形状记忆复合材料可展桁架在轨热分析

传统星载桁架结构需通过驱动器实现展开/收拢动作,应用形状记忆复合材料可突破该限制。对新型可展桁架各组件进行热控方案设计,基于I-DEAS/TMG软件建立热分析数值模型,对桁架各组件在轨外热流以及温度场变化进行计算分析。结果表明:最外端桁架在轨运行4个周期后其温度场呈周期性变化特征;不同多层隔热材料(multi-layer insulation material,MLI)表面辐射特性对内/外端纵杆温度影响明显;热控方案能实现有效的在轨温度控制。     

隔热材料导热系数的数值模拟预测

对氧化锆空心球隔热材料进行合理的简化,用数值模拟方法计算氧化锆空心球隔热材料导热系数,并分析空心球半径、温度、发射率等对导热系数的影响。数值模拟结果表明,减小空心球半径,降低空心球表面发射率,抽真空等都有助于降低隔热材料导热系数。数值模拟与实验测量结果良好吻合,用数值模拟计算隔热材料导热系数是一个行之有效的方法。     

屏片间自身辐射的交换所产生的热负荷分布不均匀性

本文对锅炉屏式过热器管片自身辐射的分配规律进行了研究,通过分析否定了屏片间自身辐射的交换对屏的热偏差和壁温没有影响的观点,提出了计算屏片自身辐射投射到相邻屏片的入射热负荷分布的等温模型。最后绘出了工程尺寸范围内屏自身辐射投射到相邻屏片的入射热负荷分布曲线。     

形状记忆可展桁架在轨热变形分析研究

本文借助I-DEAS软件建立了针对形状记忆可展桁架的热-结构耦合分析模型,并试验验证了分析模型的准确性。在此基础上,采用多层隔热复合材料作为热控措施,计算分析有/无热控措施及预紧力大小对桁架温度与热变形的影响。结果表明,包覆多层隔热材料效果明显,可将桁架在轨周期内的温度差减小85%,位移差减小80%,有利于对可展桁架进行温控,实现展开与收拢,减小运行期间振动的影响。桁架变形大小由预紧力和热应力共同决定,随着预紧力增大,桁架位移差逐渐减小。     

多层反射型保温结构热经济性优化

通过分析间距对多层圆筒反射型保温结构散热损失及当量导热系数的影响 ,计算了不同条件下散热损失最小的间距分布 ,得出了最佳间距分布 ,提出了多层圆筒型反射型保温结构的优化变间距分布布置设想。与等间距结构对比 ,这种新型结构可进一步改善隔热保温效果 ,提高热经济性     

高周波活塞热冲击计算与分析

本文用6150柴油机燃气温度拟合成三角形热冲击模式，作为活塞顶面的热激励源，建立了高周波三角形热冲击及集总参数导热模型，计算该活塞顶面温度响应曲线及其变化规律，以作为活塞顶面热疲劳分析和研究的基础。     

隔热材料导热系数预测及其在发动机排气管隔热中的应用

由于排气管隔热在特种车辆中的重要性,在对排气管隔热方案分析的基础上,采用大型通用CFD软件STAR-CD,模拟氧化锆空心球隔热材料的导热系数,并对排气管真实的流固耦合模型进行大量的数值模拟试验。数值模拟可以分析隔热结构中隔热材料厚度、表面发射率、隔热方式等因素对排气管隔热效果的影响;通过隔热材料与真空层的匹配,得到既满足紧凑性要求,又能高效隔热的排气管隔热方案。     

ISP工艺中卷取箱内板卷导热数学模型的研究

依据ISP工艺中卷取箱内板带的表面特性、板带厚度和板间接触压力对板卷径向热量的传递有较大影响,建立了能真实反映该影响因素的板带间径向等效导热系数计算模型,并建立了适用于求解为非连续介质的板卷导热数学模型。通过对模型的模拟求解,计算分析了板卷热过程,板卷最大温差为12℃,满足轧制工艺的要求,并为计算分析箱内热过程提供理论依据。     

