Lakshminarayanan et al., International Journal of Advanced Engineering Technology E-ISSN

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1 Research Paper OPTIMIZATION OF SINGLE AND MULTI PASS SERPENTINE FLOW CHANNEL OF POLYMER ELECTROLYTE MEMBRANE FUEL CELL (PEMFC) V.Lakshminarayanan 1a, P.Karthikeyan 2b,D.S.Kiran Kumar 3c, G.Madhu Sudan 3d Address for Correspondence 1,3 Department of Mechanical Engineering, KGISL Institute of Technology, Saravanampatti,Coimbatore , Tamil Nadu, India., 2 Department of Automobile Engineering, PSG College of Technology, Peelamedu, Coimbatore , Tamil Nadu, India. ABSTRACT: In this paper, optimization of operating and design parameters such as pressure, temperature, inlet reactant mass flow rate and various rib width to channel width (L: C) 1:1, 1:2, 2:1 and 2:2 on the single and multi-pass serpentine flow channel of 25cm 2 ective area was taken into consideration for performance enhancement of the PEMFC. Creo Parametric 1.0 and CFD Fluent 14.0 software packages were used to create the 3 Dimensional (3-D) model and simulation of PEMFC. The optimization was carried out of the various parameters with MINITAB 17 software. It is concluded that the landing to channel width (L: C) - 1:2 of single pass and multi-pass serpentine flow channel has the maximum influence on fuel cell performance and square of response factor (R 2 ) was achieved from the Taguchi method by MINITAB 17 software as and % respectively. The optimum combination of parameters achieved for various L: C of single pass and multi-pass serpentine flow channel of PEM fuel cell using by MAT LAB software. KEYWORDS: Optimization; Operating parameters; Design parameters; Taguchi method; MAT LAB; Optimization. 1. INTRODUCTION Fuel cells are the electrochemical energy converting device which converts chemical energy into electrical energy without any conventional combustion process. Among many types of fuel cells Polymer Electrolyte Membrane fuel Cell (PEMFC) is produced with high power density with low operating temperature for light weight and compact with negligible pollution studied by Maher A.R [1]. The internal combustion engine can be replaced by PEMFC for transportation due to its high energy icient, quick startup, quiet and clean. Since a PEMFC simultaneously involves electrochemical reactions, current distribution, water balance and heat transfer studied by Sukkee Um et al [2]. J.P. Owejan et al [3] analyzed in his study that the water is the byproduct of the electrochemical reaction and accumulated water in the gas diffusion layers and flow fields, affects the performance of the PEMFC. Xianguo Li and Chi-Young Jung [4, 5] has addressed in their study that hydration of membrane is used to maintain the performance of PEMFC. If it is not maintained properly, flooding and dehydration would occur which will affect the PEMFC performance. So identifying the proper channel and flow field design are also affecting the performance of fuel cell considerably. Sukkee Um [6] revealed in his study that the water transport in PEMFC was discussed to show various water transport regimes, such as anode side water loss, cathode side flooding and the equilibrium condition of water at the channel outlets. Hence, the ects of the flow channel, membrane thickness, and inlet gas humidity are important to enhance the performance of PEM fuel cell. Dyi-Huey Chang et al [7] studied the ect of flow channel depth and flow rates on performance of PEMFC and concluded that the optimum flow rate was essential to maintain sufficient pressure which forces the reactant into channel to get proper water balance. Nicholas S. Siefert [8] concluded in his study that the serpentine channels are very ective to remove the liquid because of its high gas velocity. However, Water accumulation leads the fuel cell performance unpredictable and unreliable under the nominally identical operating conditions. So the critical issue for PEMFCs can be resolved through appropriate design of flow channels for ective removal of water built on the flow field (bipolar) plates. Wei-Lung Yu et al [9] analyzed the two stages of optimization, in the first stage DOE was used to determine the significant ects on a response and the interactions between the six operating parameters like