Capillary tube viscometers used for measurement of viscosity are based on -

Explanation:

Capillary Tube Viscometer:

• Viscometer is an instrument used for measuring the viscosity of a fluid. In the capillary tube viscometer, the pressure needed to force the fluid to flow at a specified rate through a narrow tube is measured.
• This type of viscometer is based on laminar flow through a circular pipe.
• It has a circular tube attached horizontally to a vessel filled with a liquid whose viscosity has to be measured. Suitable head (hf ) is provided to the liquid so that it can flow freely through the capillary tube of certain length (L) into a collection tank as shown in figure.
• The flow rate (Q) of the liquid having specific weight wl can be measured through the volume flow rate in the tank.
• The Hagen-Poiseuille equation for laminar flow can be applied to calculate the viscosity (µ) of the liquid.

\(\mu = \left( {\frac{\pi }{{128}}} \right)\frac{{{W_l}{h_f}{d^4}}}{{QL}}\)