Random Motion Of Nanoparticles Research Articles

Cattaneo-Christov heat and mass fluxes model of Casson fluid employing non-Fourier double diffusion theories with ion slip and Hall effects

It is vitally important to comprehend non-Newtonian fluids flow behaviour from an industrial perspective. Non-Newtonian fluids are needed for a number of industrial and technical processes, including the production of paper, photographic films, and polymer sheet extrusion. There are several industrial applications for heat and mass transfer. However, thermal and solute relaxation time phenomena can't be predicted by classical heat and mass transfer laws (Fourier and Fick laws). This work aims to apply the modified Ohm law to thermal and mass transfer which are based on Fick's and generalized Fourier principles, respectively. The current study examines the three-dimensional Darcy-Forchheimer flow of non-Newtonian fluid “Casson fluid” via porous medium with ion slip and Hall effects across a stretched sheet. Thermophoresis and Brownian motion aspects are also considered. The diffusion phenomena are modelled using the Boungrino model. The modified Buongiorno model (MBM) for nanofluids is used to investigate the enhancement of heat transport. Together with practical nanofluid properties, it covers the mechanics of thermo-migration and random motion of nanoparticles. By adding the appropriate similarity transformations, this collection of (PDEs) that reflect the mathematical model is transformed into an (ODEs) system, which it is subsequently resolved utilizing the Lobatto IIIA technique's powerful computing capabilities via Matlab software. Data visualisations and numerical examples are presented considering many physical restrictions affect the fluctuation of velocities, temperatures, concentration, dimensionless shear stress, Nusselt number, and Sherwood number. According to certain findings, the existence of Hall and ion slip effects, and other factors contribute to an increase in horizontal velocity distribution. Furthermore, Fourier's law produces a wider temperature distribution than the Cattaneo-Christov heat flux model.

Introduction to Brownian Motion in Class XII Senior High School 5 Bengkulu City

Brownian motion is the random motion of nanoparticles in the fluid. The concept of Brownian motion is one of the abstract concepts of physics. Thus, it is difficult to learn. Most schools also don't teach Brownian motion in depth in high school. Including the Senior High School 5 Bengkulu City. In fact, there are a lot of Brown motion applications. For this reason, the introduction of Brownian motion in easy-to-understand language needs to be taught to students. The method used in this research is the method of preparation, implementation, and evaluation. From this research, it can be seen that students are very enthusiastic about listening and answering every question that is asked. There is also a very active participation. The competitive spirit of students is also visible. So, it can be concluded that, no matter how difficult and abstract Brown's motion is, if it is taught in simple language, students are also able to understand it well.

The impact of the movement of the gyrotactic microorganisms on the heat and mass transfer characteristics of Casson nanofluid

This article focuses on analyzing the impact of the movement of gyrotactic microorganisms on the heat and mass transfer characteristics of Casson nanofluid flowing between divergent. Further, the analysis is performed through simulation to have a better understanding of the impact. Since the microorganisms are self-propelled, they move on their own in the nanofluid due to the concentration gradient and stabilize the nanoparticle suspension. This movement of microorganisms constitutes the formation of bioconvection. Further, the random motion of nanoparticles gives rise to two major slip mechanisms termed thermophoresis and Brownian motion. The mathematical model comprising these effects is designed using partial differential equations that are converted to ordinary differential equations with the help of suitable similarity transformation. The resulting system of equations is then solved using the differential transformation method and the outcomes are interpreted through graphs. It is indicated that the nanoparticle concentration and the motile density profiles increase with the increase in Schmidt number and also, the concentration profile is found to be increasing for higher Brownian motion parameter and lower thermophoretic parameter. The simulations performed through the finite element method portrayed that the heat flow in the diverging channel is occurring along the isothermal planes.

Experimental investigation of heat transfer and pressure drop in a minichannel heat sink using Al2O3 and TiO2–water nanofluids

Nanofluids are known as a new generation of coolants. These fluids have attracted more attention in cooling applications, like electrical, optical, and solar systems recently, because of their unique rheological and thermal properties. In the present study, to evaluate the thermal behavior of the nanofluids, Al2O3 and TiO2 nanoparticles with the size of 20 nm were completely dispersed in distilled water and circulated in a minichannel heat sink. The heat sink consists of 10 minichannels that have designed to cool thermoelectric generators. The results showed that by only dispersion of 0.5 vol% Al2O3 nanoparticles a 9.30% heat transfer enhancement observed. It was also obtained that the TiO2-water sample showed a 4.56% heat transfer enhancement. The highest efficiency was obtained by utilizing the Al2O3-water nanofluid. This was attributed to the higher thermal conductivity of Al2O3 compared to TiO2. Using both nanofluids resulted in higher pressure drop compared to the based fluid. At the Reynolds number of 1000, the pressure drop for Al2O3 and TiO2 nanofluids increased as 3.33% and 3.88%, respectively. The increased pressure drop was attributed to higher density and viscosity of nanofluids. The classical theories are not available to justify the remarkable heat transfer enhancement obtained by adding a negligible amount of mentioned nanoparticles. It seems that new mechanisms such as the random motion of nanoparticles and generated microconvections by nanoparticle motion in the base fluid are responsible for considerable heat transfer enhancement.