operating pressures, anode and cathode humidification temperatures, operating temperatures, anode and cathode stoichiometric flow ratios. In the second stage, the optimal combination of factors of a fuel cell was analyzed by Taguchi method. It was concluded that the possible way to increase the performance of PEM fuel cell by simultaneously increasing both the operating pressure and temperature and the remaining factors were at appropriate conditions. M. Zeroual et al [10] analyzed that the ects of inlet pressure and channel height on the distribution and consumption of reagents. The gas flow was assumed as incompressible, isothermal, unsteady and laminar, straight channeled flow fields were modeled in the anode and cathode sides. The simulation results showed that the increasing inlet pressure will improve consumption of oxygen and hydrogen and more homogeneous distribution. The ect of height was more important for a higher pressure inlet. It was noticed that an increased consumption of species and consequently an increase in water production if the height of the channel was smaller.atul Kumar, Ramana G. Reddy [11] studied the improvement on the performance of polymer electrolyte membrane fuel cell through optimization of the channel dimensions and shape in the flow-field of bipolar plates. Single-path serpentine flow-field design was used for studying the ect of channel dimensions on the hydrogen consumption at the anode. Nattawut Jaruwasupant and Yottana Khunatorn [12] studied the ects of serpentine flow channel designs on PEM fuel cell for reaction gas distributions, the relationship between channel curvature, channel length, velocity distribution and characteristics of flow field with pressure drop by using the threedimensional computational fluid dynamics (CFD) numerical model for the on the performance of Polymer Electrolyte Membrane fuel cells. Effects of curve channel length and widths of a flow field plate were studied in an ort to optimize the channel dimensions and it was concluded that a better design of the gas flow field was required to improve the gas

2 distribution and water management. M.Grujicic, K.M.Chittajallu [13] concluded that the single-phase two-dimensional electrochemical model was coupled with a nonlinear constrained optimization algorithm to find an optimum design of the fuel cell with respect to the design and operating parameters of cathode like the cathode length, thickness, width of shoulders and air inlet pressure in the interdigitated air distributor. Horng-Wen Wu and Hui-Wen Gu [14] has applied the Taguchi method to find the optimal combination of six operating parameters like operating and anode, cathode humidification temperatures, flow orientation, anode, and cathode stoichiometric flow ratios of a PEM fuel cell. The results showed that the flow orientation, operating temperature and anode and cathode humidification temperatures were significant factors for affecting the performance of the fuel cell. P.Karthikeyan et al. [15] was optimized a single channeled fuel cell with ten operating and design parameters of 125 mm flow channel length using Taguchi method. It is clearly understood that there is a need for immediate attention towards analyzing and optimizing the simultaneous influence of operating and design parameters of single and multi-pass serpentine flow channel of 25 cm 2 ective area for the performance of the PEMFC using CFD Fluent 14.0 and MATLAB software packages. Hence this paper has a detailed study about the optimization of various pressure ranges 1,1.5,2 and 2.5 bar temperature of 323K,333K,343K and 353K, anode, cathode inlet reactant mass flow rate 3,3.5,4 and 4.5 times to the theoretical value and various rib to channel width (L: C)-1:1,1:2,2:1&2:2 on single pass and multi-pass serpentine flow channel of PEMFC and their influence in the performance were compared. 