Thermal Mass Flow Meter Insertion in pipe
Thermal Mass Flow Meter
Thermal Mass Meter installation
Thermal Mass Flow Meter

Thermal Mass Meter

A Thermal Mass Meter works by measuring the total mass flow rate of a fluid flowing through a pipe or duct.  In a thermal flowmeter’s simplest working configuration, fluid flows past a heated thermal sensor and a temperature sensor.  As the molecules of the fluid flow past the heated thermal sensor, heat is lost to the flowing fluid.

Thermal mass flow meters, also known as thermal dispersion or immersible mass flow meters comprise a family of instruments for the measurement of the total mass flow rate of a fluid, primarily gases, flowing through closed conduits.  A second type is the capillary-tube type of thermal mass flow meter.  Many mass flow controllers (MFC) which combine a mass flow meter, electronics and a valve are based on this design.  Furthermore, a thermal mass flow meter can be built by measuring temperature differential across a silicon-based MEMS chip.

 

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Description

Thermal Mass MeterThe Thermal Mass Meter is widely used devices for measuring the flow rate of gases or liquids in various industries.  Also, these meters operate based on the principles of thermal conductivity and heat transfer.  In this response, I will aim to provide a comprehensive description of thermal mass flow meters, along with their advantages, disadvantages, and the industries in which they find application.

Thermal mass flow meters consist of a sensor that measures the heat dissipation or cooling effect caused by the fluid passing through the meter.  In addition, the rate of heat transfer is directly proportional to the mass flow rate.  Also, by accurately measuring the change in temperature of the fluid and utilizing the heat transfer principle, these meters determine the flow rate.

Working Principle

Thermal mass flow meters work based on the principle of thermal conductivity.  Also, the meter consists of a sensor or probe that contains two temperature sensors: one measures the fluid’s temperature and the other acts as a reference sensor.  When the fluid flows through the meter, it comes into contact with the heated sensor.  In addition, as the fluid absorbs heat from the sensor, it causes a temperature difference between the two sensors.  finally, by analyzing this temperature difference, the meter determines the mass flow rate.

Sensor Types

There are two common types of thermal mass flow meters: Constant Temperature (CT) and Constant Heat (CH).

Constant Temperature (CT):

In CT thermal mass flow meters, the sensor heats up to maintain a constant temperature difference between the heated and reference sensors.  Moreover, as the fluid flows, it absorbs some of the heat, and the power required to maintain the temperature difference changes.  This power is proportional to the mass flow rate, allowing the meter to calculate the flow rate accurately.

Constant Heat (CH):

CH thermal mass flow meters operate by maintaining a constant heat input to the fluid.  In addition, the temperature difference between the sensors is measured, and the flow rate is determined based on the amount of heat required to maintain the temperature difference.

Applications and Benefits

Thermal mass flow meters find applications in various industries due to their unique characteristics and benefits:

Gas Flow Measurement:

These meters are widely used for measuring the flow rates of gases, such as natural gas, compressed air, and various hydrocarbon gases.  Furthermore, they provide accurate and reliable measurements for gas flow monitoring, custody transfer, and process control.

Liquid Flow Measurement:

Thermal mass flow meters can also measure the flow rates of liquids, making them suitable for liquid transfer and process applications.  However, they are primarily preferred for measuring gas flow due to their thermal properties.

Direct Mass Flow Measurement:

One of the primary advantages of thermal mass flow meters is that they provide direct mass flow measurement without the need for additional calculations or conversions.  This makes them highly accurate and eliminates the potential for errors associated with volumetric flow measurements.

Low Pressure Drop:

Thermal mass flow meters typically have a low pressure drop, meaning they cause minimal restriction to the fluid flow.  In addition, this characteristic is especially crucial in applications were maintaining system efficiency and reducing energy consumption is important.

Wide Rangeability:

These meters offer a wide rangeability or turndown ratio, allowing them to measure flows from very low to extremely high velocities accurately.  This flexibility makes them suitable for various flow rate requirements in different industries.

Low Maintenance:

Thermal mass flow meters are known for their durability and low maintenance requirements.  They have no moving parts or obstructions that can impede the flow or require frequent maintenance, leading to reduced downtime and increased operational efficiency.

It’s important to note that the specific features and capabilities of thermal mass flow meters can vary depending on the manufacturer and model.  Therefore, when selecting a thermal mass flow meter for a particular application, it’s essential to consider factors such as flow range, fluid properties, accuracy requirements, and environmental conditions to ensure optimal performance.

