Graphene Nanofluids Research Articles

Surfactant assisted dispersion of graphene: A review

Graphene is having high thermal conductivity which makes it a suitable candidate for heat transfer applications. The main challenge for the utilization of graphene-based nanofluids is an agglomeration of graphene nanosheets. To overcome the agglomeration of graphene, surfactants are used in an aqueous solution. The various surfactants used for the stable dispersion of graphene are reviewed. In addition, the thermophysical and rheological properties of graphene nanofluids are highlighted the physical and chemical techniques are reviewed to stabilize the graphene with the aid of surfactants. The application of an aqueous solution of graphene for heat transfer is highlighted in this review.

Study on Heat Transfer Characteristics of Graphene Nanofluids in Mini-Channels of Thermal Integrated Building.

Two kinds of rectangular mini-channels of different sizes were designed and fabricated for testing the convective heat transfer characteristics of graphene nanofluids. The experimental results show that the average wall temperature decreases with the increases in graphene concentration and Re number at the same heating power. Within the experimental Re number range, the average wall temperature of 0.03% graphene nanofluids in the same rectangular channel decreases by 16% compared with that of water. At the same heating power, the convective heat transfer coefficient increases with the increase in the Re number. The average heat transfer coefficient of water can be increased by 46.7% when the mass concentration of graphene nanofluids is 0.03% and the rib-to-rib ratio is 1:2. In order to better predict the convection heat transfer characteristics of graphene nanofluids in small rectangular channels of different sizes, the convection heat transfer equations applicable to graphene nanofluids of different concentrations in small rectangular channels with different channel rib ratios were fitted, based on factors such as flow Re number, graphene concentration, channel rib ratio, Pr number, and Pe number; the average relative error (MRE) was 8.2%. The mean relative error (MRE) was 8.2%. The equations can thus describe the heat transfer characteristics of graphene nanofluids in rectangular channels with different groove-to-rib ratios.

Experimental investigation on the static and dynamic stability of water-based graphene nanofluids prepared by one-step liquid phase shear exfoliation of graphite

Graphene nanofluids show prospects in various applications due to their outstanding optical, thermal, and mechanical properties. However, achieving the long-duration stability of graphene nanofluids prepared by the traditional two-step method is still challenging. Herein, one-step liquid phase shear exfoliation was applied to fabricate stable graphene nanofluids in water from graphite with cetyl trimethyl ammonium bromide (CTAB) as the surfactant. Results indicated that high-quality graphene with multi-layer was fabricated. The graphene production rate depends on CTAB concentration up to 0.25 mg/ml, but beyond that, the graphene concentration almost remains constant (∼18 ppm). Extending the exfoliation time could improve the production rate of graphene nanosheets without sacrificing their quality. The zeta potential of nanofluids prepared at CTAB concentrations of 1 mg/ml and 4 mg/ml is 45–60 mV, demonstrating that the nanofluids exhibit high static stability. Besides, the nanofluids' relative concentration (RC) values are over 0.95 at 20 °C and 40 °C in the flow rate range of 0–1.5 l/min. The nanofluids subjected to static heating at 60 °C are stable; however, their dynamic stability deteriorates gradually with the increasing flow rate because the physically absorbed cationic surfactant more easily falls off from graphene nanosheets, and collision frequency among graphene nanosheets intensifies at high temperatures under the flow condition. Furthermore, high-low temperature cycling could effectively relieve the deterioration of the nanofluids' stability, suggesting that once the electrostatic stabilization effect could be guaranteed by timely cooling, the graphene nanofluids would keep stable.

Mathematical model for graphene nanofluid flow over a stretching surface with velocity slips thermal convective and mass flux conditions

