Non-uniform Distribution Of Nanoparticles Research Articles

Evaluation of the performance of concrete by adding silica nanoparticles and zeolite: A method deviation tolerance study

Researchers have conducted extensive research to develop concretes with improved properties and suitable for harsh environments. The use of nanomaterials to improve the performance of concrete is one of the promising methods for developing optimized concrete. However, the non-uniform distribution of nanoparticles in the concrete matrix limits the reproducibility of the behavior of concretes studied, particularly in industrial or practical environments. The high surface energy of nanoparticles, limitations, and lack of standardization of the production process are responsible for this phenomenon. Addressing this challenge, this study aims to investigate practical implementation conditions of silica nanoparticle and zeolite reinforced concrete. The study examines deviations from the base method, involving synthesized silica nanoparticles via the sol-gel method as the main additive, alongside zeolite as a representative of pozzolanic materials. By examining four parameters influencing the behavior of concrete over a period of 7 days and 180 days, as well as conducting experiments in parallel groups to simulate the practical environment, this study attempted to improve the reproducibility of concrete with silica nanoparticles and zeolites improved behavior. As a result of the study, it was found that the presence of silica and zeolite nanoparticles in 7-day concrete weakens and improves the properties of the concrete by − 10% and + 3%, respectively, for concrete after 7 days, and this effect increases by + 30% and + 93% for concrete after 180 days. This showed that there is a significant correlation between the healing effects of these substances and the amount of time they have been hydrated. Furthermore, concrete containing silica nanoparticles performs 35% better than the control sample. In contrast, concrete containing silica nanoparticles and zeolite provided a 165% improvement over the control sample. Using a correlation analysis of the effects of different parameters on the output performance of 7-day and 180-day concrete, this study presents a more detailed analysis of improved concrete response.

Oscillation and evolution characteristics of nanofluid thermocapillary convection in rectangular cavity

To analyze the oscillation and evolution characteristics of nanofluid thermocapillary convection instability, a two-phase mixture model was utilized to simulate nanofluid thermocapillary convection in a rectangular cavity and investigate the impact of nanoparticle volume fraction on the oscillatory flow. The results indicate that the two-phase mixture model has a lower critical temperature difference compared to the single-phase model, and the oscillation mode exhibits distinct changes for small nanoparticle volume fractions. At a high Marangoni number, the thermocapillary convection displays periodic oscillatory behavior, with the flow field composed of several dynamic convection vortices. An increase in nanoparticle volume fraction results in a decrease in the critical temperature difference, as well as the amplitude and variation range of temperature oscillation. However, the oscillation period shows an approximate linear increase. Furthermore, there is a non-uniform distribution of nanoparticles at the vicinity of solid wall, especially a significant concentration gradient near the side wall.

Development of Al-Al2o3 nanocomposites by stir casting followed by hot forging and heat treatment and testing of their properties

In recent years, the reinforcement materials used in aluminum matrix composites are aluminum oxide, silicon carbide, titanium carbide and tungsten carbide in nano and micron size. The secondary processing of particle reinforced composites offers substantial benefits such as vanishing of defects, improvement in distribution of particles and thereby enhances their properties. In this study the properties of the hot forged and heat-treated nanocomposites were evaluated and compared with as cast and cast & heat-treated nanocomposites. Al6061-Al2O3 nanocomposites fabricated by varying the weight percentage of Al2O3 with 0, 2.5, 3.0, 3.5 and 4.0 in Al6061 alloy. After Casting, Al6061-Al2O3 composites were subjected to hot forging and heat treatment. Aluminum matrix nanocomposites were subjected to various tests to study their physical and mechanical properties. FESEM, EDAX and microhardness test of the developed composite have been carried out. The results revealed that among all the Cast, Heat treated and Hot Forged-Heat treated nanocomposites, the composites reinforced with 3.5 wt% Hot Forged-Heat treated composites have shown excellent micro structural homogeneity with uniform distribution of particles. It has been observed that mechanical properties like tensile strength, impact strength and Compressive strength, of hot forged-heat treated composites reinforced with 3.5 wt% possessed maximum values. Further, increase in wt.% resulted in decrease in properties due to clustering and non-uniform distribution of nanoparticles at 4 wt%.

