Gas pockets in a wastewater rising main: a case study.
This paper presents a case study of an existing wastewater rising main (WWRM) in which an extreme transient event produced by simultaneous power failure of the pumps caused the rupture of a 1.2 m (48 in) prestressed concrete cylinder pipe (PCCP), causing an important leakage of sewage. The event and the methodology followed in order to validate the diagnostics of the failure are described. The detail study included in situ observation of the system, experimental investigation in a setup, hydraulic analysis, as well as details of the structural strength of the WWRM. After the extensive investigation and several simulations of fluid transients for different scenarios and flow conditions, it was found that stationary small gas pockets accumulated at high points of the WWRM were identified as the principal contributory factor of the failure. This case study serves as clear warning of the consequences of operating a WWRM with gas pockets at its high points.
Investigation on critical equilibrium of trapped air pocket in water supply pipeline system
A trapped air pocket can cause a partial air lock in the top of a hump pipe zone. It increases the resistance and decreases the hydraulic cross section, as well as the capacity of the water supply pipeline. A hydraulic model experiment is conducted to observe the deflection and movement of the trapped air pocket in the hump pipe zone. For various pipe flow velocities and air volumes, the head losses and the equilibrium slope angles are measured. The extra head losses are also obtained by reference to the original flow without the trapped air pocket. Accordingly, the equivalent sphere model is proposed to simplify the drag coefficients and estimate the critical slope angles. To predict the possibility and reduce the risk of a hump air lock, an empirical criterion is established using dimensional analysis and experimental fitting. Results show that the extra head losses increase with the increase of the flow velocity and air volume. Meanwhile, the central angle changes significantly with the flow velocity but only slightly with the air volume. An air lock in a hump zone can be prevented and removed by increasing the pipe flow velocity or decreasing the maximum slope of the pipe.中文概要目 的输水管道的驼峰气阻是指由于管路高峰位置的滞 气作用使气体不断聚积在峰顶附近、产生的气体 阻碍水流的局部水力现象。它能够导致管路过水 断面减小、输水能耗增加、输送效率降低和管路 压力振荡等后果, 严重威胁海底管道输水的稳定 性和安全性。本文旨在分析滞留气团在供水管道 中的力学平衡、能量损失、移动和溢出机理, 研 究水流流速对气团的推移特性, 提出预测和消除 驼峰气阻的方法, 使输水管道免受驼峰气阻的危 害, 提高输水管道的供水效率。创新点1. 设计了具有连续坡角变化的圆弧形驼峰管道实 验, 该实验可以定量模拟气团体积和平衡角度; 2. 建立了驼峰气阻的水头损失经验公式和恒定 流情况下驼峰气阻的管道坡角和流速的对应关 系式, 可用于预测和消除驼峰气阻的危害。方 法1. 通过驼峰气团的受力特性分析, 获得满足量纲 和谐的力学平衡方程; 2. 采用试验观察和测试获 得有无气泡情况下的水头损失和平衡状态下的 坡角, 通过等价球体方法对测试数据进行无量纲 拟合, 获得气阻的水头损失方程系数, 并通过流 速和平衡坡角建立恒定流情况下的临界平衡方 程; 3. 基于试验拟合获得临界平衡方程, 建立预 测和评估气阻的准则系数, 并提出消除气阻的水 流临界流速。结 论1. 当管路流速较小时, 供水管路的驼峰顶端可能 滞留和聚集气体, 形成驼峰气阻; 气体体积越大 对水流阻碍越明显, 可能造成的水头损失也越 大; 2. 利用等价球体法可以极大地简化驼峰气阻 的形状, 并良好地模拟气阻的平衡特性和阻力特 性; 3. 管道流速是影响驼峰气阻临界平衡位置的 最重要因素, 通过减小管道起伏的坡角或增加水 流流速可以防止和消除驼峰气阻的危害。
Peritoneal eosinophils during intermittent peritoneal dialysis.
Peritoneal eosinophil counts were investigated in 61 intermittent dialysis patients over the course of 1 year. The peritoneal eosinophil percentage fell from 18 +/- 2% (mean +/- SEM) in the first 2 months of dialysis to 3 +/- 0.4% after 6 months of dialysis. Absolute eosinophils per cubic millimeter fell from 586 +/- 126 to 61 +/- 18 (p less than 0.01 for both percentage and absolute values). There was a wide range in the mean eosinophil percentages per patient in the first 6 months of dialysis (0-84%) that narrowed to 0-9% after 6 months. The majority of the high initial eosinophil counts resolved after 2 months. Peripheral eosinophilia was seen in 8 of the 10 patients with the highest mean peritoneal eosinophil percentages during the first 2 months of dialysis. Patients who developed peritonitis had a significantly lower percentage of eosinophils in the first 1.5 months of dialysis than patients who did not develop peritonitis. At the time of diagnosis of peritonitis, the peritoneal eosinophil count was near zero. 4 cases of peritoneal eosinophilia which developed after antibiotic therapy are described.