Nowadays graphene is emerging as one of the most exciting nanomaterial due to its continuous 29 electrically conducting behavior even at zero carrier concentration. With this initiation, we investigate the flow of magnetohydrodynamic (MHD) water, water−30%EG, water−50%EG, graphene nanofluid over a stretched surface with thermal convection, and zero mass flux conditions and velocity slips comprising motile microorganisms and nanoparticles. Thermal radiation and Arrhenius activation energy are also be under consideration. The governing fluid equations are solved by Homotopy analysis method (HAM) and computed numerically with shooting technique after employing appropriate transformations. The consequence of numerous physical parameters on velocity, concentration, temperature, and density of motile microorganisms graphs as well as table are used for ethylene glycol based and water-based graphene nanoparticles. Additionally, numerically analyze the designed skin friction, Nusselt number, Sherwood number, and density of motile microorganisms. It is observed that due to heat generation and temperature the improvement of the nonlinear convection variable improves the wall friction. It is also originate that increasing the volume fraction of nanoparticles effectively boosting the thermal conductivity of water−50%EG when compared with water−30%EG and water nanofluids. Ethylene glycol based graphene nanofluids take less time for process as compared to water based nanofluids.

Evaluation of Thermophysical Properties and Thermal Performance of Amine-Functionalized Graphene Oxide/Deep Eutectic Solvent Nanofluids as Heat-Transfer Media for Desalination Systems

The study mainly focuses on the synthesis and characterization of amine-functionalized graphene oxide (GO-NH2) nanoparticles. It also reports the thermal properties and stability analysis of deep eutectic solvent (DES)- and GO-NH2- based nanofluids. DES is composed of diphenyl ether as the hydrogen bond acceptor and DL-menthol as the hydrogen bond donor in the molar ratio 1:1. The nanofluid was prepared by a two-step method where two different concentrations of functionalized graphene nanofluids, namely, 0.0033 volume fraction (NF1) and 0.0101 volume fraction (NF2), were reported. XRD and FTIR analyses were used to validate the nanoparticle’s identity. Additionally, the morphology and composition of GO-NH2 nanoparticles were investigated using FESEM, FETEM, EDS, and Raman analyses. After that, the stability of the nanofluids was assessed using ζ potential measurements. The ζ potential measurements revealed increased stability, indicating that no agglomeration occurred in the DES-based nanofluid. Excellent thermal conductivity enhancement was observed at a higher temperature for the GO-NH2 nanofluid. The density and viscosity of the base fluid and nanofluid decreased with an increase in temperature from 25 to 85 °C. Further, the specific heat capacity of the nanofluids also increased with the increase in temperature and volume fractions of the nanofluid. Thermogravimetric analysis was also performed to evaluate the thermal degradation of the nanofluid under a nitrogen atmosphere. The nanofluid was used in brine recirculation multistage flash desalination where the gained output ratio of less than 10 was obtained through ASPEN simulation.

A Critical Review on the Thermal Transport Characteristics of Graphene-Based Nanofluids

Over the past few years, considerable research work has been performed on the graphene-based nano-dispersion for improvement of the thermal conductivity and thermal characteristics of base fluid. Graphene-based dispersion shows the good stability, better enhancement in thermal conductivity, and heat transport behavior compared to the other nano-dispersions drawing significant attention among researchers. This article carries out comprehensive reviews on the heat transport behavior of graphene-based nano-dispersion over the past ten years. Some researchers have carried out the investigations on the various methods adopted for the preparation of graphene-based nano-dispersion, techniques involved in making good dispersion including stability characterizations. There needs to be a better agreement in results reported by the various researchers, which paves the way for further potential research needs. Some researchers studied thermo-physical properties and heat transport behavior of graphene nanofluids. Only a few researchers have studied the usage of graphene nanofluids in various fields of application, including automobile radiators, electronics cooling, heat exchangers, etc. This article reviews the different challenges faced during its development in broad areas of application, and this could be a referral to have explicit knowledge of graphene dispersions with their characterization. Moreover, this study explores the various parameters that influence the effective thermal conductivity and heat transport behavior of the graphene dispersions for the various heat transport applications, which could be a reference guide to find the potential benefits as well as drawbacks of the graphene-based nano-dispersion for future research works.

