Fabrication and Thermal Conductivity Characterization of Polyetherimide Nanofoam

2012 ◽  
Author(s):  
Sriharsha S. Sundarram ◽  
Wei Jiang ◽  
Wei Li
Keyword(s):  
Thermal Conductivity ◽  
Pore Size ◽  
Effective Thermal Conductivity ◽  
Saturation Pressure ◽  
Effective Porosity ◽  
Analytical Models ◽  
Pore Sizes ◽  
Foaming Process ◽  
The Individual ◽  
Foaming Temperature

A number of analytical models exist to predict the thermal conductivity of foams; however, they do not consider the effect of pore size on the effective thermal conductivity. It is speculated that foams with smaller pore sizes would have much lower thermal conductivity owing to the Knudsen effect. This study aims at fabricating polymer nanofoams with pore sizes on the level of nanometers and to characterize their thermal conductivity. Polyetherimide (PEI) foams were fabricated using solid state foaming. Process parameters such as saturation pressure and duration, desorption time and foaming temperature were varied to obtain foams with pore sizes ranging from a few hundred nanometers to two microns. The microstructures of the samples were characterized using scanning electron microscopy. Throughout the cross section of the foams, there exist regions with varying pore size and porosity. The effective porosity and thermal conductivity of the individual regions were determined based on a series model for effective thermal conductivity. It is confirmed that as the pore size is reduced while maintaining a fixed porosity, the thermal conductivity also decreases.

The thermal conductivity of polymethylsilsesquioxane aerogels and xerogels with varied pore sizes for practical application as thermal superinsulators

2014 ◽  
Vol 2 (18) ◽  
pp. 6525-6531 ◽  
Author(s):  
G. Hayase ◽  
K. Kugimiya ◽  
M. Ogawa ◽  
Y. Kodera ◽  
K. Kanamori ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Pore Size ◽  
Gas Pressure ◽  
Practical Application ◽  
Practical Applications ◽  
Pore Sizes ◽  
The Relationship

The relationship between the thermal conductivity, gas pressure and pore size of polymethylsilsesquioxane aerogels and xerogels has been investigated for practical applications.

Design of High Thermal Conductivity Particle Filled Polymer Using Effective Thermal Conductivity Models

2012 ◽  
Vol 714 ◽  
pp. 21-24 ◽  
Author(s):  
B. Garnier ◽  
F. Danes
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Thermal Contact Resistance ◽  
Volume Fraction ◽  
Thermal Contact ◽  
Analytical Models ◽  
Finite Element Models ◽  
Inner Diameter ◽  
Conductive Particles ◽  
Conductivity Models

The context of this work is the enhancement of the thermal conductivity of polymer by adding conductive particles. It will be shown how we can use effective thermal conductivity models to investigate effect of various factors such as the volume fraction of filler, matrix thermal conductivity, thermal contact resistance, and inner diameter for hollow particles. Analytical models for lower bounds and finite element models will be discussed. It is shown that one can get some insights from effective thermal conductivity models for the tailoring of conductive composite, therefore reducing the amount of experimental work.

scholarly journals An analysis of effective thermal conductivity of heterogeneous materials

2014 ◽  
Vol 14 (1) ◽  
pp. 14-21 ◽  
Author(s):  
Guocheng Zhu ◽  
Dana Kremenakova ◽  
Yan Wang ◽  
Jiri Militky ◽  
Funda Buyuk Mazari
Keyword(s):  
Thermal Conductivity ◽  
Numerical Simulation ◽  
Thermal Property ◽  
Effective Thermal Conductivity ◽  
Contact Area ◽  
Heterogeneous Materials ◽  
Inclusion Size ◽  
Analytical Models ◽  
Important Index ◽  
Inclusion Shape

