Brownian Motion Of Nanoparticles Research Articles

A microscopic experimental study of nanoparticle motion for the enhancement of oxygen absorption in nanofluids

Abstract The behavior of nanoparticle motion has a great influence on gas-liquid mass transfer. However, it has been very difficult to characterize the motion of nanoparticles from a micro view in mass transfer experiments. In this study, a novel method was proposed to investigate nanoparticle Brownian motion through the application of the total internal reflection fluorescence microscope in a self-designed sample (a quasi-static liquid micro-groove) and the mass transfer enhancement of nanoparticles. Nanoparticle movement behavior was photographed using an electron-multiplying charge coupled device, and 100 consecutive images were recorded using Micro-Manager software at a rate of 20 fps. The images were processed through the particle tracking velocimetry algorithm to calculate two-dimensional motion rates of nanoparticles caused by Brownian movement. It showed that nanoparticle loadings influenced the motion rates significantly, and the motion rates were larger with smaller particle sizes under the same operating condition. The mass transfer coefficients in the quasi-static gas-liquid mass transfer system were calculated and analyzed through microscopic measurement. Based on the above thought, three important non-dimensional numbers [Sherwood (Shp ), Reynolds (Rep ), and Schmidt (Scp ) numbers] for mass transfer theory were studied.

A model for entropy generation in stagnation‐point flow of non‐Newtonian Jeffrey, Maxwell, and Oldroyd‐B nanofluids

AbstractWe present a generalized model to describe the flow of three non‐Newtonian nanofluids, namely, Jeffrey, Maxwell, and Oldroyd‐B nanofluids. Using this model, we study entropy generation and heat transfer in laminar nanofluid boundary‐layer stagnation‐point flow. The flow is subject to an external magnetic field. The conventional energy equation is modified by the incorporation of nanoparticle Brownian motion and thermophoresis effects. A hydrodynamic slip velocity is used in the initial condition as a component of the stretching velocity. The system of nonlinear equations is solved numerically using three different methods, a spectral relaxation method, spectral quasilinearization method, and the spectral local linearization method, first to determine the most accurate of these methods, and second as a measure to validate the numerical simulations. The residual errors for each method are presented. The numerical results show that the spectral relaxation method is the most accurate of the three methods, and this method is used subsequently to solve the transport equations and thus to determine the empirical impact of the physical parameters on the fluid properties and entropy generation.

Determination of nanolayer thickness and effective thermal conductivity of nanofluids

Nanofluids having high thermal conductivity enhancement relative to conventional pure fluids are fluids engineered by suspending solid nanoparticles into base fluids. In the present study, calculating the Van der Waals interaction energy between a nanoparticle and an ordered liquid nanolayer around it, the nanolayer thickness was determined, the average velocity of the Brownian motion of nanoparticles in a fluid was estimated, and by taking into account both the aggregation of nanoparticles and the presence of a nanolayer a new thermal conductivity model for nanofluids was proposed. It has been shown that the nanolayer thickness in nanofluids is independent on the radius of nanoparticles when the radius of the nanoparticles is much greater than the nanolayer thickness and determines by the specific interaction of the given liquid and solid nanoparticle through the Hamaker constant, the surface tension and the wetting angle. It was proved that the frequency of heat exchange by fluid molecules is two orders of magnitude higher than the frequency of heat transfer by nanoparticles, so that the contribution due to the Brownian motion of nanoparticles in the thermal conductivity of nanofluids can be neglected. The predictions of the proposed model of thermal conductivity were compared with the experimental data and a good correlation was achieved.

Numerical simulation of couple stress nanofluid flow in magneto-porous medium with thermal radiation and a chemical reaction

We present a study of heat and mass transfer for a couple stress nanofluid flow in a magneto-porous medium with thermal radiation and heat generation. The flow is generated by a stretching surface and the temperature and concentration distributions are studied subject to nanoparticle Brownian motion and thermophoresis effects. The nonlinear model equations have been solved using a spectral quasi-linearization method. The solution method has been used in a limited number of studies in the resent past. Its general reliability for a wider range of problems remains to be determined. Thus in order to determine the accuracy of the solutions, and the convergence of the method, a qualitative presentation of residual errors for different parameters is given. Additionally, for some special flow cases, the current results have been compared with previously published work and found to be in good agreement. A limited parametric study showing the influence of the flow parameters on the fluid properties is given. The numerical analysis of the residual error of PDEs and convergence properties of the method are also discussed. The method is computationally fast and gives very accurate results after only a few iterations using very few grid points in the numerical discretization process. The aim of this manuscript is to pay more attention of residual error analysis with heat and fluid flow on couple stress nanofluids to improve the system performance. Also the fluid temperature in the boundary layer region rise significantly for increasing the values of thermophoresis and Brownian motion parameter. The results show that wall shear stress increases by increasing couple stress parameter.

