内连接隔热油管隔热性能分析及应用

以内连接隔热油管为研究对象,建立一维传热和径向传热的数学公式推导,计算出现场注蒸汽过程中使用的E级隔热油管和接箍的综合视导热系数;通过Wellflo软件建立蒸汽吞吐模型,输入综合视导热系数0.173 W/(m·℃),计算出井筒的温度压力分布,结合现场注汽中的实际测试数据,将软件计算数据与实测数据进行拟合度,拟合度高达0.994 6。论证了试验得出的注汽中隔热油管和接箍的综合视导热系数0.173 W/(m·℃)符合现场实际,为日后的渤海油田规模化提供了现场工艺数据支撑。     

隔热涂层降低建筑空调负荷效果的参数分析

从降低建筑空调负荷的角度出发,对外壁面有隔热涂层的房间建立了稳态传热模型,用数值方法逐一分析了涂层的各种参数,包括导热系数、厚度、表面太阳吸收率、发射率以及地区因素等对空调负荷的影响。研究发现：隔热涂层能显著降低空调负荷及能耗；仅当涂层热阻与墙体热阻之比大于0．2时,涂层导热系数的降低才会对空调负荷产生显著影响；涂层表面太阳吸收率和发射率对空调负荷的影响非常大,是起主导作用的因素；隔热涂层用在太阳辐照密度越大、日最高气温越低、日较差越大的地区节能率越高,越有利于发挥其降低空调负荷及日累计能耗的功能；决定着空调运转时间长短的当地室外气温分布状况对于评价隔热涂层节能效果也有重要影响。     

接箍导热系数测试方法研究

本文基于单宗量热物性参数导热反问题理论,对接箍的导热系数进行反演.建立正、反问题模型,利用黄金分割法反演了接箍导热系数,然后用CFD软件模拟了温度场分布,最后分析了测量位置对导热系数反演的影响.研究结果表明,黄金分割法能够适用于单宗量热物性参数的反演,通过测量外表面温度,能够准确地反演隔热油管接箍导热系数.     

双面受热太阳能平板接收器热性能模拟研究

为提高太阳能光热转换效率,建立同轴非完整型平移抛物面聚光系统。分析双面受热平板接收器的能量传递及转换过程,采用热阻网络图的分析方法建立平板接收器的理论计算模型。利用MATLAB 7.0软件编制程序实现了平板接收器的热性能计算。在结构参数、环境参数和进口参数确定的情况下,当吸热板导热系数、厚度和吸热板表面发射率变化时,分析温度、能量及热性能的变化趋势。研究表明：导热系数和吸热板厚度达到一定数值,继续增加对于提高接收器的热性能基本没有太大意义;吸热板表面发射率对热性能影响显著,采用发射率为0.1的选择性涂层可实现能量最大转化;环境温度在0～30 ℃变化时,双面受热比单面受热的热效率提高了8.18%～37.01%。     

分层岩土中地埋管换热器传热解析模型与分析

为准确预测地埋管换热器在分层岩土中的传热特征,采用分离变量法和格林函数法,基于单个圆环热源基本传热单元问题的解答,建立考虑岩土结构分层和横观各项同性特征的地埋管传热解析模型。该模型适用于工程中常见的垂直钻孔和桩基埋管换热器分层传热问题,具有较好的普适性。以2层岩土为例,利用模型解答对分层岩土中地埋管的传热特征以及分层参数对其影响规律进行研究。结果表明：均匀介质假设计算误差随作用时间的增加而逐渐增大,在靠近热源处误差更加明显,预测地埋管长时间温度响应时,应采用分层传热模型;在临界区域范围内,可用均质假设模型预测地埋管的传热特性,均质等效热物性参数取为对应岩土分层的热物性参数值;分层岩土导热系数对地埋管传热性能影响较大,岩土平衡温度随分层导热系数比的增大而明显降低;地埋管长度和直径的比值对地埋管传热性能有所影响,岩土平衡温度随长径比的增大而升高,且其影响程度随分层导热系数比的减小而增强。     

