scholarly journals Micro-Macro Modelling Approach of Vegetal Wools Thermal Conductivity

Author(s):  
Clément Piégay ◽  
Philippe Glé ◽  
Etienne Gourlay ◽  
Emmanuel Gourdon ◽  
Sandrine Marceau

Biosourced materials such as vegetal wools offer major thermal insulation advantages in the green buildings field. Experimental characterisations of vegetal wools thermal conductivity as a function of their density show the existence of an optimum conduction-radiation coupled value. This specific point, as well as the properties of vegetal wools are related to the large variability of shapes and sizes of their fibres. In order to take this specificity into account, it seems particularly relevant to use micro-macro modelling methods to predict the thermal conductivities related to both conduction and radiation heat transfer phenomena. In a first time, a self-consistent method based on a cylindrical geometry (SCMcyl) is used as a modelling approach for conduction transfers. Then, a modelling approach developed by Bankvall and based on an equivalent fibre radius value is used for radiation transfers. So, by coupling these two approaches, it is possible to obtain an equivalent thermal conductivity of fibrous materials as a function of density. Finally, this method is validated by comparison with experimental data.

2018 ◽  
Vol 2018 (1) ◽  
pp. 41-43
Author(s):  
Takashi Fukue ◽  
Hirotoshi Terao ◽  
Koichi Hirose ◽  
Tomoko Wauke ◽  
Hisashi Hoshino ◽  
...  

Energies ◽  
2021 ◽  
Vol 14 (14) ◽  
pp. 4158
Author(s):  
Haiyan Yu ◽  
Haochun Zhang ◽  
Heming Wang ◽  
Dong Zhang

Currently, there are few studies on the influence of microscale thermal radiation on the equivalent thermal conductivity of microscale porous metal. Therefore, this paper calculated the equivalent thermal conductivity of high-porosity periodic cubic silver frame structures with cell size from 100 nm to 100 µm by using the microscale radiation method. Then, the media radiation characteristics, absorptivity, reflectivity and transmissivity were discussed to explain the phenomenon of the radiative thermal conductivity changes. Furthermore, combined with spectral radiation properties at the different cross-sections and wavelength, the radiative transmission mechanism inside high-porosity periodic cubic frame silver structures was obtained. The results showed that the smaller the cell size, the greater radiative contribution in total equivalent thermal conductivity. Periodic cubic silver frames fluctuate more in the visible band and have better thermal radiation modulation properties in the near infrared band, which is formed by the Surface Plasmon Polariton and Magnetic Polaritons resonance jointly. This work provides design guidance for the application of this kind of periodic microporous metal in the field of thermal utilization and management.


2018 ◽  
Vol 25 (6) ◽  
pp. 1157-1165
Author(s):  
Taoufik Mnasri ◽  
Adel Abbessi ◽  
Rached Ben Younes ◽  
Atef Mazioud

AbstractThis work focuses on identifying the thermal conductivity of composites loaded with phase-change materials (PCMs). Three configurations are studied: (1) the PCMs are divided into identical spherical inclusions arranged in one plane, (2) the PCMs are inserted into the matrix as a plate on the level of the same plane of arrangement, and (3) the PCMs are divided into identical spherical inclusions arranged periodically in the whole matrix. The percentage PCM/matrix is fixed for all cases. A comparison among the various situations is made for the first time, thus providing a new idea on how to insert PCMs into composite matrices. The results show that the composite conductivity is the most important consideration in the first case, precisely when the arrangement plane is parallel with the flux and diagonal to the entry face. In the present work, we are interested in exploring the solid-solid PCMs. The PCM polyurethane and a wood matrix are particularly studied.


2013 ◽  
Vol 2013 ◽  
pp. 1-7 ◽  
Author(s):  
Kan Ankang ◽  
Han Houde

Based on the fractal theory, the geometric structure inside an open cell polyurethane foam, which is widely used as adiabatic material, is illustrated. A simplified cell fractal model is created. In the model, the method of calculating the equivalent thermal conductivity of the porous foam is described and the fractal dimension is calculated. The mathematical formulas for the fractal equivalent thermal conductivity combined with gas and solid phase, for heat radiation equivalent thermal conductivity and for the total thermal conductivity, are deduced. However, the total effective heat flux is the summation of the heat conduction by the solid phase and the gas in pores, the radiation, and the convection between gas and solid phase. Fractal mathematical equation of effective thermal conductivity is derived with fractal dimension and vacancy porosity in the cell body. The calculated results have good agreement with the experimental data, and the difference is less than 5%. The main influencing factors are summarized. The research work is useful for the enhancement of adiabatic performance of foam materials and development of new materials.


2000 ◽  
Vol 123 (3) ◽  
pp. 273-277 ◽  
Author(s):  
Robert J. Samuels ◽  
Nancy E. Mathis

The present study examines the relationship between thermal conductivity and planarity in polyimide films. The samples tested were specially prepared to range in orientation from three dimensionally random to highly planar. The molecular structure and orientation of the polyimide film have been characterized by polarizing microscope techniques, while the thermal conductivity measurements were done using a new rapid nondestructive technique. This correlation represents the first time thermal conductivity has been measured by modified hot wire techniques and related to the internal structure of polyimide. This work contributes to a deeper theoretical understanding of thermal conductivity and heat transfer mechanisms as they relate to orientation. Thermal conductivity evaluation could provide a new tool in the arsenal of structural characterization techniques. This relationship between thermal conductivity and orientation is key for applications of directional heat dissipation in the passive layers of chip assemblies. Such a correlation has potential to speed the development cycles of new materials during formulation as well as assure properties during production.


Author(s):  
Dagoberto E. Venera Pontón ◽  
Javier Reyes ◽  
Guillermo Diaz Pulido

Porites colonensis is a coral from the Caribbean Sea; colonies are foliaceous, undulated, and plate-like. Polyps are dark brown or red with small bright white or green centers; pali are present in corallites and the septal plan is bisymmetrical, conformed by three fused ventral septa, a dorsal solitary septum, and two pairs of lateral septa at each side of the dorso-ventral axis. P. colonensis is similar and can be confused with the smooth varieties of Porites astreoides and Porites branneri. There are three specimens collected from Colombia and previously identified as P. colonensis: one from Golfo de Urabá (Darién ecoregion), other from Islas del Rosario (Coralline Archipelagos ecoregion), and another from an unspecified locality, in addition to one published observation from the Golfo de Urabá without collected specimens. A recent finding of other specimens in the Tayrona National Natural Park (TNNP, Tayrona ecoregion) and the absence of a rigorous taxonomic revision for all specimens collected from Colombia showed that it was necessary to review the presence and distribution of P. colonensis in the Colombian Caribbean. A taxonomic review was done for all specimens collected from Colombia and previously identified as P. colonensis. Then, the morphologic variability of specimens that were confirmed as P. colonensis was described. Only the specimens from TNNP agreed with the holotype description of P. colonensis, while others agreed with flat varieties of P. astreoides. Thus, the presence of P. colonensis is confirmed for the first time for Colombia, but its presence in other Colombian localities outside Tayrona ecoregion could not be demonstrated. This is the only confirmed record of this species for the South American continental shelf. Furthermore, the skeletal characteristics of Colombian P. colonensis corallites showed large variability, exceeding the ranges previously described for the species.


Sign in / Sign up

Export Citation Format

Share Document