Generating vapour; 6 old ways versus 1 new

March 7, 2018 James Walton

Why generating vapour is easier, quicker and more accurate

Generating vapour is a perfect example of how technology development in one area can benefit multiple industries. By combining the accuracy and digital performance of modern mass flow metering and control technology, alongside temperature control, you can control the properties of vapour as never before.

Vapour production has always been a necessary, yet complex and expensive process. There have been multiple methods employed to achieve the dispersion of liquid into a gas phase. The variety of methods used is a reflection of the bespoke approach taken by many to compensate for the lack of awareness of a commercially viable solution.

Some of the examples that we have come across

  • Dew-point generator (bubbler)
  • Mixed-flow Generator
  • Static method of humidity generation
  • Two-Pressure process
  • Two-temperature process
  • Saturated salt solutions
Each of these methods has been developed to control the concentration (volume per volume) of liquid in gas to achieve the desired end result.

CEM: Controlled Evaporation Mixing system
CEM: Controlled Evaporation Mixing system

What is the end goal?

There are many industries that need, or would benefit from vapour generation to achieve their end goal, we have been talking to biomedical researches, technical fabric manufacturers, glass coating companies, catalysis research & development, graphene research & development and bulk food packaging machine manufacturers.

As always there are a few common themes amongst each of the people that we speak to. In application development the drive is always to increase or decrease something, it could be: cost, waste, yield or raw materials. Almost anything associated with an application will either have an increase or decrease requirement.

How do we achieve the goal of increase and decrease?

Multiple factors can be improved by installing a Bronkhorst Controlled Evaporating Mixing system (CEM) or Vapour Delivery Module (VDM) in your installation, these include:

  • Speed of response to process changes
  • Reduced raw materials costs
  • Accurate temperature control
  • Quick turnaround on substrate
  • Choice of Parts per Million, Parts Per Billion, Mole or concentration output conditions

How does the Bronkhorst Controlled Evaporating Mixing sytem (CEM) or Vapour Delivery Module (VDM) system achieve these things?

Vapour is generated through the addition of a liquid into a gaseous stream, usually under temperature. We add control to each of the inputs, thereby acquiring control of the output. If we take the first example from the list at the beginning of this blog, Dew-point generation, then we can see;

  • Evaporation of the fluid can cause concentration changes in vapour
  • Differences in back pressure created by changing fluid levels
  • Flow rate changes with fluid level resulting in changing process conditions
  • Variations in thermostat accuracy can add temperature variations to the fluid
  • High energy consumption from heating a fluid bed


Dew-point generator (bubbler)
Dew-point generator (bubbler)
Example Fluidat on the Net
Example Fluidat on the Net

By removing those sources of variation from the input, combining liquid flow control with a Coriolis mass flow meter (MFM) and gas flow control with thermal bypass mass flow controller (MFC) with a temperature controlled flow path you can predict the conditions of the resultant vapour more accurately. Once an output has been achieved with a known input combination, it can be replicated repeatably.

For example, in the picture below we know that the input conditions entered will achieve the desired process conditions, that level of control is not available in the other process.
With direct control of the liquid and gas flows into a temperature controlled flow path it is easy to change the input conditions  and predict consistent process conditions. The Coriolis liquid mass flow meter and thermal bypass gas flow controller are directly linked to a 3-way mixing valve on top of a temperature controlled flow path. By passing the liquid and gas through  the valve orifice the combined flow is aerosolized before being heated and this ensures complete vaporisation of the liquid in the gas stream.

Taking this a stage further, if you have a specific composition in mind then check out our online free to use database called Fluidat, go to register and you can check out yourself what is possible.

Looking at the 6 old ways and 1 new, the innovation and thought that has gone into the original and still used old methods of vapour generation is clear.
However the beauty of society is that we can learn from one another, another technology is available.


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