Abstract
Hybrid or binary nanofluids have superior mechanical and thermal characteristics but the tri-hybrid nanofluids comprise of more embellished thermal properties, better physical strength, and enhanced stability. The present work characterizes the thermal and physical aspects of the hybrid and tri-hybrid nanofluids. The nano-composition of graphene oxide (Go) and cobalt (Co) is used in the amalgamation of hybrid nanofluid Go-Co/H2O, whereas the addition of zirconium oxide (ZrO2) in this mixture gives rise to the ternary Go-Co-ZrO2/H2O hybrid nanofluid. The activation energy and viscous dissipation terms are also amended in the governing equations. The mathematical framework consists of a complex natured dynamical system. However, a numerical algorithm based on finite-difference discretization is developed which can solve the system numerically via the MATLAB software. A comparison with the existing literature is provided in order to validate the numerical procedure. From the outcomes, it is noticed that the temperature of hybrid as well as tri-hybrid nanofuid increases rapidly with change in concentration of zirconium oxide and cobalt. Temperature increases up to 20% by taking 0.1 volume fraction of both zirconium oxide and cobalt. Porous medium and activation energy resist the flow and concentration respectively. A comparative judgment evidently reveals that tri-hybrid Go-Co-ZrO2/H2O nanofluid has a substantial effect on temperature as equated to hybrid or pure nanofluid.
Introduction
The nanofluids are engineered in a systematic way having solid fragments of metals or metallic oxides. The metallic or non-metallic materials gives rise to nanofluids when mix in a base liquid.
These fluids not only increase the thermal conductivity but also embellish the thermal characteristics of the base liquids. A substantial increase in the physical and thermal characteristics of the host liquids owe to nanofluids.1–4 Even a lot of struggle has been made to explore the thermal characteristics of the nanofluids but still efforts are continued. As a result of this queue, the investigations have been extended from nano to hybrid and tri-hybrid nanofluids. The composition of two distinct nanoparticles together with base fluids generates the hybrid nanofluids but the ternary or tri-hybrid nanofluids are composed of three different nano-materials which are immersed in the host liquid. The host liquid may be the engine oil, water, sodium alginate, kerosene oil, ethylene glycol, paraffin, alcohol, and so on. In the same way, tri-hybrid nano-composition may be composed of metals, nitrides, carbides, or metallic oxides materials. The tri-hybrid nanofluids can provide new opportunities to improve mechanical and thermal characteristics in a variety of applications.5–7
The ternary case of nanofluids has been examined recently by various researchers. Shao et al. 8 examined the ternary nanofluid considering the impact of natural convection in the flow. The geometry used in this analysis was the porous enclosure. Two hot movable baffles in the enclosure caused the motion of fluid. The prominent effect of Darcy number was studied, in this research, using a simulation method. A review analysis was presented by Adun et al., 9 in which, they discussed the stability and thermophysical properties of mono as well as tri-hybrid case of nanofluids. Algehyne et al. 10 investigated the ternary nanoparticles MgO, CoFe2O4, and TiO2 using the Non-Fourier's concept. Their work was based on numerical analysis that designated the fact that tri-hybrid case of nanofluids would contain better efficiency than usual fluids subject to heat transfer enhancement. Elnaqeeb et al. 11 interpreted the dynamics of automobiles cooling systems using three different nanomaterial (tri-hybrid case). The importance of heat transport characteristics was also elaborated. The water base flow of three particles Ag-TiO2-Cu was investigated by Li et al. 12 subject to Thomson slip and temperature jump conditions. The RKF-45 technique was adopted to perform simulations. The results of this study spotted that the velocity slip would be the factor for which the flow speed got reduced.
The present analysis incorporates the nanoparticles such as graphene oxide, cobalt, and zirconium oxide for the composition of ternary mixture Go-Co-ZrO2/H2. Each type of nanoparticles has its own special thermal characteristics. Cobalt is a metal with silvery-blue color. The preparation of magnets owe to the cobalt. Some materials like aluminum and nickel when alloyed with the cobalt produce the power magnets. Nowadays, the treatment of cancer has also been carried out with the use of radioactive cobalt. The cobalt oxide (CO3) has been synthesized in water by Salari et al. 13 to prepare the water-based nanofluid. They used some experimental methods like SEM and XRD to illustrate the mechanisms of nanomaterial. Sekhar et al. 14 measured the relative viscosity of cobalt-based nanofluid at high temperature. The temperature range limit varied from 30 °C to 60 °C. Cobalt ferrite COFe2O4 and silver Ag were comparatively studied by Farooq et al. 15 The purpose of this work was to notice that which nanoparticle (out of COFe2O4 and Ag) would exhibit better efficiency. Santhosh and Sivaraj 16 and Murtaza et al. 17 proposed the cobalt particles in the preparation of nanofluid. Both of these studies consisted of numerical analysis of the respective problems. The first one considered the effect of magnetohydrodynamics and the other one taken the second-order slip effect in the model equations.
Graphene oxide and the zirconium oxide also possess better features. The oxidation process of graphite gives rise to the graphene oxide (Go) which is single-atomic-layered material. It is readily available cheap material. The oxide form of graphene (Go) is easily dissolvable in H2O and other solvents. It is not conductive as the oxygen exists in the lattice graphene. The usages of graphene oxide involve water purification, catalysts, bio-sensors, energy storage devices, and so forth. The zirconium di-oxide ZrO2 or the zirconia (other name) is often obtained by the fusion of zirconium silicate which is also known as zircon sand. The potential uses of ZrO2 have been widely found in the ceramic industry. This metal usually exhibits an inorganic behavior. It has strong chemical inertness but low solubility. Some recent studies investigating the features of graphene oxide and zirconium oxide are referred to the references.18–20
The aim to present this work is the interpretation of three distinct nanoparticles such as graphene oxide, cobalt, and zirconium oxide which make amalgamation Go-Co-ZrO2 in the water (base fluid). The nano-composition of graphene oxide, cobalt, and zirconium oxide has not been analyzed yet, specifically, taking the combined impacts of activation energy and the viscous dissipation. The new features of water based Go-Co-ZrO2 ternary hybrid nanofluids are investigated. The analysis also interprets the thermal aspects of hybrid as well as pure nanofluids using Go/H2O and Go-Co/H2O respectively.
Mathematical description of the model
Ternary hybrid nanofluid flow is being assumed in a porous medium. Different types of nanofluids such as graphene-oxide-based mono nanofluid Go/H2O and cobalt-graphene-oxide-based hybrid nanofluid Go-Co/H2O have been taken into account. A tri-hybrid nano-composition is obtained when the zirconium oxide is amalgamated in the water which is base fluid in the present case. In this way, a tri-hybrid nanoparticles Go-Co-ZrO2-H2O nano-composition is prepared. The concentrations and temperatures are specified at the surface and away from surface and are respectively denoted by

