Thermal Dispersion

No. One of the big benefits of thermal mass flow meters is that they are generally low maintenance. Since there are no moving parts in contact with the gas and low mechanical stress on components, there’s very little wear and tear over time. The solid state sensors (RTD`s) and electronics are built for long term stability. In normal operation, you typically won’t need to frequently service or replace parts on a thermal flow meter.

For most applications, maintenance is limited to occasional checks or cleaning of the sensor tip or flow straightener if used. If the gas is dirty (to ensure no buildup on the sensors) it’s also wise to verify calibration periodically (for example, annually) to ensure accuracy, but day to day operation does not require constant upkeep. Overall, they are designed for long term, continuous use with minimal intervention, which is why they’re often chosen as a low maintenance flow meter solution. For guidance on maintenance schedules and best practices for your application, contact KOBOLD.

Thermal dispersion mass flow meters can measure both gases and certain liquids, but they are primarily designed for gas flow applications. They excel at measuring clean gases such as air, nitrogen, natural gas, oxygen, argon, carbon dioxide, and many other industrial gases, even at low pressures and low flow rates.

For liquids, thermal flow meters are not typically used for precise measurement because liquids absorb and transfer heat differently than gases. Specialized thermal flow sensors and flow switches exist for monitoring certain liquid flows, such as water or water based liquids, but these are generally used to confirm the presence of flow rather than provide exact flow rates.

For accurate liquid flow measurement, other technologies such as magnetic or ultrasonic flow meters are often preferred. Thermal dispersion meters are most effective when the fluid is clean, stable, and free from particulates or coatings that could affect sensor performance.

Thermal mass flow meters are built using durable materials designed to withstand industrial conditions and ensure long term reliability, mechanical strength and thermal conductivity. Common materials include:

1. Stainless Steel (KEC/KEP probe; MAK/MAS housing): Primarily used for sensor probes and flow bodies in industrial grade meters. Stainless steel is strong, corrosion resistant, and suitable for high temperatures and pressures, making it ideal for harsh or corrosive gas applications.
2. Brass: Often used for flow bodies or fittings in meters for moderate conditions. Brass offers good corrosion resistance and is cost effective for low to medium pressure applications.
3. Engineering Grade Plastics (KET/KEP housing): Materials such as polycarbonate, PPS (Polyphenylene Sulfide), or nylon are used in housings, non wetted parts, or in flow bodies for less demanding applications. These plastics are lightweight, cost efficient, and suitable for clean or low pressure environments.

The choice of material directly impacts the meter’s chemical compatibility, temperature and pressure limits, and durability. Selecting the appropriate construction material ensures optimal performance and prevents corrosion or damage over time. Always verify that the meter’s materials are compatible with the specific gas or liquid in your system.
 To know more about material suitability for your application, contact us.

Thermal mass flow meters come in various models, and their pressure and temperature limits depend on how they’re built. In general They can handle from around vacuum conditions up to about 6 bar (~90 psi) in basic models, and robust designs can go up to 100 bar or more (~1450 psi). There are even specialized high pressure versions for certain industries. Always check the specified maximum pressure (p_max) for the particular model you’re interested in, as it can vary widely.

Standard thermal dispersion flow meters typically operate up to roughly 50°C (122°F) to 100°C (212°F) without issue. For higher temperatures, there are high temp versions with extended probes or cooling arrangements that can handle process gas temperatures around 150°C to 180°C (302–356°F). Some advanced designs might allow even higher temperatures by distancing electronics from the heat. Again, the maximum temperature (t_max) tolerance is model specific.

Because these limits differ model wise, it is important to review the specific product specifications for your application. If your process involves high pressure or extreme temperatures, ensure you select a thermal flow meter model that is rated for those conditions. The good news is that there are thermal mass flow meters available for a wide range of conditions  from low pressure HVAC ducts to high pressure industrial gas lines and from sub zero freezer environments to hot furnace exhaust streams.

To know more about the suitable range for your process, contact our industry expert.

Thermal dispersion  flow meters are well known for providing reliable accuracy in gas flow measurement, although the exact accuracy depends on the meter design, calibration, and application conditions.

Typical accuracy ranges include:

1. General accuracy: Most thermal mass flow meters offer accuracy in the range of ±1% to ±5% of full scale (FS). Our KEC/KEP/KET models can achieve an accuracy of ±1.0% of reading and ±0.3% of full scale on request.
2. Higher performance models: When properly calibrated for a specific gas and operating range, some models can achieve accuracy of ±1–2% of reading, along with excellent repeatability.
3. Economy or basic models: Lower cost or general purpose designs may specify accuracy closer to ±3–5% of full scale.
4. Measurement vs. switching accuracy: When used as a continuous flow measurement device, accuracy is typically specified as a percentage of reading or full scale. However, when the instrument functions as a flow switch (detecting whether flow is above or below a setpoint), the switching accuracy is usually around ±10% of the set value, which is acceptable for on/off or alarm based applications.

