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Learn more about how Coriolis-based flow meters can be used as microfluidic flow meter instead of thermal flow meters. Read the customer story of a microfluidics system builder who used Bronkhorst products.
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Laminar flow and turbulent flow are two important aspects to take into account when measuring flow. When does a turbulence effect occur? What is the effect on your flow meter? And very important: What can you do to minimise the disadvantageous effects of turbulent flow?
All kinds of questions which come to mind when working with flow meters.
In this blog I’ll share my top 3 tips with you to minimise the disadvantageous effects of turbulent flow.
''Turbulence is a dangerous topic which is often at the origin of serious fights in the scientific meetings devoted to it since it represents extremely different points of view, all of which have in common their complexity, as well as an inability to solve the problem”. Marcel Lesieur, 1987.
In practice you will encounter a turbulent flow quite often. A turbulent flow can be caused by (too many) restrictions in an installation, such as valves or adapters, in combination with a high velocity of the used fluid. This effect is known as ‘turbulence effect’. In every restriction, the flow has been disrupted and the speed of the gas will change. Besides the usage of restrictions, the pipe length is something to take into account as well. As it takes some time for a turbulent flow to get laminar again, it is important to use the right pipe length.
A turbulent flow is something you would like to prevent at the inlet of your flow measurement instrument, as it can affect the accuracy of your measurement. It is preferable to have a laminar flow just before your flow instrument. However, the instrument itself used as flow controller, with a valve behind the meter, can cause a turbulent flow again.
Not all kinds of flow meters experience this as disadvantageous. Mainly thermal flow meters using the bypass principle are sensitive for this effect. Flow meters based on the Coriolis, CTA (Constant Temperature Anemometry) or Ultrasonic principle are independent of turbulence.
In general it can be said that there are two types of flows: a laminar flow and a turbulent flow. You can see in the picture that laminar flow has been visualised by an experiment using ink in a cylindrical tube. The ink has been injected into the middle of a glass tube through which water flows. When the speed of the water is still low, the ink does not appear to mix with water, the stream lines are parallel; this is called laminar flow.
If the speed of the water increases, a sudden change will occur at a certain speed. The flow completely disrupts and the water turns homogeneous through the ink. The stream lines are chaotic, not linear anymore, which is called turbulent flow.
In theory the flow pattern depends on four variables:
If you use thermal mass flow meters based on the ‘bypass’ sensor principle, I advise you to do the following:
It depends very much on the application what the consequences are of turbulent flow. In semicon processes for example, particularly in coating processes such as layer deposition, turbulent flow is a no-go! A stable process is essential here. However, in other coating processes, like flame spray techniques, the impact of turbulences will be less due to the high pressure in the flow. If you need advise on choosing the best flow meter for your application, please let us know.
The choice of piping is important for your flow meter. Check out why and read the tips of our Field Engineer.
When you install a flow meter you want the best performance right away. Check out our top 10 tips for installing your flow meter.
Blog series - Part 1/5: What are low liquid flows? A blog series about how to handle low liquid flows including the definitions and tips.
Bronkhorst High-Tech designs and manufactures innovative instruments and subsystems for low-flow measurement and control for use in laboratories, machinery and industry. Driven by a strong sense of sustainability and with many years of experience, we offer an extensive range of (mass) flow meters and controllers for gases and liquids, based on thermal, Coriolis and ultrasonic measuring principles. Our global sales and service network provides local support in more than 40 countries. Discover Bronkhorst®!