Compressed Air Flow Meter Thermal Mass Flowmeter

The thermal mass flowmeter is a flow meter based on the principle of thermal diffusion. The device uses the constant temperature difference method to measure the gas accurately. It has the advantages of small size, high digitization, easy installation, accurate measurement and so on.

  • Measuring the mass flow or volume flow of gas
  • Do not need to do temperature and pressure compensation
  • Wide range: 0.5Nm/s~100Nm/s for gas.
  • The meter also can be used for gas leak detection
  • Good vibration resistance and long service life
  • No moving parts and pressure sensorin transducer
  • Easy installation and maintenance
  • RS485 or HART interface to realize factory automation and integration
Enquiry

Thermal gas mass flow meter is designed on the basis of thermal dispersion, and adopts method of constant differential temperature to measuring gas flow. It has advantages of small size, easy installation, high reliability and high accuracy, etc.

Thermal mass flowmeter family

The sensor part of the thermal gas mass flow meter consists of two reference platinum resistance. When the flow meter is in the working state, a temperature sensor continuously measures the medium temperature T1. The other sensor will be heated to a temperature T2. And this sensor is a speed sensor to check the flow rate. T2 is greater than T1. There is a temperature difference △T=T2-T1.

When gas flow going through, the gas molecules in the process will take away temperature, so that the value of T2 has been decreased. So if you want to make sure △T unchanged, it must increase the speed sensor power supply current. The greater the velocity of the medium, the greater the power supply current of the speed sensor. At the same time, there is a specific functional relationship between the velocity of the gas and the heat, that is the connotation of the constant temperature difference principle.

V=[K(Q/△T)^1.87]/ρg  …………(1)

 

In the formula:ρg — specific gravity of fluid (related to medium density)

V — Flow rate

K – equilibrium coefficient

Q — heat added (related to specific heat)

△T — temperature difference

Since the sensor temperature is always about 30 ° C higher than the medium (ambient) temperature automatically, the thermal gas mass flow meter does not need temperature compensation in principle.

The thermal gas mass flow meter is suitable for the medium temperature range of -40-220℃.

ρ=ρn*[(101.325+P)/101.325]*[(273.15+20)/(273.15+T)]……(2)

 

In the formula:ρ — medium density under working conditions (kg/m3)

ρn — medium density under standard conditions (101.325kPa, 20℃) (kg/m3)

P — Operating pressure (kPa)

T — Operating temperature (℃)

As we can see equation (1) and (2),  the function of medium flow rate and operating pressure, gas density and operating temperature has been determined.

The thermal mass flow meter using the principle of constant temperature difference, so it needn’t temperature and pressure compensation.

Features

-No pressure and temperature compensation, direct measurement of gas mass flow, simple composition, small probability of failure.

-Wide range ratio (greater than 100:1), convenient loading and unloading, easy to use.

-Fast response, high accuracy, no moving parts, strong structure, vibration resistance.

-High sensitivity, especially suitable for large diameter, low flow rate measurement.

-Scene display, signal output, upper and lower alarm, etc.

-It can be used in high temperature and corrosive environment.

-If site conditions permit, continuous installation and maintenance can be achieved (special customization is required).

Specifications

Performance Technical parameter
Structural form plug-in pipelined
Measuring medium All gases (except acetylene)
Pipe diameter range Caliber DN32 or higher DN10~DN2000mm
Velocity range 0.1~120Nm/s
Precision ±1~2.5%
Operating temperature Sensor:-40℃~+220℃        convertor:-20℃~+45℃
Working pressure Medium pressure≤2.5Mpa Medium pressure≤4.0Mpa
Power supply DC24V or AC220V≤18W
Response speed 1s
Output signal 4-20mA (Photoelectric isolation, large load 500Ω)、pulse、RS-485 (photoelectric isolation)、HART agreement
Alarm 1-2 relay normally open contact、10A/220V/AC、*/30V/DC
Type of supply Separate structure, integrated structure
Pipe material Carbon steel, stainless steel, plastic, etc
Field display Four lines of Chinese liquid crystal display
Display content Mass flow, standard volume flow, cumulative flow, standard time, cumulative running time, standard flow rate, etc
Protection grade IP65
Sensor material Stainless steel Stainless steel, carbon steel

Upper Range Value of Common Gas

(Unit: Nm3/h. The follow table can be extended)

Nominal Diameter (mm) Air NitrogenN2 OxygenO2 Hydrogen(H2)
15 65 65 32 10
25 175 175 89 28
32 290 290 144 45
40 450 450 226 70
50 700 700 352 110
65 1200 1200 600 185
80 1800 1800 900 280
100 2800 2800 1420 470
125 4400 4400 2210 700
150 6300 6300 3200 940
200 10000 10000 5650 1880
250 17000 17000 8830 2820
300 25000 25000 12720 4060
400 45000 45000 22608 7200
500 70000 70000 35325 11280
600 100000 100000 50638 16300
700 135000 135000 69240 22100
800 180000 180000 90432 29000
900 220000 220000 114500 77807
1000 280000 280000 141300 81120
1200 400000 400000 203480 91972
1500 600000 600000 318000 101520
2000 700000 700000 565200 180480

The flow rate in standard condition: The flow rate is in the condition of 20℃ temperature and 101.325kPa pressure.

The unit of flow rate is optional: Nm3/h, Nm3/min, L/h, L/min, t/h, t/min, kg/h or kg/min.

The reduction formula of flow rate in working condition and flow rate in standard condition:

Qs: The flow rate in standard condition (Nm3/h).

Qn: The flow rate in working condition (m3/h).

t: The medium temperature in working condition (℃).

p: The medium pressure in working condition (Gauge pressure, MPa).