scholarly journals Conduction of heat through powders and its dependence on the pressure and conductivity of the gaseous phase

1926 ◽  
Vol 113 (764) ◽  
pp. 459-477 ◽  
Keyword(s):  
Carbon Dioxide ◽  
Thermal Conductivity ◽  
Gaseous Phase ◽  
Linear Relation ◽  
Gas Pressure ◽  
Pumice Stone ◽  
Solid Part ◽  
Thermal Conductivities

The object of our investigation has been to study the conduction of heat through a light powder and to find how it depends upon the pressure and thermal conductivity of the gas in which the powder is immersed. A solution of this question is part of the solution of the problem of the conduction of heat through a certain class of “solid” heat insulators—a class which includes those of lowest thermal conductivity. The class of insulator referred to are solids dispersed in gases, or gases dispersed in solids, and consists of three kinds of substances, (1) fibrous substances ( e.g., wool, eiderdown, asbestos), (2) cellular substances (e. g., cork, pumice stone) and (3) powders (e. g., lamp-black, powdered cork, silox or monox). It might be expected that substances so different as those mentioned would have very different thermal conductivities. Actually their conductivities range from about 8 to 11 times 10 -5 cal. cm. -1 deg. -1 sec. -1 . As there is nothing common to the solid part of these substances, their conductivities, it would seem probable, are determined mainly by the factor which is common to them all, that is, the gaseous part, which is air. Our experiments have been made with a very light powder known as monox or silox, and the conductivity of this powder when immersed in air, in carbon dioxide, and in hydrogen at various pressures has been determined. We find that there is a linear relation between the conductivity of the powder and the logarithm of the pressure of the gas in which it is immersed, so that if k is the measure of the conductivity of the powder, k 0 that of the gas in which it is immersed, and p the measure of the gas pressure, then k = ½ k 0 log 10 p/n approximately, where n is a constant for a given gas.

Viscosity and Thermal Conductivity of Dry Air in the Gaseous Phase

1985 ◽  
Vol 14 (4) ◽  
pp. 947-970 ◽  
Author(s):  
K. Kadoya ◽  
N. Matsunaga ◽  
A. Nagashima
Keyword(s):  
Thermal Conductivity ◽  
Gaseous Phase ◽  
Dry Air

An electrical analyzer for carbon dioxide in respiratory gases

1962 ◽  
Vol 17 (1) ◽  
pp. 126-130
Author(s):  
Leon Bernstein ◽  
Chiyoshi Yoshimoto
Keyword(s):  
Carbon Dioxide ◽  
Thermal Conductivity ◽  
Medical Students ◽  
Venous Blood ◽  
Mixed Venous Blood ◽  
The Subject ◽  
Respiratory Gases ◽  
Rebreathing Method ◽  
Mixed Venous

The analyzer described was de signed for measuring the concentration of carbon dioxide in the bag of gas from which the subject rebreathes in the “rebreathing method” for estimating the tension of carbon dioxide in mixed venous blood. Its merits are that it is cheap, robust, simple to construct and to service, easy to operate, and accurate when used by untrained operators. (Medical students, unacquainted with the instrument, and working with written instructions only, obtained at their first attempt results accurate to within ±0.36% [sd] of carbon dioxide.) The instrument is suitable for use by nurse or physician at the bedside, and also for classes in experimental physiology. Some discussion is presented of the theoretical principles underlying the design of analyzers employing thermal conductivity cells. Submitted on July 13, 1961

Effects of Nb doping on thermoelectric properties of Zn4Sb3 at high temperatures

2009 ◽  
Vol 24 (2) ◽  
pp. 430-435 ◽  
Author(s):  
D. Li ◽  
H.H. Hng ◽  
J. Ma ◽  
X.Y. Qin
Keyword(s):  
Thermal Conductivity ◽  
Electrical Resistivity ◽  
High Temperatures ◽  
Thermoelectric Properties ◽  
Figure Of Merit ◽  
Thermoelectric Performance ◽  
Temperature Range ◽  
A Value ◽  
Nb Doping ◽  
Thermal Conductivities

