Experimental Investigations on the Thermal Conductivity of Silica Aerogels by a Guarded Thin-Film-Heater Method

2009 ◽  
Vol 131 (7) ◽  
Author(s):  
Sandra Spagnol ◽  
Bérangère Lartigue ◽  
Alain Trombe ◽  
Florence Despetis
Keyword(s):  
Thin Film ◽  
Experimental Data ◽  
Thermal Conductivity ◽  
Direct Measurement ◽  
Silica Aerogels ◽  
Experimental Investigations ◽  
Experimental Setup ◽  
Insulating Materials ◽  
Grain Sizes ◽  
Major Interest

A thin-film-heater method is setup to measure the thermal conductivity of super insulating materials such as silica aerogels. The experimental setup is purposely designed for insulating materials and allows direct measurement of the thermal conductivity. Few experimental data are available in the literature concerning thermal conductivity of aerogels even though these materials are of major interest in thermal insulation. More data are necessary in order to understand thermal transport and to validate existing models. Monolithic and granular silica aerogels are investigated. Our experimental technique enables to quantify the influence of important parameters, such as air pressure and distribution of grain sizes, on the insulating performance of this material.

Influence of Vacancies on Optical Properties of Sic Nanocrystallites

1999 ◽  
Vol 579 ◽  
Author(s):  
K.J. Plucinski ◽  
I.V. Kityk ◽  
A. Kassiba ◽  
C. Charpentier
Keyword(s):  
Experimental Data ◽  
Optical Properties ◽  
Experimental Methods ◽  
The Other ◽  
Experimental Investigations ◽  
Dynamic Boundary Conditions ◽  
Band Energy ◽  
Grain Sizes ◽  
Dynamics Simulations ◽  
Theoretical Simulations

ABSTRACTTo investigate the origin of vacancies in SiC nanopowders, complex theoretical and experimental investigations of SiC nanopowders of different geometry sizes were carried out. Our theoretical approach included ab initio band energy calculations and molecular dynamics simulations with dynamic boundary conditions. Experimental methods included EPR spectra. The significant influence of nanocrystallite and grain sizes on the concentration and type of vacancies is demonstrated. On the other hand, our comparison of experimental data and theoretical simulations show that vacancies influence the optical properties of SiC nanocrystallites.

Phonon transport characteristics across silicon thin film pair: Presence of a gap between the films

2015 ◽  
Vol 40 (3) ◽  
Author(s):  
Haider Ali ◽  
Bekir S. Yilbas
Keyword(s):  
Thin Film ◽  
Experimental Data ◽  
Thermal Conductivity ◽  
Temperature Difference ◽  
Radiation Heat Transfer ◽  
Phonon Transport ◽  
Radiative Energy ◽  
Gap Size ◽  
Boltzmann Transport ◽  
Silicon Thin Film

AbstractPhonon transport across silicon thin film pair with minute gap (Casimir limit) between the films is studied. Phonon transport characteristics across the gap are examined for various gap sizes, and the transient solution of the frequency-dependent Boltzmann transport equation is presented according to relevant boundary conditions incorporating the gap between the film pair. Since the gap size is minute (Casimir limit), the radiative energy transport between the edges of the film pair is incorporated. In addition, phonon transmission and reflection is introduced at the gap edges, thus satisfying energy conservation. The thermal conductivity predicted is validated through experimental data reported in the open literature. Predicted thermal conductivity data agree well with the experimental data reported in the open literature. Increasing gap size alters the phonon transport characteristics across the film pair. Increasing gap size enhances temperature difference between the edges of the gap; in which case, the effect of phonon transmittance is more significant on the temperature difference than that corresponding to the radiation heat transfer due to Casimir limit.

Computational Analysis of Structural Defects in Silica Aerogels

MRS Advances ◽  
2019 ◽  
Vol 4 (46-47) ◽  
pp. 2479-2488
Author(s):  
Hunter Gore ◽  
Luis Caldera ◽  
Xiao Shen ◽  
Firouzeh Sabri
Keyword(s):  
Computational Analysis ◽  
Silica Aerogels ◽  
Structural Defects ◽  
Experimental Setup ◽  
Proof Of Concept ◽  
Structural Failure ◽  
Insulating Materials ◽  
Technological Advances ◽  
Defective Region ◽  
Formation Of Cracks

AbstractTechnological advances in synthesis and preparation of aerogels have resulted in formulations that have the mechanical integrity (while retaining flexibility) to be utilized in a broad range of applications and have overcome the initial brittleness that this class of materials was once known for. Both structural and functional aerogels show a drop in performance when subjected to certain cyclic thermal or impact loading due to the wear and formation of cracks, which reduces their lifespan. Here we present the proof-of-concept of a computational toolset that connects the change in thermal profile to structural failure and degradation. In combination with an appropriate finite element (FEM) solver, we have developed a genetic algorithm that can reconstruct the size and shape of the defective region in silica aerogels given the temperatures from a sensor grid. Results show that a heatmap can be used as the foundation for reconstructing faults and defects in thermally insulating materials. Furthermore, the model developed in this study can be expanded to accommodate other material types. Experimental setup can used to benchmark and refine the computational toolset.

