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Types of Mass Flow Meter: Comparing Coriolis and Thermal Dispersion Tech
Quick Answer: Coriolis mass flow meters measure true mass flow directly. They work for liquids and gases across a huge range. Thermal dispersion meters measure gas mass flow using heat transfer principles. Choose Coriolis when you need high accuracy on liquids or gases and can accept a higher price. Choose thermal dispersion when you measure low pressure gas or need a simpler insertion style meter for large pipes.
What a Mass Flow Meter Actually Does
Mass flow meters measure the mass of fluid moving through a pipe per unit of time. The units are kg/h, lb/min, or tonnes per hour. This is different from volumetric flow meters that measure m³/h or L/min. Why does mass matter. Because gas volume changes with temperature and pressure. Liquid volume shifts a little with temperature. Mass stays the same no matter what. A kilo of nitrogen is a kilo of nitrogen at 5 bar or 50 bar. Engineers in chemical dosing, custody transfer, and combustion control care about mass. Not volume.
Two technologies dominate the mass flow meter market today. Coriolis mass flow meters and thermal dispersion mass flow meters. They work on completely different physics. Their ideal applications barely overlap. We will break down both types with real specs, real prices, and real installation notes from customer sites in Thailand, Nigeria, Chile, and Saudi Arabia.
Coriolis Mass Flow Meters: Direct Mass Measurement
A Coriolis meter forces fluid through one or two vibrating tubes. When fluid passes through the vibrating tubes, it causes a phase shift in tube oscillation. This phase shift is directly proportional to mass flow rate. No compensation needed for temperature, pressure, density, or viscosity changes. The meter also measures fluid density from the natural frequency of the tubes. So you get mass flow, density, and temperature from one device. Some models can infer volume flow too.
Silver Instruments makes the SI-CMF series for line sizes from DN03 up to DN300. The DN15 model handles 0 to 1000 kg/h with an accuracy of ±0.1 percent of reading for liquids. The wetted parts come in 316L stainless steel as standard. Hastelloy C-22 is available for corrosive chemicals like hydrochloric acid or sodium hypochlorite. Process connections include tri-clamp for food and beverage plants or ANSI flanges for oil and gas pipework. Output options are 4-20 mA HART, pulse, RS485 Modbus, or PROFIBUS DP.
A paint manufacturer in Malaysia uses the SI-CMF-25 on solvent transfer lines. The meter runs at 2 bar and 35 degrees Celsius. Viscosity of the solvent is around 80 cP. The Coriolis meter handles this without any correction factor. A turbine meter or oval gear meter would need recalibration when the solvent formulation changes. The plant manager told us the Coriolis meter paid for itself in 11 months through reduced solvent waste and fewer batch rejects.
But. Coriolis meters have limits. They are sensitive to mechanical vibration from nearby pumps and compressors. Installation must include proper pipe supports and sometimes flexible connections. Bubbles in the liquid cause measurement errors. So you need adequate back pressure. High viscosity above 2000 cP creates excessive pressure drop across the meter. The upfront cost is higher than any other flow meter type. A DN25 Coriolis meter from Silver Instruments costs more than a thermal meter of the same size.
ATEX Zone 1 and Zone 2 certifications are available for gas group IIC. We have supplied SI-CMF meters to oil terminals in Nigeria where the ambient temperature hits 48 degrees Celsius and the meter sits under direct sun. No drift issues after 18 months of continuous operation. The density measurement helps detect product interface changes in multi-product pipelines.
Thermal Dispersion Mass Flow Meters: Heat Transfer Based
Thermal dispersion meters use two PT100 RTD sensors inserted into the gas stream. One sensor measures the process gas temperature. The other sensor is heated to a constant temperature difference above the gas temperature. As gas flows past the heated sensor, it carries heat away. The electronics measure how much power is needed to maintain the temperature difference. This power consumption is proportional to the mass flow of gas molecules cooling the sensor. More gas mass equals more cooling equals more power required.
Silver Instruments builds the SI-TMF series for pipe sizes from DN15 to DN3000. The inline version suits small pipes up to DN50. The insertion version goes into large ducts and stacks through a 1.5 inch ball valve with hot tap capability. You can install and retract the probe without shutting down the process. This matters for biogas plants and wastewater treatment aeration basins that run 24 hours a day.
