Characterization of Anisotropic and Irregularly-Shaped Materials by High-Sensitive Thermal Conductivity Measurements

2007 ◽  
Vol 124-126 ◽  
pp. 1641-1644 ◽  
Author(s):  
M. Gustavsson ◽  
Hideaki Nagai ◽  
Takeshi Okutani
Keyword(s):  
Thermal Conductivity ◽  
Structural Changes ◽  
Bulk Material ◽  
Thermal Contact ◽  
Measurement Techniques ◽  
High Sensitivity ◽  
Conductivity Measurements ◽  
Destructive Testing ◽  
Analysis And Design ◽  
Wide Range

In modern thermal analysis and design involving thermal transport in solid components it is necessary to apply different modeling of the thermal heat flow in bulk material and across solid surface interfaces either in shape of a layer or a solid-solid interface. Similar differences occur when applying different measurement techniques. Some techniques have been developed specifically for the purpose of performing measurements of bulk properties by removing the influence from thermal contact resistance between the measurement probe and the sample material. Thermal conductivity measurements on metal and ceramic objects of various geometries such as thin bars, thin sheets as well as coatings or layers are here described when using the Transient Plane Source technique. A summary overview of the recent developments of this technique, including its ability to be applied in measurement situations covering a wide range of length and time scales, is also presented. Structural changes in anisotropy can be recorded with high sensitivity by comparative measurements. The technique may be applied in situations requiring non-destructive testing, e.g. samples of particular geometry used for mechanical or tensile testing.

scholarly journals Overview of Popular Techniques of Raman Spectroscopy and Their Potential in the Study of Plant Tissues

Molecules ◽  
2021 ◽  
Vol 26 (6) ◽  
pp. 1537
Author(s):  
Aneta Saletnik ◽  
Bogdan Saletnik ◽  
Czesław Puchalski
Keyword(s):  
Raman Spectroscopy ◽  
Cell Walls ◽  
Structural Changes ◽  
Spatial Information ◽  
Technological Development ◽  
Analytical Techniques ◽  
High Sensitivity ◽  
Plant Tissues ◽  
Wide Range ◽  
Identification Technique

Raman spectroscopy is one of the main analytical techniques used in optical metrology. It is a vibration, marker-free technique that provides insight into the structure and composition of tissues and cells at the molecular level. Raman spectroscopy is an outstanding material identification technique. It provides spatial information of vibrations from complex biological samples which renders it a very accurate tool for the analysis of highly complex plant tissues. Raman spectra can be used as a fingerprint tool for a very wide range of compounds. Raman spectroscopy enables all the polymers that build the cell walls of plants to be tracked simultaneously; it facilitates the analysis of both the molecular composition and the molecular structure of cell walls. Due to its high sensitivity to even minute structural changes, this method is used for comparative tests. The introduction of new and improved Raman techniques by scientists as well as the constant technological development of the apparatus has resulted in an increased importance of Raman spectroscopy in the discovery and defining of tissues and the processes taking place in them.

Thermal Conductivity Measurements of Nylon 11-Carbon Nanofiber Nanocomposites

2005 ◽  
Author(s):  
Antonette T. Cummings ◽  
Li Shi ◽  
Joseph H. Koo
Keyword(s):  
Thermal Conductivity ◽  
Thermal Contact Resistance ◽  
Carbon Nanofiber ◽  
Thermal Contact ◽  
Conductivity Measurements ◽  
Fire Retardancy ◽  
Commercial Use ◽  
Transmission Electron ◽  
Nylon 11 ◽  
Microscopy Images

Nylon 11, a popular material for commercial use, has been combined with low-percent loads of carbon nanofibers (CNFs) to tailor mechanical, fire retardancy, and thermal properties. Transmission electron microscopy images show that the CNFs are randomly aligned in the polymer matrix. We show that the thermal conductivity is minimized at a certain percent loading of CNFs due to a large thermal contact resistance between the CNFs and the medium.

Influence of Contact Mechanics in the Prediction of the Effective Thermal Conductivity of Spheroid Packed Beds

2003 ◽  
Author(s):  
G. Buonanno ◽  
A. Carotenuto ◽  
G. Giovinco ◽  
L. Vanoli
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Statistical Approach ◽  
Thermal Contact ◽  
Peak Height ◽  
Thermal Contact Conductance ◽  
Curvature Radius ◽  
Packed Beds ◽  
Wide Range ◽  
Thermal Phenomena

Thermal contact conductance is an important parameter in a wide range of thermal phenomena, and consequently a large number of experimental, numerical and statistical investigations have been carried out in literature. In the present paper an analysis of thermal contact resistance is carried out to predict heat transfer between spherical rough surfaces in contact, by means of a statistical approach. The micro-geometry of the surface is described through a probabilistic model based on the peak height variability and invariant asperity curvature radius. The numerical model has been applied to evaluate the effective thermal conductivity of packed beds of steel spheroids and validated through the comparison with the experimental data obtained by means of an apparatus designed and build up for this purpose.

scholarly journals Immobilized Enzymes in Biosensor Applications

Materials ◽  
2019 ◽  
Vol 12 (1) ◽  
pp. 121 ◽  
Author(s):  
Hoang Hiep Nguyen ◽  
Sun Hyeok Lee ◽  
Ui Jin Lee ◽  
Cesar D. Fermin ◽  
Moonil Kim
Keyword(s):  
Point Of Care ◽  
Measurement Techniques ◽  
Diagnostic Testing ◽  
High Sensitivity ◽  
Immobilized Enzymes ◽  
Clinical Analysis ◽  
Safety Control ◽  
Wide Range ◽  
Piezoelectric Measurement ◽  
Innovative Techniques

