The World Market for Thermal Flowmeters, 2nd Edition  
Now available!
    

Can thermal flowmeters help reverse climate change?  We think they can play a big role. These cost-effective meters are ideally suited to measuring greenhouse gas and other emissions. The World Market for Thermal Flowmeters, 2nd Edition, published in January 2018, found that environmental awareness and the need for continuous emissions monitoring (CEM) are driving growth in thermal flowmeters.

Environmental awareness propels growth

The new age of environmental awareness that has spawned the Kyoto Accord, the Paris Agreement, and other greenhouse gas initiatives, has resulted in a rewriting of the rules on measuring greenhouse gas emissions. There is now a need and a demand to measure greenhouse gases in applications that formerly may have gone unnoticed. Many of these applications present opportunities for thermal flowmeters, including:

• Measurement and recovery of landfill gas 

• Ethanol distillation and refining 

• Measuring emissions from steam generators, boilers, and process heaters

• Biomass gasification from organic industrial waste and food waste 

• Recovery of methane from coal mines

• Monitoring of flue gas 

• Measurement and monitoring of flare gas flow 

Thermal flowmeters are uniquely suited to make these measurements because they can accurately measure different mixtures of gases and because their insertion technology allows them to handle large pipe sizes. Insertion thermal flowmeters, for example, can measure two principal causes of acid rain -- sulfur dioxide (SO2) and nitrous oxide (NOx). They determine how much is being released into the atmosphere by combining a measurement of the flowrate with a measurement of the concentration of SO2 and NOx.

Popular in water & wastewater treatment
The water and wastewater industry is another key segment driving thermal flowmeter success. Thermal flowmeters have established themselves in this industry and are a replacement choice for traditional technologies such as differential pressure, as they do not introduce pressure drop into the process flow and require less maintenance.

One of the more common wastewater treatment applications is the measurement of the air/oxygen gas used to promote the secondary treatment of sludge. Careful  measurement ensures that this step is conducted within ideal parameters, and that no energy is unnecessarily wasted in pumping more air or oxygen than the process requires.

Further downstream within a treatment plant, thermal flowmeters can be found in distribution pipes and aeration basins. And, on heading toward the output side, the decomposed sludge is exposed to anaerobic treatment using other specific bacteria chosen for this purpose. The result of this step is the production of water and a mixture of gases, primarily carbon dioxide and methane, which thermal meters can measure.  Methane, also called digester gas or biogas, is a growing source of a type of renewable energy. It has come into use to power on-site plant operations, and is also available as a commercial product.

Advantages and limitations
Thermal flowmeters have fast response times and excel at measuring low flowrates. They can also handle some difficult-to-measure flows and  provide a direct means of measuring mass flow. 

One limitation of thermal flowmeters is that they are used almost entirely for gas flow measurement. They  have difficulty measuring liquid flows because of the slow response time involved in using the thermal principle on liquids. Some companies, however, have released thermal flowmeters for liquid flow measurement.

A second limitation is in their accuracy. Thermal flowmeters are not nearly as accurate as Coriolis meters, and typical accuracy levels are in the one percent to three percent range. However, thermal suppliers are working to improve the accuracy of their flowmeters. Expect wider use of thermal flowmeters as their accuracy levels increase.

How they work
While all thermal flowmeters use heat to make their flow measurements, there are two different methods for measuring how much heat is dissipated:

• The constant temperature differential method uses thermal flowmeters with two temperature sensors: a heated sensor and another sensor that measures the temperature of the gas. Mass flowrate is computed based on the amount of electrical power required to maintain a constant difference in temperature between the two temperature sensors.

• The constant current method uses thermal flowmeters with a heated sensor and another one that senses the temperature of the flowstream. The power to the heated sensor is kept constant. Mass flow is measured as a function of the difference between the temperatures of the heated sensor and the flowstream. 

Both methods rely on the idea that greater cooling results from higher velocity flows. Both  measure mass flow based on the measured effects of cooling in the flowstream.

Mass flow controllers
One type of thermal flowmeter, a mass flow controller, contains an integrated control valve that is used to control the flow as well as measure it. Most mass flow controllers use thermal principles to determine mass flow, although some use a pressure-based measurement. 

The mass flow controller market is one of the most rapidly developing markets in the flowmeter world today. Mass flow controllers are not included in this study, although Flow Research has published a separate study on this market. 

History of thermal flowmeters

The roots of thermal flowmeters go back to the hot wire anemometers that were used for airflow measurement in the early 1900s, but thermal flowmeters were first introduced for industrial applications in the 1970s. The story of how they came on the market is a fascinating one.

Articles about Thermal Flowmeters

About the 2009 Study

Mass Flow Controller Study

All Flowmeter Studies