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范钰熙 2012-05-03
Interim Report on Pressure Effect on Waxy-Crude Pipeline-Restart Conditions Investigated by a Model System Yield Phenomenon and Pipeline Restart. Yield stress is the threshold stress required to initiate flow of a viscoplastic ᤙ... Interim Report on Pressure Effect on Waxy-Crude Pipeline-Restart Conditions Investigated by a Model System Yield Phenomenon and Pipeline Restart. Yield stress is the threshold stress required to initiate flow of a viscoplastic fl uid. Waxy crude-oil gels are viscoplastic in nature and exhibit time-dependent Bingham plastic flow behavior during restart under imposed constant pumping pressure. The yielding process of a gel is a complicated process, and different models have been proposed to explain this phenomenon. Wardhaugh and Boger (1991) defined yield stress as the “shear stress at which the gelled oil ceases to behave as a Hookean solid.” Chang et al. (1998) adopted a three-yield stress concept: elastic limit (which defines the onset of viscoelastic creep), static (where fracture occurs), and dynamic yield stress (which describes the broken down structure after yielding). Among these three, only the static yield stress is used to design the restart pump for initiation of flow after shut-in. Several types of apparatus and different techniques (direct and indirect) have been used for determining the yield stress. The results obtained and conclusions regarding their validity and usefulness differ widely. Setups used are capillary U-tubes, large pilot pipeline facilities, lab-scale model pipelines, controlled-stress or -shear rotational rheometry experiments (CSR). The capillary tube and pilot-scale pipeline measurement tech-niques have been criticized as being unsuitable for understanding the yielding behavior of statically cooled waxy crude oils because of nonlinear pressure distribution, pipe compressibility effects, porosity of wax structure, and contraction effects (Wardhaugh and Boger 1991). However, the authors added that an exception to their conclusion was the work by Ronningsen (1992), where reasonable estimates of the yield stress as compared to model pipeline results were obtained with a constant stress rheometer. Recently, Lee et al. (2007) also reported the consistency between the concentric rheometer and a model pipeline system. In fact, model pipeline test is the most common laboratory method resorted to in gel strength measurement because of its geometrical resemblance to the real pipeline. In such tests, gel is formed under controlled conditions (cooling rate, aging temperature, etc.) and pressure is then slowly applied on one end of the gel until flow is observed. The gel strength (τ) is then calculated by: 公式1
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hljqx123
中期报告Waxy-Crude压力的影响Pipeline-Restart条件研究模型系统

屈服现象和管道重启。屈服应力是应力要求启动阈值的一个理想塑性流动fl uid。蜡原油凝胶剂具有理想塑性性质的,展览时间宾厄姆塑性流动行为在重新在对泵送压力恒定。

它是一种凝胶材料的屈服过程是一个复杂的过程,并提出了不同的模型来解释这一现象。Wardhaugh和Boger(1991)定义为“剪切屈服应力的胶凝油停止表现得像Hookean固体。"长丁晓萍。(1998)采用了一个three-yield应力概念:弹性极限(定义发作的粘弹性蠕变)、静态(在骨折发生),和动态屈服应力(描述分解结构屈服后)。在这三个,只有静态屈服应力是用来设计重新开始流泵关后。

用几种不同类型的设备和各种不同的方法(直接和间接)被用于确定屈服应力。所得结果和结论对他们的有效性和实用性大相径庭。应用毛细管U-tubes机构、大型飞行员管道设施,lab-scale模型管道、controlled-stress或-shear旋转流变仪实验(CSR)。

毛细管和管道测量tech-niques作用而受到批评是不适合的理解的屈服行为的静态蜡原油冷却因非线性压力分布、管道可压缩性的影响,孔隙度蜡的结构和收缩效应(Wardhaugh和Boger 1991)。然而,作者说,他们的结论是一个例外所做的工作被Ronningsen(1992),在合理的估计相比,屈服应力模型管道结果用恒应力流变仪。Z近,李丁晓萍。(2007年)》也报道了一致性模型的同心仪管路系统。事实上,模型管道测试是Z常见的实验室方法采取在凝胶强度测试,因为它的几何与真正的管道。在这样的测试中,凝胶形成受控条件下(冷却速度、老化温度等)和压力然后慢慢地应用于凝胶的一端,直到流观测。水泥浆胶凝强度(τ)是分析计算。
12 0 2012-05-04 0条评论 回复
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用我的没错的! There is one day you enter my heart, and you will 希望能帮到您,以后英语方面有什么问题就来找我吧!专业为您翻译多种中英文,
13 0 2012-05-04 0条评论 回复
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