Insertion style Thermal Mass Meter:

Include a sensor & probe assembly that is inserted into the process gas flow conduit to allow the process gas to flow across the flow sensing elements.  Our insertion style flow meters are available with 3/4″, or 1″ OD probes.  Tube fittings and ball valve retractor assemblies, with or without a mounting flange, are also available from the factory as options.  The tube length must be specified upon ordering.  For other probe diameters and lengths, please consult the factory.

Integral style Thermal Mass Meter

have all of the electrical components and connections located within one enclosure.  The enclosure is mounted directly to the insertion probe assembly at the point of measurement.  The enclosure includes all of the electrical connections as well as the linearizing electronics and the display/keypad assembly.

Principle

Thermal mass meter uses the principle of convective heat transfer to directly measure mass flow.  ProFlow’s proprietary thermal mass flow sensors use two ratiometrically matched, reference-grade platinum Resistance Temperature Detectors (RTDs).  The platinum sensing element wire is encapsulated in a 316 Stainless Steel sheath or, if specified, a Hastelloy C sheath.  Our microcontroller operated smart sensor technology preferentially heats one RTD; the other RTD acts as the temperature reference.  The process gas flow dissipates heat from the first RTD.  This causes an increase in the power required to maintain a balance between the RTDs.  This increase is directly related to the gas molecular rate of flow.  Our sensors are temperature compensated for a wide process gas temperature range and insensitive to pressure changes.  This will confirm the output signal is a true mass flow rate signal.

In conclusion, thermal mass flow meters offer several advantages, including a wide range of measurements and direct mass flow measurement.  Other advantages are low pressure drop, high accuracy, and compatibility with various fluids.  However, they also have limitations related to gas composition changes, initial cost, and dependency on fluid properties.  Finally, these flow meters find applications in diverse industries such as oil and gas, chemical and petrochemical.  Other industries are HVAC systems, pharmaceutical and biotechnology, and food and beverage.  This is contributing to efficient and reliable flow rate measurements throughout these sectors.

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Additional information

Weight 9 lbs
Dimensions 24 × 14 × 14 in
Size

3/4", 1", 1-1/2", 2", 3", 4"
Pressure Class

150LB, 300LB, 600LB
Connections

NPT, Flanged, Triclamp
Display

Yes, No
Voltage

24 VDC, 120 VAC
Communication Protocol

RS485, HART
Output

4-20 MA, 0-10 VDC
Classification

Explosion Proof, Intrinsically Safe

Specifications

Approvals:

Currently no product agency approvals.

Enclosure Certifications by manufacturer
CSA – CL. I. GR. A,B,C,D; CL. II. GR. E,F,G; CL. III.;TYPE 4X
US – CL. I. GR. A,B,C,D; CL. II. GR. E,F,G; CL. III.;TYPE 4X
IECEx – Ex d IIC Gb, Ex t IIIC Db, Exia (intrinsically safe)
ATEX – II 2G Ex IIC Gb, II 2Dd Ex t 111C Db

Linear signal output
0–5 VDC & 4–20 mA (Flow and Temperature)

Event Relay Rating one with Frequency or two, 1 Amp @ 30Vdc (33W)

Signal Interface
RS232 & RS485 Modbus RTU embedded, HART , LCD (flow rate, flow total, gas temperature)

Accuracy, including linearity (Ref.: 21°C)
±(1% of Reading + 0.5% of Full Scale + GTC)

Repeatability
±0.2% of Full Scale

Sensor response time
1 second to 63% of final value

Turn down ratio
100:1 @ 10 SFPM (.051 NMPS) Minimum Reading

Electronics PCB temperature range
-40° to 158°F (-40° to +70°C)

Environmental temperature range
-40° to 140°F (-40° to +60°C)

Gas temperature range
-40°–392°F (-40°–200°C)

Gas temperature coefficient (GTC)
0.02% Full Scale/°C

Gas pressure effect
Negligible over ± 20% of absolute calibration pressure

Pressure rating maximum
500 PSI Std.

Input power requirement
24VDC @ 250mA, 115 VAC 50/60 Hz optional, 230 VAC 50/60 Hz optional

Flow Transmitter power requirements
5 watts maximum

RAM Back-up
Lithium Battery

Wetted materials
316 Stainless Steel (Hastelloy optional)

Standard temperature & pressure (STP)
70°F & 29.92″ Hg (Air .075 lb./cubic foot)

NIST traceable calibration
Standard

NOTE: Specifications subject to change without notice.

Installation

Installing a thermal mass flow meter correctly is crucial for ensuring accurate measurements and reliable operation. Here’s a general procedure to follow:

Preparation

Read the Manual:

  • Before starting, thoroughly read the manufacturer’s installation manual. Each flow meter may have specific requirements.

Safety First:

  • Ensure that you have the necessary safety gear and are following all safety procedures, especially if you are working with hazardous fluids or high temperatures.

