Comparison of Liquid Water Dynamics in Bent Gas Channels of a Polymer Electrolyte Membrane Fuel Cell with Different Channel Cross Sections in a Channel Flooding Situation

Abstract

Abstract:The transport characteristics of water slugs in a bent gas channel of a polymer electrolyte membrane (PEM) fuel cell are numerically studied using the volume of fluid (VOF) method. To investigate the effects of channel cross-sectional shape in a channel flooding situation, the gas channels (GCs) with one rectangular and two trapezoidal cross sections are compared. Parametric studies are also conducted to evaluate the effects of the contact angle of the top and side walls, the contact angle of the gas diffusion layer (GDL) surface, and the air inlet velocity. Considering both of the water volume fraction (WVF) and GDL water coverage ratio (WCR), the trapezoidal channel with open angles of 60 degrees provides the most favorable performance in a channel flooding condition. Among all the top and side wall contact angles considered, the hydrophobic contact angle of 120 degrees shows the best results. Among the three GDL contact angles of 90, 110 and 140 degrees, the hydrophobic GDL contact angle of 140 degrees provides the most favorable water removal characteristics in a channel flooding situation. For all cross-sectional shapes, the water removal rate increases and the liquid water interface shows more complex patterns as the air inlet velocity increases.

Numerical Investigation of Gas-Liquid Two-Phase Flow inside PEMFC Gas Channels with Rectangular and Trapezoidal Cross Sections

“…To quantify the liquid water behavior in the GC, a control volume with the length of L cv (= 4.2 mm) is defined in Figure 1a-c. In addition to the rectangular GC, the GC with trapezoidal cross-sectional shape are reported to provide favorable water removal characteristics based on experimental and numerical investigations [7,8,17,18]. Lu et al reported that sinusoidal or trapezoidal cross-sectional shapes are recommended for stamped metal plates and molded carbon composite plates, which are more feasible for the mass production of PEM fuel cell flow fields [17].…”

“…The PEM fuel cell has many advantages which include high power density, zero emissions, a low operating temperature range, and a wide range of applications. One major technological issue of the PEM fuel cell is proper water management to avoid membrane dehydration and the so-called water flooding phenomena [5][6][7][8]. A properly hydrated membrane produces the best performance and the cathode gas diffusion layer (GDL) surface should be free of liquid water to provide sufficient amounts of oxygen.…”

“…The main geometric parameters include flow field configuration, flow direction, channel length, number of channels, use of baffles in GC, channel cross-sectional shape, channel and rib width, channel depth, and height to width ratio of the channel cross section. Several experimental and numerical investigations were conducted to study the effect of GC cross-sectional geometry [7,8,[14][15][16][17][18][19][20]. Owejan et al measured the volume of accumulated liquid water in the GCs with triangular and rectangular cross-sectional shapes in operating fuel cells using the neutron radiography method [15].…”

“…The trapezoidal cross sections with open angle of 50 • and 60 • resulted in a better water removal behavior compared to other cross-sectional shapes. Kim et al investigated the liquid water dynamics in bent gas channels with one rectangular and two trapezoidal cross sections in a channel flooding situation [8]. The trapezoidal channel with open angle of 60 • showed the most favorable combined WVF and WCR characteristics.…”

“…In this paper, the dynamics of liquid water in a straight GCs with the rectangular and trapezoidal channel cross sections with the same cross-sectional area is investigated via the VOF method. Compared to the previous studies [7,8] which were rather limited to the liquid water film or slug flow situation without continuous water supply from GDL surfaces, four different water inlet configurations are adopted to simulate complex water accumulation patterns in the cathode GC. While fixing the contact angle of the GDL surface as the hydrophobic contact angle of 130 • , parametric studies are conducted to evaluate the effects of the contact angle of the top and side walls, the water inlet configuration, and the air inlet velocity.…”