Pulsating flow and magnetic field effects on the convective heat transfer of TiO2-water nanofluids in helically corrugated tube

Both passive heat transfer enhancement techniques; nanofluids, helically corrugated rib and active heat transfer enhancement techniques; pulsating flow, magnetic field on the convective heat transfer and flow characteristics in the helically corrugated tube are investigated. Experiments set up are designed and constructed to test by varying nanofluids mass flow rate of 0.01–0.10 kg/s, nanofluids concentrations of 0.25%, 0.50% by volume, and nanofluids pulsating flow frequency of 10, 15, 20 Hz and the helically corrugated rib with the depth and pitch of 1.25 mm, 6.35 mm, respectively. As comparing with the plain tube, the physical properties by using nanoparticles and disturbing at the thermal boundary zone of working fluid have significant effect on the enhancement of heat transfer. In addition, the disturbing of nanoparticles Brownian motion suspending in the based fluid by magnetic field and pulsating flow frequency have also significant increment of heat transfer. It can be seen that a combined heat transfer enhancement techniques are satisfy the practical applications to improve the thermal performance of thermal devices.

Three-dimensional rotating flow of MHD single wall carbon nanotubes over a stretching sheet in presence of thermal radiation

In this article the modeling and computations are exposed to introduce the new idea of MHD three-dimensional rotating flow of nanofluid through a stretching sheet. Single wall carbon nanotubes (SWCNTs) are utilized as a nano-sized materials while water is used as a base liquid. Single-wall carbon nanotubes (SWNTs) parade sole assets due to their rare structure. Such structure has significant optical and electronics features, wonderful strength and elasticity, and high thermal and chemical permanence. The heat exchange phenomena are deliberated subject to thermal radiation and moreover the impact of nanoparticles Brownian motion and thermophoresis are involved in the present investigation. For the nanofluid transport mechanism, we implemented the Xue model (Xue, Phys B Condens Matter 368:302–307, 2005). The governing nonlinear formulation based upon the law of conservation of mass, quantity of motion, thermal field and nanoparticles concentrations is first modeled and then solved by homotopy analysis method (HAM). Moreover, the graphical result has been exposed to investigate that in what manner the velocities, heat and nanomaterial concentration distributions effected through influential parameters. The mathematical facts of skin friction, Nusselt number and Sherwood number are presented through numerical data for SWCNTs.

Radiation and heat generation effects in magnetohydrodynamic mixed convection flow of nanofluids

Radiation and heat generation effects in unsteady magnetohydrodynamic (MHD) mixed convection flow of nanofluids along a vertical channel are investigated. Silver ()Ag nanoparticles of spherical shapes and of different sizes in water as a convectional base fluid are incorporated. The purpose of this study is to measure the effect of different sizes of nanoparticles on velocity and temperature. Keeping in mind the size, particle material, shape, clustering and Brownian motion of nanoparticles, Koo and Kleinstreuer model is used. The problem is modelled in terms of partial differential equations with physical boundary conditions. Analytical solutions are obtained for velocity and temperature, plotted and discussed. It is concluded that increasing the size of Ag nanoparticles (up to specific size (30 nm ) results in a very small velocity increment while for large particle size (30 nm -100nm ), no change in velocity is observed. As the small size of nanoparticles has the highest thermal conductivity and viscosity. This change in velocity with size of nanoparticles is found only in water-based nano fluids with low volume fraction 0.01 while at low volume concentration, no change is observed.

Solidification enhancement of PCM in a triplex-tube thermal energy storage system with nanoparticles and fins

This study is on the application of nanoparticles and fins for improved phase change material (PCM) solidification in a heat exchanger. A major challenge in using PCMs is their poor thermal conductivities which consequently prolongs phase change processes giving rise to very slow charging/discharging rates. This seriously affects energy storage and recovery times, signifying the need for heat transfer enhancement in these systems. A model that considers heat conduction in the fins, natural convection in the liquid PCM, and Brownian motion of nanoparticles in the PCM was developed and validated with experimental data in this study. The influence of different dimensions of fins and volume concentrations of nanoparticles on PCM solidification evolution was studied. The effect of using fins alone, nanoparticles alone and combination of both on the solidification was investigated. Because of the extra added volume which limits available volume for PCM storage, the fin, nanoparticle and total volume fractions were used to evaluate volume usage associated with each technique. Results from the study show remarkable findings including substantial reduction in the PCM solidification time. It was also found that the application of fins alone shows better enhancement than using either nanoparticles alone or combination of fins and nanoparticles.

