Analysis of Heat Conduction in Dilute Nanofluids

2009 ◽  
Author(s):  
Le-Ping Zhou ◽  
Bu-Xuan Wang ◽  
Xiao-Ze Du ◽  
Yong-Ping Yang
Keyword(s):  
Thermal Conductivity ◽  
Heat Conduction ◽  
Steady State ◽  
Effective Thermal Conductivity ◽  
Effective Medium Theory ◽  
Constant Heat Flux ◽  
Brownian Diffusion ◽  
Uniform Temperature ◽  
Medium Theory ◽  
Basic Fluid

In this paper, we assume that a nanofluid is a mixture consisting of a continuous base fluid component and a discontinuous nanoparticle component. Then, based on the analysis of Buongiorno in 2006 for critical slip mechanisms in nanofluids, we consider the effects of Brownian diffusion and thermophoresis of nanoparticles on heat and mass flux in nanofluid. With the coupled conservation equations, we analyze the heat conduction properties of general nanofluids under three conditions: 1) stationary fluid with uniform temperature, 2) stationary fluid under constant temperature boundary, and 3) stationary fluid under constant heat flux boundary. The results show that nanofluid effective thermal conductivity depends on the thermal conductivity of nanoparticle and basic fluid, particle concentration, particle size, particle distribution, Brownian and thermal diffusion, boundary condition and time. It indicates that the nanofluid effective thermal conductivity can be well predicted for stationary fluid with uniform temperature from classical effective medium theory such as Maxwell’s approach. However, the measurements applying steady or unsteady heat conduction methods for pure materials fail to predict correctively the effective thermal conductivity of nanofluid and are influenced by boundary conditions. Preliminary conclusions include approximate correlations of effective thermal conductivity of dilute nanofluids using steady state and quasi-steady state measuring methods.

On the Effective Thermal Conductivity of Nanofluids With Fractal Aggregation

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
C. G. Subramaniam
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Effective Medium Theory ◽  
Functionally Graded ◽  
Fractal Aggregates ◽  
Medium Theory ◽  
Analytical Approximations ◽  
Proposed Model ◽  
Dispersing Medium ◽  
Dilute Limit

A generalized effective medium theory (EMT) is proposed to account for the fractal structure of the dispersed phase in a dispersing medium under the dilute limit. The thermal conductivity of nanofluids with fractal aggregates is studied using the proposed model. Fractal aggregates are considered as functionally graded spherical inclusions and its effective thermal conductivity is derived as a function of its fractal dimension. The results are studied for self-consistency and accuracy within the limitations of the analytical approximations used.

Effective Thermal Conductivity of MoSi2/SiC Composites

2005 ◽  
Vol 492-493 ◽  
pp. 551-554
Author(s):  
Guang Zhao Bai ◽  
Wan Jiang ◽  
G. Wang ◽  
Li Dong Chen ◽  
X. Shi
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Effective Medium Theory ◽  
Thermal Conductance ◽  
Inclusion Size ◽  
Laser Flash ◽  
Flash Method ◽  
Medium Theory ◽  
Interfacial Thermal Conductance ◽  
Sic Composites

Thermal conductivity of as-prepared MoSi2/SiC composites has been determined by Laser Flash method. Interfacial thermal conductance for composites with 100nm SiC and with 0.5µm has been determined by using effective medium theory. The results of interfacial thermal conductance exhibit that both the inclusion size and the clustering of the inclusions play an important role in determining composite thermal conductivity.

Particle Aspect-Ratio Effects on the Thermal Conductivity of Micro- and Nanoparticle Suspensions

2008 ◽  
Vol 130 (8) ◽  
Author(s):  
Anna S. Cherkasova ◽  
Jerry W. Shan
Keyword(s):  
Thermal Conductivity ◽  
Silicon Carbide ◽  
Aspect Ratio ◽  
Effective Thermal Conductivity ◽  
Effective Medium Theory ◽  
Effective Medium ◽  
Particulate Composites ◽  
Interfacial Thermal Resistance ◽  
Recent Experimental Data ◽  
Medium Theory

The influence of particle anisotropy on the effective thermal conductivity of a suspension is experimentally investigated. Suspensions of micron-sized, silicon-carbide particles with varying aspect-ratio distributions were prepared and measured. It is shown that the conductivity of the silicon-carbide suspensions can be quantitatively predicted by the effective medium theory of Nan et al. (1997, “Effective Thermal Conductivity of Particulate Composites With Interfacial Thermal Resistance,” J. Appl. Phys. 81(10), pp. 6692–6699), provided the volume-weighted aspect ratio of the particles is used. Recent experimental data on multiwalled-nanotube-in-oil suspensions by Yang et al. (2006, “Thermal and Rheological Properties of Carbon Nanotube-in-Oil Dispersions,” J. Appl. Phys., 99(11), 114307) are also analyzed and shown to be in at least qualitative agreement with the effective-medium-theory prediction that the thermal conductivity of suspensions is enhanced by large aspect-ratio particles.

scholarly journals Effect of Alignment on Enhancement of Thermal Conductivity of Polyethylene–Graphene Nanocomposites and Comparison with Effective Medium Theory

Nanomaterials ◽  
2020 ◽  
Vol 10 (7) ◽  
pp. 1291
Author(s):  
Fatema Tarannum ◽  
Rajmohan Muthaiah ◽  
Roshan Sameer Annam ◽  
Tingting Gu ◽  
Jivtesh Garg
Keyword(s):  
Thermal Conductivity ◽  
Thermal Management ◽  
Laser Scanning ◽  
Effective Medium Theory ◽  
Laser Scanning Confocal Microscopy ◽  
Effective Medium ◽  
Medium Theory ◽  
K Value ◽  
Graphene Nanocomposites ◽  
Scanning Confocal Microscopy

