The rheology and hydrodynamic analysis of grease flows in a circular pipe

Abstract

The shear-rate dependent viscosities of two NLGI grade No. 2 greases, Grease A and Grease B, -were measured using a capillary tube viscometer within a temperature range of 5°-35°C. The yield stresses of these greases were directly measured without extrapolation process as a function of temperature. Two types of the yield stresses were found to exist: One was a start-up yield stress below which grease does not start flowing, and the other was a stopping yield stress at which the grease stopped flowing. The former is substantially larger than the latter and should play an important role in the design of an automatic grease pumping system, a system normally operated in an intermittent mode rather than in a continuous mode. In general, the yield stress of Grease A increased with increasing temperatures whereas that of Grease B decreased with increasing temperatures. Continuous pumping tests with Grease A were conducted in four different diameter pipes. A new friction coefficient-Reynolds number correlation was found: F = 18.8/Rea, where the Reynolds number was calculated based on the apparent viscosity of the grease. © 1993 Taylor & Francis Group, LLC.