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Mass Flowmeter Types, Selection & Working Principle
Quick Answer
Mass flowmeters measure fluid mass directly, not volume or velocity. The two types most engineers use are Coriolis mass flow meters and thermal mass flow meters. Pick Coriolis for liquids, high viscosity, slurries, or when you need live density. Choose thermal for dry gas: compressed air, nitrogen, natural gas, biogas. Silver Automation Instruments supplies both with 4-20 mA HART, pulse, RS485, and ATEX options.
Mass Flowmeter Types
Industrial users really deal with two direct mass measurement technologies. Here is the thing, Coriolis covers liquids and slurries. Thermal handles gas and costs less. Other types like differential pressure based mass flow exist but are not direct mass meters. We focus on what works in real plants.
A Coriolis mass flow meter has one or two vibrating tubes. An excitation coil keeps the tubes oscillating at their natural frequency. Fluid mass moving through the vibrating tubes generates a Coriolis force. That force creates a tiny phase shift between the inlet and outlet legs. Two pick-off sensors measure the time delay. That delay is proportional to mass flow rate. You do not need separate temperature or pressure compensation. The same meter also calculates fluid density, which is useful for quality checks. We have seen a brewery in Mexico use density readings from our Coriolis meter to track Plato degree of wort in real time.
These meters handle pipe sizes from DN1 up to DN300. Wetted parts are typically 316L stainless steel or Hastelloy C22 for aggressive chemicals. Standard accuracy is 0.1 to 0.2 percent of rate. They handle viscosity up to 100,000 cP. Last year a palm oil processor in Indonesia ordered a DN15 Coriolis meter. Fluid was crude palm oil, 80 cP at 60 degree C, flow range 0 to 500 kg/h, pipe size DN15. They needed ATEX Zone 1 and 4-20 mA HART. We delivered model SLW-C-DN15 within three weeks. No straight pipe requirement made installation easy.
A thermal mass flow meter works on heat dissipation. It inserts two PT100 sensors into the gas stream. One sensor is heated at constant power, the other measures gas temperature. Gas molecules flow past and carry away heat. The cooling effect directly relates to mass flow, not volumetric changes. So you avoid separate pressure and temperature transmitters. This technology fits clean, dry gas only. We often ship thermal meters to textile mills in Bangladesh. They measure compressed air from 0 to 1000 Nm3/h in a DN80 pipe. Output is 4-20 mA plus RS485 Modbus. No moving parts means years of zero maintenance.
Selection Guidelines for Mass Flowmeters
Start with your fluid. Is it liquid or gas? For liquids, even viscous ones, Coriolis is the most accurate solution. For dry gas like instrument air or nitrogen, thermal mass is simpler. If the gas is wet or dirty, Coriolis can still work but expect a higher pressure drop. Most engineers choose Coriolis for chemicals, edible oils, fuel, and pharmaceutical ingredients. Thermal dominates compressed air, digester gas, and natural gas distribution monitoring.
Next, define flow range in kg/h or t/h, pipe size DN, and process conditions. Give us pressure in bar and temperature in degree C. A natural gas line in Nigeria at 40 bar needs a thermal mass meter with high
Material matters. A desalination plant in Saudi Arabia measured brine. They used a Coriolis with Hastelloy C tubes to prevent corrosion. Standard 316L would not last. In food and beverage, 316L with sanitary Tri-Clamp connections is common. For highly corrosive acids we sometimes use PTFE lining, but that is less frequent in mass flow meters.
Here is another real case. A chemical plant in Vietnam needed to measure methyl acetate flow. Pipe DN25, flow 0 to 2000 kg/h, pressure 10 bar, temperature 30 degree C. They requested explosion-proof with local display and 4-20 mA HART. We supplied a Coriolis SLW-C-DN25. Commissioning took one afternoon. They liked how the meter showed density online and helped catch wrong solvent batches.
Working Principle Overview
A Coriolis meter uses inertia. The vibrating tubes accelerate the fluid mass. That creates a twisting force. Two pick-offs measure the slight time lag between the inlet and outlet sides. The time lag is a direct measure of mass flow. The electronics also read oscillation frequency and calculate density. So one device outputs mass flow, density, and temperature via a built-in PT100. No moving seals, no drift.
A thermal mass meter relies on convective heat transfer. Constant power heats one RTD sensor. Gas flow carries heat away. The temperature difference between the heated sensor and the reference sensor changes with mass flow. The electronics linearize this signal. No moving parts. Customers on biogas lines often install them and forget them for ten years.
FAQ
What accuracy can I expect from a Coriolis mass flow meter?
Standard models give plus minus 0.2 percent of reading. High-accuracy versions reach 0.1 percent. This stays stable even if viscosity or density changes.
Can a thermal mass meter measure liquid?
No. Thermal mass flow meters are for gas only. Even a small amount of liquid droplets causes reading errors. Use a Coriolis meter for any liquid application.
Do Coriolis meters need straight pipe runs?
Normally no. You can install them directly after a pump or elbow. Only in very high velocity cases a short straight run helps. Thermal meters need 10D to 15D upstream for a stable gas velocity profile.
What is the pressure drop across a Coriolis meter?
It depends on tube geometry and flow rate. Straight-tube designs have lower pressure drop than bent-tube types. For viscosities up to 1000 cP, pressure drop is usually acceptable. Send us your data and we will calculate it.
How do I request a quote and delivery time?
Send us your fluid name, flow range in kg/h, pipe size DN, pressure in bar, temperature in degree C, and any certifications you need. Email sales at flow-meter.com.au. We reply with a formal quote within 8 business hours. For popular models, you can also check our partner site flow-meter.com.au for fast stock delivery.
Still unsure? Send us your process details. We will pick the right mass flow meter and prepare a quote with lead time.
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