scholarly journals Relationship between the Transport Coefficients of Polar Substances and Entropy

Entropy ◽  
2019 ◽  
Vol 22 (1) ◽  
pp. 13
Author(s):  
Ivan Anashkin ◽  
Sergey Dyakonov ◽  
German Dyakonov
Keyword(s):  
Experimental Data ◽  
Thermal Conductivity ◽  
Diffusion Coefficient ◽  
High Pressures ◽  
Thermal Conductivity Coefficient ◽  
Good Description ◽  
Transport Coefficients ◽  
Viscosity Coefficient ◽  
Wide Region ◽  
Good Agreement

An expression is proposed that relates the transport properties of polar substances (diffusion coefficient, viscosity coefficient, and thermal conductivity coefficient) with entropy. To calculate the entropy, an equation of state with a good description of the properties in a wide region of the state is used. Comparison of calculations based on the proposed expressions with experimental data showed good agreement. A deviation exceeding 20% is observed only in the region near the critical point as well as at high pressures.

Self-Diffusion Coefficient and Viscosity in Fluids

2011 ◽  
Vol 9 (1) ◽  
Author(s):  
Lawrence Novak
Keyword(s):  
Experimental Data ◽  
Diffusion Coefficient ◽  
Transport Coefficient ◽  
Transport Coefficients ◽  
Dynamics Simulation ◽  
Residual Entropy ◽  
Transport Reaction ◽  
Self Diffusion ◽  
Coefficient Corrélation ◽  
Self Diffusion Coefficient

Rate-based models suitable for equipment or transport-reaction modeling require a capability for predicting transport coefficients over a sufficient range of temperature and pressure. This paper demonstrates a relatively simple novel approach to correlate and estimate transport coefficients for pure components over the entire fluid region.The use of Chapman-Enskog transport coefficients for reducing self-diffusion coefficient and viscosity to dimensionless form results in relatively simple mathematical relationships between component dimensionless transport coefficients and residual entropy over the entire fluid region. Dimensionless self-diffusion coefficients and viscosities were calculated from extensive molecular dynamics simulation data and experimental data on argon, methane, ethylene, ethane, propane, and n-decane. These dimensionless transport coefficients were plotted against dimensionless residual entropy calculated from highly accurate reference equations of state.Based on experimental data, the new scaling model introduced here shows promise as: (1) an equation of state-based transport coefficient correlation over the entire fluid region (liquid, gas, and critical fluid), (2) a component transport coefficient correlation for testing transport data consistency, and (3) a component transport coefficient correlation for interpolation and extrapolation of self-diffusion coefficient and viscosity.

Dual Role of Nanoparticles in the Thermal Conductivity Enhancement of Nanoparticle Suspensions

2005 ◽  
Author(s):  
Calvin H. Li ◽  
G. P. Peterson
Keyword(s):  
Experimental Data ◽  
Thermal Conductivity ◽  
Brownian Motion ◽  
Theoretical Models ◽  
Conductivity Enhancement ◽  
Nanoparticle Suspensions ◽  
The Difference ◽  
Physical Phenomena ◽  
Good Agreement

Experimental evidence exists that the addition of a small quantity of nanoparticles to a base fluid, can have a significant impact on the effective thermal conductivity of the resulting suspension. The causes for this are currently thought to be due to a combination of two distinct mechanisms. The first is due to the change in the thermophysical properties of the suspension, resulting from the difference in the thermal conductivity of the fluid and the particles, and the second is thought to be due to the transport of thermal energy by the particles, due to the Brownian motion of the particles. In order to better understand these phenomena, a theoretical model has been developed that examines the effect of the Brownian motion. In this model, the well-known approach first presented by Maxwell, is combined with a new expression that incorporates the effect of the Brownian motion and describes the physical phenomena that occurs because of it. The results indicate that the enhanced thermal conductivity may not in fact be due to the transport of energy by the particles, but rather, due to the stirring motion caused by the movement of the nanoparticles which enhances the heat transfer within the fluid. The resulting model shows good agreement when compared with the existing experimental data and perhaps more importantly helps to explain the trends observed from a fundamental physical perspective. In addition, it provides a possible explanation for the differences that have been observed between the previously obtained experimental data, the predictions obtained from Maxwell’s equation and the theoretical models developed by other investigators.

scholarly journals An Analysis of Relations for Determining the Thermal Conductivity of Rigid Polymer Foams

2018 ◽  
Vol 23 (4) ◽  
pp. 1015-1023 ◽  
Author(s):  
A. Alsabry ◽  
V.I. Nikitsin ◽  
V.A. Kofanov ◽  
B. Backiel-Brzozowska
Keyword(s):  
Experimental Data ◽  
Thermal Conductivity ◽  
Porous Media ◽  
Thermal Conductivity Coefficient ◽  
Geometrical Structure ◽  
Polymer Foams ◽  
Conductivity Method ◽  
Thermal Exchange ◽  
Rigid Polymer ◽  
Structure Calculations

