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5 factors affect the performance of your thermal mass flow meter

thermal mass flow meter performance

Accurate flow measurements are a vital part of all chemical and industrial processes and can’t be doubted at all. There are a lot of different types of applications in which flow meters can be used but it is important that you understand that different flow meters are intended for different applications.

Anytime the quality of the profile drops, the flow meter’s accuracy also tends to waver. The main factors which affect the flow profile are the piping and straight run flow upstream of the flow sensor, with a slight impact from the downstream straight run. In an ideal world, the preferred fully developed flow profile happens with a smooth and long straight pipe which comes before the meter’s sensor.

In reality, however, most pipelines don’t have enough straight run, and flow disturbances tend to arise due to elbows, flanges, valves, regulators, heat exchangers, knockout drums, strainers, filters, bends, headers, tees, valves, reducers, expanders and couplings or fittings.

The straight run that precedes the meter needs increased distances to deliver the proper flow profile. Longer lengths are needed for other upstream configurations. Attaining an adequate enough straight run is unattainable to ensure a fully developed flow profile. Flow conditioning is a great option for you to check out in these conditions.

Thermal mass flow meter location:

The location where you install your flow meter is usually overlooked but choosing an installation location is very essential as you need to take into consideration, the location’s flow disturbances prior to choosing it.

Gas flow meter factory calibration:

Your flow meter calibration needs to be done at the factory with conditioning. It is vital that the manufacturer should understand the process of the end user so that they can conduct the flow meter calibration accordingly.

Here are 5 factors that you should consider:

1. Pipe size

Assess the size of the pipes being installed along with the identification of the pipe schedule and the full-scale flow rate of the flow of gas. Let your manufacturer know about this to ensure that there is proper instrument calibration being done.

2. Gas composition

Calibrate the meter with the gas that the end user plans to measure as each gas has its own thermal properties. Along with any changes in the gas composition, this can also lead to incorrect results. Although some gases are near to being pure – like argon or nitrogen – others, such as biogas, are made up of a variety of different gases. In the latter case, it is important to understand and let your manufacturer know the variety of components including the carbon dioxide content and methane.

3. Wet gas

If any particles or moisture is present in the gas, installation modifications can prevent condensate from hitting the sensor. The main cause of thermal mass flow measuremements includes heat flow caused by the flow of gas. Condensed moisture in the gas which contacts the heated sensor rapidly increases the transfer of heat, causing the instrument to react, causing inaccurate flow measurement.

4. Upstream straight run

The location where you choose to install the meter is vital. Any disturbances affect the flow of the gas in a negative way. The higher the flow disturbance upstream, the longer the length of the straight pipe upstream should be to attain a fully developed flow profile.

5. Thermal mass flow meter sensor insertion depth

The flow meter sensor must be in the center of the pipe due to the highest flow of velocity flow which will be detected the furthest away from the pipe walls. There are two ways for probe insertion to the pipe center.

Flow conditioning straight run requirements

Any disturbances which occur upstream of the meter tend to have an impact on the entire flow profile. If attaining the appropriate straight pipe length upstream is not possible, then flow conditioning is also a practical alternative.

Flow conditioners can deliver a uniform flow profile at the sensor location which is not similar to the fully developed flow profile which happens when there is an acceptable straight run length, making it essential to calibrate the flow meter with the flow conditioner with an understanding of the site’s other parameters such as installation depth, straight upstream run length, pipe characteristics and gas types.

Captive Flow Conditioning – A captive flow conditioner assembly is made up of two conditioning plates which are located between two flanges for maximum effectiveness. The end user supplies the flanges for this configuration.

Inline Flow Body – The flow conditioning is built into the flow meter body for one inline flow body meter.

Flow Conditioners – If an insufficient run exists, two conditioner styles deliver a uniform flow profile.

When considering thermal mass flow meter accuracy in any application, determine the location wisely and bear in mind that the most convenient location will probably not give the most accurate results.

Author Bio: Edward Simpson works for RS Calibration Services and has a knack for finding faults in machines and does not rest until they are rectified to perfection. He lives in Pleasanton, CA and loves to write about how machines work and about the importance of proper care and calibration of equipment. When he's not working or writing, he loves to run to stay fit.

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