Wetting behavior of multi-walled carbon nanotube nanofluids

Application of Nanofluids in Gas Turbine and Intercoolers-A Comprehensive Review

Today, the optimal use of non-renewable energy sources, reducing pollution, and increasing the efficiency of power-generating cycles are of particular importance. There are several ways to increase the efficiency of gas turbines; one that has recently attracted attention is to use an intercooler. However, the efficiency of the heat exchanger used in intercoolers depends on the type of heat exchanger, the characteristics of the operating fluid and the thermal boundary layers, and the pump speed. Improving the thermophysical properties of the working fluid is a passive method of increasing heat transfer, which has attracted the attention of those researching engineering applications. The current review addresses the latest methods of improving gas turbine efficiency using nanofluids and includes experimental and numerical studies. First, the general principles governing turbines are described, then the commonly used types of heat exchangers are introduced. Finally, studies on the use of nanofluids in heat exchangers are reviewed. The technology of producing nanoparticles that can be used in heat exchangers is also discussed. This review article can provide the reader with comprehensive information on making nanofluids and using them in heat exchangers used as intercoolers.

Experimental study and predicted model analysis of nanofluid wetting behavior under high voltage

To explore the wetting behavior of nanofluid under high voltage, a contact angle measurement system under electric field is designed and set up. The effects of mass concentration, the type of nanoparticles and the temperature of dielectric layer are considered. The experimental results manifest that the contact angle reduction rate of SiO₂-water nanofluid is gradually increased with the increase of nanofluid concentrations from 0 to 0.05 wt%. While, it is decreased when the concentration is varied from 0.05 to 0.25 wt%. On the other hand, the contact angle reduction rate of Al₂O₃-water nanofluid is generally greater than SiO₂-water nanofluid with the same volume concentration. In addition, the reduction rate of the contact angle of the SiO₂-water nanofluid would be gradually increased with the increase of the surface temperature of the dielectric layer. Moreover, the experimental values are greatly deviated from the results calculated by Young-Lippmann equation and its modified form of nanofluid. Hence, the present study proposes a dimensionless surface tension correct factor to obtain the modified equation which is based on the Young-Lippmann equation. The influence of electric charge, electric field force, drag force and Brownian force on nanoparticles under high voltage are considered in the modified equation. The results show that the modified equation can predict the trend of the nanofluid contact angle under higher voltage.

Preparation, characterization, and analysis of multi-walled carbon nanotube-based nanofluid: an aggregate based interpretation

Nanofluids are gaining attention as an attractive solution for the sustainable machining of difficult-to-cut materials. Despite the enormous recent work in the literature, there are still contradictions concerning the effect of different preparation factors on the characteristics of nanofluids and the underlying mechanisms governing them. In the present study, the effect of varying the preparation factors, namely, multi-walled carbon nanotube (MWCNT) concentration, sonication time, and surfactant amount on various nanofluid characteristics and the interactions among these characteristics were studied. The characteristics are divided into two categories: (a) dispersion/stability and (b) viscosity/wettability. The analysis showed strong interactions between these two categories which were mainly attributed to aggregates' formation and dynamics. For the stability/dispersion responses, the effect of aggregation and saturation phenomena is discussed in relation to the different preparation factors. Our analysis shows that the nanofluid viscosity is strongly dependent on aggregate morphology. As for wettability, a novel mechanism is proposed and used to explain the nanoparticles' influence on wettability based on the nanolayering theory. Finally, multi objective optimization (MOO) based on grey relational analysis (GRA) was performed. It was found that moderate MWCNT concentration, high sonication time, and low surfactant amount show the optimal characteristics within the current study design variables search domain. The novelty in the present study lies in its consideration of the simultaneous interaction between the nanofluids' properties and stability. Unlike the common practice in the literature, which focuses on one or two aspects of nanofluids, our approach broadens the analysis and provides in-depth insights into the nanofluid as a complete physical system.

Multiprespective analysis of MWCNTs nanofluids.

Navigation of Silver/Carbon Nanoantennas in Organic Fluids Explored by a Two-Wave Mixing

Within this work are analyzed third-order nonlinear optical properties with a potential influence on the dynamic mechanics exhibited by metal/carbon nanofluids. The nanofluids were integrated by multiwall carbon nanotubes decorated with Ag nanoparticles suspended in ethanol or in acetone. Optical third-order nonlinearities were experimentally explored by vectorial two-wave mixing experiments with a Nd-YAG laser system emitting nanosecond pulses at a 532 nm wavelength. An optically induced birefringence in the metal/organic samples seems to be responsible for a significant modification in density and compressibility modulus in the nanosystems. The measured nonlinear refractive index was associated with a thermal process together with changes in density, compressibility modulus and speed of sound in the samples. Nanofluid diffusivity was studied to characterize the dynamic concentration gradients related to the precipitation of nanostructures in the liquid solutions. The evolution of the nanoparticle density suspended in the nanofluids was considered as a temporal-resolved probabilistic system. It is stated that the incorporation of Ag nanoparticles in carbon nanotubes produces strong mechanical changes in carbon-based nanofluids. According to numerical simulations and optical evaluations, immediate applications for developing dynamic nanoantennas optical logic gates and quantum-controlled metal/carbon systems can be contemplated.

