Thermal equilibrium at temperatures below 1° absolute

1938 ◽  
Vol 34 (2) ◽  
pp. 301-307 ◽  
Author(s):  
E. S. Shire ◽  
J. F. Allen
Keyword(s):  
Thermal Conductivity ◽  
Liquid Helium ◽  
Thermal Equilibrium ◽  
Lattice Vibrations ◽  
Ammonium Alum

By measuring the resistance of a phosphor bronze wire in thermal equilibrium via various substances with crystals of iron ammonium alum it is shown that the time for thermal equilibrium between the ionic magnets of the salt and its lattice vibrations is less than 0·5 sec. for all temperatures above 0·025° T*. When liquid helium or a german silver tube forms part of the cooled portion of the apparatus, the time for equilibrium is increased to a few seconds for temperatures below 0·4° K. It appears possible that the thermal conductivity of german silver is less than 10−8 cal. cm.−1 sec.−1 degree−1 below 0·05° T*, and there are indications that the thermal conductivity of liquid helium at temperatures below 0·3° K. is small compared with its value at 2° K.

Experiments on the flow of heat in liquid helium below 0.7 °K

1958 ◽  
Vol 246 (1246) ◽  
pp. 390-405 ◽  
Keyword(s):  
Thermal Conductivity ◽  
Liquid Helium ◽  
Free Path ◽  
Empirical Relation ◽  
Mean Free Path ◽  
Series Of Experiments ◽  
The Mean ◽  
Set Up ◽  
Low Pressures ◽  
Measured Thermal Conductivity

A series of experiments has been performed to study the steady flow of heat in liquid helium in tubes of diameter 0.05 to 1.0 cm at temperatures between 0.25 and 0.7 °K. The results are interpreted in terms of the flow of a gas of phonons, in which the mean free path λ varies with temperature, and may be either greater or less than the diameter of the tube d . When λ ≫ d the flow is limited by the scattering of the phonons at the walls, and the effect of the surface has been studied, but when λ ≪ d viscous flow is set up in which the measured thermal conductivity is increased above that for wall scattering. This behaviour is very similar to that observed in the flow of gases at low pressures, and by applying kinetic theory to the problem it can be shown that the mean free path of the phonons characterizing viscosity can be expressed by the empirical relation λ = 3.8 x 10 -3 T -4.3 cm. This result is inconsistent with the temperature dependence of λ as T -9 predicted theoretically by Landau & Khalatnikov (1949).

scholarly journals Investigation of thermal conductivity of single-wall carbon nanotubes

2011 ◽  
Vol 15 (2) ◽  
pp. 565-570 ◽  
Author(s):  
Mahmoud Jafari ◽  
Majid Vaezzadeh ◽  
Momhamad Mansouri ◽  
Abazar Hajnorouzi
Keyword(s):  
Thermal Conductivity ◽  
Carbon Nanotubes ◽  
Theoretical Model ◽  
Potential Energy ◽  
Experimental Results ◽  
Single Wall Carbon Nanotubes ◽  
Lattice Vibrations ◽  
Single Wall Carbon ◽  
Thermal Potential ◽  
Conductivity Behavior

In this paper, the thermal conductivity of Single-wall carbon nanotubes (SWCNTs) is determined by lattice vibrations (phonons) and free elections. The thermal conductivity of SWCNTs is modeled up to 8-300 K and the observed deviations in K-T figures of SWCNTs are explained in terms of phonon vibrations models. An suitable theoretical model is shown for thermal conductivity behavior with respect to temperature and is generalized for experimental results. This model enables us to calculate thermal conductivity SWNTs and Thermal Potential Energy (TPE).

Ultrastructural features of the sensori-motor cortex of the primate

1979 ◽  
Vol 285 (1006) ◽  
pp. 123-139 ◽  
Keyword(s):  
Thermal Conductivity ◽  
Motor Cortex ◽  
Thin Layer ◽  
Liquid Helium ◽  
Thermal Insulation ◽  
Solid Surfaces ◽  
The Other ◽  
Experimental Chamber ◽  
Short Discussion ◽  
Inside Wall

cooled to 2°K or lower. Rollin (1936) found that the thermal insulation of vessels containing liquid helium was much worse below than above the A point. He explained his observation by assuming the existence of a thin layer of liquid helium on the inside wall of the connecting tube, and thought it probable that the change in thermal conductivity of this film at the A point gave rise to the anomalous effects observed. As the result of more recent (unpublished) experiments Rollin and Simon* have put forward the other explanation that the film creeps up the tube and evaporates eventually. It is obvious that all these phenomena may have a common explanation and it was the object of the experiments described in this paper and the following paper to investigate the behaviour of He 11 in contact with solid surfaces systematically. The phenomena had to be investigated from various aspects and this made experiments necessary which varied in purpose and character to some extent. For simplicity’s sake we will therefore give, together with the description of each experiment, a short discussion and summarize at the end of the second paper all results in a general discussion on the whole phenomenon. All experiments were carried out in the same cryostat; and for different experiments only the experimental chamber and the experimental arrangement in it were altered.

