scholarly journals Modelling of Effective Thermal Conductivity of Composites Filled with Core-Shell Fillers

Materials ◽  
2020 ◽  
Vol 13 (23) ◽  
pp. 5480
Author(s):  
Jan Czyzewski ◽  
Andrzej Rybak ◽  
Karolina Gaska ◽  
Robert Sekula ◽  
Czeslaw Kapusta
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Thermal Conduction ◽  
Hexagonal Boron Nitride ◽  
Core Material ◽  
Core Shell ◽  
Glass Spheres ◽  
Materials Modelling ◽  
Properties Of Materials ◽  
Good Agreement

An effective model to calculate thermal conductivity of polymer composites using core-shell fillers is presented, wherein a core material of filler grains is covered by a layer of a high-thermal-conductivity (HTC) material. Such fillers can provide a significant increase of the composite thermal conductivity by an addition of a small amount of the HTC material. The model employs the Lewis-Nielsen formula describing filled systems. The effective thermal conductivity of the core-shell filler grains is calculated using the Russel model for porous materials. Modelling results are compared with recent measurements made on composites filled with cellulose microbeads coated with hexagonal boron nitride (h-BN) platelets and good agreement is demonstrated. Comparison with measurements made on epoxy composites, using silver-coated glass spheres as a filler, is also provided. It is demonstrated how the modelling procedure can improve understanding of properties of materials and structures used and mechanisms of thermal conduction within the composite.

Brownian-Motion-Based Convective-Conductive Model for the Effective Thermal Conductivity of Nanofluids

2005 ◽  
Vol 128 (6) ◽  
pp. 588-595 ◽  
Author(s):  
Ravi Prasher ◽  
Prajesh Bhattacharya ◽  
Patrick E. Phelan
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Particle Sizes ◽  
Brownian Movement ◽  
Liquid Temperature ◽  
Interfacial Resistance ◽  
Conduction Model ◽  
Order Of Magnitude ◽  
Base Liquid ◽  
Good Agreement

Here we show through an order-of-magnitude analysis that the enhancement in the effective thermal conductivity of nanofluids is due mainly to the localized convection caused by the Brownian movement of the nanoparticles. We also introduce a convective-conductive model which accurately captures the effects of particle size, choice of base liquid, thermal interfacial resistance between the particles and liquid, temperature, etc. This model is a combination of the Maxwell-Garnett (MG) conduction model and the convection caused by the Brownian movement of the nanoparticles, and reduces to the MG model for large particle sizes. The model is in good agreement with data on water, ethylene glycol, and oil-based nanofluids, and shows that the lighter the nanoparticles, the greater the convection effect in the liquid, regardless of the thermal conductivity of the nanoparticles.

scholarly journals Composites with Excellent Insulation and High Adaptability for Lightweight Envelopes

Energies ◽  
2018 ◽  
Vol 12 (1) ◽  
pp. 53 ◽  
Author(s):  
Liang Guo ◽  
Wenbin Tong ◽  
Yexin Xu ◽  
Hong Ye
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Flow Direction ◽  
Base Material ◽  
Core Material ◽  
Insulation Materials ◽  
The Core ◽  
Cross Section Area ◽  
Heat Flow Direction ◽  
Section Area

Lightweight insulation materials are widely used in lightweight buildings, cold-chain vehicles and containers. A kind of insulation composite, which can combine the super insulation of state-of-the-art insulation materials or structures and the machinability or adaptability of traditional insulation materials, was proposed. The composite consists of two components, i.e., polyurethane (PU) foam as the base material and vacuum insulation panel (VIP) or silica aerogel as the core material. The core material is in plate shape and covered with the base material on all sides. The thermal conductivity of the core material is nearly one order lower than that of the base material. The effective thermal conductivity of the insulation composite was explored by simulation. Simulation results show that the effective thermal conductivity of the composite increases with the increase of the thermal conductivity of the core material. The effective thermal conductivities of the composites decrease with the increase of the cross-section area of the core material perpendicular to heat flow direction and the thicknesses of the core material parallel with heat flow direction. These rules can be elucidated by a series-parallel mode thermal resistance network method, which was verified by the measured results. For composite with a VIP as the core material, when the cross-section area and thickness of the VIP are respectively larger than 60% and 21% of the composite, the composite’s effective thermal conductivity can be 50% or less than that of the base material. Simulated heat loss of the envelope adopting the insulation composites with VIP as the core material is nearly a half of that of the envelope adopting traditional insulation materials.