Peristaltically assisted nanofluid transport in an asymmetric channel

This paper aims to study the diffusion-thermo analysis on the peristaltic flowing pseudoplastic nanofluid in an asymmetric channel. Mathematical formulation is based on basic laws and governing equations of pseudoplastic nanofluid under long wavelength approach. Solution is developed numerically with a focus towards the effects of thermophoretic diffusion and Brownian motion of nano particle. Diverse parameters approaching the problem are studied on velocity, stream function, concentration, pressure drop and temperature. Moreover, comparison between pseudoplastic and viscous nanofluid is also given in the present study.

Effect of nanoparticles Brownian motion and uniform sinusoidal roughness elements on natural convection in an enclosure

The aim of the present study is to examine natural convection heat transfer in a square cavity filled with Al2O3–water nanofluid using lattice Boltzmann method. Right and left walls are kept at hot and cold constant temperatures, respectively, while uniform sinusoidal roughness elements are placed on both walls. Effective viscosity and thermal conductivity of nanofluid are obtained using Koo–Kleinstreuer model implementing Brownian motion of nanoparticles. The influence of pertinent parameters, such as Rayleigh number, solid volume fraction of nanoparticles, frequency and dimensionless amplitude of uniform sinusoidal roughness elements, on flow and heat transfer fields is investigated in the present paper. Results show an increase in Nusselt number with increasing nanoparticles volume fraction for various Rayleigh numbers with their most prominent effect at φ = 0.04 for Ra = 103. Moreover, it was observed that mean Nusselt number decreases by increasing frequency and dimensionless amplitude of roughness elements for the whole range of Rayleigh numbers. In general, effect of nanoparticles on heat transfer enhancement is more highlighted by considering the role of Brownian motion.

Experimental study on laminar pulsating flow and heat transfer of nanofluids in micro-fins tube with magnetic fields

A combined heat transfer enhancement techniques: pulsating flow, nanofluids, micro-fins tube, and magnetic field on the heat transfer and flow characteristics in the micro-fins tube are investigated. Experiments are performed under conditions of nanofluids Reynolds number varying from 1000 to 2400 and nanofluids concentrations of 0.25%, 0.50% by volume. The inlet nanofluids and uniform wall heat input are 20 °C, and 120–160 W, respectively while the nanofluids frequency pulsating flow through the test section is 10–20 Hz. The results obtained from the micro-fins tube with magnetic field are compared with those without magnetic field and those from the smooth tube with and without magnetic fields. It can be seen that a combined heat transfer enhancement techniques are a good potential to improve the thermal performance of thermal devices. The pulsating flow and magnetic field have an advantage on the Brownian motion of nanoparticles in the base fluid flowing through the system. Results show that the heat transfer enhancement increases significantly with increase in nanoparticle concentration, magnetic field strength, and with the pulsating frequency. However, they are slightly effect on the pressure drop.

Lattice Boltzmann simulation of temperature jump effect on the nanofluid heat transfer in an annulus microchannel

In this study, laminar forced convection heat transfer of water-alumina nanofluid flow inside an annular microchannel in slip flow regime is investigated by lattice Boltzmann method. Uniform velocity and temperature distributions are assumed at the microchannel inlet. Internal wall is insulated and outer wall is heated uniformly with constant heat flux. In both models that are used to express the kinematic viscosity and thermal conductivity of the nanofluid, the effects of nanoparticles size and Brownian motion are considered. A lattice-Boltzmann computer code is developed and the results are compared with the existing analytical solutions in the literature. In this paper, the effect of various parameters such as nanoparticles volume fraction (0–0.05), diameter (10–100 nm), microchannel radius ratio (0.2–0.8), Reynolds number (5, 10 and 50) and the slip factor (0.005–0.1) on the flow and temperature field are studied. Furthermore, variations of slip velocity, temperature jump, friction factor and Nusselt number along the walls are provided. Results indicate that higher slip factor, radius ratio, Re and volume fractions and also smaller particle diameters, increases the Nusselt number. Also slip velocity and temperature jump increases with slip factor. Nanoparticles volume fraction doesn't have significant effect on slip velocity, while increases the temperature jump.

