风冷压缩单元式空调器节能探讨

从分析风冷压缩单元式空调器的制冷原理入手,提出了两种空气源热泵热水模块＋空气源压缩制冷模块机,为提高能源综合利用效率、节约建筑能耗提供了一定的实践思路。     

Oxidation of ZrC-30 vol% SiC composite in air from low to ultrahigh temperature

Oxidation of ZrC-30 vol.% SiC is investigated in air using furnace and oxyacetylene torch. The microstructure and phase composition of oxide scales are analyzed via SEM, XRD, and Raman. At 800 and 1100 °C, SiC is embedded in the porous and cracked ZrO₂ scales, which have a single-layer structure and are almost non-protective. At 1300 and 1500 °C, the protective effect of oxide scales is enhanced by the formed SiO₂. The scales consist of two subscales, outer and inner layers, during oxidation at 1300 °C for ≥1 h, and 1500 °C for ≥15 min. The growth kinetics of both layers is analyzed. At ∼1700 °C, a new layer is observed between the outer and inner layers, which should contain less carbon than the inner layer. At ∼2100 °C, the oxide scale is porous and contains many big holes. This scale shows a single-layer structure, which mainly consists of ZrO₂.     

Wind effects on flame projection probability from a compartment with opposing openings

This paper investigates flame projection probability from a compartment with opposing openings under assisting wind environment. The effect of external wind on the flow conditions at the door, hot gas velocity at the window and flame projection probability was investigated. Results showed that when the external wind is absent or at low wind velocities, bidirectional flow can be seen at the door. With the increment of the wind velocity, the bidirectional flow will become unidirectional at low fuel supply rate. At high wind velocities, the unidirectional flow can be seen at the door regardless of the fuel supply rate. Correlations for hot gas velocity at the window are formulated based on the mass conservation of the flow in the compartment. The calculated results have a good agreement with the experimental data. Due to fluctuations of the gases ejected from the window, flames eject from the compartment intermittently. The intermittent characteristic of flame ejecting from the compartment is influenced by the temperature and velocity of the hot gas velocity at the window. The model to predict flame projection probability is modified based on previous study without external wind.     

精化齿坯热锻工艺浅析

齿坯闭式模锻锻件分精密级和普通级,但国家标准定义的精密级锻件留有单边加工余量,仍需进行粗车和精车。在精密锻造基础上,研究精化齿坯热锻工艺,以进一步提高锻件精度等级,达到减少单边加工余量,进而使精化齿坯直接用于精车。本文对精化齿坯热锻工艺进行了定义,并明确该工艺单边加工余量的范围。因制坯和预锻是决定精化齿坯热锻工艺质量的关键,因此对其工艺流程和工艺重点进行了分析,同时对满足该工艺的设备和模座进行了论述。     

Effect of hot isostatic pressing (HIP) on Al composite parts made from laser consolidated Al/Fe2O3 powder mixtures

Selective laser melting (SLM) was used to manufacture Al composite parts from Al/5–15 wt%Fe₂O₃ powder mixtures and followed by hot isostatic pressing (HIP) post-treatment, in order to assess the influence of HIP on density, hardness and microstructure. It was found that the HIP post-treatment slightly increased the density, but it failed to efficiently densify the material due to formation of thick oxide bands between solids within SLM process, expanding with increasing the iron oxide. The hardness also decreased after HIP, attributed to high temperature annealing impact of HIP post-treatment on microstructure (such as coarsening, coalescence and transformation of phases). The microstructural phases before HIP were a combination of equilibrium and stable phases (i.e. Al₁₃Fe₄ and α-Al₂O₃) plus phases such as Al₂Fe, AlFe, Fe₃Al, and intermediate-Al₂O₃ (formed in high Fe₂O₃ contents), but only equilibrium and stable phases remained after HIP post-treatment.     

Causes of chatter in a hot strip mill: Observations, qualitative analyses and mathematical modelling

Severe vibrations, known as chatter, occur often in both hot and cold rolling of steel. A recent chatter outbreak at the second stand of hot strip mill in Hastings, Australia, prompted an investigation into the causes of chatter by a literature review, the development and deployment of mathematical models, and a rigorous analysis of plant observations. The investigation suggests that the frictional conditions in the roll gap are the principal cause of chatter in this mill, though residual chatter marks on work rolls can occasionally cause it. The frictional conditions appear to be associated with the thickness and properties of oxide formed on rolls.     

The sticking behavior of an ultra purified ferritic stainless steel during hot strip rolling

During hot rolling of ferritic stainless steels (FSSs), sticking can cause severe surface defects both on work rolls and strips especially for ultra purified FSSs with the total amount of carbon and nitrogen being less than 150 ppm. In the present paper, high temperature oxidization behavior of the ultra purified FSSs was characterized. A new experimental method was invented to simulate the sticking behavior of ultra purified 21%Cr FSS, by which specially designed specimens were hot compressed with different processing parameters to simulate hot strip rolling process. The specimens were surface conditioned prior to the simulation test, either by mechanically polishing or by pre-oxidization to form oxide scales with certain thickness. Observation on the cross-section of sticky regions indicated that cracks had been formed by cyclic heating and cooling during hot deformation had been acting as nucleation sites for sticking particles. The results indicated that oxide scale could avoid the direct contact between roll surfaces and rolled materials to help reducing the sticking occurrence. The temperature region for easy sticking occurrence in the ultra purified 21%Cr FSS has been measured to be from 900 to 1100 °C, which is enlarged as compared to other plain FSSs. The tendency for sticking occurrence decreased with increasing strain rate and decreasing the hammer or work roll surface roughness.     

热等静压机炉内流动传热分析

本文通过数值研究的方法,对热等静压机内的流动与换热情况进行了模拟。通过对炉内复杂几何条件下的建模,采用变物性参数的方法,获得了炉内的温度分布和流动特征。并对炉内快速冷却过程的监控点的变化进行研究。研究结果表明,仿真分析三维模型基本符合需求,网格设计满足仿真分析要求;快冷原理得到初步验证,混合装置结构、原理得到验证,可以进行均匀快速冷却的详细设计和实物验证。     

基于改进的RBF神经网络的热轧板冲击功预报模型

为了对Q345B中厚板的冲击吸收功进行预报并指导生产,采用RBF网络预测冲击吸收功与化学成分、工艺参数、屈服强度及抗拉强度等因素间的关系.针对RBF神经网络的不足,采用改进的遗传算法优化RBF网络结构和权值参数,并建立了基于改进遗传算法的RBF神经冲击功预测模型.实验结果表明,用这种改进的遗传算法优化后的神经网络算法是有效的、可行的.     

几种新型热作模具钢的性能对比研究

利用洛氏硬度计和冲击试验机对SDCM1、SDCM2、SDCM3、SDCM4等4种热作模具钢作硬度和冲击试验,得到了这4种钢的最佳热处理工艺参数。利用BAHR DIL805A相变仪、SDT CM600热重/DSC联用热分析仪、LFA 457激光导热系数测量仪等设备测量了这4种材料的膨胀系数、比热和热扩散系数。结果表明:SDCM3具有最佳的综合力学性能,SDCM4在这4种材料中具有最好的热作模具性能。