How to Select Gas Flow Meters

Image Credit: OMEGA Engineering Inc., Aalborg Instruments, Clark Solutions

Gas flow meters are used for measuring the flow or quantity of a moving gas.  Measuring the flow of fluids is a critical need in many industrial plants. The ability to conduct accurate flow measurements allows process operators to properly monitor and control flow. In some cases, inaccurate flow measurements or failure to take measurements can cause serious (or even disastrous) results.

The basis of good flow meter selection is a clear understanding of the parameters surrounding a particular application. These may include gas type, gas viscosity, possible contaminants or corrosive elements, pipe or system size, etc. Gas flow meters can be classified based on type, performance specifications, and features.

Types of Gas Flow Meters

There is a vast array of different types of flow meters, but most can be classified by the means in which it measures flow.

• Differential pressure flow meters rely on Bernoulli's principle, measuring pressure drop over an obstruction inserted in the flow to correlate to gas flow.
• Velocity flow meters measure the velocity at one or more points of flow and integrate the flow velocity (v) over the area (A) to calculate flow (Q), using the relationship:

Q = v x A

• Positive Displacement flow meters measure gas flow by precision-fitted rotors in which rotation is proportional to the volume of the displaced fluid.
• Mass flow meters use various means such as heat to measure mass flow rate.

Performance Specifications

The GlobalSpec SpecSearch Database provides industrial buyers the ability to select gas flow meters based on performance specifications. These include the flow rate range, operating temperature, and operating pressure.

• Flow rate range is the range of fluid flow that the device is designed to measure. Mass, velocity, or volumetric flow rates above or below the specified values may not be measurable by the device and could damage the instrument or its calibration.
• Operating temperature is the accepted range of temperatures in which the device can properly operate. Handling media outside this range could damage the instrument.
• Operating pressure is the accepted range of pressures in which the device can properly operate. Pressures below this range may not be measurable and those exceeding this range could cause device failure.

Features

Gas flow meters can include a number of additions to make the device compatible with the system. These include mounting types, various end fittings, interface options, and electrical outputs. They may also include a number of different features to offer additional measuring capabilities such as temperature or density.

References

Engineering Toolbox - Types of Fluid Flow Meters

• Ultrasonic Gas Flow Meters
  Ultrasonic meters include Doppler Effect meters and time of flight meters. Doppler meters measure the frequency shifts caused by liquid flow. The frequency shift is proportional to the liquid's velocity. Time of flight ultrasonic meters use the speed of the signal traveling between two transducers...
• Advancing Thermal Mass Gas Flow Meters for 21st Century Process & Plant Needs
  Process, instrument and plant engineers are challenged. continuously by productivity and plant operating. efficiency objectives as well as ensuring plant compliance. with an ever expanding list of regulations. This situation. burdens the plant's process engineering and operations. team with...
• Greenhouse Gas Flow Monitoring (.pdf)
  in the US meeting the criteria for reporting of greenhouse gases. Air/gas flow meters are an essential tool in GHG emission monitoring. ./04828189-833a-495f-9755-50cb27dcf025 Technical Publication. Greenhouse Gas Flow Monitoring. By Allen Kugi, Member Technical Staff. Fluid Components...