New micro-channel test stand at CERN
Jennifer Toes (CERN), 29/11/2017

D. Hellenschmid (left) and P. Petagna (right) at the new test facility. The vacuum vessel hosting the control and measurement unit and the TRACI CO2 unit (green cabinet) are visible in the background. (Image: G. Berruti)

The AIDA-2020 project has produced a new testing station for micro-channel devices. The station makes use of CO₂ evaporating flows and will provide modellers with key data for designing future devices.

As the electronic components of detectors become more complex, so too does their need for quality thermal management systems. Recent trends show a shift towards the use of CO₂ as an evaporating coolant, combined with pipes of increasingly smaller sizes.

As a coolant, CO₂ carries some unique physical properties which must be taken into account during the modelling process. As such, researchers need reliable data to be able to design and deploy this technology effectively.

At present, most of the available studies of CO₂ evaporating flows are primarily concerned with larger channels, with little data for mini- or micro-pipes with an inner diameter below 3mm. This makes it difficult to obtain reliable forecasts of the boiling properties of CO₂ at a small scale.

In an effort to plug this gap in the knowledge base, researchers from AIDA-2020’s Work Package 9 (WP9) set out to provide a reliable, adaptable test station for studying new designs of micro-channel devices. In addition, their work will help establish an accurate and systematic bank of data on the properties of CO₂ flows for channels measuring from 2mm down to 0.1mm.

Paolo Petagna, CERN Research Scientist and WP9 Coordinator, said “Developing a new generation of particle detectors often requires pushing forward the state-of-the-art knowledge in some other fields. We are here in one of those cases, where we need to generate experimental data which until now has simply been unavailable in the specialized scientific literature, in order to develop reliable design methods for the CO₂ evaporators of the future silicon trackers.”

The test station is comprised of two modules: a refrigeration and circulation unit, and a control and measurement unit.

CERN developed the refrigeration and circulation unit, also known as Transportable Refrigeration Apparatus for CO₂Investigation (TRACI). Based on a patent jointly owned by CERN and Nikhef, this is the first refrigeration unit providing controlled continuous liquid CO₂ flow for laboratory applications. The unit makes use of a two-phase accumulator control loop known as I-2PACL, which offers a high degree of control and wide range of temperatures.

The control and measurement unit regulates the conditions of the CO₂, ensuring parameters such as temperature, flow rate and vapour quality are within the correct margins. The unit itself is composed of several systems and a test section.

The test section is located inside a vacuum vessel, designed at CERN and manufactured at UCLouvain. The design allows the installation of complex microchannel devices and simple small diameter pipes, where their measurements are recorded by a data acquisition system based on high quality National Instruments modules.

Once the accuracy of the flow measurement and controls have been established, the facility will begin a rigorous experimental testing schedule.

Once fully commissioned, the facility will become a global pioneer in mini- and micro- channel testing using CO₂ evaporating flows, offering heightened levels of control over testing conditions and providing much-needed data to the detector designers of tomorrow and to the external scientific user community specialized in the physics of two-phase flows.