(a) Physical model of the problem. (b) Mesh sensitivity analysis.
Flow assumptions
The prominent impacts of porosity (porous medium), viscous dissipation, and activation energy have been assumed in the current analysis.
Porous medium
The pores through which a fluid flows involve the interconnected void spaces that can be referred to as porous medium. The Darcy's law typically expresses the flow through a porous medium and according to this law, the characteristic length scale (L) and the dynamic viscosity (μ) are inversely proportional to the volumetric flow rate (q). On the other hand, q is in direct proportion to the pressure gradient (ΔP). Mathematically, this relation can be written as:
k is proportionality constant and expresses the permeability of the porous medium. The negative sign indicates that flow occurs in the direction of decreasing pressure.
Viscous dissipation
The mechanical energy conversion, due to the internal friction within a fluid flow, into heat is known as viscous dissipation. It can be formulated using the Navier-Stokes as well as the energy equations and is typically expressed in terms of the rate of thermal energy generation per unit volume
The above equation portrays that the rate of viscous dissipation is proportional to the dynamic viscosity of fluid and square of the velocity gradient.
Activation energy
The minimum amount of energy (e.g. the fundamental concept in chemical kinetics) relates to activation energy which is required for a chemical reaction to occur. This energy creates the energy barrier for which the molecules must overcome for a reaction to proceed. Arrhenius equation correlates a mathematical relation between the temperature (T), the rate constant (k), and the activation energy Ea at which the reaction occurs:
e is the base of the natural logarithm,
A is the pre-exponential factor or frequency factor,
R is the gas constant.
The Arrhenius equation indicates that a lower rate constant will be due to a higher activation energy at a given temperature. This equation can be used to estimate activation energies from experimental data.
Governing equations
The model equations relating the tri-hybrid or ternary hybrid nanofluids have the following form21–23:
The transformed equations
The similarity variables, using boundary layer theory, have been taken in the form
24
:
In above equations, the terms
Using equation (9), BCs take the form as:
Physical quantities and thermal properties of nanoparticles
The relations for the physical quantities that have been frequently used in the engineering applications are deliberated as:
Thermal properties of paraffin cobalt, gold, and zirconium oxide.
Numerical solution
Equations (6) and (8) not only comprise of nonlinear terms but also they are coupled. In this situation, the analytical solution may not be possible. If so, it will be so much time consuming. However, one of the choices to solve such type of equations is the numerical approach. We determine the approximate solutions of the problem by incorporating finite-difference discretization. A complete methodology procedure can be further studied in the articles by Ahmad et al.27–29 The system (6)–(8) is discretized using following relations:
The comparison in Table 3 leads towards the precision of algorithmic procedure and accuracy of the code as well.
A comparison with the Prandtl number (
Results and discussion
This section comprises of the consequences of the physical parameters on the ternary Go-Co-ZrO2/H2O, hybrid Go-Co/H2O, and usual nanofluids Go/H2O. The volume concentrations of grapheme oxide, cobalt, and zirconium oxide are respectively represented by

