Nanofluid Heat Transfer Research Articles

An experimental study of the influence of Fe3O4, MWCNT-Fe3O4, and Fe3O4@MWCNT nanoparticles on the thermophysical characteristics and laminar convective heat transfer of nanofluids: A comparative study

In this study, the main objective is to investigate the impact of single, hybrid, and doped magnetic nanoparticles (NPs) on the convective heat transfer capabilities of a water/ethylene glycol (EG)-based nanofluid (NF) under the influence of a magnetic field (MF). The NFs were prepared by incorporating Fe3O4, Fe3O4-multi-walled carbon nanotubes (Fe3O4-MWCNT), and Fe3O4@MWCNT in concentrations of 0.05, 0.1, and 0.2 wt.%. The NPs were characterized using various techniques such as XRD, SEM, VSM, Raman spectroscopy, and FTIR to confirm their properties. The stability of the NFs was assessed through dynamic DLS and zeta potential measurements. The study then focused on evaluating the effects of these nano-additives on thermal conductivity (TC), viscosity at 25 °C, convective heat transfer coefficient (CHTC), and friction factor in a circular tube under laminar flow regime with a constant wall flux, both with and without the application of a MF. The results of present preliminary study with limited samples revealed that the CHTC of NFs containing Fe3O4 and Fe3O4@MWCNT NPs increased with NP concentration and application of a MF, with maximum increases of approximately 19.01 % and 32.84 %, respectively. However, in the case of NFs containing MWCNT-Fe3O4 NPs, the CHTC decreased when the MF was applied at concentrations higher than 0.1 wt.%. Furthermore, the NFs containing 0.2 wt.% of Fe3O4, MWCNT-Fe3O4, and Fe3O4@MWCNT NPs exhibited the highest friction when subjected to a 400 G MF, resulting in increases of 5.2 %, 9.2 %, and 5.9 %, respectively, compared to the base fluid. The performance index, which assesses the effectiveness of using NFs instead of the base fluid, indicated that all samples had a performance index greater than one, indicating their efficacy. The maximum performance index achieved was 1.343, corresponding to the NF containing 0.2 wt.% of Fe3O4@MWCNT NPs at a Reynolds number (Re) of 2200 and a MF strength of 400 G.

Effect of variable thermal conductivity of ternary hybrid nanofluids over a stretching sheet with convective boundary conditions and magnetic field

In this study, a partial velocity slip of the boundary layer flow and an analysis of the MHD two-dimensional ternary hybrid nanofluid with fluid based on polymers with variable thermal conductivity are conducted. On a stretching sheet with a convective boundary condition, the investigation was conducted. Model equations with boundary conditions were transformed into a set of ODEs in order to study the flow. The resulting system of equations was solved by using the Runge-Kutta fourth-order method in conjunction with the shooting method. A numerical analysis was done to determine the impact of several key factors on the system's heat transfer characteristics and flow field velocity. Computed the flow field's velocity and heat transfer properties by varying these physical parameters, then graphically displayed the results. Additionally, tables covered the local shear stress and rate of heat transfer respectively, describe the flow's resistance to motion and the rate of local heat transfer of ternary hybrid nanofluid. For a thorough comparison, the results were compiled in tables. Additionally, the results were compared to data already available for regular fluids, and it was discovered that there was a very high degree of agreement between the two sets of results. This raises confidence in the precision of their numerical computations. New findingsThe explicit formulas that have been derived make it simple to understand how changes in temperature-dependent thermal conductivity and nanoparticle volume fraction affect significant parameters, such as sk.fsdain friction and heat transfer rate, in the study of ternary hybrid nanofluids.

Magneto-Bio-Convection Enhanced heat transfer in Prandtl hybrid nanofluid with inclined magnetization and microorganism migration

Keeping in view the applications of the hybrid nanofluids in the engineering and industries such as heating and cooling, food processing and heat generation, the focus of this investigation is to explore the effect of mixture base hybrid nanofluid with bio convection effect over linearly convectively heated stretched surface due to the motile micro organisms. The high thermal conductivity of the hybrid nanofluid play significant role in heat transmission. The effect of inclined magnetization on heat transfer of the hybridized bioconvective flow is also examined in this study. Prandtl hybrid nanofluid is used along with silver and magnetite nano-particles. The flow governing equations have been converted into dimensionless form through a suitable similarity transfer. The flow governing model equations are highly non linear and can’t be tackled analytically. Therefore, the formulated problem has been addressed using the BVP-4C technique. It was observed that when inclination angle of the magnetization is kept at 60 degrees and magnetic force is in the range of 0.5<M≤4, the velocity profile increase. Raising the level of bioconvection impact decline microorganism migration, on contrary high levels of Peclet number reverse this effect. Significant improvement has been observed in heat transfer shift and shear stress by raising thermal Biot number. The outcomes of the present study have been validated with already published results, the outcomes of our results were found in good agreement with previously published results.