Effective Thermal Conductvity of Three-Phase Soils

2012 ◽  
Author(s):  
Fabio Gori ◽  
Sandra Corasaniti
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Heat Fluxes ◽  
Water Volume ◽  
Two Phase ◽  
Empirical Constant ◽  
Three Phase ◽  
Theoretical Predictions ◽  
Porosity Ratio ◽  
Good Agreement

The aim of the present paper is to determine the effective thermal conductivity of three-phase soils, made of a quasi-spherical solid grain, and surrounded by two phase, which can be water and air or water and ice. The effective thermal conductivity is obtained theoretically by integrating the conduction equation under the thermal distribution of parallel heat fluxes in steady-state. The effective thermal conductivity is evaluated at a given degree of porosity (ratio between the void volume and the total one) and different degrees of saturation (ratio between the water volume and the void one) from dryness up to saturation. Comparisons between experimental data and theoretical predictions confirm that the present model can predict the effective thermal conductivity with a fairly good agreement without using any empirical constant.

scholarly journals Modelling Thermal Conduction in Nanoparticle Aggregates in the Presence of Surfactants

Nanomaterials ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 2288
Author(s):  
Nikolaos P. Karagiannakis ◽  
Eugene D. Skouras ◽  
Vasilis N. Burganos
Keyword(s):  
Thermal Conductivity ◽  
Fractal Dimension ◽  
Thermal Conduction ◽  
Numerical Technique ◽  
Experimental Studies ◽  
Aggregate Formation ◽  
Number Density ◽  
Nanoparticle Aggregates ◽  
Transfer Properties ◽  
Good Agreement

Many theoretical and experimental studies have shown that the addition of nanoparticles into conventional fluids may generate nanofluids with significantly improved heat transfer properties. In the present work, the effect of nanoparticle aggregation on the thermal conductivity of nanofluids is studied, considering also the effect of surfactants that are typically added to stabilise the nanofluid. A method for simulating aggregate formation is developed here that allows tailoring of the fractal dimension and the number density of the nanoparticles to desired values. The method is shown to be computationally simple and fast. Data that are extracted from electron microscope images are compared with simulation results regarding surface porosity and the autocorrelation function. The surfactants are modelled as a layer around the particles, and the effective thermal conductivity is calculated with a meshless numerical technique. Significant increase in conductivity is observed for small values of the fractal dimension and for large number density of particles in the aggregate. The simulations are in good agreement with experimental results. It is also concluded that prediction of the conductivity of such nanofluids requires the knowledge of the type and the amount of the surfactant added.

Numerical Simulation on the Effective Thermal Conductivity of Porous Material

2012 ◽  
Vol 557-559 ◽  
pp. 2388-2395
Author(s):  
Shan Qi Liu ◽  
Yong Bing Li ◽  
Xu Yao Liu ◽  
Bo Jing Zhu ◽  
Hui Quan Tian ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Numerical Simulation ◽  
Porous Material ◽  
Effective Thermal Conductivity ◽  
Random Distribution ◽  
Simulation Method ◽  
Solid Skeleton ◽  
Material Models ◽  
Application Prospects ◽  
Good Agreement

The thermal conductivity of porous material is an important basic parameter, but it is not easy to study, due to the complexity of the structure of porous material. In the present work, we show a numerical simulation method to study the thermal conductivity of the porous material. We generate 200 material models with random distribution of solid skeleton and air for a fixed porosity, then we get the effective thermal conductivity of the porous material by Monte Carlo statistical analysis. The results are in good agreement with the previous empirical formula. The numerical results show that the effective thermal conductivity of porous material depends on the thermophysical properties of solid skeleton and air, the pore distribution and pore structure, the numerical error decreases with the increase in the number of grids, this finite element method can be used to estimate the effective thermal conductivity of composites and maybe has broad application prospects in terms of computing the effective thermal conductivity and other physical properties of composite material with known components.