Insightful study of the characterization of the Cobalt oxide nanomaterials and hydrothermal synthesis

In this paper, nanoparticles of cobalt oxide (Co3O[Formula: see text] are prepared at different temperatures [Formula: see text]C, [Formula: see text]C and [Formula: see text]C using the hydrothermal method. Cobalt nitrate hexahydrate: Co (NO[Formula: see text]H2O is used as precursor and potassium hydroxide (KOH) is used as precipitating agent. Particle size is controlled using precursor concentration. It is also investigated in this research that particle size increases at high-temperature. Nanoparticles of size between (13.62–17.81 nm) are obtained using this technique (Hydrothermal method). SEM results provide nonuniform distribution of nanoparticles with sharp grain boundaries. Electrical characterization confirms the semiconducting behavior of the material as resistivity decreases with increase in temperature. Electrochemical measurements show detection of hydrogen peroxide H2O2 by nanoparticles of Co3O4.

The role of accumulative roll bonding after stir casting process to fabricate high-strength and nanostructured AA2024-(SiO2+TiO2) hybrid nanocomposite

Major challenges in casting routes for the fabrication of metal matrix nanocomposites are the weak bonding between reinforcement and matrix, porosity and nonuniform distribution of nanoparticles in the matrix alloy following in the presence of agglomerated nanoparticles and reinforcing nanoparticle free zones. Applying accumulative roll bonding as a severe plastic deformation process can improve the microstructure of the matrix alloy and the distribution of reinforcing nanoparticles in the metal matrix after the production of the casting nanocomposite. In this study, the accumulative roll bonding process was used to complete the composite fabrication process on the as cast AA2024-(SiO2+TiO2) hybrid nanocomposites. The microstructural and mechanical examinations of the accumulative roll bonded hybrid nanocomposites were characterized by measurement of density using the Archimedean immersion method, optical metallography, field emission scanning electron microscopy, high resolution transmission electron microscopy, X-ray diffraction, and hardness and tensile tests. The results showed that the microstructure of the accumulative roll bonded hybrid nanocomposite had a great distribution of nanoparticles in the matrix without any significant porosity. In the final nanostructured hybrid nanocomposite, the grain size of 100 nm was obtained. Mechanical examinations also indicated that the hardness, ultimate tensile strength and yield stress of the nanocomposite increased as the number of accumulative roll bonding cycles increased. After five accumulative roll bonding cycles, hardness, ultimate tensile strength and yield stress values of the nanocomposite increased about 160%, 110% and 300% rather than those of non-accumulative roll bonded monolithic product, respectively.

Development of novel supported iridium nanocatalysts for special catalytic beds

In the present paper, an experimental study of the catalytic decomposition of hydrous hydrazine was investigated on the different structural forms of the catalyst. The synthesized iridium catalysts have been usually used directly and have not been evaluated in the laboratory reactor. This study includes the preparation of iridium-based catalysts supported on spherical (alumina), honeycomb monoliths (cordierite) and foams (alumina) for the evaluation of catalytic activity in the laboratory reactor. The characterizations of these catalysts were evaluated by the TGA, FESEM and BET analysis. The result of the catalytic characterization of monolithic support was shown a homogeneous distribution of active metal without any problem of sintering (average size 25 nm) on the support surface. While the surface of the spherical and foam supports were shown non-uniform distribution of nanoparticles on the support skeleton (average size 55 nm). The monolithic catalyst exhibits higher decomposition rate and H2 selectivity than other supports due to uniform in shape and particle size distribution.Graphic abstract

Different distributions of gold nanoparticles on the tumor and calculation of dose enhancement factor by Monte Carlo simulation