Abstract In the paper the authors present the effectiveness of the generalized thermal conductivity method for polymer foams, including modelling their geometrical structure. Calculations of the effective thermal conductivity coefficient λ are based on the generally accepted assumption of the additivity of different thermal exchange mechanisms in porous media and this coefficient is presented as a sum the coefficients of conductive λq, radiative λp, and convective λk thermal conductivity. However, in literature not enough attention is given to relations determined by means of the theory of generalized conductivity, including modelling the geometrical structure. This paper presents an analysis of these relations and verifies their ability to predict experimental data in comparison with the best formulae included in the paper [2].

scholarly journals Thermal Conductivity of Al2O3 and CeO2 Nanoparticles and Their Hybrid Based Water Nanofluids: An Experimental Study

2020 ◽  
Vol 65 (1) ◽  
pp. 50-60
Author(s):  
Mohammed Saad Kamel ◽  
Otabeh Al-Oran ◽  
Ferenc Lezsovits
Keyword(s):  
Experimental Data ◽  
Thermal Conductivity ◽  
Volume Concentration ◽  
Experimental Models ◽  
Deionized Water ◽  
Thermal Conductivity Enhancement ◽  
Hybrid Nanofluid ◽  
Step Method ◽  
Conductivity Enhancement ◽  
Good Agreement

In many heat exchange systems, there is a demand to improve the thermal conductivity of the working fluids to make those fluids more efficient, and this can be done by dispersing solid nanomaterials into conventional liquids. In the present work, the thermal conductivity of alumina, ceria, and their hybrid with ratio (50:50) by volume-based deionized water nanofluids was experimentally measured. The nanofluids were prepared by two-step method with a range of dilute volume concentration (0.01-0.5 % Vol.), and measured at various temperatures (35, 40, 45, and 50 ºC). The experimental data for basefluid and nanofluids were verified with theoretical and experimental models, and the results have shown good agreement within the accuracy of the thermal conductivity tester. The results demonstrated that the higher thermal conductivity enhancement percentages for Al2O3, CeO2, and their hybrid nanofluids were (5.3 %, 3.3 %, and 8.8 %) at volume concentration (0.5 % Vol.) and temperature (50 ºC) compared to deionized water, respectively. Moreover, a correlation was proposed for the thermal conductivity enhancement ratio of the hybrid nanofluid and showed good accuracy with measured experimental data.

Phonon Thermal Conductivity of Superlattice Nanowires for Thermoelectric Applications

2003 ◽  
Vol 793 ◽  
Author(s):  
C. Dames ◽  
M. S. Dresselhaus ◽  
G. Chen
Keyword(s):  
Experimental Data ◽  
Thermal Conductivity ◽  
Size Effects ◽  
Three Dimensional ◽  
Small Diameter ◽  
Particle Model ◽  
Phonon Thermal Conductivity ◽  
Alloy Scattering ◽  
Classical Size ◽  
Good Agreement

ABSTRACTAn incoherent particle model has been developed to predict the phonon thermal conductivity of nanowires and superlattice nanowires. It is argued that the surface roughness of most real nanowires prevents the formation of idealized confined dispersion relations for typical temperatures and diameters. Instead, the three-dimensional bulk dispersion is used, thus addressing only classical size effects. Four adjustable parameters capture the effects of diameter, superlattice, Umklapp, impurity, and alloy scattering. Predictions are compared with experimental data for nanowires and superlattice nanowires down to 22 nm diameter and 20 K, and are in good agreement above ∼40 nm diameter. The analysis suggests that ideal low thermal conductivity nanowires for thermoelectric applications would have small-diameter, alternating alloy segments that are acoustically dissimilar but electrically similar.

Molecular Dynamics Calculations of InSb Thermal Conductivity

2010 ◽  
Vol 297-301 ◽  
pp. 1400-1407
Author(s):  
Giovano de Oliveira Cardozo ◽  
José Pedro Rino
Keyword(s):  
Experimental Data ◽  
Thermal Conductivity ◽  
Molecular Dynamics ◽  
Infinite System ◽  
Thermal Conductivity Coefficient ◽  
Direct Method ◽  
Molecular Dynamics Calculations ◽  
Non Equilibrium Molecular Dynamics ◽  
Three Body ◽  
Non Equilibrium

Equilibrium and non-equilibrium molecular dynamics calculations of thermal conductivity coefficient are presented for bulk systems of InSb, using an effective two- and three-body inter atomic potential which demonstrated to be very transferable. In the calculations, the obtained coefficients were comparable to the experimental data. In the case of equilibrium simulations a Green-Kubo approach was used and the thermal conductivity was calculated for five temperatures between 300 K and 900 K. For the non equilibrium, or direct method, which is based on the Fourier’s law, the thermal conductivity coefficient was determined at a mean temperature of 300K. In this case it was used a pair of reservoirs, placed at a distance L from each other, and with internal temperatures fixed in 250 K, for the cold reservoir, and 350 K for the hot one. In order to obtain an approach to an infinite system coefficient, four different values of L were used, and the data was extrapolated to L→∞.

