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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 flow. 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.


Vapor Generation with a Controlled Evaporation Mixer

Our partners at Bronkhorst have worked diligently to develop a system that offers vapor flow control. This system is the Controlled Evaporation Mixer (CEM), which is a vapor delivery unit 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 flow meter for liquid. 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.

Features of Bronkhorst CEM

  • 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
  • optional control by PC / PLC (RS232 / fieldbus)

Vapor Delivery with a Controlled Evaporation System

The Controlled Evaporation Mixer is a critical component for vapor flow technology. However, the CEM alone cannot generate streams of vapor and require other components to complete the Controlled Evaporation System. A Controlled Evaporation System (CES) or CEM System is required to connect all the components and usually consists of:

Applications For Vapor Delivery Systems, CES

The Controlled Evaporation System has been used successfully in a wide variety of markets with many different applications. Below you can find many of our common CEM System applications, which require precise vapor generation and vapor flow control.

Flow Scheme of Chemical Vapor Deposition in a Controlled Evaporation Mixer

CVD (Chemical Vapor Deposition)

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.

Flow Scheme of Humidification

Humidification of Gases

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.

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

Calibration of Gas Chromatographs

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.

Fuel Cell Research and Testing

The efficiency of the fuel cells depends on the composition and amount of humidified hydrogen and air, their flow speed, pressure conditions, and the pressure difference across membranes. The sweet spot for optimal performance is also influenced by external factors, such as the required electrical load together with ambient and fluid temperatures.

To keep it simple: The flow meters and pressure instruments take care of the main liquid, gas, and pressure measurement and control related tasks. It’s simple to see the fluidic dependencies and interactions.

The represented Controlled Evaporation System is typically used for low flow and low humidification levels. For higher flows we often advise towards cascaded systems.


Vapor Flow Control in Aseptic Packaging

The solution consists of two Bronkhorst CEMs – one side for PET bottles, cartons or pouches, and another side for caps. The hydrogen peroxide (35% H2O2 in water) is injected as a vapor for better concentration control. The vapor condenses at the inside surfaces of the packaging, where the H2O2 in the liquid phase performs its sterilizing action. In a subsequent drying step, the condensate is removed using hot air supplied by a gas mass flow controller, after which the dry and aseptically sterilized packaging is ready to be filled.

The vapor-generating CEM systems each consist of a liquid mass flow controller (thermal LIQUI-FLOW or Coriolis-based mini CORI-FLOW), an EL-FLOW Select mass flow controller for air as a carrier gas (and for drying afterwards), and a temperature-controlled mixing and evaporation device

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