尾水管高度和宽度对水轮机水力性能的影响

针对不同高度和宽度的尾水管,通过分析其内部水流的流动情况,论述了高度和宽度对尾水管设计的重要性,同时采用CFD分析和模型试验的方法来确定尾水管高度和宽度对水轮机水力性能的影响。     

Boiling hysteresis at low temperature on enhanced tubes

The boiling hysteresis phenomenon is studied for a real scale enhanced evaporator tube (2 m long Turbo-B type) with R134a refrigerant used in the flooded evaporator of a centrifugal brine chiller for the ice-making facility. Unlike previous studies of the boiling heat transfer with uniform heat flux and uniform wall temperature, the wall temperature varies along the tube in the present experiment. To see if the similar hysteresis occurs as in the case of uniform wall temperature, a careful control of refrigerant temperature and heat flux is made. We have found hysteresis of the temperature overshoot (TOS) at the onset of nucleate boiling initially at the inlet section of the tube, before it gradually moved downstream section of the tube until the nucleate boiling occupied the whole section of the tube as the inlet temperature increased. The hysteresis became stronger at low refrigerant temperatures. The decreasing trend of heat flux after the contents of the whole tube boiled was different from the increasing trend. This paper provides a guideline how to design the evaporator in order to avoid the abnormal operation of the chillers.     

Reasons for drop in shell-and-tube condenser performance when replacing R22 with zeotropic mixtures. Part 1. Analysis of experimental findings

An experimental and theoretical investigation was made to find out the reasons for the drop in shell-and-tube condenser performance when replacing R22 with a zeotropic mixture R407C. Measurements show that at lower condenser loads the reduction in performance can be as large as 70% compared to the full condenser load. Calculation results are compared with experimental results for two different condensers, one with micro-finned tubes and one with 3-D finned tubes. Calculations show that the degree of mixing of the newly formed condensate on a tube and the drained condensate is a factor influential enough to explain the performance drop. 3-D finned tubes seem to have better mixing in the condensate than integral finned tubes.     

PIV测试水轮机尾水管锥管流场

介绍了PIV(ParticleImageDisplacementVelocimetry ,简称PIV)的工作原理 ,以尾水管为研究对象 ,采用PIV技术详细测量了在某些工况下尾水管的内部流场 ,给出了观测面的测量结果。     

Experimental study of the gravity effect on the distribution of refrigerant flow in a multi-pass condenser

Gravity in multi-pass condensers affects the refrigerant flow rate distribution, owing to the gravitational pressure drop that occurs mainly in the U-bend tubes in fin and tube condensers with horizontal tubes. This effect was studied using an experimental approach. A condenser with two ‘nU’ circuits was selected, and the temperature variation of the refrigerant side was measured and compared along each circuit. The critical air velocity, which indicated the initiation of the gravity effect, was found for a given refrigerant flow rate. As the air velocity increased beyond the critical air velocity, the gravity effect (or mal-distribution of the refrigerant flow) developed further. Similarly, the critical refrigerant flow rate was also determined for a given air velocity. As the refrigerant flow rate decreased below the critical refrigerant flow rate, the gravity effect also developed further. The gravity-affected region was shown in the table with rows of air velocities and columns of refrigerant flow rates, and expressed using a single parameter for a given refrigerant flow circuit.     

双动铝挤压机液压定针控制技术

介绍了双动卧式铝挤压机液压定针系统的结构、工艺流程及其自动控制系统。该控制系统响应快,定针精度高,具有很高的可靠性。目前该液压定针控制系统已应用于实际生产,定针控制精度≤1mm,完全满足工艺要求,对后续同类产品的设计起到了借鉴作用。     

高压换热器爆管的原因分析

对高压换热器爆管样品进行化学成分、力学性能、腐蚀产物和金相的检验,分析裂纹形成的原因。裂纹的产生是由应力腐蚀引起的。产生应力腐蚀有两个原因,一是换热管在制造过程中有磨损,表层形成形变马氏体。二是换热管弯管成形后弯管段消除应力热处理不彻底。     

纺织子管应用模式的应用研究

简要介绍了纺织子管技术的特点,详细阐述了纺织子管空管、叠加、小纺织管等应用模式的具体应用及应用时需注意的有关问题,并通过应用案例进一步阐述了纺织子管技术的优越性。     

Optimal design of a light commercial freezer through the analysis of the combined effects of capillary tube diameter and refrigerant charge on the performance

In this work, a discussion on a methodology to optimize the performance of a commercial freezer by using a simulation tool is presented. In order to provide a practical tool for deciding the best combination of refrigerant charge and capillary tube diameter, the results of the numerical studies are shown in the form of two-dimensional maps. The usefulness of this type of representation lies in the possibility of selecting the best operating point of the system, taking into account not only the efficiency or the power consumption but also the technical constrictions imposed by parameters such as the suction line temperature, the condenser subcooling, the evaporator superheat, and the run-time ratio. The discussion leads to the conclusion that the useful performance map is drastically reduced when all the operation requirements must be satisfied. Once the system design had been optimized, an additional numerical study, aimed at identifying the influence of the external conditions on the system behavior, was performed. The results show that the performance reduction can be effectively minimized modifying the refrigerant charge.     

管束式集装箱的组装工艺和型式试验要求

大容积无缝钢瓶、管柬式集装箱和长管拖车作为专用气体储运装备在我国使用和制造已有10年时间，在检验检测和安全监管方面已基本形成相应的安全规范，但设计制造缺乏标准支撑。本文对管柬式集装箱的设计制造资质、组装工艺和型式试验要求进行简要介绍，包括大容积无缝钢瓶和长管拖车的相应要求。