How do you measure low airflow ？

Silver Automation Instruments frequently encounters requests to measure extremely low airflows, sometimes as minimal as 0.02 standard cubic centimeters per minute (sccm). Measuring such minute flow rates presents significant challenges due to the limitations of conventional flow measurement technologies.

Why we need low air flow measurement?

Measuring low airflow is crucial in various industries, from ensuring optimal HVAC system performance, measuring low airflow for leak detection to maintaining precise conditions in laboratory environments. But why is it important, and what makes it challenging? Let’s dive into the details.

Challenges in Measuring Low Airflow

Measuring low airflow isn’t straightforward. Traditional flow meters often struggle with low flow rates due to their limited sensitivity, such as turbine flow meter can only measure min 2 m3/h air flow ,variable area flow meter or we call it rotameters can only measure min 50L/h air low flow. Factors like turbulence, pressure drops, and sensor accuracy can further complicate measurements.

Another challenge is calibration for low flow air, calibration facilities for low-flow air flow meters are relatively scarce. This scarcity can pose challenges for industries and laboratories that require precise measurements of minimal airflow rates. Limited access to specialized calibration services may lead to increased costs and longer turnaround times, potentially impacting the accuracy and reliability of critical applications.

Additionally, low airflow is often accompanied by minimal pressure changes, making it harder for conventional devices to detect and measure accurately.

Micro Thermal Mass Flow Meters: The Ideal Solution

One of the most effective tools for measuring low airflow which is often recommended by silverinstruments.com is the thermal mass flow meter. This small air flow metering device operates on the principle of heat transfer, making it highly sensitive to low flow rates.

How small air flow meter Works 

Thermal mass flow meters use a heated sensor and a temperature sensor. As air flows past the heated sensor, it carries away heat, causing a temperature difference between the two sensors. The meter calculates the airflow rate based on the amount of heat lost, which is directly proportional to the mass flow rate of the air.

Advantages of Thermal Mass Flow Meters for low air flow measurement

1. High Sensitivity air flow sensor : These air flow sensors excel at detecting extremely low airflow rates, often as low as 0.02 ml/min, ideal for identifying minor air leakages or lab use.
2. No Moving Parts: With no mechanical components of low flow air sensor, they are less prone to wear and tear, ensuring long-term reliability.
3. Wide Rangeability: They can measure both low and high flow rates, turn down ratio can reach to 100:1 ,for example our micro air flow sensor can measure 0.03 ~ 3 sccm low air flow range, making them versatile for various applications.
4. Low Pressure Drop: Thermal flow meters minimize pressure loss, which is critical in low-flow scenarios for low flow air measurement.
5. Direct Mass Flow Measurement: These micro air flow meters measure the mass flow directly, eliminating the need for additional temperature or pressure compensation

Key Technical Parameters of low flow air flow meter

- Flow Range: Typically measures from 0.02 ml/min to 3000 SLM, depending on the model.
- Accuracy: Offers high accuracy, often within ±1% of the reading.
- Response Time: Fast response times, it can best reach to 0.2 second response time
- Output Options: Digital air flow meter not like traditional rotameters, it can provide analog (4-20 mA) or digital outputs (MODBUS RTU) for easy integration with control systems.

Installation Tips for mini air flow measurement

Adding filter： Air must be purified, avoid dust, liquids and oil. If necessary, install a filter.

Use for corrosive gas :The materials used for the flowmeter channel are: SUS 316L (00Cr17Ni14Mo2), SUS 417J1(00Cr30Mo2), fluorine rubber and other corrosion resistant materials. It can be used to controlgeneral corrosiveness when other users use corrosive gas and organic solvent gas under the condition that the user's system has no soda, low leakage, diligence, and good use. It should be stated at the time of ordering. With special corrosive gases, all sealing materials must be changed accordingly.

Installation position

The micro air flow controller is best installed to maintain the level of the installation surface, but not particularly sensitive to the location, can be installed at any position, if the zero offset is found when installing in non-horizontal position, you can adjust the zero point after work.

Calibration and conversion of different gases at low flow rate

The flow meter is usually calibrated by nitrogen (N2). If other gas calibration is required, special orders should be made with the salesperson when ordering. When users of micro flow meter is calibrated with nitrogen use other gases, they can be converted by the conversion factor of the appendix.

Conclusion

Measuring low airflow is a critical but challenging task. Thermal mass flow meters, with their sensitivity, reliability, and ease of installation, provide an ideal solution. Whether for HVAC systems, medical devices, or air leakage detection, these small air flow meters ensure accurate and efficient low airflow measurement, making them indispensable in modern applications.