Thermal degradation behaviors of spherical cellulose

Thermal Science and Engineering Thermal science and engineering encompass a vast array of principles and applications that are crucial in understanding and harnessing energy in various forms. From the design of efficient heating and cooling systems to the development of advanced materials for energy storage, the field plays a pivotal role in modern technology and industry. At its core, thermal science deals with the transfer, conversion, and utilization of heat energy, while engineering applies these principles to practical solutions and innovations. One of the key perspectives to consider in thermal science and engineering is the importance of sustainability. With the increasing concerns about climate change and environmental degradation, there's a growing emphasis on developing sustainable energy solutions. This includes improving the efficiency of existing thermal systems, such as powerplants and HVAC (heating, ventilation, and air conditioning) systems, as well as advancing renewable energy technologies like solar thermal and geothermal systems. By optimizing energy usage and minimizing waste heat, engineers can contribute to reducing greenhouse gas emissions and mitigating the impacts of climate change. Another critical aspect to consider is the role of thermal science and engineering in addressing global energy challenges. As the demand for energy continues to rise, especially in developing countries, there's a pressing need for reliable and affordable energy sources. Thermal power generation, including fossil fuels and nuclear energy, remains a significant contributor to the global energy mix. However, concerns about resource depletion, air pollution, and nuclear safety highlight the importance of developing cleaner and safer alternatives. Advances in thermal energy storage, high-temperature materials, and advanced power cycles hold promise for enhancing the efficiency and sustainability of future energy systems. Moreover, thermal science and engineering play a vital role in enhancingindustrial processes and manufacturing operations. From metal casting and glass production to chemical processing and food preservation, heat plays a fundamental role in shaping the properties and quality of materials. By optimizing thermal processes and equipment design, engineers can improve productivity, reduce energy consumption, and enhance product quality. This is particularly relevant in sectors such as automotive, aerospace, and electronics manufacturing, where precisetemperature control and thermal management are critical for ensuring product performance and reliability. On a more personal level, thermal science and engineering offer exciting career opportunities for individuals passionate about science, technology, and innovation. Whether working in academia, research institutions, or industry, professionals in this field have the chance to make meaningful contributions to society while pursuing their interests. The interdisciplinary nature of thermal science also allows for collaboration with experts in other fields, such as materials science, fluid dynamics, and renewable energy, leading to innovative solutions to complex challenges. Furthermore, the study of thermal science and engineering provides valuable insights into the fundamental laws of thermodynamics and heat transfer, which have wide-ranging applications beyond engineering. Understanding how heat flows and energy transforms enables us to comprehend natural phenomena, from the Earth's climate system to the behavior of stars and galaxies. This knowledge not only enriches our understanding of the universe but also informs practical decisions related to energy policy, environmental management, and sustainable development. In conclusion, thermal science and engineering are indispensable disciplines that play a crucial role in shaping the future of energy, industry, and society. By focusing on sustainability, addressing global energy challenges, enhancing industrial processes, and fostering career opportunities, this field offers both practical solutions and profound insights into the nature of heat and energy. As we strive to build a more sustainable and prosperous world, the principles and practices of thermal science and engineering will continue to guide us towards a brighter future.。

辐射强度与波长与温度的关系英文解释Radiation intensity is a term used to describe the amount of energy radiated by a source in a given direction at a specific wavelength. The intensity of radiation is determined by factors such as the temperature of the source and the wavelength of the radiation. The relationship between radiation intensity, wavelength, and temperature is of great importance in understanding the behavior of electromagnetic radiation and its impact on different materials.According to Planck's law of blackbody radiation, the intensity of radiation emitted by a black body at a certain temperature is directly related to the wavelength of the radiation. As the temperature of the black body increases, the peak intensity of the radiation shifts towards shorter wavelengths. This is known as Wien's displacement law, which states that the wavelength of maximum intensity is inversely proportional to the temperature of the source.In simple terms, as the temperature of a black body increases, the intensity of radiation emitted at shorter wavelengths also increases. This can be observed in everyday examples such as the glowing red color of a hot metal rod, which indicates that it is emitting radiation at longer wavelengths. Asthe temperature of the rod increases, the color of the glow changes to orange, yellow, and eventually white, indicating a shift towards shorter wavelengths and higher intensities.The relationship between radiation intensity, wavelength, and temperature can also be explained using theStefan-Boltzmann law, which states that the total energy radiated by a black body is directly proportional to the fourth power of its temperature. This means that as the temperature of a black body increases, the total energy radiated also increases significantly. This relationship is crucial for understanding the heating effects of radiation and the thermal behavior of objects exposed to high-intensity radiation.In addition to temperature, the wavelength of radiation also plays a critical role in determining the intensity of radiation. Different materials have different absorption and emission properties at different wavelengths, which can affect the amount of energy they absorb or emit. For example, certain materials may be transparent to certain wavelengths of radiation while absorbing others, leading to variations in the intensity of radiation observed at different wavelengths.The relationship between radiation intensity, wavelength, and temperature is further influenced by the nature of the sourceof radiation. For example, a black body emits radiation at all wavelengths and intensities according to its temperature, while a selective emitter only emits radiation at specific wavelengths. This can lead to variations in the observed intensity of radiation at different wavelengths, depending on the properties of the source.In conclusion, the relationship between radiation intensity, wavelength, and temperature is a complex and interconnected one that plays a crucial role in understanding the behavior of electromagnetic radiation. By studying how these factors influence each other, scientists and engineers can develop a better understanding of the thermal properties of materials, the heating effects of radiation, and the behaviors of different sources of radiation. This knowledge is essential for a wide range of applications, from designing more efficient energy systems to developing advanced materials for various industries.。