The thermoelectric properties of Nb-doped Zn4Sb3 compounds, (Zn1–xNbx)4Sb3 (x = 0, 0.005, and 0.01), were investigated at temperatures ranging from 300 to 685 K. The results showed that by substituting Zn with Nb, the thermal conductivities of all the Nb-doped compounds were lower than that of the pristine β-Zn4Sb3. Among the compounds studied, the lightly substituted (Zn0.995Nb0.005)4Sb3 compound exhibited the best thermoelectric performance due to the improvement in both its electrical resistivity and thermal conductivity. Its figure of merit, ZT, was greater than the undoped Zn4Sb3 compound for the temperature range investigated. In particular, the ZT of (Zn0.995Nb0.005)4Sb3 reached a value of 1.1 at 680 K, which was 69% greater than that of the undoped Zn4Sb3 obtained in this study.

Design of a Steady-State, Parallel-Plate Thermal Conductivity Apparatus for Nanofluids and Comparative Measurements With Transient HWTC Apparatus

2010 ◽  
Author(s):  
Milivoje M. Kostic ◽  
Casey J. Walleck
Keyword(s):  
Thermal Conductivity ◽  
Steady State ◽  
Parallel Plate ◽  
Measurement Method ◽  
Mixture Theory ◽  
Hot Wire ◽  
Electro Magnetic ◽  
Magnetic Phenomena ◽  
Thermal Conductivities

A steady-state, parallel-plate thermal conductivity (PPTC) apparatus has been developed and used for comparative measurements of complex POLY-nanofluids, in order to compare results with the corresponding measurements using the transient, hotwire thermal conductivity (HWTC) apparatus. The related measurements in the literature, mostly with HWTC method, have been inconsistent and with measured thermal conductivities far beyond prediction using the well-known mixture theory. The objective was to check out if existing and well-established HWTC method might have some unknown issues while measuring TC of complex nano-mixture suspensions, like electro-magnetic phenomena, undetectable hot-wire vibrations, and others. These initial and limited measurements have shown considerable difference between the two methods, where the TC enhancements measured with PPTC apparatus were about three times smaller than with HWTC apparatus, the former data being much closer to the mixture theory prediction. However, the influence of measurement method is not conclusive since it has been observed that the complex nano-mixture suspensions were very unstable during the lengthy steady-state measurements as compared to rather quick transient HWTC method. The nanofluid suspension instability might be the main reason for very inconsistent results in the literature. It is necessary to expend investigation with more stable nano-mixture suspensions.

Through-Plane Thermal Conductivity of PEMFC Porous Transport Layers

2010 ◽  
Vol 8 (2) ◽  
Author(s):  
Odne S. Burheim ◽  
Jon G. Pharoah ◽  
Hannah Lampert ◽  
Preben J. S. Vie ◽  
Signe Kjelstrup
Keyword(s):  
Thermal Conductivity ◽  
Contact Resistance ◽  
Thermal Contact Resistance ◽  
Thermal Contact ◽  
Residual Water ◽  
Order Of Magnitude ◽  
Thermal Conductivities

We report the through-plane thermal conductivities of the several widely used carbon porous transport layers (PTLs) and their thermal contact resistance to an aluminum polarization plate. We report these values both for wet and dry samples and at different compaction pressures. We show that depending on the type of PTL and the existence of residual water, the thermal conductivity of the materials varies from 0.15 W K−1 m−1 to 1.6 W K−1 m−1, one order of magnitude. This behavior is the same for the contact resistance varying from 0.8 m2 K W−1 to 11×10−4 m2 K W−1. For dry PTLs, the thermal conductivity decreases with increasing polytetrafluorethylene (PTFE) content and increases with residual water. These effects are explained by the behavior of air, water, and PTFE in between the PTL fibers. It is also found that Toray papers of differing thickness exhibit different thermal conductivities.

