Raghuvir B. Pai’s research while affiliated with Manipal Academy of Higher Education and other places

In this paper, the stability characteristics of a tri-taper journal bearing are analyzed theoretically. The time dependent form of Reynolds equation in two dimensions for incompressible fluid is solved numerically by finite difference method, satisfying the Reynolds boundary conditions. Dynamic coefficients are determined using the method of linearization of bearing reactions. A study with various ramp size's and L/D ratio's predicts that a bearing with higher ramp size and higher L/D ratio results in an increased mass parameter and improved stability margin of the bearing. © 2012 Elsevier Editora Ltda. and Brazilian Metallurgical, Materials and Mining Association.

Effectiveness of micellar copper oxide and zinc phosphates as antiwear additives in mineral oil has been investigated as a function of their disintegration in tribochemical processes. The use of copper tribofilm coating can provide reasonable very low wear and friction coefficient. The mechanism of wear reduction by micellar copper oxide is based on the formation of metallic copper durable film on the rubbing steel surface during following tribochemical reaction: Cu2+ + 2etribo -> Cu0. This phenomen is named selective transfer. As an effect of the given above reaction, decrease in the concentration of copper and of the other metals, e.g., iron, in oil formulation is observed. Other process responsible for formation of metallic copper is proposed: 2Fe+2 (or Fe0) + 3CuO + 2H2O -> Fe2O3 + 3 Cu0 + 4H+. Zinc phosphates as micellar [Zn(PO3)2] hardcore reverse micelles (RMs) are directly introduced in the sliding contact and undergo physicochemical changes during the film build-up. Consequently, tribochemical reaction with zinc phosphate RMs and iron oxide, through friction-induced cross-linking processes, takes place: [Zn(PO3)2l(RMs) + 2FeO -> Fe2Zn(PO4)2

The steady state characteristics of water lubricated journal bearings having multiple axial grooves are obtained theoretically. The novelty of these bearings is that the lubricant (water) is fed under pressure from one end of the bearing, through the multiple axial grooves (groove angles may vary). These bearings can use the process fluid as the lubricant, as in the case of feed water pumps. The Reynolds equation is solved numerically by the finite difference method satisfying the Jacobsson- Floberg-Olsson boundary conditions. Experimental results indicate that the pressure remains constant for a major portion of the groove, while theory predicts a linear pressure drop from inlet to exit. Comparison of load capacity, attitude angle, volume flow rate and friction variable for various bearing number and eccentricity ratios, assuming linear pressure drop along the groove, shows that there is a significant difference between those obtained by the Reynolds model and the Jacobsson-Floberg-Olsson model. The Jacobsson-Floberg-Olsson model takes into account continuity of flow at both cavitation and reformation boundaries and therefore gives a better prediction of bearing characteristics.