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ISRN Mechanical Engineering
Volume 2012 (2012), Article ID 603460, 7 pages
http://dx.doi.org/10.5402/2012/603460
Research Article

A Study on the Performance of a Magnetic-Fluid-Based Hydrodynamic Short Journal Bearing

1Department of Mechanical Engineering, Faculty of Technology, Dharmsinh Desai University, Nadiad 387001, Gujarat, India
2Department of Mechanical Engineering, Sardar Vallabhbhai National Institute of Technology, Surat 395007, Gujarat, India
3Department of Mathematics, Sardar Patel University, Vallabh Vidyanagar, Anand 388120, Gujarat, India

Received 20 September 2011; Accepted 16 October 2011

Academic Editors: S. W. Chang and A. Corigliano

Copyright © 2012 N. S. Patel et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Efforts have been made to study and analyze the performance of a hydrodynamic short journal bearing under the presence of a magnetic fluid lubricant. With the usual assumptions of hydrodynamic lubrication, the associated Reynolds equation for the fluid pressure is solved with appropriate boundary conditions. In turn, this is then used to calculate the load-carrying capacity which results in the calculation of friction. The computed results presented in graphical form suggest that the bearing system registers an improved performance owing to the magnetic fluid as compared to the conventional lubricant. It is clearly observed that the load-carrying capacity increases nominally while the coefficient of friction decreases significantly. Besides, it is seen that the bearing can support a load even when there is no flow of lubricant. In addition, this type of study may offer an additional degree of freedom from design point of view in terms of the forms of the magnitude of the magnetic fluid.

1. Introduction

Oliver [1] made a comparison between the lubricating performance of Newtonian and highly elastic liquid. It was seen that the elastic liquid induced load enhancement ratio and reduction in the coefficient of friction. Lin [2] dealt with the theoretical study of squeeze film behavior for a finite journal bearing lubricated with couple stress fluid. It was evaluated that the couple stress effects increased the load-carrying capacity significantly and lengthened the response time of the squeeze film.

Kuzma [3] presented an analysis of an infinitely long journal bearing for the case of an electrically conducting fluid in the presence of a magnetic field. It was found that the bearing performance got improved due to the magnetization as compared to the case of conventional lubricant-based bearing. Chang et al. [4] considered two types of four-pad step-pocket journal bearing, lubricated with a ferromagnetic fluid. It was observed that the ferrofluid lubrication yielded higher overall bearing performance. Besides, the side leakage of the ferrofluid at both ends was found to be avoided.

Nada et al. [5] derived the modified Reynolds equation based on the momentum and continuity equation for a ferrofluid under an applied magnetic field, in order to analyze the effect of using current carrying wire model in the design of a hydrodynamic journal bearing lubricated with a ferrofluid. The results concluded that the magnetic lubrication provided higher load-carrying capacity and reduced friction coefficient as compared to a conventional fluid-based bearing.

Naduvinamani et al. [6] made an investigation on the rheological effects of the couple stress fluids on the static and dynamic behavior of squeeze films in a short porous journal bearing. It was revealed that as compared to the Newtonian lubricants, the lubricant which sustains the couple stresses yielded an increase in the load-carrying capacity. Shah and Bhat [7] discussed the squeeze film behavior in an infinitely long journal bearing using the ferrofluid flow models of Neuringer-Rosensweig and Jenkins and Shliomis models for uniform and nonuniform magnetic fields. It was established that a uniform magnetic field failed to produce magnetic pressure in the Neuringer-Rosensweig model, on the other hand, it could affect the bearing performance characteristics in the Shliomis model owing to the rotational viscosity parameter. Further, the load-carrying capacity and squeeze time were more in the case of nonuniform magnetic field than in the case of a uniform magnetic field. Nada and Osman [8] investigated the problem of lubrication of a finite hydrodynamic journal bearing lubricated with magnetic fluids considering the couple stress effects. The results indicated that the influence of couple stresses and magnetic effects on the bearing performance characteristics were significantly apparent. It was concluded that fluids with couple stresses were better than Newtonian fluids and the magnetic effect enhanced the performance characteristics. Urreta et al. [9] conducted a theoretical analysis with numerical solutions of the associated Reynolds equation for the pressure distribution in a hydrodynamic journal bearing, based on viscosity modulation for ferrofluid and Bingham model for MR fluid. It was demonstrated that the magnetic fluid could be used to manufacture active journal bearings. Gertzos et al. [10] carried out CFD analysis of hydrodynamic journal bearing lubricated by a Bingham lubricant. The charts presented here could be used by the designer to design smart journal bearings. Further, the results obtained from the developed 3D CFD model were found to be in very good agreement with experimental data from previous investigations on Bingham fluids.

