The stability, viscosity and thermal conductivity of carbon nanotubes nanofluids with high particle concentration: A surface modification approach

Highly homogeneous and stable single-walled carbon nanotubes dispersion modified by polyvinylpyrrolidone and alkanolamine in water

A novel noncovalent surface modification of commercial single-walled carbon nanotubes (SWCNTs) was successfully carried out by using ball grinding technology between SWCNTs and mixed dispersants (polyvinylpyrrolidone (PVP) and alkanolamine), affording a highly homogeneous and stable PA-SWCNTs dispersion in water. The homogeneous dispersibility and long storage stability were systematically investigated by transmittance spectroscopy, absorption spectroscopy, zeta potential analyzer, sedimentation photo and transmittance electron microscopy. Under the optimized conditions, the PA-SWCNTs dispersion modified with 0.7 wt% PVP and 0.25 wt% alkanolamine under the condition of total 6 h ball grinding time using paint shaker can be easily well-dispersed in water and has good storage stability, and no sedimentation is observed more than one month. From an industrial perspective, this method is green and easy to operate in industry.

Toward a better understanding of microalgal photosynthesis in medium polluted with microplastics: a study of the radiative properties of microplastic particles

Due to the wide presence of microplastics in water, the interaction between microplastic particles and microalgae cells in medium merits the attention of researchers. Microplastic particles can impact the original transmission of light radiation in water bodies since the refractive index of microplastics is different from that of water bodies. Accordingly, the accumulation of microplastics in water bodies will certainly impact microalgal photosynthesis. Therefore, experimental measurements and theoretical studies characterizing the radiative properties of the interaction between light and microplastic particles are highly significant. The extinction and absorption coefficient/cross-section of polyethylene terephthalate and polypropylene were experimentally measured using transmission and integrating methods in the spectral range of 200-1,100 nm. The absorption cross-section of PET shows remarkable absorption peaks in the vicinity of 326 nm, 700 nm, 711 nm, 767 nm, 823 nm, 913 nm, and 1,046 nm. The absorption cross-section of PP has distinctive absorption peaks near 334 nm, 703 nm, and 1,016 nm. The measured scattering albedo of the microplastic particles is above 0.7, indicating that both microplastics are scattering dominant media. Based on the results of this work, an in-depth understanding of the interaction between microalgal photosynthesis and microplastic particles in the medium will be obtained.

Optimizing the heat transfer characteristics of MWCNTs and TiO2 water-based nanofluids through a novel designed pilot-scale setup

This study aimed to investigate the effect of titanium dioxide (TiO₂) nano additives on the thermal performance of a pilot-scale cross-flow cooling tower. Moreover, it is a continuation of our previous study on the effect of using multi-walled carbon nanotubes (MWCNTs) nanofluid, and the results were compared with the results of TiO₂ and previous work. An experimental design by response surface methodology (RSM) based on central composite design (CCD) with two factors (concentration and flow rate) was used to study the effectiveness of the setup, Merkel number, and the cooling range. The nanofluids were prepared by the two-step method. The stability tests were performed considering different surfactants such as Gum Arabic, Triton X-100, and sodium dodecyl sulfate, and Gum Arabic was determined as the optimal surfactant. The visual method, dynamic light scattering (DLS), and Zeta potential analyses were used to ensure the stability of the nanofluids and determine the size distribution of the nanoparticles in the nanofluids. The findings revealed that the heat transfer characteristics of the working fluid were improved with the addition of nanoparticles. Moreover, by comparing the effect of nanoparticles, it was found that MWCNTs could enhance the thermal features better than TiO₂. The nanofluid containing 0.085 wt% of the MWCNTs improves the Merkel number, effectiveness, and cooling range by 28, 10.2, and 15.8%, respectively, whereas these values for TiO₂ containing nanofluids are 5, 4.1, and 7.4%, respectively. MWCNTs nanofluid with a concentration of 0.069 wt% and a flow rate of 2.092 kg/min was proposed for optimal system setup. Under these conditions, the cooling range, effectiveness, and Merkel number were about 23.5, 55.75%, and 0.64, respectively.

Thermal Conductivity Enhancement of Atomic Layer Deposition Surface-Modified Carbon Nanosphere and Carbon Nanopowder Nanofluids

In this paper, we present a study on thermal conductivity and viscosity of nanofluids containing novel atomic layer deposition surface-modified carbon nanosphere (ALD-CNS) and carbon nanopowder (ALD-CNP) core-shell nanocomposites. The nanocomposites were produced by atomic layer deposition of amorphous TiO2. The nanostructures were characterised by scanning (SEM) and transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, thermogravimetry/differential thermal analysis (TG/DTA) and X-ray powder diffraction (XRD). High-concentration, stable nanofluids were prepared with 1.5, 1.0 and 0.5 vol% nanoparticle content. The thermal conductivity and viscosity of the nanofluids were measured, and their stability was evaluated with Zeta potential measurements. The ALD-CNS enhanced the thermal conductivity of the 1:5 ethanol:water mixture by 4.6% with a 1.5 vol% concentration, and the viscosity increased by 37.5%. The ALD-CNS increased the thermal conductivity of ethylene-glycol by 10.8, whereas the viscosity increased by 15.9%. The use of a surfactant was unnecessary due to the ALD-deposited TiO2 layer.

