United States. Researchers at the Department of Energy at Oak Ridge National Laboratory (Ornl) have captured distortion-free photos of refrigerants flowing through small heat exchangers, helping to further clarify heat transfer characteristics.
The researchers used additive manufacturing and neutron imaging capabilities to examine microchannel heat exchangers, which contain refrigerants used to move thermal energy and provide cooling or heating in many applications. The non-invasive techniques allowed the researchers to visualize how refrigerants react to different temperature levels without interrupting the flow of refrigerant.
Previous research has focused on refrigerant heat exchange, but Ornl's team claims it is the first to make use of neutron imaging in microchannel studies. The team partnered with 3D printing company Fabrisonic to specifically design microchannels for neutron images.
To look at the effects of heat on microchannels, the researchers ran the refrigerants through the microchannels and subjected them to increasing amounts of heat for more than five days. In a series of medium cold and high heat stages, the team used neutrons from the high-flow Ornl Reactor to take images of the coolant.
The microchannels rested horizontally, and the expected result was that gravity would cause the liquid portion of the coolant/vapor mixture to sink to the bottom of the microchannel, leaving less area for heat transfer. Instead, the images showed that the surface tension properties of the microchannels caused the coolant to stick to all sides of the microchannel, maximizing the amount of area available for heat transfer. Only at elevated temperatures was the coolant forced to the center by steam and was not able to absorb and take heat from the microchannel walls at a rapid rate.
