TY  - JOUR
T1  - Role of pressure dependent viscosity in measurements with falling cylinder viscometer
A1  - Průša, Vít
A1  - Rajagopal, K. R.
A1  - Srinivasan, Shriram
JA  - International Journal of Non-Linear Mechanics
Y1  - 2012
VL  - 47
IS  - 7
SP  - 743–750
M2  - doi: 10.1016/j.ijnonlinmec.2012.02.001
KW  - experimental error
KW  - falling cylinder viscometer
KW  - pressure dependent viscosity
N2  - The fallingcylinderviscometer is frequently used in measuring the dependence of the viscosity on the pressure. The viscosity is calculated using an indirect procedure, namely by appealing to the linear relation between the time taken for the fall and the viscosity that is a consequence of assuming that inertial effects can be neglected. Under certain assumptions, the coefficient of proportionality can be derived analytically, and one gets the classical formula for the viscosity as a function of geometric parameters of the device, density of the fluid and the sinker, gravitational acceleration, and the distance and the time of the fall. Although the classical formula is valid only for fluids with constant viscosity, it is indiscriminately used even for fluids with pressure dependent viscosity. We investigate the role of variable viscosity, and we derive a heuristic correction to the classical formula for the case of fluids with pressure dependent viscosities. The systematic error introduced by the unwarranted application of the classical formula for fluids with pressure dependent viscosity is analysed, and it is shown it is measurable and it can in some cases significantly influence the experimental results.
ER  -