Laminar nanofluid flow in microheat-sinks

In response to the ever increasing demand for smaller and lighter high-performance cooling devices, steady laminar liquid nanofluid flow in microchannels is simulated and analyzed. Considering two types of nanofluids, i.e., copper-oxide nanospheres at low volume concentrations in water or ethylene glycol, the conjugated heat transfer problem for microheat-sinks has been numerically solved. Employing new models for the effective thermal conductivity and dynamic viscosity of nanofluids, the impact of nanoparticle concentrations in these two mixture flows on the microchannel pressure gradients, temperature profiles and Nusselt numbers are computed, in light of aspect ratio, viscous dissipation, and enhanced temperature effects. Based on these results, the following can be recommended for microheat-sink performance improvements: Use of large high-Prandtl number carrier fluids, nanoparticles at high volume concentrations of about 4% with elevated thermal conductivities and dielectric constants very close to that of the carrier fluid, microchannels with high aspect ratios, and treated channel walls to avoid nanoparticle accumulation.     

基于纳米流体热管的研究综述

综述了国内外基于纳米流体热管的研究状况,并对其未来的发展进行了展望。     

Active-passive controls of liquid di-hydrogen mono-oxide based nanofluidic transport over a bended surface

This study unfolds the hydrothermal features of nanofluidic transport over a curved surface. The texture of the curved surface has been assumed to be stretched and the bended structure is coiled inside a circular section having radius R. Active passive controls of tiny ingredients at the surface influenced by Brownian and thermophoretic migration are incorporated at molecular level to frame the analysis. The nanoparticles are dispersed into base solution of liquid Di-Hydrogen Mono-Oxide to explore the heat and mass diffusion. Foremost system of equations are provided to explore the hydrothermal integrity and diffusivity of nanofluidic liquid Di-Hydrogen Mono-Oxide in an extensive way. After that, those equations are simplified using RK-4 based shooting scheme. Influence of dynamic parameters on the transport systems are deliberated using requisite graphs, tables. Deviation in streamlines, 3D view of pressure and pressure gradient, velocity are depicted. Heat and mass diffusion are reviewed and discussed in detail. Results extract that mass diffusion of liquid di-Hydrogen mono-oxide based nanofluid intensifies for Brownian motion plus Lewis factor. Low reduction in heat transport is assured for passive flow. Rheological analysis of such liquid Di-Hydrogen Mono-Oxide based nanofluidic diffusive flows renders truthful submission in diverse fields of thermal, mechanical and industrial sectors and rheological study and behaviour of such flows are very rare in open literature. Thus we hope our study would advance the thermal energy and diffusivity analysis of nanofluidic transport in most promising way.     

Evaluation of turbulent forced convection of non-Newtonian aqueous solution of CMC/CuO nanofluid in a tube with twisted tape inserts

The present paper investigates the turbulent flow and heat transfer of non-Newtonian aqueous solution of Carboxymethyl cellulose (CMC) and CuO nanoparticles in a plain tube and also tube with twisted tape inserts. The aqueous solution of CMC and CuO/CMC nanofluid show a shear-thinning (pseudo-plastic) rheological behavior, resulting in a higher viscosity than that of water. The consistency index and the power law index are evaluated based on available experimental data. The single phase approach with temperature dependent thermo-physical properties is applied to simulate the nanofluid flow and heat transfer. Simulation results are presented at different nanoparticle concentrations and twisted tape ratios. Only an axial flow is identified in the plain tube whereas both axial and swirl flows are detected in the tube with twisted tape inserts. The turbulence kinetic energy in the tube with twisted tapes is significantly higher than that in the plain one, which is useful for non-Newtonian fluid with higher viscosity. Also, the temperature fields in the tube with twisted tapes are disturbed relative to those in the plain one, due to stronger turbulence intensity and better fluid mixing. Higher amounts of nanoparticles concentration and lower twist ratios, giving maximum values of total efficiency, display the advantage of using non-Newtonian nanofluid in the tube with twisted tape inserts rather than non-Newtonian base fluid in the plain one.     

