The Problem of Choice-  Flow technology selection can often be a challenge (Part 2)

The Problem of Choice- Flow technology selection can often be a challenge (Part 2)

February 4, 2020

In the first part of the article, I have gone into the difficult choice process when you look for a flowmeter and which questions you should ask yourself before the purchase.  Now I focus on fluid parameters.

Process fluids come in many forms and include clean liquids, viscous liquids, slurries (liquids with solids), gases, liquified gases as well as saturated and superheated steam. Due to the different properties of these fluids, different flow technologies for measurement are required.
On the vast majority of process plants in operation, due to the range of fluids they are required to measure, you will find a number of different flow technologies deployed.

Fluid parameters

The most important fluid parameters to investigate when looking to select a flowmeter include:

  • Flowrate (Minimum, Nominal and Maximum)
    Ensuring that the flowmeter can meet the desired flow ranges to be experienced onsite is essential. Many flow technologies, like vortex, DP based and variable area, have minimum measurable flows. If the flowrate drops below this value, then you can no longer get a flow measurement from the flowmeter.
  • Pressure
    This is typically not an issue on liquid applications, as liquids are non-compressible fluids. However, on gas and steam applications, the process pressure will have a large impact on fluid density. If the pressure will vary in the process, this is also important to consider, as you may need a specific technology or external compensation calculations.
  • Temperature
    Both the density of a fluid and the viscosity of a fluid are linked to its temperature. Typically, as temperature increases, the density and viscosity will decrease.
  • Density
    The fluid density will impact the measurable range of many flow technologies.
  • Viscosity
    A number of flow technologies, like vortex and DP based, are limited to low viscosity liquids. If the viscosity gets too high, the flowmeter can no longer operate and measure correctly. Hence, if the liquid viscosity is high, the available flow technologies become more restricted.

Additional considerations

After working through the fluid parameters, the purpose of making the flow measurement and what outputs you require, there are still some more items worth considering. These include the installation requirements of the flowmeter, such as straight pipe length, desired process connection, and hazardous area approvals.

Lastly is the cost of the flowmeter. Don’t base your flow selection on price first, as often the more expensive technologies are this way because of their accuracy, the types of fluids and flow ranges they can measure and the diagnostics they can provide. If you try to base the decision only on price, then it is very easy to select a flowmeter that won’t do the job properly (or sometimes at all) and will cause more headaches in the long run.

Flow technology selection can seem like a daunting process. However, by spending a short amount of time to clearly define what you are measuring and why you need to measure it, the answers can help guide you towards the correct flow technology selection.

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