Tribological mechanism of carbon group nanofluids on grinding interface under minimum quantity lubrication based on molecular dynamic simulation

Carbon group nanofluids can further improve the friction-reducing and anti-wear properties of minimum quantity lubrication (MQL). However, the formation mechanism of lubrication films generated by carbon group nanofluids on MQL grinding interfaces is not fully revealed due to lack of sufficient evidence. Here, molecular dynamic simulations for the abrasive grain/workpiece interface were conducted under nanofluid MQL, MQL, and dry grinding conditions. Three kinds of carbon group nanoparticles, i.e., nanodiamond (ND), carbon nanotube (CNT), and graphene nanosheet (GN), were taken as representative specimens. The [BMIM]BF4 ionic liquid was used as base fluid. The materials used as workpiece and abrasive grain were the single-crystal Ni-Fe-Cr series of Ni-based alloy and single-crystal cubic boron nitride (CBN), respectively. Tangential grinding force was used to evaluate the lubrication performance under the grinding conditions. The abrasive grain/workpiece contact states under the different grinding conditions were compared to reveal the formation mechanism of the lubrication film. Investigations showed the formation of a boundary lubrication film on the abrasive grain/workpiece interface under the MQL condition, with the ionic liquid molecules absorbing in the groove-like fractures on the grain wear’s flat face. The boundary lubrication film underwent a friction-reducing effect by reducing the abrasive grain/workpiece contact area. Under the nanofluid MQL condition, the carbon group nanoparticles further enhanced the tribological performance of the MQL technique that had benefited from their corresponding tribological behaviors on the abrasive grain/workpiece interface. The behaviors involved the rolling effect of ND, the rolling and sliding effects of CNT, and the interlayer shear effect of GN. Compared with the findings under the MQL condition, the tangential grinding forces could be further reduced by 8.5%, 12.0%, and 14.1% under the diamond, CNT, and graphene nanofluid MQL conditions, respectively.

Effect of Fullerene and Graphene Nanoparticles on the AC Dielectric Strength of Natural Ester

The current study addresses the impact of the addition of fullerene and graphene nanoparticles on the AC breakdown voltage (AC BdV) of natural ester (FR3). The nanofluids (NFs) were prepared following the two-step process, and the AC BdV was performed in compliance with IEC 60156 standards. Five different concentrations of NPs were considered (0.1 g/L, 0.2 g/L, 0.3 g/L, 0.4 g/L, and 0.5 g/L). A Student’s t-test was performed to compare the base liquid’s AC BdV data with different nanofluids. The experimental data were checked to see if they obeyed the Weibull distribution fitting curve, and the AC BdV at 1%, 10%, and 50% risk levels were then calculated. The performed t-test provides evidence that AC BdV data from the base liquid were different from those of different NFs (except 0.2 g/L fullerene, and 0.1 g/L and 0.4 g/L graphene NFs). It is also shown that the Weibull distribution fit the BdV data of all liquids (except 0.5 g/L fullerene NF), and remarkable improvements of AC BdVs at 1%, 10%, and 50% were observed. The best improvement was obtained with 0.4 g/L fullerene and 0.3 g/L graphene NFs. These results show the importance of using nanofluids as substitutes for the existing insulating liquids for current oil-filled power transformers.

A Review of Working Fluids and Flow State Effects on Thermal Performance of Micro-Channel Oscillating Heat Pipe for Aerospace Heat Dissipation

A MCOHP (micro-channel oscillating heat pipe) can provide lightweight and efficient temperature control capabilities for aerospace spacecraft with a high power and small size. The research about the heat flow effects on the thermal performance of MCOHPs is both necessary and essential for aerospace heat dissipation. In this paper, the heat flow effects on the thermal performance of MCOHPs are summarized and studied. The flow thermal performance enhancement changes of MCOHPs are given, which are caused by the heat flow work fluids of nano-fluids, gases, single liquids, mixed liquids, surfactants, and self-humidifying fluids. The use of graphene nano-fluids as the heat flow work medium can reduce the thermal resistance by 83.6%, which can enhance the maximum thermal conductivity by 105%. The influences of gravity and flow characteristics are also discussed. The heat flow pattern changes with the work stage, which affects the flow mode and the heat and mass transfer efficiency of OHP. The effective thermal conductivity varies from 4.8 kW/(m·K) to 70 kW/(m·K) when different gases are selected as the working fluid in OHP. The study of heat flow effects on the thermal performance of MCOHPs is conducive to exploring in-depth aerospace applications.