我的发现之热胀冷缩原理英语作文Thermal Expansion and Contraction: A Fundamental Principle of Physics.Thermal expansion and contraction are fundamental physical phenomena that describe the change in size and shape of materials due to variations in temperature. This phenomenon is observed in solids, liquids, and gases and plays a crucial role in various scientific and engineering applications.Microscopic Origin of Thermal Expansion.At the microscopic level, thermal expansion and contraction can be attributed to the vibrations of atoms or molecules within a material. As the temperature of a material increases, the average kinetic energy of its individual particles increases. This leads to an increase in the amplitude of their vibrations, causing the particles to occupy a larger average volume. Consequently, thematerial expands. Conversely, when the temperature decreases, the average kinetic energy of the particles decreases, and the particles move closer together,resulting in contraction.Linear, Area, and Volume Expansion.Thermal expansion can occur in one dimension (linear expansion), two dimensions (area expansion), or three dimensions (volume expansion). Linear expansion refers to the change in length of an object along a specific direction. Area expansion pertains to the change in the surface area of an object, while volume expansion describes the change in the total volume of an object. The extent of expansion or contraction depends on the material's coefficient of thermal expansion, which quantifies the amount of expansion or contraction per unit temperature change.Types of Thermal Expansion.There are two main types of thermal expansion:isotropic and anisotropic. Isotropic expansion occurs whena material expands or contracts uniformly in all directions. This behavior is observed in amorphous solids and liquids. Anisotropic expansion, on the other hand, occurs when a material expands or contracts differently in different directions. This phenomenon is common in crystals, wherethe arrangement of atoms or molecules can lead to varying degrees of expansion along different axes.Applications of Thermal Expansion.Thermal expansion has numerous practical applicationsin various fields. In engineering, it is crucial for designing structures that can withstand temperature variations without catastrophic failure. For example, bridges, buildings, and pipelines are designed to accommodate thermal expansion and contraction to prevent cracking or buckling.In metrology, thermal expansion must be taken into account when measuring the dimensions of objects with high precision. Precision instruments like calipers andmicrometers are often calibrated at specific temperatures to ensure accurate measurements regardless of temperature fluctuations.Additionally, thermal expansion is utilized in various temperature-sensing devices, such as thermostats and bimetallic strips. In a thermostat, a bimetallic strip composed of two metals with different coefficients of thermal expansion is used to detect temperature changes. As the temperature varies, the strip bends due to the differential expansion of the two metals, actuating a switch to control heating or cooling systems.Conclusion.Thermal expansion and contraction are fundamental physical principles that describe the change in size and shape of materials due to temperature variations. Understanding this phenomenon is essential for a wide range of scientific and engineering applications, from the design of structures to the development of temperature-sensing devices. By harnessing the effects of thermal expansion,engineers can create innovative solutions that improve our lives and enhance technological advancements.。

A steady state thermal duct model derived by fin-theory approachand applied on an unglazed solar collectorB.Stojanovic´*,D.Hallberg,J.Akander Building Materials Technology,KTH Research School,Centre for Built Environment,University of Ga ¨vle,SE-80176Ga ¨vle,SwedenReceived 12November 2008;received in revised form 28January 2010;accepted 15June 2010Available online 24August 2010Communicated by:Associate Editor Brian NortonAbstractThis paper presents the thermal modelling of an unglazed solar collector (USC)flat panel,with the aim of producing a detailed yet swift thermal steady-state model.The model is analytical,one-dimensional (1D)and derived by a fin-theory approach.It represents the thermal performance of an arbitrary duct with applied boundary conditions equal to those of a flat panel collector.The derived model is meant to be used for efficient optimisation and design of USC flat panels (or similar applications),as well as detailed thermal analysis of temperature fields and heat transfer distributions/variations at steady-state conditions;without requiring a large amount of computa-tional power and time.Detailed surface temperatures are necessary features for durability studies of the surface coating,hence the effect of coating degradation on USC and system performance.The model accuracy and proficiency has been benchmarked against a detailed three-dimensional Finite Difference Model (3D FDM)and two simpler 1D analytical models.Results from the benchmarking test show that the fin-theory model has excellent capabilities of calculating energy performances and fluid temperature profiles,as well as detailed material temperature fields and heat transfer distributions/variations (at steady-state conditions),while still being suitable for component analysis in junction to system simulations as the model is analytical.The accuracy of the model is high in comparison to the 3D FDM (the prime benchmark),as long as the fin-theory assumption prevails (no ‘or negligible’temperature gradient in the fin perpendicularly to the fin length).Comparison with the other models also shows that when the USC duct material has a high thermal conductivity,the cross-sectional material temperature adopts an isothermal state (for the assessed USC duct geometry),which makes the 1D isothermal model valid.When the USC duct material has a low thermal conductivity,the heat transfer course of events adopts a 1D heat flow that reassembles the conditions of the 1D simple model (for the assessed USC duct geometry);1D heat flow through the top and bottom fins/sheets as the duct wall reassembles a state of adiabatic condition.