Discovery of Two-way Flows in Water Bridge

By revisiting the century-old problem of water bridge, we discover that it is in fact a dynamic system composed of two coaxial currents that carry different charges and flow in opposite directions. Initially, the inner flow is facilitated by the cone jet that is powered by H+ and flows out of the anode beaker. The flow from cathode is established later and is derived from a stacking phenomenon to take the route of outer layer. This two-way flow is supported by the test results by fluorescein, carbon powder, and FeCl3, and the detail flow field by Particle Image Velocimetry. The different flux on these opposing coaxial flow leads to a net transport of water to the cathode beaker, in spite of the pressure difference to equate the water level from the connecting pipe. Combined with the result of ph-value test, the above information allows us to estimate the speed of these two opposing flow as a function of voltage.