The metal foams used in this experiment had three different cell
densities: 20, 30, and 40 ppi. They were installed inside the capillary
tube. A cell density higher than 40 ppi was not used because it
would have shifted the flow to a critical flow regime such as a
creeping flow. The foam diameter and length were similar to the
inner diameter and length of the capillary tube, with clearance to
allowit to fit. The metal foamwas made of nickel, which is the most
common material for DCFC applications. A bulk nickel foam sample
is shown in the left photographs of Fig. 2