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A particle based constitutive model for MR (magnetorheological) fluids.

機譯：基于粒子的MR（磁流變）流體本構模型。

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摘要

A microstructural model of the motion of particle pairs in MR fluids is proposed. The model considers the relative motion of particle aggregates and the evolution of aggregates of two particles as opposed to tracking individual particles as the existing constitutive models do. The model accounts for both hydrodynamic and magnetic field forces. The magnetic force expression is consistent with the dipole-dipole approximation, unlike in the existing models that consider an ad-hoc expression for it in order to fit model predictions to experimental data. In addition, the effect of interparticle dipole interactions, i.e. the effect of dipoles from the same chain, has been included in the expression of the magnetic force.;A fluid constitutive equation that allows prediction of velocity and particle structure is derived. Results for cases of no flow and flow condition, when the magnetic field is on, are discussed. Simple shear and elongational flows are analyzed assuming that either the particle pairs remain in close contact so that they are hydrodynamically equivalent to an ellipsoid of aspect ratio two, or they separate during flow. Shear flow results, for the close contact condition, indicate that particle pairs rotate continuously with the flow at low magnetic fields while a steady state is reached at high fields. The steady state orientation is tilted toward the direction of the larger magnitude force.;The analysis of particle separation during flow provides needed information for fluid's yield stress calculation. The yield stress is determined by the stress level required to separate any two particles, inside the fluid, exposed to a certain shear rate and magnetic field strength. The particles separation is assumed dependent on the local shear rate, rather than the apparent shear rate. Predictions of the yield stress, for low to moderate magnetic fields, are in good agreement with experimental results and predictions made with other models reported in literature. At higher magnetic fields, the differences between model predictions and experimental data are attributed to possible changes in the assumed chain breakage mechanism, and in the neglect of the particle pair interactions with neighboring particle clusters.
機譯：提出了磁流體中粒子對運動的微觀結構模型。該模型考慮了粒子聚集體的相對運動以及兩個粒子的聚集體的演化，而不像現(xiàn)有的本構模型那樣跟蹤單個粒子。該模型考慮了流體動力和磁場力。磁力表達與偶極-偶極近似一致，與現(xiàn)有模型不同，該模型考慮了即席表達以使模型預測適合實驗數(shù)據(jù)。另外，在磁力的表達中已經包括了粒子間偶極相互作用的影響，即來自同一鏈的偶極的影響。導出了可以預測速度和粒子結構的流體本構方程。討論了在磁場開啟時無流動和流動條件的情況下的結果。假設顆粒對保持緊密接觸，從而使它們在流體力學上等效于長寬比為2的橢圓體，或者在流動過程中它們分開，則分析簡單的剪切流動和伸長流動。對于緊密接觸條件，剪切流的結果表明，在低磁場下，粒子對隨流連續(xù)旋轉，而在高磁場下達到穩(wěn)態(tài)。穩(wěn)態(tài)取向向較大的力方向傾斜。；流動過程中的顆粒分離分析為流體的屈服應力計算提供了所需的信息。屈服應力由將流體中暴露于一定剪切速率和磁場強度的任何兩個顆粒分離所需的應力水平確定。假定顆粒分離取決于局部剪切速率，而不是表觀剪切速率。對于中低磁場，屈服應力的預測與實驗結果以及文獻報道的其他模型的預測非常吻合。在較高的磁場下，模型預測和實驗數(shù)據(jù)之間的差異歸因于假定的鏈斷裂機理中可能的變化，以及忽略了粒子對與相鄰粒子簇的相互作用。

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  • 作者

    Ciocanel, Constantin.;

  • 作者單位

    The University of Toledo.;

  • 授予單位 The University of Toledo.;
  • 學科 Engineering Chemical.;Engineering Mechanical.
  • 學位 Ph.D.
  • 年度 2006
  • 頁碼 117 p.
  • 總頁數(shù) 117
  • 原文格式 PDF
  • 正文語種 eng
  • 中圖分類
  • 關鍵詞

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