Entropy generation analysis for peristaltically driven flow of hybrid nanofluid

Present study investigates entropy generation analysis for peristaltic motion of hybrid nanofluid. Hybrid nanofluid is composed of iron-oxide and copper nanoparticles suspended in water. Effects of Hall current, Ohmic heating and mixed convection are taken into account. Governing equations are simplified by utilizing lubrication approach. The numerical solutions for resulting system of differential equations are obtained with the aid of Shooting method. Attention has been given to the analysis of hybrid nanoparticles, Hall parameter and Grashoff number on entropy generation, heat transfer rate, velocity profile and pressure gradient. Outcomes reveal that insertion of nanoparticles decreases the temperature of hybrid nanofluid. It is found that increase in Hall parameter reduces the heat transfer rate at wall. Increment in Hall parameter reduces the entropy generation. Velocity and pressure gradient increases by enhancing Grashoff number. It is believed that the present flow model can prove useful in improving the efficiency of similar thermodynamical systems.     

基于基液连续假设的大体系Cu-H2O纳米流体输运特性的模拟研究

分子动力学模拟是研究纳米流体的输运特性的重要手段, 但计算量庞大. 为研究能体现流动传热过程的大体系纳米流体的输运特性, 本文对基液采用连续介质假设, 将基液的势能拟合在纳米团簇的势能中, 大幅度减小了计算量, 使得大体系输运特性的模拟成为可能, 且模拟结果与多组实验结果吻合较好. 采用此方法模拟研究了速度梯度剪切对Cu-H₂O纳米流体颗粒聚集过程和聚集特性的影响, 进而对Cu-H₂O纳米流体在流动传热过程中的热导率和黏度进行了模拟计算, 定量揭示了宏观流动传热过程中不同的速度梯度、速度、平均温度和温度梯度对于Cu-H₂O纳米流体热导率和黏度的影响.     

Pumping power of nanofluids in a flowing system

Nanofluids have the potential to increase thermal conductivities and heat transfer coefficients compared to their base fluids. However, the addition of nanoparticles to a fluid also increases the viscosity and therefore increases the power required to pump the fluid through the system. When the benefit of the increased heat transfer is larger than the penalty of the increased pumping power, the nanofluid has the potential for commercial viability. The pumping power for nanofluids has been considered previously for flow in straight tubes. In this study, the pumping power was measured for nanofluids flowing in a complete system including straight tubing, elbows, and expansions. The objective was to determine the significance of two-phase flow effects on system performance. Two types of nanofluids were used in this study: a water-based nanofluid containing 2.0–8.0 vol% of 40-nm alumina nanoparticles, and a 50/50 ethylene glycol/water mixture-based nanofluid containing 2.2 vol% of 29-nm SiC nanoparticles. All experiments were performed in the turbulent flow region in the entire test system simulating features typically found in heat exchanger systems. Experimental results were compared to the pumping power calculated from a mathematical model of the system to evaluate the system effects. The pumping power results were also combined with the heat transfer enhancement to evaluate the viability of the two nanofluids.     

电加热结构内纳米流体稳定性实验研究

实验以比例为4:6的乙二醇水溶液(EGW)为基液,采用两步法制备了质量分数为0.5%、1.0%、1.5%和2.0%的Cu-EGW、Al₂O₃-EGW和Fe₃O₄-EGW纳米流体。通过分段加热测试,对比分析了三种纳米流体在电加热结构中的加热效果,并研究了Cu-EGW纳米流体的热稳定性。实验结果表明,在三种纳米流体中Cu-EGW纳米流体获得了最优的加热效果;在30天后再次测试发现以Cu-EGW纳米流体作为加热工质时,中间翅片上部平均温度降低了7.4%,被加热环境平均温度降低了3.8%。     

Models base study of inclined MHD of hybrid nanofluid flow over nonlinear stretching cylinder

Focus of the present analysis is on the stagnation point flow of hybrid nanofluid with inclined magnetic field over a moving cylinder. The extended version of two models (e.g. Xue model and Yamada-Ota model for hybrid nanofluids) are considered in this study). A mathematical model of hybrid nanofluid flow is developed under certain flow assumptions. Boundary layer approximations are also utilized to model a system of partial differential equations. The systems of partial differential equations are further converted to dimensionless systems of ordinary differential equations by means of suitable similarity transformations. A numerical solution is obtained by applying bv4c technique. Effects of variation in physical parameters involved are depicted through graphs. Skin friction coefficient and Nusselt number are highlighted through tables. Our main objective is to investigate the heat transfer rate on the surface of the nonlinear stretching cylinder. The results of Xue model and Yamada-Ota model for the hybrid nanofluid due to nonlinear stretching cylinder are computed for comparison. In both cases, velocity and temperature profiles are best compared to the decay results.     