Gold nanoparticles can be used to increase the dose of the tumor due to its high atomic number as well as being free from apparent toxicity. The aim of this study is to evaluate the effect of distribution of gold nanoparticles models, as well as changes in nanoparticle sizes and spectrum of radiation energy along with the effects of nanoparticle penetration into surrounding tissues in dose enhancement factor DEF. Three mathematical models were considered for distribution of gold nanoparticles in the tumor, such as 1-uniform, 2- non-uniform distribution with no penetration margin and 3- non-uniform distribution with penetration margin of 2.7 mm of gold nanoparticles. For this purpose, a cube-shaped water phantom of 50 cm size in each side and a cube with 1 cm side placed at depth of 2 cm below the upper surface of the cubic phantom as the tumor was defined, and then 3 models of nanoparticle distribution were modeled. MCNPX code was used to simulate 3 distribution models. DEF was evaluated for sizes of 20, 25, 30, 50, 70, 90 and 100 nm of gold nanoparticles, and 50, 95, 250 keV and 4 MeV photon energies. In uniform distribution model the maximum DEF was observed at 100 nm and 50 keV being equal to 2.90, in non-uniform distribution with no penetration margin, the maximum DEF was measured at 100 nm and 50 keV being 1.69, and in non-uniform distribution with penetration margin of 2.7 mm, the maximum DEF was measured at 100 nm and 50 keV as 1.38, and the results have been showed that the dose was increased by injecting nanoparticles into the tumor. It is concluded that the highest DEF could be achieved in low energy photons and larger sizes of nanoparticles. Non-uniform distribution of gold nanoparticles can increase the dose and also decrease the DEF in comparison with the uniform distribution. The non-uniform distribution of nanoparticles with penetration margin showed a lower DEF than the non-uniform distribution without any margin and uniform distribution. Meanwhile, utilization of the real X-ray spectrum brought about a smaller DEF in comparison to mono-energetic X-ray photons.

Thermal Stability of the Structure and Microhardness of the Al–0.05 vol % Al2O3 Nanocomposite Fabricated by Accumulative Roll Bonding

The evolution of the microstructure and microhardness of the Al–0.05 vol % nAl2O3 nanocomposite (where nAl2O3 are aluminum nanoparticles) and aluminum without nanoparticles fabricated by accumulative roll bonding with annealing in a temperature range of 373–573 K is investigated. Ball-shaped Al2O3 nanoparticles with an average diameter of 50 nm are introduced between rolled plates of technically pure aluminum from the first to fourth rolling cycles, while the fifth to the tenth rolling cycles are performed without nanoparticles. The average grain size and aspect ratio of elements of the material grain–subgrain structure in the initial state and after annealing at 473 K are measured using transmission electron microscopy. It is shown that the nanocomposite microhardness is 5–13% higher than the corresponding value of HV for aluminum over the entire studied annealing temperature range. The main factor of the higher nanocomposite microhardness is precipitation hardening due to Al2O3 nanoparticles. The contribution of the substructural and grain-boundary hardening is identical in both materials. The thermal stability of the nanocomposite microhardness is only ~25 K higher than that of aluminum, which is caused by the nonuniform distribution of nanoparticles in the matrix and their low volume fraction. The high thermal stability of the fine-grain structure itself, formed by accumulative roll bonding, when compared with other methods of intense plastic deformation, also plays a role. It is established that most Al2O3 nanoparticles remain at the grain boundaries of nanocomposite after annealing at 473 K; therefore, the ability to fasten the boundary by Al2O3 nanoparticles under the conditions under study is retained at least to 473 K.

Acousto-Optical Properties of Heterogeneous Media with a Nonuniform Distribution of Nanoparticles

The possibility of efficiently using metamaterials in acousto-optics has been demonstrated. Diffraction reflection and transmission curves of metamedia with a nonuniform spatial distribution of nanoparticles have been studied taking into account absorption of light. The influence of size (geometric) effects of nanoparticles on diffraction reflection and transmission curves has been shown. In particular, it has been shown that the variation of the concentration of dielectric nanoparticles in a medium allows completely removing extraneous oscillations and suppressing the “tails” of the diffraction reflection curve. It has been demonstrated that the response function of acousto-optical devices can be controlled by varying the material, concentration, size, shape, and spatial orientation of inclusions, as well as the polarization of incident radiation.

