Stability and thermophysical properties of water-based nanofluids containing triethanolamine-treated graphene nanoplatelets with different specific surface areas

Potent antibacterial activity of MXene-functionalized graphene nanocomposites

Two dimensional (2D) nanomaterials display properties with significant biological utility (e.g., antimicrobial activity). In this study, MXene-functionalized graphene (FG) nanocomposites with Ti3C2T x in varying ratios (FG : Ti3C2T x , 25 : 75%, 50 : 50%, and 75 : 25%) were prepared and characterized via scanning electron microscopy, scanning electron microscopy-energy dispersive X-ray (SEM-EDX), high-resolution transmission electron microscopy (HRTEM), and zeta potential analysis. Their cytotoxicity was assessed using immortalized human keratinocytes (HaCaT) cells at three different timepoints, and antibacterial activity was assessed using Gram-positive Methicillin resistant Staphylococcus aureus, MRSA, and Gram-negative neuro-pathogenic Escherichia coli K1 (E. coli K1) in vitro. The nanomaterials and composites displayed potent antibacterial effects against both types of bacteria and low cytotoxicity against HaCaT cells at 200 μg mL-1, which is promising for their utilization for biomedical applications.

Frictional Pressure Drop and Cost Savings for Graphene Nanoplatelets Nanofluids in Turbulent Flow Environments

Covalent-functionalized graphene nanoplatelets (CF-GNPs) inside a circular heated-pipe and the subsequent pressure decrease loss within a fully developed turbulent flow were discussed in this research. Four samples of nanofluids were prepared and investigated in the ranges of 0.025 wt.%, 0.05 wt.%, 0.075 wt.%, and 0.1 wt.%. Different tools such as field emission scanning electron microscopy (FE-SEM), ultraviolet-visible-spectrophotometer (UV-visible), energy-dispersive X-ray spectroscopy (EDX), zeta potential, and nanoparticle sizing were used for the data preparation. The thermophysical properties of the working fluids were experimentally determined using the testing conditions established via computational fluid dynamic (CFD) simulations that had been designed to solve governing equations involving distilled water (DW) and nanofluidic flows. The average error between the numerical solution and the Blasius formula was ~4.85%. Relative to the DW, the pressure dropped by 27.80% for 0.025 wt.%, 35.69% for 0.05 wt.%, 41.61% for 0.075 wt.%, and 47.04% for 0.1 wt.%. Meanwhile, the pumping power increased by 3.8% for 0.025 wt.%, 5.3% for 0.05 wt.%, 6.6% for 0.075%, and 7.8% for 0.1 wt.%. The research findings on the cost analysis demonstrated that the daily electric costs were USD 214, 350, 416, 482, and 558 for DW of 0.025 wt.%, 0.05 wt.%, 0.075 wt.%, and 0.1 wt.%, respectively.

A critical review on thermal conductivity enhancement of graphene-based nanofluids

Nanofluids which consist of nanoparticles added to conventional fluids (or base fluids) are considered as promising heat transfer fluids. Compared to metal, metal oxide nanoparticles and carbon nanotubes, graphene with its extremely high intrinsic thermal conductivity became the best candidate to design nanofluids. Such nanofluids have the potential to be highly-efficient heat transfer fluid by reducing loss of heat and increasing cooling rates. Over the last ten years, graphene-based nanofluids have shown significant thermal conductivity enhancements, however due to the numerous and interlinked parameters to consider, optimisation of their efficiency is still challenging. The present review article analyses and discusses the reported thermal conductivity in term of performance with respect to the amount of the used graphene to develop the prepared nanofluids. The enhancement of thermal conductivity must meet the minimal graphene amount due to its production cost and because graphene nanoparticles induces high viscosity in the nanofluid leading to higher energy consumption for the heat transfer systems. Unprecedented in the literature, this work proposes a simple approach to quantitatively compare the enhancement of the thermal conductivity of the nanofluids. The thermal conductivity performance parameter introduced could be applied to all nanofluid families and may become a reference tool in the nanofluid community. Such tool will help to determine the optimal preparation conditions without compromising the superior thermal performances.

Efficient Stabilization of Mono and Hybrid Nanofluids

Currently; the transfer of new technologies makes it necessary to also control heat transfer in different industrial processes—both in practical and research—applications. Not so long ago water and ethylene glycol were the most frequently used media in heat transfer. However, due to their relatively low thermal conductivity, they cannot provide the fast and effective heat transfer necessary in modern equipment. To improve the heat transfer rate different additives to the base liquid are sought, e.g., nanoadditives that create mono and hybrid nanofluids with very high thermal conductivity. The number of scientific studies and publications concerning hybrid nanofluids is growing, although they still represent a small percentage of all papers on nanofluids (in 2013 it was only 0.6%, and in 2017—ca. 3%). The most important point of this paper is to discuss different ways of stabilizing nanofluids, which seems to be one of the most challenging tasks in nanofluid treatment. Other future challenges concerning mono and hybrid nanofluids are also thoroughly discussed. Moreover, a quality assessment of nanofluid preparation is also presented. Thermal conductivity models are specified as well and new representative mono and hybrid nanofluids are proposed.