Entropy generation minimization and statistical declaration with probable error for skin friction coefficient and Nusselt number

Main emphasis of present work is to analyze the novel feature of entropy generation in MHD nanomaterial flow between two rotating disks. Heat transfer process is explored in the presence of Joule heating and thermal radiation. Tiwari–Das nanofluid model is employed in mathematical modeling. Aluminum oxide and copper water nanoparticles are accounted. Statistical declaration and probable error for problem accuracy are computed. Total entropy generation subject to Bejan number is scrutinized. Suitable variables are utilized to transform nonlinear PDEs to ordinary ones. Convergent series solutions are computed. Zeroth and mth order problems are discussed for stability analysis. The impact of physical flow variables like Reynolds number, magnetic parameter, porosity parameter, stretching parameter, rotational parameter, radiation parameter, Eckert number, suction injection parameter, Brinkman number and temperature ratio parameter on velocities, temperature, total entropy generation and Bejan number are examined and discussed through graphs. Velocity and thermal gradients at the surface of disks are computed.     

Nanofluidics in the Debye layer at hydrophilic and hydrophobic surfaces

By using evanescent waves, we study equilibrium and dynamical properties of liquid-solid interfaces in the Debye layer for hydrophilic and hydrophobic surfaces. We measure velocity profiles and nanotracer concentration and diffusion profiles between 20 and 300 nm from the walls in pressure-driven and electro-osmotic flows. We extract electrostatic and zeta potentials and determine hydrodynamic slip lengths with 10 nm accuracy. The spectacular amplification of the zeta potential resulting from hydrodynamic slippage allows us to clarify for the first time the dynamic origin of the zeta potential.     

Peristaltic transport of magneto-nanoparticles submerged in water: Model for drug delivery system

Recent development in biomedical engineering has enabled the use of the magnetic nanoparticles in modern drug delivery systems with great utility. Nanofluids composed of magnetic nanoparticles have the characteristics to be manipulated by external magnetic field and are used to guide the particles up the bloodstream to a tumor with magnets. In this study we examine the mixed convective peristaltic transport of copper–water nanofluid under the influence of constant applied magnetic field. Nanofluid is considered in an asymmetric channel. Aside from the effect of applied magnetic field on the mechanics of nanofluid, its side effects i.e. the Ohmic heating and Hall effects are also taken into consideration. Heat transfer analysis is performed in presence of viscous dissipation and heat generation/absorption. Mathematical modeling is carried out using the lubrication analysis. Resulting system of equations is numerically solved. Impact of embedded parameters on the velocity, pressure gradient, streamlines and temperature of nanofluid is examined. Effects of applied magnetic field in presence and absence of Hall effects are studied and compared. Results depict that addition of copper nanoparticles reduces the velocity and temperature of fluid. Heat transfer rate at the boundary enhances by increasing the nanoparticles volume fraction. Increase in the strength of applied magnetic field tends to decrease/increase the velocity/temperature of nanofluid. Further presence of Hall effects reduces the variations brought in the state of fluid when strength of applied magnetic field is increased.     

基于晶格-Boltzmann方法的纳米流体流动和传热模型

纳米流体是由流体与纳米粒子组成的悬浮体.悬浮在流体中的纳米粒子会受到运动阻力、布朗力、扩散力和重力等作用力的影响,因而其运动规律极其复杂.本文运用晶格-Boltzmann(LB)方法,建立纳米流体流动和传热模型模型,对纳米流体的流型结构和温度场进行了模拟和分析.     

