A types of rotameter is used to measure the flow rate of a fluid in a closed tube. It consists of a vertical, tapered tube with a float inside that can move up and down. The float is designed to move up in the tube as the flow rate increases and down as the flow rate decreases. The float’s position within the tube is directly proportional to the flow rate of the fluid. Rotameter are commonly used in industrial and laboratory settings to measure the flow rate of liquids and gases.