Stress distributions in a horizontal pressure vessel and the saddle supports

This paper presents analysis results of stress distributions in a horizontal pressure vessel and the saddle supports. The results are obtained from a 3D finite element analysis. A quarter of the pressure vessel is modeled with realistic details of saddle supports. In addition to presenting the stress distribution in the pressure vessel, the results provide details of stress distribution in different parts of the saddle separately, i.e. wear, web, flange and base plates. The effect of changing the load and various geometric parameters is investigated and recommendations are made for the optimal values of ratio of the distance of support from the end of the vessel to the length of the vessel and ratio of the length of the vessel to the radius of the vessel for minimum stresses both in the pressure vessel and the saddle structure. Physical reasons for favoring of a particular value of ratio of the distance of support from the end of the vessel to the length of the vessel are also outlined.     

Dominant frequency of pressure drop signal as a novel diagnostic tool for the water removal in proton exchange membrane fuel cell flow channel

In this work, a transparent assembly was self-designed and manufactured to perform ex situ experimental study on the liquid water removal characteristics in PEM fuel cell parallel flow channels. It was found that the dominant frequency of the pressure drop across the flow channels may be utilized as an effective diagnostic tool for water removal. Peaks higher than 1 Hz in dominant frequency profile indicated water droplet removals at the outlet, whereas relatively lower peaks (between 0.3 and 0.8 Hz) corresponded to water stream removals. The pressure drop signal, although correlated with the water removal at the outlet, was readily influenced by the two phase flow transport in channel, particularly at high air flow rates. The real-time visualization images were presented to show a typical water droplet removal process. The findings suggest that dominant frequency of pressure drop signal may substitute pressure drop as a more effective and reliable diagnostic tool for water removal in PEM fuel cell flow channels.     

Experimental study on the two phase flow behavior in PEM fuel cell parallel channels with porous media inserts

In this study, the air–water two phase flow behavior in PEM fuel cell parallel channels with porous media inserts was experimentally investigated using a self-designed and manufactured transparent assembly. The visualization images of the two phase flow in channels with porous media inserts were presented and three patterns were summarized. Compared with the traditional hollow channel design, the novel configuration featured less severe two phase flow mal-distribution and self-adjustment to water amount in channels, although a higher pressure drop was introduced due to the porous media inserts. The dominant frequency of pressure drop signal was found to be a diagnostic tool for water behavior in channels. The novel flow channel design with porous media inserts may become a solution to the water management problem in PEM fuel cells.     

Performance evaluation of flattened tube in boiling heat transfer enhancement and its effect on pressure drop

An experimental investigation has been carried out to study heat transfer and pressure drop characteristics of R-134a flow boiling inside a horizontal plain tube and different flattened tubes. Round copper tubes with an inner diameter of 8.7 mm were flattened into an oblong shape with an internal height of 6.6 mm, 5.5 mm, 3.8 mm, and 2.8 mm. The test apparatus was basically a vapor compression refrigeration system equipped with all necessary measuring instruments. Analysis of the collected data showed that, by flattening the round tube, the heat transfer coefficient and pressure drop increased simultaneously. The performance of these tubes from the point of view of heat transfer enhancement and pressure drop increasing were evaluated. It was concluded that, the tube with an internal height of 5.5 mm has the best performance compared with the other flattened tubes. Finally, based on the present experimental pressure drop data, a correlation was developed to estimate the pressure drop in flattened tubes. This correlation predicts the experimental data of the present study within an error band of ± 20%.     

