What is a Thermal Mass Flow Meter ?

The thermal mass flow meter is also called Thermal mass flow sensors, or thermal gas flow meters. The thermal mass flow meter is a meter that uses the principle of heat transfer to detect flow.

That is, the measurement is performed based on the heat exchange relationship between the flowing fluid and the heat source (the object heated outside the fluid or the heating body outside the measuring tube).

The main measurement gas. Thermal gas mass flow meters are mainly divided into two categories, namely: thermally distributed and immersed (or plug-in).

What is a Thermal Mass Flow Meter?

Thermal mass flow meter working principle

Thermal gas mass flow meter is designed on the basis of thermal dispersion. And adopts method of constant differential temperature to measuring gas flow. It has advantages of small size, easy installation, high reliability and high accuracy, etc.

The meter contains two platinum resistance temperature sensors. The thermal principle operates by monitoring the cooling effect of a gas stream as it passes over a heated sensor. Gas flowing through the sensing section passes over two sensors. One of which is used conventionally as a temperature sensor, whilst the other is used as a heater. The temperature sensor monitors the actual process values whilst the heater is maintained at a constant differential temperature above this by varying the power consumed by the sensor. The greater the gas velocity, the greater the cooling effect and power required to maintain the differential temperature. The measured heater power is therefore a measure of the gas mass flow rate.

The format of gas velocity and power is shown as below:

thermal mass flow meter equation

Where:

  • ρg is the specific gravity of the medium
  • V is velocity
  • K is the balance coefficient
  • Q is heater power
  • Δ T is a differential temperature
  • The medium temperature range of the meter is -40℃~220℃.

In the format (1), the specific gravity of medium is related to the density:

thermal mass flow meter equation 2

Where:

  • ρg is the medium density in working condition(kg/m3)
  • ρn is the medium density in standard condition, 101.325kPa, and 20℃ (kg/m3)
  • P is the pressure in working condition(kPa)
  • T is the temperature in working condition (℃)

In the formats (1) and (2), there is a certain functional relationship between the velocity and pressure in working condition, medium density, the temperature in working condition.

Due to the sensor temperature is always 30℃ higher than the medium temperature (environment temperature), and the meter adopts the method of constant differential temperature, therefore the meter do not need to do temperature and pressure compensation in principle.

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Know more about How Thermal Mass Flow Meter Technology Works?

Video source: https://www.youtube.com/watch?v=YfQSf2NBGqc

Thermal mass flow meter applications

The thermal measuring principle is widespread in the industry, and is being used successfully in many applications with gas flow, for example:

  • Oxygen, nitrogen, hydrogen, chlorine, and multi-component gas measurement.
  • Blast furnace gas and coke oven gas measurement.
  • Flue gas measurement.
  • Aeration and chlorine measurement in biogas and water treatment.
  • Compressed air measurement.
  • Gas flow measurement for natural gas, liquefied gas, flame gas, etc.
  • Primary air and secondary airflow measurement of power plant blast furnace
  • Flow measurement of underground ventilation or exhaust system

Further reading: Industrial LPG/Propane flow meter

Generally, Thermal mass flow meters produced in China are used to measure gas mass flow.

If you need to measure liquid mass flow. Please contact our sales engineer. We will provide you with detailed product recommendations.

Extended reading: Liquid Mass Flow Meter

Due to the continuous demand for energy due to the development of industrial automation. Natural gas as an energy source is used because of its green environmental protection and economic benefits. The metering of natural gas is very important.

The flow measurement of natural gas is divided into volume flow and mass flow. We mainly introduce the application of thermal gas mass flowmeter in natural measurement.

The main component of natural gas is methane, which contains relatively high molecular weight alkanes (mainly ethane. Natural gas is an explosive and flammable mixed gas. Some natural gas contains toxic sulfides, so the level of safety measurement requirements is high.

Natural gas is measured in the United States using normal cubic meters (corresponding to 101.325 kPa, zero degrees Celsius as the standard) standard cubic feet (corresponding to 14.73 psia, 60 degrees Fahrenheit as the standard.) Commercial natural gas has a combustion calorific value of approximately 10.8 kWh per normal state Cubic meters or 1000 BTU per standard cubic foot. Changes in its gas composition will cause changes in calorific value.

