Thermal mass flow meters, well known as thermal dispersion mass flow meters. It comprises a descent of instruments for the measurement of the total mass flow rate of primary gases flowing through closed conduits pipe and ducts. They are mainly used in air and gas flow measurement applications.There are two main types of thermal flow meters, Thermal Dispersion/Immersible Type, and Capillary Tube Type. Thermal Dispersion/Immersible Type generally used to measure the high flow rate in pipes and ducts whereas the Capillary Tube Type is used to measure the low flow of gas.