A thermal mass flow meter is an instrument that precisely and constantly measures the rate of flow of a fluid, normally a gas, through a pipe or conduit in some sort of industrial application. Thermal mass flow meters insert directly into the center of flow of the fluid they’re measuring. They may operate as a system that mounts to the outside of the conduit with a probe entering through a port. Otherwise, thermal mass flow meters may operate as a completely contained inline system that acts as part of the conduit itself.
A thermal mass flow meter will provide a way to accurately monitor gas flow in an essentially passive manner. This has a near-zero impact on the wider processes the gasses are involved in. They also offer high reliability and extremely low maintenance requirements in comparison to other types of flow meters. This is thanks to the elegant, simple design of thermal mass flow meters.
Many applications use thermal mass flow meters where it’s important to carefully monitor the flow rate of a fluid. To many, it might seem like a narrow field of applications, but it’s actually shockingly broad. Carefully metering gas flow is crucial in everything from manufacturing to municipal operations to environmental protection and beyond.
While the full list of thermal flow meter applications is far too long to include in a single article, the following represent just a few common applications for the technology:
Compressed air offers wide use in industrial settings to run everything from large pneumatic machines right down to hand tools. A thermal mass flow meter will allow plants to control how compressed air distributes to stations from central sources and measures total use in order to identify costly and potentially dangerous leaks.
Combustion in manufacturing produces greenhouse gasses that require careful tracking and reporting for companies to maintain compliant with environmental regulations. These regulations are set by local governing bodies such as the rules from the EPA in the United States. For example, thermal mass flow meters are useful for accurately measuring the flow of greenhouse gasses exiting plants. This allow companies to both stay in compliance with the law as well as finding opportunities to reduce emissions.
Natural gas is a common fuel for industrial combustion, and while it’s cheaper than many other fuels, waste is still a big problem. Thermal mass flow meters measure the flow rate of natural gas into boilers, furnaces, and heaters. These flow meters closely track and optimize fuel flow to identify inefficient systems that are sucking up more fuel than they should.
Aeration is a key step in municipal water treatment that uses oxygen injection to feed the bacteria that break down waste. Too much or too little oxygen renders the process less efficient and drives up costs. Municipal water treatment plants use thermal mass flow meters to ensure the ideal amount of air bubbles into the water to keep costs down and happy bacteria working efficiently.
The applications above make up only a tiny fraction of the full scope of flow metering’s usefulness. However, it’s clear from each that the process is exceptionally important to the bottom line, the effectiveness of production, and the environmental impact of industrial processes.
Thermal mass flow meters offer users a way to meter gas flows with a number of significant benefits including, but not limited to:
In essence, thermal mass flow meters provide a way to tackle the important process of metering gas flow. Thermal mass flow meters are highly accurate, reliable, repeatable, and economical, thus leading to better metering, lower waste, and higher safety.
An advantage of thermal mass flow meters is their simplicity, both in design and the concepts that drive their function. To understand how thermal mass flow meters work, it’s first important to understand what thermal mass is. After all, it’s in the name. Thermal mass refers to a material’s ability to absorb and release heat. In your house, the wood, brick, and concrete act as thermal masses that help regulate the interior temperature. In thermal mass flow metering, the thermal mass is the gas flow, which also has the capability to absorb and move heat.
All thermal mass flow meters work by inserting two probes into the center of the gas stream. One is a passive probe that measures the temperature of the surrounding gas. The other, is an active heat probe that remains at a constant temperature in relation to the passive temperature sensor. As gas flows through the probes, it carries some of the heat away from the active sensor. Higher flow velocities equal more heat loss.
As that cooling effect occurs, the control system must use more electrical current to keep the temperature spread between the two sensors consistent. And the electronics constantly monitor that change in current. In turn, using a phenomenon known as King’s law, the system calculates the exact flow rate of the fluid to within 1% accuracy or better.
All thermal mass flow meters work on the same core principles. However, they can mount and operate differently depending on the type chosen. Each type has advantages and disadvantages that suit more or less to any given application, but all deliver an accurate, repeatable metering process.
Insertion and inline flow meters differ in how they mount to the pipe or conduit carrying the target gas. Inline thermal mass flow meters are permanent installations that include their own section of pipe. They fit inline with the flow pipe and attach at either end with threading or flanges. Inline flow meters come in a variety of sizes, which allows them for use with many common pipe diameters. And while they typically cost more than insertion meters, inline meters offer set-and-forget installation ideal for long-term use.
Insertion thermal mass flow meters insert into a conduit from the outside through a port. They provide identical accuracy and repeatability as inline flow meters. However, since they aren’t integrated into the system body itself, they represent a lower cost. Furthermore, they are a semi-permanent solution that’s more ideal for intermittent or temporary metering.
Constant temperature and constant current thermal mass flow meters both measure the same thing – the heat change across two probes. However, they differ in how the active heat probe acts within the system. In a constant temperature system, the heat probe remains a constant temperature relative to the opposing probe. The change in the current necessary to maintain that constant spread is the variable that the electronics measure.
In a constant current system, the amount of current to the heat probe remains steady. The fluctuating temperature of the probe in relation to the passive surrounding temperature is the variable that the electronics measure. Both systems are effective, but constant temperature probes offer a faster response and are generally a better option.
Thermal mass flow meters offer an ideal solution to the problem of accurately measuring gas flows in industrial, municipal, and environmental applications. Their simplicity, ease of installation, and low maintenance requirements make them extremely affordable. Moreover, their high level of accuracy and repeatability make them arguably the most effective option available.
Eldridge Products, Inc. designs and manufactures inline and insertion thermal mass flow meters and control software for use in a wide variety of industries. To find out more about how our flagship Master-Touch or budget-conscious ValuMass lines of thermal mass flow meters can meet your needs, send us an email today: [email protected].
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