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High Temperature Gas Flow Meter Selection: Thermal Mass vs Vortex for Saturated Vapor Lines
Quick Answer: For saturated vapor lines above 150°C, choose a vortex flow meter with pressure and temperature compensation. Thermal mass flow meters are not a good fit for wet saturated vapor because liquid droplets cause sensor drift and fouling. Send your pressure (bar), temperature (°C), pipe size (DN), and flow range to Silver Instruments for a direct model selection.
Many engineers ask us this question when they deal with steam headers, reboilers, jacket heating lines, or saturated vapor from waste heat boilers. The answer changes once you know the actual vapor condition. Saturated vapor is not always a clean dry gas. It sits close to the dew point. A small pressure drop or heat loss can produce liquid. That liquid damages thermal mass flow meter sensors. Vortex flow meters handle this condition better.
What Works on a Saturated Vapor Line
Vortex flow meters use a bluff body in the pipe. The vapor sheds vortices at a frequency proportional to flow velocity. There are no moving parts in the flow stream. The sensor body can be made from 316L stainless steel. The electronics can be remote mounted for high temperature lines. We have installed these on steam lines up to 250°C with PT100 temperature sensors and pressure transmitters for density compensation.
Most engineers skip this part. Saturated vapor density changes with pressure and temperature. A vortex meter gives velocity data. You need compensation to get mass flow in kg/h. Silver Instruments offers vortex flow meters with integrated 4-20 mA HART output. You can connect a pressure transmitter and PT100 to the flow computer. The output can be mass flow, standard volume flow, or energy flow.
Why Thermal Mass Flow Meters Struggle on Wet Saturated Vapor
Thermal mass flow meters measure heat loss from a heated sensor to the gas. Wet droplets hit the sensor. The droplets cool the probe in a nonlinear way. The reading spikes or drifts. Condensate also forms on the probe surface. That changes the heat transfer coefficient. In practice, a thermal mass flow meter needs a clean dry gas. It works well on compressed air, nitrogen, biogas, or superheated vapor. Do not use it on saturated vapor lines that can carry condensate.
Here is the thing. Some suppliers still recommend thermal mass flow meters for steam because the sensor can be ordered for high temperature. The probe may survive 200°C. But survival is not the same as accuracy. We have seen this on customer sites many times. A paint manufacturer in Southeast Asia replaced a thermal mass flow meter on a saturated vapor line after three months. The probe was coated. The flow readings were unstable. The replacement vortex flow meter lasted years with no major drift.
Pressure, Temperature, and Pipe Size Data You Should Prepare
Before you ask for a high temperature gas flow meter quote, collect these four data points. Pressure in bar, temperature in °C,
Silver Instruments supports DN15 to DN300 vortex flow meters for many gas and vapor applications. For high temperature lines above 200°C, we recommend remote mount electronics. The flow sensor can handle process temperatures up to 250°C or 300°C depending on the model. We can also supply ATEX Zone 1 options for hazardous areas.
Output Signals and System Integration
Our vortex flow meters come with 4-20 mA HART as standard. You can also get pulse output, RS485 Modbus, or a local display. For steam mass flow, we normally supply a flow computer or use your DCS to calculate mass flow from the analog signals. If you need a packaged solution, we can include a pressure transmitter and PT100 in one shipment.
For dry gas and superheated vapor lines, we supply thermal mass flow meters with direct mass flow output. These meters are good for line sizes from DN15 to DN100. They work well on gas fuel lines, compressed air headers, and flue gas measurement. But for saturated vapor, the vortex meter is the safer choice.
Customer Example from Vietnam
Last year a customer in Vietnam asked us for a flow meter on a saturated steam line at 7 bar and 170°C. The pipe size was DN80. The flow range was 400 to 4000 kg/h. We supplied a vortex flow meter with a PT100 and a pressure transmitter. The local integrator wired the 4-20 mA HART signals into a PLC. The plant now reads mass flow directly on the screen. The total installed cost was lower than a thermal mass flow meter with a special high temperature probe.
FAQ
Can a thermal mass flow meter measure saturated steam?
No. Liquid droplets cause sensor fouling and unstable readings. Use a thermal mass flow meter only for dry gas or superheated vapor.
What pipe sizes do Silver Instruments vortex flow meters cover?
We cover DN15 to DN300 for most models. Larger sizes are available on request.
Do I need pressure and temperature compensation for saturated vapor?
Yes. Saturated vapor density changes with pressure and temperature. Compensation is needed for kg/h mass flow output.
What output signals are available?
4-20 mA HART is standard. Pulse, RS485 Modbus, and local display options are available.
How do I request a quote for a high temperature gas flow meter?
Send us your pressure (bar), temperature (°C), pipe size (DN), and flow range. Contact Silver Instruments at +86-25-68650347 or WhatsApp +86-25-52155837. WeChat is +86 15365082610.
Silver Automation Instruments supplies vortex flow meters, thermal mass flow meters, and complete steam measurement packages. Send us your pressure (bar), temperature (°C), pipe size (DN), and flow range. We will return a model selection with price and delivery.
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