Ó2010Elsevier Ltd.All rights reserved.Keywords:Unglazed solar collector;Roof integrated;Duct;Modelling;Fin-theory;Benchmarking1.IntroductionHeat transfer simulations and calculations on absorption of heat in flat-plate solar collectors,have generally been based on simplified one-dimensional (1D)heat transfer modelling (e.g.see:Duffie and Beckman,2006;Fischer et al.,2004).Traditionally,a fluid element flowing through the collector (or arbitrary duct)is assumed to absorb heatfrom its ambient in a 1D manner,along its flow path(Duffie and Beckman,2006).This approach renders a model that requires small computational resources and time,which is beneficial in system simulations when sea-sonal or annual performances are analysed.The efficiency and accuracy of the model is adequate for analysing energy performance,calculating bulk or outlet fluid temperatures,or ordinary absorber plate and fluid temperature distribu-tions (Duffie and Beckman,2006).If detailed analysis of temperature fields and heat transfer distributions/variations at steady-state or dynamic conditions are required,more0038-092X/$-see front matter Ó2010Elsevier Ltd.All rights reserved.doi:10.1016/j.solener.2010.06.016*Corresponding author.Tel.:+4626648137;fax:+4626648181.E-mail address:bojan.stojanovic@hig.se (B.Stojanovic´)./locate/solenerSolar Energy 84(2010)1838–1851sophisticated and complex models have to be used.For instance,this is needed when solar collectors have a duct/ tubefluid volume circumference that is significantly larger ()2)than the heat-absorbing surface.In this case regarding the duct/tube as a point in the absorber plate(e.g.Duffie and Beckman,2006;Hilmer et al.,1999)is not appropriate. Or in other cases,the thermal bridging between the absorb-ing surface and the backside,via the duct walls,cannot be neglected(Ammari,2003;Cristofari et al.,2002),nor the heat exchange between a duct wall and the collectorfluid (Ammari,2003;Hachemi,1999;Yeh et al.,2002).Detailed thermal modelling(of e.g.solar collectors)usually result in a multi-dimensional numerical model(e.g.Hassan and Bel-iveau,2007).The model can vary in complexity,depending on the desired level of detail.However,a detailed numerical model requires a substantial amount of computational power and time,which primarily makes it suitable and use-ful for specific and detailed case studies;not suitable as a component in system simulations.Furthermore,multi-dimensional numerical models have afixed geometrical lay-out of nodes/elements/volumes(depending on mathemati-cal discretisation principle),which makes the task of changing and comparing different solar collector designs tedious.In some cases there is a need to have a model which can calculate/simulate detailed thermal distributions and varia-tions,without requiring a large amount of pre-processing or computational power and time;thereby attaining a model suitable for component analysis while being useful in system simulations.The advantages are that solar collec-tor analysis and optimisation can be performed in junction to system operation at different geographical locations, during long-term simulation scenarios.As an example,this procedure is useful in durability assessments of solar collector absorber surfaces(e.g.see Carlsson et al.,1994).Annual simulations of solarNomenclatureA area(m2)bfin thickness(m)C equation constant(unit)C[T f(z)]equation constant as a function offluid temper-ature(unit)c heat capacity(J/K)c p specific heat capacity(J/kg K)d diameter(m)G global solar irradiance on a surface(W/m2)h heat transfer coefficient(W/m2K)K parameter for simplifying thefin temperature equation constants(–)Lfin length(m)q[x i,T f(z)]heatflux in an infinite smallfin element as a function of position in afin andfluid tempera-ture(W/m2)Q heat transfer rate(W)Q[x i,T f(z)]heat transfer rate in an infinite smallfin ele-ment as a function of(W)position in afin andfluid temperatureQ[T f(z)]heat transfer rate as a function offluid temper-ature(W/m)R thermal resistance(m2K/W)t time(s)T temperature(K)T(z)temperature as a function of USC duct length position(K)T(in)inlet temperature(K)T[x i,T f(z)]temperature as a function of position in afin andfluid temperature(K)V ambient air speed(m/s)U total heat loss coefficient(W/m2K)x coordinate parameter(–)y coordinate parameter(–)z coordinate parameter(–)_m massflow(kg/s)Nu Nusselt number(–)Greek symbolsa solar thermal absorptance(–)b parameter for simplifying thefin temperatureequation constants(unit)c[T f(z)]parameter as a function offluid temperature for simplifying thefin temperature equation con-stants(unit)D difference(–)e long wave(IR)emittance(–)j thermal conductance(W/K)k thermal conductivity(W/m K)q density(kg/m3)r Stefan–Boltzmann constant(W/m2K4) Subscriptsa ambientb backsideffluidh hydraulici nodal numberj nodal numberk nodal numberm materialn number of time-stepr radiations surfacefinfinsky skyUSC unglazed solar collectorB.Stojanovic´et al./Solar Energy84(2010)1838–18511839collectors operating in system solutions are performed atdifferent geographical locations,in order to assess the absorber surface microclimatic exposure to relevant degra-dation agents,such as temperatureet al.,1994;Van der Linden et al.,In general,durability issues of to a number of problems:lation or freezing (Wennerholm,issues are the exposure to various temperature,wind,rain/humidity,lutants)as a result of outdoor These contribute to a degradation tion of the collector material performance due to change in Carlsson et al.,1994;Stojanovic´assess this degradation,the tude of degradation agents (e.g.has to be detailed.Degradation nying degradation mechanisms and be strongly affected by for actively heated and cooled only be physicochemical activation values are passed.If only being degradation agents and assessment on degradation will in –time of wetness (TOW)is an degradation experiments exposure testing,e.g.see Carlsson that degradation agents and and that dose levels under a certain ute to a negligible rate of threshold values are exceeded.These changes in optical posed throughout the system,ciency (Hollands et al.,1992),economical and environmental a result of these types of changes,assessment is needed,so that the the performance lowering assessed.Work on assessing the mance due to solar collector tion of microclimate in/on solar of the most important steps (Carlsson et al.,1994;Hollands 2009).1.1.Background:a roof-integrated An unglazed solar collector the EU project Endothermic cient Housing in the EU unched in strated the use of a solar-assisted 2008;Stojanovic´,2009; e.g.see 2007)to provide the annual heating,cooling and hot water houses in different regions of the USC is a dual-purpose component that integrates with the building to form its