Stafford, Texas

What is a Controlled Evaporation Mixer (CEM)?

We have many customers that have applications where two components must be mixed. Traditionally, bubbler systems or Vapor Source Controllers have been used when dealing with vapor. These devices have their shortcomings, for example they have been proven to not be able to handle large quantities of liquid with a low vapor pressure. Furthermore, they can’t provide vapor from a mixture of liquids with different vapor pressures. The controlled evaporation mixer is a new technology that can offer improved process control compared to bubblers.

Liquid Delivery System with a Controlled Evaporation Mixer

Our partners at Bronkhorst have worked hard to develop a system that has Mass Flow Control of Vapors. This system is our Controlled Evaporation Mixer (CEM), which is a liquid delivery system that can be applied for atmospheric, pressurized and vacuum processes. It can vaporize liquid flows from 0.25 to 1200 g/h of water and with most other fluids the capacity will be even higher.

How the CEM Works

At room temperature the liquid is drawn from the container with an inert gas blanket and measured by a Bronkhorst Liquid Mass Flow Meter. The required flow rate is controlled to the set-point value by a control valve. The liquid is then delivered into the evaporator to begin the evaporation process.


  • accurately controlled gas/liquid mixture
  • fast response
  • high reproducibility
  • very stable vapor flow
  • flexible selection of gas/liquid ratio
  • lower working temperature than conventional systems u optional control by PC/PLC (RS232/fieldbus)


The set-up of a CEM-system usually consists of:

  • Mass Flow Controller for Gases
  • Mass Flow Meter for Liquids
  • CEM 3-way Mixing Valve and Evaporator
  • Power Supply/Readout System
  • Interconnecting Cables

Applications For the CEM

The CEM-System has been used successfully in a wide variety of markets with many different applications. Today we want to examine some of the most common applications

CVD (Chemical Vapor Deposition)

Flow Scheme of Chemical Vapor Deposition in a Controlled Evaporation Mixer

This chemical process used to produce highly purified solid materials. This is a common application in surface treatment, hardening processes and manufacturing of high temperature superconductors.

Humidification of Gases

Flow Scheme of Humidification

The CEM is perfect for precise adjusting of moisture levels. The large dynamic range and high accuracy ensure that the moisture level can be controlled with great flexibility from only a few ppm up to virtually 100%, whilst also maintaining a very high stability in dew point.

Calibration of Gas Chromatographs

Flow Scheme of Calibrating of Gas Chromatographs in a Controlled Evaporation Mixer

With the combination of the CEM and Mass Flow Controllers, gas phase concentrations can be produced as desired. This application with the CEM is both highly reproducible and highly accurate.

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