Solidification enhancement in a triplex-tube latent heat energy storage system using nanoparticles-metal foam combination

Thermal storage systems utilizing Phase Change Materials (PCMs) are known to exhibit slow thermal response. This is mainly due to the relatively low thermal conductivity of most PCMs used in the systems. Thus packing the PCMs in better performing containment vessels and/or employing heat transfer enhancement additives is required for improved performance of these systems. Nanoparticle-metal foam combination as a compound enhancement approach along with triplex-tube heat exchanger as a modified exchanger design were used in this study to improve the PCM solidification rate. A mathematical model based on the thermal equilibrium assumption which takes into account the non-Darcy effects of porous foam and the Brownian motion of nanoparticles was formulated and validated with previous related experimental studies. The influence of nanoparticle volume fraction and metal foam porosity on the evolution of the solid-liquid interfaces, distribution of isotherms, and liquid-fraction profile over the whole solidification process was studied. Results show that dispersing nanoparticles in the presence of metal foams results in total time saving up to 96% depending on foam structure and volumetric nanoparticle concentration.

Numerical simulation of the nanoparticle diameter effect on the thermal performance of a nanofluid in a cooling chamber

The thermal performance of a nanofluid in a cooling chamber with variations of the nanoparticle diameter is numerically investigated. The chamber is filled with water and nanoparticles of alumina (Al2O3). Appropriate nanofluid models are used to approximate the nanofluid thermal conductivity and dynamic viscosity by incorporating the effects of the nanoparticle concentration, Brownian motion, temperature, nanoparticles diameter, and interfacial layer thickness. The horizontal boundaries of the square domain are assumed to be insulated, and the vertical boundaries are considered to be isothermal. The governing stream-vorticity equations are solved by using a secondorder central finite difference scheme coupled with the mass and energy conservation equations. The results of the present work are found to be in good agreement with the previously published data for special cases. This study is conducted for the Reynolds number being fixed at Re = 100 and different values of the nanoparticle volume fraction, Richardson number, nanofluid temperature, and nanoparticle diameter. The results show that the heat transfer rate and the Nusselt number are enhanced by increasing the nanoparticle volume fraction and decreasing the Richardson number. The Nusselt number also increases as the nanoparticle diameter decreases.

Melting enhancement in triplex-tube latent thermal energy storage system using nanoparticles-fins combination

Latent thermal energy storage based on Phase Change materials (PCMs) offers a promising solution for correcting the problem of availability of intermittent energy from renewable sources like solar, wind, etc. PCMs have the potential to store large amounts of energy in relatively small volumes and within nearly isothermal processes. However, a major drawback of today's PCMs is that their low thermal conductivity values critically limit their energy storage applications. Also, this grossly reduces the melting/solidification rates, thus making the system response time to be too long. In this study, three enhancement techniques: fins, nanoparticles and a combination of both were investigated with the aim of correcting this limitation. A numerical study based on enthalpy method was used to comparably examine the effects of these techniques on the PCM melting rate in triplex-tube latent heat storage system. A mathematical model that takes into account the natural convection and the Brownian motion of nanoparticles was formulated and successfully validated against previous experimental data. The influence of using different dimensions of fin and different nanoparticle volume fractions on evolution of the solid-liquid interfaces, distribution of isotherms, and temporal profile of liquid fraction over the whole melting process was studied and reported. The results indicate that PCM melting is improved by using these techniques studied. Also it was found that the use of fins alone is better than using either nanoparticles alone or a combination of fins and nanoparticles. The use of longer fins with smaller thicknesses is recommended so as to improve phase-change heat transfer and minimize the volume occupied in the energy storage space.

Preparation and characterization of hydroxyl (–OH) functionalized multi-walled carbon nanotube (MWCNT)–Dowtherm A nanofluids

ABSTRACTIn the present work, the thermal conductivity and viscosity of hydroxyl (–OH) functionalized multi-walled carbon nanotubes (MWCNTs)–Dowtherm A (eutectic mixture of biphenyl (C12H10) and diphenyl oxide (C12H10O)) nanofluids are discussed. As-received hydroxyl (–OH) functionalized MWCNTs are characterized using x-ray diffraction (XRD), FT-Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and thermogravimetry, differential thermogravimetry, and differential scanning calorimetry (TGA-DTG/DSC) analysis. Hydroxyl (–OH) functionalized MWCNT–Dowtherm A nanofluids are prepared in different concentrations (0.001–0.005 g) of MWCNT and characterized at various temperatures (303–323 K). The thermal conductivity of hydroxyl (–OH) functionalized MWCNT–Dowtherm A nanofluids increases with the concentration of carbon nanotubes as well as with temperature. The possible mechanism for the enhancement observed may be ascribed to the percolation of heat through the nanotubes to form a tri-dimensional network. Also, as the temperature increases, the viscosity of the nanofluid decreases, which results in an increase in Brownian motion of nanoparticles, this sets convection-like effects resulting in enhanced thermal conductivity.

