One dimensional nanostructured materials

Carbon nanotubes – Production and industrial applications

Arc discharge synthesis of carbon nanotubes: Comprehensive review

Over the past few decades, a new branch of plasma research, nanomaterial (NM) synthesis through plasma–liquid interactions (PLIs), has been developing rapidly, mainly due to the various, recently developed plasma sources operating at low and atmospheric pressures. PLIs provide novel plasma–liquid interfaces where many physical and chemical processes take place. By exploiting these physical and chemical processes, various NMs ranging from noble metal nanoparticles to graphene nanosheets can easily be synthesized. The currently rapid development and increasingly wide utilization of the PLI method has naturally lead to an urgent need for the presentation of a general review. This paper reviews the current status of research on PLIs for NM synthesis. The focus is on a comprehensive understanding of the synthesis process and perceptive opinions on current issues and future challenges in this field.

http://iopscience.iop.org/article/10.1088/0022-3727/48/42/424005/pdf

A review of plasma-liquid interactions for nanomaterial synthesis

Laminar forced convection heat transfer of water–Cu nanofluids in a microchannel was studied utilizing the lattice Boltzmann method (LBM). The entering flow was at a lower temperature compared to the microchannel walls. Simulations were performed for nanoparticle volume fractions of 0.00 to 0.04 and slip coefficient from 0.005 to 0.02. The model predictions were found to be in good agreement with earlier studies. The effects of wall slip velocity and temperature jump of the nanofluid were studied for the first time by using lattice Boltzmann method. Streamlines, isotherms, longitudinal variations of Nusselt number, slip velocity and temperature jump as well as velocity and temperature profiles for different cross sections were presented. The results indicate that LBM can be used to simulate forced convection for the nanofluid micro flows. Moreover, the effect of the temperature jump on the heat transfer rate is significant. Also, the results showed that decreasing the values of slip coefficient enhances the convective heat transfer coefficient and consequently the Nusselt number (Nu) but increases the wall slip velocity and temperature jump values.

Simulation of copper-water nanofluid in a microchannel in slip flow regime using the lattice Boltzmann method

Continuous carbon nanotube production in underwater AC electric arc

A comparative study between computational and experimental results for pressure-driven binary gas flows through long microchannels is performed. The theoretical formulation is based on the McCormack kinetic model and the computational results are valid in the whole range of the Knudsen number. Diffusion effects are taken into consideration. The experimental work is based on the Constant Volume Method, and the results are in the slip and transition regime. Using both approaches, the molar flow rates of the He–Ar gas mixture flowing through a rectangular microchannel are estimated for a wide range of pressure drops between the upstream and downstream reservoirs and several mixture concentrations varying from pure He to pure Ar. In all cases, a very good agreement is found, within the margins of the introduced modeling and measurement uncertainties. In addition, computational results for the pressure and concentration distributions along the channel are provided. As far as the authors are aware of, this is the first detailed and complete comparative study between theory and experiment for gaseous flows through long microchannels in the case of binary mixtures.

Comparative study between computational and experimental results for binary rarefied gas flows through long microchannels

A slip-flow boundary condition has been developed in the lattice Boltzmann model combining an interpolation method and a simple slip boundary condition for straight walls placed at arbitrary distance from the last fluid node. An analytical expression has been derived to connect the model parameters with the slip velocity for Couette and Poiseuille flows in the nearly continuum limit. The proposed interpolation method ensures that the slip velocity is independent of the wall position in first order of the Knudsen number. Computer simulations have been carried out to validate the model. The Couette and Poiseuille flows agree with the analytical results to machine order. Numerical simulation of a moving square demonstrates the accuracy of the model for walls moving in both the tangential and normal directions.

Slip-flow boundary condition for straight walls in the lattice Boltzmann model

The flow of binary gas mixtures through long micro-channels with triangular and trapezoidal cross sections is investigated in the whole range of the Knudsen number. The flow is driven by pressure and concentration gradients. The McCormack kinetic model is utilized to simulate the rarefied flow of the gas mixture, and the kinetic equations are solved by an upgraded discrete velocity algorithm. The kinetic dimensionless flow rates are tabulated for selected noble gas mixtures flowing through micro-channels etched by KOH in silicon (triangular and trapezoidal channels with acute angle of 54.74°). Furthermore, the complete procedure to obtain the mass flow rate for a gas mixture flowing through a channel, based on the dimensionless kinetic results, which are valid in each cross section of the channel, is presented. The study includes the effect of the separation phenomenon. It is shown that gas separation may change significantly the estimated mass flow rate. The presented methodology can be used for engineering purposes and for the accurate comparison with experimental results.

Rarefied gas flow of binary mixtures through long channels with triangular and trapezoidal cross sections

A Knudsen layer theory is presented within the framework of a high-order lattice Boltzmann model obtained from the fourth-order Gauss-Hermite quadrature. The Kramers problem is analyzed in detail. We employ a multi-relaxation collision operator which is shown to permit a variable layer width. Computer simulations are performed which give excellent agreement with the theoretical derivations. Good qualitative agreement is achieved with the accurate numerical solution of the Boltzmann equation for hard sphere molecules. Our theoretical result clearly indicates that the lattice Boltzmann models with high symmetric velocity sets naturally develop to physically relevant Knudsen layers due to the discrete ordinate origin of the method.

https://iopscience.iop.org/article/10.1209/0295-5075/80/24003/pdf

Lajos Szalmás

Papers

Continuous carbon nanotube production in underwater AC electric arc

Comparative study between computational and experimental results for binary rarefied gas flows through long microchannels

Slip-flow boundary condition for straight walls in the lattice Boltzmann model

Rarefied gas flow of binary mixtures through long channels with triangular and trapezoidal cross sections

Knudsen layer theory for high-order lattice Boltzmann models