地下U形埋管传热及土壤温度分布研究

对地源热泵系统核心组成部分的地下U形埋管的传热性能进行了深入研究。首先建立了真实的地下U形埋管换热器的模型,然后对地下U形埋管换热器在不同工况下的运行进行了模拟计算。重点研究了U形埋管入口水温、水流速度和回填土导热系数对U形埋管传热和土壤温度分布的影响。结果表明：最佳水流速度应为0.6～0.8m/s;最佳回填土导热系数应比土壤导热系数大,且小于土壤导热系数的2倍;U形埋管组最佳管间距应保持在6m左右;增大入口水温、水流速度及回填土导热系数都会使土壤温度有所升高。     

混凝土导热系数与其饱和度及温度的关系

在已有混凝土导热系数影响因素研究成果的基础上,以普通混凝土、泡沫混凝土、植物纤维陶粒混凝土、棉花秸秆石膏混凝土四种不同混凝土为研究对象,采用QTM-500导热测试仪分别对四种混凝土不同饱和度时不同温度下(-30~20℃)的导热系数进行试验,并分析不同饱和度下各混凝土导热系数随温度(-30~20℃)的变化规律,最后采用压汞仪对四种混凝土的孔隙率、孔径分布等参数进行测试,从微观孔隙角度深入分析各混凝土导热系数随温度的变化规律。结果表明,各混凝土的导热系数与其饱和度呈显著的正相关性,干燥状态下,四种混凝土的导热系数随温度变化不显著;饱和状态下,各混凝土导热系数在一定温度范围内会发生突变,当超出温度敏感区域后,各混凝土的导热系数基本趋于稳定值;在试验温度范围内,混凝土导热系数变化规律与其孔隙参数有关。该研究结果可为寒冷地区大体积混凝土结构、建筑节能混凝土的导热系数试验及分析提供参考。     

200MW富氧燃煤锅炉传热特性研究

对常规空气燃烧传热计算方法进行了修正,使其适用于富氧燃烧方式,并对灰气体加权模型(WSGG)的参数进行优化和修正,得到了烟气发射率与温度、辐射层有效厚度和分压比的关系;以美国国家标准技术局(NIST)数据库数据为标准,对富氧燃烧方式下烟气各组分的导热系数、运动黏度和普朗特数等物性参数进行拟合,采取先组分后混合的方式对对流传热计算方法进行了改进,并对200 MW富氧燃煤锅炉进行传热性能研究.结果表明:富氧燃烧方式下烟气中CO2物性参数的拟合结果与真实值的误差小于0.61％;在富氧燃烧干循环26％O2体积分数、湿循环29 ％O2体积分数下,各受热面的吸热量和出口烟气温度等主要参数均能与空气燃烧方式下的对应参数较好吻合,基本可以达到同一锅炉系统2种燃烧方式的兼容运行.     

空气冷却式膜蒸馏构型的传热分析

在膜蒸馏的不同构型中,直接采用环境空气作为冷却媒介的空气冷却式构型很大程度上简化了系统配置。在强化传热的条件下,其跨膜通量与水冷构型接近。对空气冷却式膜蒸馏构型的传热过程进行理论分析,并通过量化分析各参数对膜蒸馏传热性能的影响,构建综合的传热模型。引入关联热阻系数这一概念,用以量化空气冷却的参数对膜蒸馏过程总传热系数的抑制作用。通过模拟计算研究了冷凝板导热系数、空气流速、冷凝板肋化系数、料液温度等参数对膜蒸馏传热性能的影响,并分析和量化多参数对关联热阻系数的综合影响。结果表明冷凝板导热系数、空气流速、冷凝板肋化系数是影响关联热阻系数的重要因素,各参数对膜蒸馏传热性能的综合影响得以量化。以上研究为后续传质模型的研究提供了指导。     

船舶管道多层隔热结构的传热机理分析和实验研究

采用能量平衡方程和P-1阶微分近似建立了船舶管道系统多层隔热结构的稳态传热模型.讨论了在船舶管道系统上采用多层隔热结构的可行性,并进行了相应的实验验证.结果表明,在硅酸铝纤维隔热材料层间添加金属铝箔纤维布能提高材料的隔热性能,且随着使用温度升高,提升幅度增大.对于中低温的管道系统,因隔热效果提升有限,不推荐采用多层隔热结构.     