Mhd flow of nanofluids in the presence of porous media, radiation and heat generation through a vertical channel

Aim of present study is to identify the effects of radiation and heat generation in unsteady MHD mixed convective flow of nanofluids along a upstanding channel through porous medium. Four types of nanofluids were studied (i) Water based – Ag (ii) Water based – Al2O3. Water is taken as convectional base fluid and Ag and Al2O3 particles are incorporated in this base fluid. Keeping in mind the congregating and random motion of nanoparticles, “Koo and Kleinstreuer model” is used. The main characteristics of the nanofluids have finer thermo physical properties such as high thermal conductivity, minimal bloking in flow passage, long term solidity and uniformity. The governing boundary layer equations are formulated and reduced to a set of ordinary differential equations using perturbation technique. Solutions are obtained for motion and temperature, discussed and pertinent results are shown through graphs.

Entropy Generation and Consequences of Binary Chemical Reaction on MHD Darcy-Forchheimer Williamson Nanofluid Flow Over Non-Linearly Stretching Surface.

The current article aims to present a numerical analysis of MHD Williamson nanofluid flow maintained to flow through porous medium bounded by a non-linearly stretching flat surface. The second law of thermodynamics was applied to analyze the fluid flow, heat and mass transport as well as the aspects of entropy generation using Buongiorno model. Thermophoresis and Brownian diffusion is considered which appears due to the concentration and random motion of nanoparticles in base fluid, respectively. Uniform magnetic effect is induced but the assumption of tiny magnetic Reynolds number results in zero magnetic induction. The governing equations (PDEs) are transformed into ordinary differential equations (ODEs) using appropriately adjusted transformations. The numerical method is used for solving the so-formulated highly nonlinear problem. The graphical presentation of results highlights that the heat flux receives enhancement for augmented Brownian diffusion. The Bejan number is found to be increasing with a larger Weissenberg number. The tabulated results for skin-friction, Nusselt number and Sherwood number are given. A decent agreement is noted in the results when compared with previously published literature on Williamson nanofluids.

A solid-liquid local thermal non-equilibrium lattice Boltzmann model for heat transfer in nanofluids. Part II: Natural convection of nanofluids in a square enclosure

The novel solid-liquid local thermal non-equilibrium lattice Boltzmann model, developed in Part I of this paper series [1], is applied to the classical problem of natural convection of nanofluids in a square enclosure with vertical walls at differential temperatures. Effects of Rayleigh numbers, nanoparticles random motion, nanoparticles volume fraction and nanoparticles non-uniform distribution in natural convection of nanofluids are studied. Because random motions of nanoparticles are intensified with temperature, vertical velocity and temperature profiles in the nanofluid are asymmetric with respect to the hot and cold vertical walls. Distribution of nanoparticles in the nanofluid inside the enclosure is affected by both the Rayleigh number and random motion of nanoparticles, and nanoparticles’ distribution become relatively non-uniform at relatively high Rayleigh numbers. The non-uniform distribution of nanoparticles also affect local vertical velocity distribution, local temperature distribution, and the average Nusselt numbers. The effect of random motion of nanoparticles is shown to be responsible for enhanced convection at small Rayleigh numbers, the increasing viscosity of nanofluids is shown to be responsible for the deteriorating effects on heat transfer at intermediate Rayleigh numbers and non-uniform distribution of nanoparticles is shown to be responsible for ascending trend of Nusselt numbers at high Rayleigh numbers. The non-monotonous variation of the Nusselt number with respect to the Rayleigh number are in qualitative agreement with existing experimental data.

A solid-liquid local thermal non-equilibrium lattice Boltzmann model for heat transfer in nanofluids. Part I: Model development, shear flow and heat conduction in a nanofluid

A solid-liquid local thermal non-equilibrium lattice Boltzmann model for hydrodynamics and heat transfer in a nanofluid is developed in this paper. In this proposed model, interactions between fluid and solid nanoparticles, random motion of nanoparticles as well as heat transfer between nanoparticles and the base fluid are taken into consideration. This novel model is applied to two simple nanofluids problems: isothermal shear flow between two parallel plates moving at different velocities, and heat conduction between two parallel plates at different temperatures. For the problem of shear flow, it is found that nanoparticles random motion causes the instantaneous velocity distribution of a nanofluid to become non-linear in the shear flow between two parallel plates at microscopic level. At macroscopic level, it is found that as nanoparticles volume fraction increases, effects of nanoparticles random motion are enlarged and the time-average velocity distribution of a nanofluid deviates more from a linear distribution in a shear flow. For the problem of heat conduction between parallel plates at different temperatures, it is found that random motion of nanoparticles together with their high thermal diffusivity and thermal conductivity, causing the instantaneous temperature distribution in the nanofluid to become non-linear between two parallel plates at different temperatures. Temperature inside a nanoparticle is shown to be non-uniform, and temperature gradients in the fluid near a nanoparticles are elevated, thus heat transfer rate is enhanced near a nanoparticle. Time-average temperature gradients of a nanofluid at hot/cooled wall are higher than those of a pure fluid in heat conduction between parallel plates at different temperatures. Comparisons of calculated dynamic viscosity and thermal conductivity based on this novel model are found in good agreement with existing correlation equations. Thus, the accuracy of this novel solid–liquid local thermal non-equilibrium model for a nanofluid is validated.