roof (Virk,2008).The collector propi-tiously blends into its surroundings (different shapes and col-1840 B.Stojanovic´et al./Solar Energy 84(2010)1838–1851prevailing local climatic conditions.These modificationsconsisted in a variation of system:build-up,operation and control strategy.Regarding the USCs,no changes in the design of the component was made for the different systems,except for:coating colour,length of the extruded USC and number of USC panels used in the assembled system and rate of flow of the heat transfer fluid.The USC consists of an extruded aluminium profile which comes in two shapes,flat and bold rolled (see Fig.1).After extrusion,the ends are sealed and in-/outlet pipes are attached by welding.Thereafter,the panels are painted with a polyester powder coating.Each panel has a fixed:width (0.22m),number of ducts and material thickness (see also Table 2),while the length can vary up to a maximum of 6m.Feet and folds enable fixation onto the roof and inter-locking between adjacent panels.The following panel is interlocked to the previous and thereafter fixated.This forms an assembling chain that integrates the USCs into the roof and forms a homogenous surface.The heat transfer liquid flows through the panel in one homogenous direction,where each duct makes up an individual parallel flow streak (see Fig.2).The USC circuit has a flow regime that can vary from serial to parallel,depending on how the panels are con-nected.The fluid is distributed to and from the panels by a manifold.The fluid flow in the USC roof circuit is obtained via one or several circulation pumps.1.2.ObjectivesThis paper presents thermal modelling of the Endohous-ing USC flat panel that uses heat transfer liquids.The aimis to produce a detailed yet swift thermal steady-state model.The model is analytical,1D and derived by fin-the-ory approach.It represents the thermal performance of an arbitrary duct with applied boundary conditions equal to the flat panel USC;hence the model is also applicable for other thermal duct calculations.As the USC predomi-nantly consists of angular ducts,the traditional thermal modelling approach of the duct/tube being a point in the absorber is not appropriate (if detail analysis of tempera-ture fields and heat transfer distributions/variations is required);in this case the ducts constitute the absorber,hence the USC flat panel model development.The derived model is to be used for efficient optimisation and design of the USC flat panels (or similar applications),as well as detailed thermal analysis at steady-state conditions;with-out requiring a large amount of computational power and time.Detailed surface temperatures are necessary fea-tures of the fin-theory based USC thermal duct model in order to be useful for durability studies of the surface coat-ing,hence the effect of coating degradation on USC andsystem performance (see Section 1and reference Stojanovic´et al.,2008).The model accuracy and proficiency is bench-marked against a detailed 3D numerical model as well as two 1D analytical models.The paper objective is also to present results,discussion and conclusions of the different benchmarking models comparison,as these are commonly used for this type of application;in line with the work pre-sented by Schnieders (1997).1.3.Model assumptionsThis section represents a summary of assumptions applied in the derivation of the various USC thermal mod-els.Table 1displays which assumption is applicable to each model.1.The fluid temperature in each duct is equal,as the flow in the USC panel is parallel (see Section 1.1).The USC roof installation should also be seen as having a parallel circuit,as is the case in theSwedish Endosite system (Virk,2008;Stojanovic´,2009).2.The thermal effects of the feet and folds on the USC flat panel are neglected (see Figs.1and 3).Panel feet affect the USC by thermally bridging the duct assem-bly (especially the adjacent ducts)to the substrate by conduction.A roof integrated USC installation con-sists of a number of panels that are interlocked with each other,the last duct in one panel and the firstTable 2The geometrical dimensions of the modelled USC half duct;representing the actual dimensions of the flat panel USC developed and used in the Endohousing project.Note that the wall fin/sheet thickness is not eligible for the 1D simple steady-state C models Half duct inner with (m)Half duct inner height (m)Top and bottomfin/sheet thickness (m)Wall fin/sheet thickness (m)USC duct length (m)For all models0.01250.0130.0020.0015Table 1A summary of assumptions applied in the derivation of the various USC models.Assumption Fin-theory steady state 3D steady state FDM 1D isothermal steady state 1D simple steady state 1x x x x 2x x x x 3x x x x 4x x x x 5x x x x 6x x x 7x x x x 8x xx x 9xx x 10x11xNote :A detailed thermal analysis at the specific USC flat panel boundary conditions of the panel feet and the end duct wall is beyond the scope of this paper or the presented thermal duct models.B.Stojanovic ´et al./Solar Energy 84(2010)1838–18511841in a neighbouring panel will have a different build-up than a centrally placed duct.This is especially appar-ent at the duct wall,which will have a different heat transfer than the wall of a centrally placed duct.3.Boundary effects at the perimeter of the roof are neglected due to marginal impact on overall USC roof performance.4.The duct fluid temperature is isothermal (no temper-ature gradient,fully mixed)in each cross-section,except at the thermal boundary layer which gives rise to the convective heat transfer coefficient (Holman,2002).5.The average Nusselt number for(cross-section aspect ratio 1/2)wall heat flux and fully applied for the duct convection (1978).6.A linearisation of the equation energy (heat)transfer rate by tion (Duffie and Beckman,2006the discussion in Section 2.1.7.No heat exchange by long wave within the duct since the heat (see Section 1.1).8.Material,fluid and heat transfer exception of long wave stants,independent of 9.The model assumes that there is pendicular to the USC duct 10.The USC duct consists of a material cross-section.11.The USC duct consists of a temperature difference over and and the lower USC duct wall sheet/fin is adiabatic.The sheets/fins have each a their respective fin,which is length.2.Fin-theory based USC thermal model derivation A 1D steady state thermal model based on fin-theory isderived in order to obtain a tool that swiftly calculates and assesses the USC’s performance:material temperature and heat transfer distribution/variation and fluid temperature.This section presents the model derivation procedure.The basic concept of the 1D steady state fin-theory is that heat is transported from the fin-base throughout the fin-material in length direction;there is no ‘or negligible’temperature gradient in the fin perpendicularly to the fin length.While conduction prevails,heat is either emitted or absorbed by the fin depending on the interaction with the ambient (Holman,2002).The USC flat panel cross-section represented in Fig.3shows that a thermal symmetry can be applied on a USC flat panel duct,dividing it into a half duct.The USC half duct becomes a system of three fin sheets.Fig.4presents the thermal system with applied boundary conditions and defined energy flows used in the fin-theory based model.These boundary conditions represent the thermal course of event in a central duct on flat panel USC.As previously discussed,by adopting that statements 1,2and 3repre-sented in Section 1.3(see also Table 1),the heat transfer occurring in a centrally placed duct can be seen as repre-senting an entire USC panel or roof (see also Fig.3).Addi-tionally,please also observe the notification at the end of Section 1.3.Analytical thermal modelling of ducts in similar applica-tions has also been presented by Ammari (2003),Hachemi (1999)and Yeh et al.