Thermal and multiphase flow simulations of polytetrafluoroethylene-based grease flow in restricted geometry

Abstract

This work presents a numerical model for predicting flow behaviour and temperature distribution of polytetrafluoroethylene thickened grease in a roller bearing configuration of obstructed flow. A finite-element code with a laminar flow multiphase mixture model is used to predict the flow patterns and volume fraction distribution of a thickener in a rectangular channel with two cylindrical rollers rotating at constant angular speeds ranging from 50  to 200 r/min. A heat transfer analysis has been done to study the temperature variation near the rollers. Simulations are carried out for 5%, 10% and 20% concentrations of the thickener. Rheological characterisation of the proposed grease samples is done. An experimentally developed rheological model is incorporated in the numerical model. The rheological characteristics of the samples follow the Herschel–Bulkley model. The velocity profiles obtained from the present numerical model are compared with the nearest available experimental microparticle image velocimetry profiles for lithium complex grease to find qualitative similarity. The variation of volume fraction distribution and temperature at different times and locations of the channel is predicted. The rotation of rollers affects the local distribution of a thickener as well as the rate of homogenisation with the oil. As polytetrafluoroethylene grease is able to maintain its rheology even at elevated temperatures, most of the channel portion is thermally unaffected due to heat dissipation up to 5 W.