Why flow is one of the most important parameters
Choice is the act of selecting between two or more possibilities. Generally, choice can be an exciting experience, but sometimes it can also be very difficult. We are all familiar with the saying, “there is no such thing as too much choice”. However, after a number of studies by psychologists and economists on the issue, they have been concluding that an overload of options can paralyse people or push them into making incorrect decisions.
When the number of possibilities to choose from becomes high and the impact of making an incorrect choice can have significant consequences, it can make the decision process very uncomfortable. This can often be the case when trying to select the correct flow technology to use in your plant.
Flow is one of the most important parameters in many industrial processes. It lets us know how much fluid is passing through a pipe or duct over a specific period of time. By knowing the accurate flow of a fluid, we can optimise dosing rates, ensure tanks or packaging are not overfilled, ensure the correct volume is being delivered and check plant balancing.
When we look at the most common issues found in incorrect flow measurements today, the biggest contributor is the incorrect selection of the flowmeter. Some flow measurement technologies can only work on specific fluids or in specific flow ranges. If you get these incorrect, the flowmeter will not perform as desired, or sometimes at all. Examples of this are trying to use an electromagnetic flowmeter on a gas application or trying to use a vortex flowmeter on a very viscous (thick) liquid.
How do you choose the right flowmeter?
Unfortunately, there is no “one size fits all” flowmeter available that can cover each and every application on a plant. These days there are a large number of different technologies that can be used to measure the flow of a fluid. They range from mechanical flowmeters, like positive displacement, turbine, gear meters and variable area flowmeters (Rotameter) to electrical flowmeters like magnetic, vortex and Coriolis. Added to the mix of possible options are also differential pressure-based flowmeters, like orifice, nozzle, venturi, and averaging pitot tubes.
Then we add some of the latest flow technologies like thermal and sonar. With so much choice available it can appear very confronting.
While for some specific applications there are only one or two flow technologies that can work effectively, on many applications there are numerous flow technologies available to choose from. So how do we go about making the correct selection of flow technology for a specific application? With the below simple tips, you can help ensure you make a more informed and better selection.
Steps for selecting a flow technology
The first step in the selection of a flow technology is to take a step back. With a clear mind, ask yourself, why do I need to measure this flow and what do I need to get from the flowmeter? These simple questions can help guide you toward the desired flow technologies before you even look at the process conditions.
1. Why do I need to measure this flow? (i.e. Purpose)
Understanding why you need to make the measurement can help identify the correct flowmeter to employ.
If the purpose is for dosing or batching, then a highly accurate and highly repeatable flowmeter would be required to ensure that the exact volume, or mass, is transferred and any wastage is minimised.
If the purpose is for a control application, then having a repeatable flow measurement with the correct type and number of outputs will be the drivers in the decision-making process. Repeatability is more valuable here than accuracy.
If the flowmeter is only needed for a local indication of the flow, then a simpler device could be employed.
2. What do I need from the flowmeter?
Along with knowing the purpose of the flow measurement, knowing what types and number of outputs are required from the flowmeter is also critical for correct selection.
If you need electronic outputs, like analog (4-20mA) or pulse (Hz), it is important to check that the selected device can provide the type and number of outputs required. For many manufacturers, outputs other than a simple analog signal are often an option, and if the desired output type is not selected at the time of the flowmeter purchase, they generally cannot be added later.
In the second part of this article, I will describe the most important fluid parameters involved in the correct selection of a flowmeter.
Picture credits: 3D generator-stock.adobe.com
