What is a Mass Flow Controller?

Mass flow controller

Suppose you would like to supply a gas, vapour or liquid to a chemical process, then mass flow controllers are suitable devices. They are used in processes regarding: 

In all these examples, a reproducible and accurate supply of chemical compounds is necessary for the process. This way you can proceed in a controlled way and reach optimum product yield and minimum risk of process under- or overperformance, like waste of unused reactants or process run-away. Mass flow controllers are used for this purpose.

Go directly to our product portfolio of GAS or LIQUID mass flow controllers:

GAS mass flow controllers LIQUID mass flow controllers

1. How does a mass flow controller work?

A mass flow controller is a compact device that supplies one or more chemical compounds – gas or liquid - to a process by accurately controlling the flow rate. To this end, the flow rate of the compound(s) to be supplied is set electronically by a voltage, current or digital (fieldbus) source. The amount of gas or liquid that flows through the device is measured by an internal sensor. This measurement value is compared with the setpoint value. To achieve that both values are equal, a control valve will vary the size of the flow passage (by opening or closing). 

In the basics, a mass flow controller is a mass flow meter (i.e. the sensor) combined with control valve and feedback electronics between sensor and valve. This control function (also known as PID, proportional-integral-derivative) is often a standard part of the device electronics, whereas the control characteristics can be adjusted for fast or smooth control by means of user software.

2. Why would you control mass flow instead of volume flow?

Simply because in many research and production processes, the important variable is mass and not volume. Mass flow controllers can provide direct control of mass flow. From an economical point of view, the mass of a gas or liquid is an independent value, no matter what the operating temperature or pressure of a process is. Therefore, mass flow devices are immune to fluctuations in temperature and pressure of the incoming flow.

To meet users' preferences for expressing compressible gas flow as volume flow anyway, conditions are agreed upon under which mass flow is converted into volume flow. These ‘normal’ reference conditions are a temperature of 0 °C and an absolute pressure of 1 atm, indicated by the subscript “n” in the unit of volume used.

3. Which types of mass flow controllers do exist?

3A) Thermal mass flow controllers

thermal mass flow controller uses the heat capacity of liquids or gases to control their mass flow rate. Within the Bronkhorst portfolio we have multiple thermal mass flow controllers that each have their own sensor technique: 

  • Mass flow controllers using a bypass sensor. These devices (like EL-FLOW Select and IN-FLOW) are very well suited for clean & dry gas applications where higher accuracy as well as repeatability are important. 
  • Mass flow controllers using the inline (CTA) principle. If you have an application with a slightly moist gas (humidity), or when high repeatability and robustness is more important than accuracy, devices such as the MASS-STREAM series are a perfect fit. 
  • Gas mass flow controllers using TCS (Trough Chip Sensor) technology. These devices stand out as they can both measure gas flow and temperature (e.g. FLEXI-FLOW series).
  • Whenever you have limited space for your mass flow controllers, then the gas devices using MEMS chip sensor technology (such as IQ+FLOW) are a perfect fit.
  • Liquid mass flow controllers using inline (CTA/CPA) technique.

Find your Mass Flow Controller

Thermal-based Mass Flow Controller  

3B) Coriolis mass flow controllers

A Coriolis-based mass flow controller (e.g. the mini CORI-FLOW series) is often the first choice to measure and control liquid flow. Besides that, they very well can be used for gas flow processes as well. Coriolis based mass flow controllers have some advantages compared to thermal-based instruments:

  • Higher accuracy
  • Fluid independent, which means there is no need for conversion when the device is used for other liquids, and it can be used for varying and unknown mixtures. 
  • Very fast measurement
  • Can be used for supercritical gases

Coriolis Mass Flow Controllers

Coriolis-based Mass Flow Controller 

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