Abstract Effective thermal conductivity (ETC) is a very important index for evaluating the thermal property of heterogeneous materials, which include more than two different kinds of materials. Several analytical models were proposed for predicting the ETC of heterogeneous materials, but in some cases, these models cannot provide very accurate predictions. In this work, several analytical models and numerical simulations were studied in order to investigate the differences among them. In addition, some factors which would influence the ETC of heterogeneous materials were investigated by numerical simulation. The results demonstrated that the numerical simulation can provide very accurate prediction, indicated that different analytical models should be selected to predict specific problems based on their assumptions, and suggested that more variables need to be considered in order to improve these analytical models, such as inclusion shape, inclusion size, distribution of inclusions and contact area. Besides, numerical method could be an effective and reliable way to obtain the ETC of heterogeneous materials with any kind of complicated structures.

scholarly journals A 3D model to predict the influence of nanoscale pores or reduced gas pressures on the effective thermal conductivity of cellular porous building materials

2019 ◽  
Vol 43 (4) ◽  
pp. 277-300 ◽  
Author(s):  
Wouter Van De Walle ◽  
Hans Janssen
Keyword(s):  
Thermal Conductivity ◽  
Porous Materials ◽  
Effective Thermal Conductivity ◽  
Building Materials ◽  
Full Range ◽  
Advanced Materials ◽  
Future Application ◽  
High Porosity ◽  
Pore Sizes ◽  
Gas Pressures

Cellular porous materials are frequently applied in the construction industry, both for structural and insulation purposes. The progressively stringent energy regulations mandate the development of better performing insulation materials. Recently, novel porous materials with nanopores or reduced gas pressures have been shown to possess even lower thermal conductivities because of the Knudsen effect inside their pores. Further understanding of the relation between the pore structure and the effective thermal conductivity is needed to quantify the potential improvement and design new optimized materials. This article presents the extension of a 3D numerical framework simulating the heat transfer at the pore scale. A novel methodology to model the reduced gas-phase conductivity in nanopores or at low gas pressures is presented, accounting for the 3D pore geometry while remaining computationally efficient. Validation with experimental and numerical results from the literature indicates the accuracy of the methodology over the full range of pore sizes and gas pressures. Combined with an analytical model to account for thermal radiation, the framework is applied to predict the thermal conductivity of a nanocellular poly(methyl methacrylate) foam experimentally characterized in the literature. The simulation results show excellent agreement with less than 5% difference with the experimental results, validating the model’s performance. Furthermore, results also indicate the potential improvements when decreasing the pore size from the micrometre to the nanometre range, mounting up to 40% reduction for such high-porosity low-matrix-conductivity materials. Future application of the model could assist the design of advanced materials, properly accounting for the effect of reduced pore sizes and gas pressures.

Porosity, Specific Surface Area and Effective Thermal Conductivity of Anisotropic Open Cell Lattice Structures

2005 ◽  
Author(s):  
Kiran Balantrapu ◽  
Deepti Rao Sarde ◽  
Christopher M. Herald ◽  
Richard A. Wirtz
Keyword(s):  
Thermal Conductivity ◽  
Specific Surface ◽  
Effective Thermal Conductivity ◽  
Surface Area ◽  
Specific Surface Area ◽  
Structural Characteristics ◽  
Analytical Models ◽  
Lattice Structures ◽  
Open Cell ◽  
Thermally Conductive

Open-cell box-lattice structures consisting of mutually orthogonal thermally conductive cylindrical ligaments can be configured to have wide ranging porosity, a large specific surface area and effective thermal conductivity in a particular direction together with specified structural characteristics. Thermal and mechanical properties can be tuned (and anisotropy introduced) by specification of different filament diameter and pitch for the vertical and horizontal filaments. Analytical models for porosity, specific surface area and effective thermal conductivity of lattice structures having different ligament diameters and pitches (anisotropy) are developed. The models show that all three of these quantities are functions of three dimensionless lengths.   This paper was also originally published as part of the Proceedings of the ASME 2005 Heat Transfer Summer Conference.