Thermal conductivity (k) of polymers is usually limited to low values of ~0.5 Wm−1K−1 in comparison to metals (>20 Wm−1K−1). The goal of this work is to enhance thermal conductivity (k) of polyethylene–graphene nanocomposites through simultaneous alignment of polyethylene (PE) lamellae and graphene nanoplatelets (GnP). Alignment is achieved through the application of strain. Measured values are compared with predictions from effective medium theory. A twin conical screw micro compounder is used to prepare polyethylene–graphene nanoplatelet (PE-GnP) composites. Enhancement in k value is studied for two different compositions with GnP content of 9 wt% and 13 wt% and for applied strains ranging from 0% to 300%. Aligned PE-GnP composites with 13 wt% GnP displays ~1000% enhancement in k at an applied strain of 300%, relative to k of pristine unstrained polymer. Laser Scanning Confocal Microscopy (LSCM) is used to quantitatively characterize the alignment of GnP flakes in strained composites; this measured orientation is used as an input for effective medium predictions. These results have important implications for thermal management applications.

Steady-State Investigation of Vapor Deposited Micro Heat Pipe Arrays

1995 ◽  
Vol 117 (1) ◽  
pp. 75-81 ◽  
Author(s):  
A. K. Mallik ◽  
G. P. Peterson
Keyword(s):  
Thermal Conductivity ◽  
Steady State ◽  
Surface Temperature ◽  
Heat Pipe ◽  
Effective Thermal Conductivity ◽  
Heat Pipes ◽  
Temperature Gradients ◽  
Bottom Surface ◽  
Micro Heat Pipe ◽  
Micro Heat Pipes

An experimental investigation of vapor deposited micro heat pipe arrays was conducted using arrays of 34 and 66 micro heat pipes occupying 0.75 and 1.45 percent of the cross-sectional area, respectively. The performance of wafers containing the arrays was compared with that of a plain silicon wafer. All of the wafers had 8 × 8 mm thermofoil heaters located on the bottom surface to simulate the active devices in an actual application. The temperature distributions across the wafers were obtained using a Hughes Probeye TVS Infrared Thermal Imaging System and a standard VHS video recorder. For wafers containing arrays of 34 vapor deposited micro heat pipes, the steady-state experimental data indicated a reduction in the maximum surface temperature and temperature gradients of 24.4 and 27.4 percent, respectively, coupled with an improvement in the effective thermal conductivity of 41.7 percent. For wafers containing arrays of 66 vapor deposited micro heat pipes, the corresponding reductions in the surface temperature and temperature gradients were 29.0 and 41.7 percent, respectively, and the effective thermal conductivity increased 47.1 percent, for input heat fluxes of 4.70 W/cm2. The experimental results were compared with the results of a previously developed numerical model, which was shown to predict the temperature distribution with a high degree of accuracy, for wafers both with and without the heat pipe arrays.

Study on Radial Temperature Distribution of Aluminum Dispersed Nuclear Fuels: U3O8-Al, U3Si2-Al, and UN-Al

2018 ◽  
Vol 4 (3) ◽  
Author(s):  
Jayangani I. Ranasinghe ◽  
Ericmoore Jossou ◽  
Linu Malakkal ◽  
Barbara Szpunar ◽  
Jerzy A. Szpunar
Keyword(s):  
Thermal Conductivity ◽  
Heat Conduction ◽  
Steady State ◽  
Temperature Gradient ◽  
Heat Conduction Equation ◽  
Conduction Equation ◽  
Temperature Profiles ◽  
Nuclear Fuels ◽  
State Heat ◽  
Steady State Heat

The understanding of the radial distribution of temperature in a fuel pellet, under normal operation and accident conditions, is important for a safe operation of a nuclear reactor. Therefore, in this study, we have solved the steady-state heat conduction equation, to analyze the temperature profiles of a 12 mm diameter cylindrical dispersed nuclear fuels of U3O8-Al, U3Si2-Al, and UN-Al operating at 597 °C. Moreover, we have also derived the thermal conductivity correlations as a function of temperature for U3Si2, uranium mononitride (UN), and Al. To evaluate the thermal conductivity correlations of U3Si2, UN, and Al, we have used density functional theory (DFT) as incorporated in the Quantum ESPRESSO (QE) along with other codes such as Phonopy, ShengBTE, EPW (electron-phonon coupling adopting Wannier functions), and BoltzTraP (Boltzmann transport properties). However, for U3O8, we utilized the thermal conductivity correlation proposed by Pillai et al. Furthermore, the effective thermal conductivity of dispersed fuels with 5, 10, 15, 30, and 50 vol %, respectively of dispersed fuel particle densities over the temperature range of 27–627 °C was evaluated by Bruggman model. Additionally, the temperature profiles and temperature gradient profiles of the dispersed fuels were evaluated by solving the steady-state heat conduction equation by using Maple code. This study not only predicts a reduction in the centerline temperature and temperature gradient in dispersed fuels but also reveals the maximum concentration of fissile material (U3O8, U3Si2, and UN) that can be incorporated in the Al matrix without the centerline melting. Furthermore, these predictions enable the experimental scientists in selecting an appropriate dispersion fuel with a lower risk of fuel melting and fuel cracking.

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