Nanoparticle dispersion and distribution in XLPE and the related DC insulation performance

In this paper, loading content was adjusted and nanoparticle surface modification by silane coupling agent was applied to obtain different XLPE/TiO2 nanocomposites. Polymer surface etching, a traditional method, was innovatively and effectively used to characterize the nanoparticle dispersion and distribution in nanocomposites. Distinct scanning electron microscope images of nanoparticle dispersion were obtained. It was proved that the surface modification improved nanoparticle dispersion, which was analyzed to relate directly to DC insulation performance and morphology. The introduction of nano-TiO2 decreased DC conductivity, suppressed homocharge injection, enhanced DC dielectric strength, increased crystallinity and changed morphology. And well nanoparticle dispersion at same loading content achieved by surface modification had positive cooperative effect to the influence above. DC breakdown strength was increased by 13.5%. Decrement of injected homocharge density was calculated, and it can reach 91.5 μC·m−2. Moreover, the non-uniform distribution of nanoparticles in semi-crystalline polymer based nanocomposites was first proposed and discussed. The nanoparticles can be divided into four regions, the boundary zone, the amorphous zone, the nucleation zone and the inter-lamella zone.

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.

Direct absorption solar collector (DASC) modeling and simulation using a novel Eulerian-Lagrangian hybrid approach: Optical, thermal, and hydrodynamic interactions

A novel two-way coupled Eulerian-Lagrangian hybrid approach was used to model nanofluid-based direct absorption solar collectors via a transient in-house code. By capturing the discrete nature of nanoparticles as well as motion and temperature slips between the carrier and dispersed phases, the proposed approach overcomes limitations of fully-continuous models by coupling the fully-resolved local nanoparticle concentration with the nanofluid optical and thermal properties. In particular, it was established that the non-uniform distribution of nanoparticles results in the spatially non-uniform attenuation of solar radiation due to spatial variations in the nanofluid optical properties. Moreover, the volumetric absorption and temperature fields were computed and compared to the conventional fully-continuous fields generated based on a homogeneous nanoparticle distribution assumption. The Reynolds number was found to have a strong effect on the local nanoparticle distribution in the flow of a nanofluid in a direct absorption solar collector, which greatly affects optical and thermal properties and performance of the nanofluid and collector. A critical flow Reynolds number was identified, after which the assumption of a homogenous particle distribution becomes inacceptable, and the homogeneous, fully-continuous modeling approach yields inaccurate results. In particular, the fully-continuous Eulerian modeling approach increasingly overestimates solar radiation extinction in vicinity of the channel top surface with an increase in Reynolds number, especially for Reynolds numbers ≥1. Effects on the coupled optical, thermal, and hydrodynamic interactions within the direct absorption solar collector due to the deviation of local nanoparticle distribution from the commonly-used homogeneous-nanoparticle-distribution assumption were investigated. Namely, new insights have been gained with regards to the impact of transverse nanoparticle migration, flow Reynolds number, mean nanoparticle concentration, and nanoparticle material type on the nanofluid temperature distribution, spectral radiation heat flux distribution, nanofluid optical properties, and collector optical and thermal performance metrics and losses. It was found that nanofluid optical properties in the visible radiation spectrum are highly dependent on the local nanoparticle concentration, which is in contrast to the infrared spectrum, where variations in the nanoparticle distribution have little effect on optical properties. The obtained results systematically identify the limitations of conventional direct absorption solar collector design tools and propose a new modeling approach that resolves those limitations as well as expands our physical understanding of the coupled optical, thermal, and hydrodynamics interactions within a volumetric absorption system.

Numerical analysis of nanofluid flow inside a trapezoidal microchannel using different approaches

In this study, developing laminar forced convection of Al2O3/water nanofluid flow inside a trapezoidal microchannel has been investigated. The numerical simulation is conducted using two different methods which consider the effect of non-uniform nanoparticle distribution: Buongiorno’s Two-component nonhomogeneous model, and Eulerian-Lagrangian two-phase method. The results are compared to experimental data and also single-phase and dispersion methods. It is shown that the Eulerian-Lagrangian method predicts microchannel Nusselt number more accurately than Buongiorno’s model. Particle distribution is not uniform in the cross section of microchannel, and with increasing Reynolds number this nonuniformity is more. Moreover, the effect of different forces on heat transfer is discussed. It is found that the influence of Saffman’s lift force is negligible while Brownian and thermophoretic forces affect the heat transfer coefficient slightly. Furthermore, it is shown that the use of experimental correlation for nanoparticle Nusselt number makes the numerical results more accurate, so it is important to take into account the scale effects and use the suitable correlations.

