Selection and installation of thermal gas mass flowmeter

Thermal gas flowmeter is an instrument that uses the principle of heat transfer to detect the flow rate, that is, the flow rate is detected based on the heat exchange relationship between the fluid in the fluid and the heat source (the object or heating inside or outside the fluid). Measuring the body outside the tube); mainly measuring gas; thermal gas mass flow meters are mainly divided into two categories, namely heat distribution and immersion (or plug-in).

1. The characteristics of thermal gas mass flow meters

(1) The main features of the thermally distributed mass flowmeter: it can directly measure the mass flow without temperature and pressure compensation; non-contact, no moving parts, no blockage, low pressure loss, high reliability; low flow micro gas can be measured Flow rate, minimum 5mL/min (standard state); requires the gas medium to be dry and clean, free of moisture, oil, etc.; the split flow type can obtain linear characteristics, which can be used to measure large and medium pressure flow rates to ensure the use of split temperature; dynamic response is very slow, The time constant is about 5s.

(2) The main features of the immersion thermal mass flow meter: directly measure the mass flow without temperature and pressure compensation; no moving parts, high reliability; suitable for large diameter, non-circular cross-section tubes, narrow space measurement (plug-in type ) After testing, the platinum resistance sensor adopts a stainless steel shell, which is not sensitive to dust, solid particles, oil and moisture in other parts. The plug-in type can be taken out continuously for maintenance and replacement. It can be used to measure the measurement value of dirty liquid.

2. Use thermal gas mass flow meter

(1) For small and trace gas flows, thermally distributed mass flow meters can be used for single-component gas or fixed-proportion mixed gas measurement.

(2) The plug-in immersion thermal mass flowmeter can be selected for large-diameter flow measurement.

3. Precautions for installation and use of thermal gas mass flow meters

(1) In terms of installation posture, most thermally distributed mass flow meters can be installed in any position (horizontal, vertical or inclined), as long as the electrical zero point adjustment is performed under the working conditions pressure and temperature after installation, some instruments are Sensitive, you must strictly follow the instructions. Most immersion thermal mass flow meters are not affected by the installation posture, but should strictly follow the instructions at low flow rates.

(2) As far as the front straight pipe section is concerned, the heat distribution is not sensitive. Immersion flow sensors and plug-in instruments with measuring tubes require a certain length of straight pipe section, and follow the manufacturer’s recommendations.

(3) The vibration of the pipeline connected with the thermal mass flowmeter will not cause vibration interference in the common range; the detection rod of the plug-in thermal mass flowmeter must be fixed on the pipeline to avoid vibration.

(4) The thermal mass flowmeter has a long response time and is not suitable for pulsating flow.