Dynamic Viscosity Measurement

What is Viscosity?

Viscosity measures a fluid’s resistance to flow, determining how easily it deforms under an applied force. High-viscosity fluids like honey flow slowly, while low-viscosity fluids like water flow quickly. Viscosity is temperature-dependent, generally decreasing as the fluid warms. It’s measured in units such as poise (P) or pascal-seconds (Pa·s).

Types of Viscosity:

1. Dynamic Viscosity: Internal resistance to flow, measured in Pa·s.
2. Kinematic Viscosity: The ratio of dynamic viscosity to fluid density, measured in m²/s.

Here, we’ll focus on dynamic viscosity and how to measure it using a Brookfield Viscometer.

Step 1: Sample Preparation

• Ensure the sample is homogeneous and free of bubbles.
• Pour the required volume into the sample container.
• If necessary, maintain a constant temperature using a water bath.

Step 2: Select the Correct Spindle

• Choose the spindle based on the expected viscosity range.
• Larger spindles suit low-viscosity fluids, while smaller spindles are for higher viscosities.

Step 3: Set Up the Viscometer

• Attach the spindle securely.
• Immerse the spindle in the fluid up to the marked immersion depth.
• Check for air bubbles around the spindle.

Step 4: Adjust Speed and Start Measurement

• Select an appropriate RPM based on the fluid’s expected viscosity.
• Start the viscometer and allow it to reach a steady reading.

Step 5: Record and Analyze

• Note the torque reading, displayed either as a percentage or digitally.
• Ideal torque falls between 10% and 90%. If it’s too low or high, adjust the spindle or speed.

Calculation

Most Brookfield viscometers provide viscosity readings directly in centipoise (cP). If only a torque reading is provided, calculate viscosity using:

\eta = \text{Torque} \times \text{Viscosity Factor}

The Viscosity Factor is specific to the spindle and speed, available in the instrument manual.

Why It Matters?

Accurate viscosity measurement ensures quality control in industries like food, pharmaceuticals, and cosmetics. Understanding dynamic viscosity helps optimize processes, improve product consistency, and maintain compliance with industry standards.

Read also:

• The Basics of Soft Gelatin Capsule
• Conductivity Meter in Pharmaceutical Industry
• Rheological Properties Effect on IM Injectable Dosage Forms

Resource Person: Drx. SATISH MANE