Melting enhancement in triplex-tube latent heat energy storage system using nanoparticles-metal foam combination

Phase change material (PCM) energy storage systems have relatively low thermal conductivity values which greatly reduces the systems’ performance. In this study, a compound porous-foam/nanoparticles enhancement technique was used to significantly improve melting of a phase change material (PCM) in a triplex-tube heat exchanger applicable to liquid desiccant air-conditioning systems. A mathematical model that takes into account the non-Darcy effects of porous foam and Brownian motion of nanoparticles was formulated and validated with previous related experimental studies. The influence of nanoparticle volume fraction and metal foam porosity on the instantaneous evolution of the solid-liquid interfaces, distribution of isotherms, and liquid-fraction profile under different temperatures of the heat transfer fluid (HTF) were investigated. Results show that dispersing nanoparticles in the presence of metal foams results in melting time savings of up to 90% depending on the foam structure and volumetric nanoparticle concentration. Although the melting time decreases as the porosity decreases and/or volume fraction increases, high-porosity metal foam with low volume-fraction nanoparticles is recommended. This ensures minimal PCM volume reduction and promotes positive contribution of natural convection during the melting process.

Influence of nonlinear thermal radiation and viscous dissipation on three-dimensional flow of Jeffrey nano fluid over a stretching sheet in the presence of Joule heating

AbstractPresent exploration discusses the combined effect of viscous dissipation and Joule heating on three dimensional flow and heat transfer of a Jeffrey nanofluid in the presence of nonlinear thermal radiation. Here the flow is generated over bidirectional stretching sheet in the presence of applied magnetic field by accounting thermophoresis and Brownian motion of nanoparticles. Suitable similarity transformations are employed to reduce the governing partial differential equations into coupled nonlinear ordinary differential equations. These nonlinear ordinary differential equations are solved numerically by using the Runge–Kutta–Fehlberg fourth–fifth order method with shooting technique. Graphically results are presented and discussed for various parameters. Validation of the current method is proved by comparing our results with the existing results under limiting situations. It can be concluded that combined effect of Joule and viscous heating increases the temperature profile and thermal boundary layer thickness.

Evaluation of clustering role versus Brownian motion effect on the heat conduction in nanofluids: A novel approach

In this study, the temperature and viscosity-dependent methods were used to identify the main heat conduction mechanism in nanofluids. Three sets of experiments were conducted to investigate the effects of Brownian motion and aggregation. Image processing approach was used to identify detailed configurations of different nanofluids microstructures. The thermal conductivity of the nanofluids was measured with respect to the dynamic viscosity in the temperature range between 0 and 55°C. The results clearly indicated that the nanoparticle Brownian motion did not play a significant role in heat conduction of nanofluids, which was also supported by the observation that a more viscous sample rendered a higher thermal conductivity. Moreover, the microscopic pictures and the differences in the viscosity between theoretical and experimental values suggested the major role of particle aggregation and clustering.

Mixed convection flow of thermally stratified MHD nanofluid over an exponentially stretching surface with viscous dissipation effect

Abstract The present analysis concentrates to examine the influence of both thermal and solutal stratification on magneto-hydrodynamics (MHD) nanofluid flow along an exponentially stretching sheet. Moreover, simultaneous effects of mixed convection and viscous dissipation are also analyzed to determine the thermal conductivity within the restricted domain. Energy and concentration equation consist of two important slip mechanisms, namely: the Brownian motion of nanoparticles and the thermophoresis due to concentration difference. By the mean of compatible similarity transformed, a system of PDEs is converted into the system of nonlinear ODEs. The resulting nonlinear ODEs are successfully solved via the implicit finite difference method (FDM). Obtained numerical solutions are plotted for each profile for different and converging values of including parameters. To validate the results, numerical values of Nusselt number are compared with the existing literature for a particular case. Obtained results present the significant impact of each parameter on temperature and concentration. Nanofluid flow behaviour is also observed via velocity profile.