Calculation Of Effective Thermal Conductivity Research Articles

Investigations on micro-mechanical and thermal characteristics of glass fiber reinforced epoxy based binary composite structure using finite element method

Binary composite materials comprising of randomly oriented E-glass fiber of four different weight percentages impregnated with epoxy resin are fabricated to study their physical, mechanical and thermal properties. The experimental results are used for the validation of the results obtained by simulation using ANSYS software. The finite element (FE) model based on representative area element (RAE) approach is implemented in the finite element code ANSYS. The comparative analysis gives an acceptable error, indicating applicability of such simulation model studies in predicting material characteristics in advance. The elastic modulus evaluated both by Halpin–Tsai model and FE model are more close to experimental results as compared to the results obtained from rule-of-mixture. Similarly, the tensile strength of the composites evaluated both experimentally and by finite element method (FEM) shows close resemblance. An empirical relationship has been developed and reported for the calculation of effective thermal conductivity for two-phase composite system (i.e. fiber and matrix interface). It is observed that the order of composites with effective thermal conductivity is 45wt.% glass fiber based composite >35wt.% glass fiber based composite >25wt.% glass fiber based composite >15wt.% glass fiber based composite. The magnitude increases slightly in case of 45wt.% glass fiber based composite, whereas it remains almost constant in case of 35wt.% and shows slightly decrease in case of 25wt.% and 15wt.% glass fiber based composites. This facilitates designing/tailoring of composite materials as per structural requirements in the preliminary stages of R&D more economically.

Numerical calculations of effective thermal conductivity of porous ceramics by image-based finite element method

The effective thermal conductivity of heterogeneous or composite materials is an essential physical parameter of materials selection and design for specific functions in science and engineering. The effective thermal conductivity is heavily relied on the fraction and spatial distribution of each phase. In this work, image-based finite element method (FEM) was used to calculate the effective thermal conductivity of porous ceramics with different pore structures. Compared with former theoretical models such as effective media theory (EMT) equation and parallel model, image-based FEM can be applied to a large variety of material systems with a relatively steady deviation. The deviation of image-based FEM computation mainly comes from the difference between the two dimensional (2D) image and the three dimensional (3D) structure of the real system, and an experiment was carried out to confirm this assumption. Factors influencing 2D and 3D effective thermal conductivities were studied by FEM to illustrate the accuracy and application conditions of image-based FEM.

Roles of nanolayer and particle size on thermophysical characteristics of ethylene glycol-based copper nanofluids

Calculation of thermal conductivity and the characterization of the molecular-level mechanisms of ethylene-glycol-based copper nanofluid are conducted using the molecular dynamics (MD) Simulation when the nanoparticle size ranges from 6 to 14 Å. Layer–Maxwell model is developed for the calculation of effective thermal conductivity of the nanofluid with nanoparticle size up to 2000 Å by the application of distinct thermal conductivity in the nanolayers around nanoparticle obtained from MD simulations. The comparison between computational and experimental results reveals the roles of interfacial layer and nanoparticle size in the thermal conductivity enhancement.

Numerical simulation of a heat sink embedded with a vapor chamber and calculation of effective thermal conductivity of a vapor chamber

This study presents a numerical investigation of a whole set of thermal module, including a plate-fin heat sink embedded with a vapor chamber, subject to the influence of concentrated heat sources. Within the vapor chamber, the internal vapor is assumed as a common heat-transfer interface between the wicks. CFD simulations of the integrated heat sink are carried out with this assumption. The calculated results are in good agreement with the experiments, and show a maximum difference of 6.3% for the hotspot temperature rises. It is found that the area of the heat source has an important influence to the performance of the vapor chamber. The major spreading resistance of the vapor chamber comes from the bottom wall, where a concentrated heat source is applied. In addition, the isotropic and orthotropic approaches are proposed to calculate the effective thermal conductivities of the vapor chamber. By approximating the vapor chamber as a conduction plate, the effective conductivity can be obtained from the analytical solutions of the spreading resistances. The vapor chamber can reduce the spreading resistances sufficiently by its excellent lateral thermal spreading effect, which can be interpreted by the orthotropic approach.