Velocity

Temperature
Figures 4 and 5 provide the pictorial evidences for the velocity

Velocity

Temperature
Shear stress and heat transfer rate with change in
It is manifested from Figures 6 and 7 that nanoparticles volume concentration of cobalt and zirconium oxide increase the temperature in the flow regime in either case of nanofluids. Temperature is more prominent in case of ternary hybrid nanofluids (Go-Co-ZrO2/H2O) as compared to hybrid (Go-Co/H2O) or mono (Go/H2O) nanofluids. The temperature varies with the effect of nanoparticles depending on various factors like concentration and size of nanoparticles, type of nanoparticles, and the surrounding environment. The combination of three distinct nanoparticles can further enhance the heat transfer and modify the phase transition such as melting/boiling points. It can also generate thermoelectric, photo-thermal, and catalytic effects. The nano-composition of three different particles like graphene oxide, cobalt, and zirconium oxide (when dispersed in the base liquid) can provide improved thermal characteristics, efficient heat dissipation, and it facilitates to reduce the temperature gradients. It can be observed from Table 5 that heat transferal rate is got demoted by the Eckert number and the volume fraction of zirconium oxide but an opposite trend is noticed in case of volume fraction of cobalt which increases the heat transfer rate marginally.

Temperature

Temperature
Heat transfer rate with change in
The results of Figure 8 evidently disclose that the Eckert number causes an enhancement in the temperature of the fluid. The kinetic as well as thermal energies can be characterized, in fluid dynamics, by the Eckert number

Temperature
The mixture of water based tri-hybrid nanoparticles Go-Co-ZrO2 is assumed to have chemically reactive species. The chemical reaction phenomenon will definitely occur because of the species involvement in the flow. However, the homogeneous mixture will contain the concentration C with unit

Concentration

Concentration
Mass transfer rate with change in
Conclusions
A suitable combination of tri-hybrid nanoparticles might provide the desired results in the factual applications. The current work aims to interpret the characteristics of three distinct types of nanoparticles such as graphene oxide, cobalt, and zirconium oxide. The analysis also covers the features of the problem under the prominent effects of activation energy and viscous dissipation. An algorithmic approach is taken into account to find the numerical solutions of the problem. Some major culminations of the study are as follows:
The suction phenomenon tends to deteriorate the velocity and temperature in the flow regime. Velocity reduces but temperature enhances, in either case of nanofluids, with an increase in the porosity of the medium. Both parameters, porosity and suction, have increasing effect on the shear stresses in all cases of nanofluids (pure, hybrid, and ternary hybrid case). Nanoparticles volume concentration of cobalt (Co) and zirconium oxide (ZrO2) increase the temperature. The activation energy parameter tends to accelerate the concentration in nanofluids like Go/H2O, Go-Co/H2O and Go-Co- ZrO2/H2O. The temperature to be increase with the Eckert number.
Footnotes
Acknowledgements
Authors extend their appreciation to the Deanship of Research and Graduate Studies at King Khalid University for funding this work through Large Research Project under grant number RGP2/273/45.
Declaration of conflicting interests
The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The authors received no financial support for the research, authorship, and/or publication of this article.
