【作者】 刘博；

【导师】 夏新林；

【作者基本信息】 哈尔滨工业大学 ， 工程热物理， 2021， 博士

【摘要】 高孔隙率开孔泡沫材料,具有独特的多尺度孔隙和空间网络结构特征,是一种新型的气体换热强化技术手段,已成功应用于电子设备散热等领域。由耐高温材料制造的高孔隙率开孔泡沫材料,在太阳能高温转换、高温气体余热回收、气体燃烧、飞行器热防护等技术领域也展现出广阔的应用前景。但由于对高孔隙泡沫材料内高温传热机理和特性的认识不清、缺乏可靠的热性能设计依据,导致高温泡沫材料的开发和应用受到极大限制。在涉及高温的工程技术中,热辐射传递对泡沫材料内高温热过程起着决定性作用。所以,泡沫材料的高温热辐射特性及其输运机理,是相关技术应用的关键基础科学问题。目前,对泡沫材料的高温热辐射特性及其输运机理的研究,已进展到泡沫骨架孔隙结构尺度,但缺乏对泡沫材料肋筋微结构的辐射特性及其与泡沫骨架孔隙尺度、以及泡沫材料等效介质的多尺度辐射传输特性与机理的研究。另一方面,由于泡沫材料的强散射性,导致此类材料高温介质辐射特性的实验测量极难实现,缺乏必要的高温辐射物性参数数据。上述问题,严重制约着泡沫材料在高温技术领域的应用和创新发展。针对肋筋不透明的金属镍泡沫和肋筋半透明的氧化铝陶瓷泡沫两类典型的耐高温高孔隙率材料,本文开展了泡沫材料微细观结构测量、表征和结构模型重建,金属镍泡沫肋筋表面随机微粗糙结构的光谱反射和吸收特性建模分析,氧化铝陶瓷泡沫肋筋表面及内部随机微结构的光谱吸收、散射特性建模分析,从泡沫肋筋微结构到骨架孔隙结构的跨尺度辐射传输模拟方法与机理分析、泡沫材料辐射特性跨尺度预测方法的实验验证等研究。采用SEM和μ-CT扫描测量技术,对两类泡沫材料的肋筋微结构和孔隙尺度的细观结构进行了测试分析,获得了泡沫骨架及其肋筋微结构的微细观图像及拓扑几何结构参数数据。通过对测试图像与数据的统计分析,提出了一种重构肋筋粗糙表面几何模型的方法,同时对氧化铝泡沫肋筋内部的二次微孔隙和微多孔介质结构进行了建模研究。建立了表征两类泡沫材料肋筋表面及内部微结构的随机统计模型。基于FDTD和MCM方法,对两类泡沫材料肋筋微粗糙表面的光谱辐射特性进行了数值预测研究。得到了泡沫肋筋微粗糙表面的光谱辐射特性参数,并对相关辐射特性随入射条件的变化规律进行了分析。从不同角度对肋筋粗糙表面辐射特性与一般光滑表面的差异性进行了机理性研究。同时,对半透明的氧化铝陶瓷泡沫肋筋的等效介质光谱辐射特性参数进行了预测分析。分别针对基材不透明的金属泡沫和基材半透明的陶瓷泡沫两类高孔隙率材料,基于重构的泡沫材料细观骨架网络结构,发展了适用于孔隙尺度的辐射传输模拟和泡沫材料等效介质的光谱辐射特性的求解模型。针对两类耐高温泡沫材料,在综合考虑泡沫内部不同尺度的结构特征的基础上,提出了一种连接泡沫肋筋微尺度辐射特性计算与泡沫骨架孔隙尺度辐射传输模拟的跨尺度辐射传输的计算方法。通过泡沫材料光谱方向透射特性的常温实验测量,验证了材料辐射特性跨尺度预测方法的适用性。进而,对不同泡沫材料在常温及高温条件下的表观光谱辐射特性和等效介质光谱辐射特性进行了预测研究,讨论了泡沫材料内部不同尺度参数的结构对其光谱辐射特性的影响。通过上述研究,获得了对两类高孔隙率泡沫材料的微尺度结构特征与光谱辐射特性的深入认识,揭示了泡沫材料光谱辐射的多尺度传输机理,实现了此类材料的高温光谱辐射特性参数的预测。为泡沫材料的高温技术应用和相关研究,提供了必要的认识基础和研究方法。更多还原