Accuracy is typically ±1.5 percent of full scale plus ±0.5 percent of reading. This is less precise than a Coriolis meter. But thermal meters have almost no pressure drop. The insertion probe creates negligible obstruction. A DN1000 air duct with an insertion thermal meter loses maybe 0.5
One of our customers runs a compressed air system for a textile factory in Surabaya, Indonesia. They installed an SI-TMF-80 inline thermal meter on a 3 inch air header at 7 bar. The meter detects leaks downstream by tracking air consumption during plant shutdown hours. After fixing leaks identified through flow data, the plant saved 22 percent on compressor electricity. The meter cost was recovered in under 5 months.
Thermal meters work on clean gases. Air, nitrogen, oxygen, argon, natural gas, biogas, and flue gas are standard applications. Dirty gases with condensation, oil mist, or particulates will coat the sensors. Coated sensors lose accuracy. Some models have a purge function or sensor coating to resist contamination. But this adds cost and maintenance. Thermal meters also need to be calibrated for the specific gas composition. Switching from air to methane requires a different calibration curve. Some electronics can store multiple gas curves. Silver Instruments SI-TMF transmitters hold up to 4 gas calibrations selectable from the keypad.
Side by Side: When to Pick Which Technology
Liquid applications almost always go to Coriolis. Thermal meters cannot measure liquids at all. The heat transfer physics do not work with liquid phase. So if your fluid is water, diesel, palm oil, sodium hydroxide solution, liquid CO2, or molten sulfur, you need a Coriolis meter. No choice here.
Gas applications need more thought. For high accuracy gas measurement below DN50, a Coriolis meter makes sense. Natural gas custody transfer, pharmaceutical reactor gas feed, hydrogen blending systems all benefit from Coriolis accuracy of ±0.15 to ±0.35 percent of reading. For large duct gas measurement above DN80, thermal insertion meters win on cost and installation convenience. A Coriolis meter above DN100 becomes extremely heavy and expensive. A thermal insertion meter for DN500 costs a fraction of that.
Pressure drop tolerance matters too. A Coriolis meter on a low pressure biogas line at 50 mbar will choke the flow. The tube geometry creates a permanent pressure loss. Thermal insertion meters have almost zero pressure drop. Biogas digesters, landfill gas collection, and flare lines all run at near atmospheric pressure. Thermal is the only practical choice here.
Multi-parameter need pushes toward Coriolis. If you need density measurement, concentration calculation, or net oil detection in water, the Coriolis meter delivers all of this. A thermal meter gives mass flow and temperature only. No density data. The Coriolis density function helps food processors monitor Brix in sugar solutions or fat content in dairy streams.
Here is the thing about cost. A DN25 Coriolis meter costs roughly 2 to 3 times more than a DN25 inline thermal meter. But the Coriolis accuracy is 5 to 10 times better. The lifecycle cost calculation depends on what measurement error costs you. In a methanol dosing application where every kilogram of methanol costs money and overdose causes process problems, a Coriolis meter saves enough to justify itself quickly. In a ventilation air flow monitoring application where ±5 percent is acceptable, a thermal meter is the rational choice.
Installation and Maintenance: What Engineers Need to Know
Coriolis meter installation demands straight pipe sections. Typically 5 pipe diameters upstream and 2 diameters downstream for most models. But more important is pipe vibration isolation. Mount the meter on a rigid pipe support. Do not hang it unsupported between two flexible hoses. We have seen installations in Vietnam where a Coriolis meter was reading 3 percent high because a nearby reciprocating compressor transmitted vibration through the floor. Adding vibration dampening pads fixed it.
Zero calibration is critical for Coriolis meters. Fill the meter with the process fluid at operating temperature and pressure. Wait for conditions to stabilize. Then perform the zero adjustment. A zero error of 0.01 percent can translate to a noticeable error at low flow rates. Some plants schedule zero checks every 3 months. Others do it before every batch campaign. It takes 5 minutes and costs nothing but time.
Thermal meter installation for insertion types requires careful probe depth calculation. The sensor tip must sit at the point of average velocity in the pipe. For a clean gas in a straight pipe, this is roughly at one third of the pipe diameter from the wall. But elbows, valves, and dampers distort the velocity profile. We recommend 15 pipe diameters of straight run upstream and 5 downstream for insertion thermal meters. Inline thermal meters need less straight pipe, typically 10 diameters upstream and 5 downstream.
Most engineers skip this part. Thermal sensors drift over time. Dust accumulation, oil mist condensation, and sensor aging all contribute. A thermal meter reading can drift 2 to 3 percent per year without cleaning. Budget for annual sensor inspection. A soft brush and isopropyl alcohol clean the sensors back to factory condition in most cases. Some wastewater treatment plants clean
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