蜂窝型透明隔热材料有效导热系数的实验研究

用一套简易有效的实验装置测定了三种透明隔热材料的有效导热系数，并与通用计算模型进行对比，两者符合较好，验证了实验方法和通用计算模型的有效性。     

竖直双U型埋管地热换热器支管间热短路分析

采用地热换热器准三维传热模型和数值计算的方法,对竖直双U型埋管地热换热器支管间的热短路进行了分析,讨论了管间距和回灌材料的导热系数对热短路的影响,并提出了减少热短路的措施。     

The influence of inner material with different average thermal conductivity on the performance of whole insulation system for liquid hydrogen on orbit storage

At present, several composite insulation systems were proposed that can be used for passive insulation systems, including foam-variable density multilayer insulation (VDMLI), aerogel-VDMLI and hollow glass microspheres (HGMs)-VDMLI. The passive insulation systems with different inner material (IM) showed different performances. However, the relationship between the average thermal conductivity of IM and the insulation performance of the whole system has rarely been investigated. It is of great significance for efficient configuration and matching of the passive insulation system. In this paper, a series of average thermal conductivity of IM were assumed to predict the insulation performance of the whole system at 20 K–300 K and high vacuum. In order to further illustrate the relationship between IM and MLI/VDMLI, the foam was replaced by the HGMs as 5 mm a unit forming a series of HGMs-foam-MLI/VDMLI insulation systems. The performance of the systems was investigated. After the foam was completely replaced by the HGMs, the performance of MLI and VDMLI systems was improved 33% and 13%, respectively. Moreover, each mode of heat transfer including solid conduction, radiation, and gas conduction for foam-MLI/VDMLI and HGMs-MLI/VDMLI insulation systems were calculated and analyzed.     

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.     

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.     

Heat transfer through woven textiles

A mathematical model based on the principles of heat transfer to predict the thermal resistance of fabrics has been presented in this paper. The woven fabric is considered as a system of porous yarns, interlacements between warp and weft yarns and air pores and all the basic weaves can be depicted by this system. The conduction and radiation heat transfer together, was calculated based on the construction parameters of the fabric. The thermal insulation, which is equivalent to the thermal resistance, was predicted with the help of these parameters. The total heat transfer by conduction through each part was calculated using Fourier’s equation. Radiation heat transfer through the air pore was calculated with the help of net radiation method. Linear anisotropic scattering was used to model the radiation heat transfer through fibrous media. The total thermal resistance obtained was validated with actual values obtained from a standard thermal resistance measuring instrument.     

Modeling of Thermal Properties of Thermal Insulation Layered with Transparent,Opaque and Reflective Film

The popular and effective food preservation technology based on refrigeration is not sufficient for high-quality products while undergoing logistic operations (transport and retail). One of the basic factors that affects the quality of chilled and frozen food products during storage and transport is packaging. A protective function of packaging strongly depends on the material used and its composition. There are different kinds of thermal insulation used for food packaging. One of them, proposed by the authors is a multilayer structure of insulation made of rectangular air cells. The insulation can be prepared by means of plastic film featuring various properties. The paper presents how to improve an effective material designed for food freezing and transport aiming to enhance its thermal resistance through the application of different transparency, reflectivity and emissivity of the film. Mathematical model based on heat exchange equations, including conduction, convection and radiation throughout a number of parallel internal sheets of film of multilayer structures was proposed. Thermal properties depending on different transparency, reflectivity and emissivity of the film were analyzed. The model was verified experimentally showing its compatibility and obtaining a significant influence of thermal resistance according to the type of film used to make air structures, the number and thickness of its layers as well as the gaps between internal folds. For multi-layer insulation designed for the insulation of packed frozen food in the shape of a rectangle, it was recommended to apply film transmittance as small as possible for the internal parts of the structure.     

