Rotameter
Encyclopedia
A rotameter is a device that measures the flow rate of liquid
or gas
in a closed tube.
It belongs to a class of meters called variable area meter
s, which measure flow rate by allowing the cross-sectional area the fluid travels through to vary, causing some measurable effect.
in 1908. This is described in the German patent 215225. Felix Meyer found the first industrial company "Deutsche Rotawerke GmbH" in Aachen
recognizing the fundamental importance of this invention. They improved this invention with new shapes of the float and of the glass tube. Kueppers invented the special shape for the inside of the glass tube that realized a symmetrical flow scale.
The brand name Rotameter was registered by the British company GEC Rotameter Co, in Crawley, and still exists, having been passed down through the acquisition chain: KDG Instruments, Solartron Mobrey, and Emerson Process Management (Brooks Instrument). Rota with their "Rotamesser" are now owned by Yokogawa Electric Corp.
tube, typically made of glass with a 'float', actually a shaped weight, inside that is pushed up by the drag
force of the flow and pulled down by gravity. Drag force for a given fluid and float cross section is a function
of flow speed squared only, see drag equation
.
A higher volumetric flow rate
through a given area results in increase in flow speed and drag force, so the float will be pushed upwards. However, as the inside of the rotameter is cone shaped (widens), the area around the float through which the medium flows increases, the flow speed and drag force decrease until there is mechanical equilibrium
with the float's weight.
Floats are made in many different shapes, with spheres and ellipsoids being the most common. The float may be diagonally grooved and partially colored so that it rotates axially as the fluid passes. This shows if the float is stuck since it will only rotate if it is free. Readings are usually taken at the top of the widest part of the float; the center for an ellipsoid, or the top for a cylinder. Some manufacturers use a different standard.
Note that the "float" does not actually float
in the fluid: it has to have a higher density than the fluid, otherwise it will float to the top even if there is no flow.
constructed in 1903 a device for measuring the length of its lines of railway. That authority named the machine a Rotameter. It consisted of a four-wheel trolley with an additional large fifth wheel which traveled along the running surface of the rail. Its last recorded use was in the 1920s.
Liquid
Liquid is one of the three classical states of matter . Like a gas, a liquid is able to flow and take the shape of a container. Some liquids resist compression, while others can be compressed. Unlike a gas, a liquid does not disperse to fill every space of a container, and maintains a fairly...
or gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...
in a closed tube.
It belongs to a class of meters called variable area meter
Variable area meter
A variable area meter is a meter that measures fluid flow by allowing the cross sectional area of the device to vary in response to the flow, causing some measurable effect that indicates the rate.A rotameter is an example of a variable area meter....
s, which measure flow rate by allowing the cross-sectional area the fluid travels through to vary, causing some measurable effect.
History
The first variable area meter with rotating float was invented by Karl Kueppers in AachenAachen
Aachen has historically been a spa town in North Rhine-Westphalia, Germany. Aachen was a favoured residence of Charlemagne, and the place of coronation of the Kings of Germany. Geographically, Aachen is the westernmost town of Germany, located along its borders with Belgium and the Netherlands, ...
in 1908. This is described in the German patent 215225. Felix Meyer found the first industrial company "Deutsche Rotawerke GmbH" in Aachen
Aachen
Aachen has historically been a spa town in North Rhine-Westphalia, Germany. Aachen was a favoured residence of Charlemagne, and the place of coronation of the Kings of Germany. Geographically, Aachen is the westernmost town of Germany, located along its borders with Belgium and the Netherlands, ...
recognizing the fundamental importance of this invention. They improved this invention with new shapes of the float and of the glass tube. Kueppers invented the special shape for the inside of the glass tube that realized a symmetrical flow scale.
The brand name Rotameter was registered by the British company GEC Rotameter Co, in Crawley, and still exists, having been passed down through the acquisition chain: KDG Instruments, Solartron Mobrey, and Emerson Process Management (Brooks Instrument). Rota with their "Rotamesser" are now owned by Yokogawa Electric Corp.
Implementation
A rotameter consists of a taperedCone
A cone is a basic geometrical shape; see cone .Cone may also refer to:-Mathematics:*Cone , a family of morphisms resembling a geometric cone...
tube, typically made of glass with a 'float', actually a shaped weight, inside that is pushed up by the drag
Drag (physics)
In fluid dynamics, drag refers to forces which act on a solid object in the direction of the relative fluid flow velocity...
force of the flow and pulled down by gravity. Drag force for a given fluid and float cross section is a function
Function (mathematics)
In mathematics, a function associates one quantity, the argument of the function, also known as the input, with another quantity, the value of the function, also known as the output. A function assigns exactly one output to each input. The argument and the value may be real numbers, but they can...
of flow speed squared only, see drag equation
Drag equation
In fluid dynamics, the drag equation is a practical formula used to calculate the force of drag experienced by an object due to movement through a fully enclosing fluid....
.
A higher volumetric flow rate
Volumetric flow rate
The volumetric flow rate in fluid dynamics and hydrometry, is the volume of fluid which passes through a given surface per unit time...
through a given area results in increase in flow speed and drag force, so the float will be pushed upwards. However, as the inside of the rotameter is cone shaped (widens), the area around the float through which the medium flows increases, the flow speed and drag force decrease until there is mechanical equilibrium
Mechanical equilibrium
A standard definition of static equilibrium is:This is a strict definition, and often the term "static equilibrium" is used in a more relaxed manner interchangeably with "mechanical equilibrium", as defined next....
with the float's weight.
Floats are made in many different shapes, with spheres and ellipsoids being the most common. The float may be diagonally grooved and partially colored so that it rotates axially as the fluid passes. This shows if the float is stuck since it will only rotate if it is free. Readings are usually taken at the top of the widest part of the float; the center for an ellipsoid, or the top for a cylinder. Some manufacturers use a different standard.
Note that the "float" does not actually float
Buoyancy
In physics, buoyancy is a force exerted by a fluid that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the...
in the fluid: it has to have a higher density than the fluid, otherwise it will float to the top even if there is no flow.
Advantages
- A rotameter requires no external power or fuel, it uses only the inherent properties of the fluid, along with gravity, to measure flow rate.
- A rotameter is also a relatively simple device that can be mass manufactured out of cheap materials, allowing for its widespread use.
Disadvantages
- Due to its use of gravity, a rotameter must always be vertically oriented and right way up, with the fluid flowing upward.
- Due to its reliance on the ability of the fluid or gas to displace the float, graduations on a given rotameter will only be accurate for a given substance at a given temperature. The main property of importance is the density of the fluid; however, viscosity may also be significant. Floats are ideally designed to be insensitive to viscosity; however, this is seldom verifiable from manufacturers' specifications. Either separate rotameters for different densities and viscosities may be used, or multiple scales on the same rotameter can be used.
- Rotameters normally require the use of glass (or other transparent material), otherwise the user cannot see the float. This limits their use in many industries to benign fluids, such as waterWaterWater is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
. - Rotameters are not easily adapted for reading by machine; although magnetic floats that drive a follower outside the tube are available.
Another Definition
The New South Wales Government RailwaysNew South Wales Government Railways
The New South Wales Government Railways was the government department that operated the New South Wales Government's railways until the establishment of the Public Transport Commission in 1972. Although later known officially as the Department of Railways, New South Wales, it was still generally...
constructed in 1903 a device for measuring the length of its lines of railway. That authority named the machine a Rotameter. It consisted of a four-wheel trolley with an additional large fifth wheel which traveled along the running surface of the rail. Its last recorded use was in the 1920s.