Magneto-double-diffusive natural convection and irreversibility analysis of a nanofluid flowing in an annular concentric space

In the present article, magneto-double-diffusive density driven convection accompanied by an entropy optimization analysis of Al2O3-water nanofluid filled in a horizontal coaxial annular space is numerically addressed. The double-diffusive natural nanofluid flow which is produced due to the maintaining of constant and different temperature and solute on the inner and outer cylinders is affected by a uniform vertical magnetic field. Dimensionless governed equations which are developed through law of conservation of mass, momentum, and energy are numerically solved via finite volume approach, and parametric control analysis is developed. By using Corcione empirical correlations considering the Brownian diffusion of 4% of Al2O3 nanoparticles in water, the thermal conductivity and viscosity of the mixture nanofluid are determined. Results are performed and interpreted in detail for wide range of relevant variables: Rayleigh (102 ≤ Ra ≤ 105), Hartmann (0 ≤ Ha ≤ 30), Lewis numbers (0 ≤ Le ≤ 10), and Buoyancy ratio (−4 ≤ N ≤ 4) to evaluate the double-diffusive convective nanofluid flow, heat and solute transfer rates as well as entropies produced in the system.

Water-based nanofluid flow and heat transfer in thin film over an unsteady stretching sheet: An entropy analysis

The transfer of thermal energy is intrinsically associated with the generation of entropy. Here, we investigate the entropy generation number in nanofluid thin film flow over a radiated stretching sheet subject to different shapes of titanium oxide and copper nanoparticles in base fluid water. In addition, the impact of the magnetic field, viscous dissipation, and Joule heating were also considered. Using a suitable similarity transformation, the momentum and energy equations that describe the flow are converted into ordinary differential equations. These equations are then solved numerically using bvp4c in MATLAB. Graphs and explanations show how different physical parameters affect the velocity profile, temperature distribution, Nusselt number, skin friction coefficient, entropy generation number, and Bejan number. As the Brinkman number went up, fluid friction and Joule loss caused more entropy generation, but the Bejan number showed the opposite trend. In a certain situation, it is also important to note that as the value of the radiation parameter goes up, the irreversibility of heat transfer becomes more important. In addition, spherically shaped nanoparticles have the lowest entropy among all other forms. Hence, nanoparticles have the ability to reduce the amount of energy lost in any physical process and increase the overall productivity of systems. Understanding the flow and heat transmission within a thin film has many practical applications in industry, including aerodynamic lamination of plastic sheets, wire and fiber coating, food processing, annealing and thinning of copper wires, reactor fluidization, and many more.

Recent Development of Heat Sink and Related Design Methods

Heat sinks are vital components that dissipate thermal energy from high temperature systems, such as aero-space vehicles, electronic chips, and turbine engines. In the last few decades, considerable research efforts have been devoted to heat sinks to enhance heat dissipation, minimize temperature in the hot spot region, and reduce the temperature of hot section components. At present, the improvement of the thermal performance of heat sinks encounters many bottlenecks and demands the implementation of new designs, new materials, and flexible manufacturing. This study summarized the recent development of heat sinks over five years with a major review of heat transfer aspects, i.e., conduction, convection, radiation, phase change, and nanofluids technology, as well as perspectives in the aspect of structural design. The purpose of this work is to provide an overview of the existing studies that elevate the thermal performance of heat sinks and propose prospectives and suggestions for future studies.