Here, it has been sought to study and analyze the performance of a short journal bearing under the presence of a magnetic fluid lubricant based on Neuringer and Rosensweig model.

2. Analysis

The configuration of the bearing which is infinitely short in 𝑍-direction is presented in Figure 1. The journal has radius 𝑅𝑗 rotating inside a bearing, and the space between journal and bearing is filled with a magnetic fluid. If the journal is infinitely short, the pressure gradient 𝜕𝑝/𝜕𝑧 is much larger than the pressure gradient𝜕𝑝/𝜕𝑥, as a result of which the latter can be neglected. The magnetic field is oblique to the stator as in Agrawal [11] and its magnitude is given by𝐻2𝐵=𝑘𝑧2𝐵𝑧+2,(1) where 𝑘 is a constant to suit the dimensions and the strength of the magnetic field [10].

603460.fig.001
Figure 1: Configuration of the problem.

In 1964, Neuringer and Rosensweig developed a simple model to study the steady flow of magnetic fluids in the presence of slowly changing external magnetic fields. The model consisted of the following equations:𝜌𝑞.𝑞=𝑝+𝜂2𝑞+𝜇𝑜𝑀.𝐻,(2).𝑞=0,(3)×𝐻=0,(4)𝑀=𝜇𝐻,(5).𝐻+𝑀=0,(6)

where 𝜌 is the fluid density, 𝑞=(𝑢,𝑣,𝑤)is the fluid velocity in film region, 𝑝 is the film pressure, 𝜂is the fluid viscosity, 𝜇𝑜is the permeability of free space, 𝑀 is the magnetization vector, 𝐻 is the external magnetic field, and 𝜇 is the magnetic susceptibility of the magnetic particles.

Using Equations (4) and (5), Equation (2) becomes 𝜌𝑞.𝜇𝑞=𝑝0𝜇𝐻22+𝜂2𝑞.(7)

This shows that an extra pressure 𝜇0𝜇𝐻2/2 is introduced into the Navier-Stokes equation when magnetic fluid is used as a lubricant. Thus, the modified Reynolds equation for magnetohydrodynamic short journal bearing under the usual assumptions, the lubricant film is taken to be isoviscous, incompressible, and the flow is laminar (Bhat and Deheri [12], Agrawal [11], Bhat [13]), turns out to be𝑑2𝑑𝑧2𝜇𝑝𝑜𝜇𝐻22=6𝜂𝑢3𝑅𝑑𝑑𝜃.(8)

The associated boundary conditions are 𝐵𝑝=0at𝑧=+2𝐵and2,(9)𝑑𝑝𝑑𝑧=0at𝑧=0.(10) Introduction of the dimensionless quantities,𝑧𝑍=𝐵𝑅,𝑃=𝜂𝑢𝑝,𝜇=𝑘𝐵2𝑅𝜇𝑜𝜇𝜂𝑢,(11) leads to the expression for the pressure distribution in dimensionless form:𝜇𝑃=2𝐵+3𝐶2𝜀sin𝜃(1+𝜀cos𝜃)314𝑍2.(12)

The load-carrying capacity in 𝑥 direction is given by𝑤𝑋=2𝜋00𝐵/2𝑝cos𝜃𝑅𝑑𝜃𝑑𝑧.(13)

Thus, the dimensionless load-carrying capacity in 𝑥 direction is obtained from𝑊𝑥=𝑐2𝜂𝑢𝐵3𝑤𝑥=𝜀21𝜀22.(14)

The load-carrying capacity in 𝑧 direction is given by𝑤𝑍=2𝜋00𝐵/2𝑝sin𝜃𝑅𝑑𝜃𝑑𝑧.(15)

Then, the nondimensionless load-carrying capacity in 𝑧 direction is obtained from:𝑊𝑧=𝑐2𝜂𝑢𝐵3𝑤𝑧=𝜇6+14𝜋𝜀1𝜀23/2.(16)

Therefore, the resultant load-carrying capacity is given by 𝑊=𝑊2𝑥+𝑊2𝑧,𝜀𝑊=21𝜀22+𝜇6+14𝜋𝜀1𝜀23/21/2.(17)