Comparison of the pseudo-single-phase continuum model and the homogeneous single-phase model of nanofluids

We investigate forced convection of a nanofluid in the entrance region of a cylinder and in the fully-developed region of a coaxial cylinder employing the pseudo-single-phase continuum model and the homogeneous single-phase model. While the homogeneous single-phase model assumes a uniform nanoparticle distribution, the pseudo-single-phase continuum model takes care of nonuniform nanoparticle distribution. There has been controversy regarding the cause of heat transfer enhancement in nanofluids. Whether it is caused solely by the variation of thermophysical properties or the nanoparticle distribution also affect it. This controversy may be resolved employing these two models. It is found that nanoparticles drift from hot wall to cold central region in the entrance region, while they drift from cold inner surface to hot outer surface in the fully-developed coaxial cylinder due to the thermophoresis. The resulting nonuniform distributions of nanoparticles are found to add the heat transfer enhancement slightly. On the other hand, the frictional dissipation increases when the heat transfer rate increases. In a sense, the enhanced heat transfer rate is partly achieved at the expense of a higher energy consumption.

Simultaneous effect of staggered baffles and dispersed nanoparticles on thermal performance of a cooling channel

This paper deals with laminar forced convection of Al2O3-water nanofluid in developing region of a channel with staggered baffles considering thermophoresis and Brownian motion. An extra scalar equation is considered along with other conservation equations to determine the dispersed nanoparticles distribution throughout the channel. The effect of nanoparticle concentration, Reynolds number and baffle height on the velocity and temperature fields, heat transfer rate, pressure drop and hydrothermal performance of the baffled channel is numerically investigated and the contours of nanoparticle distribution provided. The presence of nanoparticles results in a significant reduction in wall temperature, especially in dead regions in which hot spots are generated. Nanoparticle concentration decreases in recirculation regions and a wavy layer of the agglomerated nanoparticle is shaped exactly over the baffles. With decreasing Reynolds number, more non-uniform nanoparticle distribution is observed in baffled channel and the effect of nanofluid on temperature reduction becomes more pronounced. By addition nanoparticle into basefluid, the length and strength of recirculation flow decreases. Nanoparticles are of more significant effect on heat transfer enhancement and pressure drop increment when nanoparticle concentration and Reynolds number, respectively, rises and declines. The baffled channel presents a better hydrothermal performance for lower nanoparticle concentration and Reynolds number. As the baffle height is raised, more uniformity of nanoparticle distribution is observed in baffled channel and the influence of nanofluid on the wall temperature reduction in recirculation regions and reattachment points, respectively, increases and decreases. The computational results reveal that the impact of nanofluid on heat transfer and pressure drop augmentation depends on baffle height and an optimum value exists providing the best hydrothermal performance for baffled channel.

Nanofluid flow in micro-annular tubes at constant wall temperature considering the non-uniform distribution of nanoparticles

In this paper, the modified two-component non-homogeneous mixture model of Buongiorno is developed for the case of forced convection of alumina–water non-homogeneous nanofluid flow in concentric micro-annular tubes at constant wall temperature (CWT). Two different thermal boundary conditions have been considered such that for Case A the inner wall is adiabatic and the outer wall is kept at a constant temperature while for Case B the inner wall temperature remains constant and the outer wall is thermally isolated. Assuming a hydrodynamically and thermally fully developed flow, the governing equations of nanofluids in a concentric annulus are reduced to a nonlinear system of ordinary differential equations and solved using an appropriate reciprocal numerical algorithm via Runge–Kutta–Fehlberg method. The effects of NBT (from 0.7 to 10), ϕB (from 0.01 to 0.03), λ (from 0.05 to 0.2) and ζ (0.4, 0.5 and 0.6) on the non-dimensional volume fraction of nanoparticles, velocity, and temperature profiles have been investigated for both cases. It is indicated that the anomalous heat transfer enhancement depends on the thermal boundary condition as well as the ratio of thermophoresis and Brownian motion. Furthermore, for Case B, there is an optimum nanoparticle diameter around 0.5<NBT<1 that the thermal performance reaches its peak. However, for Case A, the thermal performance increases as the nanoparticle diameter increases. For both cases, the thermal performance decreases with an increase in the nanoparticle concentration.

