scholarly journals Statistical theory of turbulence IV-Diffusion in a turbulent air stream

1935 ◽  
Vol 151 (873) ◽  
pp. 465-478 ◽  
Author(s):  
Geoffrey Ingram Taylor
Keyword(s):  
Thermal Conductivity ◽  
Statistical Theory ◽  
Line Source ◽  
Transverse Component ◽  
Lagrangian System ◽  
Principal Element ◽  
Air Stream ◽  
Heated Wire ◽  
The Mean ◽  
Statistical Theory Of Turbulence

It was pointed out in Part I that experiments on the spread of heat from a line source ( e.g ., an electrically heated wire) in a turbulent air stream may be expected to give two elements of the statistical specification of turbulence. If the spread is measured near the source the value of the mean transverse component of velocity √¯ v 2 or v ' in the notation of Part I, can be found. If the spread is examined further down-stream it should be possible to analyse the results to find the correlation function R η , which is the principal element of the representation of turbulence in the Lagrangian system. Spread of heat nearer line source Recently the spread of heat from a heated wire in a wind tunnel has been measured at points near to the source by Schubauer. The stream was made turbulent by means of grids of round bars arranged in square pattern. Their diameters were 1 /5 of the mesh length and M varied from 5 inches to 1/2 inch. The width of the heat wake was found by measuring the angle subtended at the source by the two positions where the temperature rise was half that in the centre of the wake. This angle, denoted by α, depends partly on the amount of turbulence and to a less extent on the spread of heat due to the thermal conductivity of the air. By assuming that the effect of turbulence is to communicate to the air an eddy conductivity β, which is additive to, and obeys the same law as, true thermal conductivity, a virtual angle α turb can be deduced by the relation α 2 turb = α 2 — α 2 0 ,

scholarly journals Ballistic Heat Transport in Nanocomposite: The Role of the Shape and Interconnection of Nanoinclusions

Nanomaterials ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 1982
Author(s):  
Paul Desmarchelier ◽  
Alice Carré ◽  
Konstantinos Termentzidis ◽  
Anne Tanguy
Keyword(s):  
Thermal Conductivity ◽  
Molecular Dynamics ◽  
Molecular Dynamics Simulations ◽  
Free Path ◽  
Mean Free Path ◽  
Strong Increase ◽  
Moderate Increase ◽  
Energy Propagation ◽  
The Mean ◽  
Dynamics Simulations

In this article, the effect on the vibrational and thermal properties of gradually interconnected nanoinclusions embedded in an amorphous silicon matrix is studied using molecular dynamics simulations. The nanoinclusion arrangement ranges from an aligned sphere array to an interconnected mesh of nanowires. Wave-packet simulations scanning different polarizations and frequencies reveal that the interconnection of the nanoinclusions at constant volume fraction induces a strong increase of the mean free path of high frequency phonons, but does not affect the energy diffusivity. The mean free path and energy diffusivity are then used to estimate the thermal conductivity, showing an enhancement of the effective thermal conductivity due to the existence of crystalline structural interconnections. This enhancement is dominated by the ballistic transport of phonons. Equilibrium molecular dynamics simulations confirm the tendency, although less markedly. This leads to the observation that coherent energy propagation with a moderate increase of the thermal conductivity is possible. These findings could be useful for energy harvesting applications, thermal management or for mechanical information processing.

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).

Stochastic Analysis of Temperature Distribution in a Solid With Random Heat Conductivity

1988 ◽  
Vol 110 (1) ◽  
pp. 23-29 ◽  
Author(s):  
Da Yu Tzou
Keyword(s):  
Thermal Conductivity ◽  
Temperature Distribution ◽  
Heat Conductivity ◽  
Stochastic Analysis ◽  
Solid Medium ◽  
Mean Value ◽  
Random Response ◽  
Thermal Failure ◽  
Numerical Examples ◽  
The Mean

Stochastic temperature distribution in a solid medium with random heat conductivity is investigated by the method of perturbation. The intrinsic randomness of the thermal conductivity k(x) is considered to be a distribution function with random amplitude in the solid, and several typical stochastic processes are considered in the numerical examples. The formulation used in the present analysis describes a situation that the statistical orders of the random response of the system are the same as those of the intrinsic random excitations, which is characteristic for the problem with extrinsic randomness. The maximum standard deviation of the temperature distribution from the mean value in the solid medium reveals the amount of unexpected energy experienced by the solid continuum, which should be carefully inspected in the thermal-failure design of structures with intrinsic randomness.

