The Effect of the Liquid Layer Around the Spherical and Cylindrical Nanoparticles in Enhancing Thermal Conductivity of Nanofluids

2019 ◽  
Vol 141 (3) ◽  
Author(s):  
Hamid Loulijat ◽  
Hicham Zerradi
Keyword(s):  
Thermal Conductivity ◽  
Liquid Layer ◽  
Md Simulation ◽  
Volume Fraction ◽  
Liquid Argon ◽  
Number Density ◽  
Conductivity Enhancement ◽  
Solid Liquid Interface ◽  
Solid Liquid ◽  
The Impact

In this work, the equilibrium molecular dynamics (MD) simulation combined with the Green–Kubo method is employed to calculate the thermal conductivity and investigate the impact of the liquid layer around the solid nanoparticle (NP) in enhancing thermal conductivity of nanofluid (argon–copper), which contains the liquid argon as a base fluid surrounding the spherical or cylindrical NPs of copper. First, the thermal conductivity is calculated at temperatures 85, 85.5, 86, and 86.5 K and for different volume fractions ranging from 4.33% to 11.35%. Second, the number ΔN of argon atoms is counted in the liquid layer formed at the solid–liquid interface with the thickness of Δr = 0.3 nm around the NP. Finally, the number density n of argon atoms in this layer formed is calculated in all cases. Also, the results for spherical and cylindrical NPs are compared with one another. It is observed that the thermal conductivity of the nanofluid increased with the increasing volume fraction and the number ΔN. Likewise, the thermal conductivity of nanofluid containing spherical NPs is higher than that of nanofluid containing cylindrical NPs. Furthermore, the number density n of argon atoms near the surface of spherical NPs is higher than that of argon atoms attached in the curved surface of cylindrical NPs. As a result, the liquid layer around the solid NP has been considered one of the mechanisms responsible contributing to the thermal conductivity enhancement in nanofluids.

The Thermal Transport Properties of Ethylene Glycol Based MGO Nanofluids

2009 ◽  
Author(s):  
Wei Yu ◽  
Hua-Qing Xie ◽  
Yang Li ◽  
Li-Fei Chen
Keyword(s):  
Thermal Conductivity ◽  
Ethylene Glycol ◽  
Transport Properties ◽  
Volume Fraction ◽  
Metallic Oxide ◽  
Mgo Nanoparticles ◽  
Conductivity Enhancement ◽  
Classical Models ◽  
Constant Viscosity ◽  
Solid Liquid

Ethylene glycol based nanofluids containing MgO nanoparticles (MgO-EG) were prepared, and the transport properties including thermal conductivity and viscosity were measured. The results show that the thermal conductivity of MgO-EG nanofluid depends strongly on particle concentration, and it increases nonlinearly with the volume fraction of nanoparticles. The thermal conductivity of MgO-EG nanofluids is larger than that of nanofluids containing the same volume fraction of TiO2, ZnO, Al2O3 and SiO2, maybe due to its lowest viscosity among the tested metallic oxide nanofluids. Thermal conductivity enhancement of MgO-EG nanofluids appears weak dependence on temperature from 10 to 60°C, and the enhanced ratios are almost constant. Viscosity measurements show that MgO-EG nanofluids demonstrate Newtonian behavior, and the viscosity significantly decreases with temperature. The thermal conductivity and viscosity increments of nanofluids are higher than those of the existing classical models for the solid-liquid mixture.