Thermoelectric Properties of K2Bi8−xSbxSe13Solid Solutions and Se Doping

2001 ◽  
Vol 691 ◽  
Author(s):  
Theodora Kyratsi ◽  
Jeffrey S. Dyck ◽  
Wei Chen ◽  
Duck-Young Chung ◽  
Ctirad Uher ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Charge Transport ◽  
Transport Properties ◽  
Thermoelectric Properties ◽  
Solid Solutions ◽  
Figure Of Merit ◽  
Lattice Thermal Conductivity ◽  
Se Doping ◽  
Mass Fluctuation ◽  
Thermal Conductivities

ABSTRACTOur efforts to improve the thermoelectric properties of β-K2Bi8Se13, led to systematic studies of solid solutions of the type β-K2Bi8−xSbxSe13. The charge transport properties and thermal conductivities were studied for selected members of the series. Lattice thermal conductivity decreases due to the mass fluctuation generated in the lattice by the mixed occupation of Sb and Bi atoms. Se excess as a dopant was found to increase the figure-of merit of the solid solutions.

Thermal Conductivity and Prandtl Number of Carbon Dioxide and Carbon-Dioxide Air Mixtures at One Atmosphere

1961 ◽  
Vol 83 (2) ◽  
pp. 125-131 ◽  
Author(s):  
Jerome L. Novotny ◽  
Thomas F. Irvine
Keyword(s):  
Carbon Dioxide ◽  
Thermal Conductivity ◽  
Prandtl Number ◽  
Maximum Error ◽  
Intermolecular Force ◽  
Temperature Range ◽  
Average Temperature ◽  
Pure Carbon ◽  
Prandtl Numbers ◽  
Pure Carbon Dioxide

By measuring laminar recovery factors in a high velocity gas stream, experimental determinations were made of the Prandtl number of carbon dioxide over a temperature range from 285 to 450 K and of carbon-dioxide air mixtures at an average temperature of 285 K with a predicted maximum error of 1.5 per cent. Thermal conductivity values were deduced from these Prandtl numbers and compared with literature values measured by other methods. Using intermolecular force constants determined from literature experimental data, viscosities, thermal conductivities, and Prandtl numbers were calculated for carbon-dioxide air mixtures over the temperature range 200 to 1500 deg for mixture ratios from pure air to pure carbon dioxide.

Understanding Carbon Dioxide Transfer in Direct Methanol Fuel Cells Using a Pore-Scale Model

2021 ◽  
Vol 19 (1) ◽  
Author(s):  
Nathaniel Metzger ◽  
Archana Sekar ◽  
Jun Li ◽  
Xianglin Li
Keyword(s):  
Carbon Dioxide ◽  
Pressure Drop ◽  
Gas Flow ◽  
Direct Methanol Fuel Cells ◽  
Gas Pressure ◽  
Mass Transfer Resistance ◽  
Transfer Resistance ◽  
Cell Components ◽  
Direct Methanol ◽  
Methanol Fuel Cells

Abstract The gas flow of carbon dioxide from the catalyst layer (CL) through the microporous layer (MPL) and gas diffusion layer (GDL) has great impacts on the water and fuel management in direct methanol fuel cells (DMFCs). This work has developed a liquid–vapor two-phase model considering the counter flow of carbon dioxide gas, methanol, and water liquid solution in porous electrodes of DMFC. The model simulation includes the capillary pressure as well as the pressure drop due to flow resistance through the fuel cell components. The pressure drop of carbon dioxide flow is found to be about two to three orders of magnitude higher than the pressure drop of the liquid flow. The big difference between liquid and gas pressure drops can be explained by two reasons: volume flowrate of gas is three orders of magnitude higher than that of liquid; only a small fraction of pores (<5%) in hydrophilic fuel cell components are available for gas flow. Model results indicate that the gas pressure and the mass transfer resistance of liquid and gas are more sensitive to the pore size distribution than the thickness of porous components. To buildup high gas pressure and high mass transfer resistance of liquid, the MPL and CL should avoid micro-cracks during manufacture. Distributions of pore size and wettability of the GDL and MPL have been designed to reduce the methanol crossover and improve fuel efficiency. The model results provide design guidance to obtain superior DMFC performance using highly concentrated methanol solutions or even pure methanol.

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