3D printed electrolyzer with turbulence promoters
Often, turbulence promoters are added to parallel plate electrolyzers in
order to enhance mass transfer. [1,5]. This degree of mass transfer
enhancement is also widely seen in literature.[2,4-5,18,20,22,24]
However, the opposite is observed in the work of Frias ferrer et al.
[21], where the turbulence promoter reduces mass transfer. The
difference is probably due to the design of the inlet device: the
electrolyzer used by Frias-ferrer et al. [21] uses an inlet that
causes high turbulence and high rates of mass transfer. A turbulence
promoter added to this environment calms down the highly turbulent inlet
flow.
In figure 11 the performance is shown of a selection of turbulence
promoters in the 3D printed electrolyzer, with and without a 150 mm
calming section. The promoters fill the entire empty channel in both
configurations (see figure 6). In either case, the turbulence promoters
increase mass transfer significantly. The enhancement at Re = 1000
varies between a factor 2.3 and 2.8 without a calming section and
between a factor 1.8 and 4.0 with the calming section. Interestingly the
variation in enhancement is larger when a calming section is used,
despite having similar empty channel performance. A possible explanation
is that a secondary inlet effect occurs when the flow first hits the
turbulence promoter. In the first few centimeters of the promoter this
could result in higher than expected turbulence, which would initially
increase the rate of mass transfer. This would explain why promoters
such as the tube promoter perform better in the cell without calming
section. However, with the small gyroid promoter the opposite effect is
observed, as it performs better with a calming section than without.
Here it is possible that the divider type inlet is channeling the flow
into certain paths in the structure of the promoter, resulting in
localized spots with little flow and mass transfer. For the cell without
calming section, this would result in lower average mass transfer. With
a calming section, this flow channeling is smoothed out before the
electrode section is reached and therefore the effect of the localized
dead volumes is not seen.
[FIGURE 11]