【Abstract】 High porosity open-cell foam has unique multi-scale pore and ligament network characteristics.It is a new technology for gas heat transfer enhancement,and has been successfully applied in the field of heat dissipation of electronic equipment.The high porosity open cell foam made of high temperature resistant materials also has broad application prospects in the fields of high temperature conversion of solar energy,heat recovery of high temperature gas,gas combustion,and thermal protection of aircraft.However,due to the unclear understanding of the high temperature heat transfer mechanismls and the lack of reliable thermal performance design basis,the development and application of refractory foam materials are greatly restricted.In high temperature engineering technology,heat radiation transfer plays a decisive role in the high-temperature thermal process of foam materials.Therefore,the high temperature thermal radiation characteristics and transport mechanism of foam materials are the key basic scientific issues related to the application of technology.At present,the research about radiative characteristics and transport mechanism of foam materials has progressed to the pore-level analysis.However,there is no research on the radiative characteristics of the micro structure of ligaments,and the multi-scale radiative transfer characteristics and mechanism of the foam material equivalent medium.On the other hand,due to the strong scattering propert ies of foam materials,the experimental measurement of the radiati ve characteristics at high temperature is very difficult to achieve,and there is no enough data for high temperature radiative parameters.These problems seriously restrict the application and innovation development of foam materials for high temperature technology.In view of two typical refractory high-porosity materials,including nickel foam and alumina foam,the microstructure measurement,characterization and structural model reconstruction of foam materials are carried out.The spectral reflectance and absorption characteristics of the micro rough structure on the nickel ligamnet are modeled and analyzed.Modeling and analysis of the spectral absorption and scattering characteristics of the surface microstructure and internal random microstructure of alumina ligament,the simulation method and mechanism analysis of trans-scale radiation and the experimental verification of are performed.Based on the SEM and μ-CT techniques,the microstructure and pore-level structure of two kinds of foams are tested and analyzed.With the statistical analysis of test images and data,a method for reconstructing the geometric model of ligament surface is proposed.Meanwhile,secondary micro pores and micro porous structure inside the alumina ligamnet are modeled.A stochastic statistical model is established to characterize the surface and internal microstructure of two kinds of foam ligaments.With the FDTD and MCM methods,the spectral radiative properties of two kinds of ligamet surfaces are numerically predicted.The spectral radiative characteristic parameters of the micro ligamnet surface are obtained,and the variation regulations of the radiative characteristics correlated with the incident conditions are analyzed.The differences of radiation characteristics between ligamnet surface and smooth surface are studied from different aspects.At the same time,the equivalent spectral radiative characteristic parameters of semitransparent alumina ligament are predicted and analyzed.Based on the ligamnet network of reconstituted foam,the radiative transfer model of pore-level simulation are developed for different foams.For two kinds of refractory foam materials,taking into account the structural characteristics of different scales,a trans-scale radiative transfer method is proposed to calculate the radiative properties of foams.The applicability of the trans-scale method is verified by the experimental measurements.Furthermore,the apparent spectral radiative properties and equivalent volumetric radiative properties of different foamsat room temperature and high temperature are predicted.The effects of multi-scale parameters on the spectral radiative properties of foam materials are discussed.Through the above research,an in-depth understanding of the micro scale structure characteristics and spectral radiative characteristics of two kinds of high porosity foam materials can be achieved.And it is reveals that the multi-scale transmission mechanism of the spectral radiation of foam materials.It provides necessary knowledge and research methods for high temperature application s and related researches about foam materials.更多还原