Prediction of Confined Coaxial Turbulent Jet Mixing With a Streamwise Differencing Scheme

1991 ◽  
Author(s):  
M. A. R. Sharif ◽  
M. A. Gadalla
Keyword(s):  
Reynolds Stresses ◽  
Low Velocity ◽  
Mean Velocity ◽  
Jet Mixing ◽  
Air Jet ◽  
Air Stream ◽  
Constant Diameter ◽  
Flow Domain ◽  
The Mean ◽  
Secondary Air

Abstract Isothermal turbulent mixing of an axisymmetric primary air jet with a low velocity annular secondary air stream inside a constant diameter cylindrical enclosure is predicted. The flow domain from the inlet to the fully developed downstream locations is considered. The predicted flow field properties include the mean velocity and pressure and the Reynolds stresses. Different velocity and diameter ratios between the primary and the secondary jets have been investigated to characterize the flow in terms of these parameters. A bounded stream-wise differencing scheme is used to minimize numerical diffusion and oscillation errors. Predictions are compared with available experimental data to back up numerical findings.

Heat Transport by Countercurrent Blood Vessels in the Presence of an Arbitrary Temperature Gradient

1990 ◽  
Vol 112 (2) ◽  
pp. 207-211 ◽  
Author(s):  
J. W. Baish
Keyword(s):  
Thermal Conductivity ◽  
Temperature Gradient ◽  
Vascular Tissue ◽  
Asymptotic Methods ◽  
Three Dimensional ◽  
Conductive Materials ◽  
Arbitrary Temperature ◽  
The Mean ◽  
Conductive Fibers ◽  
Arteries And Veins

This paper presents a three-dimensional analysis of the temperature field around a pair of countercurrent arteries and veins embedded in an infinite tissue that has an arbitrary temperature gradient along the axes of the vessels. Asymptotic methods are used to show that such vessels are thermally similar to a highly conductive fiber in the same tissue. Expressions are developed for the effective radius and thermal conductivity of the fiber so that it conducts heat at the same rate that the artery and vein together convect heat and so that its local temperature equals the mean temperature of the vessels. This result allows vascular tissue to be viewed as a composite of conductive materials with highly conductive fibers replacing the convective effects of the vasculature. By characterizing the size and thermal conductivity of these fibers, well-established methods from the study of composites may be applied to determine when an effective conductive model is appropriate for the tissue and vasculature as a whole.

scholarly journals ASSESSING THE SUITABILITY OF TIGER NUT FIBRE FOR STRUCTURAL APPLICATIONS

2020 ◽  
Vol 3 (01) ◽  
pp. 32-38
Author(s):  
Uduakobong Okorie ◽  
Ubong Robert ◽  
Ubong Iboh ◽  
Grace Umoren ◽  
Grace Umoren
Keyword(s):  
Thermal Conductivity ◽  
Cost Effective ◽  
Waste Recycling ◽  
Cassava Starch ◽  
Fibre Content ◽  
Raw Material ◽  
Structural Applications ◽  
The Mean ◽  
Thermal Absorptivity ◽  
Reduce Health Risk

In this work, the properties of the composite produced from waste carton with various tiger nut fibre contents having cassava starch slurry as binder were investigated. The results obtained showed the ranges of the mean thermal conductivity, bulk density, specific heat capacity, thermal diffusivity, thermal absorptivity, nailability, flexural strength  and compressive strength values to be (0.0447 – 0.0603) Wm-1K-1, (683.62 – 746.32) kgm-3, (1439.811 – 1840.554) J/kg/K, (5.612 - 3.553) 10-8 m2s-1, (25.456 – 31.993) m-1, (23.9 – 100)%, (1.58 – 1.86) MPa and (2.16 – 2.78) MPa respectively between  8.3% and 43.1% of the fibre content.  It was generally observed that with a choice variation in the fibre content, the performance of the developed board can be optimized for structural applications. Hence, instead of discarding the fibre as waste, recycling it can help to provide raw material for the production of cost effective and environmentally friendly materials. This will in turn reduce health risk caused by environmental pollution due to improper waste disposal practice of such material.

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