Influence of solvents on the enhancement of thermophysical properties and stability of multi-walled carbon nanotubes nanofluid

Multi-walled carbon nanotubes (MWCNTs) are a contemporary class of nanoparticles that have a prominent thermal, electrical and mechanical properties. There have been numerous studies on the enhancement of thermophysical properties of nanofluids. However, there is only limited research on thermal and stability analysis of MWCNT nanofluids with various kinds of solvents or base fluids, namely propylene glycol, ethanol, ethylene glycol, polyethylene glycol, methanol and water. This paper reports the enhancement of thermophysical properties and stability of MWCNTs with six different base fluids in the presence of sodium dodecyl benzene sulfonate surfactant with a mass concentration of 0.5 wt%. Thermal and dispersion stabilities were determined using a thermogravimetric analyzer (TGA) and Zeta potential, along with a visual inspection method to evaluate the agglomeration or sedimentation of MWCNT nanoparticles over a period of one month. Ultraviolet-visible spectroscopy and Fourier transform infrared spectroscopy were utilized to identify the molecular components and light absorption of the formulated nanofluids at their maximum wavenumber (4500 cm^-1) and wavelength (800 nm). In addition, thermophysical properties such as thermal conductivity, specific heat capacity, viscosity and density with a peak temperature of 200 °C were also experimentally evaluated. The TGA results illustrated that MWCNT/ethylene glycol nanofluid achieved maximum thermal stability at 140 °C and it revealed a maximum zeta potential value of -61.8 mV. Thus, ethylene glycol solution was found to be the best base liquid to homogenize with MWCNTs for acquiring an enhanced thermophysical property and a long-term stability.

Engineering Water and Solute Dynamics and Maximal Use of CNT Surface Area for Efficient Water Desalination

While polymer-based membranes and the consistent plants and elements have long been considered and optimized, there are only few studies on optimization of the new generation of carbon-based porous membranes for water desalination. By modeling the elements and their corresponding parameters in a vertical configuration via COMSOL Multiphysics software, an experimental setup was modified that contained various bare and carbon nanotube (CNT)-covered microprocessed porous membranes in parallel and in series. Several design parameters such as inlet pressure, length of outlet, vertical distance of the parallel membranes, and horizontal distances of the series membranes were optimized. Taking advantage of the uttermost surface area of CNTs and the engineered particle trajectory, almost 90% NaCl rejection and 97% Allura red rejection were obtained with very high permeation values. Considering microsized outlets, the results of particle rejections are outstanding owing to the smart design of the setup. The results of this work can be extended to larger and smaller scales up to the point where the governing equations still hold.

Boron doping induced thermal conductivity enhancement of water-based 3C-Si(B)C nanofluids

In this paper, the fabrication and thermal conductivity (TC) of water-based nanofluids using boron (B)-doped SiC as dispersions are reported. Doping B into the β-SiC phase leads to the shrinkage of the SiC lattice due to the substitution of Si atoms (0.134 nm radius) by smaller B atoms (0.095 nm radius). The presence of B in the SiC phase also promotes crystallization and grain growth of obtained particles. The tailored crystal structure and morphology of B-doped SiC nanoparticles are beneficial for the TC improvement of the nanofluids by using them as dispersions. Using B-doped SiC nanoparticles as dispersions for nanofluids, a remarkable improvement in stability was achieved in SiC-B6 nanofluid at pH 11 by means of the Zeta potential measurement. By dispersing B-doped SiC nanoparticles in water-based fluids, the TC of the as-prepared nanofluids containing only 0.3 vol.% SiC-B6 nanoparticles is remarkably raised to 39.3% at 30 °C compared to the base fluids, and is further enhanced with the increased temperature. The main reasons for the improvement in TC of SiC-B6 nanofluids are more stable dispersion and intensive charge ions vibration around the surface of nanoparticles as well as the enhanced TC of the SiC-B dispersions.

Mechano-optical effects in multiwall carbon nanotubes ethanol based nanofluids

A highly sensitive technique for analyzing surface tension and dynamic viscosity of nanofluids was reported. Multiwall carbon nanotubes suspended in ethanol were evaluated. The assistance of a Fabry-Perot interferometer integrated by a small sample volume fluid allowed us to explore the stability and mechanical properties exhibited by the nanostructures. The surface tension and dynamic viscosity of the colloid was examined by using interferometric optical signals reflected from a remnant drop pending at the end of an optical fiber. Nanosecond pulses provided by a Nd:YAG laser source with 9.5 MW/mm² at 532 nm wavelength were used to induce mechano-optical effects in the liquid drop. The mechanical parameters were approximated, taking into account single optical pulses interacting with an inelastic mass-spring-damper system.