Thermal Flow Meters , Working Principle , Advantage and Disadvantage

Thermal Flow Meters work on the Convective heat transfer principle.

How does it work : In this mass flow of gas or liquid is measure when the temperature of the sensor change due to flow of the liquid.The amount of energy required to raise the temperature of the sensor helps to measure the mass flow of the liquid.In this two sensors are placed one is at constant temperature(with the help of the power source) . The other sensor temperature can be changed with the flow of liquid. When there is no flow we can measure the temperature difference between the sensors that is zero.But when the flow starts sensor1 (connected to power source increase or decrease the power supply to maintain constant temperature) meanwhile the temperature of the sensor 2 is increased due to the liquid .

We can calculate this using formula

Q = m *cp * (T2 -T1)

Q = Power input of the heater
m = mass flow rate
T2 = temperature of sensor 2
T1  = temperature of sensor 1

Advantage of Thermal mass flowmeters
• No moving parts
• Low maintenance costs
• Measure mass flow rate not volumetric flow rate
• High accuracy and repetition
• Can use in large pipes
• Excellent for gaseous product

The disadvantage of Thermal Mass flowmeters
• High installment cost
• Not high accurate for liquid.
• Not good for small pipes.