Nanofluid Suspensions as Derivative of Interface Heat Transfer Modeling in Porous Media

2009 ◽  
Author(s):  
Peter Vadasz
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Porous Media ◽  
Heat Conduction ◽  
Thermal Equilibrium ◽  
Local Thermal Equilibrium ◽  
Interface Heat Transfer ◽  
Wire Method ◽  
Special Case ◽  
Heat Conduction Process

Spectacular heat transfer enhancement has been measured in nanofluid suspensions. Attempts in explaining these experimental results did not yield yet a definite answer. Modeling the heat conduction process in nanofluid suspensions is being shown to be a special case of heat conduction in porous media subject to Lack of Local thermal equilibrium (LaLotheq). The topic of heat conduction in porous media subject to Lack of Local thermal equilibrium (LaLotheq) is reviewed, introducing one of the most accurate methods of measuring the thermal conductivity, the transient hot wire method, and discusses its possible application to dual-phase systems. Maxwell’s concept of effective thermal conductivity is then introduced and theoretical results applicable for nanofluid suspensions are compared with published experimental data.

scholarly journals Extracting Concrete Thermal Characteristics from Temperature Time History of RC Column Exposed to Standard Fire

2014 ◽  
Vol 2014 ◽  
pp. 1-10 ◽  
Author(s):  
Jung J. Kim ◽  
Kwang-Soo Youm ◽  
Mahmoud M. Reda Taha
Keyword(s):  
Thermal Conductivity ◽  
Numerical Method ◽  
Thermal Equilibrium ◽  
Time History ◽  
Radiant Heat Transfer ◽  
Unsteady State ◽  
Temperature Variations ◽  
Rc Column ◽  
Standard Fire ◽  
History Of

A numerical method to identify thermal conductivity from time history of one-dimensional temperature variations in thermal unsteady-state is proposed. The numerical method considers the change of specific heat and thermal conductivity with respect to temperature. Fire test of reinforced concrete (RC) columns was conducted using a standard fire to obtain time history of temperature variations in the column section. A thermal equilibrium model in unsteady-state condition was developed. The thermal conductivity of concrete was then determined by optimizing the numerical solution of the model to meet the observed time history of temperature variations. The determined thermal conductivity with respect to temperature was then verified against standard thermal conductivity measurements of concrete bricks. It is concluded that the proposed method can be used to conservatively estimate thermal conductivity of concrete for design purpose. Finally, the thermal radiation properties of concrete for the RC column were estimated from the thermal equilibrium at the surface of the column. The radiant heat transfer ratio of concrete representing absorptivity to emissivity ratio of concrete during fire was evaluated and is suggested as a concrete criterion that can be used in fire safety assessment.

The thermal conductivity of solid helium

1952 ◽  
Vol 214 (1119) ◽  
pp. 546-563 ◽  
Keyword(s):  
Thermal Conductivity ◽  
Thermal Resistance ◽  
Single Crystals ◽  
Liquid Helium ◽  
Solid Helium ◽  
Boundary Scattering ◽  
Conductivity Measurements ◽  
Helium Ii ◽  
Characteristic Temperatures ◽  
Thermal Conductivities

The thermal conductivities of crystals of solid helium at densities between 0⋅194 and 0⋅218 g/cm 3 have been measured at liquid-helium temperatures. In order to interpret the results, the specific heat of solid helium at these densities has been measured from 0⋅6 to 1⋅4° K. The range of densities employed is sufficient to allow the observation of Debye characteristic temperatures varying by 40 %, and of thermal conductivities varying by factors of over 10. It is shown that the conductivity measurements are in accord with the ‘umklapp’ type of thermal resistance derived by Peierls (1929, 1935). Further work was restricted by the difficulty of obtaining good single crystals in narrow tubes, but measurements of the conductivity at one density were obtained down to 0⋅3° K. In this region the conductivity is limited by boundary scattering and is higher than that observed by other authors for liquid helium II at similar temperatures.

Momentum transfer and heat flow in liquid helium II

1939 ◽  
Vol 35 (1) ◽  
pp. 114-122 ◽  
Author(s):  
J. F. Allen ◽  
J. Reekie
Keyword(s):  
Thermal Conductivity ◽  
Hydrostatic Pressure ◽  
Heat Flow ◽  
Momentum Transfer ◽  
Liquid Helium ◽  
Liquid Flow ◽  
Glass Capillary ◽  
Considerable Part ◽  
Helium Ii ◽  
Steady Heat

It has been found by one of the authors (1) in collaboration with Dr H. Jones that a flow of heat in liquid He ii is accompanied by what seems to be a transfer of momentum. The effect can be seen when the channel through which the heat and liquid flow consists of a smooth-walled glass capillary, such as shown in Fig. 1a. Due to the high thermal conductivity of He ii, a considerable part of the heat put into the reservoir is carried down through the capillary to the bath. When a steady heat flow exists, a flow of liquid takes place in the opposite direction, and the level of the liquid in the reservoir is seen to be higher than that in the bath. Smooth capillaries, however, produce a rise in level of only 1 or 2 cm. at most, since the viscosity of the liquid is small and hydrostatic pressure pulls the accumulated liquid in the reservoir back through the capillary. When the heat flow is large, violent surging is observed in the reservoir, but there is no further rise in level.

Sign in / Sign up

Export Citation Format

Share Document