Interface Thermal Resistance and Length Effect on Thermal Conductivitiy of SWNT Bundles

2012 ◽  
Author(s):  
Kasim Toprak ◽  
Yildiz Bayazitoglu
Keyword(s):  
Thermal Conductivity ◽  
Thermal Resistance ◽  
Effective Thermal Conductivity ◽  
Volume Fraction ◽  
Water Medium ◽  
Interface Thermal Resistance ◽  
Contact Points ◽  
Length Fraction ◽  
Vertically Aligned ◽  
Packing System

Using different calculations and measurement methods, the results for the thermal conductivity in a single wall carbon nanotube (SWNT) are compared. Then, the interface thermal resistance effects on the effective thermal conductivity of multiple SWNTs in a hexagonal packing system submerged in oil, air, and water are studied. The results show that as the interface thermal resistance increases, the effective thermal conductivity decreases. Moreover, length, length fraction, and volume fraction effects on the thermal conductivity of the system submerged in a water medium are approximated by including the interface thermal resistances of the nanotube-matrix and nanotube-nanotube. The systems’ length ranged between 500–3000 nm. The created models contain either vertically aligned or non-straight nanotubes. Non-straight nanotubes systems make one or two contact points with other nanotubes. These contact points’ location vary based on the length ratio known as the length fraction. It is found that the effective thermal conductivity of the SWNT bundle has the highest value when they are uniformly aligned and dispersed without contact. As the density and length of the SWNTs increase, the effective thermal conductivity of the bundle system also increases.

Study of Effective Thermal Conductivity of Glazed Hollow Bead Concrete

2016 ◽  
Vol 851 ◽  
pp. 823-828
Author(s):  
Bing Zhang ◽  
Zhong Qing Cheng
Keyword(s):  
Thermal Conductivity ◽  
Thermal Resistance ◽  
Effective Thermal Conductivity ◽  
Thermal Conductivity Coefficient ◽  
Interface Thermal Resistance

Based on analyzing the mechanism of thermal conductivity of glazed hollow bead concrete, this paper divides the channels of thermal conductivity in concrete, constructs the model of thermal conductivity coefficient based on the Theory of Minimum Thermal Resistance, and confirms the model by using the data of other related literatures and the data of our own experiment. The consequence indicates that this model can calculate the thermal conductivity coefficient under arid state exactly. In order to improve the accuracy of this model, we should take the shape of framework, the interface thermal resistance between concrete and framework into consideration

Determining the thermal resistance of a highly insulated wall containing vacuum insulation panels through experimental, calculation and numerical simulation methods

2020 ◽  
pp. 174425912098003
Author(s):  
Travis V Moore ◽  
Cynthia A. Cruickshank ◽  
Ian Beausoleil-Morrison ◽  
Michael Lacasse
Keyword(s):  
Thermal Conductivity ◽  
Thermal Resistance ◽  
Effective Thermal Conductivity ◽  
Edge Effect ◽  
3D Simulation ◽  
Simulation Methods ◽  
Zone Method ◽  
Vacuum Insulation ◽  
Thermal Bridges ◽  
Wall Assembly

The purpose of this paper is to investigate the potential for calculation methods to determine the thermal resistance of a wall system containing vacuum insulation panels (VIPs) that has been experimentally characterised using a guarded hot box (GHB) apparatus. The VIPs used in the wall assembly have not been characterised separately to the wall assembly, and therefore exact knowledge of the thermal performance of the VIP including edge effect is not known. The calculations and simulations are completed using methods found in literature as well as manufacturer published values for the VIPs to determine the potential for calculation and simulation methods to predict the thermal resistance of the wall assembly without the exact characterisation of the VIP edge effect. The results demonstrate that disregarding the effect of VIP thermal bridges results in overestimating the thermal resistance of the wall assembly in all calculation and simulation methods, ranging from overestimates of 21% to 58%. Accounting for the VIP thermal bridges using the manufacturer advertised effective thermal conductivity of the VIPs resulted in three methods predicting the thermal resistance of the wall assembly within the uncertainty of the GHB results: the isothermal planes method, modified zone method and the 3D simulation. Of these methods only the 3D simulation can be considered a potential valid method for energy code compliance, as the isothermal planes method requires too drastic an assumption to be valid and the modified zone method requires extrapolating the zone factor beyond values which have been validated. The results of this work demonstrate that 3D simulations do show potential for use in lieu of guarded hot box testing for predicting the thermal resistance of wall assemblies containing both VIPs and steel studs. However, knowledge of the VIP effective thermal conductivity is imperative to achieve reasonable results.

