The Application of Thermal Mass Flowmeters in Flow Measurement of Large-Diameter Ventilation Pipelines

Thermal mass flow meters are instruments that directly measure the mass flow rate of gases. They do not require temperature and pressure compensation and can accommodate a wide range of turn down ratios. In the flow measurement of large-diameter ventilation ducts, they can perfectly match the core working conditions of ventilation systems, such as large diameters, low flow rates, wide flow fluctuations, and clean dry gas. This solves the problems of low accuracy, complex installation, and high pressure loss of traditional differential pressure type and vortex flow meters in low-flow-rate large-diameter ventilation measurements. They have become the main choice for flow measurement in ventilation systems for industrial buildings, central air conditioning fresh air/exhaust air, and online monitoring of environmental exhaust gas emissions.

1. The core advantage of thermal mass flow meters in adapting to large-diameter ventilation ducts.

The core measurement challenges of ventilation ducts are as follows:

• large diameter (DN300 to DN3000+),

• medium being clean air / low-concentration waste gas,

• low flow rate (mainly ranging from 0.5 to 10 m/s),

• large flow fluctuation,

• high requirements for pressure loss (to avoid increasing the energy consumption of the fan),

• no need for high-precision trade settlement (process monitoring accuracy is enough).

The thermal mass flow meter's characteristics perfectly match these requirements. Compared with traditional flow meters, it has significant advantages as below.

• 1.1 Measure the mass flow directly without the need for temperature and pressure compensation. Output the mass/standard volume flow rates such as kg/h and Nm³/h directly.

• 1.2 It has strong low-flow rate measurement capability and is suitable for ventilation with low flow rates. It completely covers the main flow rate range of ventilation ducts from 0.5 to 10 m/s, and can measure extremely low flow rates ranging from 0.2 to 1 m/s. Some models can even measure down to 0.1 m/s.

• 1.3 Wide range ratio, capable of adapting to significant fluctuations in ventilation flow. The turn down ratio can reach 1:100.

• 1.4 The pressure loss can be ignored, and the energy consumption of the ventilation system fans can be reduced. For large-diameter ventilation pipes, insert-type thermal mass flow meters are mostly used. The pipe body has no throttling devices or constrictions, and the pressure loss is almost zero.

• 1.5 Installation is convenient and it is suitable for the on-site conditions of large-diameter pipelines. The insert-type does not require pipe cutting. Just one installation hole needs to be made on the pipeline to complete the installation. The construction period is short and the renovation cost is low.

• 1.6 The structure is simple and the maintenance cost is low. Daily maintenance only requires regular cleaning of the dust / oil stains on the probe surface. The maintenance is simple and the service life is long.

• 1.7 Suitable for large-diameter non-standard pipes, with flexible measurement capabilities. It can be adapted to circular and rectangular large-diameter ventilation pipes (most industrial ventilation systems use rectangular pipes).

2. Typical applications of thermal mass flow meters in large-diameter ventilation ducts.

Its applications cover industrial plant ventilation / building central air conditioning / environmental waste gas discharge / metallurgy / chemical process ventilation / low-concentration clean waste gas flow ventilation systems / industrial plant workshop ventilation / dust removal system exhaust system / displacement ventilation in furnaces of steel plants, workshops of chemical plants / supply and exhaust systems of power plant boiler rooms / primary and secondary air of industrial boiler rooms / air supply and exhaust pipe flow monitoring of flue gas ducts.