Check Compatibility:

  • Verify that the flow meter is compatible with the process conditions, including the type of fluid, temperature, pressure, and flow range.

Site Preparation

Location:

  • Choose a location that allows for easy access for maintenance and calibration. Ensure the area is free of vibrations, temperature extremes, and electromagnetic interference.

Pipe Size and Orientation:

  • Confirm that the flow meter is suitable for the pipe size and that it can be installed in the correct orientation (usually inline with the flow).

Cleanliness:

  • Ensure that the pipe and the area where the flow meter will be installed are clean and free of debris.

Installation

Turn Off and Depressurize:

  • Shut down the process and depressurize the pipe. If the fluid is hazardous, follow proper procedures for safe handling.

Pipe Preparation:

  • Clean the pipe ends where the flow meter will be installed. Remove any burrs or sharp edges to avoid damaging the flow meter.

Mounting the Flow Meter:

  • Inline Installation:
    • For inline installation, use the appropriate flanges, fittings, or clamps. Ensure that the flow meter is aligned with the pipe and securely fastened.
  • Insertion Installation:
    • If the flow meter is an insertion type, insert it into the pipe through the appropriate port. Use the provided clamps or fixtures to secure it.

Check Flow Direction:

  • Make sure the flow meter is installed in the correct direction. There should be an arrow or label indicating the direction of flow.

Electrical and Signal Connections:

  • Connect the flow meter’s electrical wiring and signal outputs according to the manufacturer’s instructions. Ensure all connections are secure and properly insulated.

Calibration and Testing:

  • After installation, calibrate the flow meter if required. Perform a test run to check for leaks and ensure the flow meter is functioning correctly.

Post-Installation

System Start-Up:

  • Slowly restart the process and monitor the flow meter for proper operation. Check for leaks and ensure that the readings are accurate.

Documentation:

  • Record the installation details, including the installation date, calibration settings, and any relevant observations.

Regular Maintenance:

  • Follow the manufacturer’s recommendations for regular maintenance and calibration to ensure continued accuracy and performance.

Troubleshooting Tips

  • Inaccurate Readings: Check for proper installation, leaks, and calibration issues.
  • Erratic Readings: Ensure that there are no obstructions or turbulence affecting the flow meter.
  • Leakage: Inspect all connections and seals to ensure they are secure.

Following these steps should help you install your thermal mass flow meter successfully and ensure it operates accurately. Always refer to the specific guidelines provided by the manufacturer for your particular model.

Maintenance

Maintaining a thermal mass flow meter is essential for ensuring its long-term accuracy and reliability.  Here’s a general maintenance procedure you can follow but be sure to consult the manufacturer’s guidelines for any model-specific recommendations.

Routine Inspection

Visual Check:

  • Frequency: Monthly or as recommended.
  • What to Look For: Inspect the flow meter for signs of physical damage, corrosion, or leaks.  Ensure that there are no loose connections or visible wear.

Verify Readings:

  • Frequency: Monthly or as part of a scheduled routine.
  • What to Check: Compare the flow meter readings with a known reference or another reliable measurement method to ensure accuracy.

Calibration

Regular Calibration:

  • Frequency:  Annually or per the manufacturer’s recommendation, or whenever a significant change in process conditions occurs.
  • Procedure:  Follow the manufacturer’s calibration instructions.  This often involves using a known standard flow rate and adjusting the meter to match it.

Post-Maintenance Calibration:

  • If any maintenance or repairs have been performed, recalibrate the meter to ensure continued accuracy.

Cleaning

Frequency:  As needed, depending on the process fluid and the level of contamination.

Procedure:

  • For Inline Meters:  If the flow meter has a self-cleaning function, ensure it is operational.  If not, you may need to remove the meter for cleaning.
  • For Insertion Meters:  Carefully remove the meter from the pipe and clean it according to the manufacturer’s instructions.  Use appropriate cleaning agents that are compatible with the meter’s materials and the process fluid.

Precautions: Always follow the manufacturer’s recommendations for cleaning agents and methods to avoid damaging the flow meter.

Checking and Tightening Connections

Frequency:  Quarterly or as part of a routine inspection.

Procedure:

  • Inspect all electrical and fluid connections to ensure they are secure.  Tighten any loose fittings or connections.  Be careful not to overtighten, as this could damage the threads or seals.

Software and Firmware Updates

Frequency:  As required or when updates are provided by the manufacturer.

Procedure:

  • Check for any available software or firmware updates for the flow meter.  Follow the manufacturer’s instructions for downloading and installing updates to ensure the meter’s functionality and compatibility with other systems.

Documentation and Records

Frequency: After each maintenance activity.