Investigation of thermo-rheological properties of Fe3O4/Ethylene glycol nanofluid in a square cavity

Many fluids used in heat transfer and transport phenomena restrict the effectiveness of heat exchange equipment on account of their low thermal conductivity. Using nanofluids, the ef-fectiveness of heat exchange equipment is enhanced by many folds. The use of magnetic nano-fluids for heat transfer generates a prospect of regulating flow and controlling the thermal and transport properties particularly the thermal conductivity and viscosity using an externally applied magnetic field. The present study involves synthesis of oleic acid-coated magnetic nanofluids at varying concentrations of 0 to 0.643% by volume, measurement of thermal conductivity, rheological properties and corresponding numerical simulation of Nanofluid in a heated square cavity. The thermal conductivity measurement have been carried out by transient hot-wire method using KD2-pro at varying concentrations of solid phase. The re-sults show a significant increase in thermal conductivity with increase in particle concentra-tion. Rheological measurements show variation in viscosity with shear rate, temperature and concentration. Moreover, it has been found that at low particle loading magnetic nanofluids exhibited Newtonian behavior unlike non-Newtonian behavior at increased concentration. Numerical simulation of the magnetic nanofluid in the heated square cavity demonstrates the immense potential of augmentation of heat transfer coefficient using such fluids.

Analysis of Nonlinear Flow and Heat Transfer Issues in Nanofluid by Using RK-4th Order Method

Nanofluids, composed of a base fluid with dispersed nanoparticles, have gained significant attention due to their unique thermal and flow characteristics. Understanding the nonlinear flow and heat transfer phenomena in nanofluids is crucial for optimizing their performance in engineering applications. In this study, we propose using the Runge-Kutta 4th order (RK-4) numerical method to analyze these issues. The RK-4 method is known for its accuracy and efficiency in solving ordinary differential equations. By applying this method to the governing equations of fluid flow and heat transfer, we can accurately capture the nonlinear behavior of nanofluids. We investigate various nonlinear phenomena, such as boundary layer separation, flow instability, and heat transfer enhancement, considering factors like nanoparticle concentration, size, shape, fluid properties, Reynolds number, and temperature gradient. The RK-4 method provides accurate solutions, revealing critical parameters that affect flow and heat transfer behavior. Comparisons with experimental data and other numerical methods validate the approach, demonstrating its reliability. Parametric studies are conducted to optimize nanofluid characteristics for improved heat transfer and fluid flow. This research enhances our understanding of nonlinear flow and heat transfer in nanofluids and enables efficient numerical analysis, opening new avenues for improving nanofluid-based systems.

Study of nanofluid flow and heat transfer in a stationary cone-disk system

Rheometric, viscosimetric, bio-medical, and several other pharmaceutical machineries utilize the structural advantages provided by the geometry of a stationary conical diffuser. The problem of the Buongiorno nanofluid flow in the conical gap of a stationary cone-disk system for isothermal boundaries is studied. The governing system, comprising the incompressibility condition, Navier–Stokes equation, energy conservation equation, and conservation of Nanoparticle Volume Fraction (NVF) equation, is analyzed. The Lie-group theory has been used to derive a self-similar model. Solutions of the self-similar equations were computed numerically, and the expressions for the Nusselt number and Sherwood number are obtained. The parametric investigation reveals that the heat and mass transfer rate subside significantly when pre-swirl is introduced to the flow. Furthermore, the nanofluid slip mechanisms enhance the effective temperature of the system.

The Mixed of Hybrid Nanofluid GO-MoS2/Engine Oil Over a Shrinking Sheet with Mass Flux Effect: Reiner-Philippoff Model

The mixed convection flow and heat transfer of the hybrid nanofluid over a shrinking sheet are investigated. Molybdenum disulphide (MoS2) and graphene oxide (GO) are employed as two hybrid nanoparticles while engine oil (EO) as the base fluid is considered. In this study, the Reiner-Philippoff model as one of non-Newtonian types is deliberated since it has the ability to function on three distinct types of fluids: viscous, shear thickening and shear thinning. The Reiner-Philippoff relation, the momentum and energy equations under Tiwari and Das model are all employed in the study. Influences from mass flux are also considered in the flow. Before computation using the bvp4c function in MATLAB, the respected equations are first converted into ordinary differential equation form using the similarity transformation. When the established and current models are discovered to be identical in a specific case, a direct comparative investigation is conducted to confirm the correctness of the current model. In addition, the present results are shown graphically and in tabular form. It is hypothesized that the presence of a hybrid nanofluid significantly affects the fluid characteristic and gives more satisfactory results than a single nanofluid. The skin friction coefficient and heat transfer rate of hybrid nanofluids are greater than the nanofluids. In terms of velocity and temperature profile, the reduction in velocity and the enhancement in temperature profile are caused by a rise in the Reiner-Philippoff parameter. The same outcome is also seen when the volume fraction of hybrid nanofluids increases.