(2002).Ammari (2003)presents a Fig.3.A cross-section of the Endohousing flat panel USC.The figure shows the applied thermal symmetry lines on a centrally placed duct that makes a half duct,which is seen as representing the USC thermal behaviour.The models neglect the thermal effects of the two lower feet and the folds at each edge.Energy 84(2010)1838–1851air-heaters.In their models,the duct walls are seen as fac-tors that increase the thermal convection from duct sur-faces to the airflow.No thermal bridging by thermal conduction via the duct walls is applied.2.1.Mathematical derivationThe following example presents the derivation of the temperature distribution expression of Fin1(see Fig.5), which is the topfin/sheet of the USC half duct.The heat balance of over an infinite small element in a cross-section of Fin1is according to Figs.4and5as:Q1½x1;T fðzÞ þQ3½x1;T fðzÞ þQ4þQ5½x1;T fðzÞ¼Q6½x1;T fðzÞ þQ2½x1þdx1;T fðzÞ ð1ÞThe rate of heat conduction to the element at x1isQ1½x1;T fðzÞ ¼Àk1ÁA1ÁdT1½x1;T fðzÞdx1ð2Þand heat conduction from the element at position x1+dx1isQ2½x1þdx1;T fðzÞ ¼Àk1ÁA1ÁdT1½x1;T fðzÞdx1þddx1Àk1ÁA1ÁdT1½x1;T fðzÞdx1dx1ð3ÞHeat transfer rate by ambient(outdoor)convection:Q3½x1;T fðzÞ ¼h aÁA1:2ÁðT aÀT1½x1;T fðzÞ Þð4ÞThe outdoor wind convection coefficient h a used through-out this paper is according to Watmuffet al.(1977)as:h a¼2:8þ3:0ÁVð5ÞEnergy(heat)transfer rate by solar radiation:Q4¼aÁA1:2ÁG USCð6ÞEnergy(heat)transfer rate by long wave(IR)radiation (Duffie and Beckman,2006):ture T1[x1,T f(z)]is a function of bothfin length/position(x1) and USC ductfluid temperature along the duct length/posi-tion(z),a representative mean value of T1[x1,T f(z)]derived in an iterate manner is used in order to calculate h r.Heat transfer rate byfluid convection:Q6½x1;T fðzÞ ¼h fÁA1:2ÁðT1½x1;T fðzÞ ÀT fðzÞÞð8ÞThe ductfluid convection coefficient h f used throughout this paper is according to Holman(2002)as:h f¼NuÁk fd hð9Þwhere the average Nusselt number for a rectangular duct(cross-section aspect ratio1/2)with constant axial wall heatflux and fully developed laminarflow is Nu= 4.123(Shah and London,1978).The combination of the above-presented equations in accordance to Eq.(1)will give:d2T1½x1;T fðzÞdx1Àðh fþh aþh rÞk1Áb1|fflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflffl}b1ÁT1½x1;T fðzÞþh fÁT fðzÞþh aÁT aþaÁG USCþh rÁT skyk1Áb1|fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}c1½T fðzÞ¼0ð10ÞThe partial differential equation of the Fin1tempera-ture distribution becomes:d2T1½x1;T fðzÞdx1Àb1ÁT1½x1;T fðzÞ þc1½T fðzÞ ¼0ð11ÞThe solution to the partial differential equation in Eq.(11)is:T1½x1;T fðzÞ ¼C11½T fðzÞ ÁeÀffiffiffiffib1pÁx1þC12½T fðzÞ Áeffiffiffiffib1pÁx1þc1½T fðzÞb1ð12ÞThe procedure for deriving thefin-temperature distribu-tion for Fins2and3is in direct analogy with the above presented example.Fins2and3are applied with the boundary conditions and heat balances that are displayed in Fig.4and presented in Appendix A.In order to be able to calculate the cross-sectional tem-perature distribution in Fins1,2and3(Eqs.(12),(A3), and(A5)),the unknown constants in thefin-temperature equations have to be solved.By using boundary conditions as illustrated in Fig4and combining the heat transfer rates exiting from onefin and entering another,provides the pos-sibility to solve the unknown constants.Fin1dT1½x1¼0;T fðzÞ1¼0;Àk1ÁA1ÁdT1½x1¼L1;T fðzÞdx1¼Àk2ÁA2ÁdT2½x2¼0;T fðzÞdx2B.Stojanovic´et al./Solar Energy84(2010)1838–18511843Fin2T2½x2¼0;T fðzÞ ¼T1½x1¼L1;T fðzÞ T2½x2¼L2;T fðzÞ ¼T3½x3¼L3;T fðzÞFin3dT3½x3¼0;T fðzÞdx3¼0;Àk3ÁA3ÁdT3½x3¼L3;T fðzÞdx3¼k2ÁA2ÁdT2½x2¼L2;T fðzÞdx2The solved unknown constants of thefin-temperature distribution equation in a USC duct cross-section are defined and presented in Appendix A.By integrating the heatflux(containing thefin-tempera-ture distribution)over the entirefin length attains the heat transfer rate from afin cross-section.Eq.(13)presents the heat transfer rate from Fin1to the USCfluid(see also Fig.4).An example of the derivation of the heat transfer rate equations to and from the USC half duct is presented in Appendix A.Q6½T fðzÞ ¼Àh fÁÀC11½T fðzÞ Áb1þC12½T fðzÞ Áb1þC11½T fðzÞ ÁeðÀffiffiffiffib1pÁL1ÞÁb1ÀC12½T fðzÞ Áeðffiffiffiffib1pÁL1ÞÁb1Àc1½T fðzÞ ÁL1Áffiffiffiffiffib1pþT fðzÞÁL1Ábð3=2Þ1 0@1Ab1ð13ÞHaving derived heat transfer rates from thefin cross-sec-tions to the USCfluid,provides the possibility to calculate thefluid temperature along the USC duct,hence thefin-temperature distribution.Eq.(14)presents the steady state fluid temperature along the USC duct.The equation assumes that there is no heat transfer perpendicular to the USC duct cross-section.T fðzÞ¼T fðinÞþC2 C1Áe zÁC1_mÁc p fÀC2C1ð14ÞBy attainment of Eq.(14),thefin-temperature distribu-tion at a USC duct cross-section,as well as along the USC duct,can be calculated at steady-state conditions.The der-ivation of Eq.(14)and definition of equation constants are presented in Appendix A.3.Benchmarking modelsThe prime objective of the benchmarking models is to be used as a comparison for thefin-theory derived USC ther-mal duct model,in order to investigate calculated/simulated results deviations,but also as a comparison amongst themselves.3.1.1D isothermal steady-state modelThis model is based on the assumption that the thermal conductivity of the duct material is infinitely large,thus making the USC duct material cross-section isothermal. Other assumptions applied are listed in Table1;please also see the discussion in the beginning of Section2.The model is basically‘equivalent’to the Hottel–Whiller–Bliss model as presented by Duffie and Beckman(2006).As the USC duct(in this case)constitutes the absorber plate,there is no absorber plate surface that is without direct contact with the ductfluid.By applying this case to the Hottel–Whiller–Bliss model(as presented by Duffie and Beckman (2006))and neglecting the bond thermal resistance between the absorber plate and tube/duct,brings that the duct material(fin)temperature is isothermal;as the model regards the duct as a point in