scholarly journals The Role of Carbonized Layers for Fire Protection of Polymer Materials

2018 ◽  
Vol 20 (1) ◽  
pp. 63
Author(s):  
Z.A. Mansurov ◽  
B.Ya. Kolesnikov ◽  
V.L. Efremov
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Thermal Oxidation ◽  
Epoxy Polymer ◽  
Burning Surface ◽  
Leading Edge ◽  
Polymer Materials ◽  
High Porosity ◽  
Flame Zone ◽  
Critical Temperatures

The present work studies the processes occurring in pre-flame zone in the form of «candle-like flame» which is spread over the surface of epoxy polymer. As exemplified by epoxy polymer, it can be seen that the dominating mechanism of heat transfer from flame to pre-flame zone of carbonized polymers is a thermal conductivity by condensed phase (to phase). The mechanism of gasification processes in pre-flame zone is proposed. Gasification of the material in front of the flame edge is a controlling process, and when selecting flame retardants, it is necessary to register their ability to influence on kinetics and mechanism of gasification. The flame leading edge is bordered with the surface of polymer, which largely determines the nature of heat transfer in pre-flame region. Due to investigations of gas-phase composition at «candle-like» combustion of epoxy polymer it has been detected a considerable amount of oxygen (up to 10‒12%) near burning surface. Its presence facilitates the thermal oxidation of polymer, moreover the rate of thermal oxidation can significantly exceed the thermal decomposition rate of the polymer. The possibility to form the heat-insulating intumescent layer during decomposition of carbonizable polymers was used at development of flame retardant coatings ‒ complex multicomponent systems. Which in turns forms the intumescent carbonized layer with high porosity and low thermal conductivity, and protects based material or construction from premature heating up to critical temperatures.

An Attempt to Uncouple the Effect of Coriolis and Buoyancy Forces Experimentally on Heat Transfer in Smooth Circular Tubes That Rotate in the Orthogonal Mode

1992 ◽  
Vol 114 (4) ◽  
pp. 858-864 ◽  
Author(s):  
W. D. Morris ◽  
R. Salemi
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Experimental Investigation ◽  
Circular Tube ◽  
Leading Edge ◽  
Combined Effect ◽  
Enhanced Heat Transfer ◽  
Coriolis Forces ◽  
Circular Tubes ◽  
Buoyancy Forces

This paper reports the results of an experimental investigation of the combined effect of Coriolis and buoyancy forces enforced convection in a circular tube that rotates about an axis orthogonal to its centerline. The experiment has been deliberately designed to minimize the effect of circumferential conduction in the tube walls by using material of relatively low thermal conductivity. A new correlating parameter for uncoupling the effect of Coriolis forces from centripetal buoyancy is proposed for the trailing and leading edges of the tube. It is demonstrated that enhanced heat transfer on the trailing edge occurs as a result of rotation. On the leading edge significant reductions in heat transfer compared to the zero rotation case can occur, but with possible recovery at high rotational speeds.

An Attempt to Experimentally Uncouple the Effect of Coriolis and Buoyancy Forces on Heat Transfer in Smooth Circular Tubes Which Rotate in the Orthogonal Mode

1991 ◽  
Author(s):  
W. D. Morris ◽  
R. Salemi
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Experimental Investigation ◽  
Forced Convection ◽  
Circular Tube ◽  
Leading Edge ◽  
Enhanced Heat Transfer ◽  
Coriolis Forces ◽  
Circular Tubes ◽  
Buoyancy Forces

This paper reports the results of an experimental investigation of the combined effect of Coriolis and buoyancy forces on forced convection in a circular tube which rotates about an axis orthogonal to its centre line. The experiment has been deliberately designed to minimise the effect of circumferential conduction in the tube walls by using material of relatively low thermal conductivity. A new correlating parameter for uncoupling the effect of Coriolis forces from centripetal buoyancy is proposed for the trailing and leading edges of the tube. It is demonstrated that enhanced heat transfer on the trailing edge occurs as a result of rotation. On the leading edge significant reductions in heat transfer compared to the zero rotation case can occur but with possible recovery at high rotational speeds.

scholarly journals Thermal Conductivity of Protein-Based Materials: A Review

Polymers ◽  
2019 ◽  
Vol 11 (3) ◽  
pp. 456 ◽  
Author(s):  
Ye Xue ◽  
Samuel Lofland ◽  
Xiao Hu
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Polymer Materials ◽  
Protein Films ◽  
Processing Technologies ◽  
Fibrous Proteins ◽  
Chemical Residues ◽  
Fast Development ◽  
High Flexibility ◽  
Transfer Direction

Fibrous proteins such as silks have been used as textile and biomedical materials for decades due to their natural abundance, high flexibility, biocompatibility, and excellent mechanical properties. In addition, they also can avoid many problems related to traditional materials such as toxic chemical residues or brittleness. With the fast development of cutting-edge flexible materials and bioelectronics processing technologies, the market for biocompatible materials with extremely high or low thermal conductivity is growing rapidly. The thermal conductivity of protein films, which is usually on the order of 0.1 W/m·K, can be rather tunable as the value for stretched protein fibers can be substantially larger, outperforming that of many synthetic polymer materials. These findings indicate that the thermal conductivity and the heat transfer direction of protein-based materials can be finely controlled by manipulating their nano-scale structures. This review will focus on the structure of different fibrous proteins, such as silks, collagen and keratin, summarizing factors that can influence the thermal conductivity of protein-based materials and the different experimental methods used to measure their heat transfer properties.

