颗粒聚集对纳米流体强化换热影响浅析

本文采用数值模拟的方法初步研究了颗粒聚集对纳米流体强化换热性能的影响。在流体中随机生成纳米颗粒团聚状态,并对其热性能进行数值模拟,结果表明,纳米颗粒的聚集将会导致流体换热性能的下降,降低程度与纳米颗粒体积分数以及聚集程度有关。     

Significance of activation energy and Wu's slip features in Cross nanofluid with motile microorganisms

The current article investigates the impact of the bioconvection in an unsteady flow of magnetized Cross nanofluid with gyrotactic microorganisms and activation energy over a linearly stretched configuration. The analysis has been performed by utilizing the realistic Wu's slip boundary and zero mass flux conditions. The effects of nonlinear thermal radiation and the activation energy are also addressed. The governing flow equations are deduced to a dimensionless form by considering suitable transformations which are numerically targeted via a shooting algorithm. The physical visualization of each physical parameter governing the flow problem has been displayed graphically for distribution of velocity, temperature, concentration and motile microorganisms. The numerical treatment for the variation of skin friction coefficient, local Nusselt number, local Sherwood number and motile density number is performed in tabular forms.     

Numerical simulation of MHD natural convection flow in a wavy cavity filled by a hybrid Cu-Al_2O_3-water nanofluid with discrete heating

We consider the combined effect of the magnetic field and heat transfer inside a square cavity containing a hybrid nanofluid(Cu-Al_2O_3-water). The upper and bottom walls of the cavity have a wavy shape. The temperature of the vertical walls is lower,the third part in the middle of the bottom wall is kept at a constant higher temperature,and the remaining parts of the bottom wall and the upper wall are thermally insulated.The magnetic field is applied under the angle γ, an opposite clockwise direction. For the numerical simulation, the finite element technique is employed. The ranges of the characteristics are as follows: the Rayleigh number(10~3≤Ra≤10~5), the Hartmann number(0≤Ha≤100), the nanoparticle hybrid concentration(?_(Al_2O_3),?_(Cu) = 0, 0.025, 0.05),the magnetic field orientation(0≤γ≤2π), and the Prandtl number P_r, the amplitude of wavy cavity A, and the number of waviness n are fixed at P_r = 7, A = 0.1, and n = 3, respectively. The comparison with a reported finding in the open literature is done,and the data are observed to be in very good agreement. The effects of the governing parameters on the energy transport and fluid flow parameters are studied. The results prove that the increment of the magnetic influence determines the decrease of the energy transference because the conduction motion dominates the fluid movement. When the Rayleigh number is raised, the Nusselt number is increased, too. For moderate Rayleigh numbers, the maximum ratio of the heat transfer takes place for the hybrid nanofluid and then the Cu-nanofluid, followed by the Al_2O_3-nanofluid. The nature of motion and energy transport parameters has been scrutinized.     

Optimal treatment of stratified Carreau and Casson nanofluids flows in Darcy-Forchheimer porous space over porous matrix

A comparative three-dimensional (3D) analysis for Casson-nanofluid and Carreau-nanofluid flows due to a flat body in a magnetohydrodynamic (MHD) stratified environment is presented. Flow is estimated to be suspended in a Darcy-Forchheimer medium. Soret and Dufour responses are also accommodated in the flow field. A moving (rotating) coordinate system is exercised to examine the bidirectionally stretched flow fields (flow, heat transfer, and mass transfer). Nanofluid is compounded by taking ethylene glycol/sodium alginate as base fluid and ferric-oxide (Fe₃O₄) as nanoparticles. Governing equations are handled by the application of optimal homotopy asymptotic method (OHAM), where convergence parameters are optimized through the classical least square procedure. The novel mechanism (hidden physics) due to appearing parameters is explored with the assistance of tabular and graphical expositions. Outcomes reveal the double behavior state for temperature field with thermal stratification/Dufour number, and for concentration field with Soret number due to the presence of turning points.     

