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.

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.

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.

A Transient Formulation of Newton's Cooling Law for Spherical Bodies

2000 ◽  
Vol 123 (1) ◽  
pp. 63-64 ◽  
Author(s):  
S. S. Sazhin ◽  
V. A. Gol'dshtein ◽  
M. R. Heikal
Keyword(s):  
Thermal Conductivity ◽  
Heat Flux ◽  
Diesel Engine ◽  
Effective Thermal Conductivity ◽  
Spherical Body ◽  
Fuel Droplet ◽  
Transient Effects ◽  
Newton's Law ◽  
Initial Stage ◽  
Newton’S Law

Newton's law of cooling is shown to underestimate the heat flux between a spherical body (droplet) and a homogeneous gas after this body is suddenly immersed into the gas. This problem is rectified by replacing the gas thermal conductivity by the effective thermal conductivity. The latter reduces to the gas thermal conductivity in the limit of t→∞, but can be substantially higher in the limit of t→0. In the case of fuel droplet heating in a medium duty truck Diesel engine the gas thermal conductivity may need to be increased by more than 100 percent at the initial stage of calculations to account for transient effects during the process of droplet heating.

Heat Flux and Variable Thermal Conductivity Effects on Casson Flow and Heat Transfer due to an Exponentially Stretching Sheet with Viscous Dissipation and Heat Generation

2016 ◽  
Vol 14 (1) ◽  
pp. 167-174 ◽  
Author(s):  
Ahmed M. Megahed
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Flux ◽  
Heat Generation ◽  
Stretching Sheet ◽  
Variable Thermal Conductivity ◽  
Constant Heat Flux ◽  
Constant Heat ◽  
Flow And Heat Transfer ◽  
Exponentially Stretching

AbstractIn this paper, we introduce a theoretical and numerical study for the effects of thermal buoyancy and constant heat flux on the Casson fluid flow and heat transfer over an exponentially stretching sheet taking into account the effects of variable thermal conductivity, heat generation/absorption and viscous dissipation. The governing partial differential equations are transformed into coupled, non-linear ordinary differential equations by using suitable transformations. Numerical solutions to these equations are obtained by using the fourth order Runge-Kutta method with the shooting technique. The effects of various physical parameters which governing the flow and heat treansfer such as the buoyancy parameter, the thermal conductivity parameter, heat generation or absorption parameter and the Prandtl number on velocity and temperature are discussed by using graphical approach. Moreover, numerical results indicate that the local skin-friction coefficient and the local Nusselt number are strongly affected by the constant heat flux.

A transient method of measuring the thermal properties of rocks

Geophysics ◽  
1993 ◽  
Vol 58 (3) ◽  
pp. 357-365 ◽  
Author(s):  
Mike F. Middleton
Keyword(s):  
Thermal Conductivity ◽  
Heat Flux ◽  
Sensitivity Analysis ◽  
Thermal Diffusivity ◽  
Sedimentary Basins ◽  
Constant Heat Flux ◽  
Transient Method ◽  
Constant Heat ◽  
Western Australian

The aim of the paper is to describe a new, rapid transient method for the determination of thermal diffusivity and thermal conductivity of rocks. The present transient method is based on the application of a constant heat flux to the top surface of a block of rock that is insulated on all other surfaces. Results of a sensitivity analysis of the method indicate that thermal diffusivity can be measured to a best accuracy of about 3 percent, and thermal conductivity of saturated rocks can be determined to a best accuracy of about 8 percent. The method provides estimates of thermal conductivity that are consistent with estimates made using the steady‐state divided‐bar apparatus. The method is applied to determine the thermal conductivity of a suite of rocks from western Australian sedimentary basins.

scholarly journals Thermal Conductivity Structure and Anisotropy of the Colossal Carbon Mesotubes

2021 ◽  
Vol 2096 (1) ◽  
pp. 012165
Author(s):  
Yu P Zarichnyak ◽  
A Yu Gorbunova ◽  
V A Korablev ◽  
V A Ivanov ◽  
N V Pilipenko ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Heat Flux ◽  
Effective Thermal Conductivity ◽  
Cross Section ◽  
Total Conductivity ◽  
Electrical Circuits ◽  
Conductivity Structure ◽  
Transverse Thermal Conductivity ◽  
Separate Estimate ◽  
Selection Of

Abstract A model of a tube with a square cross-section was compiled for the mathematical analysis of the mesotube in Cartesian coordinates, with the selection of an element of a representative volume. To estimate the effective thermal conductivity of the structure, the generalized theory of conductivity with linearization of heat flux streamlines was used. The presence of anisotropy leads to the division of the problem into a separate estimate of the longitudinal and transverse thermal conductivity. The cross-section of the model was divided into elementary sections by a system of auxiliary adiabatic and isothermal planes, then the sections of the model were presented in the form of thermal resistances connected in chains - electrical circuits. Using the analogy of the identity of thermal and electrical resistances, the total conductivity of the sections and the effective thermal conductivity of the structure were determined. This methodology satisfies the test for limit transitions.

Numerical Investigation of the Steady State Operation of a Cylindrical Capillary Pumped Loop Evaporator

2000 ◽  
Author(s):  
Y. H. Yan ◽  
J. M. Ochterbeck
Keyword(s):  
Thermal Conductivity ◽  
Heat Flux ◽  
Steady State ◽  
Effective Thermal Conductivity ◽  
Liquid Core ◽  
Phase Region ◽  
Capillary Pumped Loop ◽  
Two Phase ◽  
Cylindrical Capillary ◽  
Wick Structure

Abstract A two-dimensional numerical model was established to study the behavior of a cylindrical capillary pumped loop evaporator under steady-state operations. The influence of heat load, liquid subcooling and effective thermal conductivity of the wick structure on the evaporator performance were studied. It was found that increasing the applied heat flux and degree of liquid subcooling resulted in a decrease the temperature in the liquid core. This helped to prevent the vapor from generating in the liquid core and decreased the length of the two phase region in the wick structure. Decreasing the effective thermal conductivity also decreases the temperature in the liquid core as related to the back wick condition. It was observed that for a given liquid subcooling, a minimum heat flux exists below which vapor will generate in the liquid core and render the evaporator non-operational. It was also observed that for a given heat flux, a minimum required liquid subcooling exists. Vapor may form in the liquid core when the liquid subcooling is less than the minimum value.

Sign in / Sign up

Export Citation Format

Share Document