Study on the Effective Thermal Conductivity of Macro, Mirco and Nano Porous Materials in the Light of the Knudsen Conduction/Radiation Coupling Effect

2010 ◽  
Author(s):  
Ulrich Gross ◽  
Khaled Raed
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Pore Size Distribution ◽  
Porous Materials ◽  
Pore Size ◽  
Effective Thermal Conductivity ◽  
Size Distribution ◽  
Solid Matrix ◽  
Porous System ◽  
Gas Atmosphere

Thermal transport phenomena in porous media are characterized by conduction through solid matrix and filling gas, and also by radiation. The gas is dispersed in the porous system depending on the pore size distribution. In each pore, the gas contributes to the heat transfer between the pore surfaces. This effect is strongly influenced by pore size, gas atmosphere, accommodation coefficient and other factors. A recent publication of the present authors focused on modeling the change of the effective thermal conductivity when the gas atmosphere is changed. In the current contribution, the effect of pore size distribution on heat transfer in macro, micro, and nano insulation materials is presented. Samples were chosen from five different highly porous materials with different pore size distribution within the macro, micro, and nano classes. Porosity and pore size distribution of the samples were chosen to get a clear characterization of the materials. The effective thermal conductivity was measured by applying the radial heat flow method at temperatures up to 1000 °C. Evaluating Knudsen effect from the pore size distribution alone does not give plausible explanation for the measured thermal conductivity. However, it is important to consider the kind of connections between the pores. In case of nano materials, the radiation effect proves to be strongly dependent on the Knudsen number.

Compact Analytical Models of Effective Thermal Conductivity of Rough Spheroid Packed Beds

2004 ◽  
Author(s):  
M. Bahrami ◽  
M. M. Yovanovich ◽  
J. R. Culham
Keyword(s):  
Experimental Data ◽  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Present Model ◽  
Thermal Analyses ◽  
Contact Load ◽  
Analytical Models ◽  
Packed Beds ◽  
Wide Range ◽  
Temperature And Pressure

New compact analytical models for predicting the effective thermal conductivity of regularly packed beds of rough spheres immersed in a stagnant gas are developed. Existing models do not consider either the influence of the spheres roughness or the rarefaction of the interstitial gas on the conductivity of the beds. Contact mechanics and thermal analyses are performed for uniform size spheres packed in SC and FCC arrangements and the results are presented in the form of compact relationships. The present model accounts for the thermophysical properties of spheres and the gas, contact load, spheres diameter, spheres roughness and asperities slope, and temperature and pressure of the gas. The present model is compared with experimental data for SC and FCC packed beds and good agreement is observed. The experimental data cover a wide range of the contact load, surface roughness, interstitial gas type, and gas temperature and pressure.

Solid-State Foaming of Polycaprolactone (PCL)

2007 ◽  
Author(s):  
Hai Wang ◽  
Wei Li ◽  
Vipin Kumar
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Solid State ◽  
Room Temperature ◽  
Saturation Pressure ◽  
Crystalline Polymer ◽  
Foaming Process ◽  
Quenching Process ◽  
Foaming Temperature ◽  
Scanning Electron

Polycaprolacton (PCL) is a synthetic biodegradable polymer that is widely used in tissue engineering related studies. It is a semi-crystalline polymer, and has a glass transition temperature (Tg) of −60°C and a melting temperature of 60°C. In this paper, we report on the progress in creating porous PCL foams using the solid-state foaming process. The objective of this study is to examine the foam-ability of PCL using room temperature saturation. PCL specimens were made using compression molding. A “quenching” process was introduced to manipulate the crystallinity of PCL samples. CO2 was used for gas saturation. The effects of saturation pressure and foaming temperature were studied. The created microstructures were characterized using scanning electron microscopy (SEM). The preliminary results have shown that microstructures with pores on the scale of hundreds of nanometers were generated.

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