The model of radiation-induced heat flow in heterogeneous porous materials

2018 ◽  
Author(s):  
M. V. Alekseev ◽  
F. N. Voronin ◽  
E. B. Savenkov
Keyword(s):  
Heat Flow ◽  
Porous Materials ◽  
Radiation Induced

Microscopic Effective Medium Model for Thermal Conductivity of Two Dimensional Nano-Porous and Micro-Porous Media

2005 ◽  
Author(s):  
Ravi Prasher ◽  
David Song
Keyword(s):  
Thermal Conductivity ◽  
Heat Flow ◽  
Porous Materials ◽  
Diffusion Approximation ◽  
Three Dimensional ◽  
Effective Medium ◽  
Two Dimensional ◽  
Effective Medium Model ◽  
Medium Model ◽  
Cylindrical Pores

Two-dimensional Nano-porous (NP) and micro-porous (MP) materials are currently used in a variety of applications which require the knowledge of the thermal conductivity (k). In NP and MP materials, two pertinent length scales determine the phonon thermal conductivity: 1) the ratio of inter-pore distance, δ, and the mean free path (m.f.p.) of phonons, 1, 2) the ratio of the pore diameter, d, and the m.f.p. of phonons. This is schematically shown in Fig. 1. In the traditional diffusion-approximation (macroscopic models) based models (1 ≪ d, δ) for the thermal conductivity of porous materials, the effective thermal conductivity, keff, of the porous material for a given shape of the pores and direction of the heat flow is only a function of the volume fraction (φ) of the pores. Therefore, in the diffusion approximation, keff can be written as keff=kmf(φ)(1) where km is the thermal conductivity of the host medium. Our focus is on cylindrical pores. We only consider the heat flow in the transverse direction as shown in Fig. 1a. For example, if φ <40%, Maxwell-Garnett effective medium model (MG EMM) can be used. f(φ) for MG EMM is given by f(φ)=1−φ1+φ(2) Experimental data on two-dimensional micro-porous silicon made of cylindrical pores have shown that the macroscopic model given by Eq. (1) grossly over predicts keff of the porous materials. In MP and NP materials, the phonon transport is ballistic in nature because of the dominant scattering of phonons from the pore boundaries. Ballistic transport becomes dominant when m.f.p is comparable to or larger than d and δ. In this regime, the Boltzmann Transport Equation (BTE) must be solved without invoking the diffusion approximation. Solving the BTE for such a complex network of pores is a challenging task, and a few previous works exist where BTE was solved numerically under various simplifying assumptions regarding the geometry and the arrangement of the pores. Both of these investigations assumed rectangular pores for two-dimensional composite or cubical pores for three-dimensional composites; however, in reality, these pores are never so simple in their geometry. Typically, these pores are cylindrical in shape for two-dimensional composites and nearly spherical in shape for three-dimensional composites. The solution of BTE for the multitude of non-planar pores, although achievable, will be a very tedious task.

scholarly journals On computing the initial data for modeling of radiation-induced effects in porous materials

2018 ◽  
pp. 1-21 ◽  
Author(s):  
Mikhail Vladislavovich Alekseev ◽  
Fyodor Nikolaevich Voronin ◽  
Varvara Alekseevna Egorova ◽  
Mikhail Evgenievich Zhukovsky ◽  
Mikhail Borisovich Markov ◽  
...  
Keyword(s):  
Initial Data ◽  
Porous Materials ◽  
Radiation Induced

2 — D model for carbonation and moisture/heat flow in porous materials

1995 ◽  
Vol 25 (8) ◽  
pp. 1703-1712 ◽  
Author(s):  
Anna V. Saetta ◽  
Bernhard A. Schrefler ◽  
Renato V. Vitaliani
Keyword(s):  
Heat Flow ◽  
Porous Materials ◽  
D Model

scholarly journals Flow over evaporator in electrotechnical box

2018 ◽  
Vol 168 ◽  
pp. 02010
Author(s):  
Tomáš Puchor ◽  
Richard Lenhard
Keyword(s):  
Heat Exchanger ◽  
Heat Flow ◽  
Porous Materials ◽  
Horizontal Pipes ◽  
Simulation Process ◽  
Porous Zone ◽  
Heat Exchanger Surface