Rheological profile of graphene-based nanofluids in thermal oil with hybrid additives of carbon nanotubes and nanofibers

The evolution in nanofluid technology in the last few decades has proved the prodigious potential in several applications, especially thermal management and lubrication. An extensive investigation of nanofluid's rheological profile is vital to characterize the fluid flow behavior. This study signifies the rheological aspects of graphene and its hybrid nano-dispersions in thermal oil. The experimental investigation involves three sets of nanofluids containing graphene, graphene-carbon nanotubes, and graphene-carbon nanofiber hybrid nanofluid dispersions in thermal oil with varying loadings (0–2 mass%). The flow behaviors of all sets of nanofluids are measured at a wide shear range of 1–2000 s−1 and five different temperatures from 298 K to 338 K. The morphology and stability are validated by performing several characterizations for nanomaterials and nanofluids. Non-Newtonian fluid behavior is observed in all nanofluids. This study reveals a few interesting outcomes where the fluid behaving as a Power Law model is shifted to the Herschel-Bulkley model at high loadings of nanomaterials. A comparative analysis illustrates that both hybrid additives act as viscosity reducers for graphene-based nanofluids, where graphene-carbon nanofibers hybrid nanofluids exhibit noticeable reduction. A parametric analysis is performed on the viscous behavior involving the impact of shear rate, temperature, nanomaterial loading, and surfactant concentration. The increment in viscosity shoots up to 180 % for graphene-nanofluid at the 2000 s−1 shear rate and 338 K temperature, but still exhibits shear thinning phenomena. A correlation is also proposed for the nanofluid viscosity in terms of nanomaterial loading and temperature, indicating a good agreement at varying shear rates.

Recent advances in thermal conductivity and thermal applications of graphene and its derivatives nanofluids

• Seven factors should be considered in the study of graphene thermal conductivity. • Significant research gap exists in factors of graphene thermal conductivity. • Positive and negative effects both exist when graphene nanofluids are applied. • Economics and environment must be considered in application of graphene nanofluids. • More thermal studies on the graphene nanofluids are warranted. With the rapid development of industrial technology, more and more high-power-consumption devices are utilized, resulting in significant challenges to the durability, reliability, and efficiency of devices, facilities, and systems. Developing efficient thermal management systems for high power consumption application scenarios has evolved as a prominent research topic. Graphene nanomaterials are suitable candidates for nanofluids because of their excellent physical properties and high thermal conductivity. Although there are many studies on graphene nanofluids, there is no comprehensive review article about the influencing factors of thermal conductivity and the applications of graphene nanofluids, especially in economic and environmental analysis. This paper reviews the influencing factors of the graphene nanofluid thermal conductivity, including temperature, nanoparticle size and shape, base fluid, concentration, pH, surface modification, and ultrasonication. Moreover, the applications of graphene nanofluids in heat pipes, heat exchangers, solar collectors, and pool boiling devices are presented. Their applications are also discussed in terms of economics and the environment. In addition, the findings of thermal research on graphene nanofluids are summarized, and available opportunities and challenges are demonstrated. It is concluded that graphene nanomaterials significantly improve the thermal conductivity of the base fluid by 1.2% to 83.4%. Graphene nanofluids significantly improved the performance of thermal management devices. This comprehensive review is necessary to promote the research and effective application of graphene nanofluids in the context of sustainable development and carbon neutrality.

Experimental investigation on pH and stability of distilled water ethylene glycol mixture with graphene nanoplatelets

An efficient heat transfer medium improves the overall efficiency of the equipment, and the main difficulty is with making well-dispersed nanoparticles in base fluids. The current research is focused to study the effect of different surfactants on nanoparticle dispersion and enhancement through property modifications. The stability and pH value of various surfactants with varying sonication duration were studied and compared with the graphene nanofluids. The graphene nanofluids were prepared by a two-step method by dispersing 0.1 wt% graphene nanoparticles in distilled water and ethylene glycol with a ratio of 70:30. The surfactants namely Cetyltrimethylammonium bromide (CTAB), Polyvinylpyrrolidone (PVP K-30), and Polysorbate 60 (Tween 60) of each 0.1 wt% were used for stabilizing the nanofluids. The duration of the sonication process was set as 60, 90, and 120 min respectively followed by the magnetic stirring for 60 min duration. The stability behavior of nanofluids was studied through visual inspection, UV spectrum, and zeta potential techniques, and the corresponding pH values were measured to correlate with the performance of the heat transfer equipment. The results showed that the dispersion of graphene nanofluids strongly depends on the type and amount of dispersant in the absolute value of zeta potential. Finally, the optimum conditions were found based on the enhanced stability, pH, and sonication time of graphene nanoplatelets in distilled water-ethylene glycol mixture with Polyvinylpyrrolidone (PVP K-30) as a surfactant for the battery thermal management systems (BTMS) in electric vehicles.

