rotameter

A variable area flow meter, also known as a rotameter, is a type of flow measurement device that uses a tapered tube and a float to indicate the flow rate of a fluid. It operates based on the principle of balancing the forces of gravity and fluid drag on the float.
The construction of a variable area flow meter typically includes the following components:
Tapered Tube: The variable area flow meter consists of a vertical or inclined tube with a conical or tapered shape. The tube is transparent so that the position of the float inside can be easily observed.
Float: A float, typically a ball or a cylindrical shape, is placed inside the tapered tube. The float is free to move vertically within the tube, and its position is influenced by the flow rate of the fluid. The float is designed to have a specific density that allows it to achieve equilibrium between the upward force of fluid flow and the downward force of gravity.
Scale: The tapered tube has a scale alongside it, marked with flow rate units such as liters per minute (LPM) or cubic feet per hour (CFH). The scale indicates the flow rate corresponding to the position of the float.
The operation of a variable area flow meter can be summarized as follows:
Fluid Flow: The fluid enters the bottom of the tapered tube and flows upward, causing the float to rise.
Equilibrium: As the fluid flow increases, the upward drag force on the float increases, counteracting the downward force of gravity. The float reaches a position of equilibrium where these forces balance.
Flow Rate Indication: The position of the float inside the tapered tube corresponds to a specific flow rate, which is read from the scale alongside the tube.
The advantages of variable area flow meters include their simple design, ease of installation, and suitability for a wide range of flow rates and fluid types. They provide a visual indication of flow rate, making them easy to read and monitor in real-time. However, they may not offer the same level of accuracy as more sophisticated flow measurement technologies.
Variable area flow meters are commonly used in applications where general flow trend indication is sufficient, such as in water treatment, chemical processing, HVAC systems, and laboratories. They are particularly well-suited for measuring low to moderate flow rates of clean and non-viscous fluids.