# What is a Thermal Mass Flowmeter?

Thermal mass flow meters are used for direct measurement of gas mass flows (kg/h) without additional, expensive measuring instruments.

Typical gas flow meters record the operational volume flow of the sample that can vary due to variations in pressure, temperature and density. These additional requirements mean greater measurement complexity that can hinder processing accuracy.

A thermal mass flow meter obtains the thermal mass directly, using the normal density of the gas as a basis to calculate the volumetric flow rate.

## How does an Thermal Mass Flowmeter work?

Thermal mass flow meters use heat transfer from a hot filmanometer to the gas stream to control mass and mass flow as a product of flow rate-dependent cooling. This phenomenon is not affected by variable conditions such as pressure and temperature.

Instead, mass flow is determined by measuring the particles in direct contact with the heated surface of the film.

Thermal Mass Flowmeter
Image.. https://www.foxthermal.com

The method is based on an electrical bridge circuit with two resistors placed in the gas stream. Heat is electronically applied to one of the sensors, which is simultaneously cooled by the gas stream, while the secondary resistor controls the ambient temperature of the flowing gas.

This provides a constant differential temperature measurement between the two sensors, which along with the power loss from convective heat transfer is used to determine instrument and gas-dependent constants, including mass flow.

The relationship between mass flow and thermal cooling depending on flow rate is determined using King's Law equation. This principle is widely used for direct mass flow measurements, eliminating the risk of accuracy errors that can arise from compensating measurements for additional environmental conditions.

### Advantages of Thermal Mass Flowmeters

Thermal mass flow measurements are advantageous because they provide direct measurement of a gas stream without additional measurement uncertainties.

These components offer flawless precision, with a minimum pressure drop of 1 millibar. This eliminates the need for pressure compensation with a wide range of accuracies down to 1%.

Their simple and robust design limits additional mechanical parts for high reliability and short gas mass flow measurement response times.

#### Applications of Thermal Mass Flowmeters

Thermal mass flow meters are designed for a range of pneumatic, test bench, mechanical construction and chemical processing applications. Thermal mass flow meters are optimized for use in the digital sector, with an extended measurement range of 1:150 for improved signal quality and additional diagnostic functions as a preventive maintenance tool.

Thermal mass flow meters offer dynamic mass flow measurements for gases at various pressure conditions and compositions. High quality thermal sensors offer significant resistance to various process gases.

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