2. MODEL DEVELOPMENT Three dimensional (3-D) PEMFC model with single pass and multi-pass serpentine flow channel of various rib to channel width configurations were created by Creo Parametric 1.0 as shown in Fig.1. The modeling was done by creating individual parts of the PEMFC and the dimensions of individual parts such as the anode and cathode GDL, solid polymer electrolyte membrane, the anode and cathode catalyst layers as shown in the Table.1. The assignments of zones for various parts were done by Workbench The various geometrical models (L: C-1:1, 1:2, 2:1 and 2:2) of single pass and multi-pass serpentine flow channel were meshed by using ICEM 14.0 (a module of Ansys 14.0). After geometry building, the next step was discretization done by Ansys 14 ICEM software. Before importing the model to CFD Fluent 14.0 creating a good mesh by Ansys 14 ICEM software was one of the most difficult steps involved in modeling. It requires a careful balance of creating enough computational cells to capture the geometry without creating much. Care should be taken such that it should not exceed the available memory of the meshing computer. Many other factors must also be considered into account in order to generate a computational mesh which provides representative results when simulated [16].The meshing method was used as Cartesian grid, which helps in the formation of hexahedral mesh to get accurate results. Hence the entire cell was divided into a finite number of discrete volume elements or computational cells to solve the equations associated with the fuel cell simulation. Split block method used for blocking and meshing was done with Cartesian method. Body fitted mesh was used and projection factor was set to 1. The projection factor determines how closely the edges of the mesh match up with the grid. Fig. 1 - Various rib to channel width (L: C) single pass and multi-pass serpentine flow channel of 25 cm 2 active area. Table. 1-Dimensions and Zone type, assigning of fuel cell S.No Part Name Width Length Thickness Zone (mm) (mm) (mm) type 1 Anode & Cathode Flow channel solid 2 Anode & Cathode catalyst Fluid 3 Membrane Fluid 4 GDL anode & cathode Fluid Governing Equations The simulation was solved by simultaneous equations like conservation of mass, momentum, energy, species concentration, butler Volmer equation, Joule heating reaction and the Nernst equation to obtain reaction kinetics of the PEMFC. The model used to consider the system as 3-D, steady state, and inlet gases as ideal condition, system as an isothermal and

3 flow as laminar, fluid as incompressible, thermo physical properties as constant and the porous GDL, two catalyst layers and the membrane as an isotropic. Continuity equation. v 0 t (1) Conservation of Momentum v. vv p. v Sm t (2) Conservation of Energy T C p C p v. T k T Se t (3) 1, C p scp s Cp, 1 k 2ks 2ks k 3ks Conservation of Species pxi vi. Di xi Ss, i (4) t MH 2 Ss, H j 2 a -Rate of hydrogen consumption in the anode catalyst layer MO 2 Ss,O 2 j -Rate of hydrogen consumption in the C cathode catalyst layer MH 2O Ss,H 2 O(l) jc Afg xsat x -Rate of H2O(g) liquid vapor formation s,h 2 O(g) fg sat H2O(g) S A x x -Rate of water vapor formation Conservation of Charge.k.k -Electric current m m S m s s S s -Ionic current (5) S s ja and S m jai -At the anode catalyst layer S s jc and S m jci -At the cathode catalyst layer The final steps involved were the adoption of boundary condition with physical and operating parameters of PEMFC for solving the above mentioned reaction kinetics. The boundary conditions for the inlet gases at anode and cathode were set as mass flow-inlet whereas for the outlet of the anode and cathode was given the boundary conditions as pressure-outlet". The anode was grounded (V = 0) and the cathode terminal was set at a fixed potential that was less than the open-circuit potential and gradually increasing by 0.1Volt. Both the terminals should be assigned the boundary type as "wall". Voltage jump zones can optionally be placed between the various components (such as between the gas diffusion layer and the current collector) and the ect of gravity was neglected. Solver A control volume approach based on commercial solver FLUENT 14.0 was used to solve the various governing equations. The 3D, double precision and serial processing were used for this model. The species concentration on anode side of H 2, O 2, and H 2 O were 0.8, 0, and 0.2 respectively. Similarly, on the cathode side were 0, 0.2 and 0.1 respectively. The porosity and viscous resistance at anode and cathode side was 0.5 and 1E12 (1/m 2 ). Open circuit voltage was set at 0.95 V on the anode side and was grounded. The cathode