Exploring the thermo-physical characteristic of novel multi-wall carbon nanotube-Therminol-55-based nanofluids for solar-thermal applications

This work aims to develop a novel nanofluid using Therminol-55 (T-55) as heat transfer fluid and multi-wall carbon nanotubes (MWCNTs) as dispersants with various volume concentrations of 0.05, 0.1, 0.3, and 0.5% and assess its thermo-physical properties for solar-thermal applications. The pH values of nanofluid MWCNT/T-55 with various particle loading were too far-flung from the pH (I) value, which confirmed the good dispersion stability of nanofluid. The measured density shows tremendous deviation from predicted density with increasing MWCNT loading owing to the non-considering of microstructural parameters in Pak & Cho correlation predication. The highest augmentation in nanofluid thermal conductivity was 16.83% for 0.5 vol. % MWCNT at 60 °C. The maximum improvement in dynamic viscosity of nanofluid with 0.5 vol. % of MWCNT is found to be 44%, and this rise is reduced at higher temperatures. The thermal effectiveness of the nanofluids demonstrates that nanofluid with all volume fractions of MWCNTs was favorable at higher temperatures in the laminar region. Mouromtseff number ratio decreases with a rise in temperature and MWCNT volume concentration. It is concluded that the excellent thermo-physical properties and prolonged thermal stability of the MWCNT will be highly beneficial in improving the overall performance of various kinds of heat transfer fluids (HTFs) for process heating and solar-thermal applications.

Rotating Flow in a Nanofluid with CNT Nanoparticles over a Stretching/Shrinking Surface

The steady three-dimensional rotating flow past a stretching/shrinking surface in water and kerosene-based nanofluids containing single and multi-walled carbon nanotubes (CNTs) is investigated. The governing equations are converted to similarity equations, and then numerically solved using MATLAB software. The impacts of rotational, suction, and nanoparticle volume fraction on the flow and the thermal fields, as well as velocity and temperature gradients at the surface, are represented graphically and are analyzed. Further, the friction factor and the heat transfer rate for different parameters are presented in tables. It is found that the heat transfer rate increases with increasing nanoparticle volume fraction as well as suction parameter in water and kerosene-based nanofluids of single and multi-walled CNTs. However, the increment in the rotating flow parameter decreases the rate of heat transfer. Multi-walled carbon nanotubes and kerosene-based nanofluid contribute to heat transfer rates better than single-walled carbon nanotubes and water-based nanofluid, respectively. A unique solution exists for the stretching surface, while two solutions are obtained for the shrinking surface. Further analysis of their stabilities shows that only one of them is stable over time.

Carbon Nanotori Structures for Thermal Transport Applications on Lubricants

Carbon nanostructures have been recently applied to improve industrial manufacturing processes and other materials; such is the case for lubricants used in the metal-mechanic industry. Nanotori are toroidal carbon nanostructures, obtained from chemical treatment of multi-wall carbon nanotubes (MWCNTs). This material has been shown to have superb anti-wear and friction reduction performance, having the ability to homogeneously disperse within water in concentrations between 1–2 wt.%. Obtained results of these novel nanostructures under water mixtures and novel additives were a set point to our studies in different industrial lubricants. In the present work, nanotori structures have been applied in various filler fractions as reinforcement to evaluate the behavior in thermal transport of water-based (WB) and oil-based (OB) lubricants. Temperature-dependent experiments to evaluate the thermal conductivity were performed using a thermal water bath ranging from room temperature up to 323 K. The obtained results showed a highly effective and favorable improvement in the heat transport of both lubricants; oil-based results were better than water-based results, with nanotori structures increasing the lubricants’ thermal transport properties by 70%, compared to pure lubricant.

Study on preparation, stability, thermal conductivity, and viscosity of silver nanoparticles-decorated three-dimensional graphene-like porous carbon hybrid nanofluids

In the present study, a novel silver nanoparticles-decorated three-dimensional graphene-like porous carbon (Ag/3D GPC) nanocomposite has been synthesized via the method of carbonization and reduction of silver ions at the same time. This Ag/3D GPC nanocomposite possess an interconnected network of well crystalized and submicron-sized macropores with thin graphene walls of several nanometers, where silver nanoparticles distributing uniformly. The water based and ethylene glycol based Ag/3D GPC hybrid nanofluids have been prepared without any surfactant. The hybrid nanofluids with low concentration (<0.8 wt%) can be steadily dispersed for more than six months. The thermal conductivity enhancement for the nanofluids with 0.1 wt% can reach 10.3% and 8.8% at 25 °C compared with pure water and ethylene glycol, respectively. The viscosity of nanofluids is investigated, the temperature dependence of the dynamic viscosity obeys an Arrhenius-like behavior. The prepared Ag/3D GPC hybrid nanofluids with good stability and thermal conductivity are promisingly considered to be used in heat transfer field.