Heat Transfer and Fluid Flow Behavior of a Carbon-Based Hybrid Nanofluid in a Microchannel Heat Sink

In this article, detailed work on the heat transfer and fluid flow behavior of carbon-based hybrid nanofluid (multi-walled carbon nanotubes + graphene nanoplatelets/H2O) was studied numerically. The carbon-based hybrid nanofluids have been prepared experimentally and their measured properties were used for this study. The numerical study was carried out by passing the nanofluids under laminar flow through the tube side of the microchannel heat sink (MCHS). A constant heat flux on the heat sink base was applied and a single-phase model approach was used for analyzing the heat transfer. The nanofluid volume concentration varied from 0.01% to 0.2%. The improvement in the heat transfer coefficient is observed to be a maximum of 73%, with a maximum of 18% pressure drop variation across the MCHS for 0.2 vol%. The pressure drop variation across the MCHS is minimal for all the considered volume fractions of the nanomaterials. The results confirmed that the hybrid nanofluid possesses a remarkable heat transfer characteristic for transporting heat effectively.

Microfluidic controllable synthesis and size-dependent flow boiling heat transfer of silica nanofluids

Microchannel flow boiling heat transfer with nanofluids is an effective approach to enhance the heat transfer performance of high-power electronics. However, conventional nanofluids are plagued by laborious fabrication procedures, poor stability, and uncontrollable nanoparticle sizes, which compromise the overall heat transfer efficiency. To address these challenges, a facile microfluidic synthesis strategy is developed to prepare highly stable and size-controllable silica nanofluids in a continuous, efficient, and high-throughput methodology. The introduction of silica nanofluid aims to facilitate surface bubble formation and delay coalescence, ultimately enhancing the critical heat flux (CHF) and heat transfer coefficient (HTC) for efficiently cooling silica chips. Through the specifically designed spiral microchannel reactor, nanofluids with controllable nanoparticle sizes ranging from several tens of nanometers to a few hundreds of nanometers can be synthesized with long-term (>30 days) dispersion stability at both room temperature (25 °C) and high temperature (75 °C). Importantly, with negligible changes in pressure drop, the CHF and HTC of the synthesized nanofluids increase by maximum of 55 % and 63 % respectively compared to the basic fluid. Furthermore, our results suggest that smaller-sized nanoparticles outperform larger ones at higher flow rates. These findings not only provide important guidelines for the controllable preparation of nanofluids, but also shed new light on the rational design of efficient nanosystems for two-phase cooling.

Radiation and Nanoparticles Shape Effect on Aligned MHD Jeffrey Hybrid Nanofluids Flow and Heat Transfer over a Stretching Inclined Plate

The study through a stretching medium is a topic in the field of fluid dynamics and heat transfer. It involves investigating the behaviour of fluid flow and heat transfer phenomena in situations where a medium, such as a solid surface, is continuously stretched or deformed. Jeffrey fluid are found in the applications in various fields, including engineering, materials science, and biomedical engineering. Water was combined with copper (Cu) and aluminium oxide (Al2O3) is used in this study by considering the influence of nanoparticles shape which are spherical, brick, cylindrical, platelet and blade. The Keller Box method is used to solve numerically the Jeffrey hybrid nanofluid's governing nonlinear partial differential equations (PDEs) to nonlinear ordinary differential equations (ODEs) using similarity transformation. The results for both the velocity and temperature profiles of Jeffrey hybrid nanofluids (Deborah number, β) as well as the skin friction and Nusselt number are presented graphically and in tabulated form. The result shows that the momentum boundary layer thickness is decrease for any increment of the value alignment angle of the magnetic field parameter, the interaction of the magnetic field parameter, alignment angle of the incline plate, the mixed convection parameter, the radiation parameter, and the nanoparticles shape except the value of the volume fraction of the nanoparticles for the increasing value of Deborah number (β). The skin friction is increases as any increment value of an alignment angle of magnetic field, interaction of magnetic parameter, radiation parameter and volume fraction of nanoparticles increase, while the Nusselt number is decrease for the value of radiation parameter. It also observed that the factor of nanoparticles shape result is significant with the Jeffrey hybrid nanofluids which is the nanoparticles shape with the highest skin friction coefficient and Nusselt number is blades shape.

