A Transient Technique for Measuring the Effective Thermal Conductivity of Saturated Porous Media With a Constant Boundary Heat Flux

2006 ◽  
Vol 128 (11) ◽  
pp. 1217-1220 ◽  
Author(s):  
H. T. Aichlmayr ◽  
F. A. Kulacki
Keyword(s):  
Thermal Conductivity ◽  
Heat Flux ◽  
Porous Media ◽  
Effective Thermal Conductivity ◽  
Constant Heat Flux ◽  
Infinite Cylinder ◽  
Saturated Porous Media ◽  
Transient Heating ◽  
Effective Thermal Diffusivity ◽  
Data Reduction Technique

An experimental technique for measuring the effective thermal conductivity of saturated porous media is presented. The experimental method is based on the transient heating of a semi-infinite cylinder by a constant heat flux at the boundary. The data reduction technique is unique because it avoids determining the effective thermal diffusivity and quantifying the boundary heat flux. The technique is used to measure the effective thermal conductivity of glass-water, glass-air, and steel-air systems. These systems yield solid-fluid conductivity ratios of 1.08, 25.7, and 2400, respectively. The solid phases consist of 3.96mm glass spheres and 14mm steel ball bearings, which give mean porosities of 0.365 and 0.403. In addition, particular attention is paid to assessing experimental uncertainty. Consequently, this study provides data with a degree of precision not typically found the literature.

On the Effective Thermal Conductivity of Saturated Porous Media

2005 ◽  
Author(s):  
H. T. Aichlmayr ◽  
F. A. Kulacki
Keyword(s):  
Thermal Conductivity ◽  
Heat Flux ◽  
Effective Thermal Conductivity ◽  
Constant Heat Flux ◽  
Infinite Cylinder ◽  
Transient Heating ◽  
Effective Thermal Diffusivity ◽  
Fluid Systems ◽  
Data Reduction Technique ◽  
Transient System

Carefully quantified effective thermal conductivity measurements of saturated porous systems are reported. Solid-fluid systems considered include glass-water, glass-air, steel-water, and steel-air. These systems yield solid-fluid conductivity ratios of 1.08, 25.7, 102, and 2400, respectively. The solid phases consist of 3.96 mm glass spheres and 14 mm steel ball bearings, which give mean porosities of 0.365 and 0.403. The experimental method is based on the transient heating of a semi-infinite cylinder by a constant heat flux at the boundary. The data reduction technique is unique because it avoids determining the effective thermal diffusivity and quantifying the boundary heat flux. In addition, particular attention is paid to assessing experimental uncertainty. Consequently, this study provides data with a degree of precision not typically found the literature. A complete accounting of energy storage and transport in the transient system is conducted to complement the uncertainty analysis. A thorough literature review is also presented to facilitate a critique of the experimental results.

scholarly journals Time dependence of snow microstructure and associated effective thermal conductivity

2008 ◽  
Vol 49 ◽  
pp. 43-50 ◽  
Author(s):  
P.K. Satyawali ◽  
A.K. Singh ◽  
S.K. Dewali ◽  
Praveen Kumar ◽  
Vinod Kumar
Keyword(s):  
Thermal Conductivity ◽  
Heat Flux ◽  
Temperature Gradient ◽  
Effective Thermal Conductivity ◽  
Constant Heat Flux ◽  
Constant Density ◽  
Significant Control ◽  
Increase With Increase ◽  
Snow Microstructure ◽  
Sequential Evaluation

AbstractThis paper presents a sequential evaluation of snow microstructure and its associated thermal conductivity under the influence of a temperature gradient. Temperature gradients from 28 to 45 Km–1 were applied to snow samples having a density range 180–320 kgm–3. The experiments were conducted inside a cold room in a specially designed heat-flux apparatus for a period of 4weeks. A constant heat flux was applied at the base of the heat-flux apparatus to produce a temperature gradient in the snow sample. A steady-state approach was used to estimate the effective thermal conductivity of snow. Horizontal and vertical thick sections were prepared on a weekly basis to obtain snow micrographs. These micrographs were used to obtain snow microstructure using stereological tools. The thermal conductivity was found to increase with increase in grain size, bond size and grain and pore intercept lengths, suggesting a possible correlation of thermal conductivity with snow microstructure. Thermal conductivity increased even though surface area and area fraction of ice were found to decrease. The outcome suggests that changes in snow microstructure have significant control on thermal conductivity even at a constant density.

Boundary-value problems in the kinetic theory of gases. Part 2. Thermal creep

1971 ◽  
Vol 45 (4) ◽  
pp. 759-768 ◽  
Author(s):  
M. M. R. Williams
Keyword(s):  
Thermal Conductivity ◽  
Heat Flux ◽  
Temperature Gradient ◽  
Kinetic Theory ◽  
Effective Thermal Conductivity ◽  
Half Space ◽  
Thermal Creep ◽  
Kinetic Theory Of Gases ◽  
Boundary Wall ◽  
Creep Velocity

The effect of a temperature gradient in a gas inclined at an angle to a boundary wall has been investigated. For an infinite half-space of gas it is found that, in addition to the conventional temperature slip problem, the component of the temperature gradient parallel to the wall induces a net mass flow known as thermal creep. We show that the temperature slip and thermal creep effects can be decoupled and treated quite separately.Expressions are obtained for the creep velocity and heat flux, both far from and at the boundary; it is noted that thermal creep tends to reduce the effective thermal conductivity of the medium.

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