Nanofluids: Key Parameters to Enhance Thermal Conductivity and Its Applications

This review article summarizes the progress of research on carbon nanomaterial-based lubricants witnessed in recent years. Carbon nanomaterials, such as graphene, carbon nanotubes (CNTs), fullerenes and carbon nanostructures, are at the center of current tribological research on attaining superior lubrication performance. The development of nanomaterial-based solid lubricants, lubricant additives and bulk materials and the related issues in their processing, characterization and applications as well as their tribological performance (coefficient of friction and wear rate) are listed in a structured tabulated form. Firstly, regarding nanomaterial-based solid lubricants, this study reveals that carbon nanomaterials such as graphite, graphene, graphene-based coatings and diamond-like carbon (DLC)-based coatings increase different tribological properties of solid lubricants. Secondly, this study summarizes the influence of graphene, carbon nanotubes, fullerene, carbon nanodiamonds, carbon nano-onions, carbon nanohorns and carbon spheres when they are used as an additive in lubricants. Thirdly, a structured tabulated overview is presented for the use of carbon nanomaterial-reinforced bulk material as lubricants, where graphene, carbon nanotubes and carbon nanodiamonds are used as reinforcement. Additionally, the lubricity mechanism and superlubricity of carbon nanomaterial-based lubricants is also discussed. The impact of carbon nanotubes and graphene on superlubricity is reviewed in detail. It is reported in the literature that graphene is the most prominent and widely used carbon nanomaterial in terms of all four regimes (solid lubricants, lubricating additives, bulk material reinforcement and superlubricity) for superior tribological properties. Furthermore, prospective challenges associated with lubricants based on carbon nanomaterials are identified along with future research directions.

/pdf/carbon-nanomaterial-based-lubricants-review-of-recent-2ofehmwh.pdf

Carbon Nanomaterial-Based Lubricants: Review of Recent Developments

Utilizing phase change materials (PCMs), which can be tailored to melt or solidify at specific temperatures, as an energy storage medium provides an effective way to store latent thermal heat for diverse applications. However, conventional PCMs exhibit significant disadvantages, such as low thermal conductivity and leakage. Therefore, highly-thermally-conductive composite phase change materials (CPCMs) have received increasing research interest by virtue of integrating nanofillers with high thermal conductivity and thermal stability, such as hexagonal boron nitride (hBN), into the organic PCM matrices. While several nanomaterials-reinforced composites, such as graphene-based CPCMs, have been reviewed extensively, however, there are no critical reviews on the thermal performance of BN-enhanced organic CPCMs in energy storage applications. Therefore, this literature review highlights and comprehensively summarizes the latest research on the thermal improvements of BN-filled organic CPCMs with a focus on different types of BN allotropes, including hBN, BN nanoplatelets, BN nanosheets and BN nanotubes. Moreover, this review provides an extensive discussion on the fabrication processes, effects of functionalization and porous scaffolds, as well as the applications of BN fillers as shell materials. Specifically, the novel theoretical and experimental methodologies for achieving high thermal conductivities are reviewed and compared. Additionally, some other fundamental parameters associated with thermal properties, such as latent heat of fusion, thermal cycle stability, and thermal-to-solar efficiencies are also discussed. Finally, current challenges in the field of BN-incorporated CPCMs are listed/discussed, and recommendations for the future development of BN-enhanced organic CPCMs with better thermal properties to cater the future needs in energy storage are provided. 

Effects of boron-nitride-based nanomaterials on the thermal properties of composite organic phase change materials: A state-of-the-art review

Carbon nanotubes and nanofibers (CNFs) are well-known nano additives to produce coating materials with high electrical and thermal conductivity and corrosion resistance. In this paper, coating materials incorporating hydrogen bonding offered significantly lower electrical resistance. The hydrogen bonding formed between functionalized carbon nanotubes and ethanol helped create a well-dispersed carbon nanotube network as the electron pathways. Electrical resistivity as low as 6.8 Ω cm has been achieved by adding 4.5 wt% functionalized multiwalled carbon nanotubes (MWNT-OH) to 75%polyurethane/25%ethanol. Moreover, the thermal conductivity of polyurethane was improved by 332% with 10 wt% addition of CNF. Electrochemical methods were used to evaluate the anti-corrosion properties of the fabricated coating materials. 75%polyurethane/25%ethanol with the addition of 3.0 wt% of MWNT-OH showed an excellent corrosion rate of 5.105 × 10-3mm year-1, with a protection efficiency of 99.5% against corrosive environments. The adhesion properties of the coating materials were measured following ASTM standard test methods. 75%polyurethane/25%ethanol with 3.0 wt% of MWNT-OH belonged to class 5 (ASTM D3359), indicating the outstanding adhesion of the coating to the substrate. These nanocoatings with enhanced electrical, thermal, and anti-corrosion properties consist of a choice of traditional coating materials, such as polyurethane, yielding coating durability with the ability to tailor the electrical and thermal properties to fit the desired application. 

