Thermophoresis Of Particles Research Articles

Thermophoretic particle deposition and double-diffusive mixed convection flow in non-Newtonian hybrid nanofluids past a vertical deformable sheet

PurposeThermophoresis deposition of particles is a crucial stage in the spread of microparticles over temperature gradients and is significant for aerosol and electrical technologies. To track changes in mass deposition, the effect of particle thermophoresis is therefore seen in a mixed convective flow of Williamson hybrid nanofluids upon a stretching/shrinking sheet.Design/methodology/approachThe PDEs are transformed into ordinary differential equations (ODEs) using the similarity technique and then the bvp4c solver is employed for the altered transformed equations. The main factors influencing the heat, mass and flow profiles are displayed graphically.FindingsThe findings imply that the larger effects of the thermophoretic parameter cause the mass transfer rate to drop for both solutions. In addition, the suggested hybrid nanoparticles significantly increase the heat transfer rate in both outcomes. Hybrid nanoparticles work well for producing the most energy possible. They are essential in causing the flow to accelerate at a high pace.Practical implicationsThe consistent results of this analysis have the potential to boost the competence of thermal energy systems.Originality/valueIt has not yet been attempted to incorporate hybrid nanofluids and thermophoretic particle deposition impact across a vertical stretching/shrinking sheet subject to double-diffusive mixed convection flow in a Williamson model. The numerical method has been validated by comparing the generated numerical results with the published work.

Analysis of fouling in domestic boilers fueled with non-woody biomass

The greater sustainability of agricultural and industrial wastes (non-woody biomass) when compared to the widely used high-quality forestry biomass encourages their usage in small-scale thermal devices (residential and domestic applications). However, the typical significant ash and alkali-compounds content of agro-industrial wastes may form undesirable deposits over the heat exchange surfaces that could require additional cleaning systems (thus increasing the cost and complexity of the boilers). This work analyses the fouling tendency of exhausted olive cake and almond shells when used in a biomass boiler (with a nominal thermal capacity of 55 kW) at partial and nominal load, trying to highlight the main mechanism leading to the deposits growth depending on the fuel properties and load. Inertial impaction of coarse fly ash governs deposition at partial load for almond shells, this is attributed to the low K, Cl and S content and the lower bed temperature reached (431 °C vs 528 °C at nominal load). Among the deposition mechanisms associated to K-salts condensates, direct condensation on the incipient layers dominates over thermophoresis of submicron particles at nominal load. Although no additional maintenance procedures seem to be required when using almond shells, it is highly recommended to remove K/Cl components from exhausted olive cake through prior water leaching or by using additives to retain these species in the bottom ash.

Investigating the Impact of Magnetohydrodynamic (MHD) and Radiation on the Casson-Based Nanofluid Flow over a Linear Stretching Sheet in a Porous Medium with Heat Source or Sink

This study delves into the magnetohydrodynamic (MHD) flow of Casson-based nanofluids over a linear stretching sheet, accounting for multiple influencing factors. These findings offer significant real-time applications across a spectrum of fields, including energy generation, environmental engineering, and materials science. The acquired insights into Casson-based nanofluid behaviour within magnetohydrodynamic contexts can foster efficiency improvements, energy conservation, and enhanced overall system and process performance. Furthermore, the current study aims at Casson-based nanofluid's magnetohydrodynamic flow across a linear stretching sheet considering effects of thermal radiation, heat source/sink, and porosity. The governing equations are converted to ordinary differential equations by using similarity transformations. The Runge-Kutta-4 method, along with the shooting technique, is used to solve the reduced equations. The effects of dimensionless parameters, magnetic, Casson, thermophoresis, thermal radiation, and Brownian motion on velocity, thermal, and concentration profiles are considered in the study. As the magnetic and Casson parameters are increased, the findings indicate a reduction in the thickness of the momentum boundary layer. Moreover, the fluid temperature intensifies with the enhancement of thermophoresis and Brownian motion of particles. Finally, for various combinations of applied parameters, the values of skin friction coefficient, Nusselt number, and Sherwood number are obtained and are shown in the tables. The research is unique in a way that incorporates the impacts of heat source/sink and porosity as well as a more precise description of Casson nanofluid flow when compared to earlier findings. The novelty of the investigation lies in the implementation of a heat source/sink and porosity to obtain refined Casson nanofluid flow.

