fig2

Figure 2. Effects of external field enhancement on bubble separation^[18,22,25]. (A) convection created by magnetic fields of different directions, voltage: 4 V, electrode distance: 10 mm, KOH: 40 wt%, magnetic field intensity: 4.5 T. These figures are quoted with permission from Martin^[18]; (B) the photograph of the electrode surface during a hydrogen bubble evolution process at 0.05 A·cm^-2 with normal gravity conditions and supergravity fields. These figures are quoted with permission from Wang et al.^[22]; (C) a mechanism of bubble elimination in ultrasonic fields. This figure is quoted with permission from Cho et al.^[25].