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What is a Controlled Evaporation Mixer (CEM)?

  • There are limited options for generating vapor streams when it comes to manufacturing and laboratory research.
  • Traditional glass bubbler systems are useful for generating vapor streams, however, they often generate vapor in an unreliable manner with limited control on delivery.
  • Our Vapor Generation Systems incorporate a special vaporizing mixing chamber with liquid and gas flow meters and controllers to offer a highly accurate, repeatable, and controllable vapor stream.

Traditionally, bubbler systems or Vapor Source Controllers are a standard when dealing with vapor generation. However, these devices have their shortcomings. For example, bubblers have are 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. For this reason, we have developed a controlled evaporation mixer, this 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 device that offers vapor generation and control capabilities. As a result, the Controlled Evaporation Mixer (CEM) exists as a vapor delivery unit that’s useful for atmospheric, pressurized, and vacuum processes. Moreover, it can vaporize liquid flows from 0.25 to 1,200 g/h of water. And with most other fluids, the capacity will be even higher.

How the CEM Works

At room temperature, the liquid draws from the container with an inert gas blanket. A flow meter for liquids is able to control and regulate the liquid flow. A control valve is able to control the necessary flow rate from the set-point value. Then, the liquid can enter the vaporizer of the CEM to begin the evaporation process.

Features of Bronkhorst CEM

  • accurate control of gas/liquid mixtures
  • fast response
  • high reproducibility
  • very stable vapor flow
  • flexible selection of gas / liquid ratio
  • lower working temperature than conventional bubbler systems
  • control by Vapor Generation Controller System

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. Moreover, it requires additional components to complete the Vapor Generation System. A Vapor Generation Controller is necessary to connect all the components. Along with its unique, highly capable control, it also offers ethernet access via protocols such as Modbus. As a benefit, the ethernet connectivity allows data logging, remote access, and more. A full vapor generation system usually consists of:


Applications For Vapor Delivery Systems, CES

The Controlled Evaporation System is useful 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)

Chemical Vapor Deposition is a process that produces highly pure solid materials. For example, it’s useful in surface treatment, hardening processes, coatings, and manufacturing of high temperature superconductors.

Humidification of Gases

The CEM is perfect for precise adjusting of moisture levels. The large dynamic range and high accuracy ensure moisture level control with great flexibility from only a few ppm up to virtually 100%. In addition, it maintains a very high stability in dew point.

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

The combination of the CEM and Mass Flow Controllers can produce gas phase concentrations as necessary. As a result, 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. In addition, flow speed, pressure conditions, and the pressure difference across membranes are important. External factors also affect the sweet spot for optimal performance. For example, the electrical load together with ambient and fluid temperatures can impact performance.

To keep it simple, the flow meters and pressure instruments take care of the main liquid, gas, and pressure measurement and control tasks. It’s simple to see the fluidic dependencies and interactions. The Controlled Evaporation System is useful for low flow and low humidification levels. Furthermore, for higher flows, we often advise towards cascade systems.

Vapor Generation Control in Aseptic Packaging

The solution consists of two Bronkhorst CEMs. One side sterilizes PET bottles, cartons or pouches, and the other side is for caps. Hydrogen peroxide (35% H2O2 in water) injects 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. Later, in a subsequent drying step, the condensate is removed using hot air supplied by a gas mass flow controller. After, the dry and aseptically sterilized packaging is ready for filling.

The vapor-generating CEM systems each consist of several components. First, a liquid mass flow controller (thermal LIQUI-FLOW or Coriolis-based mini CORI-FLOW) is able to control the liquid flow. Then, a gas mass flow controller is used to control the carrier gas and subsequent drying, for example, an EL-FLOW Select. Last, a temperature-controlled mixing and evaporation device, or CEM, is used to vaporize, mix, and deliver the vapor stream.

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