The research applications of new heat insulation composite material in automobiles

With the rapid development of its unique advantages, nonwoven fabric has become the leading material of automotive textiles. Nonwoven fabric has become an ideal material for automobiles and replaced traditional textiles and plastic products. This paper takes a car as the research model. A DRL‐2B thermal conductivity tester was used to test thermal conductivity of the material based on the plate method. Material systems and structures of new types of heat insulation composite materials were determined according to test results and the theory of heat transfer. Then, the final new type of heat insulation material was determined by calculating and comparing average heat transfer coefficients and heat transfer between traditional insulation materials and new types of heat insulation materials. The calculated results were verified by experiments in this paper. All the test results show that the new type of composite insulation material is significantly better than traditional insulation materials, and the test results match the calculated results.     

Thermomechanical Coupling of non-Fourier Heat Conduction with the C-V Model: Thermal Propagation in Coating Systems

A coupled thermomechanical model is established for multilayered structure subjecting to heat deposition, and specified for a thermal barrier system. The thermomechanical interaction including the C-V (Cattaneo–Vernotte) model of heat conduction law for the homogeneous linear thermoelastic material is developed, in which the Non-Fourier heat conduction law and the influence of stress and strain to heat transfer are taken into account. The variation of thermal stress with the heat wave due to the coupled relationship is quite significant. Under a pulse heat deposition on the surface, a model thermal barrier system's (trilayer structure) transient thermal and stress fields are investigated. The result indicates that a high tensile stress is developed, especially near the interface between ceramic coating and oxide layer, which is the most likely damage region, and the failure mechanism is related to the propagation of the coupled thermal-mechanical wave. The maximum stress in the oxide layer is affected by the size of material system.     

Numerical and experimental investigation on the thermal insulation performance of low temperature cold box

A new modeling method with the discrete ordinate (DO) model and GKT model was proposed to simulate the thermal insulation performance of a low temperature cold box. Experimental data from the thermal insulation experiment of a cold box were used to validate the model. The thermal insulation performance and the coupled radiation and conduction heat transfer were analyzed at various pressures, shield numbers and shield positions. The results confirmed that the thermal insulation performance can be significantly improved by the addition of a thermal insulation shield. It was found that the effects of shield position on the thermal insulation performance are different at lower pressure (<3 × 10^− 2 Pa) from higher pressure. A practical application was presented by the usage of the new model in analyzing the performance of the cold box in a cold neutron source. A composite thermal insulation method was proposed to reduce the cold loss by 18.3% and 9% respectively compared with those with the aluminum foil wrapping and shield insulating methods.     

Thermal performance of a non-air-conditioned building with PCCM thermal storage wall

This paper presents a time-dependent periodic heat transfer analysis of a non-air-conditioned building having a south-facing wall of phase-changing component material (PCCM). A rectangular room (6 × 5 × 4 m) based on the ground is considered. The effects of heat transfer through walls and roof, heat conduction to the basement ground and furnishings, heat gain through window and heat loss due to air ventilation have been incorporated in the periodic time-dependent heat transfer analysis. The time-dependent heat flux through the PCCM south-facing wall has been obtained by defining the effective thermal properties of the PCCM for a conduction process with no phase change. Numerical calculations are made for a typical mild winter day (7 March 1979) at New Delhi for heat flux entering through the wall and inside air temperature. Further, a PCCM wall of smaller thickness is more desirable, in comparison to an ordinary masonry concrete wall, for providing efficient thermal energy storage as well as excellent thermal comfort in buildings.     

Comparison of vacuum glazing thermal performance predicted using two- and three-dimensional models and their experimental validation

Thermal performance of vacuum glazing predicted by using two-dimensional (2-D) finite element and three-dimensional (3-D) finite volume models are presented. In the 2-D model, the vacuum space, including the pillar arrays, was represented by a material whose effective thermal conductivity was determined from the specified vacuum space width, the heat conduction through the pillar array and the calculated radiation heat transfer between the two interior glass surfaces within the vacuum gap. In the 3-D model, the support pillar array was incorporated and modelled within the glazing unit directly. The predicted difference in overall heat transfer coefficients between the two models for the vacuum window simulated was less than 3%. A guarded hot box calorimeter was used to determine the experimental thermal performance of vacuum glazing. The experimentally determined overall heat transfer coefficient and temperature profiles along the central line of the vacuum glazing are in very good agreement with the predictions made using the 2-D and 3-D models.