the Maxwellian thin-film flow via mono nanoparticles. The existence of a porous medium in the thin-film flow region offers a notable drag to flow. Subsequently, the porous medium is noted as a momentum controlling factor in the thin-film flow of Maxwell fluid. The heat generation process in hybrid nanofluid is faster that the heat generation in mono nanofluid.

Thermal conductivity enhancement of nanofluid by adding multiwalled carbon nanotubes: Characterization and numerical modeling patterns

Nanofluid is divided in two major section, mono nanofluid (MN) and hybrid nanofluid (HN). MN is created when a solid nanoparticle disperses in a fluid, whereas HN has more than one solid nanomaterial. In this research, iron (III) oxide (Fe3O4) is MN, and Fe3O4 plus multiwalled carbon nanotube (MWCNT) is HN, whereas both are mixed and dispersed into the water basefluid. Thermal conductivity (TC) of Fe3O4/water and MWCNT/Fe3O4/water was measured after preparation and numerical model performed on the resulted data. After that, field emission scanning electron microscope (FESEM) was studied for microstructural observation of nanoparticles. MN and HN TC were studied at temperature ranges of 25 to 50°C and volume fractions of 0.2% to 1.0%. For MN and HN, thermal conductivity enhancement (TCE) of 32.76% and 33.23% was measured at 50°C temperature—1.0% volume fraction, individually. Different correlations have been calculated for numerical modeling, with R2 = 0.9. Deviation of 0.6007% and 0.6096% was calculated for given correlations for MN and HN individually. Deviation of 0.5862% and 0.6057% was calculated for trained models, for MN and HN individually. Thus, by adding MWCNT to Fe3O4‐H2O nanofluid, TC is enhanced 0.47%, and this HN has agreeable heat transfer potential.

Numerical investigation on transport of momenta and energy in micropolar fluid suspended with dusty, mono and hybrid nano-structures

Computational fluid dynamics (CFD) tools are applied to model transportation activity in micropolar fluid suspension with density particles and mono and hybrid metallic nano-sized structures. Highly complex computational models obtained by CFD simulations are executed via the finite element method. Galerkin residuals are approximated by Galerkin approximations. The assembled nonlinear system is linearized and solved iteratively under reasonable computational tolerance. A notable impact of vortex viscosity is observed during transportation of macro- and micro-momentum. The velocity of dust particles has been predicted via the variation of dust particle interaction parameter. Angular velocity for both mono and hybrid nanofluids is found to increase as a function of vortex viscosity. Furthermore, it is noted that the micro-rotation field associated with mono–nanofluid has a higher value than the micro-rotation field associated with hybrid nanofluids.

Effect of surfactants on thermal conductivity of graphene based hybrid nanofluid

Various hybrid nanofluids have been researched in this decade. The quality of this said-to-be alternate heat transfer medium depends on two major features – long term stability and high thermal conductivity. In recent years, graphene-based nanofluid was reported to exhibit distinguished heat transfer performance compared to most materials investigated in past studies. This study aims to compare the effect of different surfactants on thermal conductivity of graphene-based nanofluid. Sodium dodecylbenzenesulfonate (SDBS) and hexadecyltrimethylammonium bromide (CTAB) were mixed separately in advance with the mixture of water and ethylene glycol. After mixing surfactants and base fluid, total 0.025 to 0.1 wt% of nanoparticles were added into the mixture and followed by ultrasonication. Mono nanofluid was produced by adding graphene nanoplatelets (GnP) only whereas a novel hybrid combination was composed of graphene nanoplatelets and titanium dioxide. Stability of each sample was inspected using zeta potential analysis and Uv-vis spectroscopy. Thermal conductivity of samples from 30 °C to 60 °C was measured using Decagon KD2 Pro. Both surfactants contributed to high zeta potential value and minimal sedimentation for all nanofluids. CTAB improved the thermal conductivity of hybrid nanofluid more compared to SDBS, with 11.72% difference at 0.1 wt% nanoparticles concentration when compared to base fluid at 60 °C. The highest enhancement (23.74%) on base fluid was spotted at 60 °C, where 0.1 wt% of GnP was mixed with CTAB. These findings could strengthen literature on suitable surfactant to be used on graphene based nanofluid since limited comparison work has been done. High thermal conductivity of the hybrid nanofluid at high temperature could be used as coolant in cooling system.

Impact of different surfactants and ultrasonication time on the stability and thermophysical properties of hybrid nanofluids

Graphene based nanofluids are getting more attention among researchers due to their exceptional thermal conductivity. In the present study, stable hybrid nanofluids were produced by dispersing graphene nanoplatelets (GnPs) and titanium dioxide (TiO2) in a mixture of distilled water and ethylene glycol (DW/EG) using a two-step method. For comparison purpose, GnPs were dispersed into the same base fluid and labelled as mono nanofluid. The impact of different surfactants and sonication time on nanofluids' stability was determined by sedimentation method, zeta potential analysis, and absorbency test. It was observed that the addition of hexadecyltrimethylammonium bromide (CTAB) showed the highest degree of stability in all analyses, with minimal sedimentation up to 40 days. Thermophysical properties of nanofluids with CTAB were measured from 30 °C to 70 °C at 0.1, 0.075, 0.05, and 0.025 wt% concentrations of nanoparticles. The maximum thermal conductivity enhancement of base fluid was found to be 23.74% when 0.1 wt% of COOH-GnP was added at 60 °C. Hybrid nanofluid showed higher thermal conductivity than mono nanofluid at all concentration and temperature ranged from 30 to 50 °C. Both mono and hybrid nanofluids showed Newtonian behaviour in which shear stress increased linearly with increasing shear rate. Mono nanofluid with 0.1 wt% concentration showed the highest viscosity at 40 °C, which was 32.54% and 4.85% higher than base fluid and 0.1 wt% hybrid nanofluid, respectively. The enhanced properties of this hybrid nanofluid could be used as an alternate heat transfer medium in an automobile cooling system.