The friction force is determined by𝑓=02𝜋𝜂𝑢𝐿𝑅𝑑𝜃,(18) which gives the nondimensional friction force as𝐶𝐹=𝑓=𝜂𝑈𝐿𝐵2𝜋1𝜀21/2.(19)

The coefficient of friction is given by𝐹𝜇=𝑊=2𝜋1𝜀21/21𝜀21𝜀22+𝜇6+14𝜋𝜀1𝜀23/21/2.(20)

3. Results and Discussion

The variation of pressure distribution, load-carrying capacity, friction force, and coefficient of friction are presented in Equations (12), (16), (19), and (20), respectively. A theoretical comparison with the conventional lubricants suggests that the nondimensional pressure and load-carrying capacity get increased while friction force and coefficient of friction get decreased.

From Figure 2, it is clear that the pressure increases marginally with respect to the magnetization parameter. This is due to the fact that the magnetic pressure adds generated by the magnetic force developed due to the magnetic particles suspended in the lubricant. Figures 3, 4, and 5 indicate that the pressure increases substantially with respect to 𝑍, 𝐵/𝐶, and eccentricity ratio, respectively. If 𝐵/𝐶 is less, then more fluid passes through the gap between journal and bearing and, therefore, more pressure develops. Increase in eccentricity ratio increases the convergent region of fluid film between the bearing and the journal which again increases the pressure. Also, Figures 6 and 7 show pressure distribution with respect to 𝑍 for different values of 𝐵/𝐶 and eccentricity ratio. Figure 8 states that the pressure decreases significantly with increase in 𝑍. Figure 9 represents the pressure distribution versus 𝜀 which makes clear that increase in pressure is significant at higher value of eccentricity ratio. Figures 10 and 11 represent pressure distribution versus 𝐵/𝐶 and 𝜀 for different values of and 𝜃, respectively. It makes clear that the pressure increases substantially at 𝜃=135°. Besides, it is found from Figure 12 that the load-carrying capacity increases as the magnetic parameter increases. It is clear from Figure 13 that the effect of magnetic parameter decreases with increase in eccentricity ratio. In addition to this, it is found from Figure 14 that the coefficient of friction decreases with respect to the increasing values of the magnetic parameter. This probably due to the fact that the magnetic force increases the load-carrying capacity and decrease the friction. Figure 15 indicates that decrease in coefficient of friction is considerable at higher value of eccentricity ratio.

603460.fig.002
Figure 2: Nondimensional pressure distribution 𝑝 versus 𝜃 for different values of magnetic parameter 𝜇.
603460.fig.003
Figure 3: Nondimensional pressure distribution 𝑝 versus 𝜃 for different values of 𝑍.
603460.fig.004
Figure 4: Nondimensional pressure distribution 𝑝 versus 𝜃 for different values 𝐵/𝐶.
603460.fig.005
Figure 5: Nondimensional pressure distribution 𝑝 versus 𝜃 for different values of 𝜀.
603460.fig.006
Figure 6: Nondimensional pressure distribution 𝑝 versus 𝑍 for different values of 𝐵/𝐶.
603460.fig.007
Figure 7: Nondimensional pressure distribution 𝑝 versus 𝑍 for different values of 𝜀.
603460.fig.008
Figure 8: Nondimensional pressure distribution 𝑝 versus 𝑍 for different values of 𝜃.
603460.fig.009
Figure 9: Nondimensional pressure distribution 𝑝 versus 𝐵/𝐶 for different values of 𝜀.
603460.fig.0010
Figure 10: Nondimensional pressure distribution 𝑝 versus 𝐵/𝐶 for different values of 𝜃.
603460.fig.0011
Figure 11: Nondimensional pressure distribution 𝑝 versus 𝜃 for different value of 𝜀.
603460.fig.0012
Figure 12: Nondimensional load-carrying capacity versus 𝜀 for different value of magnetic parameter 𝜇.
603460.fig.0013
Figure 13: Nondimensional load-carrying capacity versus 𝜇 for different value of 𝜀.
603460.fig.0014
Figure 14: Coefficient of friction versus 𝜀 for different value of magnetic parameter 𝜇.
603460.fig.0015
Figure 15: Coefficient of friction versus 𝜇 for different value of magnetic parameter 𝜀.

This article reveals that a proper selection of the eccentricity ratio and the magnetic parameter may result in a better performance. The present investigation not only presents the method for enhancing the performance of bearing system but also provides sufficient scopes for extending the life period of the bearing system.