scholarly journals Thermal Conductivities of Unidirectional Materials

1967 ◽  
Vol 1 (2) ◽  
pp. 166-173 ◽  
Author(s):  
George S. Springer ◽  
Stephen W. Tsai
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Thermal Conductivity ◽  
Thermal Model ◽  
Longitudinal Shear ◽  
Unidirectional Composite ◽  
Shear Loading ◽  
Square Packing ◽  
Good Agreement ◽  
Thermal Conductivities

In this paper the composite thermal conductivities of unidirec tional composites are studied and expressions are obtained for pre dicting these conductivities in the directions along and normal to the filaments. In the direction along the filament an expression is presented based on the assumption that the filaments and matrix are connected in parallel. In the direction normal to the filaments composite thermal conductivity values are obtained first by utiliz ing the analogy between the response of a unidirectional composite to longitudinal shear loading and to transverse heat transfer; second by replacing the filament-matrix composite with an idealized ther mal model. The results of the shear loading analogy agree reason ably well with the results of the thermal model particularly at filament contents below about 60%. These results were also com pared to experimental data reported in the literature and good agreement was found between the data and those theoretical re sults that were derived for circular filaments arranged in a square packing array.

Evaluation of soil thermal conductivity models

2015 ◽  
Vol 52 (11) ◽  
pp. 1892-1900 ◽  
Author(s):  
D. Barry-Macaulay ◽  
A. Bouazza ◽  
B. Wang ◽  
R.M. Singh
Keyword(s):  
Experimental Data ◽  
Thermal Conductivity ◽  
Detailed Analysis ◽  
Soil Parameters ◽  
Soil Thermal Conductivity ◽  
Moisture Contents ◽  
Saturated Sands ◽  
Good Agreement ◽  
Different Soils ◽  
Conductivity Models

Numerous models have been developed to predict the thermal conductivity of soils at a range of different densities and moisture contents. This paper evaluates four thermal conductivity models, developed by various researchers, by comparing their performance against experimental results obtained on 27 different soils prepared at a range of saturation levels and densities. The results demonstrate that, in general, all four models show good agreement between experimental thermal conductivity and modelled thermal conductivity. The only significant shortfall is observed in low-saturated sands when using two of the models. A detailed analysis of the empirical soil parameters used in three of the recent models is presented. It shows that the accuracy of the three models can be improved by modifying the empirical soil parameters to fit the experimental data.

scholarly journals Direct stochastic molecular modelling of transport processes in gases

2021 ◽  
Vol 2056 (1) ◽  
pp. 012003
Author(s):  
V Ya Rudyak ◽  
E V Lezhnev
Keyword(s):  
Thermal Conductivity ◽  
Diffuse Reflection ◽  
Thermal Conductivity Coefficient ◽  
Rarefied Gas ◽  
Transport Coefficients ◽  
High Accuracy ◽  
Transport Processes ◽  
Modeling Transport ◽  
Gas Molecules ◽  
First Time

Abstract The stochastic molecular modeling method (SMM) of transport processes in rarefied gases developed by the authors is systematically discussed in this paper. It is shown that, it is possible to simulate the transport coefficients of rarefied gas with high accuracy, using a relatively small number of molecules. The data of modeling the thermal conductivity coefficient are presented for the first time. The second part of the paper is devoted to the generalization of the SMM method for modeling transport processes in confined conditions. To describe the dynamics of molecules in this case, the splitting of their evolution by processes is used: first, the movement of molecules in the configuration space is simulated, and then their dynamics in the velocity space is imitated. Anisotropy of viscosity and thermal conductivity in nanochannels has been established. The interaction of gas molecules with walls is described by specular or specular-diffuse reflection laws. Gas viscosity can be either greater than in the bulk or less, depending on the law of gas interaction with the channel walls.

scholarly journals Study the Migration Process of Chemical Substances through the Packaging/Food Interface during Microwave Treatment

2013 ◽  
Vol 2013 ◽  
pp. 1-3 ◽  
Author(s):  
Fang Duan ◽  
Ming-qing Chen ◽  
Yong Zhu ◽  
Hui Zhang ◽  
Jing Zhang
Keyword(s):  
Experimental Data ◽  
Diffusion Coefficient ◽  
Diffusion Process ◽  
Microwave Treatment ◽  
Research Community ◽  
Packaging Materials ◽  
Migration Process ◽  
Chemical Substances ◽  
Good Agreement

The diffusion of chemical substances from packaging into food endangers people’s health. The migration amount of the chemical substances increases with the time and temperature, but the diffusion process for different kinds of packaging materials differs much. Most recently, the research community showed a renewed interest on the diffusion process of chemical substances through packaging/food interface during microwave treatment. In this study, the diffusion coefficient model is suggested and then the migration process is studied based on Fick’s diffusion law. The results are finally compared with the experimental data, showing good agreement.

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