A mathematic model considering the effect of Brownian motion for subcooled nucleate pool boiling of dilute nanofluids

A new mathematic model was presented to investigate the nucleate pool boiling of nanofluids. The model considered the heat exchange due to Brownian motion of nanoparticles. A new closure correlation is also included in the model to count the active site density and the bubble departure diameter, which were calculated based on the experimental data of a nucleate pool boiling. The new model combines with two-fluid boiling model was used to simulate the nucleate pool boiling process. The simulation focused on the heat transfer due to Brownian motion of nanoparticle. The purpose is to improve surface heat exchange which was induced by the random motion of nanoparticles during the boiling process. The results give a reasonable agreement with the experimental data of nanofluids nucleation boiling with lower heat flux (lower than 100kW/m2) and Nusselt number of 200. The simulation result indicates that the predicted accuracy for a nucleate boiling process of nanofluids can be improved by taking into account both the Brownian motion of nanoparticles and the nucleate site density due to the surface morphology modification.

Nanofluids transport model based on Fokker-Planck equation and the convection heat transfer calculation

In current research about nanofluid convection heat transfer, random motion of nanoparticles in the liquid distribution problem mostly was not considered. In order to study on the distribution of nanoparticles in liquid, nanofluid transport model in pipe is established by using the continuity equation, momentum equation and Fokker-Planck equation. The velocity distribution and the nanoparticles distribution in liquid are obtained by numerical calculation, and the effect of particle size and particle volume fraction on convection heat transfer coefficient of nanofluids is analyzed. The result shows that in high volume fraction (φ = 0.8% ), the velocity distribution of nanofluids characterizes as a “cork-shaped” structure, which is significantly different from viscous fluid with a parabolic distribution. The convection heat transfer coefficient increases while the particle size of nanoparticle in nanofluids decreases. And the convection heat transfer coefficient of nanofluids is in good agreement with the experimental result both in low (φ ⩽0.1% ) and high (φ=0.6% ) volume fractions. In presented model, Brown motion, the effect of interactions between nanoparticles and fluid coupling, is also considered, but any phenomenological parameter is not introduced. Nanoparticles in liquid transport distribution can be quantitatively calculated by this model.

Many‐body effects in optically‐trapped metallic nanoparticles under thermal fluctuations

AbstractWe have theoretically studied light‐induced many‐body dynamics of metallic nanoparticles (NPs) under the focused laser beam and the thermal fluctuations in liquid medium at room temperature. The effect of surface ionization is also taken into account. The random motion of NPs by collisions of medium molecules can be suppressed with increasing the laser intensity, and the transition from a diffusive state to metastable states of metallic NPs is possible. Obtained results will provide a novel way to control the phase transitions in assembled structure of NPs under the balance of optically‐modulated interparticle forces and thermal fluctuations. Such a mechanism is significantly different from a conventional gas‐liquid‐solid transition based on spontaneous interparticle forces because it is based on the transient anisotropic force controlled by light (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

COLLISION EFFICIENCY OF BROWNIAN COAGULATION FOR NANOPARTICLES TAKING INTO ACCOUNT THE SLIP BOUNDARY CONDITION ON THE PARTICLE SURFACE

The collision efficiency of Brownian coagulation for monodisperse nanoparticles is considered. A new expression for friction coefficient of particle pair is proposed based on an assumption from a statistical point of view and the relative diffusion coefficient is thus be modified in order to take into account this influence as well as the effects of slip. The modified diffusion coefficient increases the collision efficiency to some extent as expected whether van der Waals interparticle potential is considered or not. A comparison with experimental measurements shows the accuracy of the results predicted by modified theory and the necessity of considering the decrease of friction coefficient due to the random motion of nanoparticles as well as the slip effects arising from the finite mean free path of gas molecules.

Facilitated transport enhances spray layer-by-layer assembly of oppositely charged nanoparticles

We investigate the fundamental mechanism of spray-assisted layer-by-layer (LbL) assembly of oppositely charged silica nanoparticles. Alteration of the major operating parameters such as suspension concentration, spray flow rate, and spray duration allows us to develop a kinetic model for spray-assisted LbL deposition. The spray-deposition mechanism is broken down into two sequential mass transport steps: bulk spray flux to the substrate surface followed by random motion of nanoparticles through a thin liquid film that adheres to the substrate throughout the spray procedure. We demonstrate that the second transport step limits the overall deposition rate, and we examine the importance of a convective driving force in accelerating this random motion close to the substrate by controlling the depth of the liquid film atop the substrate. Finally, we generalize the idea of convective acceleration and find that sufficient agitation can be used to enhance the rate of dip layer-by-layer assembly as well.