- Capillary Viscometer (Ostwald Viscometer) measures viscosity by timing liquid flow through a narrow tube.
- Capillary Viscometer (Ostwald Viscometer) is widely used in labs for comparing fluid viscosities.
Principle:
- Based on Poiseuille’s Law, which describes the laminar flow of liquid through a capillary.
- Time taken for a fixed volume of liquid to flow between two marks under gravity is proportional to viscosity.
$\eta = K \cdot \rho \cdot t$
- Where:
- η: viscosity
- K: viscometer constant
- ρ: density
- t: flow time
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Types:
- Ostwald viscometer
- Ubbelohde viscometer
Application:
- Suitable for Newtonian fluids only (constant viscosity).
- Accurate for dilute solutions (e.g., sugar solutions, alcohols).
Advantages:
- Simple, inexpensive
- Good for quality control of low-viscosity fluids
Limitations:
- Not suitable for non-Newtonian fluids (as viscosity changes with shear)
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