Numerical Modeling of Nanofluid Thermal Conductivity: The Effect of Nanonetwork on Thermal Transport Behavior

2019 ◽  
Vol 141 (12) ◽  
Author(s):  
Binjian Ma ◽  
Debjoyti Banerjee
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Thermal Transport ◽  
Strong Dependence ◽  
Contemporary Literature ◽  
Theoretical Models ◽  
Conductivity Enhancement ◽  
Transport Behavior ◽  
The Impact ◽  
Different Levels

Abstract Nanofluids have drawn increasing attention in heat transfer applications due to their anomalous enhancement of the thermophysical properties in contemporary literature. Various studies have shown that the addition of minute concentration of the nanoparticles to a base solvent can yield dramatic enhancement of the effective thermal conductivity. A number of parameters have been reported to affect the level of such enhancement such as size, shape, morphology, concentration, and material properties of the nanoparticles. Many different theoretical models have also been proposed in the past literature for predicting the thermal conductivity of nanofluids under different conditions. In general, these models are based on either simplified static composite model or nanoconvection effect considering the Brownian motion of the nanoparticles. However, a few studies have explored the impact of nanoparticle aggregation on the nanofluid thermal conductivity. In particular, the formation of porous percolation structure by the nanoparticles can alter the effective thermal conductivity of nanofluid substantially. In this study, a two-stage numerical simulation is performed to analyze the thermal transport behavior inside nanofluid considering different levels of percolation network formed by the nanoparticles. Based on the simulation results, an empirical model is developed to predict the effective thermal conductivity of nanofluid as a function of nanoparticle size, concentration, and the permeability of nano-aggregation. The results demonstrated a strong dependence of nanofluid thermal conductivity on the nanocluster density, where a looser nanonetwork can yield a significantly higher level of thermal conductivity enhancement under the same particle size and concentration conditions.

Numerical Simulations of Thermal Transport in Random Porous Materials and Powder Systems Using the Smoothed Particle Hydrodynamics Method

2017 ◽  
Author(s):  
Deepak Shah ◽  
Alexey N. Volkov
Keyword(s):  
Thermal Conductivity ◽  
Porous Materials ◽  
Effective Thermal Conductivity ◽  
Smoothed Particle Hydrodynamics ◽  
Thermal Transport ◽  
Thermal Contact Conductance ◽  
Powder Bed ◽  
Particle Hydrodynamics ◽  
Smoothed Particle ◽  
Powder Particles

A numerical method to solve thermal transport problems in powder bed systems and porous materials with finite thermal contact conductance at interfaces between individual powder particles or grains is developed based on the Smoothed Particle Hydrodynamics approach. The developed method is applied to study the effective thermal conductivity of two-dimensional random powder bed systems with binary distribution of powder particles radii. The effects of particle size distribution parameters, density parameter, and effective interface area between particles on the effective thermal conductivity are studied. It is found that at finite Biot number, which characterizes the ratio of the interfacial conductance to the conductance of the bulk powder material, the effective thermal conductivity of porous samples increases with increasing fraction of particles of larger size.

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.

THE EFFECT OF VERTICAL AIR GAPS TO THERMAL TRANSMITTANCE OF HORIZONTAL THERMAL INSULATING LAYER

2009 ◽  
Vol 15 (3) ◽  
pp. 309-315 ◽  
Author(s):  
Jolanta Šadauskienė ◽  
Andrius Buska ◽  
Arūnas Burlingis ◽  
Raimondas Bliūdžius ◽  
Albinas Gailius
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Thermal Insulation ◽  
Standard Method ◽  
Mineral Wool ◽  
Insulating Layer ◽  
Air Gaps ◽  
Thermal Transmittance ◽  
Thermal Insulating ◽  
The Impact