New thermodynamics of entropy generation minimization with nonlinear thermal radiation and nanomaterials

This research addressed entropy generation for MHD stagnation point flow of viscous nanofluid over a stretching surface. Characteristics of heat transport are analyzed through nonlinear radiation and heat generation/absorption. Nanoliquid features for Brownian moment and thermophoresis have been considered. Fluid in the presence of constant applied inclined magnetic field is considered. Flow problem is mathematically modeled and governing expressions are changed into nonlinear ordinary ones by utilizing appropriate transformations. The effects of pertinent variables on velocity, nanoparticle concentration and temperature are discussed graphically. Furthermore Brownian motion and thermophoresis effects on entropy generation and Bejan number have been examined. Total entropy generation is inspected through various flow variables. Consideration is mainly given to the convergence process. Velocity, temperature and mass gradients at the surface of sheet are calculated numerically.     

Thermal performance of Joule heating in Oldroyd-B nanomaterials considering thermal-solutal convective conditions

The nanotechnology expansion has contributed vastly in explaining major difficulties in industrial and medicinal sciences. Flexibility of nanofluids prepared of nanoparticles is recognized essentially to the magnitude, shape, variety and ionic structure of the elements. Explicitly, the usage of nanofluids for heat intensification and mass transport is of varied application and it is increasing concern from investigators. In current study we incorporated convective conditions in chemically reactive radiated Oldroyd-B nanofluid with buoyancy influence. Additionally, magnetic and Joule heating aspects are considered. The noteworthy alterations altered the PDEs into ODEs and interpreted via homotopic algorithm. The aspects of influential variables are depicted and conferred. Here thermal and solutal Biot numbers have analogous impact respectively, on temperature and concentration fields. The current outcomes are also authenticated with obtainable prose.     

Optimization of ultrasonication period for better dispersion and stability of TiO2–water nanofluid

Nanofluids are promising in many fields, including engineering and medicine. Stability deterioration may be a critical constraint for potential applications of nanofluids. Proper ultrasonication can improve the stability, and possibility of the safe use of nanofluids in different applications. In this study, stability properties of TiO₂–H₂O nanofluid for varying ultrasonication durations were tested. The nanofluids were prepared through two-step method; and electron microscopies, with particle size distribution and zeta potential analyses were conducted for the evaluation of their stability. Results showed the positive impact of ultrasonication on nanofluid dispersion properties up to some extent. Ultrasonication longer than 150 min resulted in re-agglomeration of nanoparticles. Therefore, ultrasonication for 150 min was the optimum period yielding highest stability. A regression analysis was also done in order to relate the average cluster size and ultrasonication time to zeta potential. It can be concluded that performing analytical imaging and colloidal property evaluation during and after the sample preparation leads to reliable insights.     

Impacts of ultrasonication time and surfactants on stability and optical properties of CuO,Fe3O4, and CNTs/water nanofluids for spectrum selective applications

The prime objective of the present experimental work is to evaluate the impact of ultrasonication time and surfactants on the optical characteristics (transmittance and absorbance) and stability of CuO/water, CNTs/water, and Fe₃O₄/water nanofluids to be used in spectrum selective applications. Two-step method with various ultrasonication times (30 min, 60 min, and 90 min) was employed to prepare nanofluids (having volume fractions of 0.004 % and 0.0004 %). Furthermore, various surfactants (anionic, cationic, and polymer) were added to the base fluid. The study results revealed that surfactants have a significant effect on the stability of nanofluids over ultrasonication time. The nanofluids prepared using sodium dodecylbenzene sulfonate (SDBS) have the highest zeta potential values than other surfactants used in the experimentation. The increase in transmittance of nanofluid was more prominent for lower concentration (0.0004 %) after one week of preparation. The concentration of nanoparticles, ultrasonication time, temperature, and surfactants influenced the optical characteristics of nanofluids. The most stabled CNTs nanofluid with 0.004 % concentration and 90 min of ultrasonication obtained an average of 67.6 % and 74.6 % higher absorbance than stabled CuO and Fe₃O₄ nanofluids, respectively. The irradiance transmitted through nanofluid was strongly dependent on the concentration and type of nanoparticles.     

