scholarly journals Effect of char layer on transient thermal oxidative degradation of polyethylene

2007 ◽  
Vol 11 (2) ◽  
pp. 23-36 ◽  
Author(s):  
Javad Esfahani ◽  
Ali Abdolabadi
Keyword(s):  
Heat Transfer ◽  
Heat Source ◽  
Solid Phase ◽  
Early Stage ◽  
Radiation Heat Transfer ◽  
Oxidative Degradation ◽  
Degradation Process ◽  
Thermal Oxidative Degradation ◽  
Char Layer ◽  
Effect Of Oxygen

A transient one dimensional model has been presented to simulate degradation and gasification of polyethylene, in early stage of fire growth. In the present model effect of oxygen on degradation and rate of polymer gasification while the sample is subjected to an external radiative heat source is numerically investigated. This model includes different mechanism, which affect the degradation process, such as in depth thermal oxidative decomposition, in depth absorption of radiation, heat transfer, volatiles advection in solid phase and convective heat transfer on surface. Also effects of radiative parameters, due to formation of char layer such as surface reflectivity and absorptivity on thermal degradation of polyethylene are investigated. The results for 40 kW/m2 heat source are reported and yielded realistic results, comparing to the published experimental data. The results show that an increase in oxygen concentration leads to considerable increase in gasification rate and also leads to sharp increase of surface temperature. .

Maxwell Fluids Unsteady Mixed Flow and Radiation Heat Transfer Over a Stretching Permeable Plate With Boundary Slip and Nonuniform Heat Source/Sink

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Liancun Zheng ◽  
Ning Liu ◽  
Xinxin Zhang
Keyword(s):  
Heat Transfer ◽  
Differential Equations ◽  
Heat Source ◽  
Mixed Boundary ◽  
Radiation Heat Transfer ◽  
Radiation Heat ◽  
Boundary Slip ◽  
Analytical Approximations ◽  
Maxwell Fluids ◽  
Source Sink

This paper presents an analysis for the unsteady mixed boundary-layer flow and radiation heat transfer of generalized Maxwell fluids toward an unsteady stretching permeable surface in presence of boundary slip and nonuniform heat source/sink. The governing partial differential equations are converted into nonlinear ordinary differential equations and analytical approximations of solutions are derived by homotopy analysis method (HAM). The effects of the unsteadiness parameter, nonuniform heat source/sink parameter, suction/injection parameter, thermal radiation parameter and slip parameter on the fluid flow, and heat transfer characteristics are shown graphically and analyzed.

scholarly journals ПІДВИЩЕННЯ ВОГНЕЗАХИСНОЇ ЕФЕКТИВНОСТІ ІНТУМЕСЦЕНТНИХ ЕПОКСИДНИХ ПОКРИТТІВ СПОЛУКАМИ ІНТЕРКАЛЬОВАНОГО ГРАФІТУ

2021 ◽  
Vol 152 (6) ◽  
pp. 55-65
Author(s):  
Л. М. Вахітова ◽  
В. П. Плаван ◽  
В. І. Шологон ◽  
К. В. Калафат ◽  
Н. А. Таран ◽  
...  
Keyword(s):  
Epoxy Resin ◽  
Oxidative Degradation ◽  
Fire Retardant ◽  
Ammonium Polyphosphate ◽  
Thermal Oxidative Degradation ◽  
Char Residue ◽  
Temperature Range ◽  
Char Layer ◽  
Polymer Component ◽  
Intumescent System