Local/volumetric entropy production analysis of natural convective flow using lattice Boltzmann method for heat exchanger application

PurposeThe purpose of this study is the hydrothermal analysis of the natural convection phenomenon within the heat exchanger containing nanofluids using the lattice Boltzmann method (LBM).Design/methodology/approachThe thermal conductivity as well as dynamic viscosity of the CuO–water nanofluid is estimated using the Koo-Kleinstreuer-Li model. The LBM has been used with unique modifications to make it flexible with the curved boundaries. The local as well as total entropy generation assessment, local Nusselt variation, as well as heatline visualization are used.FindingsThe solid volume percentage of the CuO–water nanofluid, a range of Rayleigh numbers (Ra) and thermal settings of internal operational fins and bodies are all factors that have been thoroughly researched to determine their effects on entropy production, heat transfer efficiency and nanofluid flow.Originality/valueThe originality of this work is using a novel numerical method (i.e. curved boundary LBM) as well as the local/volumetric second law analysis for the application of heat exchanger hydrothermal analysis.

A Revised Work on the Rayleigh-Bénard Instability of Nanofluid in a Porous Medium Layer

To reveal the mechanism of the enhanced heat transfer in nanofluids, Buongiorno (ASME J. Heat Transfer, vol. 128, 2006, pp. 240–250) developed a convective transport model by considering the slip mechanisms of nanoparticles migration. By now, many extended researches are based on his model. Among them, the study on porous medium flow pioneered by Nield &amp; Kuznetsov (Int. J. Heat &amp; Mass Transfer, vol. 52, 2009, pp.5796–5801) has received much attention. Their work employed the Darcy model and Buongiorno’s model to investigate the thermal instability in a horizontal porous medium layer saturated by a nanofluid. Through a sophisticated analysis, they obtained an approximate formula capable of predicting the stability threshold. However, a potential contradiction exists in their analysis owing to an improper assumption about the thermophoretic coefficient, which may lead to an unphysical result. To date, much of current works still adopted this improper assumption in various extended problems. To resolve this contradiction, the present study revises their work by considering the dependence of thermophoretic coefficient on the volume fraction of nanoparticles. A nonlinear basic-state solution of concentration is obtained and then used to implement the linear stability analysis. In comparison with Nield’s formula, the present result shows that the threshold of instability shifts to a lower concentration by more than one order of magnitude. The mechanism causing the shift is discussed and the novelty of the present study is stressed.

Nanofluid Heat Transfer and Flow Characteristics in a Convex Plate Heat Exchanger Based on Multi-Objective Optimization

Convex plate heat exchangers have drawn much interest across various industries thanks to their improved heat transfer efficiency and compact design. Research examines the characteristics of convex plate heat exchangers in this study through a combined experimental and numerical method. A mixture that contains water and copper nanoparticles is known as a copper-water nanofluid. A multi-objective optimization technique is used in this study to give an experimental and numerical evaluation of the nanofluid heat transfer and flow properties of a convex plate heat exchanger. Numerical execution is performed using the ANSYS software, and the materials for the convex plate are copper and water. This study aims to improve the nanofluid flow performance and the heat transfer efficiency of heat transfer of the heat exchanger by optimizing its design parameters. The heat exchanger’s temperature distributions and pressure drops are measured using an experimental setup, and numerical execution is used to forecast the heat transfer coefficients and pressure losses. The ideal design parameters that concurrently maximize heat transmission and minimize pressure drop are discovered using a multi-objective optimization technique. The findings of this study enable the creation of more effective and affordable heat exchanger layouts for various industrial applications by offering useful insights into the transfer of heat and flow behavior of the convex plate heat exchanger.

Study on heat transfer and pressure drop characteristics for nanofluids in microchannel heat exchangers

The microchannel heat exchanger (MCHE) is considered the next-generation heat exchanger owing to its high-performance thermal management systems and fabrication processes. The MCHE is used in many cooling applications, such as x ray medical devices, high-power microelectronics, and high-heat flux devices. Comprehensive exploration of different nanofluids, their concentrations, and impacts on pressure drop and heat transfer within the context of MCHEs was the main focus of the current study. The experiments were conducted at Reynolds numbers ranging from 100 to 500 for laminar flow. Additionally, nanoparticles (np) such as Al2O3, CuO, and carbon nanotubes (CNT) were added to de-ionized water at weight percentages of 0.01, 0.03, and 0.05. The results indicated that heat transfer significantly increased at a particle concentration 0.05 by wt. % for all nanofluids (nf). Furthermore, at a particle of 0.05 by wt. %, the heat transfer of the CNT-based nf increased by 37%, whereas those of the Al2O3- and CuO-based nf increased by 24.01% and 6.23%, respectively. The nanofluid pressure drop (PD) increases with an increase in the Reynolds number owing to the increase in the viscosity of the liquid compared to de-ionized water (base fluid) and requires more pumping power.

