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]