堇青石基透波材料的抗热震性能分析

随着微波技术的发展,透波材料成为材料制备领域的研究热点。堇青石具有热膨胀系数低、热导率小、介电常数低、抗热震性能好及化学稳定性好等优点,将其作为微波冶金的承载体材料,满足了微波冶金过程的使用要求和适用条件。采用MgO、Al_2O_3、SiO_2三种原料,同时添加部分纳米SiO_2粉体代替工业SiO_2,在不同的原料配比下微波烧结合成Mg-Al-Si-O系堇青石基透波材料,并测定分析所得样品在未热震前、热震4次及热震8次的测试下,样品的弯曲强度及抗热震性能的变化。     

Dynamic Behavior of Thermal Stress in a Functionally Graded Material Thin Film Subjected to Thermal Shock

In the present article, a one-dimensional dynamic thermoelastic problem in a functionally graded material (FGM) thin film subjected to a thermal shock loading is analyzed. An exact analytical solution is obtained by employing techniques of the space-variable transformation and Laplace transform, in the case where variations in material properties of the FGM thin film are expressed as exponential functions of the space-variable. Numerical calculations for time histories of thermal stresses have been carried out. Obtained numerical results reveal that the thermal stress oscillation is unsteady when the mechanical impedance depends on the space-variable, whereas it is monotonic and periodic when the impedance is independent of the space-variable. The factor which causes the different behavior of the thermal stress oscillations is also investigated based on the analytical and numerical results.     

活塞热冲击问题理论分析

摘要本文依据活塞受热特点,以R M Morse和H Feshbach提出的双曲线型导热方程为基础,建立了一种分析活塞热冲击问题的数学模型,并利用拉普拉斯变换对其进行求解.文中以PA6-280柴油机活塞为例,对热冲击期间活塞表面一层内的温度及热应力的变化规律做了较详细的分析.计算结果表明:活塞在热冲击期间表现的温度及热应力的动力学效应是必须加以考虑的.     

DQM-Based Thermal Stresses Analysis of a Functionally Graded Cylindrical Shell Under Thermal Shock

The transient thermal stresses of a functionally graded (FG) cylindrical shell subjected to a thermal shock are investigated. The dynamic temperature fields of FG shells are obtained by using the Laplace transform and power series method. The differential quadrature method is developed to obtain the transient thermal stresses by solving dynamic governing equations in terms of displacements. The effects of the material constitutions on the transient temperature and the thermal stresses are analyzed in the cases of obverse thermal shock and reverse thermal shock. It turns out that the thermal stresses could be alleviated by means of changing the volume fractions of the constituents.     

基于冷热冲击性能的新型散热器主片设计和优化

为了在现有生产设备和工艺条件下提高散热器主片的耐冷热冲击性能,分析了散热器失效模式,设计了新型T型结构主片并通过有限元分析(FEA)进行结构和工艺优化,使得散热器耐冷热冲击的周期得到了大幅度提高,同平直主片相比寿命提高了66%,对乘用车散热器可靠性研究提供了好的借鉴。     

一种新型多层反射型保温结构材料

作者对多层反射型保温结构材料应用于不同场合时的保温性能进行了深入分析计算,并将此结构的技术经济性能与常规保温材料进行了比较,结果表明,此新型保温结构具有更优的综合技术经济性能。     

水膜式热力除氧器的改造

对除氧头主要内件－－起膜管的试验进行分析,论证了起膜管的最佳结构型式。针对水膜式热力除氧器运行中存在的问题,提出了改造的具体实施方法,为电厂水膜式热力除氧器的改造提供了新思路。     

热膜式气体质量流量计设计

介绍能够测定空气质量流量,且可自动补偿温度及压力变化对空气流量影响,测量精度高的热膜式气体质量流量计的原理、构造和性能。这种流量计可以满足各种发动机进气流量测量,特别是排放测试的需要。     

深度冷热冲击条件下工程机械用柴油机的可靠性研究

以某型工程机械用柴油机为研究对象,采用深度冷热冲击方法进行了柴油机可靠性试验,测量了零部件磨损情况,考察了柴油机的燃油消耗量、功率、扭矩、活塞漏气量、润滑油消耗等参数的变化规律,分析可靠性试验过程中柴油机最低油耗区的迁移规律。研究结果表明,冷热冲击试验后,柴油机转速为1500r/min时的燃油消耗率上升约5g/k W·h,标定工况点燃油消耗率约上升3g/(k W·h);各工况下柴油机功率和扭矩均有所下降;随着试验时间的延长,各工况下柴油机的活塞漏气量均有所上升,柴油机的润滑油消耗呈先上升再下降,然后逐步缓慢下降的趋势;柴油机的最低油耗区分布在转速1600~2100r/min范围内的中等负荷区域,最低油耗区的覆盖面积缩小。     

活塞热冲击集总参数模型的随机温度分析

将随机过程理论与热传导理论相结合，分析了内燃机随机热冲击的随机成分对活塞温度场的影响，建立了热冲击试验台加热环境相适应的矩形热冲击模型和集部参数导热模型，求得了相应的解析解，并利用迭代法求得其随机解及其均值，均方值和方差。在试验台上的活塞温度场测试结果表明随机热激励模型可以更精确地模拟活塞的受热响应。集总参数模型给出了活塞随机温度随时间变化的基本规律，为定性分析活塞温度场随机变化规律提供了依据。     

Numerical Thermal Analysis of Applying Insulation Material to Holes in Hollow Brick Walls by the Finite-Volume Method

A numerical study by self-programming three-dimensional software which can efficiently deal with complicated heat transfer is conducted to investigate the effect on the thermal performance of pasting 10 mm insulation around holes in external walls constructed from 240 × 115 × 90 mm hollow bricks. A comprehensive parametric investigation includes varying the arrangement of holes, insulation, or building materials. The results show that adopting this method can markedly reduce the equivalent thermal conductivity by between 20.3 and 61.1%, and choosing higher-thermal resistance mortar or hollow brick material achieves better insulation performance whereas the optimum configuration of hollow bricks is barely affected.