Search results

Accurate prediction of temperature and heat is crucial for the design of various nano/micro devices in engineering. Recently, investigation has been carried out for calculating the heat flux of gas flow using the concept of sliding friction because of the slip velocity at the surface. The purpose of this study is to exetend the concept of sliding friction for various types of nano/micro flows.

A new type of Smoluchowski temperature jump considering the viscous heat generation (sliding friction) has recently been proposed (Le and Vu, 2016b) as an alternative jump condition for the prediction of the surface gas temperature at solid interfaces for high-speed non-equilibrium gas flows. This paper investigated the proposed jump condition for the nano/microflows which has not been done earlier using four cases: 90° bend microchannel pressure-driven flow, nanochannel backward facing step with a pressure-driven flow, nanoscale flat plate and NACA 0012 micro-airfoil. The results are compared with the available direct simulation Monte Carlo results. Also, this paper has demonstrated low-speed preconditioned density-based algorithm for the rarefied gas flows. The algorithm captured even very low Mach numbers of 2.12 × 10⁻⁵.

Based on this study, this paper concludes that the effect of inclusion of sliding friction in improving the thermodynamic prediction is case-dependent. It is shown that its performance depends not only on the slip velocity at the surface but also on the mean free path of the gas molecule and the shear stress at the surface. A pressure jump condition was used along with the new temperature jump condition and it has been found to often improve the prediction of surface flow properties significantly.

This paper extends the concept of using sliding friction at the wall for micro/nano flows. The pressure jump condition was used which has been generally ignored by researchers and has been found to often improve the prediction of surface flow properties. Different flow properties have been studied at the wall apart from only temperature and heat flux, which was not done earlier.

The purpose of this study is to provide a micro-nano chip automatic alignment system. Used for micron and nanometer channel alignment of microfluidic chip.

In this paper, combined with the reconstructed micro–nanoscale Hough transform theory, a “clamp–adsorb–rotate” chip alignment method is proposed. The designed alignment system includes a microscopic identification device, a clamping device and a suction device. After assembly, the straightness of the linear slide rail in the horizontal and vertical directions was tested, respectively. The results show that in the horizontal and vertical directions, the linearity error of the linear slide is +0.29 and 0.30 µm, respectively, which meets the requirement of chip alignment accuracy of 15 µm. In the direction of rotation, the angular error between the microchannel and the nanochannel is ±0.5°. In addition, an alignment flow experiment of the chip is designed. The results demonstrate that the closer the angle between the microchannel and the nanochannel is to 90°, the fluid fills the entire channel. Compared with the conventional method, the method and the assembly system realize fully automatic double-layer chip alignment.

A mechanical device designed by Hough transform theory can realize microfluidic chip alignment at nanometer and micron level.

The automatic alignment device adopts Hough transform principle and can be used for microfluidic chip alignment.

This paper aims to extend the hybrid atomistic-continuum multiscale method developed by Vu et al. (2016) to study the gas flow problems in long microchannels involving density variations.

The simulation domain is decomposed into three regions: the bulk where the continuous Navier–Stokes and energy equations are solved, the neighbourhood of the wall simulated by molecular dynamics and the overlap region which connects the macroscopic variables (density, velocity and temperature) between the two former regions. For the simulation of long micro/nanochannels, a strategy with multiple molecular blocks all along the fluid/solid interface is adopted to capture accurately the macroscopic velocity and temperature variations.

The validity of the hybrid method is shown by comparisons with a simplified analytical model in the molecular region. Applications to compressible and condensation problems are also presented, and the results are discussed.

The hybrid method proposed in this paper allows cost-effective computer simulations of large-scale problems with an accurate modelling of the transfers at small scales (velocity slip, temperature jump, thin condensation films, etc.).

The purpose of this paper is to focus on the stratified phenomenon through vertical stretching cylinder in the region of stagnation point with slip effects.

Homotopy analysis method is used to find the series solutions of the governing equations.

Velocity profile decreases with an increase in stratified parameters due to temperature and concentration. Velocity and thermal slips cause a reduction in the velocity profile. Thermally stratified and thermal slip parameters reduce the temperature field.

The present analysis has not been existed in the literature yet.

The purpose of this paper is to explore the sensitive parameters affecting the friction resistance of sliding bearings under different interface slip conditions and the influence of the texture position of circular pits on the friction force of sliding bearings.

Based on the mechanical equilibrium equation and Newton's viscous fluid mechanics formula and wedge oil film model, the calculation model of sliding bearing friction resistance under interface slip state is established, and the influence of interface slip on friction resistance under different slip conditions is analyzed by means of ANSYS. Friction simulation model of circular pit textured journal bearing under different interface slip conditions.

The friction resistance of bearings is mainly determined by journal linear velocity, oil film slip ratio, pressure of inlet and outlet of bearings, oil film thickness and bearing capacity. When both the upper and lower surfaces of the oil film slip, the friction resistance decreases significantly, which is only 4-17 per cent of that without slip. And the friction force of the texture model of circular pit at the exit is better than that at the entrance and the middle of the pit.

