5 Types of Flow Meters
What is the Purpose of a Flow Meter?
A flow meter is used in different types of applications to measure the volumetric flowrate or mass flowrate. The specific application defines the type and capacity of the flow meter. Fluids, gases and liquids, are measured in terms of volumetric flowrate and mass flowrate. Both are related to material's density with volumetric flowrate denoted by Q and mass flowrate by ṁ in the equation ṁ=Q x ρ.
What are the Different Kinds of Flow Meters?
There are numerous types of flow meters depending upon the application, the specific fluid and the construction, including materials, of the flow meter. The 5 basic classification of flow meters include:
1. Differential Pressure Flow Meters
Differential pressure flow meters measure the differential pressure across an orifice where flow is directly related to the square root of the differential pressure produced. There are also primary and secondary elements in differential flow meters. The primary element produces change in kinetic energy using either flow nozzle, pitot tube, orifice plate, or venturi flow meters. The secondary element measures the differential pressure and provides the signal.
Differential pressure meters represent around 1/5 of all flow meters around the world. They are commonly used in the oil & gas industry, along with HVAC, beverage, water, pharma, mining, paper and chemical applications.
2. Positive Displacement Flow Meters
Positive displacement (PD) flow meters measure the volume filled with fluid, deliver it ahead and fill it again, which calculates the amount of fluid transferred. It measures actual flow of any fluid while all other types of flow meters measure some other parameter and convert the values into flowrate. In PD flow meters, output is directly related to the volume passing through the flow meter. PD flow meters include piston meters, oval-gear meters, nutating disk meters, rotary vane type meters, etc.
Positive displacement flow meters are known for their accuracy. They are commonly used in the transfer of oils and fluids, like gasoline, hydraulic fluids as well as in-home use for water and gas applications.
3. Velocity Flow Meters
Velocity meters measure velocity of the stream to calculate the volumetric flowrate. These are less sensitive when the Reynolds number of fluid is higher than 10000. Velocity flow meters include turbine, paddlewheel, vortex shedding, electromagnetic and sonic/ultrasonic flow meters.
4. Mass Flow Meters
Mass flow meters are more effective in mass related processes as they measure the force that results from the acceleration of mass. More specifically, the force is measured as the mass moving per unit of time, instead of the volume per unit of time. Mass flow meters include Coriolis mass meters and thermal dispersion meters.
Typical applications for mass flow meters are tied to chemical processes. In addition to the chemical and gas industries, typical industries using mass meters include pharma, power, mining and wastewater.
5. Open Channel Flow Meters
Measurement of liquid in open channels include v-notch, weirs and flumes. These dam-like structures, or overflows, allow for a limited or concentrated free-flow of liquids based on the unique shape and size of the structure. This type of flow meter allows for a reading of the flowrate to be calculated.
Common applications of open channel meters include free flowing liquids like streams, rivers, irrigation channels and sewer/watewater systems.