Phonon thermophoresis of crystalline nanoparticles in liquids.

Our nonequilibrium thermodynamic model of thermodiffusion in molecular liquid systems is used to examine the role of thermal phonons in the thermophoresis of liquid suspensions of crystalline nanoparticles, which tend to have high thermal conductivity. The Soret coefficient used to characterize stationary thermodiffusion is related to differences in entropy between a particle and the body of liquid that it displaces. Calculated phonon Soret coefficients for graphite and diamond nanoparticles in three polar solvents are used to establish parameters where the phonon mechanism is expected to dominate particle thermophoresis compared to slip-flow caused by forces induced in the surface layer by the temperature gradient. Because the active mode of thermal conductivity in crystals varies with particle size, phonon thermophoresis is expected to dominate within a specific range of particle size, which varies with the properties of the particle and suspending liquid. For graphite and diamond particles in polar solvents the model estimates a size range of around 10-100 nm. Finally, thermophoretic particle accumulation is ultimately limited by the increasing concentration of particles having high thermal conductivity because the zone of particle concentration decreases the local temperature gradient that drives thermophoresis. The respective nonperturbing concentration is evaluated as the function of the size of a given material.

The role of boundary conditions in the theory of aerosol particle thermophoresis

The force affecting a macroscopic particle in an inhomogeneously heated gas under conditions of a near free molecular regime is calculated on the basis of the solution of the kinetic equation. As a boundary condition, an integral relation is used that relates the distribution functions of the velocities of molecules reflected and incident on the particle through the scattering kernel. Quantitative calculations of the thermophoretic force are carried out with the use of different known scattering kernel models. By comparing the developed theory with experimental data, the reliability of these scattering kernels is analyzed and the values of their accommodative parameters are determined.

Negative thermophoresis of nanoparticles in liquids

The thermophoresis of suspended particles in a fluid is usually from high to low temperature. In the present paper, the negative thermophoresis (from low to high temperature) of nanoparticles in liquids is investigated by molecular dynamics simulations. It is found that the solid–liquid intermolecular coupling strength has a significant effect on the direction and magnitude of the thermophoretic force. Positive thermophoresis can be observed for strong couplings, while negative thermophoresis emerges for weak couplings. The negative thermophoresis is induced by the density gradient which pushes the particle from high to low density. Based on the analysis of the potential mean force of the solid–liquid interfacial layer, it is revealed that the switch between positive and negative thermophoresis is associated with the sign change of the averaged potential mean force for the interfacial layer. Therefore, the sign of the averaged potential mean force can be used as a criterion to predict the occurrence of negative thermophoresis. The results of this work provide insights for the microscopic manipulation of nanoparticles.

Effect of Particle Thermophoresis on Convection of Magnetic Fluids in Narrow Channels Heated from Below

Effect of Particle Thermophoresis on Convection of Magnetic Fluids in Narrow Channels Heated from Below

Surface hydrophilicity-mediated migration of nano/microparticles under temperature gradient in a confined space

HypothesisParticle transport by a temperature gradient is prospective in many biomedical applications. However, the prevalence of boundary confinement in practical use introduces synergistic effects of thermophoresis and thermo-osmosis, causing controversial phenomena and great difficulty in understanding the mechanisms. ExperimentsWe developed a microfluidic chip with a uniform temperature gradient and switchable substrate hydrophilicity to measure the migrations of various particles (d = 200 nm − 2 μm), through which the effects of particle thermophoresis and thermo-osmotic flow from the substrate surface were decoupled. The contribution of substrate hydrophilicity on thermo-osmosis was examined. Thermophoresis was measured to clarify its dependence on particle size and hydrophilicity. FindingsThis paper reports the first experimental evidence of a large enthalpy-dependent thermo-osmotic mobility χ ∼ ΔH on a hydrophobic polymer surface, which is 1–2 orders of magnitude larger than that on hydrophilic surfaces. The normalized Soret coefficient for polystyrene particles, ST/d = 18.0 K-1µm−1, is confirmed to be constant, which helps clarify the controversy of the size dependence. Besides, the Soret coefficient of hydrophobic proteins is approximately-four times larger than that of hydrophilic extracellular vesicles. These findings suggest that the intrinsic slip on the hydrophobic surface could enhance both surface thermo-osmosis and particle thermophoresis.