Enzyme-based biosensing devices have been extensively developed over the last few decades, and have proven to be innovative techniques in the qualitative and quantitative analysis of a variety of target substrates over a wide range of applications. Distinct advantages that enzyme-based biosensors provide, such as high sensitivity and specificity, portability, cost-effectiveness, and the possibilities for miniaturization and point-of-care diagnostic testing make them more and more attractive for research focused on clinical analysis, food safety control, or disease monitoring purposes. Therefore, this review article investigates the operating principle of enzymatic biosensors utilizing electrochemical, optical, thermistor, and piezoelectric measurement techniques and their applications in the literature, as well as approaches in improving the use of enzymes for biosensors.

Effective Thermal Conductivity of Coal Ash Deposits at Moderate to High Temperatures

1987 ◽  
Vol 109 (2) ◽  
pp. 215-221 ◽  
Author(s):  
D. W. Anderson ◽  
R. Viskanta ◽  
F. P. Incropera
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Thermal History ◽  
Coal Ash ◽  
Physical Structure ◽  
Conductivity Measurements ◽  
Wide Range ◽  
Particulate Form ◽  
Order Of Magnitude ◽  
Deposit Structure

The effective thermal conductivity of coal ash deposits strongly influences heat transfer in pulverized coal-fired boilers. In this study thermal conductivity measurements were performed over a wide range of temperatures for fly ash, slagging deposits, and fouling deposits. The effects of ash particle size, thermal history, and physical structure of the deposit are discussed. Thermal history and deposit structure were observed to have the greatest influence on the local thermal conductivty, which increased by an order of magnitude with particle melting. Conductivities for solid-porous deposits were twice those of the same sample in particulate form.

Thermal Conductivity and Thermal Contact Resistance of Metal Foams

2009 ◽  
Author(s):  
Ehsan Sadeghi ◽  
Nedjib Djilali ◽  
Majid Bahrami
Keyword(s):  
Thermal Conductivity ◽  
Contact Resistance ◽  
Thermal Contact Resistance ◽  
Metal Foam ◽  
Thermal Contact ◽  
High Surface ◽  
Metal Foams ◽  
Analytical Models ◽  
Cross Sectional ◽  
Wide Range

Unique specifications of metal foams such as relatively low cost, ultra-low density, high surface-area-to-volume ratio, and most importantly, the ability to mix the passing fluid provide them a great potential for a variety of thermal-fluidics applications. In the present study, a compact analytical model for evaluating the effective thermal conductivity of metal foams is developed. The medium structure is represented as orthogonal cylindrical ligaments that are equally spaced and sized. A unit cell is taken to represent the metal foam. The model accounts for varying cross-sectional ligaments which is consistent with microscopic images. A numerical analysis is performed to verify the proposed analytical models. The model predictions are in good agreement with existing experimental data and the present numerical results. A parametric study is then performed to investigate the effects of variation in ligament cross-section geometry, uniformity, and aspect ratio over a wide range of porosities. Moreover, Thermal contact resistance phenomenon is included in the analysis.

scholarly journals In-Plane Thermal Conductivity of PEM Fuel Cell Gas Diffusion Layers

2011 ◽  
Author(s):  
Ehsan Sadeghi ◽  
Ned Djilali ◽  
Majid Bahrami
Keyword(s):  
Thermal Conductivity ◽  
Fuel Cell ◽  
Effective Thermal Conductivity ◽  
Thermal Contact ◽  
Pem Fuel Cell ◽  
Gas Diffusion ◽  
Carbon Paper ◽  
Test Bed ◽  
Diffusion Layers ◽  
Wide Range

Heat transfer through the gas diffusion layer (GDL) is a key process in the design and operation of a PEM fuel cell. The analysis of this process requires determination of the effective thermal conductivity. This transport property differs significantly in the through-plane and in-plane directions due to the anisotropic micro-structure of the GDL. In the present study, a novel test bed that allows the separation of in-plane effective thermal conductivity and thermal contact resistance in GDLs is described. Measurements are performed using Toray carbon paper TGP-H-120 samples for a range of PTFE content at a mean temperature of 65–70°C. The measurements are complemented by a compact analytical model that achieves good agreement with the experimental data. The in-plane effective thermal conductivity is found to be about 12 times higher than the through-plane conductivity and remains approximately constant, k ≈ 17.5 W/mK, over a wide range of PTFE content.

scholarly journals Correction on the influence of thermal contact resistance in thermal conductivity measurements using the guarded hot plate method

2009 ◽  
Vol 6 (3) ◽  
pp. 479-488 ◽  
Author(s):  
Nenad Stepanic ◽  
Nenad Milosevic
Keyword(s):  
Thermal Conductivity ◽  
Thermal Contact Resistance ◽  
Thermal Contact ◽  
Correction Method ◽  
Conductivity Measurements ◽  
Hot Plate ◽  
Plate Method ◽  
Conductive Materials ◽  
Guarded Hot Plate ◽  
Material Sample

This work considers the influence of finite thermal contact resistances which exist in thermal conductivity measurements of homogeneous and poor thermal conductive materials using the guarded hot plate method. As an example of correction method proposed in this work, different experimental results obtained from a standard reference material sample (with the conductivity of about 1 W/mK) have been presented.

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