The article focus on heat flow generated by heat points over evaporator in eletrotechnical box. The evaporator consists of horizontal pipes supplemented with vertical ribs to enlarge the heat exchanger surface. This ribs were changed as porous zone for simulation process. The evaporator is located in a hermetically sealed electrotechnical box. Observes the spread of heat in the porous materials and air over evaporator and space inside the electrical box.

Radiation-Induced Precipitation at Thin Foil Surfaces in Ni-Be Alloys

1982 ◽  
Vol 40 ◽  
pp. 598-599
Author(s):  
T. Mukai ◽  
T. E. Mitchell
Keyword(s):  
Electron Microscopy ◽  
High Voltage ◽  
Electron Irradiation ◽  
High Vacuum ◽  
Thin Foil ◽  
Homogeneous Precipitation ◽  
High Voltage Electron Microscopy ◽  
Voltage Electron ◽  
High Voltage Electron ◽  
Radiation Induced

Radiation-induced homogeneous precipitation in Ni-Be alloys was recently observed by high voltage electron microscopy. A coupling of interstitial flux with solute Be atoms is responsible for the precipitation. The present investigation further shows that precipitation is also induced at thin foil surfaces by electron irradiation under a high vacuum.

Annealing Of Radiation Damage in Tungsten

1970 ◽  
Vol 28 ◽  
pp. 412-413
Author(s):  
Robert C. Rau ◽  
John Moteff
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Radiation Damage ◽  
Thermal Annealing ◽  
Neutron Fluence ◽  
Dislocation Loops ◽  
Defect Clusters ◽  
Polycrystalline Tungsten ◽  
Transmission Electron ◽  
Radiation Induced

Transmission electron microscopy has been used to study the thermal annealing of radiation induced defect clusters in polycrystalline tungsten. Specimens were taken from cylindrical tensile bars which had been irradiated to a fast (E > 1 MeV) neutron fluence of 4.2 × 1019 n/cm2 at 70°C, annealed for one hour at various temperatures in argon, and tensile tested at 240°C in helium. Foils from both the unstressed button heads and the reduced areas near the fracture were examined.Figure 1 shows typical microstructures in button head foils. In the unannealed condition, Fig. 1(a), a dispersion of fine dot clusters was present. Annealing at 435°C, Fig. 1(b), produced an apparent slight decrease in cluster concentration, but annealing at 740°C, Fig. 1(C), resulted in a noticeable densification of the clusters. Finally, annealing at 900°C and 1040°C, Figs. 1(d) and (e), caused a definite decrease in cluster concentration and led to the formation of resolvable dislocation loops.

Radiation-induced surface decomposition

1983 ◽  
Vol 41 ◽  
pp. 368-369
Author(s):  
M. L. Knotek
Keyword(s):  
Ionizing Radiation ◽  
Atomic Structure ◽  
Chemical Bonding ◽  
Neutral Species ◽  
Radiation Induced ◽  
Physical And Chemical ◽  
Surface Decomposition ◽  
The Relationship ◽  
Electron And Photon ◽  
Surface Bond

Modern surface analysis is based largely upon the use of ionizing radiation to probe the electronic and atomic structure of the surfaces physical and chemical makeup. In many of these studies the ionizing radiation used as the primary probe is found to induce changes in the structure and makeup of the surface, especially when electrons are employed. A number of techniques employ the phenomenon of radiation induced desorption as a means of probing the nature of the surface bond. These include Electron- and Photon-Stimulated Desorption (ESD and PSD) which measure desorbed ionic and neutral species as they leave the surface after the surface has been excited by some incident ionizing particle. There has recently been a great deal of activity in determining the relationship between the nature of chemical bonding and its susceptibility to radiation damage.

Sign in / Sign up

Export Citation Format

Share Document