The interface wall heat flux distributions and local heat transfer
coefficients for metal foam filled double-pipe and hollow doublepipe
heat exchangers are shown in Fig. 4. The interface wall heat
flux decreased significantly from the inlet to the outlet, as shown
in Fig. 4a. The heat flux at the inlet location is about 4.5 times that
at the outlet location, while previous models neglect this variation
trend. The predicted average interface wall heat flux in the case of
exchangers filled with metal foams is a little lower than the case
without foams due to the significant extension of surface area.
The local heat transfer coefficient for metal foam-filled double-pipe
exchangers is much higher than the air flow across smooth plate
from the analytical solution by Frank et al. [24], which is attributed
to the increased specific surface area by metal foams, as seen in
Fig. 4(b).