Flow measurement is the process of putting a fluid flow into quantity when it is moving through a pipe section to determine and restrict the flow rate. The flow measurement process is done using various technological devices known as flow meters.
Flow meters measure, regulate, control, and monitor the flow rate of gases, water, chemicals, air, solids, or steam.
Flow measurement technologies can be classified into five groups depending on the working or operational mode. This article will discuss the five groups in detail, with examples of each case.
1. Differential Pressure Flow Meters
It is a flow measurement technology that many industries use in various applications. The working principle of this flow meter states that a decrease in the fluid flow pressure increases the fluid velocity and vice versa. Pressure drop across the meter is usually proportional to the flow rate square.
Therefore, to get the flow rate value, you need to measure the differential pressure, find its square root and multiply the answer with the coefficient of meter area. Differential pressure has a detecting pressure component that works with the unit of measurement.
Examples of flow meters under this type are; orifice plates, Venturi meters, target meters, elbow meters, flow nozzles, pitot, and flow tubes
2. Velocity Flowmeters
Velocity flow meters usually operate under uniform flow locations where they measure the velocity of the flowing fluid. The fluid speed and the flow rate correlates with the flow rate volume. They can both be intrusive and non-intrusive.
For intrusive velocity meters, pressure loss may be increased due to their location inside the pipe, which acts as the flow path as opposed to non-intrusive
meters which are situated outside the line, although they may need conduits and sensors for effective operation.
Examples of velocity flow meters include;
a)Vortex flow meters.
b) Ultrasonic flow meters.
c) Turbine meters
d) Propeller flow meters
e) Magnetic flow meters.
f) Calorimetric flow meters.
3. Open Channel Control Structures
Open channel flow meters are flow measurement technologies that determine the flow rate by measuring the flow area stream and the fluid head generating the flow. Available channel flow meters come in two main types, i.e., weirs and control flumes.
Weirs have an obstruction with an opening across the channel, which increases the water level behind the weirs. The flow rate of a flowing fluid over the Weir is always the water depth function above the Weir crest. An excellent example of Weir construction is v-notch, broad-crested, and rectangular.
On the other hand, the flume control flow meter starts with a reduction in the flume cross-section. Flowing fluids generate a discharge by leaving some water surface depths through the flowing path. Hence the utilisations of head versus flow measurement relationship discharge.
The accuracy level of the two open channel flow meter devices is always the same. However, weirs are much cheaper than flume control flow meters.
4. Other Closed Conduits Flowmeters
Examples are positive displacement flow meters and mass flow meters. Positive displacement flow meters work by separating and calculating the fluid volumes flowing in a pipe to measure the flow rate. Different types of positive displacement flow meters use various calculation means of measurement depending on their design.
The accuracy range with positive displacement flow meters lies in a range of 0.5% over a 10:1 fluid flow rate, and they do not need straight pipe lengths to operate effectively.
On the other hand, mass flow meters, sometimes known as the Coriolis or inertial flow meters, work by measuring the mass flow rate of a fluid in a group per unit of time. The mass flow rate of a fluid divided by its density usually brings out the flow rate volume.
Conversation of mass flow rate to flow rate volume may bring inaccurate results under certain conditions like air bubbles.
5. System Generated Curves
Examples include; current meter flow measurement and dye dilution.
They measure the fluid flow rate under an extensive flow range by creating a pump speed check and the fluid flow as the flow measurement is recorded. These devices usually need a permanent installation of pressure taps to ease the operation process.
The area velocity and dye dilution methods are the commonly used procedures for measuring water flow in a specific area.
Flow measurement technologies help in accomplishing various industrial applications. The types of applications will determine which flow measurement technology is the best to employ.