Enhanced electrical conductivity of anticorrosive coatings by functionalized carbon nanotubes: effect of hydrogen bonding

Phase change materials can store or release large amounts of energy during phase change. An increasing number of authors are studying the influence of the dispersion of nanometric particles on these materials. This article presents the design and experimental characterization of temporal stability, thermal conductivity, isobaric heat capacity, phase change transitions, rheological behaviour, and dielectric properties of nano-enhanced phase change materials based on carbon black (CB) dispersions in polyethylene glycol (PEG200) by using polyvinylpyrrolidone (PVP) as surfactant. We studied the temporal stability of carbon black nanoparticles dispersed in PEG200 using dynamic light scattering and spectrophotometry techniques. All the samples showed good temporal stability, since the temporal measurement of the hydrodynamic size of the nanoparticles are practically constant and the wavelength observed by UV-vis shows a small variation of around 4% for static conditions. We observed small changes in thermal conductivity and isobaric heat capacity. Nevertheless, the thermograms evidence how the latent heat clearly increases with the load of carbon black nanoparticles up to four times that of the PEG200. The viscosity studies do not show variation with shear rate, indicating a Newtonian behaviour excluding 2.0 wt% CB/PVP+PEG200 nanofluid. Additionally, we noticed frequency dependent and independent regions for permittivity. 

Thermophysical, rheological and dielectric behaviour of stable carbon black dispersions in PEG200

An investigation was conducted to examine the extent to which the thermal conductivity of materials in polyethylene glycol (PEG) fluids could be improved using the concept of hydrogen bonding and long chains. Boron nitride (BN), hydroxyl functionalized multiwall nanotube (MWNT-OH), and carbon nanofibers (CNFs) were mixed and exfoliated to form hydrogen bonds between the particles and the PEG fluids. Following this bonding process, clear enhancements in the thermal conductivity were observed. In addition, the long chain boron nitride nanotubes (BNNTs) and carbon nanofibers were shown to significantly enhance the thermal conductivity, due to the resulting increase in the contact and interfacial surface areas. The results of this experimental investigation indicated that PEG400 with a loading of 7.5 wt% MWNT-OH yielded a thermal conductivity increase as high as 89.7% over the base fluid. PEG400 loaded with a combination of 2 wt% CNF and 2 wt% BNNT resulted in a thermal conductivity increase of 73.1%. These results are significantly higher than the best results previously reported in the literature and may in part be attributed to the use of a three roll milling technique to enhance contact. The results presented here will open the way for further exploration of the use of novel phase change materials for thermal energy storage applications.

Improved thermal conductivity of PEG-based fluids using hydrogen bonding and long chain of nanoparticle

Electronics depend on their ability to shed operational heat to maintain operating temperature. Inferior grease can create preventable problems in electronics. This is typically achieved through a thermal grease or paste. If this grease fails to dissipate heat or maintain thermal contact, then the equipment will have faults. Greases with less-than-optimal performance create excessive wear, heat, and reduced life expectancy. This can cause equipment failures and malfunctions at the most inopportune moments. Thermal greases are applied to Central Processors (CPU) and Graphics Processors (GPU) in avionics LRUs, computers, Solar panels, HVAC systems, and other electronics. A high-performance novel nano grease will shed excess heat and increase device life expectancy. The fabricated nano greases show improvements of up to 80% in thermal conductivity measurements. CPU testing resulted in a 100% decrease in the standard deviation of temperature variation from commercial greases.

https://www.mdpi.com/2075-4442/10/8/172/pdf?version=1658928250

CPU Performance Improvement Using Novel Thermally Conductive Carbon Nano Grease

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Improved thermal conductivity of PEG-based fluids using hydrogen bonding and long chain of nanoparticle

CPU Performance Improvement Using Novel Thermally Conductive Carbon Nano Grease