Theoretical analysis of the gravity driven capillary viscometers

CLAUDIO L. A. BERLI, JULIO A. DEIBER

REVIEW OF SCIENTIFIC INSTRUMENTS

American Institute of Physics

Año: 2004 vol. 75 p. 976 - 982

0034-6748

Gravity driven capillary viscometers (GDCVs) are used to obtain the viscosity function of non-Newtonian fluids from measurements of the instantaneous fluid height in the overhead reservoir. The reliability of this viscometry depends on two main aspect, namely the accomplishment of the required flow condition in the apparatus and the appropriate conversion of raw data into rheometric functions. This work presents a rigorous theoretical analysis of the GDCV, thus providing criteria to achieve accurate measurements. The equations describing the rheometric flow in a GDCV are deduced from the basic laws of momentum and mass conservations. From these equations the flow dynamics of the apparatus is studied and the constraints required to attain a quasi steady state flow are established. Under these conditions, the rheometric functions are written in terms of the instantaneous fluid height. In addition, a method to process experimental data of non-Newtonian fluids is proposed, which can handle the ill-posed problem associated with the determination of the viscosity function in this viscometry.