In order to reduce the amounts of work at the construction site, single‐ply dual density thermal insulating roofing boards are used with increasing frequency for thermal insulation of flat roofs. In this case, the joints between boards are not overlapped by the other ply over it; therefore gaps of varying width form between the sides of the boards through the entire thickness of the insulating layer, whose effect on the effective thermal conductivity of the thermal insulating layer must be evaluated. The aim of this project was to assess the reliability of standard method, used to determine the impact of such air gaps on the effective thermal conductivity of the thermal insulating layer by comparing the results of calculations and the results of measurements of thermal conductivity, also to determine the correction factors for thermal transmittance of horizontal thermal insulation layers due to the forming vertical air gaps between the single‐ply mineral wool boards. After measurements of thermal resistances of 50 mm thick thermal insulation board with the air gaps which width varied from 3 mm to 20 mm, it was determined that the thermal conductivity value of the air gaps increases with the increment of the width of air gaps. After completion the experimental measurements of thermal conductivity it was determined that the height of closed and unventilated or partly ventilated air gaps has no effect on the properties of effective thermal conductivity of the thermal insulation layer when the air gap width is up to 5 mm. When wider unventilated or partly ventilated air gaps occur, the effective thermal conductivity coefficient increases proportionally as the height of the air gaps increases. Calculated according to the standard method the affix to the thermal transmittance is overly general and not always appropriate. In some cases it is 6 times higher or 4 times lower than the measured one. In this paper a method to evaluate the effects of air gaps by the use of correction factor to the thermal transmittance of the horizontal thermal insulating layer is proposed. Santrauka Nornt sumažinti darbų apimtis statybos vietoje, stogams šiltinti vis dažniau naudojamos vienu sluoksniu klojamos dvitankės termoizoliacinės plokštės. Šiuo atveju plokščių sandūros neperdengiamos, todėl tarp plokščių kraštinių susidaro įvairaus pločio plyšių, kurių įtaka termoizoliacinio sluoksnio šilumai perduoti turi būti įvertinta. Šio darbo tikslas yra įvertinti standartinio metodo, taikomo tokių plyšių poveikiui sluoksnio šilumos laidumui, patikimumui nustatyti lyginant skaičiavimo ir šilumos laidumo matavimų rezultatus, nustatyti horizontaliojo termoizoliacinio sluoksnio šilumos perdavimo koeficiento pataisas dėl vertikaliųjų oro plyšių susidarymo. Apskaičiavus 50 mm storio termoizoliacinio sluoksnio oro plyšių šilumines varžas, kai plyšių plotis yra nuo 3–20 mm, nustatyta, kad oro plyšių šilumos laidumo koeficiento vertė didėja didėjant oro plyšio pločiui. Atlikus eksperimentinius šilumos laidumo matavimus, nustatyta, kad susidarančių uždarų ir nevėdinamų arba iš dalies vėdinamų oro plyšių aukštis neturi įtakos termoizoliacinio sluoksnio šilumos laidumo savybėms, kai oro plyšys yra iki 5 mm pločio. Esant platesniems uždariems ir nevėdinamiems oro plyšiams, šilumos laidumo koeficientas proporcingai didėja didėjant oro plyšių aukščiui. Pagal standartinį metodą skaičiuotas šilumos perdavimo koeficiento priedas yra per daug apibendrinantis ir ne visada tinkamas. Kai kuriais atvejais jis yra 6 kartus didesnis arba 4 kartus mažesnis už išmatuotąjį. Šiame darbe pasiūlytas horizontaliojo termoizoliacinio sluoksnio šilumos perdavimo koeficiento priedo, naudojamo plyšių įtakai įvertinti, skaičiavimo metodas.

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.

Dual Role of Nanoparticles in the Thermal Conductivity Enhancement of Nanoparticle Suspensions

2005 ◽  
Author(s):  
Calvin H. Li ◽  
G. P. Peterson
Keyword(s):  
Experimental Data ◽  
Thermal Conductivity ◽  
Brownian Motion ◽  
Theoretical Models ◽  
Conductivity Enhancement ◽  
Nanoparticle Suspensions ◽  
The Difference ◽  
Physical Phenomena ◽  
Good Agreement