A generalized self-consistent method for calculation of effective thermal conductivity of composites with interfacial contact conductance

The effective thermal conductivity of composites can be obtained by the generalized self-consistent method (GSCM). The effect of contact conductance that exists at the interface between the matrix and the inclusion, on the effective thermal conductivity is investigated. The particulate composite, transversely isotropic fiber composite, and multi-layered composite are considered in this study. Based on the energy balance, a simple criterion B eff = 0, yet new and analytical, for determining the effective thermal conductivity of the composite is rigorously derived. The temperature distribution of the matrix and the inclusion can also be obtained by GSCM. This is the by-product of the method, which many other methods do not provide.

Contact Resistance Measurement and Its Effect on the Thermal Conductivity of Packed Sphere Systems

There has been a growing interest in porous systems with a smaller length-scale modeling requirement on the order of each particle, where the existing tools tend to be inadequate. To address this, a Discrete Conduction Model was recently proposed to allow for the transient temperature calculation of 3D random packed-sphere systems for various microstructures. Since many of the motivating applications involve contacting spheres and since there has been a limited number of contact-resistance studies on spheres undergoing elastic deformation, the objective of this study is to obtain measurements of the contact resistances between metallic spheres in elastic contact, as well as to quantify their influence on the effective thermal conductivity. To accomplish this, an experiment was constructed utilizing air and interfacial resistance to replace the functions of the guard heater and vacuum chamber, and in so doing, enabled transient observations. The overall uncertainty was estimated to be ±6%, and the results were benchmarked against available data. A correlation was obtained relating the contact resistance with the contact radius, and results showed the contact resistance to have minimal transient behavior. The results also showed that the neglect of contact resistance could incur an error in the effective thermal conductivity calculation as large as 800%, and a guideline was presented under which the effect of the contact resistance may be ignored. A correlation accounting for the effect of contact resistance on the effective thermal conductivity was also presented.

Effective thermal conductivity and thermal diffusivity of some rare earth oxides

Thermal conductivity and thermal diffusivity of three rare earth oxide powders (Gadolinium oxide, Samarium oxide and Yttrium oxide) are measured experimentally using Transient Plane Source (TPS) technique at ambient temperature. An attempt has been made to accommodate the effect of porosity of the powders on thermal conductivity. Calculation of effective thermal conductivity on the basis of a theoretical model has been carried out and it has been found that the theoretical results are in good agreement with the experimental values. Further it has been shown that the TPS technique is an effective method for the measurement of thermal conductivity of powders.

Heat conduction and porosity correction for diverse two-phase systems

Some experimental results show the existence of a correction term for the calculation of effective thermal conductivity of dissimilar two-phase materials. Because of this, a correction for porosity has been suggested in a theoretical model initially developed for two-phase systems. A general expression for porosity correction has been derived empirically for diverse two-phase materials from experimental results reported in the literature. It is found that the correction term is dependent on the ratio of thermal conductivities of the constituents and the porosity of a two-phase system. The theoretical expression so obtained predicts values of effective thermal conductivity that are quite close to the experimental results.

Thermal conductivity of porous latticed materials

The results of theoretical and experimental studies of the effective thermal conductivity of a composite material based on woven metal lattices are presented. It is shown that the material has a definitely expressed thermal anistropy. The theoretical analysis of heat transfer in the material is based on detailed discussion of its structure and mechanism of heat transfer. The results of the analysis make it possible to deduce theoretical relationships for the calculation of effective thermal conductivity along the main axes of the thermal anisotropy. An experimental study was undertaken to verify the theoretical results. The effective thermal conductivity along the main axes was measured by direct steady-state methods. The appraisal of the accuracy of measurement results confirms their validity. The experimental results, both those of the authors and those of other researchers, prove that the predicted relationships can be appied to calculate the effective thermal conductivity of porous latticed materials.

A thermal conductivity model for two phase media

A model is proposed for the calculation of effective thermal conductivity of two phase media with a single continuous phase. This model has been shown to satisfy the limiting conditions and also to correlate the experimental data well. Though this model is based on the Ohm's law, it is in very good agreement with rigorously derived results based on the Fourier law.