How to accurately measure flow rates in your microfluidic setup using Bronkhorst® flow sensors ?

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How to measure very low flow rates with very high accuracy ?

The aim of this application note is to show how to easily perform a very accurate flow rate measurement.

Thanks to our “plug and play” software, Bronkhorst® flow sensors and standard connectors, you will be able to perform easily and quickly an accurate flow measurement anywhere in you setup.

Bronkhorst flow sensor, “Mini Cori-flow”, measures the flow thanks to the Coriolis Effect. The value of the mass flow is independent from the density, the temperature or the pressure.

The Elveflow® smart software allows you to control and analyze intuitively the results of your experiment and is compatible with all Elveflow® instruments.

Coriolis flow measurement – Advantages

Using the Coriolis Effect (describing how moving object deflects from a straight path when viewed from a rotating frame) on a fluid going through a vibrating tube, it is possible to derive the mass flow through the tube, and also the density of the fluid at secondary output.

This direct measurement is very accurate because there is no need to correct it with temperature, pressure and density and does not depend on fluid specific heat like Thermal mass flow meters.

Furthermore, Coriolis flow meters can be used with gas and liquids and distinguish themselves by their high accuracy over a large range and a fast response time.

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Coriolis Principle

Mini Cori-Flow operate according to the Coriolis principle. The mini-cori-flowinstrument can be used to simultaneously measure the mass flow, temperature and density. When a fluid flows through a vibrating tube, Coriolis forces are generated which bend or twist the tube. The extremely small tube displacements are detected by optimally positioned sensors and evaluated electronically. Since the measured phase shift of the sensor signals is proportional to the mass flow, the mini CORI-FLOW measures the mass flow directly. The measurement principle is independent of the density, temperature, viscosity, pressure, heat-capacity or conductivity. The tubes always vibrate at their natural frequency, which is a function not only of the tube geometry and the tube material properties but also the mass of the fluid in the vibrating tubes.

Bronkhorst® flow sensor

Setup

This section describes step by step how to perform the flow measurement.

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Adjustable ranges suited for microfluidic applications:

From [1.67µL/min; 83µL/min] to [1.67µL/min; 3.3mL/min]
Best accuracy on the market: 0.2% of the range anywhere on the range, excellent repeatability
Low internal volume: 13µL
Adapted for many gas and liquids
High velocity measurement
Direct mass flow measurement, independent of fluid properties

Components list

Setup Diagram

For this setup, the following Elveflow® devices are needed:

  • Elveflow® pressure & flow control instrument (OB1)
  • Microfluidic Tubing for the fluidic connection of the setup elements
  • Microfluidic Fittings & Connectors
  • Bronkhorst flow sensor

The flow sensor can be used as a standalone unit with your own system to flow liquid or in combination with our flow controller. Here, we use it with the OB1 MkIII in pressure control mode.

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Step by step control with Elveflow® smart software

Make sure that all the cables and tubing are well connected to your Elveflow® instruments (USB cable, 24V DC, Flow sensor data cable, etc). Perform leakage tests and remove any air bubbles before starting your experiment.

Choosing the proper fittings is the first step towards success. If you are not familiar with microfluidic fittings, you may read our specific tutorials.

The flow sensor is very sensitive to vibrations and movement perturbations so it is recommended to fix it to a stable surface as often as possible.

The flow sensor can be used as a standalone unit with your own system to flow liquid or in combination with our flow controller. Here, we use it with the OB1 MkIII in pressure control mode.

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1) First launch the Elvefow® smart interface (ESI)

Click on « Add Instrument ».

2) Add your Bronkhorst ® flow sensor (Cori-flow).

3) Click on the refresh button at the top left corner to see the Cori-flow also as an instrument.

4) The Cori-flow is now recognized both as a sensor and an instrument.

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5) Open the Cori-flow window.

You can now directly read the flow measurment or open a graph to see the evolution of the flow during all the time of your experiment.

On the above image we are sending a pulse wave with the OB1 MkIII pressure controller and the flow rate is displayed on the right scale.

Stop by the Bronkhorst® flow sensor product webpage.

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To go further

See our tutorial on regulating the flow with a Bronkhorst® flow sensor and a OB1 Mk3 pressure controller. The PID algorithm allows volume control as a syringe pump without speed and accuracy concessions.

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