It is important to note that the stated accuracy is influenced by proper calibration, gas composition, flow profile, and installation conditions. Many manufacturers specify accuracy as a combined value (±% of reading plus ±% of full scale), so reviewing the product datasheet is essential.

Overall, thermal dispersion flow meters deliver stable, repeatable, and application appropriate accuracy for a wide range of gas flow monitoring and process control applications. To know the suitable accuracy range for your application, get in touch with us

Thermal mass flow meters are widely used across many industries wherever accurate; low flow or mid flow gas measurement is needed. Some common application areas and industries include:

1. Compressed Air Systems: Monitoring compressed air usage in factories, detecting leaks, and optimizing compressor operation. For example, they are used in air audits and to measure airflow in distribution lines without causing pressure drop.
2. Natural Gas Measurement: Measuring natural gas flow for burners, boilers, heaters, or fuel consumption tracking. Thermal flow meters provide direct mass flow readings for natural gas in industrial plants, commercial boilers, and even some residential gas sub metering.
3. Biogas and Flare Gas: Monitoring biogas production (e.g., in digesters at wastewater treatment plants or landfills) and measuring flare gas or waste gas emissions. They handle the low pressure, variable flow nature of biogas well and are useful for environmental compliance (emissions monitoring) and process optimization.
4. HVAC and Building Management: Measuring airflow in heating, ventilation, and air conditioning systems. They can monitor ventilation rates, exhaust flows, or airflow in cleanrooms and help in energy management for large facilities.
5. Environmental & Emissions Monitoring: Used in stack gas or flue gas measurement for pollution control (when the gas composition is known and compatible). They measure mass flow of exhaust gases in chimneys, incinerators, or processing plant outlets to ensure environmental regulations are met.
6. Industrial Process Gases: Controlling and monitoring gases like oxygen, nitrogen, carbon dioxide, argon, hydrogen, etc., in various manufacturing processes. For instance, in chemical and petrochemical plants, thermal meters help regulate gas flow in reactors or packaging. In steel and metal production, they measure gases (like argon purging in steelmaking).
7. Semiconductor & Electronics Manufacturing: Maintaining precise flow rates of ultra pure gases (such as silane, ammonia, nitrogen trifluoride, etc.) for processes like CVD, etching, and wafer fabrication. The high sensitivity at low flows is crucial here.
8. Food and Beverage Industry: Monitoring CO₂ for carbonation or fermentation (breweries, beverage bottling) and controlling gas flow in packaging or blanketing processes. Also used for gas flow in chillers and freezer systems.
9. General Industrial OEM Applications: Thermal mass flow sensors are integrated into machines or systems (like air sampling devices, analytical instruments, or drying systems) where gas flow needs to be measured or controlled reliably.

From large scale industrial facilities to OEM instruments, these meters help improve energy efficiency, process control, and product quality by providing accurate gas flow dat

Moisture can affect the performance of a thermal mass flow meter, so it is an important consideration in gas flow applications.

1. Humidity (water vapor in the gas): A small amount of moisture vapor, such as normal humidity in air or process gases, usually has only a minor effect on the measurement. In most cases, the impact is negligible, especially when the humidity level remains stable. A slight increase in humidity may cause a small positive bias in the measured flow because water vapor transfers heat differently than dry gas.
2. Liquid moisture or condensation: The presence of liquid water droplets or condensation can significantly affect accuracy and should be avoided. Liquid water absorbs much more heat than gas, which can cause the meter to indicate a higher flow rate than is actually present. This may lead to unstable or inaccurate readings. If moisture accumulates on the sensor, performance may be affected until the sensor dries completely.
3. Practical considerations: Thermal mass flow meters perform best with clean, dry gases. In applications involving humid gas, it is recommended to keep the gas temperature above the dew point to prevent condensation, or to use upstream moisture separators or filters. While some advanced thermal flow meters can compensate for humidity to a limited extent, supplying dry gas ensures the most accurate and stable measurement.

