Thermal Mass Flow meter Working Principle
Thermal flowmeters can be divided into the following two categories:
- Flowmeters that measure the rise in temperature of the fluid after a known amount of heat has been added to it. They can be called heat transfer flowmeters.
- Flowmeters that measure the effect of the flowing fluid on a hot body. These instruments are sometimes called hot-wire probes or heated-thermopile flow meter.
Both types of flowmeters can be used to measure flow rates in terms of mass, which is a very desirable measurement, especially on gas service.
Range :- From 0.5 sccm to 40,000 lbm/h (10,000 kg/h)
Design Pressure : Up to 1000 PSIG (69 bars)
Rangeability :- 10:1 to 100:1
Process Fluid :- Air, gas, liquids, and slurries
Design Temperature: – Up to 350 ° F (176 ° C), higher with special designs
Price :- Thermal mass flowmeter costs around $500
Installation : Easy to installed
Thermal mass flow meter advantages and disadvantages
Advantage thermal mass flow meter:-
- Thermal flow meters have no moving parts, which reduces maintenance and permits the use in demanding application areas, including saturated gas.
- Gas mass meters calculate mass flow rather than volumetric flow and do not require temperature or pressure correction, which means there is no additional expense for the purchase and installation of other equipment.
- Thermal flowmeters provide excellent accuracy and repeatability over a wide range of flow rates.
- Thermal flow meters can measure flow in large pipes.
Disadvantage of thermal mass flow meter :-
- It is used for gas measurements only.
- It requires inlet and outlet sections.
- Condensation of moisture in saturated gases on temperature detector will cause thermometer to read low. Moreover, coating as well as material build up on sensor will inhibit heat transfer. This causes meter to read low.
- The other sources of error in meter readings include variation in specific heat caused due to changes in composition of gas.
How to install and calibrate a Thermal mass flow meter
How to calibrate your mass flow meter
Calibrating a thermal mass flow meter requires using the factor to correct the output for each gas. By default, thermal mass flow meters are calibrated for nitrogen/air. Thus, the flow meter range listed is valid only for nitrogen/air. Higher end models will have the option to choose the gas and the output will be corrected accordingly.
Calibration is typically done using the actual fluid. By comparing the flow rate to the recommended range listed, you can calibrate the mass flow meter until the actual flow rate matches the recommended range.
Here are the steps you need to follow when installing a mass flow meter
- Make sure the piping system is clean before installation
- Install a filter upstream to ensure a moisture and oil-free gas stream and a downstream filter if back flow is a concern
- Make sure the piping diameter is adequate for the flow rate and that there are no abrupt angles or objects in the flow path which can cause turbulence. Recommended pipe diameter is 10 times the distance between an angle and the inlet of the flow instrument
- Mount your mass flow meter in a horizontal position and avoid installing near heat sources or mechanical vibrations
- Check your system for leaks before applying fluid pressure
Installation of Inline Flow Meters
The inline style flow meter assembly includes the flow sensing element, temperature sensing element, bridge amplifier/signal output board, microprocessor circuit board, transmitter enclosure, and flow section. Depending on the flow section size and/or other requirements, the flow section may include flow conditioning plates.
Installation of Insertion Flow MetersThe insertion style flow meters include the flow sensing element, temperature sensing element, bridge amplifier/signal output board, microprocessor circuit board, transmitter enclosure, and the probe assembly which supports the sensing elements. This design requires the probe assembly to be inserted into the process gas flow conduit. Insertion styles are available with 1/2″, 3/4″ or 1″ OD probes. Insertion style flow meters may be installed with properly sized bored-through tube fittings to mount them in place. Tube fittings, with or without mounting flange, are available from the factory as an option. Installing the tube fitting consists of preparing the flow conduit to accept the fitting by first drilling a clearance hole for the transmitter probe assembly, welding it in place, or threading it into the proper size half coupling which has been welded to the flow conduit. The tube length will be determined by EPI™ based upon the installation specifications. Optional ball valve assemblies are available through EPI™ which allow the removal of the insertion style averaging tubes for service, calibration, cleaning, etc. The valve provides a means to seal off leaks of the process gas at the point of insertion after the probe assembly has been removed. Installation requires fitting the flow section to which the insertion probe assembly will be inserted with a threaded half coupling of the proper size to accommodate the ball valve retractor. In some instances, this requires direct threading together (or with a reducing bushing) of the retractor assembly. In other cases, it requires welding the half coupling in place and drilling a clearance hole through for the probe assembly. If the flow section is under pressure, a hot tap drill rig (not available through EPI) may be required.
Thermal Mass flow meter Manufacturer
|Thermal Mass Flow meter Manufacturers / Vendors||Country||Website||Phone No.|
|ABB AG||GERMANY||www.abb.de||+49 62143810|
|ABB LIMITED||UK||www.abb.com||+44 1925741111|
|BOPP & REUTHER MESSTECHNIK GMBH||GERMANY||www.burmt.de||+49 6232657508|
|ENDRESS & HAUSER||GERMANY||www.endress.com||+49 71562090|
|TOKYO KEISO CO||JAPAN||www.tokyokeiso.co.jp||+81 334311625|