Enhancing the effective thermal conductivity of Kapton-type polyimide sheets via the use of hexagonal boron nitride

2018 ◽  
Vol 662 ◽  
pp. 1-7 ◽  
Author(s):  
Masashi Haruki ◽  
Jun Tada ◽  
Keitaro Tanaka ◽  
Hajime Onishi ◽  
Yukio Tada
Keyword(s):  
Thermal Conductivity ◽  
Boron Nitride ◽  
Effective Thermal Conductivity ◽  
Hexagonal Boron Nitride

On: “An analytical study of a two-layer transient thermal conduction problem as applied to soil temperature surveys” by T. H. Larson and A. T. Hsui (February 1992 GEOPHYSICS, p. 306–312)

Geophysics ◽  
1992 ◽  
Vol 57 (12) ◽  
pp. 1644-1645
Author(s):  
Virgil J. Lunardini
Keyword(s):  
Thermal Conductivity ◽  
Thermal Diffusivity ◽  
Thermal Conduction ◽  
Thermal Response ◽  
Periodic Surface ◽  
Ground Temperatures ◽  
Ground Conditions ◽  
Thermal Properties Of Materials ◽  
Properties Of Materials ◽  
Transient Thermal

This paper presents a solution to the two‐layer conduction problem, a problem which has already been solved exactly and published (Lachenbruch, 1959; Lunardini, 1981). In fact the three‐layer solution is also available, (Lachenbruch, 1959). Unfortunately the Larson and Hsui paper uses an incorrect boundary condition for the energy flow continuity between the layers; this refers to the last equation after equation (3), or equation (A-20) of their paper. The temperature gradient must be multiplied by the thermal conductivity, not the thermal diffusivity as the paper has done. The results obtained in the paper are only valid if the heat capacities ρc of the two layers are equal. However, few soils have the same heat capacity, as can be seen from the thermal properties of materials often encountered in geotechnical situations, given in Table 1. Thus, a second parameter is required for interpreting ground temperatures: the ratio of the thermal conductivities of the two layers. The interpretation given to the effects of only the thermal diffusivity ratios is then open to question. Calculations of the same ground conditions as used by Larsen and Hsui, with the same diffusivity ratios but with realistic thermal conductivity ratios, give significantly different temperature predictions. Of course, the general conclusions of the paper on the profound effect of layering on the thermal response of soils to periodic surface temperatures are still true.

A MODEL FOR PREDICTING THE EFFECTIVE THERMAL CONDUCTIVITY OF NANOPARTICLE-FLUID SUSPENSIONS

2006 ◽  
Vol 05 (01) ◽  
pp. 23-33 ◽  
Author(s):  
S. M. S. MURSHED ◽  
K. C. LEONG ◽  
C. YANG
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Body Centered Cubic ◽  
Geometrical Structures ◽  
New Model ◽  
Water Based ◽  
Classical Models ◽  
Theoretical Results ◽  
Enhanced Thermal Conductivity ◽  
Good Agreement

The uniformity and homogeneously dispersed nanoparticles in base fluids contribute to enhanced thermal conductivity of the mixture. By considering the uniformity and geometrical structures (e.g., body-centered cubic) of homogeneously dispersed nanoparticles in base fluids, a model for determining the effective thermal conductivity (ETC) of such nanoparticle-fluid suspensions, commonly known as nanofluids is proposed in this study. The theoretical results of the effective thermal conductivities of TiO 2/Deionized (DI) water and Al 2 O 3/DI water-based nanofluids are presented, and they are found to be in good agreement with our experimental results and also with those reported in the literature. The new model presented in this study shows a better prediction of the effective thermal conductivity of nanofluids compared to other classical models attributed to Maxwell, Hamilton–Crosser, and Bruggeman.

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