Investigation of the effect of nitrate oxide graphite on the parameters of char layer, obtained from the system of ammonium polyphosphate / melamine / pentaerythritol / epoxy resin under the influence of temperatures of 200–800 °С.  Methodology.  A  fire  retardant  mixture  was  chosen  as  a  model  intumescent  system  ammonium polyphosphate / melamine / pentaerythritol. As a polymer component was used bisphenols A / F epoxy resin together with a polyamidoamine hardener. Nitrate oxide graphite was obtained by oxidation of natural scaly graphite  with fuming  nitrogen  acid.  The  effect  of  impurities  of  nitrate  oxide  graphite  was  determined  by thermogravimetry  on  the  intumescence  coefficient  of  intumescent  compositions  and  the  mass  of  the  char residue intumescent compositions in temperature range of 200–800 °С.  Findings. The influence of nitrate oxide graphite on the characteristics was studied of char layer of epoxy intumescent system ammonium polyphosphate / melamine / pentaerythritol / epoxy resin. The study of thermal  oxidative  degradation  was  carried  out  intumescent  compositions  in  the  temperature  range  200–800 °С. It was shown that intercalated graphite compounds increase the thermal stability of the formed char layer at temperatures > 600 °С. Determined intumescence coefficients and thermogravimetric analysis of modified intumescent systems was performed nitrate oxide graphite with different degrees of intercalation, in the conditions of 200–800 °С. It was established that the optimal parameters of the char layer are in terms of volume intumescence coefficient and mass of the char residue are provided by graphites, which contain 15–25% of intercalant in its composition. But the results obtained allow us to determine nitrate oxide graphite as a promising modifier of epoxy intumescent systems to increase its fire protection efficiency. Originality.  The  influence  of  degree  of  intercalation  of  nitrate  oxide  graphite  was  studied  on  the characteristics of char layer of epoxy intumescent system for the first time.  Practical value. The optimal content of intercalant in nitrate oxide graphite was established for the development of formulations of intumescent epoxy coatings with increased fire retardant properties.

scholarly journals INFLUENCE OF PROOXIDANT NATURE ON EVOLUTION OF FORMALDEHYDE FROM OXO-DEGRADABLE POLYETHYLENE

2019 ◽  
Vol 62 (2) ◽  
pp. 101-107
Author(s):  
Vladimir I. Korchagin ◽  
Alena M. Surkova ◽  
Lubov N. Studenikina ◽  
Artem V. Protasov
Keyword(s):  
Gas Phase ◽  
Oxidative Degradation ◽  
Degradation Process ◽  
Thermal Oxidative Degradation ◽  
Degradation Index ◽  
Natural Conditions ◽  
Iron Copper ◽  
Destructive Processes ◽  
Technical Solutions ◽  
Degree Of Isolation

In the article, methods of oxo-destruction of polyethylene modified with pro-oxidants of various nature are considered taking into account ecotoxicological aspects. A comparative evaluation of the indexes of degradation of polyethylene under the influence of air oxygen under accelerated thermal aging and under natural conditions is presented. It was revealed that the degradation index rises in the series "iron <copper <cobalt". The amount of formaldehyde in the gas-air extraction of oxo-degradable polyethylene modified with iron, cobalt and copper stearate is determined with accelerated thermal-oxidative degradation. The degree of isolation of formaldehyde increases in the series "copper <iron <cobalt", which indicates different periods of induction of the degradation process initiated by prooxidates, as well as the presence of side processes that affect the depth of destructive processes. It has been established that a polyethylene film modified with cobalt stearate contributes to the increase in formaldehyde emissions, while the formaldehyde content in the gas phase is 0.065 mg / m3 (per 1 g of sample), which exceeds MAC m.o.t by 1.3 times. The content of formaldehyde precipitates in the gas phase is reduced by 3.25 times, with the use of ferrous sterate. Individual carcinogenic risks (ICR) for oxo-degradable films based on iron, copper and cobalt stearates are predicted to equal 6.593·10-5, 5.595·10-5 2.864·10-4, respectively. A comparative analysis of prooxidants allows us to conclude that the use of iron and copper stearates contributes to a slower degradation of polyethylene and reduces its ecotoxicological hazard, the use of cobalt based pro-oxidants contributes to a faster and deeper destruction, but is accompanied by increased release of formaldehyde in the oxodegradation of modified polyethylene. Of interest is the further study of complex prooxidants on the basis of iron with trace amounts of cobalt as highly effective and environmentally friendly modifiers of polyolefins, contributing to their accelerated oxidation in the environment, as well as the development of technical solutions to reduce the risk in the case of cobalt stearate as an effective prooxidant.

Combined Natural Convection–Conduction and Radiation Heat Transfer in a Discretely Heated Open Cavity

1996 ◽  
Vol 118 (1) ◽  
pp. 56-64 ◽  
Author(s):  
A. A. Dehghan ◽  
M. Behnia
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Heat Source ◽  
Radiation Heat Transfer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Radiation Heat ◽  
Transfer Coefficients ◽  
Thermal Fields ◽  
Discrete Heat Source

Combined natural convection, conduction, and radiation heat transfer in an open-top upright cavity containing a discrete heat source has been modeled numerically. The surface emissivity has been varied and its effects on the flow and thermal fields have been determined for different values of Rayleigh number. The complex interaction of the three modes of heat transfer mechanisms is explored by solving the coupled convection, conduction, and radiation equations. It is noted that the inclusion of radiation has a significant effect on the flow, resulting in the formation of a recirculation zone within the cavity. Comparison of the local heat transfer coefficients for the conjugate analysis and no radiation case reveals that the inclusion of radiation has a negligible effect on the heat transfer performance of the heat source. However, comparison of the numerical results with experimental observations shows that accurate prediction of the flow and thermal fields is strongly dependent on the consideration of radiation heat transfer in the numerical case.

