USED CARS测量对撞式扩散火焰的温度分布

介绍了用USED CARS技术测量对撞式甲烷/空气扩散火焰前滞止区和尾流区的温度分布剖面。在滞止区富甲烷边观察到甲烷燃烧前的热解过程;尾流区温度高于滞止区温度,表明在滞止区有未完全燃烧的中间产物存在,在尾流区发现C2及CH的光谱也证明了这一点。     

Improvement of the Fatigue Properties of Investment-cast Steels as a Result of HIPing

Abstract

Two alloys, a ferritic stainless steel, 17/4PH, and a 3% CrMo low alloy steel, CLA3, were produced as investment-cast bars, processed in air. For each alloy, half the number of bars were heat-treated and machined to provide rotating bend fatigue test pieces. The others were HIPed and heat-treated before preparation of the test pieces. Tensile tests and a limited metallographic examination were carried out. The results show that HIPing gives considerable improvements in tensile ductility and fatigue strength, as judged by the Fatigue Endurance Ratio (FER). For the 17/4 PH alloy, a FER of 0.42 was obtained, whilst for the CLA3 alloy, the FER was 0.47, each about 90% of the wrought state value. HIPing also reduced the scatter in the test results. For interest, the results are compared with those obtained during a recent NEL/BICTA project.     

DESIGN AND CONTROL OF AN ULTRAPRECISION STAGE USED IN GRATING TILING

In petawatt laser system, the gratings used to compose pulse compressor are very large in size which can be only acquired currently by arraying small aperture gratings to form a large one instead, an approach referred to as grating tiling. Theory and experiments have demonstrated that the coherent addition of multiple small gratings to form a larger grating is viable, the key technology of which is to control the relative position and orientation of each grating with high precision. According to the main factors that affect the performance of the grating tiling, a 5-DOF ultraprecision stage is developed for the grating tiling experiment. The mechanism is formed by serial structures. The motion of the mechanism is guided by flexure hinges and driven by piezoelectric actuators and the movement resolution of which can achieve nanometer level. To keep the stability of the mechanism, capacitive position sensors with nanometer accuracy are fixed on it to provide feedback signals with which to realize closed-loop control, thus the positioning precision of the mechanism is within several nanometers range through voltage control and digital PID algorithm. Results of experiments indicate that the performance of the mechanism can meet the requirement of precision for grating tiling.     

Numerical simulation of quenching of large sized blocks of 718 steel used for plastic dies

Abstract

The 718 steel used for plastic dies is required to be prehardened to 29 – 35HRC. For large sized blocks, it is relatively difficult to additionally guarantee uniform hardness with the greatest hardness difference of 3HRC and without any quenching cracks after heat treatment. In this paper, the transient temperature field and microstructure transformation during the quenching process of large sized blocks of 718 steel have been simulated numerically. Based on the simulation and experimental results, an appropriate quenching process, that is, direct air cooled quenching after austenitising at higher temperatures such as 880 – 930°C, was recommended in order to reach hardness uniformity and avoid quenching cracks.     

EXPERIMENTAL RESEARCH AND DESIGN ON HEAT TRANSFER OF EVAPORATOR USED IN THE LARGE QUICK FREEZE PLANT

The evaporator is the main part of a quick-freeze equipment. There are many factors influencing the heat transfer coefficient of an evaporator. The most important factors among them are the fin shape, tube diameter, distance of fin space, frost, and velocity of air flow etc. They mainly influence the thermal efficiency of an evaporator, and therefore its thermal efficiency has direct relationship with the whole efficiency of the quick freeze plant. Evaporators with different structural types have different heat transfer efficiency. In order to obtain high efficiency structure of evaporator, 8 evaporator models with different fin shape, tube diameter and tube arrangement are analyzed and compared. The calculation results show that the integral waved fins, equilateral-triangle arranged small diameter tubes and varying fin-spacing has the highest heat transfer coefficient. The experimental result also shows that the evaporator with this type of structure has better thermal efficiency. The experimental result is in good agreement with the calculation result. It can instruct engineering design for usual designer. A real quick-freeze equipment is designed and put into production. The result shows that, compared with traditional domestic quick-freeze equipments, this equipment decreases by 40% in size and by 20% in energy consumption.     

用单次脉冲非稳腔空间增强探测CARS技术测量火焰温度

采用宽带相干反斯托克斯拉曼散射(CARS)技术测量了甲烷-空气预混火焰温度场分布,并分析了温度测量的不确定度.建立的宽带CARS实验系统采用非稳腔空间增强探测(USED)相位匹配构造,其横向空间分辨率约0.1 mm,纵向空间分辨率约3 mm,该系统能实现10 Hz重复频率测量火焰瞬时温度.采用宽带非稳腔空间增强探测CARS在甲烷-空气预混火焰中获得了单次激光脉冲的高信噪比氮气Q支CARS实验谱,用CARS理论计算软件拟合理论谱和实验谱确定了预混火焰的温度随高度的分布,采用单次激光脉冲的氮气Q支CARS实验谱测量火焰温度的不确定度小于5%.