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Mass Gas Flow Meter: Reviewing Thermal Dispersion and Coriolis Sizing
Quick Answer: Thermal dispersion meters are the standard choice for clean industrial gases in lines from DN25 to DN200. Coriolis meters give direct mass flow and density for high value gas, custody transfer, and wide turndown applications. For a fast quotation, send us your gas composition, pressure in bar, temperature in degrees C, pipe size DN, and flow range in kg/h.
Why Gas Flow Measurement Starts With Mass
Many engineers still size a gas flow meter using volumetric units. A volumetric reading works only if pressure and temperature stay constant. In practice, gas density shifts with ambient temperature, compressor load, and line pressure. Mass flow avoids that correction step.
Silver Automation Instruments supplies two main gas mass flow meter types. One is thermal dispersion. The other is Coriolis. Both report mass flow directly.
But the right choice depends on gas type, moisture level, pressure, pipe size, and accuracy target.
For natural gas boilers in Southeast Asia we often see pipe sizes from DN40 to DN100. Operating pressure is usually 0.5 to 4 bar. Thermal dispersion works well there.
Thermal Dispersion Gas Flow Meters in the Field
A thermal dispersion meter uses two PT100 sensors. One sensor is heated. The other reads gas temperature. Gas flow removes heat from the heated sensor. The electronics convert the cooling effect into mass flow.
These meters are direct insertion or inline. For DN15 and DN20 pipes we usually recommend an inline body. For DN50 and larger, insertion types reduce cost and pressure drop.
Silver Instruments TMF-100 inline thermal mass flow meter covers DN15 to DN50. The TMF-200 insertion type covers DN50 to DN300. Both use PT100 sensors and 4-20 mA HART output.
We have seen reliable results on compressed air, nitrogen, natural gas, biogas, and oxygen lines. The gas must be clean and dry. Liquid droplets or heavy condensate cause measurement drift.
Here is the thing. Thermal meters are not ideal for wet biogas. A wastewater digester in New Zealand learned this before they switched to a Coriolis meter. Moisture and H2S were too aggressive for the thermal sensor.
Output options include 4-20 mA HART, RS485 Modbus, and pulse. ATEX Zone 1 versions are available for hazardous gas areas.
Coriolis Mass Flow Meters for Gas Service
A Coriolis mass flow meter measures mass flow directly by detecting phase shift in vibrating tubes. The Coriolis meter also reports density and temperature. The density signal helps with gas composition changes.
We recommend Coriolis for gas flow in custody transfer, reactor feed lines, fuel gas to turbines, and pilot plant applications. Accuracy in gas service is often 0.2 to 0.5 percent of rate. Coriolis accuracy beats thermal dispersion in many low flow and high turndown cases.
Silver Instruments CMF-300 Coriolis mass flow meter covers DN3 to DN150. It outputs mass flow, density, and temperature. HART and Modbus are standard options.
A paint manufacturer in Vietnam needed nitrogen and solvent vapor measured in one line. The density output from a Silver Instruments Coriolis meter showed when solvent loading changed. The density signal gave the plant a direct process alarm.
For gas applications, you need to check pressure drop. Coriolis meters introduce more pressure loss than thermal insertion probes. So we always calculate velocity and pressure drop before proposing a line size.
For gas viscosity above 0.02 cP, we check the Reynolds number and sensor drive gain. The viscosity check matters for fast density shifts or high molecular weight gases.
Sizing Rules Engineers Actually Use
We ask for five data points. Gas composition, pressure in bar, temperature in de
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For thermal dispersion, minimum measurable flow is often 0.5 Nm3/h on small lines. For Coriolis, gas density at low pressure can reduce accuracy. A general rule is to keep gas velocity below 100 m/s for mass flow meters.
Pressure matters. At 1 bar, gas density is low. A Coriolis meter may need a larger line or higher pressure to generate enough mass flow signal. In many plant air systems at 7 bar, both meter types perform well.
Temperature also matters. Standard thermal meters in the Silver Instruments TMF series handle process temperatures from -40 degrees C to 200 degrees C. Standard Coriolis meters handle -50 degrees C to 200 degrees C. High temperature versions go up to 350 degrees C.
Pipe size DN is not just mechanical. It changes flow velocity, pressure drop, and total cost. For DN100 natural gas, an insertion thermal meter is often the most cost effective. For DN25 reactor gas feed, a Coriolis meter works better because of low flow and density output.
Most engineers skip the gas density check. This mistake causes trouble later. So we always calculate density at the minimum pressure and maximum temperature before proposing a meter.
How to Choose Between Thermal Dispersion and Coriolis
Choose thermal dispersion when the gas is clean, dry, and the application is industrial process control or utilities. Think compressed air, nitrogen blanketing, natural gas to burners, and oxygen distribution.
Choose Coriolis when you need custody transfer accuracy, density output, wide turndown, or measurement of wet and dirty gas. Coriolis is also stronger for very low flow rates on small lines.
Cost is not the only factor. A Coriolis meter for DN50 gas may cost more than a thermal insertion meter. But in a chemical reactor feed line, the density output can prevent a batch failure. That value outweighs the price difference.
We have supplied gas mass flow meters to projects in Malaysia, Australia, Vietnam, Chile, Saudi Arabia, and South Africa. Many of these were replacement projects where a volumetric meter was giving errors because of temperature swings.
A marine fuel gas line in Singapore used a Coriolis meter to handle natural gas and diesel pilot flow. The density output helped the crew verify fuel changeover.
FAQ: Five Gas Flow Meter Sizing Questions
Which meter is better for compressed air flow measurement? Thermal dispersion meters are the usual choice because they handle clean dry air from DN25 to DN200 with low pressure drop and easy insertion installation.
Can a Coriolis mass flow meter measure biogas? Yes. Coriolis meters handle wet gas and changing density better than thermal dispersion. We have supplied Coriolis meters for biogas lines in wastewater plants.
What is the minimum gas pressure for a thermal dispersion meter? Most thermal dispersion meters work down to 0.2 bar gauge. Some insertion designs can measure at atmospheric pressure. Low pressure applications still require a velocity check.
Does a Coriolis meter require straight upstream pipe? A properly sized Coriolis meter needs less straight run than an orifice plate or turbine meter. In most installations, 0 to 5 pipe diameters of straight run is enough. The meter geometry also reduces swirl.
What information do you need for gas flow meter sizing? Send us gas composition, pressure in bar, temperature in degrees C, pipe size DN, and flow range in kg/h. We will reply with a model recommendation and price.
Send us your pressure (bar), temperature (°C), pipe size (DN), and flow range. Add gas composition if it is not air. Tel: +86-135-1213-1526. Whatsapp: 86-135-12131526. WeChat: +86 13512131526.
For more product details, visit flow-meter.com.au.
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