the absorber plate cross-sec-tion.Fig.6illustrates the model set-up.The heat balance of afluid element,having the massflow_m in z-direction and temperature T f(z),gives that the increase influid tempera-ture dT f(z)due to heat supply corresponds to:h fÁðL1þL2þL3ÞÁdzÁðT s½T fðzÞ ÀT fðzÞÞ|fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}Q6½T fðzÞ þQ9½T fðzÞ þQ12½T fðzÞ¼h aÁL1ÁdzÁðT aÀT s½T fðzÞ Þ|fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}Q3½T fðzÞþaÁG USCÁL1Ádz|fflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflffl}Q4þh rÁL1ÁdzÁðT skyÀT s½T fðzÞ Þ|fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}Q5½T fðzÞþU bÁL3ÁdzÁðT bÀT s½T fðzÞ Þ|fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}Q13½T fðzÞð15ÞThe equation above can be reformulated with constants C1,C2and C3as expressed below.C1¼aÁL1ÁG USGþh aÁL1ÁT aþh rÁL1ÁT skyþU bÁL3ÁT bh aÁL1þh rÁL1þU bÁL3þh fÁðL1þL2þL3Þð16ÞC2¼Àðh aÁL1þh rÁL1þU bÁL3Þðh aÁL1þh rÁL1þU bÁL3þh fÁðL1þL2þL3ÞÞð17ÞC3¼h fÁðL1þL2þL3Þ_mÁc pfð18ÞLocal cross-sectional material/surface isotherm can accordingly be found such that:T s½T fðzÞ ¼aÁG USCÁL1þh aÁL1ÁT aþh rÁL1ÁT skyþU bÁL3ÁT bþh fÁðL1þL2þL3ÞÁT fðzÞf123a1r1b3ð19ÞConsidering that the inlet temperature T f(in)will increase to be the outlet temperature T f(z)at the duct length z,the heat balance of thefluid element can be inte-grated such that:Z T fðzÞT fðinÞdT fðzÞC1þC2ÁT fðzÞ¼C3ÁZ zdzð20ÞThe solution for Eq.(20)isfinallyT fðzÞ¼T fðinÞþC1C2Áe C2ÁC3ÁzÀC1C2ð21Þ1844 B.Stojanovic´et al./Solar Energy84(2010)1838–1851。

Thermochimica Acta 547 (2012) 120–125Contents lists available at SciVerse ScienceDirectThermochimicaActaj o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /t caKinetics and volatile products of thermal degradation of building insulation materials Lingling Jiao a ,Guangdong Xu b ,Qingsong Wang a ,Qiang Xu b ,Jinhua Sun a ,∗a State Key Laboratory of Fire Science,University of Science and Technology of China,230026Hefei,PR China bSchool of Chemical Engineering,Nanjing University of Science and Technology,210094Nanjing,PR Chinaa r t i c l ei n f oArticle history:Received 22May 2012Received in revised form 17July 2012Accepted 17July 2012Available online 23 August 2012Keywords:PolymersThermal degradation ThermogravimetrySimultaneous thermal analysisa b s t r a c tThe thermal degradation of three typical organic insulation materials,rigid polyurethane (PU)foam,extruded polystyrene (XPS)and expanded polystyrene (EPS)were investigated using thermogravimetry (TG)and simultaneous thermal analysis (STA)coupled with mass spectrometry and Fourier transform infrared spectroscopy (TG–DSC–MS–FTIR).The Kissinger–Akahira–Sunose method was utilized for cal-culating the activation energy values of the materials.Volatile products obtained from the degradationwere identified by MS and FTIR.The results of TG–DTG–DSC curves under 10◦C/min heating rate in a nitrogen environment revealed the differences in characteristics of the three materials during the ther-mal degradation.Only one obvious mass loss stage of EPS was observed,and XPS shows two degradationstages and the second one is the main stage.While PU is more complex,and the degradation process involves three steps and the whole mass loss is continuous.The largest heat absorption is in the mainmass loss stage.© 2012 Elsevier B.V. All rights reserved.1.IntroductionOrganic insulation materials are widely used in building insu-lation system because of its excellent integrated performance.However,the biggest shortcoming of these materials is flamma-bility.With the increasing application of these materials,more and more fires were caused,resulting in great economic and life loss,even serious social impact.The big fire occurred at China Central Television (CCTV)new site building,in February 9,2009,leaded to direct economic losses of 163.83million RMB,due to the employ-ment of extruded polystyrene (XPS)as the building external wallinsulation material.Soon after that,in November 2010,another big fire at residential high-rise in Shanghai Jing’an district caused 58people killed and morethan 70people injured.The investigations to these fire disasters showed that combustion caused by organic insulation material could quickly spread from the fire origin to the entire building.As a consequence,the degradation behavior and products of such materials are thus significant to be studied.Many researchers have conducted numerous studies on thermal degradation of various polymers [1–6].It is thought that ther-mal degradation is always the initial step of solid combustionprocesses and provides flammable volatile products to supportthe combustion.The objective of this work is to research the∗Corresponding author.Tel.:+865513606425;fax:+865513601669.E-mail address:sunjh@ (J.Sun).thermal degradation characteristics and volatile products of insu-lation materials,such as PU,XPS and EPS.2.ExperimentalThe experiment is composed of two parts.The first part (TG experiment)is to obtain the kinetics of materials thermaldegradation and the second part (STA experiment)is for the char-acterization and volatile products.2.1.Experimental apparatusThermogravimetry experiment was carried out on a Mettler-Toledo TGA/SDTA 851e thermal analyzer.And simultaneous thermal analysis experiment was performed on a NETZSCH STA449C,NETZSCH-QMS403C,and NICOLET6700FTIR coupling system [7].It can provide both the thermal behavior and MS-FTIR of gaseous products during degradation process.2.2.MethodsThermogravimetric analyses were conducted under the heatingrates (5,10,15,20◦C/min)in a nitrogen environment from 50◦C to 700◦C and the gas flow was 30L min −1.The samples were cut with scissor to fine particles for ensuring heated evenly.In order to reduce the impact of sample size on the results,the error caused by weighing should not more than 0.02mg.0040-6031/$–see front matter © 2012 Elsevier B.V. All rights reserved./10.1016/j.tca.2012.07.020建筑绝缘材料热动力学和热分解产物三种典型绝缘材料热降解调查同步热分析仪质谱仪傅里叶变换光谱仪挥发性物质揭示三种材料热降解性质的不同一阶降解二阶降解热吸收国际热化学学报挤塑住宅高层建筑热降解易燃燃烧产物热解产物热降解特性2个部分组成获得热分析动力学参数获得挥发产物和表征装置TG梅特勒托利多耐驰热行为和气体产物氮气气氛剪成小粒受热均匀称量上的偏差应小于原理L.Jiao et al./Thermochimica Acta 547 (2012) 120–125121Simultaneous analyses were begun from room temperature to 600◦C with a heating rate of 10◦C/min.The environment gas and purge gas were both nitrogen with gas flow rate 20ml min −1.Sam-ples were cut into small particles as well.3.Results and discussion3.1.Kinetics of PU,XPS and EPS degradationThe TG and DTG results of PU,XPS and EPS under various heating rates (5,10,15,20◦C/min)in a nitrogen environment are presentedin Figs.1–3,respectively.There are many methods for calculating non-isothermal kineticparameters.The choice of kinetic analysis method should take into account the amount of noise in experimental data.Integral methodsare best suitable for analyzing integral data.Whereas,differentiat-ing integral data tends to magnify data noise and smoothing may introduce a systematic error (shift)in the smoothed data that would ultimately convert into a systematic error in kinetic parameters [8].Kissinger–Akahira–Sunose (KAS)method and Ozawa–Flynn–Wall (OFW)method are both integral isoconversional methods,com-monly used to evaluate the activation energy E in polymers thermalanalysis [9–11].Compared to the OFW method,KAS methodimproves significantly in the accuracy of E [8].That is the reasonwhy KAS method is used in this study.m a s s [%]temperat ure [°C](a)D T G [%/°C ]temper ature[°C](b)Fig.1.TG and DTG curves of PU degradation under different heating rates.20406080100m a s s [%]temperature [°C](a)temperature[°C]D T G [%/°C ](b)Fig.2.TG and DTG curves of XPS degradation under different heating rates.The equation of KAS method islnˇiT 2˛,i=Const −E ˛RT ˛(1)where ˇi ,E ˛and T ˛,i are heating rate,activation energy and absolute temperature respectively,the index i here is to indicate different heating rates,and R is the gas constant.According to Eq.