Hall current effect on the peristaltic motion of synovial nanofluid with magnetohydrodynamics

This paper examines the influence of magnetic field on peristaltic flow of synovial nanofluid in an asymmetric channel. Hall current, thermophoresis, and Brownian motion effects are taken into account. Our problem is discussed for two models, in the first model which referred as Model (I), viscosity is considered exponentially dependent on the concentration, and Model (II) Shear thinning index is considered function of concentration. The governing problem is reformulated under the assumption of low Reynolds number and high wavelength. Resulting system of equations are solved numerically with the aid of Parametric ND Solve. Detailed comparisons have been made between Model (I) and Model (II) and found unrealistic results between them. Results for velocity, temperature and nanoparticle concentration distributions as well as pressure gradient and pressure rise are offered graphically for different values of various physical parameters. It is found that the velocity of fluid decreases in semi‐curved lines in case of Model (I) with the increase of while, in Model (II) it decreases in the left side of the channel and increases in the right side of that channel. Such models are applicable to rheumatoid arthritis treatment.     

An experimental study of drag reduction by nanofluids in slug two-phase flow of air and water through horizontal pipes☆

This study investigates the effect of injecting nanofluids containing nano-SiO2 as drag reducing agents (DRA) at different concentrations on the pressure drop of air–water flow through horizontal pipe....     

Numerical analysis of nanofluid flow inside a trapezoidal microchannel using different approaches

In this study, developing laminar forced convection of ${\text{Al}}_2{\text{O}}_3$/water nanofluid flow inside a trapezoidal microchannel has been investigated. The numerical simulation is conducted using two different methods which consider the effect of non-uniform nanoparticle distribution: Buongiorno’s Two-component nonhomogeneous model, and Eulerian-Lagrangian two-phase method. The results are compared to experimental data and also single-phase and dispersion methods. It is shown that the Eulerian-Lagrangian method predicts microchannel Nusselt number more accurately than Buongiorno’s model. Particle distribution is not uniform in the cross section of microchannel, and with increasing Reynolds number this nonuniformity is more. Moreover, the effect of different forces on heat transfer is discussed. It is found that the influence of Saffman’s lift force is negligible while Brownian and thermophoretic forces affect the heat transfer coefficient slightly. Furthermore, it is shown that the use of experimental correlation for nanoparticle Nusselt number makes the numerical results more accurate, so it is important to take into account the scale effects and use the suitable correlations.     

Free convection of water–Fe3O4 nanofluid in an inclined cavity subjected to a magnetic field: CFD modeling,sensitivity analysis

Modeling of natural convection heat transfer in an inclined C-shape cavity is studied in this paper. The enclosure is filled with H₂O-Fe₃O₄ nanofluid under the effect of magnetic field. The operating range of parameters used in this study were Hartmann number (Ha) from 0 to 80, Rayleigh number (Ra) from 1E2 to 1E6, nanoparticles volume fraction (φ) from 0 to 0.1, inclination angle (α) from 0 to 90 deg, and aspect ratio (AR) from 0.2 to 0.8. The employed model is solved using CFD tools based on the finite element method. The comparison with reference experimental data indicated the accuracy and generalization capability of the model. In addition, a novel correlation and an artificial neural network (ANN) model were productively developed for predicting Nu number as a function of aforementioned independent variables. The influence of the model parameters on the Nu number is precisely presented and discussed. It is shown that Ra number and aspect ratio have more impact on Nu than the other variables.     

Density maximum effects on mixed convection in a square lid-driven enclosure filled with Cu-water nanofluids

In this paper, the authors investigate the laminar mixed convection flow of Cu-water nanofluid near density maximum of water in a lid-driven enclosure. The governing equations based on the Boussinesq and non-Boussinesq homogenous models are solved using a pressure-based finite volume method. Four different lid-driven cases are simulated when volume fractions of nanoparticles range from 0.0, 0.03 and 0.05 and the Richardson (Ri) number varies from 0.01, 0.1, 1, 10 and 100 under both the Boussinesq and non-Boussinesq approximations. Streamlines, isotherms, mid-plane velocities, mid-plane temperature and the average Nusselt (Nu) number in various boundary conditions have been analyzed. Results show that the flow pattern and thermal behavior of the nanofluid strongly depend on the density inversion of water and the presence of nanoparticles. Further, the findings indicate that the density inversion phenomenon leads to a lower average Nu number under the non-Boussinesq approximation compared to the Boussinesq approximation, suggesting that studies with the Boussinesq approximation may overestimate heat transfer performance. In addition, the average Nu number increases as the volume fractions of nanoparticles increase. Finally, the maximum value of the average Nu number can be achieved under the Boussinesq approximation when the shear-driven force is aligned with the buoyancy force.