voltage has been varied from 0.05 V to 0.95 V used for solving kinetics reaction in order to get the current flux density, H 2, O 2, and H 2 O fractions along with the flow field design. Multigrid settings were modified as F-Cycle for all equations and entered termination restriction value was set as for H 2, O 2, H 2 O and water saturation. The electric and proton potential values were set at Stabilization method BCGSTAB was selected for H 2, O 2, H 2 O, water saturation, electric and proton potential. The reference current density in the anode, cathode sides were set to as 10000, 20 A/cm 2 and the reference concentration, exchange coicient on the anode and cathode side were 1 and 2 kmol/m 3 respectively. The hydrogen, oxygen and water reference diffusivity were set as 3E-5 m 2 /s. Adaptation of Taguchi method Taguchi method can be used to find out the most optimum combination among the input parameters (Operating and Design) which will result in getting the maximum possible output which cause in the performance enhancement of PEMFC. In Taguchi method L16 standard orthogonal array with 4-level and 4 factors was used and the parameters were considered as low, high and medium range values. When this orthogonal array was used, significance of factors and optimum combination can be found during 16 runs itself. The factors considered for the first stage of analysis, L: C, pressure, temperature, stoichiometric ratio. stoichiometric ratio of the reactants as 3, 3.5, 4 and 4.5 means that number of times the theoretical mass flow rate to be multiplied. The theoretical value of hydrogen in the anode side was 4.33E-07 kg/sec and cathode side was 3.33E-06 kg/sec. 3. RESULTS AND DISCUSSION As per L16 orthogonal array, the inputs were given to the analysis software and having all other parameters constant. The power density from polarization curve was found by a numerical study using CFD Fluent 14.0 software package for all 16 runs and the corresponding Signal/Noise (S/N) ratios were found from MINITAB 17 software and were shown in Table 2. The optimization was performed for Larger the Better type of Taguchi method. Since the power output of PEMFC must be maximized. The S/N ratio plot for the same were obtained using MINITAB 17 software and the corresponding maximum S/N ratio gives better performance as analyzed based on larger the better as shown in the Fig.3. It was concluded that the design parameter, landing to channel ratio of single pass and multi-pass serpentine flow channel having 1:1 as P1 and E1, and the operating parameters like pressure 2.5 bar as Q4 and F4, temperature 323 K as R1 and G1, theoretical consumption of mass flow rate 3.5 as S2 and H2 were the optimum parameters to show better performance of PEMFC.

4 Table.2- Factors, levels, power density and S/N ratio of single pass serpentine and multi-pass serpentine flow channel for 16 runs of coarse optimization. Rib width SINGLE PASS MULTI PASS to SERPENTINE SERPENTINE Pressure Temperature Stoichiometri Run Channel Power Power (bar) (K) c ratio S/N width Density Density S/N Ratio (L:C) (W/cm 2 Ratio ) (W/cm 2 ) : : : : Overall mean of S/N ration (η) Fig.2 - Mean S/N ratio plot for L: C (P&E), Pressure (Q&F), Temperature (R&G), Stoichiometric ratio (S&H) of single pass serpentine and multi-pass serpentine flow channel But in this analysis, all the factors were considered higher significance. It was found that the temperature irrespective of their significance for better was the predominant factor affecting the performance performance on PEMFC. The level with a higher S/N ratio was considered to be optimum level and optimum combination of operating and design parameters was founded for single pass and multipass serpentine flow channel on Fig.2 to be P1Q4R1S2 and E1F4G2H2 respectively. The optimization results of various parameters were based on S/N ratios and the significance of each of fuel cell followed by pressure, rib to channel width (L: C) of single pass serpentine and multi-pass serpentine flow channel and stoichiometric ratio respectively. The regression equation obtained from Minitab 17 was fed into the MATLAB software and the various combinations of L: C, pressure, temperature and stoichiometric ratio were obtained in the single pass factor by ranking them according to their and multi-pass serpentine flow channel as shown in performance. The Delta value of each factor available in the MINITAB 17 software itself was shown in Table 3. The factor in highest delta value indicates the table.4. The fig.3 shows the scatter diagram for the predicted values of various parameters are closer to the true value. Fig.3. Scatter diagram of various parameters Single pass serpentine and multi-pass serpentine