The requirements for the flowmeter thermal gas mass flowmeter during the measurement process:

  1. The mass flow can be measured directly without temperature and pressure compensation.
  2. Understanding the precise gas composition is the main parameter that determines the energy content.
  3. Maintain long-term measurement accuracy
  4. High-precision measurement can be restored by simply cleaning the probe
  5. Low flow rate, low flow rate, high sensitivity signal

Read more about: Natural Gas Flow Meter Selection Guide

Thermal mass flow meter advantages

  1. No need for temperature and pressure compensation for gas flow measurement. Convenient and accurate measurement;
  2. Wide range ratio, can be used for gas leak detection;
  3. Measuring flow rate range: 0.1Nm/s~100Nm/s.
  4. Good seismic performance and long service life, free from the influence of vibration on measurement accuracy;
  5. Overall digital circuit measurement, accurate measurement and convenient maintenance;
  6. Using RS-485 communication, factory automation and integration can be realized. click for inqueries
  7. No pressure loss, suitable for pipes of any shape with known cross-sectional area.
  8. Corrosion-resistant sensor, suitable for measuring corrosive gas.
  9. It is especially suitable for large-caliber measurement to ensure the accuracy of measurement and is suitable for trade settlement.
  10. The amount of construction is very small. Due to the plug-in structure, it can be installed and maintained online.
  11. The base-type instrument can display on-site and control with alarm.

Thermal mass flow meter disadvantages

  1. The thermal mass flow meter responds slowly.
  2. Places where the measured gas composition changes greatly. Due to changes in the cp value and thermal conductivity, the measured value will vary greatly and cause errors.
  3. For small flow, the meter will bring considerable heat to the gas to be measured.  
  4. For thermally distributed thermal gas mass flow meters, if the measured gas deposits a scale layer on the pipe wall, the measured value will be affected. Must be cleaned regularly. The thin tube type instrument has the disadvantage of being easy to be blocked, and it cannot be used under normal circumstances.
  5. The use of pulsating flow will be restricted.
  6. Thermal mass flow meters for liquids are also restricted in the use of viscous liquids.

Extended reading:
What is the K-factor in a flow meter?
Cryogenic Flow Meters|Liquid Nitrogen-Liquid Oxygen-LNG fluids

FAQ

Thermal mass flowmeters can be divided into contact and non-contact types according to different heat sources and temperature measurement methods.

1. Contact thermal mass flow meter

The heating element and temperature measuring element of this mass flowmeter are placed in the pipe of the fluid to be measured. In direct contact with the fluid, it is often called Thomas flowmeter. It is suitable for measuring the larger mass flow of gas. Due to heating and measuring elements Direct contact with the measured fluid, so the components are susceptible to fluid corrosion and wear. It affects the measurement sensitivity and service life of the instrument. It is not suitable for measuring high flow rate and corrosive fluid, which is the shortcoming of contact type.

2. Non-contact thermal mass flow meter

The heating and temperature measuring components of this flowmeter are all placed outside the fluid pipeline. They do not directly contact the measured fluid. Overcoming the shortcomings of contact.

Mass flow rate refers to the flow rate of fluid quantity expressed by mass.
The mass flow rate can be expressed by the formula: qm=m/t=ρ×u×A.
In the formula, QM is the mass flow rate, kg/s.
m is the unit fluid mass, kg.
ρ is the fluid density, kg/m3.
t is the unit time, s.
u is the average flow velocity in the pipe, m/s.
A is the cross-sectional area of ​​the pipeline, m2.

Extended reading: U-series Liquid Mass Flow Meter | Liquid-slurry flow measure

Mass Flow Rate vs Volumetric Flow Rate

Mass flow rate vs Volumetric flow rate is what we must use in flow measurement and control. In this post, we compare the concept of volume flow and mass flow and the conversion between the two.

Commonly used flow meters, such as orifice plates. Turbine flowmeter. Vortex flowmeter. Electromagnetic Flowmeter. Rotameter. The flow measurement value of ultrasonic flowmeter and oval gear flowmeter is the volume flow of fluid. Coriolis mass flow meters and thermal gas mass flow meters measure mass flow.

Read more about: New Guide: Mass Flow Rate vs Volumetric Flow Rate

Gas mass flow controller

The gas mass flow controller is based on the principle of thermal mass flow measurement. With control valve. The Micro Gas Flow Controller (MFC) is used to precisely measure and control the mass flow of gas.

Read more about: Gas mass flow controller working principle

Air mass flow meter VS Controller

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Sino-Inst offer over 10 Thermal Mass Flow Meters, with Best Price.

A wide variety of Thermal Mass Flow Meters options are available to you, such as free samples, paid samples. All of our flow meters can work with the AMS NEW TREX. About 13% of these are magnetic flow meter. 14% are Insertion Magnetic Flow Meter. 25% are Venturi flow meter. 13% are Handheld ultrasonic flow meter, and others are Liquid Turbine Flow Meters.

Sino-Inst is Thermal Mass Flow Meter suppliers, located in China. Mass flow meter products are most popular in North America, Mid East, and Eastern Europe.

The United States, and India, which export 99%, 1%, and 1% of Thermal Mass Flow Meter respectively.

You can ensure product safety by selecting from a certified supplier, with ISO9001, ISO14001 certification.

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