📌 Rotameter

A Rotameter is a simple, reliable device used to measure the flow rate of liquids and gases in pharmaceutical, chemical, and other industries. It belongs to the variable area flowmeter family.

🔬 Principle of Rotameter

• Works on the variable area principle:

  • A float is placed inside a tapered vertical tube.

  • Fluid enters from the bottom, creating an upward force on the float.

  • The float rises until the upward drag force (fluid flow + buoyancy) balances the downward gravitational force.

  • The float’s stable position indicates the flow rate on a calibrated scale.

Equation:

Fg=Fb+FdF_g = F_b + F_dFg​=Fb​+Fd​

Where:

• FgF_gFg​ = Weight of float (gravity)

• FbF_bFb​ = Buoyancy force

• FdF_dFd​ = Drag force from fluid flow

⚙️ Working of Rotameter

1. Fluid enters the rotameter from the bottom inlet.

2. The rising fluid pushes the float upwards.

3. As the float moves up, the annular area between the float and tapered tube increases.

4. The increased area allows more fluid to pass, reducing velocity, until forces balance.

5. The float settles at a height proportional to flow rate, which can be directly read on the graduated scale.

🛠️ Construction of Rotameter

• Tapered Tube: Transparent (glass, acrylic) or metallic, wider at the top than bottom.

• Float: Made of stainless steel, glass, or plastic; shaped for stable movement.

• Scale: Calibrated in flow units (L/min, m³/hr, etc.).

• End Fittings: For inlet/outlet connection to pipeline.

• Enclosure (optional): For protection in industrial applications.

🔎 Types of Rotameters

1. Glass Tube Rotameter

   • Most common, low cost, transparent tube.

   • Limited to non-corrosive, clear fluids.

2. Plastic Tube Rotameter

   • Lightweight, economical, resistant to corrosion.

   • Used in water treatment, pharma utilities.

3. Metal Tube Rotameter

   • Rugged, used for opaque, corrosive, or high-pressure fluids.

   • Float position sensed magnetically or electronically.

4. Purge Rotameter

   • Small size, used for low flow rates (e.g., purging gas lines).

5. Digital/Smart Rotameter

   • Equipped with sensors, transmitters, and digital display.

   • Suitable for integration with SCADA/DCS systems.

📌 Applications in Pharmaceuticals

• Monitoring utility lines (compressed air, nitrogen, water).

• Flow measurement in purified water (PW), WFI, clean steam systems.

• Controlling air flow in laminar air flow units and HVAC systems.

• Monitoring gas flow during fermentation or bioprocesses.

✅ In short:
A Rotameter is a variable area flowmeter that measures flow rate based on float position in a tapered tube. It is simple, reliable, and widely used in pharma, chemical, and water treatment industries.