Effects of nanoparticle migration on non-Newtonian nanofluids in a channel with multiple heating and cooling regions

Laminar forced convection nanofluids based non-Newtonian flow in a horizontal parallel channel with multiple regions of heating and cooling are investigated, taking into account the inhomogeneous distribution of nanoparticles. The non-Newtonian behaviour of nanofluids is described by the power-law model. The velocity, temperature and concentration fields, heat transfer coefficient ratio, and pressure drop are obtained numerically by solving the coupled momentum, energy and concentration equations. Results based on assumption of homogeneous and inhomogeneous distribution of nanoparticles are compared with each other. It is found that the detailed information of velocity, temperature and pressure drop obtained by these two opposite assumptions are largely different. The non-uniform distribution of nanoparticles has a much weaker influence on temperatures compared to the uniform distribution; and the non-uniform distribution of nanoparticles in the base fluid results in a smaller pressure drop than the uniform cases do. The above findings highlight the necessity and significance of studying the effects of nanoparticles’ sedimentation and precipitation on heat and mass transfer for related industrial applications. And the thermal performance of power-law nanofluids investigated in this paper may shed some light on more efficient design of heat exchangers.

Acousto-optical properties of metamaterials

The possibility of the effective use of metamaterials in acousto-optics is demonstrated. It is shown that photoelastic constants that determine a change in the dielectric constant of a heterogeneous medium under the action of a sound wave can significantly exceed the corresponding constants for conventional crystals. We have analysed the mechanisms of the dielectric constant variation in a heterogeneous medium consisting of nanoparticles in the form of ellipsoids and have found explicitly the values of the photoelastic constants. It is shown that the mechanism of the dielectric constant variation in a longitudinal sound wave is reduced to a change in the local concentration of nanoparticles in the bulk and in a transverse acoustic wave – to a local rotation of space-oriented nanoellipsoids. It is also shown that the use of metamedia with a nonuniform distribution of nanoparticles provides a unique opportunity for designing qualitatively new instruments and devices that cannot be produced on the basis of conventional crystals. It is noted that metamaterials open ample opportunities for creating devices of the IR region of the spectrum due to the absence of restrictions on the size of such media.

Акустооптические свойства метаматериалов

The possibility of the effective use of metamaterials in acousto-optics is demonstrated. It is shown that photoelastic constants that determine a change in the dielectric constant of a heterogeneous medium under the action of a sound wave can significantly exceed the corresponding constants for conventional crystals. We have analysed the mechanisms of the dielectric constant variation in a heterogeneous medium consisting of nanoparticles in the form of ellipsoids and have found explicitly the values of the photoelastic constants. It is shown that the mechanism of the dielectric constant variation in a longitudinal sound wave is reduced to a change in the local concentration of nanoparticles in the bulk and in a transverse acoustic wave – to a local rotation of space-oriented nanoellipsoids. It is also shown that the use of metamedia with a nonuniform distribution of nanoparticles provides a unique opportunity for designing qualitatively new instruments and devices that cannot be produced on the basis of conventional crystals. It is noted that metamaterials open ample opportunities for creating devices of the IR region of the spectrum due to the absence of restrictions on the size of such media.

Magnetic field effects on nanoparticle migration and heat transfer of alumina/water nanofluid in a parallel-plate channel with asymmetric heating

The present paper is a theoretical investigation on the effects of nanoparticle migration and asymmetric heating on magnetohydrodynamic forced convection of alumina/water nanofluid in a parallel-plate channel. Walls are subjected to different heat flux; q″ t for the top wall and q″ b for the bottom wall, such that q″ t > q″ b . A two-component mixture model is used for the nanofluid in the hypothesis that Brownian motion and thermophoretic diffusivities are the only significant slip mechanisms between solid and liquid phases. Considering the hydrodynamically and thermally fully developed flow, governing equations including continuity, momentum, and energy equations have been reduced to ordinary differential equations and solved numerically. It is revealed that nanoparticles eject from the heated walls, construct a depleted region, and accumulate in the core region, but are more likely to take place toward the wall with the lower heat flux. Also, the non-uniform nanoparticle distribution makes the velocities move toward the wall with the higher heat flux and enhances the heat transfer rate there. In addition, it is shown that the advantage of nanoparticle inclusion is increased in the presence of a magnetic field, though heat transfer enhancement is decreased.