NUMERICAL AND EXPERIMENTAL ANALYSES OF FLOW AND HEAT TRANSFER CHARACTERISTICS IN A CHEVRON-TYPE CORRUGATED PLATE HEAT EXCHANGER WITH GRAPHENE NANOFLUID

NUMERICAL AND EXPERIMENTAL ANALYSES OF FLOW AND HEAT TRANSFER CHARACTERISTICS IN A CHEVRON-TYPE CORRUGATED PLATE HEAT EXCHANGER WITH GRAPHENE NANOFLUID

MORPHOLOGICAL EVOLUTION OF Al2O3 AND CNT NANOFLUID DROPLETS DURING SOLIDIFICATION

Nanofluid is an emerging heat transfer fluid with good heat transfer and thermal conductivity properties. It is important to investigate the phase change properties and morphological evolution during the freezing of nanofluid droplets to understand their practical applications. The effect of dynamic wettability on the deformation of a single droplet of aluminum trioxide (Al<sub>2</sub>O<sub>3</sub>-H<sub>2</sub>O) and graphene (CNT-H<sub>2</sub>O) nanofluids at different mass concentrations and substrate temperatures was investigated by visualizing the droplet freezing. The formation of solid-like and freezing front motions inside the droplet during the freezing process of these droplets was investigated. The solidification process was strongly influenced by the temperature gradient perpendicular to the cold surface and the change in the solid–liquid interface wettability during the phase change, resulting in volume redistribution at the top of the droplet. The freezing shape of Al<sub>2</sub>O<sub>3</sub>-H<sub>2</sub>O nanodroplets resembled a "moon crater," and the influence of wettability decreased with increasing concentration, leading to a relative increase in the aperture of the top platform. The fully frozen state of the nanofluid droplet had an increasingly pointed tip, with a strong relationship between the substrate temperature and solidification time when the CNT-H<sub>2</sub>O concentration was 5 times higher and showed no change in the freezing droplet deformation rate under the experimental conditions. The contact angle of the two nanofluid droplets did not fluctuate significantly with increasing concentration, while that of the 1% nanofluid droplets remained at an average value of 85° during freezing. Under different freezing conditions, the freezing shape of Al<sub>2</sub>O<sub>3</sub>-H<sub>2</sub>O droplets tended to increase in diameter as the subcooling temperature decreased, with the final deformation rate of 1% Al<sub>2</sub>O<sub>3</sub>-H<sub>2</sub>O being twice that at 5% concentration, while the contact angle of the same mass concentration of Al<sub>2</sub>O<sub>3</sub>-H<sub>2</sub>O decreased by 1° as the subcooling temperature dropped. The CNT-H<sub>2</sub>O droplet became sharper at the tip as the subcooling temperature increased, and its contact angle did not change with temperature.

Investigation of thermal properties of graphene-silicone oil nanofluid

All electronic and mechanical devices are getting modified and modernized in compact sizes to increase performance. The thermal management of these systems is challenging because of the high heat rate from compact devices. Improper thermal management leads to short circuits in the electronics and poor performance in mechanical devices because the overheating and converting into waste pollutes the environment. This work attempts to prepare stable and homogeneous nanofluid with graphene nanoplatelets as the nanoparticles and silicone oil as the base fluid and evaluate the trend of thermal conductivity and viscosity of the prepared nanofluid for varying temperatures from 30 °C to 55 °C. Our attention is also on the ultrasonication time of prepared silicone oil graphene nanofluids. So, three ultrasonication times of 1 h, 2 h, and 3 h are chosen to check the effect of ultrasonication time on the nanofluid's thermodynamic properties (thermal conductivity and viscosity). In this work, nanofluids of particle concentrations 0.05 %, 0.1 %, and 0.15 % weight of 3 each for different ultrasonication times of 1 h, 2 h, and 3 h are prepared. The sodium lauryl sulphate was used as a surfactant for better stability of particles. The thermal conductivity test was conducted with thermal conductivity apparatus works on Debye's concept and calculated with a modified Bridgman equation. A rheometer was used for the viscosity measurement. This nanofluid is used as a coolant in transformers, automobile fan-clutch assemblies, and coolant in international space station radiators.