Experimental evidence exists that the addition of a small quantity of nanoparticles to a base fluid, can have a significant impact on the effective thermal conductivity of the resulting suspension. The causes for this are currently thought to be due to a combination of two distinct mechanisms. The first is due to the change in the thermophysical properties of the suspension, resulting from the difference in the thermal conductivity of the fluid and the particles, and the second is thought to be due to the transport of thermal energy by the particles, due to the Brownian motion of the particles. In order to better understand these phenomena, a theoretical model has been developed that examines the effect of the Brownian motion. In this model, the well-known approach first presented by Maxwell, is combined with a new expression that incorporates the effect of the Brownian motion and describes the physical phenomena that occurs because of it. The results indicate that the enhanced thermal conductivity may not in fact be due to the transport of energy by the particles, but rather, due to the stirring motion caused by the movement of the nanoparticles which enhances the heat transfer within the fluid. The resulting model shows good agreement when compared with the existing experimental data and perhaps more importantly helps to explain the trends observed from a fundamental physical perspective. In addition, it provides a possible explanation for the differences that have been observed between the previously obtained experimental data, the predictions obtained from Maxwell’s equation and the theoretical models developed by other investigators.

Thermal Transport in Nanotube Composites for Large-Area Macroelectronics

2005 ◽  
Author(s):  
Satish Kumar ◽  
Muhammad A. Alam ◽  
Jayathi Y. Murthy
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Thermal Transport ◽  
Channel Length ◽  
Tube Length ◽  
Finite Volume Scheme ◽  
Large Area ◽  
Contact Conductance ◽  
Channel Lengths ◽  
Contact Parameters

Thermal transport in a new class of nanocomposites composed of isotropic 2D ensembles of nanotubes or nanowires in a substrate is considered for use as the channel region of thin film transistors. The random ensemble is generated numerically and simulated using a finite volume scheme. The effective thermal conductivity of a nanotube network embedded in a thin substrate is computed. Percolating conduction in the composite is studied as a function of wire/tube densities and channel lengths. The conductance exponents are validated against available experimental data for long channels devices. The effect of tube-tube contact conductance, tube-substrate contact conductance and substrate-tube conductivity ratio is analyzed for various channel lengths. It is found that beyond a certain limiting value, contact parameters do not result in any significant change in the effective thermal conductivity of the composite. It is also observed that the effective thermal conductivity of the composite saturates beyond a limiting channel-length/tube length ratio for the range of contact parameters under consideration.

scholarly journals Lattice thermal transport in two-dimensional alloys and fractal heterostructures

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Aravind Krishnamoorthy ◽  
Nitish Baradwaj ◽  
Aiichiro Nakano ◽  
Rajiv K. Kalia ◽  
Priya Vashishta
Keyword(s):  
Thermal Conductivity ◽  
Thermal Transport ◽  
Lattice Thermal Conductivity ◽  
Material Design ◽  
Two Dimensional ◽  
Scale Free ◽  
Dopant Atoms ◽  
Non Equilibrium Molecular Dynamics ◽  
Dynamics Simulations ◽  
The Impact

AbstractEngineering thermal transport in two dimensional materials, alloys and heterostructures is critical for the design of next-generation flexible optoelectronic and energy harvesting devices. Direct experimental characterization of lattice thermal conductivity in these ultra-thin systems is challenging and the impact of dopant atoms and hetero-phase interfaces, introduced unintentionally during synthesis or as part of deliberate material design, on thermal transport properties is not understood. Here, we use non-equilibrium molecular dynamics simulations to calculate lattice thermal conductivity of $${\mathrm {(Mo|W)Se_2}}$$ ( Mo | W ) Se 2 monolayer crystals including $${\mathrm {Mo}}_{1-x}{\mathrm {W}}_x{\mathrm {Se_2}}$$ Mo 1 - x W x Se 2 alloys with substitutional point defects, periodic $${\mathrm {MoSe_2}|\mathrm {WSe_2}}$$ MoSe 2 | WSe 2 heterostructures with characteristic length scales and scale-free fractal $${\mathrm {MoSe_2}}|{\mathrm {WSe_2}}$$ MoSe 2 | WSe 2 heterostructures. Each of these features has a distinct effect on phonon propagation in the crystal, which can be used to design fractal and periodic alloy structures with highly tunable thermal conductivities. This control over lattice thermal conductivity will enable applications ranging from thermal barriers to thermoelectrics.

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