Effect of Particle Thermophoresis on Convection of Magnetic

The effect of positive thermodiffusion of colloidal particles under convection of magneticfluids in connected vertical channels of 3.2 × 3.2 mm2 square cross-section and height 50 mm heated from below is analyzed. Below the critical Rayleigh number, particle thermophoresis in vertical generates unstable density stratification in fluid at rest. This leads to rapid bursts (~1 min) of concentration convection arising periodically (~4 h). Under developed convection, above the critical Rayleigh number particle thermophoresis in horizontal direction generates concentration inhomogeneities in the neighborhood of the channel walls and provokes convective flow instability that leads to the periodicchange (~1 h) in the direction of convective stream. The reasons of the oscillatory instability of mechanical equilibrium observed experimentally at positive sign of the Soret coefficient are discussed.

Numerical analysis of thermophoresis of charged colloidal particles in non-Newtonian concentrated electrolyte solutions.

Thermophoresis of colloidal particles in aqueous media is more frequently applied in biomedical analysis with processed fluids as biofluids. In this work, a numerical analysis of the thermophoresis of charged colloidal particles in non-Newtonian concentrated electrolyte solutions is presented. In a particle-fixed reference frame, the flow field of non-Newtonian fluids has been governed by the Cauchy momentum equation and the continuity equation, with the dynamic viscosity following the power-law fluid model. The numerical simulations reveal that the shear-thinning effect of pseudoplastic fluids is advantageous to the thermophoresis, and the shear-thickening effect of dilatant fluids slows down the thermophoresis. Both the shear-thinning and shear-thickening effects of non-Newtonian fluids on a thermodiffusion coefficient are pronounced for the case when the thickness of electric double layer (EDL) surrounding a particle is moderate or thin. Finally, the reciprocal of the dynamic velocity at the particle surface is calculated to approximately estimate the thermophoretic behavior of a charged particle with moderate or thin EDL thickness.

Physical attributes of bio-convection in nanofluid flow through a paraboloid of revolution on horizontal surface with motile microorganisms

Nanofluids are unique functional fluids some of which are designed to reduce power losses while boosting thermal resistance. The subatomic particle thermophoresis and Brownian motion are necessary components in heat conduction in these fluids. This report describes the characteristics of bio-convection aspects of Casson nano fluid incorporated with thermal radiation with activation energy beyond a horizontal paraboloid region. Several studies examined the blood flow in the circulatory system employing non-Newtonian fluid models. The influence of prominent parameters, like Brownian diffusion and thermophoresis effects with bioconvection Lewis numbers are used. The coupled nonlinear governing PDEs are supposed to be transformed into nonlinear ODEs via similarity transformation. The obtained highly non-linear ODEs are tackled with shooting scheme, the solution of transformed equations is numerically obtained using ‘bvp4c,’ a MATLAB technique, to examine the problem. A schematic diagram is extensively employed to really see the influence of different effective factors. Graphical as well as numerical results against the velocity, temperature, concentration, and, motile microorganism profiles. As noticed that the findings, although the velocity profile decline as mounting values of magnetic parameter and upshot as small increment in the value of mixed convection parameter. In supporting flow circumstances, temperature profile overshoot is noticed, as small amount of radiation parameter. Biot number is increased in local Nusselt number and motile microorganisms. The results are computed in different ways like figures, tables and bar charts. The efficiency is observed for different values of various parameters.