The Influence of Nickel Oxide Nanoparticle Dispersion on the Thermo Stability of Lubricant Oil

The homogeneous and substantial dispersion of nanoparticles into base fluids is vital since the final properties of any nanolubricant are estimated by their quality of stability. This paper addresses the effect of NiO nanoparticles dispersion into SN500 lubricant oil and its nonisothermal thermo stability. The dispersion of NiO nanoparticles is achieved by ultrasonication method. The thermo stability is estimated by Thermo Gravimetric Analysis (TGA), Differential Thermal Analysis (DTA) and Differential Scanning Calorimetry (DSC). The result shows that the thermo stability of base fluid enhances up to 0.3[Formula: see text]wt.% particle concentration then it decreases due to agglomeration of dispersed nanoparticles. The findings recommend that 0.1[Formula: see text]wt.% and 0.3[Formula: see text]wt.% of NiO-nanolubricant can be used for the temperature-dependent applications up to 200∘C.

The influence of covalent and non-covalent functionalization of GNP based nanofluids on its thermophysical, rheological and suspension stability properties

Covalent functionalization (CF-GNPs) and non-covalent functionalization (NCF-GNPs) approaches were applied to prepare graphene nanoplatelets (GNPs). The impact of using four surfactants (SDS, CTAB, Tween-80, and Triton X-100) was studied with four test times (15, 30, 60, and 90 min) and four weight concentrations. The stable thermal conductivity and viscosity were measured as a function of temperature. Fourier transform infrared spectroscopy (FTIR), thermo-gravimetric analysis (TGA), X-ray diffraction (XRD) and Raman spectroscopy verified the fundamental efficient and stable CF. Several techniques, such as dispersion of particle size, FESEM, FETEM, EDX, zeta potential, and UV-vis spectrophotometry, were employed to characterize both the dispersion stability and morphology of functionalized materials. At ultrasonic test time, the highest stability of nanofluids was achieved at 60 min. As a result, the thermal conductivity displayed by CF-GNPs was higher than NCF-GNPs and distilled water. In conclusion, the improvement in thermal conductivity and stability displayed by CF-GNPs was higher than those of NCF-GNPs, while the lowest viscosity was 8% higher than distilled water, and the best thermal conductivity improvement was recorded at 29.2%.

Effects of Temperature and Particles Concentration on the Dynamic Viscosity of Graphene-NiO/Coconut Oil Hybrid Nanofluid: Experimental Study

In practice, lubricants are used to minimize the friction and wear of frictional surfaces. The disposal of mineral-based lubricating oil possesses environmental issues and forced the development of bio-degradable lubricating agents. The simultaneous mono-dispersion of metallic and metal oxides nanomaterials into lubricating agents may concurrently reveal superior thermo-physical and rheological characteristics. This paper proposes an experimental and theoretical investigation on the dynamic viscosity enhancement of flat platelets textured Graphene/NiO-coconut oil hybrid nanofluids. The results reveal that the dynamic viscosity enhancement of hybrid nanofluids increases with nanomaterial concentration and decreases with temperature. The squat hybrid nanomaterial concentration has less collusion probability and dynamic contact between the mono-dispersed hybrid nanomaterials as it has enough interfacing gaps to conquer superficial surface energy. The high nanomaterial concentration revamps the formation of lamellar-composite agglomerated particles and enhances the dynamic viscosity of base fluid. Further, a theoretical correlation is recommended to estimate the dynamic viscosity of hybrid nanofluid with minimum margin of deviation using artificial neural network (ANN).

Variations of thermophysical properties and heat transfer performance of nanoparticle-enhanced ionic liquids

The ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate ([EMIm]Ac) was investigated as a promising absorbent for absorption refrigeration. To improve the thermal conductivity of pure [EMIm]Ac, IL-based nanofluids (ionanofluids, INFs) were prepared by adding graphene nanoplatelets (GNPs). The thermal stability of the IL and INFs was analysed. The variations of the thermal conductivity, viscosity and specific heat capacity resulting from the addition of the GNPs were then measured over a wide range of temperatures and mass fractions. The measured data were fitted with appropriate equations and compared with the corresponding classical models. The results revealed that the IL and INFs were thermally stable over the measurement range. The thermal conductivity greatly increased with increasing mass fraction, while only slightly changed with increasing temperature. A maximum enhancement in thermal conductivity of 43.2% was observed at a temperature of 373.15 K for the INF with a mass fraction of 5%. The numerical results revealed that the dispersion of the GNPs in the pure IL effectively improved the local heat transfer coefficient by up to 28.6%.

Surface modification of co-doped reduced graphene oxide through alkanolamine functionalization for enhanced electrochemical performance

The synergistic effect of heteroatom co-doping and triethanolamine functionalization on reduced graphene oxide resulted in impressive electrochemical features.

Heat transfer enhancement of water-based highly crumpled few-layer graphene nanofluids

Backward-facing step heat transfer of transitional and turbulent flows investigates in the presence of water-based HCFLG nanofluids.

Heat transfer performance of water-based tetrahydrofurfuryl polyethylene glycol-treated graphene nanoplatelet nanofluids

In order to improve the colloidal stability of graphene nanoplatelets (GNPs) in aqueous media, GNPs were first functionalized with tetrahydrofurfuryl polyethylene glycol in a quick electrophilic addition reaction method.