A Method for Predicting the Mean Thermal Conductivity of Insulating Materials at Other Than Experimental Conditions

1963 ◽  
Vol 85 (2) ◽  
pp. 185-186
Author(s):  
C. E. Jones
Keyword(s):  
Experimental Data ◽  
Thermal Conductivity ◽  
Operating Conditions ◽  
Conductivity Data ◽  
Experimental Conditions ◽  
Insulating Materials ◽  
Thermal Conductivity Data ◽  
Test Conditions ◽  
The Mean

A procedure whereby experimental thermal conductivity data can be readily extrapolated to operating conditions quite different from test conditions is presented. Use of this technique can also lessen the amount of experimental data that must be collected and ease experimental problems.

scholarly journals CALCULATION OF THE THERMAL CONDUCTIVITY OF POROUS MEDIA

1958 ◽  
Vol 36 (7) ◽  
pp. 815-823 ◽  
Author(s):  
William Woodside
Keyword(s):  
Experimental Data ◽  
Thermal Conductivity ◽  
Approximate Equation ◽  
Spherical Particles ◽  
Insulating Materials ◽  
Cubic Lattice ◽  
Dry Air ◽  
Thermal Insulating ◽  
Experimental Values ◽  
Good Agreement

The problem of determining the effective thermal conductivities of porous and other composite materials from the conductivities and volume fractious of their constituents is examined. An approximate equation is derived for the case of a cubic lattice of identical spherical particles in a medium having properties different from those of the particles. This equation is applied to the calculation of the thermal conductivity of snow at different densities in the range 0.10 to 0.48 gm/cc. The effect of water vapor diffusion in snow under a temperature gradient is taken into account by adding a latent heat term to the conductivity value for dry air. Conductivity values for snow, calculated in this manner, are found to agree satisfactorily with experimental data. An equation due to Russell is also shown to give conductivity values for several cellular thermal insulating materials which are in good agreement with experimental values.

scholarly journals Phase Relations in the ZrO2-MgO-FeOx System: Experimental Data and Assessment of Thermodynamic Parameters

2021 ◽  
Author(s):  
Ivan Saenko ◽  
O. Fabrichnaya
Keyword(s):  
Electron Microscopy ◽  
Experimental Data ◽  
Solid Solution ◽  
Thermodynamic Parameters ◽  
Spinel Phase ◽  
Experimental Investigations ◽  
X Ray ◽  
Heat Treated ◽  
Preliminary Phase ◽  
Scanning Electron

AbstractThermodynamic parameters were assessed for the MgO–FeOx system and combined with already available descriptions of ZrO2-FeOx and ZrO2-MgO systems to calculate preliminary phase diagrams for planning experimental investigations. Samples of selected compositions were heat treated at 1523, 1673 and 1873 K and characterized using x-ray and scanning electron microscopy combined with energy dispersive x-ray spectroscopy (SEM/EDX). Experiments indicated extension of cubic ZrO2 solid solution into the ternary system at 1873 K (75 mol.% ZrO2, 10 mol.% FeOx and 15 mol.% MgO) and limited solubility of 4 mol.% ZrO2 in spinel phase. Based on the obtained results thermodynamic parameters of C-ZrO2 and spinel phase were optimized.

scholarly journals Validation of MATLAB algorithm to implement a two-step parallel pyrolysis model for the prediction of maximum %char yield

2021 ◽  
Vol 1 (1) ◽  
Author(s):  
Ibiba Taiwo Horsfall ◽  
Macmanus Chinenye Ndukwu ◽  
Fidelis Ibiang Abam ◽  
Ololade Moses Olatunji ◽  
Ojong Elias Ojong ◽  
...  
Keyword(s):  
Experimental Data ◽  
Isothermal Condition ◽  
Char Yield ◽  
Experimental Investigations ◽  
Time Saving ◽  
Pyrolysis Products ◽  
Pyrolysis Model ◽  
Experimental Yield ◽  
By Products ◽  
Good Agreement

AbstractNumerical modeling of biomass pyrolysis is becoming a cost and time-saving alternative for experimental investigations, also to predict the yield of the by-products of the entire process. In the present study, a two-step parallel kinetic model was used to predict char yield under isothermal condition. MATLAB ODE45 function codes were employed to solve a set of differential equations that predicts the %char at varying residence times and temperatures. The code shows how the various kinetic parameters and mass of pyrolysis products were determined. Nevertheless, the algorithm used for the prediction was validated with experimental data and results from past works. At 673.15 K, the numerical simulation using ODE45 function gives a char yield of 27.84%. From 573.15 K to 673.15 K, char yield ranges from 31.7 to 33.72% to 27.84% while experimental yield decreases from 44 to 22%. Hence, the error between algorithm prediction and experimental data from literature is − 0.26 and 0.22. Again, comparing the result of the present work with the analytical method from the literature showed a good agreement.

Modal Analysis of the Axial Compressor Blade: Advanced Time-Dependent Electronic Interferometry and Finite Element Method

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Mykhaylo Tkach ◽  
Serhii Morhun ◽  
Yuri Zolotoy ◽  
Irina Zhuk
Keyword(s):  
Experimental Data ◽  
Mathematical Model ◽  
Finite Element ◽  
High Reliability ◽  
Axial Compressor ◽  
Time Dependent ◽  
Experimental Setup ◽  
Vibration Modes ◽  
Compressor Blades ◽  
Isoparametric Finite Element

AbstractNatural frequencies and vibration modes of axial compressor blades are investigated. A refined mathematical model based on the usage of an eight-nodal curvilinear isoparametric finite element was applied. The verification of the model is carried out by finding the frequencies and vibration modes of a smooth cylindrical shell and comparing them with experimental data. A high-precision experimental setup based on an advanced method of time-dependent electronic interferometry was developed for this aim. Thus, the objective of the study is to verify the adequacy of the refined mathematical model by means of the advanced time-dependent electronic interferometry experimental method. The divergence of the results of frequency measurements between numerical calculations and experimental data does not exceed 5 % that indicates the adequacy and high reliability of the developed mathematical model. The developed mathematical model and experimental setup can be used later in the study of blades with more complex geometric and strength characteristics or in cases when the real boundary conditions or mechanical characteristics of material are uncertain.

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