3D printed electrolyzer with different entrance lengths
In figure 10 the effect on mass transfer of adding a calming section
between the inlet and the electrolyzer is shown. When no calming section
is used, the type of inlet is important as the turbulence generated by
it greatly enhances mass transfer. By adding a calming section, this
effect is diminished and for a calming section of 550 mm the type of
inlet no longer seems to matter. According to eq. 5 the laminar entrance
length is 240 mm at the highest Reynolds number measured (Re = 1200).
Therefore, it makes sense that an inlet well beyond this distance would
no longer influence the mass transfer to the electrodes. Furthermore,
the divider type inlet seems to perform similar at any length of calming
section. This implies that a good inlet design can enable
hydrodynamically fully developed laminar flow.
[FIGURE 10]
Despite using a 550 mm long calming section, our correlations still do
not completely match the hydrodynamically fully developed laminar flow
correlation established by Ong at Reynolds numbers below 500. As
previously mentioned, an overestimation of mass transfer occurs at low
Reynolds numbers, since the current is not fully stabilized after 7
seconds. Apart from this effect, additional experimental error is
expected due to the limitations of 3D printing. A first limitation is
that due to the print process imperfections may be introduced into the
channel wall. These imperfections lead to increased surface roughness,
which may result in higher mass transfer and an earlier transition to
the turbulent regime. Secondly, because the longest dimension of a print
is limited to around 200 mm, the assembly consists out of multiple
smaller parts with joints between them. At these joints, minor
protrusions may exist that can introduce turbulence.