Effect of Magnetic Field and Impingement Jet on the Thermal Performance and Heat Transfer of Hybrid Nanofluids

In this paper, we focus on modeling the flow and heat transfer behavior of SiO2–CuO/water hybrid-nanofluid impingement jet used for CPU cooling, where this flow is subject to a magnetic field. For this purpose, a new geometry has been adopted that contributes to the processor’s cooling while controlling the dynamic field and making it stable. The assessments were performed using two-phase mixture model under laminar forced convection flow setting. The working liquid consists of SiO2 and CuO nanoparticles with a diameter of 20 nm dispersed in the base fluid. The flow field, heat transfer, thermal efficiency, loss pressure and entropy production were analyzed in terms of volumetric concentration, Hartmann number, and Reynolds number. The simulation approach was applied to compare previous research findings, and a considerable agreement was established. Results indicate that the use of outside magnetic forces aids in maintaining the working fluid’s stability. Boosting the Hartmann number to maximum values increases pressure drop and pumping power while lowering system efficiency by 5%, 5% and 19%, respectively. Compared to pure water, hybrid nanofluids yield to a considerable drop in mean CPU temperature up to 10 K. The hybrid nanofluid’s efficiency improves as the Reynolds number and nanoparticle volume fraction rise, where the improvement in the best conditions reaches up to 21% and 27%, respectively. Using the following nanoparticles: SiO2, CuO and SiO2–CuO improves the Nusselt number of the base fluid by 15%, 36% and 30%, respectively. While the pressure drop values increase by 5%, 17% and 11%. Regarding the entropy production, the results reveal that the total entropy values increase slowly with the volume fraction of the nanoparticles, and the maximum increase does not exceed 5% in the best case. On the other hand, the increase in the total entropy values reaches 50% when Ha = 20. Lastly, two correlations for the Nusselt number and the friction factor are suggested, with errors of no more than ±9% and ±7%, respectively.

Significance of Cattaneo-Christov double diffusion and induced magnetic field on Maxwell ternary nanofluid flow with magnetic response boundary

The present study delves into the significance of Cattaneo-Christov double diffusion and the induced magnetic field (IMF) on a stagnation-point flow of Maxwell ternary nanofluids. A new boundary condition with the magnetic response is designed to study superior heat and mass transfer of Maxwell ternary nanofluid combined with double diffusion and IMF. The governing equations are formulated by mathematically modeling of the current flow in a Cartesian coordinate system and solved using an improved shooting method and the Runge-Kutta method. Through the application of similarity transformations, the governing equations are transformed into a system of initial boundary value ordinary differential equations. These equations are further transformed into linear equations with initial value problems using the shooting method and subsequently solved using the Runge-Kutta method and Newton's iterative techniques. The numerical results and correlation analysis vividly demonstrate the profound influence of double diffusion and IMF on thermal and concentration patterns via graphical representations. It is found that the double diffusion and the induced magnetic field always helps to achieve lower temperature and concentration. The magnetic response boundary leads to higher heat and mass transfer efficiency for the suction case. The magnetically responsive boundary is verified to be effective for regulating the heat and mass transfer of ternary nanofluid.

Effects of Brownian Motions and Fractal Structure of Nanoparticles on Natural Convection

The study simulated heat transfer in alumina-water nanofluid in a natural convection flow and Rayleigh-Benard configuration considering the Brownian motions and fractal structure of the nanofluids. The simulations were based on a two-dimensional, Eulerian-Eulerian method. Many simulations have been performed to examine the effect of aspect ratio, heat flux, and para-meters related to the structure of the nanoclusters including size, fractal dimension, and volume fraction on the natural convective heat transfer coefficient. The comparison between the simulation results and the experimental data of heat transfer coefficient indicates a good agreement. The simulation results indicated that the enhancement of aspect ratio, heat flux, and fractal dimension increases the heat transfer coefficient. On the other hand, the reduction of nanoclusters and nanoparticle size decreased this coefficient. Moreover, the simulation results showed that in high heat transfer fluxes, the heat transfer coefficient first increases by increasing the nanoparticles solid volume fraction and then decreases. However, heat transfer coefficient decreased steadily with the increase in the nanoparticles solid volume fraction in low heat transfer fluxes. The results suggested that using the nanoparticles Brownian motion mechanism along with their fractal structure can be well-applied in natural-convection heat transfer modelling of nanofluids.