Fluid flow measurement is used in almost every process from small-scale medical applications to large petroleum refineries. Industries use flow metering devices to regulate the amount of chemicals to be reacted or separated in a continuous process and accurately determine the production rate. Flow meters are also indispensable in the supply of utilities such as water and gas to your home. There are many types of flowmeters used in industry, but all flowmeters need to be calibrated.
A rotameter consists of a graduated tapered glass tube mounted vertically in a frame with the larger end up. The fluid flows upward through the tapered tube and suspends a float (or bob) in the flowing stream. The float indicates the relative flow rate of the fluid using the graduations on the glass scale. Measurements using the float are made at its largest cross-section which is at the center of a spherical float.
At a given flow rate the float maintains an equilibrium position and therefore does not move. The three forces acting on the float are: (1) the weight of the float ß , (2) the buoyant force of the fluid on the float Ý , and (3) the drag force on the float Ý .
A simplified rotameter equation is used to describe the rotameter operation.
Areameters
In case of Full-Bore meters, the variation of flow rate through a constant area is related to the flow rate. Unlike full-Bore meters, area flow meters are devices in which pressure drop is constant and the area through which the fluid flows varies with flow rate.
Rotameter
Rotameter is a typical area meter. It consists of gradually tapered glass mounted vertically in a frame with the large end up. Fluid flows upward through the tapered tube and suspends freely a float (which is submerged in the fluid). Float is the indicating element, and the greater the flow rate, the higher the float rides in the tube.
The tube is marked in divisions, and the reading of the meter is obtained from the scale reading at the reading edge of the float, which is taken at the largest cross section of the float.
A calibration curve must be available to convert the observed scale reading to flow rate.
Advantages of a Rotameter
Can be modified to cater to the needs of individual operation. For example, in case of a rotameter with a metal case, the float can have an extension.
The float of the rotameter rotates to indicate smooth operation. Float shapes and proportions can be varied for different applications.