Analytical model of heat transfer in porous insulation around cold pipes

A thermal insulation system is analysed that consists of a cold tube insulated with a porous material faced with a vapour retarding foil.Water vapour will diffuse through the vapour retarding foil and condense on the cold tube. To avoid build-up of water in the insulation a hydrophilic wicking cloth is wrapped around the cold tube and extended through a slit in the tubular insulation and a slot in the facing to the ambient so that condensed water can evaporate into the air. Some of the moisture in that part of the wicking cloth situated in the slit in the tubular insulation will diffuse backwards to the cold pipe and contribute to the heat uptake of the cold tube. This part is calculated for the stationary case and compared with the sensible heat transfer through the tubular shaped insulation material, using measured dry λ values and measured fictitious moist λ values.     

含二氧化硅气凝胶和相变材料三层玻璃窗热性能分析

为了研究含二氧化硅气凝胶和相变材料三层玻璃窗对严寒地区建筑能耗的影响,建立了相变材料层与其他透明壁层结合发生的传热数值模型。分析了含二氧化硅气凝胶和相变材料三层玻璃窗在不同二氧化硅气凝胶厚度、导热系数和不同保温材料下的动态热调节性能,得到了含二氧化硅气凝胶和相变材料三层玻璃窗内表面热流密度和液相率随时间的变化规律。结果表明:随着二氧化硅气凝胶厚度增加,总传热量降低和液相率增加,当二氧化硅气凝胶厚度为20～30 mm时,可以实现有效的利用太阳能;随着二氧化硅气凝胶导热系数增加,总传热量升高和液相率降低;当二氧化硅气凝胶的导热系数从0.022降低到0.014 W/(m·K)时,最大液相率从0.83增加到1.00。二氧化硅作为保温层比相变材料作为保温层具有更好的保温隔热作用。     

Heat transfer through fibrous assemblies incorporating reflective interlayers

Fibrous insulation has many applications including functional protective clothing, sleeping bags, buildings and construction, and aircrafts, particularly under extreme climatic conditions. It has been realized that reflective interlayers can be incorporated into the fibrous materials to block radiative heat transfer. However, since reflective interlayers generally have greater thermal conductivity than the bulk fibrous materials, the optimization of the construction of the fibrous insulation is important in maximizing the overall thermal insulation. In order to analyze this complex optimization problem, a two-flux radiative heat transfer model was built for the heat transfer through fibrous assemblies incorporating reflective interlayers. By using finite control volume method, the solution was obtained. After validation it was applied to predict the optimum constructional parameters of such an assembly for maximizing thermal insulation. It was found that (1) although extinction coefficient of Al-coated interlayer fibers decrease unidirectionally as the fiber diameter increases, the total heat flux first decreases and then increases with minimum heat flux at the fiber diameter of about 2 μm; Consequently, the thermal resistance reaches a maximum value when the fiber diameter d is about 2 μm; (2) the optimum construction is determined by the balance of the weakening of conductive thermal resistance and enhancement of the radiative thermal resistance as a result of incorporating thin reflective interlayers. For relatively thick reflective interlayer, the assembly with lower interlayer fiber volume fraction has a higher thermal resistance. On the other hand, for very thin reflective interlayers, relatively high fiber volume fraction is beneficial to the overall thermal insulation.     

Modeling and optimization of composite thermal insulation system with HGMs and VDMLI for liquid hydrogen on orbit storage

The passive thermal insulation system for liquid hydrogen (LH₂) on orbit storage mainly consists of foam and variable density multilayer insulation (VDMLI) which have been considered as the most efficient and reliable thermal insulation system. The foam provides main heat leak protection on launch stage and the VDMLI plays a major role on orbit stage. However, compared with the extremely low thermal conductivity of VDMLI (1 × 10⁻⁵ W/(m·K)) at high vacuum, the foam was almost useless. Recently, based on hollow glass microspheres (HGMs) we have proposed the HGMs-VDMLI system which performs better than foam-VDMLI system. In order to improve insulation performance and balance weigh and environmental adaptability of passive insulation system, the HGMs-VDMLI insulation system should be configured optimally. In this paper, the thickness of HGMs and the number and arrangement of spacers of VDMLI were configured optimally by the “layer by layer” model. The effective thicknesses of HGMs were 25 mm for 60 layers MLI and 20 mm for 45 layers VDMLI. Compared with 35 mm foam and 45 layers VDMLI system, the heat flux of 20 mm HGMs and 45 layers VDMLI system was reduced by 11.97% with the same weight, or the weight of which was reduced by 9.91% with the same heat flux. Moreover, the effects of warm boundary temperature (WBT) and vacuum pressure on thermal insulation performance of the system were also discussed.     

