Kapillaariviscometri

Kapillaariviscometri is a method used to determine the viscosity of a liquid by measuring the time it takes for a known volume of liquid to flow through a narrow capillary tube under its own weight. This technique relies on Poiseuille's Law, which describes the laminar flow of a Newtonian fluid through a cylindrical tube. The law states that the volume flow rate is directly proportional to the pressure difference and the fourth power of the capillary radius, and inversely proportional to the viscosity of the fluid and the length of the capillary.

In practice, a viscometer, often a U-shaped glass tube with a capillary section, is filled with the liquid. The liquid is then allowed to flow from one reservoir to another, passing through the capillary. By measuring the time it takes for the liquid level to drop between two marked points on the viscometer, and knowing the volume between these points, the flow rate can be calculated. This flow time is directly proportional to the dynamic viscosity of the liquid, assuming the density is also known or accounted for.

Kapillaariviscometri is a relatively simple and inexpensive method, making it suitable for a wide range of applications in laboratories and industrial settings. It is commonly used for analyzing oils, solvents, polymers, and other liquids where viscosity is a critical property. The accuracy of the measurement depends on factors such as the precise dimensions of the capillary, the temperature control of the liquid, and the cleanliness of the apparatus. Variations in temperature significantly affect liquid viscosity, so precise temperature regulation is essential for reliable results. Different types of capillary viscometers exist, including Ostwald, Ubbelohde, and Cannon-Fenske viscometers, each designed with specific features for convenience and accuracy.