Extruded Microchannel-Structured Heat Exchangers

Abstract

In the search for more compact air/liquid heat exchangers, one possible way is to increase the heat transfer coefficient and surface area by a decrease of the size of the fluid channels. A practical example could be air/water cross-flow heat exchangers used in cars. These exchangers are designed so that air pressure drop is minimised at a given thermal power exchanged from water to air. In this case, minimisation of the total volume leads to a very thin structure with a large frontal area, with a lot of small and short air channels. This configuration is very inconvenient for most practical applications and also difficult to manufacture at low cost. Using this rationale, we have designed and patented a cross-flow heat transfer surface with microchannels that has such a structure, but can be manufactured industrially at reasonable cost by extrusion either in aluminium or in polymers. Moreover, the arrangement of the heat transfer surfaces is very flexible and allows for different configurations (accordion, serpentine, cylindrical, star...) so that various geometric configurations, adapted to specific applications, can be obtained. The thermo-hydraulic performance of the structure has been simulated using standard correlations and CFD codes. Prototypic structures made by stereolithography have been manufactured in glass reinforced polymer and are currently being tested on a test bench. In order to validate our simulation code, a single structure and an accordion arrangement heat exchanger are under investigation. Compared to classical heat exchangers, our design is superior in flexibility and compactness for air/liquid applications. An additional interest of our design would be to increase performance in humid air cooling applications, since our structure may drain condensates more easily. We are currently looking for a partnership to develop this design for industrial applications.