复合激光诱导荧光定量标定技术及其对喷雾特性研究的应用Ⅱ:喷射参数和环境参数对喷雾特性的定量分析

在改变喷射控制参数和环境参数的喷雾特性研究中,应用定量标定的试验结果深入开展了喷油压力、喷孔孔径、环境密度和环境温度对喷雾各个特性参数影响的研究。研究中发现,提高喷射压力能提高喷雾动能,加速液相喷雾的破碎、促进液相蒸发形成气相喷雾,提高贯穿速率,有利于喷雾的扩散和蒸发。小孔径的喷油嘴,虽然能够减少贯穿距离,但也同时减弱了喷雾和空气的混合空间范围;由于小孔径促进了喷雾的破碎和蒸发,气相喷雾分布均匀程度明显提高。环境密度高的条件下明显减小了喷雾的贯穿距离,这样虽然导致喷雾的扩散速率降低,但由于单位体积内气体量的大幅增加,加快了环境气体和喷雾之间的互相作用,更容易形成气相。环境温度对喷雾的蒸发速率起关键作用,液相喷雾贯穿距离随温度升高而减小,同时,气相最大当量比出现时间提前,这些说明环境温度升高,加速了环境气体和喷雾间的热交换,提高了喷雾的蒸发速率,最终促进气相快速形成。     

100 t顶吹转炉三维可压缩流场的数值模拟

通过利用Fluent流体软件及标准κ-ε方程模型,研究氧气压力(11.46×10⁵Pa和6.88×10⁵ Pa)及氧枪位置(1.2~1.5 m)对钢厂100 t顶吹转炉氧枪射流特性及钢液表面冲击的影响。结果表明,随氧气压力的增大,氧气在转炉内高速区范围变大,射流核心段长度变长,且气流的压能增加;氧气压力为11.46×10⁵Pa时,当枪位由1.2 m提到1.5 m时,钢液表面氧气流最大冲击速度由240 m/s降低至194 m/s,高速区面积减少,钢液凹坑深度由0.37~0.43 m降至0.30~0.36 m,同时凹坑最大直径由0.70~0.80 m增至0.80~0.95 m。     

致密砂岩气藏水相圈闭损害自然解除行为研究

致密砂岩气藏的高毛细管力及强水湿性使其易产生水相圈闭损害,影响气藏及时发现、准确评价及经济开发。目前消除水相圈闭的物理化学方法,由于可能诱发其他储层损害,应用尚受到限制。选取鄂尔多斯盆地渗透率小于0.1×10^-3μm²、介于(0.1~0.3)×10^-3μm²之间和大于0.3×10^-3μm²的致密砂岩岩样,利用氮气在恒定高压差与递增压差驱替原地有效应力下饱和模拟地层水岩样的实验,揭示致密砂岩水相自然返排行为。结果表明：随着时间增加,含水饱和度逐渐下降,渗透率越高,含水饱和度降低幅度越大,残余水饱和度越低;渗透率介于(0.1~0.3)×10^-3μm²之间的岩样,在前150h递增驱替比恒定高压差驱替含水饱和度降低慢,但水相返排率更高。分析表明,致密砂岩水相圈闭损害严重,孔隙结构、渗透率和压力梯度是影响水相返排的重要因素,孔喉非均质性强的储层宜采用递增压差驱替的方式;水相返排过程包括驱替和蒸发2个阶段,当气相在不同孔喉中形成渗流通道后,可适当提高压差加速水相蒸发。     

综采工作面坚硬顶板管理

针对井田内煤层顶板坚硬、难冒落的特点,介绍了爆破放顶和压力注水弱化顶板两项措施,通过对两种处理坚硬顶板的效果及优缺点比选,提出了适合同晟达煤业公司的最优顶板管理方法,可为具有该类顶板的矿井在顶板控制方面提供一定的参考和借鉴.     

浅谈综采工作面压力观测与预防

汾西矿业集团新柳矿403综放工作面由于顶板来压、地板鼓起等矿压显现,已严重制约了正常生产.探讨了应做好工作面压力检测工作,以降低矿山压力显现带来的危害,确保工作面安全.掌握顶板状况观测统计的内容和衡量指标,及时采取措施,就能预防工作面顶板压力显现带来的危害.     

反应堆压力容器承压热冲击分析研究

依据RCC-M规范和美国NRC 10CFR50.61,对存在假想裂纹的反应堆压力容器堆芯带区进行承压热冲击分析研究.计算核电厂寿期末的基准温度,并采用承压热冲击筛选准则进行评定;计算了承压热冲击瞬态作用下裂纹尖端的应力强度因子,并按RCC-M规范进行评定.