Procedure:

  • Maintain detailed records of all maintenance activities, including inspections, calibrations, cleanings, and repairs. Document the date, actions taken, and any observations or adjustments made.

Troubleshooting

Frequency: As needed.

Procedure:

  • Erratic Readings:  Check for obstructions, leaks, or turbulence.  Ensure that the meter is correctly calibrated.
  • Inaccurate Readings:  Recalibrate the meter and verify the process conditions.  Check for any installation issues or changes in the process fluid.
  • Mechanical Issues:  Inspect for signs of physical damage or wear.  If necessary, consult with the manufacturer or a qualified technician for repairs.

Professional Service

Frequency: As required or based on the manufacturer’s recommendations.

Procedure:

  • If you encounter persistent issues or complex problems, contact the manufacturer or a certified service technician for professional assistance and servicing.

Summary

  • Monthly:  Perform visual checks and verify readings.
  • Annually:  Calibrate the flow meter.
  • As Needed:  Clean the meter, check and tighten connections, and update software/firmware.
  • Documentation:  Keep detailed records of all maintenance activities.

By following these maintenance procedures, you can help ensure that your thermal mass flow meter continues to operate accurately and efficiently over its service life.

Q&A

Q:  What is a Thermal Mass Flow Meter?
A:  A Thermal Mass Flow Meter is a device used to measure the flow rate of a fluid by calculating the heat transfer from a heated sensor to the flowing fluid.

Q: How does a Thermal Mass Flow Meter work?
A:  The Thermal Mass Flow Meter works based on the principles of convective heat transfer.  The heated sensor within the meter measures the heat dissipation as the fluid passes over it, and this heat dissipation is directly proportional to the mass flow rate of the fluid.

Q: What are the advantages of using a Thermal Mass Flow Meter?
A: Some advantages of using a Thermal Mass Flow Meter include high accuracy, ability to measure low flow rates, minimal pressure drop, wide turndown ratio, and suitability for various types of gases.

Q: What are the applications of a Thermal Mass Flow Meter?
A: Thermal Mass Flow Meters are commonly used in industries such as oil and gas, chemical processing, pharmaceuticals, power generation, food and beverage, and HVAC systems to measure the flow of gases.

Q: How do you calibrate a Thermal Mass Flow Meter?
A: Calibration of a Thermal Mass Flow Meter involves comparing the meter readings to a reference standard. This is typically done by a certified calibration lab or using a calibration gas of known properties.

I hope this Q&A helps you understand more about Thermal Mass Flow Meters! If you have any specific questions or need more information, feel free to ask.

Advantages / Disadvantages

Advantages of Thermal Mass Flow Meters:

Wide Range of Measurements:

Thermal mass flow meters can accurately measure a broad range of flow rates, from low to high velocities, making them suitable for various applications.

Direct Mass Flow Measurement:

These meters provide direct measurement of mass flow rate, eliminating the need for additional calculations or conversions.

Low Pressure Drop:

Thermal mass flow meters have a relatively low pressure drop, minimizing the impact on the system’s overall performance.

High Accuracy:

Modern thermal mass flow meters offer exceptional accuracy, enabling precise measurement and control of fluid flow.

Compatibility:

These meters can handle a wide range of fluids, including gases and liquids, making them versatile for different industries.

Disadvantages of Thermal Mass Flow Meters

Limited Applicability to Gas Composition Changes:

Thermal mass flow meters are sensitive to variations in the composition of the gas being measured.  If the composition changes significantly, it may affect the accuracy of the measurement.

High Initial Cost:

Compared to some other flow meter technologies, thermal mass flow meters can have a higher initial cost.

Dependency on Fluid Properties:

Certain fluid properties, such as specific heat and thermal conductivity, can influence the accuracy of thermal mass flow meters.  Calibration may be required for different fluids or fluid compositions to ensure accurate readings.

Applications

Industries Utilizing Thermal Mass Flow Meters:
Oil and Gas:

Thermal mass flow meters are extensively used in the oil and gas industry for measuring the flow of natural gas, flare gas, compressed air, and various hydrocarbon gases.

Chemical and Petrochemical:

These meters find applications in the chemical and petrochemical industries for measuring gas flow rates in processes such as reactor feeding, gas blending, and combustion control.

HVAC Systems:

Thermal mass flow meters are commonly used in heating, ventilation, and air conditioning (HVAC) systems to measure airflow and monitor energy consumption.

Pharmaceutical and Biotechnology:

These industries utilize thermal mass flow meters for measuring gas and liquid flows.  This is commonly done during the production of pharmaceuticals and biotechnology products.

Food and Beverage:

Thermal mass flow meters play a crucial role in the food and beverage industry.  This is where they are used for measurements related to gas flow rates, liquid transfers, and process control during manufacturing processes.

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