Modeling and Experiments of Laser Cladding With Droplet Injection

2005 ◽  
Vol 127 (9) ◽  
pp. 978-986 ◽  
Author(s):  
J. Choi ◽  
L. Han ◽  
Y. Hua
Keyword(s):  
Fluid Flow ◽  
Laser Cladding ◽  
Dynamic Motion ◽  
Cladding Layer ◽  
Melt Pool ◽  
Material Deposition ◽  
Modeling And Experiments ◽  
Solid Liquid Interface ◽  
Solid Liquid ◽  
The Impact

Laser aided Directed Material Deposition (DMD) is an additive manufacturing process based on laser cladding. A full understanding of laser cladding is essential in order to achieve a steady state and robust DMD process. A two dimensional mathematical model of laser cladding with droplet injection was developed to understand the influence of fluid flow on the mixing, dilution depth, and deposition dimension, while incorporating melting, solidification, and evaporation phenomena. The fluid flow in the melt pool that is driven by thermal capillary convection and an energy balance at the liquid–vapor and the solid–liquid interface was investigated and the impact of the droplets on the melt pool shape and ripple was also studied. Dynamic motion, development of melt pool and the formation of cladding layer were simulated. The simulated results for average surface roughness were compared with the experimental data and showed a comparable trend.

Numerical Simulation of Thermal Conductivity of Nanofluids

2010 ◽  
Author(s):  
Jing Fan ◽  
Liqiu Wang
Keyword(s):  
Thermal Conductivity ◽  
Heat Conduction ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Interfacial Thermal Resistance ◽  
Thermal Conductivity Ratio ◽  
Radius Of Gyration ◽  
Particle Volume ◽  
Geometrical Structures ◽  
Conductivity Enhancement

The recent first-principle model shows a dual-phase-lagging heat conduction in nanofluids at the macroscale. The macroscopic heat-conduction behavior and the thermal conductivity of nanofluids are determined by their molecular physics and microscale physics. We examine numerically effects of particle-fluid thermal conductivity ratio, particle volume fraction, shape, aggregation, and size distribution on macroscale thermal properties for nine types of nanofluids, without considering the interfacial thermal resistance and dynamic processes on particle-fluid interfaces and particle-particle contacting surfaces. The particle radius of gyration and non-dimensional particle-fluid interfacial area in the unit cell are two very important parameters in characterizing the effect of particles’ geometrical structures on thermal conductivity of nanofluids. Nanofluids containing cross-particle networks have conductivity which practically reaches the Hashin-Shtrikman bounds. Moreover, particle aggregation influences the effective thermal conductivity only when the distance between particles is less than the particle dimension. Uniformly-sized particles are desirable for the conductivity enhancement, although to a limited extent.

scholarly journals Nanofluid Thermal Conductivity and Effective Parameters

2018 ◽  
Vol 9 (1) ◽  
pp. 87 ◽  
Author(s):  
Sarah Simpson ◽  
Austin Schelfhout ◽  
Chris Golden ◽  
Saeid Vafaei
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Nanoparticle Concentration ◽  
Effective Parameters ◽  
Conductivity Enhancement ◽  
Nanoparticle Shape ◽  
Hybrid Nanofluids ◽  
Different Characteristics ◽  
The Impact ◽  
Base Liquid

Due to the more powerful and miniaturized nature of modern devices, conventional heat-transfer working fluids are not capable of meeting the cooling needs of these systems. Therefore, it is necessary to improve the heat-transfer abilities of commonly used cooling fluids. Recently, nanoparticles with different characteristics have been introduced to base liquids to enhance the overall thermal conductivity. This paper studies the influence of various parameters, including base liquid, temperature, nanoparticle concentration, nanoparticle size, nanoparticle shape, nanoparticle material, and the addition of surfactant, on nanofluid thermal conductivity. The mechanisms of thermal conductivity enhancement by different parameters are discussed. The impact of nanoparticles on the enhanced thermal conductivity of nanofluids is clearly shown through plotting the thermal conductivities of nanofluids as a function of temperature and/or nanoparticle concentration on the same graphs as their respective base liquids. Additionally, the thermal conductivity of hybrid nanofluids, and the effects of the addition of carbon nanotubes on nanofluid thermal conductivity, are studied. Finally, modeling of nanofluid thermal conductivity is briefly reviewed.