Investigation of cation-assisted, chemically and thermally enhanced nitrogen-doped graphene nanofluid application as an efficient micro-emulsifier from EOR perspective

Innovatively designed additives have been introduced in last decade to make EOR processes more efficient under challenging conditions. However, nitrogen-doped graphene (NDG) is not known as such a stable efficient method to be injected into reservoir under harsh thermodynamic condition. Some treatment has been applied to molecular structure of commonly used nitrogen-doped graphene aqueous solution for improvement of stability and quality of aqueous solution. These treatments involve both nano-structure and the aqueous carrier fluid properties. Nano-structure modification has been conducted in three successive steps: oxidation with acid vapor and modified Hummers method, citric acid polymerization and heat treatment that succeed in NDG functionalization with carboxyl and hydroxyl groups and structure enhancement in molecular scale. Existing free mono- and divalent cations in aqueous carrier phase improve the emulsification dominant mechanism from Pickering unstable emulsion toward more stable micro-emulsion mechanism which appeared to be superior to conventional emulsifiers used in EOR process because of improved solubility and more facile transport through porous media. Zeta potential of solution has increased from −30 to −12.2 mV highlighting more emulsion stability. The interfacial tension between aqueous fluid containing 500 ppm APH-NDG11acidized, functionalized, heated nitrogen doped graphene. and free mono- and divalent cations and crude oil would be 50 % less in comparison to distilled water/crude oil IFT. Furthermore, APH-NDG, regardless of carrier aqueous type, causes a great decrease in contact angle and as a result, makes the rock surface become more water-wet.

The MHD graphene nanofluid flow between two stretching discs

Consider a two-dimensional steady axisymmetric flow of an incompressible fluid with graphene nanoparticles between two infinite stretching discs with accelerated velocity and a magnetic field of strength B 0 is applied to the flow at the angle τ . The similarity transformation technique is adopted to find the analytical solution for the considered Navier–Stokes equation presented in a cylindrical coordinate form. The exact solution is analysed for the effect of stretching the Reynolds number and stretching velocity ratio. Pressure is high at the upper disc than at the lower disc when the stretching velocity ratio is less than unity. Then the effect of inclined MHD on the 2-D flow between stretching sheet discs yielding the solution in terms of an analytical method. The potential applications of these problems are used in the field of engineering and medical field, such as cancer tumour treatment and magnetic devices for cell separation.

Impact of Graphene Nanofluid on Ionic Polarization in Reservoir Sandstone under Electric Double Layer

The improved oil recovery (IOR) is a way of enhancing the reservoir properties with the use of nanomaterials to detach the oil molecule from the trapped zone. The polarization effect on reservoir sandstone under an electric double layer is one of the major research interests. The nanoparticles agglomeration such as graphene nanofluid due to poor dispersion in reservoir zone can be a major challenge that can lead to low reservoir permeability are well elucidated. This study investigated the influence of graphene nanofluid on the ionic polarization under an electric double layer in reservoir sandstone. Saturated Berea sandstone was used to investigate the interaction of ionic species on reservoir sandstone with the aid of Field-emission microscopy (FESEM), Energy dispersive X-ray mapping (EDX), Fourier Transform Infrared Spectroscopy (FTIR), Raman spectral analysis, and Core flooding experiment. This research gives information on the adsorption of ions within an electric double layer and its polarization mechanisms. It was revealed from the experimental result that ionic polarization occurs at 9.97 GHz with a 5.8nm wavelength shift which improves the mobility of the reservoir and in turn increases oil recovery factors. Graphene nanoparticles show a positive effect on both reservoir oil viscosity and stabilization characteristics of drilling fluids, wettability alteration, interfacial tension, and improving the emulsion Keywords: Nanomaterials, Sandstone, Electric double layer, Graphene