(1),acti-vation energy E ˛can be obtained from the slope of the straight lineln(ˇi /T 2˛,i )vs.1/T ˛at each given ˛.Based on these data obtained by TG experiment,the activation energy E of the three materials can be calculated and the depen-dence of E on the extent of conversion is given in Fig.4.Comparing the activation energies of PU,XPS and EPS,we can find that the E values of PU are much lower than that of the other two materials.The curve of PU activation energy with ˛in Fig.4shows that the value of E is not constant through the entire ther-mal degradation process.The value first increase in the conversion range of ˛=0.05–0.25and decrease when ˛=0.25–0.45,then main-tain an approximate constant from ˛=0.45to 0.80.PU requires less activation energy at the initial stage of thermal degradation,and this indicates that the material is easy to degrade when subjectedto heat in this condition.During the thermal degradation of XPS,the activation energy increases before ˛=0.25and then the value stabilizes in the rangeof 220–230kJ mol −1.Through the entire process,the E values of从室温到600度N‚Q 流速结果与讨论热分解动力学of:非等温条件下的热动力学积分的方法最适合对积分数据进行微分平滑后的数据转化成了系统误差等转化率法积分的计算KAS 提高了计算E 的精确度本计算中使用KAS 法绝对温度气体常数先升丆后降维持一个值在这个气氛下受热更易降解增加丆然后稳定在***122L.Jiao et al./Thermochimica Acta 547 (2012) 120–125m a s s [%]temperature[°C](a)D T G [%/°C ]temperature[°C] Fig.3.TG and DTG curves of EPS degradation under different heating rates.XPS are always smaller than that of EPS and they show different dependence on the degree of conversion.This reveals that under nitrogen environment,the thermal degradation of XPS is easier than EPS.In the range of ˛=0.1–0.85for thermal degradation of EPS,the differences of activation energies are very small in regard toαE [k J m o l -1]Fig.4.The dependence of activation energy values E on the extent of conversion ˛for the three insulation materials in N 2environment,obtained by KAS method.Table 1TG results of the three materials.MaterialMass (mg)T onset (◦C)T end (◦C)Mass loss (%)PU 1.90071.0234.011.58234.0400.050.07400.0599.210.32XPS1.140228.0298.07.10342.0456.087.55EPS0.220377.4417.378.73Table 2DSC results of the three materials.MaterialMass (mg)Heat (J g −1)Peak temperature (◦C)T onset (◦C)T end (◦C)PU 1.900−132319.6264.8350.7−30.33432.5425.1447.3XPS1.140−1153421.9387.4447.1EPS0.220−2807403.4386.6417.3experimental errors and the average value of E is about 245kJ mol −1,thus we can regard the value of E as a constant.Itindicates that the thermal degradation process of EPS in a nitro-gen environment can be approximated as a single reaction step.Atthe initial and final stage of the reaction of the three materials,the change of E values is larger and the results show a high standarderror.3.2.Simultaneous analysisThis part was conducted on a simultaneous TG–DSC–MS–FTIR system that possesses outstanding performances.Tables 1and 2show the related data values of TG and DSC results of the threematerials.Fig.5represents the TG–DTG–DSC curves of PU in the heatingrate 10◦C/min.Three degradation steps can be observed,indicating that PU undergoes a complex degradation process in this condition,and this process involves a wide temperature range.In the first mass loss stage,between 71.0◦C and 234.0◦C,the mass loss ratio is11.58%.The second stage (234.0–400.0◦C)is the primary mass loss stage and the mass loss is 50.07%,the largest heat absorption peak is also in this temperature range as DSC curve shows and the two heat absorptions are 132J g −1and 30.33J g −1listed in Table 2.The thirdstage is from 400.0◦C to 599.2◦C,material mass loss percentage is10.32%,which is smaller than that of the first two.10020 030040 0500602030405060708090100M a s s [%]Temperature [°C]-1.0-0.50.00.51.0DSC [mW/mg]DTG [%/°C]TGDTGDSC-0.6-0.4-0.20.0Fig.5.TG–DTG–DSC scans of PU degradation at 10◦C/min in a nitrogen atmosphere.KAS 理论求得的N2气氛下三种材料的E 值XPS 的E 值一直小于EPS 的丆并且他们表现出对转化率依赖程度较低实验误差非常小E 均值是**因此我们可以认为E 值不变热降解过程可以近似于一个单步反应反应的初始和终止阶段E 变化大并且表现出高的标准差联用分析显示了TG 、DSC 数据的相关性代表经历了第一阶段失重比率DSC 显示了两个吸热峰第三阶段失重丆比前两个都小L.Jiao et al./Thermochimica Acta 547 (2012) 120–1251231002003040050600700020406080100DSC [mW/mg]M a s s [%]Temper ature [°C]TG DSC-8-6-4-224-2.5-2.0-1.5-1.0-0.50.00.5DTGDTG [%/°C]Fig.6.TG–DTG–DSC scans of XPS degradation at 10◦C/min in a nitrogen atmo-sphere.There are two obvious mass loss stages of XPS degradationon the TG curve showed in Fig.6.The decline of the first stage (228.0–298.0◦C)is more gentle as the mass loss ratio is only 7.10%,a small peak on DSC curve can be observed in this stage as well.However,mass loss ratio of XPS in the second temperature range (between 342.0◦C and 456.0◦C)reaches up to 87.55%and DSC shows an obvious heat absorption peak of 1153J g −1.It can be seen in Fig.7,EPS shows only one obvious mass loss stage under this condition.However,DTG curve displays two peaks,the first peak at around 120◦C,indicating that the TG curve of EPS should exhibit a mass loss stage around this temperature but is notobvious from the experimental result.It is due to the amount ofmass loss is so small that can hardly be observed clearly.The mainmass loss ratio of EPS is 78.73%in a narrow temperature rangefrom 377.4to 417.3◦C and the heat absorption is up to 2807J g−1concentrated in this stage.As the TG results show,the initial degradation temperature of PU is much lower than that of XPS and EPS.This result can be explained from the structure of polymer that phenyl is the side chain of PS,resulting in crowded space and shielding effect.The FTIR spectra of volatile products obtained from thermal degradation of the three materials at different temperatures are presented in Figs.8–10.Fig.8a shows that signals for the absorption of volatile prod-ucts of PU can be observed at 90◦C in the first temperature range(71–234.0◦C).OH (absorption bands at 800and 3050cm −1)and010 0 20030040 0 50060020406080100DTG [%/°C]DSC [mW/mg]M a s s [%]Temperature [°C]TGDTGDSC-28-21-14-707142128-2-1Fig.7.TG–DTG–DSC scans of EPS degradation at 10◦C/min in a nitrogen atmosphere.050 