Thermal hydraulic performance of 10 PPI aluminium foam as alternative for louvered fins in an HVAC heat exchanger

Abstract

In this paper, two heat exchangers for an HVAC application are compared. The first one is a commercially available high quality louvered fin heat exchanger, while the second heat exchanger is a prototype in-house made using 10 PPI open-cell aluminium foam. Heat transfer and pressure drop measurements were performed in a wind tunnel with free stream air velocities between 1.1 and 3.1 m/s. The comparison between both heat exchangers is done based on a well-defined performance evaluation criterion for foam. It is revealed that the heat exchangers have a similar performance at low air velocity (1.1 m/s), while the louvered fin heat exchanger performs slightly better at higher velocities.Furthermore, the influence of the contact resistance is studied based on literature. The pressed-fit foam heat exchanger experiences very high contributions of the contact resistance (up to 70% of the overall thermal resistance), while for the louvered fin heat exchanger this contribution is much smaller (up to 11.1%), due to the presence of a fin collar. When comparing the airside convective resistance only, the foam heat exchanger performs better at high velocity range (2.5–3.1 m/s). The influence of changing the bonding technology is also assessed. It is demonstrated that a hypothetical brazed metal foam coil should have a same performance than the louvered fin unit at a low velocity range (1.1–2.5 m/s).