Microscale Thermophoresis in Liquids Induced by Plasmonic Heating and Characterized by Phase and Fluorescence Microscopies

Thermophoresis denotes the motion of particles along temperature gradients. Insignificant in most daily-life observations, this peculiar effect can become dominant in applications involving nano- and microscale heating in fluids. Recent studies in nanoplasmonics observed significant thermophoresis of molecules and particles, in particular in plasmonic trapping, SERS, and biosensing. Evidencing the presence of thermophoresis is not obvious and quantifying its magnitude is even less accessible considering existing techniques. In this article, we introduce a method capable of quantifying the thermophoresis of particles in the context of nanoplasmonic applications. A gold nanoparticle array under illumination is used to create microscale temperature gradients, and a dual fluorescence-phase microscopy technique is used to map both temperature and concentration in parallel. This association enables the determination of Soret coefficients for a wide range of temperatures from a single image acquisition. This metrology technique paves the way for broader fundamental research in microscale thermophoresis in liquids and better-controlled applications in nanophotonics involving thermoplasmonic effects.

The role of thermophoresis on aluminum oxide lobe formation

This work studies the influence of phoretic motion (thermophoresis and diffusiophoresis) of fine alumina particles (“smoke”) produced during the combustion of aluminum. Direct numerical simulations on a single aluminum droplet burning in a quiescent environment suggest that thermophoresis is the main mechanism driving smoke back to the aluminum surface, hence a major contributor to the oxide lobe development. The presence of this lobe is found to distort the flowfield, which favors hot and smoke-rich regions closer to the lobe, thereby enhancing thermophoresis. This combination of aerodynamic and thermophoretic effects leads to a mass rate of deposited smoke which is consistent with experimental data. A simplified model, deduced from simulation results, is able to predict the size of the final oxide residue in good agreement with measurements. This study supports that aluminum oxide present on the burning aluminum particle is largely due to material formed in the flame, subsequently desposited by thermophoresis.

Термофорез одноатомных частиц в открытых нанотрубках

Using the method of molecular dynamics, it is shown that thermophoresis of particles (atoms) inside single-walled carbon nanotubes (CNTs) is highly efficient. Placing a particle inside the CNT involved in heat transfer causes it to move in the direction of the heat flow at a constant speed, the value of which weakly depends on the length of the nanotube. The heat flow along the CNT leads to the formation of a constant thermophoresis force for the particles inside. The direction of this force coincides with the direction of heat transfer. The monatomic nature of the particle allowed us to numerically calculate this force and to determine the contribution to this force of interaction with each thermal phonon of the nanotube. It is shown that the magnitude of the force is almost completely determined by the interaction of the particle with long-wave bending phonons of the nanotube, which have a long free run path. Therefore, the speed of the particle movement and the value of the thermophoresis force depend weakly on the length of the nanotube, but are determined by the temperature difference at its ends. Because of this, the mode of thermophoresis of particles inside nanotubes is ballistic, not diffusive.

Thermal Forces from a Microscopic Perspective.

Thermal gradients lead to macroscopic fluid motion if a confining surface is present along the gradient. This fundamental nonequilibrium effect, known as thermo-osmosis, is held responsible for particle thermophoresis in colloidal suspensions. A unified approach for thermo-osmosis in liquids and in gases is still lacking. Linear response theory is generalized to inhomogeneous systems, leading to an exact microscopic theory for the thermo-osmotic flow, showing that the effect originates from two independent physical mechanisms, playing different roles in the gas and liquid phases, reducing to known expressions in the appropriate limits.

Photo- and Thermophoresis of Heated Medium-Size Spherical Aerosol Particles

A theory of photo- and thermophoresis of a heated medium-size spherical aerosol particle is proposed in the quasi-stationary Stokes approximation at relatively small Reynolds and Peclet numbers. Gas-dynamic equations are solved with allowance for power dependences of the molecular transport (viscosity and thermal conductivity) coefficients and density of the gas medium on temperature. Boundary conditions take into account effects that are linear with respect to the Knudsen number. Expressions for the total force and velocity are derived. It is shown than the above effects may substantially affect the motion of a heated particle.

