International Journal of Mechanical & Mechatronics Engineering IJMME-IJENS Vol:12 No:05 12 I J E N S IJENS © October 2012 IJENS - IJMME - 8484 - 121905 Thermal Effects on Hydrodynamic Journal Bearings Lubricated by Magnetic Fluids with Couple Stresses G.S. Nada a,* , G.T. Abdel-Jaber b , H. S. Abdo c a Department of Mechanical Engineering, Higher Technological Institute, Tenth of Ramadan city, Sharkia, Egypt. b Department of Materials Engineering & Design, Qena Faculty of Engineering, South Valley University, Qena, Egypt. c Department of Materials Engineering & Design, Aswan Faculty of Energy Engineering, Aswan University, Aswan, Egypt. Abstract -- Based on the momentum and continuity equations for ferrofluid under an applied magnetic field, assuming linear behavior for the magnetic material of the ferrofluid, and using carrying current concentric finite wire magnetic field model, the magnetic force was calculated. A modified Reynolds equation is obtained. It is simultaneously solved with the energy equation numerically by the finite difference technique. The pressure and temperature distributions have been obtained under various couple stress parameter. The solution renders the bearing performance characteristics namely; load carrying capacity, attitude angle of the journal center, frictional force at the journal surface, friction coefficient and bearing side leakage. Based on the micro-continuum theory, and by taking into account the couple stresses due to the microstructure additives, the effects of couple stresses on the performance of a finite hydrodynamic journal bearings were studied. The results have shown that fluids with couple stresses are better than Newtonian fluids. Index Term-- Magnetized journal bearings; Ferrofluid lubricants; Static characteristics; Couple stresses. I. INTRODUCTION Recent solutions that devoted to the study of the lubricant properties have been devised with other parameter being considered in predicting the journal bearing behavior, such as load variation, type of lubricant flow region (laminar or turbulent flow), type of lubricant (Newtonian or non Newtonian), inertia and acceleration effects, and magnetic effect in the case of using ferrofluid [1]. Most of these investigations did not consider the thermal aspects (used isothermal solution) and neglecting viscosity variation with change of temperature. In the practical cases, increasing in load capacity leads to increasing the friction force and consequently increasing the temperature. Although many aspects of bearing performance are fully solved, there are still needs for further investigations of the thermal effects on the bearing performance. The ferrofluid consists of three basic components namely; a base fluid or carrier fluid, ferromagnetic particles and a coating on each particle [2]. The carrier fluid may be a diester base, a hydrocarbon base, an ester base and even a water base; other base fluids, less important for lubrication, are also available. Ferrolubricants behave like ferrofluids; therefore, these lubricants can be controlled remotely by a magnetic field and they can be positioned exactly where, and only where, wear would be expected to take place. The ability to position the lubricant externally is valuable in clean- environment applications, because the lubricant does not contaminate the environment. The greatest advantages of the magnetic-oil-lubricated bearings are a long life, low friction and reduced noise. The study of the thermal aspects needs simultaneous solution of the basic Reynolds' equation coupled with the energy equation and heat transfer, thermal distribution problems may also be considered, thus the solution is assumed that the total viscous heating is dissipated in the oil only with negligible influence of the environmental conditions, assuming no heat conducted to or from the oil film to surfaces (adiabatic case). Applications of ferrofluids are usually based on their controllability by an external magnetic force [3]. Among the various applications in engineering, are those taking advantage of the possibility of collecting and holding firmly small quantities of such fluids in region with highly focused magnetic fields. From this point of view, the ferrofluids were used in liquid seals [4, 5, 6], hydrodynamic braking [7] and also in the lubrication of journal bearings with small or non-existing side leakage [8, 9, 10]. By taking into account the couple stresses due to the microstructure additives, the effects of couple stress on the performance of a finite journal bearing, are presented.