An experimental and numerical study of turbulent heat transfer enhancement for graphene nanofluids produced by pulsed discharge

• Time and cost-effective production of graphene nanofluids by pulsed discharge is tried and tested. • A new two-step method for producing graphene nanofluids has been developed. • Graphene nanofluids generated by pulsed discharge and ultrasound, like other graphene nanofluids, have high turbulent heat transfer performance (35% higher than water). • The numerical results show considerable increase in turbulent kinetic energy (8%) and velocity gradients near the wall due to physical interaction between continuous phase(water) and dispersed phase (graphene nano-particles). • The exchange of momentum and energy due to the movement of particles is considered as a cause-and-effect relationship between the aggregation of particles and the change in physical quantities in the continuous phase. Developing production methods for graphene nanofluids that can produce them in large quantities at once in a short time and at a low cost will contribute to the development of a wide range of industries that use nanofluids, and understanding their properties through mathematical modeling and experiments will lead to the development of new nanofluids. In this study, the new production method of graphene nanofluids is proposed and experimental and numerical investigations of the turbulent heat transfer performance of graphene nanofluids in a horizontal circular tube subjected to constant heat flux are conducted. The experimental investigation is conducted to evaluate the turbulent heat transfer performance of graphene nanofluids which are made by a new method using pulsed discharge and to compare them with numerical results. In the numerical investigation, the finite volume method with a Realizable k-ε model and Two-layer model is employed to solve the continuity, momentum, and energy conservation in two-dimensional domains. The Lagrangian two-phase model is applied to consider the physical interaction between the dispersed phase and continuous phase. In this model, the particles are tracked in a Lagrangian manner and coupled with the Eulerian flow description. Since the computational burden would be tremendous if individual nanoparticles were tracked in a Lagrangian manner, we defined a cluster of particles, called a parcel and treated it statistically. This concept of parcels allowed the average behavior of nanoparticles to be established as an analytical parameter. As a result, graphene nanofluids are not produced by pulsed discharge alone but are successfully produced by applying ultrasonic. Experimental investigations show a 33% increase in the Nu number of graphene nanofluid produced by pulsed discharge compared to water as the flow velocity increased. Numerical investigations confirm changes in the properties (Turbulent kinetic energy, Velocity distribution, Temperature distribution) of the continuous phase due to physical interactions between the dispersed and continuous phases. It is also shown that these changes contribute to the improved turbulent heat transfer performance of the nanofluid and that the aggregation of particles into the center of the tube is responsible for these changes.

CFD analysis of a flat tube with semi‐circular fins using graphene nanofluid and to compare performance with square type of fins

AbstractCFD analysis on a flat tube with semi‐circular fins under laminar flow conditions was performed with graphene‐based nanofluids considering the nanofluids as incompressible. Different simulations were performed at four different concentrations of nanofluids (0.01%, 0.1%, 0.2%, and 0.4%) and at different volume flow rates (4, 6, 8, and 10 LPM) and at four different forced convective heat transfer coefficients at different wind velocities at 300 K (50, 100, 150, and 200 W/m2 K). It was observed that with an increase in the concentration of nanoparticles in nanofluids, the thermal conductivity of base fluid water was increased (at 353 K the nanofluid of 0.4% volume concentration, the thermal conductivity of nanofluid increased by 200% with respect to base fluid). Graphene‐based nanofluids have higher effectiveness than most nanofluids hence it is considered for the analysis, at 0.4% concentration of nanofluid the effectiveness observed was 36.84% at 4 LPM, and for water, the effectiveness was 28.22% under similar conditions. The effect of flow rate on temperature drop was significant. At 4 LPM and at 0.4% of nanofluid, an outlet coolant temperature of 333 K was observed whereas the water outlet temperature at 10 LPM is 346.13 K. The effect of forced convective air heat transfer coefficient was significantly high. At h = 50 W/m2 K the outlet temperature of 0.4% nanofluid at 4 LPM was 345.25 K and at h = 200 W/m2 K, the outlet coolant temperature was 333.47 K. A single tube of the radiator was considered for the analysis whereas the original radiator consists of 50 tubes due to problems of Ansys in meshing.