Influence of the prooxidant nature on the evolution of formaldehyde from oxo-degradable polyethylene

1970 ◽  
Author(s):  
V.I. Korchagin ◽  
A.M. Surkova ◽  
L.N. Studenikina ◽  
A.V. Protasov
Keyword(s):  
Gas Phase ◽  
Oxidative Degradation ◽  
Degradation Process ◽  
Thermal Oxidative Degradation ◽  
Degradation Index ◽  
Iron Copper ◽  
Destructive Processes ◽  
Technical Solutions ◽  
Further Development ◽  
Degree Of Isolation

In the article methods of oxo-destruction of polyethylene modified with pro-oxidants of various nature are considered, taking into account ecotoxicological aspects. A comparative evaluation of the indices of degradation of polyethylene under the influence of air oxygen under accelerated thermal aging and under natural conditions is presented. It was revealed that the degradation index rises in the series "iron <copper <cobalt". The amount of formaldehyde in the gas-air extraction of oxo-degradable polyethylene modified with iron, cobalt and copper stearate is determined with accelerated thermal-oxidative degradation. The degree of isolation of formaldehyde increases in the series "copper <iron <cobalt", which indicates different periods of induction of the degradation process initiated by prooxidates, as well as the presence of side processes that affect the depth of destructive processes. It has been established that a polyethylene film modified with cobalt stearate contributes to the increase in formaldehyde emissions, while the formaldehyde content in the gas phase is 0,065 mg / m3 (per 1 g of sample), which exceeds MAC m.o.t by 1.3 times. The content of formaldehyde precipitates in the gas phase is reduced by 3.25 times, with the use of ferrous sterate. Individual carcinogenic risks (ICR) for oxo-degradable films based on iron, copper and cobalt stearates are predicted to equal 6.593·10-5, 5.595·10-5 2.864·10-4, respectively. A comparative analysis of prooxidants allows us to conclude that the use of iron and copper stearates contributes to a slower degradation of polyethylene and reduces its ecotoxicological hazard, the use of cobalt based pro-oxidants contributes to a faster and deeper destruction, but is accompanied by increased release of formaldehyde in the oxodegradation of modified polyethylene. Iron-based prooxidants with trace amounts of cobalt as in highly effective and ecofriendly modifiers of polyolefins that promote their accelerated oxodegradation in the environment, as well as further development of technical solutions to reduce the risk of using cobalt stearate as an effective prooxidant.

Development of hybrid method for coupled conduction-radiation heat transfer in two-dimensional irregular enclosure considering thermo-radiative effects and varying thermal conductivity

2019 ◽  
Vol 30 (4) ◽  
pp. 1815-1837
Author(s):  
Mehdi Zare ◽  
Sadegh Sadeghi
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Flux ◽  
Heat Source ◽  
Radiation Heat Transfer ◽  
Isotropic Scattering ◽  
Two Dimensional ◽  
Radiation Heat ◽  
Content Type ◽  
Irregular Enclosure

Purpose This study aims to perform a comprehensive investigation to model the thermal characteristics of a coupled conduction-radiation heat transfer in a two-dimensional irregular enclosure including a triangular-shaped heat source. Design/methodology/approach For this purpose, a promising hybrid technique based on the concepts of blocked-off method, FVM and DOM is developed. The enclosure consists of several horizontal, vertical and oblique walls, and thermal conductivity within the enclosure varies directly with temperature and indirectly with position. To simplify the complex geometry, a promising mathematical model is introduced using blocked-off method. Emitting, absorbing and non-isotropic scattering gray are assumed as the main radiative characteristics of the steady medium. Findings DOM and FVM are, respectively, applied for solving radiative transfer equation (RTE) and the energy equation, which includes conduction, radiation and heat source terms. The temperature and heat flux distributions are calculated inside the enclosure. For validation, results are compared with previous data reported in the literature under the same conditions. Results and comparisons show that this approach is highly efficient and reliable for complex geometries with coupled conduction-radiation heat transfer. Finally, the effects of thermo-radiative parameters including surface emissivity, extinction coefficient, scattering albedo, asymmetry factor and conduction-radiation parameter on temperature and heat flux distributions are studied. Originality/value In this paper, a hybrid numerical method is used to analyze coupled conduction-radiation heat transfer in an irregular geometry. Varying thermal conductivity is included in this analysis. By applying the method, results obtained for temperature and heat flux distributions are presented and also validated by the data provided by several previous papers.

