Solution of Problems Involving Grease Flow in Straight Pipe or Tubing

A SIMPLE method for solving problems involving steady flow of grease in pipes or tubing is being developed by the NLGI Subcommittee on Grease Dispensing in Central Systems. The method, based largely on a 1964 NLGI Annual Meeting paper, uses a graphical presentation of the Poiseuille equation for laminar flow. For this purpose, the Subcommittee has prepared charts that are direct reading in pressure drop and flow rate for pipe and tubing sizes commonly used in centralised systems and in transfer of grease from one point to another. The user of the charts must know the apparent viscosity characteristics of the particular grease of interest to him. When these data are plotted on the proposed NLGI chart as lines of shear stress vs. shear rate at constant temperature, various types of flow problems can be solved by drawing a few straight lines on the chart. Since the apparent viscosity is equal to the shear stress divided by the shear rate, the shear stress is found by multiplying each apparent viscosity value by its corresponding shear rate.