Laminar flow element; a critical element for flow meters

February 7, 2022 Ger Jan Dorland
Choice of piping

To obtain the best quality for our flow meters that meet the highest standards, we have been working closely together with our suppliers for the last 40 years. Working with local suppliers is important to us. In addition to short lines of communication, good delivery reliability and joint innovative strength, we also contribute to the local economy. One of these companies is Veco Precision (in Eerbeek, NL).

Together with Veco Precision we work on the development of one of the key components of our flow meters; the laminar flow element, also called LFE. The laminar flow element is the mechanical heart of our flow meters. In this blog I provide you some insights into the operation of our flow meter and why this laminar flow element is a crucial part. 

Thermal mass flow meters

Thermal mass flow meters measure the mass flow of gases, employing a combination of heated elements and temperature sensors, with thermodynamic principles used to derive actual flow. They need limited correction for changes in temperature, pressure or density and are extremely accurate, especially when measuring low and very low flow rates.

Laminar flow element; a critical element

The Laminar Flow Element as seen in Picture 1 is a critical component of the thermal mass flow meter based on the bypass principle. The functionality of the Laminar Flow Element (LFE) is to create a shunt. In the case of a thermal mass flow meter based on a bypass principle the mass flow is measured in a bypass of the main flow channel. Due to the specific dimentions of the LFE the same linear pressure/ flow characteristics as the capillary sensor tube can be created.

Laminar Flow Element, LFE; a critical element
Picture 1: Laminar Flow Element, LFE
Shunt principle of the laminar flow element; only a part of the gas flow will flow through the sensor.
Picture 2: Shunt principle of the laminar flow element (LFE); only a part of the gas flow will flow through the sensor. The rest flow will flow through the LFE.

Thin stacked plates – etched at Veco Precision- are used to create the Laminar Flow Element and allow the measurement of very small to medium flow rates (< 1 mln/min up to 20 ln/min). The bypass is a capillary tube with an internal diameter of 0.2mm, and this small size allows for fast response times and low energy requirements, as only a small tube volume needs to be heated.
The importance of a laminar flow and the difference compared to a turbulent flow is described in this blog.

Creating industry-leading products with Chemical-Etched metal parts

Miniturisation of products – and therefore components – is a necessity for manufacturers in order to create industry-leading products. For the flow discs in LFE we applied the Chemical etching process, a subtractive manufacturing method for micro-precision parts.

Chemical Etching

Chemical Etching (also known as Photo-Chemical Machining (PCM) and Chemical Milling) is as precise as it is quick and economical. Complicated, multi-level, multi-feature, high precision parts can be produced without the need for expensive tooling or machinery. Compared to ‘traditional’ machine processes such as CNC Machining, Stamping, Pressing, Wire Erosion and even more ‘contemporary’ processes such as Laser Cutting and Electro Chemical Machining, Chemical Etching with its flexible tooling and scalability provides you with an extremely competitive alternative right through from prototyping to large scale production. Rapid prototypes can be produced from your drawings in a matter of days.

Key benefits

  • Stress and burr free parts
  • Micron sized features
  • Tight tolerances
  • Wide range of materials
  • Thicknesses from 25um to 2mm
  • Round holes, sharp edges, straight or profiled edges
  • Rapid prototyping
  • Cost effective manufacturing
  • Flexible tooling allowing easy modifications

Gas flow measurement in general

Flow measurement is recognised as one of the ‘need-to-know’ process parameters, alongside temperature, pressure and level measurement. Accurate mass flow measurement of gases is critical in operations and control of many industrial and laboratory processes.
In the food and beverage sector, the chemical industry and semiconductor fabrication, flow meters accuracy is often the determining factor between optimum quality and rejected products. In areas like laboratory research, pilot plants and custody transfer, precise and repeatable measurement is equally critical.

EL-FLOW Prestige mass flow meter

EL-FLOW Prestige thermal gas flow meter is the next generation of Bronkhorst Mass Flow Meters / Controllers for gases. Nearly all core components have been redesigned and many improvements and innovations have been incorporated. With this new series Bronkhorst introduced the “Differential Temperature Balancing” technology, ensuring a superb sensor stability. You can sign in for the White Paper ‘A holistic view based on data to design components which offer optimal performance of a thermal mass flow meter/controller’, written by Bronkhorst, which describes the innovations integrated in the EL-FLOW Prestige.

Download White Paper

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