Figure of Merit-Based Optimization Approach of Phase Change Material-based Composites for Portable Electronics Using Simplified Model

2021 ◽  
Author(s):  
Ayushman Singh ◽  
Srikanth Rangarajan ◽  
Leila Choobineh ◽  
Bahgat Sammakia
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Phase Change ◽  
Effective Thermal Conductivity ◽  
Phase Change Material ◽  
Figure Of Merit ◽  
Volume Fraction ◽  
Simplified Model ◽  
Transient Temperature ◽  
Change Material

Abstract This work presents an approach to optimally designing a composite with thermal conductivity enhancers (TCEs) infiltrated with phase change material (PCM) based on figure of merit (FOM) for thermal management of portable electronic devices. The FOM defines the balance between effective thermal conductivity and energy storage capacity. In present study, TCEs are in the form of a honeycomb structure. TCEs are often used in conjunction with PCM to enhance the conductivity of the composite medium. Under constrained composite volume, the higher volume fraction of TCEs improves the effective thermal conductivity of the composite, while it reduces the amount of latent heat storage simultaneously. The present work arrives at the optimal design of composite for electronic cooling by maximizing the FOM to resolve the stated trade-off. In this study, the total volume of the composite and the interfacial heat transfer area between the PCM and TCE are constrained for all design points. A benchmarked two-dimensional direct CFD model was employed to investigate the thermal performance of the PCM and TCE composite. Furthermore, assuming conduction-dominated heat transfer in the composite, a simplified effective numerical model that solves the single energy equation with the effective properties of the PCM and TCE has been developed. The effective thermal conductivity of the composite is obtained by minimizing the error between the transient temperature gradient of direct and simplified model by iteratively varying the effective thermal conductivity. The FOM is maximized to find the optimal volume fraction for the present design.

Effective Thermal Conductivity of Functionally Graded Particulate Nanocomposites With Interfacial Thermal Resistance

2008 ◽  
Vol 75 (5) ◽  
Author(s):  
H. M. Yin ◽  
G. H. Paulino ◽  
W. G. Buttlar ◽  
L. Z. Sun
Keyword(s):  
Thermal Conductivity ◽  
Thermal Resistance ◽  
Effective Thermal Conductivity ◽  
Functionally Graded ◽  
Interfacial Thermal Resistance ◽  
Conductivity Distribution ◽  
Consistent Model ◽  
The Matrix ◽  
Graded Material ◽  
Perfect Interface

By means of a fundamental solution for a single inhomogeneity embedded in a functionally graded material matrix, a self-consistent model is proposed to investigate the effective thermal conductivity distribution in a functionally graded particulate nanocomposite. The “Kapitza thermal resistance” along the interface between a particle and the matrix is simulated with a perfect interface but a lower thermal conductivity of the particle. The results indicate that the effective thermal conductivity distribution greatly depends on Kapitza thermal resistance, particle size, and degree of material gradient.

scholarly journals Effective thermal conductivity of complicated hierarchic multilayer fabric

2014 ◽  
Vol 18 (5) ◽  
pp. 1613-1618 ◽  
Author(s):  
Jie Fan ◽  
Na Zhu ◽  
Zhi Liu ◽  
Qian Cheng ◽  
Yong Liu
Keyword(s):  
Thermal Conductivity ◽  
Thermal Resistance ◽  
Effective Thermal Conductivity ◽  
Geometric Feature ◽  
Retention Efficiency

Warm retention property of fabric is one of the most important factors for clothing comfortability. The worm retention efficiency of a multilayer fabric with hierarchic inner structure was investigated based on its geometric feature. The thermal resistance of the multilayer fabric increases as the layer of the fabric increases.

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