Yes, changes in gas composition can affect the accuracy of a thermal mass flow meter. These meters are typically calibrated for a specific gas or a defined gas mixture because different gases have different thermal properties, such as specific heat and thermal conductivity. If the gas composition changes from the calibration condition, the measurement accuracy can be impacted.
The extent of this impact depends mainly on how much the actual gas composition deviates from the calibration gas, as outlined in the following cases:

1. Calibration specific to the gas: For example, if a thermal mass flow meter is calibrated for 100% nitrogen and is later used to measure a nitrogen–helium mixture or a gas containing CO₂, the readings may be inaccurate. This is because helium and CO₂ transfer heat differently compared to nitrogen, affecting the heat dissipation used for measurement.
2. Minor composition variations: If the change in gas composition is small such as air with trace gases or natural gas with slight composition variations the effect on accuracy is usually limited. In many practical applications, minor changes may introduce only a small measurement error rather than making the reading unusable.
3. Significant composition changes: When the meter is used for significantly different gases or varying mixtures, recalibration is recommended. Alternatively, correction factors may be applied if supported by the device. Some thermal mass flow meters allow users to input gas correction factors or store multiple gas calibrations.

In summary, thermal mass flow meters rely on assumed gas properties for mass flow calculation. When these properties change, measurement deviations can occur. For applications involving variable gas mixtures, such as biogas with changing methane and CO₂ content, users should be aware of potential accuracy shifts and ensure appropriate calibration or correction methods are applied.

Consequently, the gas type and its exact composition should always be specified in detail when making an inquiry.

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Thermal mass flow meters are generally easy to install, but following a few best practice guidelines helps ensure accurate and stable measurements:

1. Straight pipe requirements: The meter should be installed in a straight section of pipe away from flow disturbances. Typically, a straight run of 5–10 pipe diameters upstream is recommended, with additional length if there are nearby elbows, valves, or reducers. A short straight run downstream is also advisable. This allows a stable and fully developed flow profile at the sensor.
   
   
    
2. Insertion depth and alignment: For insertion type meters, the probe must be inserted to the correct depth—usually near the centre of the pipe and aligned according to the flow direction markings or manufacturer instructions. Incorrect positioning can affect measurement accuracy.
3. Vibration and mechanical stress: The sensor or flow body should be mounted securely to minimize vibration. Excessive mechanical stress or pulsating flow from nearby equipment can negatively affect performance and long term reliability.
4. Electrical installation: Power and signal wiring should follow the manufacturer’s recommendations. Proper grounding and shielding may be required to prevent electrical noise from interfering with the measurement signal.
5. Environmental considerations: While the sensor is designed to handle process conditions, the transmitter or electronics should be installed within the specified ambient temperature and moisture limits unless specifically rated for harsh environments.

Manufacturers typically provide detailed installation guidelines, including recommended straight pipe lengths for different upstream disturbances. Adhering to these recommendations helps achieve optimal accuracy and reliable operation. Compared to some other flow measurement technologies, thermal mass flow meters generally do not require impulse lines or complex piping arrangements.

Thermal mass flow meters are widely used and reliable, but they do have certain limitations that should be considered during application selection:

1. Clean, non abrasive gases only: These meters are best suited for clean gases. Dust, dirt, or particulate matter can coat the sensor and affect accuracy or long term stability. Filtration may be required for contaminated gas streams.
2. Sensitivity to liquid moisture: While small amounts of water vapor typically have minimal impact, the presence of liquid droplets, mist, or condensation can significantly affect accuracy and may lead to false high readings or sensor damage. Applications should ensure the gas remains above its dew point.
3. Dependence on gas properties: Thermal mass flow meters are calibrated for a specific gas or known gas mixture. Changes in gas composition can introduce measurement errors unless correction factors or recalibration are applied.
4. Primarily for gas measurement: These meters are mainly designed for gas flow measurement. Although thermal principles exist for certain liquid applications, they are generally not suitable for measuring liquid flow rates compared to other flow technologies.
5. Temperature and process limits: Standard thermal mass flow meters operate within defined temperature ranges. Extremely high temperature or cryogenic applications may require specialized designs.
6. Initial cost: The upfront cost is typically higher than simpler devices such as orifice plates or variable area flow meters, though maintenance requirements are generally low.
7. Temperature limitations: Standard models operate within defined temperature ranges. Very high temperature or cryogenic applications may require specialized designs or alternative technologies.
8. Pressure drops: Insertion type meters introduce negligible pressure loss. In line thermal flow meters should be properly sized to avoid unintended flow restriction.

In summary, thermal mass flow meters are best suited for applications involving clean, dry gases with known and stable composition, operating within the specified process and environmental limits. Where these conditions are not met, gas conditioning or alternative flow measurement technologies may be more appropriate.