Instrumentation Reference Book, 4th Edition

Chapter 7. Measurement of Viscosity

K. Walters and W.M. Jones

7.1. Introduction

In his Principia, published in 1687, Sir Isaac Newton postulated that “the resistance which arises from the lack of slipperiness of the parts of the liquid, other things being equal, is proportional to the velocity with which parts of the liquid are separated from one another” (see Figure 7.1). This “lack of slipperiness” is what we now call viscosity. The motion in Figure 7.1 is referred to as steady simple shear flow, and if τ is the relevant shear stress producing the motion and γ is the velocity gradient ( γ = U/ d), we have

(7.1)

η is sometimes called the coefficient ...