The convective heat transfer analysis of the casson nanofluid jet flow under the influence of the movement of gyrotactic microorganisms

Jet flows provide an effective mode of energy transfer or mass transfer in industrial applications. When compared to traditional cooling through convection, jet flows have high heat and mass transfer coefficients. Further, the devices equipped with jet flow provides efficient use of fluid and also offers enhanced heat and mass transfer rates. Hence in this study, the jet flow of Casson nanofluid containing gyrotactic microorganisms that stabilises the nanoparticle suspension is discussed. To control the fluid from outside external magnetic field is imposed. The model with these characteristics are useful in the appliances like coolants in automobiles, nuclear reactors, micro-manufacturing, metallurgical process etc. Such a model is created by employing PDE, which are then transformed into a system of ODE. The DTM is employed to obtain the solution to system of equations, and the results are interpreted using graphs. It is perceived that the velocity of the nanofluid flow is decreased because of the increased yield stress created by the greater values of the Casson parameter. As a result, the temperature profile is found to be increasing. Meanwhile, it is observed that for increased value of chemical reaction parameter diminishes the nanoparticle concentration. The motile density is found to decrease for increase in the Peclet number and the bioconvection Schmidt number. Further, the thermophoresis improves the temperature and concentration profile of the nanofluid.     

Effects of g-jitter and radiation on three-dimensional double diffusion stagnation point nanofluid flow

The unsteady double diffusion of the boundary layer with the nanofluid flow near a three-dimensional (3D) stagnation point body is studied under a microgravity environment. The effects of g-jitter and thermal radiation exist under the microgravity environment, where there is a gravitational field with fluctuations. The flow problem is mathematically formulated into a system of equations derived from the physical laws and principles under the no-slip boundary condition. With the semi-similar transformation technique, the dimensional system of equations is reduced into a dimensionless system of equations, where the dependent variables of the problem are lessened. A numerical solution for the flow problem derived from the system of dimensionless partial differential equations is obtained with the Keller box method, which is an implicit finite difference approach. The effects studied are analyzed in terms of the physical quantities of principle interest with the fluid behavior characteristics, the heat transfer properties, and the concentration distributions. The results show that the value of the curvature ratio parameter represents the geometrical shape of the boundary body, where the stagnation point is located. The increased modulation amplitude parameter produces a fluctuating behavior on all physical quantities studied, where the fluctuating range becomes smaller when the oscillation frequency increases. Moreover, the addition of Cu nanoparticles enhances the thermal conductivity of the heat flux, and the thermal radiation could increase the heat transfer properties.     

Wettability alteration of carbonate rocks from strongly liquid-wetting to strongly gas-wetting by fluorine-doped silica coated by fluorosilane

Wettability alteration is an important mechanism to increase recovery from oil and gas reservoirs. In this study, effect of fluorine-doped silica coated by fluorosilane nanofluid on wettability alteration of carbonate rock was investigated. The nanoparticle synthesized by sol-gel method was characterized using XRD, FTIR, SEM, and DLS. Adsorption of nanoparticle on rock was characterized by FESEM, and composition of rock after treatment was determined by EDXA. Effect of nanofluid on wettability was investigated by measuring static, advancing, and receding contact angle and surface free energy, imbibition of water, crude oil, and condensate of untreated and treated carbonate rock. Also, stability of contact angle and thermal stability of nanofluid were studied. ?Results show that contact angles for water, condensate, and crude oil were altered from 37.95°, 0°, ?and 0° to 146.47°, 145.59°, and 138.24°. In addition, water, condensate, and oil imbibition ?decreased more than 87, 88, and 80%, indicating that wettability was altered from strongly oil wet, ?condensate wet, and water wet to strongly gas wet. The ultraoleophobic and ultrahydrophobic stability were >48 hours and 120 minutes. Surface free energy of treated rock for water, crude oil, and condensate was ?2.24, 1.17, and 1.47mN/m. Thermal stability of nanofluids and adsorbed nanoparticle was up to 150°C.     

Heat and mass transfer analysis of time-dependent tangent hyperbolic nanofluid flow past a wedge

The candid intension of this article is to inspect the heat and mass transfer of a magnetohydrodynamic tangent hyperbolic nanofluid. The nanofluid flow has been assumed to be directed by a wedge on its way. In addition, the collective stimulus of the convective heating mode with thermal radiation is inspected. The governing set of PDEs is rendered into that of the coupled nonlinear ODEs. The resulting ordinary differential equations are then solved by the well known shooting technique for two different cases; the flow over a static wedge and flow over a stretching wedge. The impact of intricate physical parameters on the velocity, temperature and concentration profiles is analyzed graphically. It is noticed that the intensifying values of the generalized Biot number, Brownian motion parameter, thermophoresis parameter and Weissenberg number enhances the dimensionless temperature profile.     

Effects of temperature change on the rheological property of modified multiwall carbon nanotubes

Applied Mathematics and Mechanics - Solvent-free nanofluids hold promise for many technologically significant applications. The liquid-like behavior, a typical rheological property of solvent-free...