非牛頓效應之磁性流體應用於頸軸承潤滑效能研究

Lubrication performance of journal bearings operating with non-Newtonian ferrofluids

李柏叡(Po-Jui Li)

指導教授 ： 洪祖全 ； 林昭仁

國立臺北科技大學/機電學院/機電整合研究所/碩士(2013年)

https://doi.org/10.6841/NTUT.2013.00389

摘要

本研究主要利用Shliomis模型的磁性流體結合Stokes微連續理論，進行非牛頓磁性流體應用於頸軸承的潤滑特性研究。考慮非牛頓偶應力效應和鐵磁粒子的旋轉效應，推導修正的雷諾方程式。對長頸軸承和短頸軸承皆進行定常態分析，而線性穩定和非線性穩定邊界分析，僅以短頸軸承作為代表。為了與牛頓非磁性流體進行比較，本研究針對不同的偶應力參數、磁性流體濃度和磁場強度之非牛頓磁性流體進行頸軸承潤滑效能之探討。
　　定常態分析分面，與傳統非磁性流體比較，短頸軸承使用磁性流體且有磁場作用下可以增加負載能力和減少摩擦參數。增加非牛頓效應，可以使得增加負載能力和減少摩擦參數的效果更明顯。根據長頸軸承的結果，與牛頓非磁性流體比較，在有磁場作用下的非牛頓磁性流體可以增加負載能力和減少零壓力梯度角與摩擦參數。使用非牛頓磁性流體且偏心率大時，負載能力會有顯著的上升。基本上，在有磁場作用下，使用非牛頓磁性流體當作潤滑液可以有效改善頸軸承的定常態運轉性能。
　　由線性穩定分析得知，在牛頓效應下，磁性流體的穩定門檻速度，其值與非磁性流體相同。而非牛頓效應會增加系統穩定度，且在高偏心率下增加磁性流體的濃度與磁場強度，會使得軸承系統的穩定門檻速率稍微增加。除此之外，固定轉速與定常態偏心率進行非線性穩定邊界分析，在非牛頓效應下，磁性流體與非磁性流體比較，其可稍微增加穩定邊界。總體來說，使用非牛頓磁性流體潤滑之頸軸承，其性能和穩定度可以藉著提升磁性流體濃度、磁場強度和偶應力效應而提升。

關鍵字

磁性流體 ； 頸軸承 ； 潤滑效能 ； 非牛頓偶應力效應 ； 定常態分析 ； 線性穩定分析 ； 非線性穩定邊界

並列摘要

On the basis of the ferrofluids model of Shliomis incorporating the micro-continuum theory of Stokes, the performance characteristics of journal bearings lubricated with non-Newtonian ferrofluids are investigated in this study. A two-dimensional modified Reynolds equation is derived by taking into account the effects of non-Newtonian couple stresses and the effects of rotation of ferromagnetic particles. As an application, both the short-bearing and long-bearing approximations are illustrated for static state analysis, and linear stability analysis and nonlinear stability boundary analysis only consider the analysis of the short-bearing approximation. In order to compare with Newtonain non-ferrofluids analysis, variables of couple stress parameter, volume concentration of ferrofluids and magnetic fields strength of the Langevin’s parameter are investigated for lubricated performance with non-Newtonian ferrofluids in this study.
For steady-state performance, as compared with conventional non-ferrofluids, short journal bearings lubricated with ferrofluids under the application of magnetic fields can provide an enhancement in the load capacity as well as a reduction in the friction parameter. In addition, as the effect of non-Newtonian fluids is considered, the enhancement of load capacity and reduction of friction parameter are more apparent. According to the results of long journal bearings, non-Newtonian ferrofluids with magnetic fields as lubricants can provide an increase in load capacity as well as a reduction in cavitated angle and friction parameter in comparison with Newtonian non-ferrofluids. For non-Newtonian ferrofluids operating under large eccentricity ratio, the enhancement of the load capacity is apparent. However, the load performances for journal bearings are improved by using non-Newtonian ferrofluids as lubricants in the presence of magnetic fields.
According to the results of linear stability analysis, the values of stability threshold speed using ferrofludis as lubricants are same with non-ferrofluids under Newtonian effects. The effects of non-Newtonian fluids can provide an increase in the stability of the rotor-bearing system. For the non-Newtonian ferrofluids bearings operating under large eccentricity, the higher values of volume concentration and magnetic fields provide a slight enhancement in the threshold stability speed. At the fixed speed and steady eccentricity ratio, the stability boundary of the non-linear orbit with non-Newtonian ferrofluds as lubricants is observed to increase in comparison with non-ferrofluids. On the whole, the performance and stability of the journal bearings using non-Newtonian ferrofluids as lubricants are observed to increase with increasing values of the volume concentration, Lagevins’ parameter and couple stress.

並列關鍵字

Ferrofluids ； Journal bearings ； Lubrication performance ； Non-Newtonian couple stress ； Static performance ； Linear stability analysis ； Nonlinear stability boundary

參考文獻

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