Thermal Conductivity Measurement for Carbon-Nanotube Suspensions with 3ω Method

2009 ◽  
Vol 60-61 ◽  
pp. 394-398 ◽  
Author(s):  
Gen Sheng Wu ◽  
Jue Kuan Yang ◽  
Shu Lin Ge ◽  
Yu Juan Wang ◽  
Min Hua Chen ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Carbon Nanotubes ◽  
Volume Fraction ◽  
Aqueous Suspension ◽  
Conductivity Measurement ◽  
3Ω Method ◽  
Conductivity Enhancement ◽  
Multi Walled Carbon Nanotubes ◽  
The Stability ◽  
Walled Carbon Nanotubes

The stable and homogeneneous aqueous suspension of carbon nanotubes was prepared in this study. The stability of the nanofluids was improved greatly due to the use of a new dispersant, humic acid. The thermal conductivity of the aqueous suspension was measured with the 3ω method. The experimental results showed that the thermal conductivity of the suspensions increases with the temperature and also is nearly proportional to the loading of the nanoparticles. The thermal conductivity enhancement of single-walled carbon nanotubes (SWNTs) suspensions is better than that of the multi-walled carbon nanotubes (MWNTs) suspensions. Especially for a volume fraction of 0.3846% SWNTs, the thermal conductivity is enhanced by 40.5%. Furthermore, the results at 30°C match well with Jang and Choi’s model.

Thermal Transport Properties of Nanofluids Containing Carbon Nanotubes

2008 ◽  
Author(s):  
Huaqing Xie ◽  
Lifei Chen ◽  
Yang Li ◽  
Wei Yu
Keyword(s):  
Thermal Conductivity ◽  
Carbon Nanotubes ◽  
Base Fluid ◽  
Volume Fraction ◽  
Thermal Conductivity Enhancement ◽  
Mechanochemical Reaction ◽  
Multiwalled Carbon ◽  
Conductivity Enhancement ◽  
Lower Viscosity ◽  
Potential Applications

Multiwalled carbon nanotubes (CNTs) have been treated by using a mechanochemical reaction method to enhance their dispersibility for producing CNT nanofluids. The thermal conductivity was measured by a short hot wire technique and the viscosity was measured by a rotary viscometer. The thermal conductivity enhancement reaches up to 17.5% at a volume fraction of 0.01 for an ethylene glycol based nanofluid. Temperature variation was shown to have no obvious effects on the thermal conductivity enhancement for the as prepared nanofluids. With an increase in the thermal conductivity of the base fluid, the thermal conductivity enhancement of a nanofluid decreases. At low volume fractions (<0.4 Vol%), nanofluids have lower viscosity than the corresponding base fluid due to lubricative effect of nanoparticles. When the volume fraction is higher than 0.4 Vol%, the viscosity increases with nanoparticle loadings. The prepared nanofluids, with no contamination to medium, good fluidity, stability, and high thermal conductivity, would have potential applications as coolants in advanced thermal systems.

Thermal Conductivity of Metal-Oxide Nanofluids: Particle Size Dependence and Effect of Laser Irradiation

2006 ◽  
Vol 129 (3) ◽  
pp. 298-307 ◽  
Author(s):  
Sang Hyun Kim ◽  
Sun Rock Choi ◽  
Dongsik Kim
Keyword(s):  
Thermal Conductivity ◽  
Particle Size ◽  
Effective Thermal Conductivity ◽  
Laser Irradiation ◽  
Volume Fraction ◽  
Suspended Particle ◽  
Titanium Dioxide Nanoparticles ◽  
Size Change ◽  
Conductivity Enhancement ◽  
Wide Range

The thermal conductivity of water- and ethylene glycol-based nanofluids containing alumina, zinc-oxide, and titanium-dioxide nanoparticles is measured using the transient hot-wire method. Measurements are performed by varying the particle size and volume fraction, providing a set of consistent experimental data over a wide range of colloidal conditions. Emphasis is placed on the effect of the suspended particle size on the effective thermal conductivity. Also, the effect of laser-pulse irradiation, i.e., the particle size change by laser ablation, is examined for ZnO nanofluids. The results show that the thermal-conductivity enhancement ratio relative to the base fluid increases linearly with decreasing the particle size but no existing empirical or theoretical correlation can explain the behavior. It is also demonstrated that high-power laser irradiation can lead to substantial enhancement in the effective thermal conductivity although only a small fraction of the particles are fragmented.

