Flow sensors are a critical part of many industrial processes and the accuracy of their measurements depends largely on correct positioning. The performance and efficiency of flow measurement devices is strongly influenced by two basic flow types: laminar and turbulent flow. In the following article, you will learn what characterizes these flow types, how they affect measurements and how you can minimize problems caused by turbulent flow in your systems.
Laminar flow: ideal condition for precision
Laminar flow can be compared to the orderly flow of water, in which each layer of liquid moves undisturbed along its own path. Here there is no cross-mixing of the layers and the velocity of the particles remains constant, resulting in a stable flow profile. This phenomenon results in an optimal condition for flow meters as it enables accurate and repeatable measurement results. Laminar flows are found especially at low fluid velocities or in systems where the flow is disturbed by few obstacles such as valves or couplings.
Turbulent flow: a challenge for measurement technology
A turbulent flow, on the other hand, is characterized by irregular vortices and discontinuities that make the flow of a medium chaotic. It occurs when the orderly flow is disturbed by high flow velocities and interaction with installations such as obstructions caused by valves, adapters or couplings. Flow meters that are influenced by this type of flow can provide imprecise measurements, which can become a significant problem in control technology.
Why laminar flow is preferred in flow measurement
- High accuracy: Laminar flow means less interference and therefore more reliable measurements, which is essential for precision in critical applications.
- Minimal pressure drops: The uniform flows cause less resistance. resistance and energy loss, which reduces the pressure drop across a flow meter and therefore energy consumption.
- Ideal for low flow rates: In scenarios in which low flow rates are measured, laminar flow is advantageous, as turbulence harbors great potential for measurement errors.
Determine laminar or turbulent flow with the Reynolds number
The Reynolds number helps you to determine whether a flow is laminar or turbulent. It is dimensionless and universally applicable, regardless of the system of units used. The Reynolds number supports the assessment and prediction of flow behavior in different conditions, such as water and air dynamics. It is determined by the following four variables:
- Density of the fluid
- Velocity of the fluid
- Diameter of the pipe
- Dynamic viscosity of the fluid
The Reynolds number can be determined using the following formula: Reynolds number (Re) = (density x velocity x pipe diameter) / dynamic viscosity
A low Reynolds number (≤ approx. 2300) indicates laminar flow, while a high number (≥ approx. 3000) indicates turbulent flow. In the transition area between these values, the flow can exhibit characteristics of both laminar and turbulent flow.
The critical Reynolds number in this context indicates the exact threshold value of the Reynolds number at which a flow state changes from laminar to turbulent (typically around 2300 for liquids).
How to find the optimum installation situation for flow monitors and volume flow meters in practice is the easiest way to find out in our new guide article.
Tips for minimizing the effects of turbulent flow
It is critical to protect flow measurements from the disruptive effects of turbulent flow to ensure the integrity and accuracy of your measurements. Here are some tips on how to adapt your systems:
- Optimizing the installation situation To minimize turbulence, unnecessary obstacles in the flow path should be avoided. If these components are necessary, a turbulence filter or rectifier can calm the flow and return it to a laminar flow.
- Adhere to the recommended inlet and outlet distances
- Optimal inlet and outlet distances are specified for each flow meter in order to calm the flow before measurement. It is recommended to maintain a sufficient distance from the measuring point, particularly behind fans and pipe bends, to ensure that the measurement result is as uniform as possible.
- Limiting the flow velocity Observe the recommended pipe length to moderate the velocity at the inlets and outlets of the flow meters and thus switch from a turbulent to a laminar flow.
- Implementation of turbulence filters: These specially developed filters help to smooth the flow pattern in front of a sensor and thus improve the accuracy of the measurements.
Application-specific aspects
Please note that turbulent flows can have different effects depending on your specific process and application. In areas such as semiconductor manufacturing, turbulent flows must often be strictly avoided to ensure process stability. In other processes, such as high pressurethe effects may be less significant.
It is essential to select the right flow meter for your application and to consider how laminar or turbulent flows can affect performance. Our experts will be happy to provide you with more in-depth advice at any time.
New in our brochure: "6 mistakes in flow measurement and how to avoid them"
Discover the most common pitfalls in flow measurement that even experienced professionals can fall into. In our latest brochure, we highlight critical errors that affect the accuracy of your measurement data and provide tried and tested solutions to avoid them. Whether you are involved in the installation, maintenance or operation of flow sensors, this guide will equip you for reliable flow measurement. Increase the efficiency of your applications by learning about common mistakes and how to avoid them.