Ultrasonically tuned surface tension and nano-film formation of aqueous ZnO nanofluids

Nanofluids’ thermophysical properties and heat transfer performance has been investigated for many years, while research on their surface tension (ST) and wetting behavior is very limited. To assess nanofluids potential as industrial products, a complete picture is required to prove their performance in a specific application. Boiling heat transfer, microfluidics and drug development are among the applications where ST is a variable. ST of water-based ZnO nanofluids were measured in the presence and absence of direct ultrasonication. The experiments covered variation of ST with ZnO concentration (0.05–0.4 vol%), ultrasonication amplitude (40% and 100%) and duration. To the best of the authors’ knowledge, this is the first report of ST– ultrasonication process relation for a nanofluid. Results showed that after direct ultrasonication, nanofluids ST is strongly affected by the temperature raise, and in those cases relative ST may provide a clearer picture. A nano-film over individual and agglomerated nanoparticles spotted via TEM imaging was affected from the ultrasonication. Such a nano-film can play a key role in the anomalous thermal transport and wettability of nanofluids. Statistical analyses revealed that changes in ultrasonication amplitude resulted in a statistically significance difference on nanofluid ST and relative ST. Changes in nanoparticle concentration caused a significant difference on the nanofluid ST while the difference in relative ST was insignificant. Variation of ultrasonication duration caused significant variations on the relative ST while the difference in nanofluid ST was not significant. This work highlights that based on specific applications ST and other related features of any nanofluid can be adjusted employing proper ultrasonication conditions.     

Physical aspects of magnetized Jeffrey nanomaterial flow with irreversibility analysis

This research presents the applications of entropy generation phenomenon in incompressible flow of Jeffrey nanofluid in the presence of distinct thermal features. The novel aspects of various features, such as Joule heating, porous medium, dissipation features, and radiative mechanism are addressed. In order to improve thermal transportation systems based on nanomaterials, convective boundary conditions are introduced. The thermal viscoelastic nanofluid model is expressed in terms of differential equations. The problem is presented via nonlinear differential equations for which analytical expressions are obtained by using the homotopy analysis method (HAM). The accuracy of solution is ensured. The effective outcomes of all physical parameters associated with the flow model are carefully examined and underlined through various curves. The observations summarized from current analysis reveal that the presence of a permeability parameter offers resistance to the flow. A monotonic decrement in local Nusselt number is noted with Hartmann number and Prandtl number. Moreover, entropy generation and Bejan number increases with radiation parameter and fluid parameter.     

Dual solutions for Casson hybrid nanofluid flow due to a stretching/shrinking sheet: A new combination of theoretical and experimental models

Using the experimental relations for approximating the effective thermophysical properties of a water/MgO-Ag hybrid nanofluid is the novelty of the present investigation in order to simulate the two dimensional MHD Casson flow past a linearly stretching/shrinking sheet with suction, radiation and convective boundary condition effects. The dual solutions along with its stability analysis are also taken into account. The Tiwari-Das mathematical formulation coupled with mass-based hybrid nanofluid model is implemented to write the governing PDEs which are then transferred to a complicated system of dimensionless ODEs with help of the similarity transformation technique. Then a well-known finite difference method with forth order accuracy in MATLAB is employed to solve them. It is proved that the selective experimental relations for effective thermophysical models must be considered more serious in the numerical modeling of hybrid nanofluids in the future. Moreover, results indicate that the range of the Casson fluid parameter for which the solution exists, enhances with radiation parameter, suction parameter and also second nanoparticle mass. Also it is shown that the magnetic field which is applied normal to the sheet results in boost up the similarity velocity profiles into the hydrodynamic boundary layer.     

卷曲效应对单壁碳纳米管电子结构的影响

利用计入卷曲效应的单壁碳纳米管(SWCNT)的能量色散关系,计算最低导带的电子速度及有效质量,并与不计入卷曲效应的结果进行了比较.计算结果表明:卷曲效应对电子速度及有效质量的影响与SWCNT的类型密切相关,金属锯齿型SWCNT对卷曲效应最为敏感,其次是扶手椅型SWCNT,最不敏感的是半导体锯齿型SWCNT.由此可以推断,卷曲效应对金属锯齿型SWCNT电子结构及低偏压输运特性影响最大,其次是扶手椅型SWCNT,影响最不明显的是半导体锯齿型SWCNT.这些结果与实验测量及密度泛函理论计算结果完全一致. 关键词： 单壁碳纳米管 卷曲效应 电子速度 电子有效质量