Insulation System Using High-Temperature Fibrous Insulation Materials

ABSTRACT

In this study, we performed a preliminary research on an insulated sandwich structure using high-temperature fibrous insulation materials. Two types of fibrous materials, Saffil alumina and KCC cerakwool insulation materials, were selected. A sandwich specimen was invented to test the heat-shielding performance of the fibrous materials which were sandwiched by an Inconel plate and a titanium plate. The insulated sandwich structure was heated to 800°C for 2,000 seconds. The temperature profiles of the back side of the titanium plate were measured to compare the heat-shielding performance of the fibrous insulation materials. The microstructure of insulation materials, such as the fiber diameter, fiber orientation, and the parent materials of the fiber, was studied to understand how those characteristics influence the radiative properties of the fiber. The difference in microstructural parameters caused a difference in thermal resistance in the fibrous materials. The Saffil alumina insulation had a better performance than KCC cerakwool insulation because of its small fiber diameter and in-plane fiber orientation. The experimental results confirmed the heat transfer simulation results for fibrous materials done by other researchers. In addition, the reusability of high-temperature fibrous insulation, one of the important issues in real applications, was tested.     

Radiative properties and heat transfer characteristics of fiber-loaded silica aerogel composites for thermal insulation

The radiative properties and heat transfer in fiber-loaded silica aerogel composites were investigated using modified anomalous diffraction theory in a combined heat conduction and radiation model. The randomly parameterized 2-D fiber distribution was generated to simulate a very realistic material structure. The finite volume method was then used to solve a two flux radiation model and the steady-state energy equation to calculate the effective thermal conductivity of the composite. The numerical results provide theoretic guidelines for material designs with optimum parameters, such as the inclination angle, diameter and length-to-diameter ratio of the fibers. The results show that the fiber extinction coefficient increases as the fiber length-to-diameter ratio is reduced or the fiber inclination angle is increased. The effective thermal conductivity of the fiber-loaded aerogel can be reduced by reducing the fiber length-to-diameter ratio and the inclination angle and by moderately increasing the fiber volume fraction. The 4–6 μm diameter silicon fibers are optimum for high-temperature thermal insulation.     

Effect of Floor Geometry on Building Heat Loss Via the Ground

This paper analyzes the heat loss from an insulated slab on the ground, focusing on the influence of floor geometry on thermal processes in the ground. The calculation model includes the vertical and horizontal structures of the building; the foundation is also included. A building with a rectangular floor is considered; the ratio between the sides of floor (defined as aspect ratio) changes from 0 to 1. The thermal analysis is carried out resorting to a finite element code, validated in accordance with the requirements of International Standard ISO 10211. Numerical results show that floor geometry has a significant influence on steady-state ground global heat transfer coefficient; ranging from a narrow rectangular floor to a square one the steady-state ground global heat transfer coefficient decreases by about 15%. The effects of the perimeter insulation are also investigated; depending on the insulating layer thickness, the decrease of the heat transfer coefficient ranges from 8% to 13%. A comparison with the results obtained by applying the International Standard method ISO 13370 is also presented.     

保温用天然生物质材料的热湿特性

实验分析一些廉价天然材料(椰壳和花生壳)的导热特性。利用同心球稳态测量方法测量确定椰壳和花生壳的导热系数,以及导热系数随温度的变化规律,同时以硅酸铝纤维材料为标准试样,与天然材料的导热性能进行对比分析。还对这些材料的低温吸湿作了初步测试,分析此类材料作为低温绝热材料的吸湿特性。研究结果表明,所有材料的导热系数均随温度的升高而增大,且增大速率都近似相等。影响天然生物质材料导热性质的因素主要有：纤维或多孔固体材料中的导热、孔隙中空气的对流换热,如果温度足够高的话,还有辐射换热。     

高温隔热纤维结构材料绝热特性分析

高温隔热纤维结构的绝热特性是决定金属热防护系统工作性能的关键因素。文中应用有限元法及有限容积法对理想化的纤维结构模型进行了数值研究,得出了纤维结构内部稳态下的温度场、热流场及速度场分布,并在此基础上计算得到纤维结构的等效导热系数,分析了温度、内部气体压力以及纤维结构密度对等效导热系数的影响。所建物理模型和分析方法可行,计算结果与实验结果吻合较好。