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Flow Rate Meter for Gases Selection: Matching Thermal Mass vs Vortex Tech to High-Pressure Pipelines
Quick Answer: For most high-pressure gas lines above 10 bar, thermal mass meters win when you need direct mass flow, wide turndown, and low-flow sensitivity. Vortex meters are often the better buy for saturated gas, dirty gas, or lines above 100 °C where an inline meter with no bypass is easy to maintain. Send us your pressure in bar, temperature in °C, pipe size in DN, and flow range. We will return a thermal mass and vortex comparison with price and delivery.
What Changes in a High-Pressure Gas Line
Gas density rises with pressure. A vortex meter sees a stronger bluff body signal because the gas has more momentum. This reduces the low flow cutoff compared to atmospheric air. Many engineers expect vortex meters to fail at low flow. In a 20 bar hydrogen line the signal can be 4 times stronger than in a 3 bar line. That changes the selection.
Thermal mass meters do not rely on density in the same way. They measure heat carried away by gas molecules. At higher pressure the sensor sees more molecules per cubic metre. So low flow sensitivity improves. But you must know the gas composition. A thermal mass meter calibrated for air will read wrong on a methane rich stream if the conversion factor is not set.
When Thermal Mass Meters Fit Better
Use a thermal mass flow meter when you need direct mass flow without a separate pressure transmitter and flow computer. This matters in combustion air, natural gas, biogas, and gas blending. A thermal mass meter gives you kg/h or Nm3/h directly. It works well for low flow cut detection and leak testing. In practice we have seen a Vietnamese biogas plant measure 0 to 200 kg/h of biogas at 8 bar with a DN50 thermal mass insertion meter. The customer wanted to know if the flare line was leaking during off-peak hours. The thermal meter caught a 3 kg/h leak that a vortex meter could not resolve.
Silver Instruments inline thermal mass gas meter model SI-TMF-100C covers DN15 to DN100. It has a welded body rated to 40 bar standard, PT100 sensors, and 4-20 mA HART output. Higher ratings are available. Typical gases include air, nitrogen, oxygen, natural gas, biogas, argon, and carbon dioxide. Send us gas composition and moisture level. Wet gas hurts the thermal sensor accuracy.
When Vortex Meters Fit Better
Choose a vortex flow meter when the gas is dirty, saturated, or above 100 °C. Vortex meters have no small heated sensor in the stream. The shedder bar is robust. In a compressed air system in a Thai food additive plant, the customer used a DN50 stainless steel vortex meter at 11 bar. The air was wet after the receiver tank. The vortex meter lasted because there was no delicate sensor to foul. The plant needed volumetric flow for cost allocation. They did not want a thermal mass meter because of the moisture.
Vortex meters also handle steam, but that is not a high-pressure gas topic. For gas lines the sweet spot is DN25 to DN200. At 25 bar a vortex meter can measure methane from about 1.5 m/s to 35 m/s. Below that velocity the signal drops out. If your minimum flow is below
High-Pressure Pipeline Installation Notes
Both meter types need straight run. A vortex meter typically needs 15D upstream and 5D downstream after an elbow or valve. Thermal mass inline meters need less, often 10D upstream and 3D downstream. Insertion thermal mass probes can work in large pipes but need a stable profile. At high pressure the gas velocity may be low even at high mass flow. For example, a DN100 line at 30 bar with 1000 kg/h of methane has an actual velocity near 2.8 m/s. A vortex meter will be close to its minimum. A thermal mass meter will read clean.
Check the pressure drop. Thermal mass meters have low pressure drop, often under 25 mbar. Vortex meters can lose 50 to 150 mbar at high flow. This matters if you are on the edge of compressor discharge pressure.
Model Selection Inputs We Ask For
Send us these five values for a model comparison.
Gas name or mixture
Pressure in bar
Temperature in °C
Pipe size in DN and schedule
Minimum and maximum flow in kg/h or Nm3/h
We do not need a long specification document. With those values we can recommend a thermal mass insertion model or a vortex inline model. We can quote EXW, FOB, or CIF to your nearest port. Most gas meter orders for Southeast Asia and Middle East ship within 10 days.
FAQ
Which meter is better for natural gas at 20 bar? Thermal mass gives direct mass flow and handles low flow. Vortex is better if the gas has heavy hydrocarbons or condensate risk. For dry natural gas with a stable composition, thermal mass often wins.
Can a vortex meter measure mass flow of gas? A vortex meter measures actual volumetric flow. You need a pressure transmitter and a temperature sensor plus a flow computer to calculate mass flow. Some Silver Instruments vortex gas meters include this compensation onboard.
What is the turndown difference? Thermal mass meters can have a 1:100 turndown. Many vortex gas meters have a 1:20 to 1:30 turndown at 10 bar. At 30 bar the vortex turndown improves but still rarely exceeds 1:50.
Do I need explosion proof certification? Many high-pressure gas lines are in ATEX Zone 1 or Zone 2. Silver Instruments can supply both meter types with Ex d or Ex ia approval. Specify the gas group and zone when you request a quote.
What about biogas with high moisture? Use a vortex meter or install a gas dryer upstream of a thermal mass meter. Moisture and H2S will damage a thermal mass sensor over time. We have seen this on customer sites many times.
Contact Silver Automation Instruments
Tel: +86-25-68650347
Whatsapp: +86-25-52155837
WeChat: +86 15365082610
Send us your pressure in bar, temperature in °C, pipe size in DN, and flow range. We will return a thermal mass and vortex comparison with price and delivery.
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