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Thermal Conductivity of Low-Density Polyethylene Foams Part Ⅱ: Deep Investigation using Response Surface Methodology

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Journal of Thermal Science 2020年第1期29卷 159-168页

作者： HASANZADEH Rezgar AZDAST Taher doniavi ali Department of Mechanical Engineering Urmia University

Here,we conducted a deep study on the thermal insulation performance of polymeric foams using response surface methodology(RSM).Cell size,foam density,and cell wall thickness were considered as variable *** of variance(ANOVA)tool was utilized to recognize the effective parameters on the different mechanisms of heat *** models were presented to forecast the different mechanisms of heat transfer and their validities were checked using ANOVA tool as well as compared to the thermal conductivity *** plots were used to study the interaction effect of significant *** optimization procedure was performed using *** density and cell wall thickness are effective parameters on the solid thermal conductivity whereas cell size and foam density were significant parameters on the thermal *** decreasing foam density,gaseous thermal conductivity and thermal radiation were increased and solid thermal conductivity was *** regression model predicted the overall thermal conductivity with an average error smaller than 3%.The results illuminated that the overall thermal conductivity in the optimum conditions was as small as 29 mW/mK.

关键词： thermal insulation polymer foams response surface methodology

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Properties inhomogeneity of AM60 magnesium alloy processed by cyclic extrusion compression angular pressing followed by extrusion

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Transactions of Nonferrous Metals Society of China 2021年第3期31卷 655-665页

作者： Siroos AHMADI Vali aliMIRZALOO Ghader FARAJI ali doniavi Department of Mechanical Engineering Urmia UniversityUrmia 57153165Iran School of Mechanical Engineering College of EngineeringUniversity of TehranTehran 11155-4563Iran Department of Industrial Engineering Urmia UniversityUrmia 57153165Iran

A new severe plastic deformation(SPD)technique for improvement of the metallurgical properties of the magnesium alloys is *** this process,a cyclic extrusion compression angular pressing(CECAP)process is followed by an extrusion step in the outlet playing the role of additional back ***,more uniform and enhanced mechanical properties are expected in comparison with equal channel angular pressing(ECAP).In order to evaluate the effectiveness and capabilities of this new method,an AM60 magnesium alloy was *** element results exhibited a significant increase in strain values as well as uniform strain distribution for the new *** addition,~110%increase in compressive stress was observed in new method compared to the conventional *** results revealed a noticeable increase in the hardness and strength of the specimens processed by the new technique as a result of the formation of finer grains and more homogeneous microstructure with good distribution of refinedβ-phase along the *** may be concluded that the new process is very promising for future magnesium alloy products.

关键词： cyclic extrusion compression angular pressing AM60 alloy strain distribution mechanical properties grain refinement

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Thermal Conductivity of Low Density Polyethylene Foams Part I: Comprehensive Study of Theoretical Models

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Journal of Thermal Science 2019年第4期28卷 745-754页

作者： REZGAR Hasanzadeh TAHER Azdast ali doniavi RICHARD Eungkee Lee Mechanical Engineering Department Urmia University

Polymeric foams are one of the most applicable thermal-insulation materials due to their low thermal conductivity,high mechanical properties,and low *** of thermal-insulation performance of polymeric foams needs a theoretical model in order to predict the overall thermal *** far,several theoretical approaches are presented in this regard but to the best knowledge of the authors,there is no comprehensive investigation on comparing the proposed ***,the study of validity of the theoretical models in comparison with the experimental results is one of the main goals of the present *** density polyethylene(LDPE)foams are selected as the case study due to the wide application *** models to predict the overall conductivity of the foam based on conduction through the combined gas and solid phases(λgs)as well as radiation thermal conductivity(λr)are *** results indicate that the best model is a model in whichλgs is calculated using Gibson and Ashby model andλr is obtained using Williams and Aldao model based on the root mean square(RMS)*** results show that the theoretical error of this model is smaller than 10%.

关键词： thermal conductivity polymeric foams theoretical models radiation

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