Experimental and numerical evaluation of the unsteady cooling of ball bearings in atmospheric air: dual influence of nonlinear natural convection and surface radiation

Abstract

Abstract The main objective of this paper is to study the unsteady cooling trends of a heated metallic ball bearing that is quenched in quiescent air at atmospheric temperature and pressure. This fundamental problem has immense practical importance in metallurgical industries. In two separate laboratory tests, the temperature evolution of a heated metallic bearing was measured experimentally and later predicted analytically and numerically. The temperature of the bearing was elevated to two different initial temperatures: one “high” at 550°C and the other “moderate” at 155°C. The mathematical modeling was postulated with the lumped model. In this regard, the change of temperature with time in the bearing was estimated with three sub-models encompassing two different mechanisms: (a) nonlinear natural convection alone, (b) surface radiation alone and (c) nonlinear natural convection united to surface radiation. Temperature distributions were determined theoretically for sub-models (a) and (b). For sub-model (c), the numerical temperature distributions were computed with an efficient Runge–Kutta–Fehlberg (RKF45) algorithm having embedded automatic step size control. At the end, the experimental observations have convincingly demonstrated that when the mechanisms of nonlinear natural convection and surface radiation are brought together, in conformity with the physics of the problem, the numerical temperature distributions pushed down markedly coming close to the measured temperature distributions at all times for the two initial temperatures employed.