Des premières images de l'écoulement de frigorigènes grâce aux neutrons

Des chercheurs du Laboratoire américain Oak Ridge ont capturé des images non déformées de l'écoulement de frigorigènes dans de petits échangeurs de chaleur, permettant ainsi de mieux appréhender les caractéristiques du transfert de chaleur.
Researchers at DOE’s Oak Ridge National Laboratory (ORNL) have captured undistorted snapshots of refrigerants flowing through small heat exchangers, helping to further elucidate characteristics of heat transfer.

The researchers used additive manufacturing and neutron imaging capabilities to examine microchannel heat exchangers. The non-invasive techniques allowed the researchers to visualise how refrigerants reacted to different temperature levels without disrupting the refrigerant flow.

Past research has focused on refrigerant heat exchange, but the ORNL team claims it is the first to make use of neutron imaging in microchannel studies. The team partnered up with 3D printing company Fabrisonic to specifically design microchannels for neutron imaging.

To observe the effects of heat on microchannels, the researchers ran refrigerants through the microchannels and subjected them to increasing amounts of heat over five days. At a number of cool-, medium- and high-heat stages, the team used neutrons from ORNL’s High Flux Isotope Reactor to take images of the refrigerant.

The microchannels rested horizontally, and the expected outcome was that gravity would cause the liquid portion of the refrigerant liquid/vapour mixture to sink to the bottom of the microchannel, leaving less area for heat transfer. Instead, the images showed that surface tension properties of the microchannels caused the refrigerant liquid to stick to all sides of the microchannel, maximising the amount of area available for heat transfer. Only at elevated temperatures was the refrigerant liquid forced to the centre by vapour and no longer able to absorb and take heat away from the microchannel walls at a rapid rate.