Visual experimental research of two-phase flow in long straight anode channels with different widths in a polymer electrolyte membrane water electrolysis cell

Abstract

The characteristics of gas-liquid two-phase flow are crucial for heat and mass transfer in polymer electrolyte membrane (PEM) water electrolyzers. In this research, visual experiments are conducted using a specially designed cell with a transparent anode end plate and flow channels of different widths (1.3 mm and 0.8 mm) under varying current densities (0.1–2 A/cm²), temperatures (60∼80 °C), and water feed rates (60∼200 ml/min), corresponding to an inlet Reynolds number range of 500∼4500. Due to channel size limitation and increased flow resistance, the two-phase flow pattern transitions in the narrower channel happen over a shorter flow distance compared to the wider channel. A flow pattern map is developed based on inlet Reynolds number and current density, revealing that bubbly flow dominates at the entrance, while slug and annular flows are prevalent at the middle and exit sections. Bubble coalescence occurs when bubbles contact with each other or pass by porous transport layer (PTL) ejection spots. A three-stage gas transport mechanism in PTL is proposed, involving fingering forward movement, bubble formation and backflow, and path breakage and reset. The findings suggest incorporating channels of different widths in large-area PEM cells may control flow velocity and void fraction, potentially improving overall efficiency.