模型蜡油混合物的沉淀蜡含量和屈服应力是通过在固定应力下冷却时停止流动来确定的

IF 3 2区 工程技术 Q2 MECHANICS
Conor G. Harris, Christina E. Rice, Abhishek Shetty, Luqman Mahir, Ronald G. Larson
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引用次数: 0

摘要

为了估计与管道中蜡沉积建模相关的屈服应力和其他流变特性,在管道中,流动是连续的,但应力随管道半径的变化而变化,在恒定的剪切应力下,以多种冷却速率冷却模型蜡油混合物,直到达到一定温度,在该温度下,由于蜡晶体的形成,凝胶作用阻止了流动。结合差示扫描量热法测定的析出蜡浓度随温度的变化规律,得出了析出蜡浓度Cp和冷却速率与表观屈服应力σy的关系。报告了两种不同浓度的蜡混合物的结果:一种是模拟油田油成分的多组分商业蜡,一种是更简单的六烷烃混合物。这些瞬态流变数据符合伪“Herschel-Bulkley”本构方程,从该本构方程中可以发现,在冷却下流动过程中获得的屈服应力通常比在冷却后无流动的类似恒温流动中获得的屈服应力低一个数量级或更多。我们还发现,随着冷却速率的降低,止动温度明显下降,即使在最低冷却速率为0.0625°C min - 1时也没有收敛,这表明在较慢的冷却下,即使在低应力下,流动也会继续。我们在恒定应力下获得的与冷却速率相关的屈服应力对流动应力下凝胶化的最新模型提出了挑战,并且与管道中的蜡沉积有关。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Precipitated wax content and yield stress of model wax-oil mixtures determined by arrest of flow during cooling at fixed stress
To estimate yield stress and other rheological properties relevant to modeling of wax deposition in pipelines where flow is continuous, but stress varies across the pipe radius, model wax-oil mixtures are cooled at multiple cooling rates under constant shear stress until a temperature is reached, at which flow is arrested by gelation due to wax crystal formation. From these data, combined with a measurement of temperature-dependence of precipitated wax concentration by differential scanning calorimetry, an apparent yield stress σy, below which flow is arrested at each temperature, is related to the concentration of precipitated wax Cp and the cooling rate. Results are reported for multiple concentrations in oil of two independent wax mixtures: a many-component commercial wax mimicking the composition of field oil, and a simpler six-alkane mixture. These transient rheological data are fit to a pseudo “Herschel–Bulkley” constitutive equation from which it is found that the yield stresses obtained during flow under cooling are generally an order of magnitude, or more, lower than the yield stresses obtained in the previous work in flow at a comparable constant temperature after cooling in the absence of flow. We also find a strong decrease in the arrest temperature with a decreasing cooling rate, with no convergence even at the lowest cooling rate of 0.0625 °C min−1, indicating that under slower cooling, flow continues even under low stresses. The cooling-rate-dependent yield stress obtained in our study under constant stress provides a challenge to the recent models of gelation under flow stress and is of relevance to wax deposition in pipelines.
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来源期刊
Journal of Rheology
Journal of Rheology 物理-力学
CiteScore
6.60
自引率
12.10%
发文量
100
审稿时长
1 months
期刊介绍: The Journal of Rheology, formerly the Transactions of The Society of Rheology, is published six times per year by The Society of Rheology, a member society of the American Institute of Physics, through AIP Publishing. It provides in-depth interdisciplinary coverage of theoretical and experimental issues drawn from industry and academia. The Journal of Rheology is published for professionals and students in chemistry, physics, engineering, material science, and mathematics.
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