Nowadays the most commonly used heat exchangers in
residential air conditioning applications for heat exchange
between air and refrigerant are of the round tube and fin type.
Recent investigations have revealed that combining round tubes
with open cell metal foam can lead to heat exchangers which
outperform their finned counterparts. The thermal contact
resistance is one of the issues which is very critical in order to
compete with the finned heat exchangers. Using flat tubes
allows for a larger base surface for the same flow area available
to the medium in the tubes. Since a larger contact area between
the foam and the tubes leads to a reduced thermal contact
resistance, flat tubes and metal foam are expected to be a good
combination. In this work a comparison is made between
commonly used louvered fin and round tube heat exchangers
and metal foam enhanced flat tube heat exchangers. The
comparison is made using computational fluid dynamics (CFD)
and a two-dimensional volume averaged model for the metal
foam. The influence of the contact resistance, pore density,
external porosity, tube spacing and tube width are investigated.
The most important parameters and their optimal values are
identified. It is revealed that the contact resistance and surface
efficiency are absolutely critical in order for the metal foam
heat exchangers to achieve good performance.
Papers presented to the 12th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Costa de Sol, Spain on 11-13 July 2016.