Relevant research results will lay a new theoretical foundation for friction reduction and optimization design of sliding bearings.

It is significant to know the real-time indexes about the turbulence flow of the ocean system, which has a deep influence on ocean productivity, distribution of the ocean populations and transmission of the ocean energy, especially the measurement of turbulence flow velocity. So, it is particularly urgent to provide a high-sensitivity, low-cost and reliable fluid flow sensor for industry and consumer product application. This paper aims to design a micro fluid flow sensor with a cross beam membrane structure. The designed sensor can detect the fluid flow velocity and has a low kinetic energy dissipation rate.

In this paper, a micro fluid flow sensor with a cross beam membrane structure is designed to measure the ocean turbulence flow velocity. The design, simulation, fabrication and measurement of the designed sensor are discussed. By testing the simply packaged sensor in the fluid flow and analyzing the experiments data, the results show that the designed sensor has favorable performance.

The paper describes the tests of the designed sensor, and the experimental results show that the designed sensor can measure the fluid flow velocity and has a sensitivity of 11.12 mV/V/(m/s)2 and a low kinetic energy dissipation rate in the range of 10-6-10-4 W/kg.

This paper provides a micro-electro-mechanical systems fluid flow sensor used to measure ocean turbulence flow velocity.

The purpose of this paper is to analyze the boundary layer flow of an Oldroyd-B fluid with Newtonian heating.

Series solutions are found by homotopy analysis method.

Temperature profile increases with an increase in conjugate parameter. Increase in parameter β and Prandtl number Pr decreases the temperature profile.

This work does not currently exist in the literature.

The purpose of this paper is to present different approaches for applying macroscopic boundary conditions in hybrid multiscale modelling.

Molecular dynamics (MD) was employed for the microscopic simulations. The continuum boundary conditions were applied either through rescaling of atomistic velocities or resampling based on velocity distribution functions.

The methods have been tested for various fluid flows with heat transfer scenarios. The selection of the most suitable method is not a trivial task and depends on a number of factors such as accuracy requirements and availability of computational resource.

The applicability of the methods has been assessed for liquid and gas flows. Specific parameters that affect their accuracy and efficiency have been identified. The effects of these parameters on the accuracy and efficiency of the simulations are investigated. The study provides knowledge regarding the development and application of boundary conditions in multiscale computational frameworks.

The purpose of this paper is to describe the micro fluid flow analysis in a micro thruster of micro‐/nano‐ satellite propulsion system and to propose the algorithm for the fluid flow simulations with the open boundary based on moving boundary method.

The analysis is based on a finite volume moving boundary method. Underlying mathematical model is the system of Navier‐Stokes‐Fourier partial differential equation describing compressible gas model. Propellant under the study is pure nitrogen gas. First, the static geometry velocity vector field is calculated and the information of the velocity at the outflow boundary is obtained; then, with the moving boundary method the outlet boundary is evolved. Evolution of the boundary is stopped when the continuum model ceases to hold. The criteria of the continuum model failure are based on the local Knudsen number.

The validations of the flow with respect to the Knudsen number showed that the continuum model is valid in the nozzle interior part (from the pressure value to the nozzle throat). The exterior nozzle part (diverging side) showed immediate raising of the Knudsen number above the continuum threshold (0.01). For the overall accurate computations of thruster flow, the continuum model must be coupled with molecular model (i.e. Boltzmann BGK).

In this paper, the authors propose a method for the computation of an open boundary flow with the application of the moving boundary method.

The purpose of this paper is to study the effect of micro-nano surface texture on the corrosion resistance of a titanium alloy and investigate the correlation between corrosion resistance and hydrophobicity.

The surface of the Ti₆Al₄V alloy was modified by laser processing and anodizing to fabricate micro-pits, nanotubes and micro-nano surface textures. Afterward, the surface morphology, hydrophobicity and polarization curve of the samples were analyzed by cold field scanning electron microscopy, contact angle measurement instruments and a multi-channel electrochemical workstation.

The micro-nano surface texture can enhance the hydrophobicity of the Ti₆Al₄V surface, which may lead to better drag reduction to ease the friction of implants in vivo. Nevertheless, no correlation existed between surface hydrophobicity and corrosion resistance; the corrosion resistance of samples with nanotubes and high-density samples with micro-nano surface texture was extremely enhanced, indicating the similar corrosion resistance of the two.

The mechanism of micro-dimples on the corrosion resistance of the micro-nano surface texture was not studied.

The density of micro-pits needs to be optimized to guarantee excellent corrosion resistance in the design of the micro-nano surface texture; otherwise, it will not fulfill the requirement of surface modification.

The influence of the micro-nano surface texture on the corrosion resistance, as well as the relationship between hydrophobicity and corrosion resistance of the titanium alloy surface, were systematically investigated for the first time. These conclusions offer new knowledge.