The first rotameter including a float was invented by Karl Kupers in Aachen in 1908. After that, the invention was improved with new float shapes and glass tube. Karl Kupers designed a special model inside the glass tube to detect the symmetrical flow scale. Rotameter is also known as variable area flow meter.
The rotameter brand name is mentioned by the English company “GEC Elliot automation”. Similarly in Germany, the brand is owned by Rota Yokogawa GmbH & Co. KG is registered. So it is currently owned by Yokogawa Electric Corp.
What is an acid rotameter?
The acid rotameter is a reliable, simple and inexpensive flow measurement tool. Therefore, this tool is used to measure the flow rate of acid or acid gas. This rotameter consists of a conical tube through a movable internal float. Sometimes, acid rotameters are also called acid gravity flowmeters, acid mechanical flowmeters, or acid variable area flowmeters (the liner has Teflon). In gravity flowmeters, the term gravity means that the rotameter must be installed vertically. The rotameter looks like the figure below.
The working principle of the acid rotameter is to measure the flow rate of the liquid as the acid is supplied throughout a conical tube. When acid is supplied throughout the pipe, its cross-sectional area increases.
Making an acid rotameter
The construction of acid rotameter can be done using different components such as transparent tube, scale, float and transmitter.
- In construction, the shape of the transparent tube is conical, which contains a range and floats inside. This transparent tube is very useful for direct observation of measurements.
- The float is a small device inside the tube of an acid rotameter with precise dimensions. The float is used to indicate the amount of liquid flow inside the pipe, which can be designed with plastic, glass or metal.
- The scale in this rotameter displays the current measurement by indicating with a float.
- Transmitters are very useful in accurately recording current measurements compared to what we see directly on the scale.
- It consists of a float and a conical tube where the float is placed inside the conical tube. At both ends of the device, the networks are arranged through a pipeline using flanged connections. Rotameters are always connected vertically in pipelines and a scale on the pipe is available to check the flow rate values directly.
How does an acid rotameter work?
In a rotameter, liquid flows through the base of the conical tube, after which some of the liquid hits the bottom of the float directly, and the remaining liquid exits the float. Therefore, the float in the rotameter experiences two forces in opposite directions, the force of gravity is a downward direction and the drag force is in an upward direction.
The flow of liquid pushes the buoyant upward due to gravity. After some time, the flow region reaches a position where the force on the floating object exactly matches the weight of the float. So the float will find equilibrium when the area in the float produces enough drag force that is equivalent to the weight.
When gravity and the weight of the float are both constant, the upward distance of the float is proportional to the velocity of the fluid flowing across the conical tube.
The components that you should consider when choosing rotameters are the following parameters.
The flow rate is the same as the volumetric flow rate of fluid and gas.
- Operating pressure
- Liquid temperature
- Diameter pipe
- Indicates the scale type
- milk requirements
Advantages and Disadvantages
The advantages of Rotameter include the following:
- Inexpensive
- The pressure drop is low.
- Good tolerance
- It is suitable for small discharges.
- It is easily used with switches, alarms or any transmitting device.
- Using these rotameters, the flow rate of corrosive liquids can be measured.
The following are the disadvantages of rotameter.
- It must be connected vertically
- The glass tube is difficult to handle.
- Not suitable for pulsating services.
- Limited to small pipe services
- Limited to low temperatures.
- Its accuracy is ± 1.2 to 10%
- It uses inline installation.
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