0 100 0 150 0 200 0 2500 3000 3500 400 0 450 0305°C°C °C 400320Wavenu mbe r [cm -1]0 500 100 0 1500200 025 0030 00 3500 4000 450 0Wavenumber [cm -1]9070240°C°C°C(a)(b) Fig.8.FTIR spectra of PU degradation products at different temperatures.H 2O (absorption bands at 1600and 3400cm −1)indicate the pres-ence of water and some other low molecular weight fragments.In the primary thermal degradation stage of PU (234.0–400.0◦C),CO 2released as absorption peaks at 2361cm −1in Fig.8b and the pres-ence of m /z 44signal in mass spectra,and the results are listed inTable 3.Two peaks at m /z 44were detected,the first one is at 250◦C (in the second stage)and the second is at around 450◦C (third stage),while the intensity of the latter one is weaker.The presence of m /z 43peak at 350◦C proved that C 2H 4O was formed in the prod-ucts.Signals from HCN at m /z 26and 27were not observed.Signals at 81and 83revealed the formation of high molecular weight.TheTable 3Mass spectrum results of PU volatile products.m /z Volatile fragmentm /z Volatile fragment12C44CO 243C 2H 4O温和展示DTG 曲线的两个峰表明EPS 的TG 曲线会有一个失重丆但实验结果不明显丆因为失重太小很难看清楚ESP 的主要失重阶段TG 表明初始失重温度丆PU 小于另两可从分子结构解释PS 的苯基侧链造成空间拥挤和屏蔽效应三种材料不同温度的挥发产物的红外光谱PU 在90度的信号表明水和一些低分子量碎片的出现吸收峰在质谱的信号也可以作为证据表明了高分子量物质的出现质谱124L.Jiao et al./Thermochimica Acta 547 (2012) 120–12550010001500200025003000350 040004500Wavenu mber [cm -1]350420460510°C°C°C °C Fig.9.FTIR spectra of XPS degradation products at different temperatures.050 0 1000150 0200 0250 0 300 0350 0400 0 450 0370400420°C °C°CWavenumber [cm -1]Fig.10.FTIR spectra of EPS degradation products at different temperatures.primary products of PU degradation are CO 2and some other highmolecular species that not be detected by MS.MS results of XPS are presented in Table 4.Only a small amountof CO 2was detected during the degradation of XPS,a very narrow but sharp peak appeared at around 470◦C.A strong peak at m /z 51between 400◦C and 450◦C is due to benzene or phenyl fragments,revealing the existence of volatile species with benzene ring,threestrong peaks at m /z 65,66and 74(425–475◦C)also provided evi-dences.Moreover,peaks at around 890–910cm −1and 3085cm−1Table 4Mass spectrum results of XPS volatile products.m /zVolatile fragmentm /zVolatile fragment12C44CO 217,18OH,H 2O 51,52C 4H 3,C 4H 427C 2H 365,66C 5H 5,C 5H 629C 2H 5Table 5Mass spectrum results of EPS volatile products.m /zVolatile fragmentm /zVolatile fragment12,28CO 45CH 3CH 2O,CH 3CHOH 17OH46CH 3CH 2OH,H 2O +C 2H 427,29C 2H 3,C 2H 551,52C 4H 3,C 4H 444CO 2in Fig.8are respectively due to v (CH 2)wagging vibrations and terminal v (C H)stretching vibrations.It proves the formation of a certain amount of monomer,dimer,trimer and some otheroligomers in the primary mass loss stage of XPS.A various types of small molecules were detected as listed in Table 5and most of these fragments are flammable.Different fromXPS,a lot of CO 2were detected during the thermal degradation of EPS under this condition.The FTIR spectra in Fig.10with low absorbance at around 667cm −1and 2350cm −1reveal the forma-tion of small amount of CO 2in this stage (around 350◦C),but twostrong peaks appeared at the previous absorption bands indicatethe predominate evolution of CO 2at high temperature between400◦C and 420◦C.A strong signal at m /z 44also proves the presenceof significant amounts of CO 2.The volume fraction of air containedin EPS is 98%and polymer reaction with air to form a considerableamount of CO 2.As same as XPS,signals at m /z 51and 52proved theexistence of phenyl (benzene).4.ConclusionsIn this work,Kissinger–Akahira–Sunose method was utilized for kinetic paring the activation energy of XPS,EPSand PU,the PU activation energy is much lower than that of the other two.The activation energy of PU first increase in the conver-sion range of ˛=0.05–0.25and decrease when ˛=0.25–0.45,then maintain an approximate constant from ˛=0.45to 0.80.Throughthe entire process,the E values of XPS are always smaller thanthat of EPS and they show different dependence on the degree of conversion.The thermal degradation process of EPS in a nitrogen environment can be approximated as a single reaction step,and the average value of E is about 245kJ mol −1.It can be concluded from the results of TG–DSC–MS–FTIR,the three insulation materials showed different thermal degradationcharacteristics at heating rate of 10◦C/min.In the first degradation stage of PU,water and some other volatile fragments released.For the volatile products of XPS and EPS in the primary mass loss stage,a various types of small molecules were detected.Most of thesefragments are flammable,such as CO,C 2H 3and C 2H 5,and signalsat m /z 51and 52proved the existence of phenyl (benzene)in theproducts.Acknowledgements This study was supported by National Basic Research Program of China (973Program,No.2012CB719702),the National Natu-ral Science Foundation of China (Nos.50976110and 51076065)and Key Technologies R&D Program of China during the 12th Five-year Plan Period (No.2011BAK07B01-02).A financial support from the Fundamental Research Funds for the Central Universities (No.WK2320000014)is also appreciated.References[1]P.Kannan,J.J.Biernacki,D.P.Visco Jr.,mbert,Kinetics of thermal decom-position of expandable polystyrene in different gaseous environments,J.Anal.Appl.Pyrolysis 84(2009)139–144.[2]K.Chrissafis,K.M.Paraskevopoulos,G.Z.Papageorgiou,D.N.Bikiaris,Ther-mal decomposition of poly(propylene sebacate)and poly(propylene azelate)XPS 在不同温度下的热解产物红外光谱EPS PU 主要热解产物是*和其他几种没被MS 发现的 高分子产物XPS 的MS 结果揭示带有苯环的挥发性物质的出现分别是*的摇摆振动和*的伸缩振动提供了XPS 在主要失重时单体二聚物三聚物和其他低聚物的出现。

Polymer Degradation and Environment Degradation methed:1 thermal degradation2 mechanical degradation3 oxydative degradation4 chemical degradation and biodegradation5 Photodegradation and light oxidationⅠthermal degradation:1 Definition:The reaction of the polymer molecular weight smaller general degradation, including depolymerization, random chain scission and reaction such as low molecular material removal。

2 The research methods of thermal degradation（1）Thermogravimetric analysis（2）Constant temperature heating method（3）Differential thermal analysis3 The main factors influencing the thermal degradation products is free radicals in the process of pyrolysis reaction ability, and participate in the chain transfer reaction of hydrogen and lively。

Ⅱmechanical degradation:1 Polymer molding, melt extrusion, and the function of the polymersolution under strong stirring or ultrasound, are likely to make the macromolecular chain rupture and degradation.2 Mechanical degradation: the mechanism of free radical mechanism Under anaerobic conditions:A. double-base disproportionation termination (formation of unsaturated end group)B. chain transfer (form branched chain)C. when the coexistence of two kinds of polymer, can also be coupled End to form a block copolymerⅢoxydative degradation1 Direct oxidation：Polymer react with certain compounds in the environment temperature。