Effect of Heating Temperature on Microstructure of Directionally Solidified Ni-43Ti-7Al Alloy

2017 ◽  
Vol 898 ◽  
pp. 552-560 ◽  
Author(s):  
Lei Zhou ◽  
Li Jing Zheng ◽  
Hu Zhang
Keyword(s):  
Volume Fraction ◽  
Heating Temperature ◽  
Thermal Gradients ◽  
Directionally Solidified ◽  
Melt Structure ◽  
Cast Sample ◽  
The Stability ◽  
Solid Liquid Interface ◽  
Solid Liquid ◽  
Liquid Metal Cooling

By liquid metal cooling (LMC) process, the Ni-43Ti-7Al (at.%) alloy has been directionally solidified (DS) at different heating temperatures (1450°C, 1550°C, 1650°C) and a constant withdrawal rate of 100μm/s. The results showed that anomalous eutectic structures which consisted of Ti2Ni and TiNi phases were formed at the grain boundaries of as-cast sample and similar structures were also observed in the intercellular regions of DS samples. However, the microstructure changed from the equiaxial structure to the cellular structure due to the axial thermal gradients imposed. After DS, the NiTi and Ti2Ni phases preferentially grew along certain orientation, but the preferred crystallographic orientations of them changed as the heating temperature increased to 1650°C, which might be related to the change of melt structure. As expected, the volume fraction of Ti2Ni increased from 3.3% to 5.2% and the cellular spacing decreased from 47.8μm to 27.0μm as heating temperature increased. In addition, the stability of solid/liquid interface decreased, resulting from the coupling effects of G and ΔT- with the heating temperature increasing.

Modeling Coupled Conduction–Convection Ice Formation on Horizontal Axially Finned and Unfinned Tubes

2017 ◽  
Vol 139 (12) ◽  
Author(s):  
Hassan M. S. Al-Sarrach ◽  
Ghalib Y. Kahwaji ◽  
Mohamed A. Samaha
Keyword(s):  
Natural Convection ◽  
Liquid Interface ◽  
Ice Formation ◽  
Finite Difference Schemes ◽  
Freezing Process ◽  
Liquid Region ◽  
Water Density ◽  
Solid Liquid Interface ◽  
Solid Liquid ◽  
The Impact

The freezing of water around immersed unfinned and finned horizontal tubes is simulated numerically. The impact of natural convection as well as the water density inversion with temperature is considered. The equations governing both fluid flow and heat transfer around the tubes and through the solid–liquid interface are solved using finite difference schemes. To follow the moving solid–liquid boundary, dynamic grid generation is performed using the elliptic partial differential equation method with iterative interpolating smoothing to avoid divergence. For validation, the present results for unfinned tubes are compared with experimental studies reported in the literature. The present numerical simulations are aimed at improving our understanding of the parameters affecting the freezing process around both finned and unfinned tubes. The results showed that the flow patterns are similar in both tube configurations with one main vortex in the liquid region when there is no inversion in the water density. The presence of fins complicates the distribution of local Nusselt number along the solid–liquid interface in comparison with the unfinned tube. The impact of natural convection on the rate of ice formation is limited to the initial period of the freezing process. The results also show the freezing enhancement when utilizing fins. An accumulated ice mass correlation is developed for each tube configuration. This model can be used to optimize the design of both finned and unfinned tubes in energy storage systems, which are viable tools for air conditioning load shifting and leveling.

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