Thermophoresis of Janus particles at large Knudsen numbers

The force and torque on a Janus sphere moving in a rarefied gas with a thermal gradient are calculated. The regime of large Knudsen number is considered, with the momenta of impinging gas molecules either obtained from a Chapman-Enskog distribution or from a binary Maxwellian distribution between two opposing parallel plates at different temperature. The reflection properties at the surface of the Janus particle are characterized by accommodation coefficients having constant but dissimilar values on each hemisphere. It is shown that the Janus particle preferentially orients such that the hemisphere with a larger accommodation coefficient points towards the lower temperature. The thermophoretic velocity of the particle is computed, and the influence of the thermophoretic motion on the magnitude of the torque responsible for the particle orientation is studied. The analytical calculations are supported by Direct Simulation Monte Carlo results, extending the scope of the study towards smaller Knudsen numbers. The results shed light on the efficiency of oriented deposition of nanoparticles from the gas phase onto a cold surface.

Experimental research of surfaced nanoparticle thermal transport in a porous medium

Experimental research on thermally induced nanocolloid transport in a porous environment is presented. Addition of excess surfactant to a colloid with dispersed phase made of surfaced nanoparticles results in a decrease of effective Soret coefficient in a porous environment. It is shown that with sufficient amounts of surfactant added, this effect extends to a reversal of nanoparticle thermophoretic transport direction, and that the effect shows a tendency of saturation. A mechanism of thermal transport that involves slip velocity of surfactant molecules appearing near pore walls is evaluated as a possible cause of the decrease of Soret coefficient. Effects of temperature on particle thermophoresis are analyzed, revealing a decrease of Soret coefficient with the increase of temperature. In order to better understand surfactant motion in the porous environment, a series of experiments characterizing thermoosmotic motion of a mixture of surfactant diluted in pure carrier fluid through a porous layer is performed.

Electrokinetically driven continuous-flow enrichment of colloidal particles by Joule heating induced temperature gradient focusing in a convergent-divergent microfluidic structure

Enrichment of colloidal particles in continuous flow has not only numerous applications but also poses a great challenge in controlling physical forces that are required for achieving particle enrichment. Here, we for the first time experimentally demonstrate the electrokinetically-driven continuous-flow enrichment of colloidal particles with Joule heating induced temperature gradient focusing (TGF) in a microfluidic convergent-divergent structure. We consider four mechanisms of particle transport, i.e., advection due to electroosmosis, electrophoresis, dielectrophoresis and, and further clarify their roles in the particle enrichment. It is experimentally determined and numerically verified that the particle thermophoresis plays dominant roles in enrichment of all particle sizes considered in this study and the combined effect of electroosmosis-induced advection and electrophoresis is mainly to transport particles to the zone of enrichment. Specifically, the enrichment of particles is achieved with combined DC and AC voltages rather than a sole DC or AC voltage. A numerical model is formulated with consideration of the abovementioned four mechanisms, and the model can rationalize the experimental observations. Particularly, our analysis of numerical and experimental results indicates that thermophoresis which is usually an overlooked mechanism of material transport is crucial for the successful electrokinetic enrichment of particles with Joule heating induced TGF.

Direct observations of thermophoresis in microfluidic systems

Particles transport driven by a temperature gradient in a solution is known as thermophoresis or Soret effect. The drift velocity of a particle is expressed as , where is a thermophoretic mobility. Therefore, the thermophoretic mobility is a parameter to characterise the nature of thermophoresis, and the systematic measurement of for various combinations of particles and solvents is necessary for its potential application. In the present work, we develop the microfluidic system called microgap Soret cell and show its validity by obtaining for wide experimental conditions. It is shown that the microgap Soret cell can rapidly and directly obtain the thermophoretic mobility of a particle with the diameter of by maintaining the large temperature gradient in the microfluidic system. Moreover, by using the microgap Soret cell, the temperature dependency of is investigated for thermophoresis of polystyrene particles in solutions of sodium hydroxide, polyethylene glycol, and glycerol.