Original Article Investigation of the micropolar lubricant and thermal effects in the slot entry hybrid journal bearings Pankaj Khatak and HC Garg Abstract The present article studies the combined influence of the micropolar lubricant and thermal effects in the slot entry hybrid journal bearings. Bearing performance characteristics are computed by the concurrent solution of modified Reynolds, three-dimensional micropolar energy, and three-dimensional conduction equations. Thermohydrostatic char- acteristics of the slot entry hybrid journal bearings have been studied vis-a `-vis isothermal characteristics. The results obtained numerically indicate that isoviscous assumption of the lubricant is incorrect and the bearing performance is significantly affected by the increase in temperature. Hence, it is essential to consider the thermal effects for the bearings operating with the micropolar lubricant for reliable performance analysis of the bearings. Keywords Slot entry, micropolar lubrication, hybrid journal bearings, isothermal, thermohydrostatic Date received: 10 September 2016; accepted: 10 May 2017 Introduction Hybrid journal bearings are commonly used fluid bearings based on the combined mechanism of the hydrostatic and hydrodynamic bearings. These bear- ings are widely used in high-load applications like rolling mills and high-speed devices like machine tools. They operate under different physical and lubri- cation conditions. The realistic behavior of bearings can be predicted by analyzing different aspects like misalignment, elasticity, roughness, restrictor types, pocket sizes, restrictor design parameter, and lubri- cant properties. The changes in the lubricant compos- ition and their properties also affect the working of the hybrid journal bearings. The microstructures are present in the lubricant due to its mineral nature and the blended additives. The additives are generally added for the enhancement of the lubricant proper- ties. This addition makes the nature of the lubricant non-Newtonian. The flow pattern inside the bearings in the presence of particles cannot be accurately pre- dicted by Newtonian mechanics. The effect of the individual particles in the lubricant can be explained by generalizing the classical fluid mechanics model. Eringen 1 explained the behavior of microparticles in the fluid flow in his micropolar fluid theory. This theory has been used in various configurations of bearings in lubrication analysis. Khatak and Garg 2 studied the applications of Eringen micropolar theory to different configurations of bearings. They showed significant performance variation in bearings with micropolar lubrication. Singh et al. were earlier contributors in the study of micropolar lubricated bearings. 3,4 They obtained Reynolds equation for the lubricant flow in presence of additives in bearings. Later many researchers studied the micropolar lubrication of bearings under different test conditions. Rahmatabadi et al. 5 demonstrated that the micropo- lar lubricants improved the performance of noncircu- lar lobe bearings. Rahmatabadi et al. 6 further proved that preload and micropolarity of the lubricant can be combined to improve the performance of multilobe bearings. The improvement in squeeze film character- istics of a short journal bearing with the micropolar lubricant was reported by Naduvinamani and Kadadi. 7 Elsharkawy and Al-Fadhalah 8 further showed that squeeze film time, pressure, and load- carrying capacity are increased by size and microrota- tions of the additives in the micropolar lubricant. Recently, Mehrjardi et al. 9 studied journal bearings Department of Mechanical Engineering, Guru Jambheshwar University of Science & Technology, Hisar, Haryana, India Corresponding author: Pankaj Khatak, Department of Mechanical Engineering, Guru Jambheshwar University of Science and Technology, Hisar 125001, Haryana, India. Email: pankajkhatak@gmail.com Proc IMechE Part C: J Mechanical Engineering Science 0(0) 1–14 ! IMechE 2017 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0954406217713519 journals.sagepub.com/home/pic