Single Serpentine Channel

Contour plots for pressure and velocity in a single serpentine channel, (a) Static pressure, (b) Dynamic pressure, (c) Total pressure, (d) Velocity magnitude. 

Typical velocity contours at different sections of the developing flow-fields. 

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The final element on the outer side of the unit cell (Figs. 1 and 2) is the current collector plate, which typically contains the machined gas flow field. These two functions of current collector and gas flow field may be fulfilled, in principle, by two separate components but, in most of the cells and and stacks tested so far, the flow field is machined in the current collector plate using a range of geometries, e.g., a single serpentine channel, parallel channel flow and series-parallel combinations. The specific flow-field geometry may be critical in fulfilling the requirements of effective water supply and effective liquid water removal from the cathode. 

Different flow channel design configurations, (a) Straight parallel channels, (b) Single serpentine curvilinear bends, (c) Single serpentine channel with square bends, (d) Dual 2-mm serpentine parallel channels, (e) Dual 1.2-mm serpentine parallel channels, (f) Dual 1-mm serpentine parallel channels, (g) Four 0.5-mm serpentine parallel channels. 

Single serpentine channels, (a) Serpentine flow channels, (b) Single channel curvilinear bends, (c) Single channel square bends. 

Contour plots for pressure and velocity for single serpentine channels are shown in Figure 10.19. A closer look at the pressure drop data shows developing flow phenomena in each channel. However, when the total pressure drop of each channel is considered, a periodic, fully developed pressure drop is noticed beyond the third channel. It can be noticed from the contour plots that the serpentine channels give rise to secondary flows near the inner side of the bends, and this causes additional losses (Boddu et al., 2009). However, flow displays a periodically, fully developed flow by the second and third turns. 

Single Serpentine Channel with Square Bends... 

For a single serpentine channel, the effective contact surface area of the gas channels can be increased by replacing circular bends with square bends. A schematic view of the single serpentine channel with square bends is shown in Figure 10.21. The operating conditions are the same as those of the serpentine channels with curvilinear bends. 

For comparison of serpentine curvilinear and serpentine square bends, contour plots of static pressure and dynamic pressure distributions are shown in Figure 10.23 for a single serpentine channel. 

Increased contact surface area and hence a more uniform gas concentration distribution can be achieved with an increased number of parallel channels and with a decrease in channel size while keeping the pressure drop on the same order as that of a single serpentine channel. 

The steam reformer is a serpentine channel with a channel width of 1000 fim and depth of 230 fim (Figure 15). Four reformers were fabricated per single 100 mm silicon wafer polished on both sides. In the procedure employed to fabricate the reactors, plasma enhanced chemical vapor deposition (PECVD) was used to deposit silicon nitride, an etch stop for a silicon wet etch later in the process, on both sides of the wafer. Next, the desired pattern was transferred to the back of the wafer using photolithography, and the silicon nitride was plasma etched. Potassium hydroxide was then used to etch the exposed silicon to the desired depth. Copper, approximately 33 nm thick, which was used as the reforming catalyst, was then deposited by sputter deposition. The reactor inlet was made by etching a 1 mm hole into the end... 

The PCR channel for these CFPCR devices can also consist of either capillary tubes [99, 100] or an on-chip annular channel [95, 101]. The serpentine channel formats on a monolithic chip can utilize thermal insulation with the aid of air gaps [102, 103] or by utilizing glass chips with a low thermal conductivity [104, 105]. Recently, a novel spiral chaimel configuration was also used to perform CFPCR on a single PC wafer with a circular arrangement of three temperature zones, allowing for a compact footprint and a minimal number of heaters for temperature control [106, 107]. CFPCR microfluidics can also use a uiudirectional PCR or oscillatory flow [108]. 

Photochemical singleliquid inlet port splits into two liquid streams, which are merged with a third channel. The latter is connected to a second port for gas feed, in such way that the two liquid streams encompass the gas stream. This section is followed by a serpentine channel passage, whidi ends in a third outlet port. The channel material is made of glass... 

FIGURE 9.1 Oxygen partial pressure as a function of current density at 70 °C and 100% RH with different backpressures. Gore -membrane-based membrane electrode assembly (MEA) area 46 cm. Gas diffusion layer (GDL) 25-DC. Stoichiometries of H2 and air 1.2 and 2.5, respectively. Single serpentine flow channel with both a width and depth of 1.0 mm [1]. 

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