基于分形理论的玻璃纤维真空绝热热工特性研究
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摘要
基于分形理论,描述了玻璃纤维多孔介质材料微尺度空间结构,建立分形等效单元体模型,分析了影响其真空下有效导热系数关键因素为固体基质导热系数、空隙率、纤维丝空间结构、分形直径、残余气体压力及导热系数、玻璃纤维材料厚度、使用环境等,并导出了气相、固相热传导计算公式和热辐射等效导热系数计算公式及材料总有效导热系数计算公式。研究表明,玻璃纤维有效导热系数随着分形直径、分形维数、残余气体压力的增大而增大,随着空隙率的增大而减小。同时,模型计算值与实验测量值比较,具有较好的一致性。文章的分析方法对新型真空绝热材料的研制和绝热性能的提高具有实用价值。
The microstructures of the porous fiber glass materials were modeled,approximated,and studied on the basis of fractal theory.The impacts of various factors,including the porosity,fiber orientation,fractal diameter and dimension,rarified air pressures,bulk thermal conductivity coefficient,thickness of the fiber glass materials,and environmental conditions,on the effective thermal conductivity in vacuum were studied.The formulae were derived to calculate the thermal conductivity of gas and solid phased fiber glass materials,the effective conductivity coefficient,and the total effective conductivity of the materials,respectively.The calculated results show that the effective thermal conductivity of the fiber glass increases with the increases of the fiber fractal diameter,fractal dimension,and residue gas pressure,but decreases with an increase of the porosity.The calculated results were found to agree fairly well with the measured data.
The microstructures of the porous fiber glass materials were modeled,approximated,and studied on the basis of fractal theory.The impacts of various factors,including the porosity,fiber orientation,fractal diameter and dimension,rarified air pressures,bulk thermal conductivity coefficient,thickness of the fiber glass materials,and environmental conditions,on the effective thermal conductivity in vacuum were studied.The formulae were derived to calculate the thermal conductivity of gas and solid phased fiber glass materials,the effective conductivity coefficient,and the total effective conductivity of the materials,respectively.The calculated results show that the effective thermal conductivity of the fiber glass increases with the increases of the fiber fractal diameter,fractal dimension,and residue gas pressure,but decreases with an increase of the porosity.The calculated results were found to agree fairly well with the measured data.
引文
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[2]Pharoah J G,Karan K,Sun W.On Effective Transport Coeff-icients in PEM Fuel Cell Electrodes:Anisotropy of the PorousTransport Layers[J].Journal of Power Sources,2006,(1):214-224
[3]Moran Wang,Jihuan He,Jianyong Yu,et al.Lattice Boltz-mannModeling of the Effective Thermal Conductivity for F-ibrous Materials[J].International Journal of Thermal Sciences2007,46:848-855
[4]温永刚,王先荣,陈光奇.FG型真空绝热板使用寿命评估[J].真空科学与技术学报,2011,31(1):110-113
[5]陈树军,江荣顺,魏蔚,等.几种组合吸气剂的吸氢等温线的测定及分析[J].真空科学与技术学报,2009,29(4):435-439
[6]Jae-SungKwon,ChoongHyo Jang,Haeyong Jung,et al.Effec-tive Thermal Conductivity of Various Filling Materials forVacuum Insulation Panels[J].International Journal of Heatand Mass Transfer,2009,52:5525-5532
[7]Eichhorn S J,Sampson W W.Statistical Geometry of Poresand Statistics of Porous Nanofibrous Assemblies[J].Journalof the Royal Society Interface,2005,24:309-318
[8]Pal R.Porosity-Dependence ofEffectiveMechanical Propertiesof Pore Solid Composite Materials[J].Journal of CompositeMaterials,2005,39(13):1147-1158
[9]Ma Y T,Yu B M,Zhang D M,et al.A Sel-f Similarity Modelfor Effective Thermal Conductivity of Porous Media[J].J Ap-plication Physics,2003,36:2157-2164
[10]Kan Ankang,Han Houde,Tang Wei.Research on EffectiveThermal Conductivity for Open-Cell Polyurethane Foam Us-ing Fractal Theory[J].Materials Review,2011,26:143-146
[11]Ramakrishnan B,Pitehtmmni R.Fractal Permeation Charac-teristics of Performs Used in Liquid Composite Molding[J].Polymer Composites,2010,24:281-296
[12]Dathe A,Thullner M.The Relationship between FractalProperties of Solid Matrix and Pore Space in Porous Media[J].Geoderma,2005,129:279-290
[13]Hunt A G.Basic Transport Properties in Natural Porous Me-dia:Continuum Percolation Theory and Fractal Model[J].Complexity,2005,10:22-37
[14]Schmierer E N,Razani A.Sel-f Consistent Open-CelledMetalFoam Model for Thermal Applications[J].J Heat TransferASME,2006,128:1194-1203
[15]Krishnan S,Murthy J Y,Garimella S V.Direct Simulation ofTransport in Open-Cell Metal Foam[J].J Heat TransferASME,2006,128:793-799
[16]Ramvir Singh,Kasana H S.Computational Aspects of Effec-tive Thermal Conductivity ofHighly PorousMetal Foams[J].Applied Thermal Engineering,2004,24:1841-1849
[17]Petroy V A.Combined Radiation and Conduction HeatTransfer in High Temperature Fiber Thermal Insulation[J].Heat Mass Transfer,1997,40:2241-2247
[18]Huai Xiulan,Wang Weiwei,Li Zhigang.Analysis of the Ef-fective Thermal Conductivity of Fractal Porous Media[J].Applied Thermal Engineering,2007,27:2815-2821