Thermal dispersion mass flow meters, often called thermal mass flow meters, rely on the transmission of heat from a body to a gas flow. Inside the flow meter sensor head, a heated resistance thermometer (RTD) is electronically compared with an unheated RTD sensor. As a gas passes the heated RTD, heat is transferred from this sensor to the gas, and hence the RTD is cooled, thereby reducing the temperature difference between the two sensors. Heat transfer from the RTD to the process gas is based on the composition of the gas, therefore the temperature difference between the two RTDs is a function of the mass flow rate of the gas.
The electronics of the meter can be an integral part of, the meter or mounted remotely (for instance for easy access …show more content…
Thermal dispersion mass flow meters are uni-directional, velocity profile dependent mass flow meters.
4.6.2 Selection of Thermal Dispersion Mass Flow Meters
The following shall be considered in the selection of thermal mass flow meters:
1. Thermal mass flow meters are mainly used for air measurements, such as ventilation air to analyzer houses, purge air flow measurements and combustion air flow to furnaces.
2. Thermal mass flow meters can also be used on gases other than air, but the composition of the process gas must be known. The variations in composition shall be small, as thermal mass flow meters perform best when the composition of the gas remains constant.
3. The gas to be measured shall be dry or saturated. Free liquid in the gas, when in contact with the heated RTD, seriously affects the performance of the flow meter.
4. Some thermal mass flow meters have a very slow response time. The required response time shall be specified.
4.6.3 Installation Requirements
1. The sensor assembly shall be placed with the sensing elements across the cross of the process pipe or …show more content…
Bearing dimensions shall be such that a permanent liquid film is maintained.
For these applications ultrasonic flow meters or Coriolis mass flow meters, having a better performance and rangeability should be considered.
The meters shall be protected against damage due to overspeeding or hydraulic shock. In liquid service, adequate filtering and degassing shall be provided.
Viscosity fluctuations affect the accuracy. The use of turbine meters is normally limited to products with relatively low viscosities, typically maximum 10 mm2/s (10 cS).
Flow straighteners shall be used with turbine meters if specified by the vendor to meet the required flow meter performance.
4.10 POSITIVE DISPLACEMENT METERS
Positive displacement meters (PD meters) shall have flanged connections. The body material shall be carbon steel unless the application requires other materials as specified by the piping
The electronics of the meter can be an integral part of, the meter or mounted remotely (for instance for easy access …show more content…
Thermal dispersion mass flow meters are uni-directional, velocity profile dependent mass flow meters.
4.6.2 Selection of Thermal Dispersion Mass Flow Meters
The following shall be considered in the selection of thermal mass flow meters:
1. Thermal mass flow meters are mainly used for air measurements, such as ventilation air to analyzer houses, purge air flow measurements and combustion air flow to furnaces.
2. Thermal mass flow meters can also be used on gases other than air, but the composition of the process gas must be known. The variations in composition shall be small, as thermal mass flow meters perform best when the composition of the gas remains constant.
3. The gas to be measured shall be dry or saturated. Free liquid in the gas, when in contact with the heated RTD, seriously affects the performance of the flow meter.
4. Some thermal mass flow meters have a very slow response time. The required response time shall be specified.
4.6.3 Installation Requirements
1. The sensor assembly shall be placed with the sensing elements across the cross of the process pipe or …show more content…
Bearing dimensions shall be such that a permanent liquid film is maintained.
For these applications ultrasonic flow meters or Coriolis mass flow meters, having a better performance and rangeability should be considered.
The meters shall be protected against damage due to overspeeding or hydraulic shock. In liquid service, adequate filtering and degassing shall be provided.
Viscosity fluctuations affect the accuracy. The use of turbine meters is normally limited to products with relatively low viscosities, typically maximum 10 mm2/s (10 cS).
Flow straighteners shall be used with turbine meters if specified by the vendor to meet the required flow meter performance.
4.10 POSITIVE DISPLACEMENT METERS
Positive displacement meters (PD meters) shall have flanged connections. The body material shall be carbon steel unless the application requires other materials as specified by the piping