4. Conclusions

This investigation reveals the following.(1)The magnetization has an overall positive effect on the performance of the bearing system.(2)The bearing can support a load even when there no motion due to magnetostatic force generated by magnetic particles.(3)The wear between bearing and the journal is decreases as the initial contact during starting period between them is less.(4)The evaluation of wear is necessary from bearing life period point of view.(5)The study establishes the crucial role of eccentricity ratio, even if there is a suitable strength of the magnetic field.

Nomenclature

𝐵: Breadth of bearing (mm)
𝑀2:Magnetic field
𝑝: Lubricant pressure (N/mm2)
𝑃:Dimensionless pressure
𝑤:Load-carrying capacity (N)
𝐹:Dimensionless friction force
𝜇:Coefficient of friction
𝑊:Dimensionless load carrying capacity
𝜇:Dimensionless magnetization parameter
𝜂: Lubricant viscosity (N.S/mm2)
𝑅𝑏:Bearing radius (mm)
𝑅𝑗:Journal radius (mm)
𝑂𝑏:Bearing center
𝑂𝑗:Journal center
𝑒:Eccentricity (mm).

Acknowledgment

The fruitful suggestions and remarks of the editors and the reviewers leading to an improvement in the presentation of the paper are gratefully acknowledged.

References

  1. D. R. Oliver, “Load enhancement effects due to polymer thickening in a short model journal bearing,” Journal of Non-Newtonian Fluid Mechanics, vol. 30, no. 2-3, pp. 185–196, 1988. View at Scopus
  2. J. R. Lin, “Squeeze film characteristics of finite journal bearings: couple stress fluid model,” Tribology International, vol. 31, no. 4, pp. 201–207, 1998. View at Scopus
  3. D. C. Kuzma, “The magneto hydrodynamic journal bearing,” Transaction of the ASME, pp. 424–428, 1963.
  4. H. S. Chang, C. Q. Chi, and P. Z. Zhao, “A theoretical and experimental study of ferrofluid lubricated four-pocket journal bearings,” Journal of Magnetism and Magnetic Materials, vol. 65, no. 2-3, pp. 372–374, 1987. View at Scopus
  5. G. S. Nada, T. A. Osman, and Z. S. Safar, “Effect of using current-carrying-wire models in the design of hydrodynamic journal bearings lubricated with ferrofluid,” Tribology Letters, vol. 11, no. 1, pp. 61–70, 2001. View at Publisher · View at Google Scholar · View at Scopus
  6. N. B. Naduvinamani, P. S. Hiremath, and G. Gurubasavaraj, “Squeeze film lubrication of a short porous journal bearing with couple stress fluids,” Tribology International, vol. 34, no. 11, pp. 739–747, 2001. View at Publisher · View at Google Scholar · View at Scopus
  7. R. C. Shah and M. V. Bhat, “Ferrofluid squeeze film in a long journal bearing,” Tribology International, vol. 37, no. 6, pp. 441–446, 2004. View at Publisher · View at Google Scholar · View at Scopus
  8. G. S. Nada and T. A. Osman, “Static performance of finite hydrodynamic journal bearings lubricated by magnetic fluids with couple stresses,” Tribology Letters, vol. 27, no. 3, pp. 261–268, 2007. View at Publisher · View at Google Scholar · View at Scopus
  9. H. Urreta, Z. Leicht, A. Sanchez, A. Agirre, P. Kuzhir, and G. Magnac, “Hydrodynamic bearing lubricated with magnetic fluids,” Journal of Physics: Conference Series, vol. 149, no. 1, Article ID 012113, 2009. View at Publisher · View at Google Scholar
  10. K. P. Gertzos, P. G. Nikolakopoulos, and C. A. Papadopoulos, “CFD analysis of journal bearing hydrodynamic lubrication by Bingham lubricant,” Tribology International, vol. 41, no. 12, pp. 1190–1204, 2008. View at Publisher · View at Google Scholar · View at Scopus
  11. V. K. Agrawal, “Magnetic-fluid-based porous inclined slider bearing,” Wear, vol. 107, no. 2, pp. 133–139, 1986.
  12. M. V. Bhat and G. M. Deberi, “Squeeze film behaviour in porous annular discs lubricated with magnetic fluid,” Wear, vol. 151, no. 1, pp. 123–128, 1991.
  13. M. V. Bhat, “Hydrodynamic lubrication of a porous composite slider bearing,” Japanese Journal of Applied Physics, vol. 17, pp. 479–481, 1978.