ENHANCED LIQUID WATER REMOVAL FROM PEM FUEL CELL FLOW CHANNELS BY SUPERIMPOSING ACOUSTIC PRESSURE WAVE ON AIR FLOW

Enhanced water removal from the flow channel of an ex-situ PEM fuel cell test section is obtained by superimposing acoustic pressure wave on air flow prior to entering into the flow channel. Water accumulation within the flow channel was visualized with a CCD camera and liquid-gas two-phase flow pressure drop was measured along the flow channel. Acoustic pressure waves were superimposed in sine waves at different frequencies between 20 and 120 Hz with a 20-Hz interval. Results indicated that water accumulation in the flow channel was lowest when acoustic pressure waves were superimposed at 80 Hz on air flow. For experiments with no acoustic vibration, the average water slug cumulative area for three runs was obtained at 288.6 mm(2) while this average was as low as 43.9 mm2 for experiments conducted at 80 Hz. For other frequencies tested (20, 40, 60, 100, and 120 Hz), water accumulation within the flow channel was less than that for experiments with no vibration but the accumulation of water was still greater than experiments conducted at 80 Hz. The two-phase flow pressure drops were also lowest for experiments conducted at 80 Hz while the highest pressure drops were obtained in experiments with no acoustic vibration. Droplets were also visualized from a side-view angle in a goniometer in order to obtain contact angles. Images showed droplet oscillation under the influence of acoustic vibration. For the three superficial air velocities tested in this study (1.30, 1.82, and 2.30 m/s) the contact angle hysteresis were almost identical with an average value around 40 degrees.