scholarly journals Characterisation of Flow and Heat Transfer in Sintered Metal Foams

2008 ◽  
Author(s):  
Jo¨rg Sauerhering ◽  
Stefanie Angel ◽  
Thomas Fend ◽  
Stefan Brendelberger ◽  
Elena Smirnova ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Combustion Chamber ◽  
Gas Turbines ◽  
Metal Foam ◽  
High Porosity ◽  
Transfer Coefficients ◽  
Sintered Metal ◽  
Flow And Heat Transfer ◽  
Wall Element

Since sintered metal foam is an innovative material with promising properties such as high porosity, good thermal conductivity, beneficial mechanical properties like strength and weldability, it has been considered to be applied as an open porous wall element in combustion chambers of gas turbines. In this application, the foam serves as a functional material capable to lead cooling air through micro- and minichannels into the inside of the combustion chamber. This cooling technique also known as effusion cooling keeps the combustion chamber walls below critical temperatures and therefore enables the burning process to be more effectively operated at higher temperatures. For a proper design of the wall element, the temperature distribution along the path of the fluid inside the foam must be known. For an exact calculation of the temperature flow and heat transfer processes inside the foam must be known. Therefore in this study the permeability and heat transfer properties of the foam have been characterized experimentally. The methods are described and the results in terms of permeability coefficients, convective heat transfer coefficients and effective thermal conductivity are presented as functions of the foam’s porosity. The method of the calculation is described and finally, the results of the calculation are presented, showing that due to the fine grained structure of the foam, the heat transfer from the solid to the cooling fluid takes place in a thin layer close to the inner surface of the camber wall.

Characterization of High Porosity Open-Celled Metal Foam Using Computed Tomography

2004 ◽  
Author(s):  
Eric N. Schmierer ◽  
Arsalan Razani ◽  
Scott Keating ◽  
Tony Melton
Keyword(s):  
Heat Transfer ◽  
Computed Tomography ◽  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Surface Area ◽  
Metal Foam ◽  
Three Dimensional ◽  
Metal Foams ◽  
High Porosity ◽  
Interfacial Surface

High porosity metal foams have been the subject of many investigations for use in heat transfer enhancement through increased effective thermal conductivity and surface area. Convection heat transfer applications with these foams have been investigated for a large range of Reynolds numbers. Common to these analyses is the need for quantitative information about the interfacial surface area and the effective thermal conductivity of the metal foam. The effective thermal conductivity of these metal foams have been well characterized, however little investigation has been made into the actual surface area of the foam and its dependence on the foam pore density and porosity. Three-dimensional x-ray computed tomography (CT) is used for determining interfacial surface area and ligament diameter of metal foam with porosities ranging from 0.85 to 0.97 and pore densities of 5, 10, 20, and 40 pores per inch. Calibration samples with known surface area and volume are utilized to benchmark the CT process. Foam results are compared to analytical results obtained from the development of a three-dimensional model of the high porosity open-celled foam. The results obtained are compared to results from previous investigations into these geometric parameters. Results from calibration sample comparison and analysis of the foam indicate the need for additional work in quantifying the repeatability and sources of error in CT measurement process.

Analytical and Numerical Modeling of Conductive and Convective Heat Transfer Through Open-Cell Metal Foams

2012 ◽  
Author(s):  
Mehrdad Taheri ◽  
Sanjeev Chandra ◽  
Javad Mostaghimi
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Numerical Modeling ◽  
Convective Heat Transfer ◽  
Effective Thermal Conductivity ◽  
Convective Heat ◽  
Thermal Equilibrium ◽  
Metal Foams ◽  
Local Thermal Equilibrium ◽  
High Porosity

In this paper, a comprehensive analytical and numerical study of conductive and convective heat transfer through high porosity metal foams is presented. In the first part a novel theoretical model for determination of effective thermal conductivity of metal foams is introduced. This general analysis can be applied to any complex array of interconnected foam cells. Assuming dodecahedron unit cell for modeling the structure of metal foams, an approximate equation for evaluation of effective thermal conductivity of foam with a known porosity is obtained. In this approximation method, unlike the previous two-dimensional (2D) models, porosity is the only geometric input parameter used for evaluation of effective thermal conductivity, while its predictions of effective thermal conductivity are in excellent agreement with the previous models. In the second part a 3D numerical model for conduction in metal foam is constructed. The foam has a square cross section and is exposed to constant temperature at both ends and constant heat flux from the sides. We assume local thermal equilibrium (LTE), i.e., the solid and fluid temperatures are to be locally equal. Comparison of the 3D numerical results to the experiments shows very good agreement. The last part of the study is concerned with the 3D numerical modeling of convective heat transfer through metal foams. Experimentally determined values of permeability and Forchheimer coefficient for 10 pores per inch (PPI) nickel foam are applied to the Brinkman-Forchheimer equation to calculate fluid flow through the foam. Local thermal equilibrium (LTE) and local thermal non-equilibrium (LTNE) methods were both employed for heat transfer simulations. While LTE method resulted in faster calculations and also did not need surface area to volume ratio (αsf) and internal convective coefficient (hsf) as its input, it was not accurate for high temperatures. LTNE should be used to obtain distinct local solid and fluid temperatures.

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