A thermal mass flow meter is a measure of the relationship between the energy of a fluid mass flow caused by a fluid flowing through a pipe heated by an external heat source, or the relationship between the energy required to increase the temperature of the fluid when the fluid is heated and the mass of the fluid. A flow meter that measures fluid mass flow.
Thermal Mass Flow Meters (TMF), which are used in China to measure calorimetric flowmeters, measure the mass flow of a fluid by using a temperature field change generated when a fluid flows through a pipe heated by an external heat source, or when using a heated fluid. A flow meter that measures the mass flow of a fluid by the relationship between the energy required to rise a certain value of the fluid and the mass of the fluid. Generally used to measure the mass flow of gas. Low pressure loss; large flow range; high precision, high repeatability and high reliability; no moving parts and can be used for very low gas flow monitoring and control. Measuring fluid with heat (or temperature) change of heating fluid The mass flow has a long history. The early TMF directly placed the heating coil and the temperature measuring element in the fluid and directly contacted with the fluid. It is a contact type flowmeter, which is greatly limited in industrial applications because it cannot solve the problems of nozzle erosion and wear and explosion. . The Thomas flowmeter is representative of this type of flowmeter. It is mainly used to measure the mass flow rate of gas at a large flow rate. By the 1950s, a boundary layer flowmeter that did not contact the fluid was proposed, which overcomes the contact flowmeter. Disadvantages, but the measurement results are susceptible to media parameters (such as thermal conductivity, specific heat capacity, viscosity, etc.) and can be used to measure large liquid flows. By the 1970s, thermal distribution type TMF based on measured fluid temperature distribution due to its The unique advantages have been developed rapidly at home and abroad, used to measure the small flow of gas. With the development of technology, after the redesign of the flowmeter structure, based on the contact flowmeter, people have proposed The immersed TMF has also been developed very quickly and can be used to measure gas flow at larger diameters. In summary, TMF is a direct mass flow meter primarily used to measure gas mass flow.
Thermal mass flow meter: A meter that uses a heat transfer principle to detect flow, that is, a meter that measures flow using a heat exchange relationship between a fluid in a flow and a heat source (a heated object in a fluid or a heating body outside a measuring tube). In the past, China used to calculate the thermal flowmeter.
Basic principle of thermal mass flow meter: The gas flow rate is measured by measuring the cooling effect of the gas flowing through the heating element in the flow meter. There are two thermal resistance elements in the measuring section through which the gas passes, one of which acts as a temperature detector and the other as a heater. The temperature sensing element is used to detect the temperature of the gas, and the heater maintains a constant temperature difference between its temperature and the temperature of the gas being measured by changing the current. As the gas flow rate increases, the greater the cooling effect, the greater the current required to maintain a constant temperature between the thermal resistances. This heat transfer is proportional to the mass flow of the gas, ie, the supply current has a corresponding functional relationship with the mass flow of the gas to reflect the flow of the gas.
Application of thermal mass flow meter :
1. Steel plant, coking plant gas flow measurement;
2. Boiler air flow, measuring the secondary air volume;
3. Measurement of the flue gas flow discharged from the chimney;
4. Measurement of waterfall gas flow in water treatment;
5. Measurement of gas flow in the production process of cement, cigarettes and glass factories;
6. Compressed air flow measurement;
7. Gas flow measurement of natural gas, gas, liquefied gas, flare gas, hydrogen, etc.
Classification OF thermal mass flow meter :
Thermal mass flow meters can be classified into contact type and non-contact type according to different heat sources and temperature measurement methods.
1. Contact thermal mass flowmeter
The heating element and the temperature measuring element of the mass flow meter are placed in the pipeline of the fluid to be tested, and are in direct contact with the fluid, often referred to as a Thomas flowmeter, and are suitable for measuring the mass flow rate of the gas. Due to the heating and measuring components Direct contact with the fluid being measured, so the components are susceptible to fluid corrosion and wear, affecting the measurement sensitivity and service life of the instrument. It is not suitable for measuring high flow rate and corrosive fluids, which is a disadvantage of contact type.
2. Non-contact thermal mass flowmeter
The heating and temperature measuring elements of the flowmeter are placed outside the fluid conduit and are not in direct contact with the fluid to be tested, overcoming the shortcomings of the contact type.
Advantages and disadvantages of thermal mass flow meter :
AdvantageS OF thermal mass flow meter :
The thermal mass flow meter can measure low flow rate (gas 0.02~2m/s) micro flow rate; immersion thermal mass flow meter can measure low to medium high flow rate (gas 2~60m/s), plug-in thermal mass flow The meter is more suitable for large diameters. 
The thermal mass flowmeter has no moving parts, the heat distributed meter without shunt tube has no obstruction, and the pressure loss is small; the heat distributed meter with the shunt tube and the immersed meter, although the choke is placed in the measuring pipe, But the pressure loss is not big.
Thermal mass flow meters are relatively reliable in performance. Compared with the derivation mass flow meter, there is no need for a temperature sensor, a pressure sensor and a calculation unit, and only a flow sensor has a simple composition and a low probability of failure.
Know more about what is a pressure transmitter.
The heat distributed instrument is used for the diatomic gas close to the ideal gas such as H2, N2, O2, CO, NO, etc. It is not necessary to use these gases to calibrate directly, and the instrument is directly calibrated by air. The experiment proves that the difference is only about 2%; for Ar The monoatomic gas such as He can be multiplied by a factor of 1.4; it can be used for other gases to be converted by specific heat capacity, but the deviation may be slightly larger.
The specific heat capacity of a gas varies with the pressure temperature, but a small change around the temperature pressure used can be regarded as a constant.
Disadvantages OF thermal mass flow meter :
Thermal mass flow meters respond slowly.
In places where the measured gas composition changes greatly, the measured value may vary greatly due to changes in cp value and thermal conductivity.
For small flows, the meter will bring considerable heat to the gas being measured.
For the heat distributed thermal mass flowmeter, if the measured gas affects the measured value in the fouling layer of the pipe wall, it must be cleaned regularly; the thin pipe type instrument is more likely to be clogged, and cannot be used under normal circumstances.
The use of pulsating flow will be limited.
Thermal mass flow meters for liquids are also limited in their use for viscous liquids.
Huaheng Instrument specializes in supplying electromagnetic flowmeter, vortex flowmeter, gas turbine flowmeter, spiral vortex flowmeter, orifice flowmeter, liquid turbine flowmeter, natural gas flowmeter, steam flowmeter, dual rotor flowmeter, target type Flowmeter, thermal gas flowmeter, elliptical gear flowmeter, ultrasonic flowmeter, magnetic flap level gauge, ultrasonic level gauge, radar level gauge, diaphragm pressure gauge, digital pressure gauge, diaphragm pressure gauge, stainless steel Series of flowmeters such as pressure gauges, bimetal thermometers, thermocouples, pressure calibrators, bench pressures, etc. It is widely used in electric power, petroleum, chemical, machinery, metallurgy, cement, glass, coking and other industries in various countries.