# Fuel Cells

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In order to obtain the flow distribution in fuel cells, the following assumptions are applied to establish a flow network model. 1) The reactant ges in consid to be steady flow in impervious channels and the temperature is uniform. 2) A fluid network is comprised of straight pipe, intake, exhaust duct and T-shape connection. 3) The influence of inertia is ultralow in contrast to the viscosity due to the low Reynolds number. Furthermore, in the straight pipe, a fully developed laminar assumption is satisfied under the condition that shape change is negligible. Numerical analysis technique the numerical analysis is performed by combining the governing equations related to the conservation of energy, conservation of mass and conservation of electrical charge to examine fluid distributions, heat transfers, mass transfers and electrochemical reactions. The assumptions used in developing the model are as follow: 1) Ideal gas law was employed for gaseous species. 2) The fluid flow in the fuel cell was laminar due to the low flow velocities and the small size of gas flow

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Therefore, the following equation is shown when the Darcy equation allowing viscous resistance for the porous structure is applied to the NaviereStoke equation for the steady-state. (5) (6)

In Eq. (6), ε is the porosity of the gas diffusion layers and K is the permeability of the gas diffusion layers. u is the surface velocity of the gas diffusion layer.

3.3. Conditions for single-cell numerical analysis Numerical analysis for a single-cell was ﬁrst performed before the ﬂow ﬁeld was analyzed to evaluate the effects of the waveform shape. The results were compared to the references. The sizes of the channel were calculated from the straight sections of the 25 unit cell channel. The width of the cathode was 0.5 mm and its length was 1 mm. The width of anode was 0.5 mm and its length was 0.6 mm. The ribs were structured every 0.5 mm on both sides of the channels. The thickness of the gas diffusion layers was 0.2 mm, that of the catalyst layers was 0.2 mm and that of the membranes was 0.05 mm.

Table 1- Physical Parameters in a PEMFC model.

Parameter Expression

Channel height 1 mm, 1.5 mm, 2 mm

Channel width 5