Conjugate Heat Transfer Study of Combined Radiation and Forced Convection Turbulent Separated Flow

2017 ◽  
Vol 18 (1) ◽  
pp. 29-39 ◽  
Author(s):  
M. Foruzan Nia ◽  
S. A. Gandjalikhan Nassab
Keyword(s):  
Heat Transfer ◽  
Gas Flow ◽  
Solid Phase ◽  
Radiation Heat Transfer ◽  
Separated Flow ◽  
Discrete Ordinates ◽  
Computational Domain ◽  
Transfer Behavior ◽  
Turbulent Gas Flow ◽  
Transfer Study

AbstractIn the current study, a numerical investigation of two-dimensional combined convection-radiation heat transfer of turbulent gas flow over a backward-facing step (BFS) in a horizontal rectangular duct is presented. The computational domain contains two different parts including gas flow and solid element that makes the problem as a conjugate one. The gas phase is considered to be a radiating media that can absorb, emit and scatter thermal radiation, where in solid phase, heat transfer takes place by conduction. The set of governing equations for gas flow is solved numerically using the CFD technique and the $$k - \varepsilon $$ model is employed for computation of turbulence fluctuations. To evaluate the radiative term in the gas energy equation, the radiative transfer equation (RTE) is solved by the discrete ordinates method (DOM). Inside the solid phase, the conduction equation is solved to obtain the temperature distribution. The effects of conduction ratio, optical thickness, radiation-conduction parameter and albedo coefficient on heat transfer behavior of the system are carried out.

Heat Transfer and Flow Characteristics of Porous Matrices With Radiation as a Heat Source

1966 ◽  
Vol 88 (1) ◽  
pp. 69-76 ◽  
Author(s):  
J. P. Chiou ◽  
M. M. El-Wakil
Keyword(s):  
Heat Transfer ◽  
Heat Source ◽  
Radiation Heat Transfer ◽  
Flow Characteristics ◽  
Incident Radiation ◽  
High Porosity ◽  
Transfer Coefficients ◽  
Space Applications ◽  
Pressure Drops ◽  
Heat Transfer Coefficients

A theoretical and experimental study of the heat transfer and flow friction characteristics of matrices of high porosity, with incident radiation from one side resulting in an exponential heat source, and with air as a coolant, is reported. In the theory, a transient solution of simultaneous convection and radiation heat transfer equations has been worked out. Used with experimental data taken in the unsteady state, it resulted in the calculation of volumetric heat transfer coefficients by convection in the matrices. Correlations with Reynolds numbers, based on a characteristic length obtained by equating pressure drops to the sum of viscous and inertia resistance terms, were obtained. Using the more familiar hydraulic radius did not result in reducing the relationships to a unified form. The matrices used in the experiments were formed from slit-and-expanded aluminum foils, blackened to high radiant absorptivity. The results of the investigation are believed useful in many solar, nuclear, and space applications.

Modeling of Fluid Flow and Heat Transfer in Laser Welding with a Moving Heat Source

2012 ◽  
Vol 622-623 ◽  
pp. 618-622
Author(s):  
Arash Karimipour ◽  
Ehsan Abedini ◽  
Hossein Ajam ◽  
S.M.H. Sarvari
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Heat Source ◽  
Phase Change ◽  
Solid Phase ◽  
Control Volume ◽  
Welding Process ◽  
Computational Method ◽  
Moving Heat Source ◽  
Thermal Buoyancy

In the present study, a numerical simulation is performed for the detailed prediction of heat transfer, phase change and fluid flow in welding process with moving heat source. This process may be considered steady with respect to the reference frame attached to the heat source for a long metal block. The problem is formulated by considering the three-dimensional equations of continuity, momentum and energy based on enthalpy model. The equations is solved using a fully implicit, control-volume-based computational method for fixed grids. The calculation domain including solid and liquid phases is solved together as a continuous region. Solid phase velocity is corrected using suitable source terms in the momentum equations. Phase change is considered based on the latent heat of evolution as a source term in the energy equation.The effects of thermal buoyancy and Marangoni flow on melting process are analyzed.

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