5 Table 3 - Mean S/N ratios, Delta and Rank for each level factor of (A) Single pass serpentine and (B) Multi-pass serpentine flow channel Factors Rib to Channel width (L:C) Pressure (bar) Temperat ure (K) Stoichiom etric ratio Level 1 Level 2 Level 3 Level 4 Delta Rank A B A B A B A B A B Table.4 Optimum power density for various combinations of parameters Flow Channel Pressure Temperature Stoichiometric L:C (bar) (K) Ratio Single pass serpentine Flow Channel 1: : : : Multi pass serpentine Flow Channel 1: : : : CONCLUSION The combined ect of all the parameters exhibited a different response compared to their individual ects. Optimizing the four different parameters using Minitab 17 the R 2 value was obtained for single and multi-pass serpentine flow channel of 25cm 2 active area of PEMFC with various landing to channel width (L:C) as 99.48% and 99.18% respectively. The optimum parameters were obtained from MATLAB software. The ect of operating and design parameters was affecting the performance of PEMFC more significantly. REFERENCES 1. Maher, A.R., Sadiq Al-Baghdadi., Three-dimensional computational fluid dynamics model of a tubularshaped PEM fuel cell,renewable Energy, 2008, 33, Sukkee Um, C.Y., Wang. and Chen, K.S., Computational Fluid Dynamics Modeling of Proton Exchange Membrane Fuel Cells, Journal of The Electrochemical Society, 2000, 147 (12), Owejan,J.P., Trabold,T.A., Jacobson,D.L., Arif,M., Kandlikar, S.G., Effects of flow field and diffusion layer properties on water accumulation in a PEM fuel cell, International Journal of Hydrogen Energy, 2007, 32, Xianguo Li., Imran Sabir. and Jaewan Park., A flow channel design procedure for PEM fuel cells with ective water removal, Journal of Power Sources, 2007, 163, Chi-Young Jung., Chi-Seung Lee. and Sung-Chul Yi., Computational analysis of transport phenomena in proton exchange membrane for polymer electrolyte fuel cells, Journal of Membrane Science, 2008, 309, Sukkee Um., Chao-Yang Wang., Computational study of water transport in proton exchange membrane fuel cells, Journal of Power Sources, 2006, 156, Dyi-Huey Chang., Jung-Chung Hung., Effects of Channel Depths and Anode Flow Rates on the Performance of Miniature Proton Exchange Membrane Fuel Cells, International Journal of Applied Science and Engineering, 2012, 10(4), Nicholas. S. Siefert., Shawn Litster., Voltage loss and fluctuation in proton exchange membrane fuel cells: The role of cathode channel plurality and air stoichiometric ratio, Journal of Power Sources, 2011, 196, Wei-Lung Yu., Sheng-Ju Wu., Sheau-Wen Shiah, Parametric analysis of the proton exchange membrane fuel cell performance using design of experiments, International Journal of Hydrogen Energy, 2008, 33, Zeroual,M., Belkacem Bouzida,S., Benmoussa,H. and Bouguettaiad,H., Numerical study of the ect of the inlet pressure and the height of gas channel on the distribution and consumption of reagents in a fuel cell (PEMFC),Energy Procedia, 2012, 18, Atul Kumar., Ramana G. Reddy., Effect of channel dimensions and shape in the flow-field distributor on the performance of polymer electrolyte membrane fuel cells, Journal of Power Sources, 2003, 113, Nattawut Jaruwasupant. and Yottana Khunatorn., Effects of difference flow channel designs on Proton Exchange Membrane Fuel Cell using 3-D Model, Energy Procedia, 2011, 9, Grujicic,M., Chittajallu,K.M., Design and optimization of polymer electrolyte membrane (PEM) fuel cells, Applied Surface Science, 2004, 227, Horng-Wen Wu., Hui-Wen Gu., Analysis of operating parameters considering flow orientation for the performance of a proton exchange membrane fuel cell using the Taguchi method, Journal of Power Sources, 2010, 195, Karthikeyana,P., Muthukumar,M., Vignesh Shanmugam,S., Pravin Kumar,P., Suryanarayanan Murali., Senthil Kumar,A.P., Optimization of Operating and Design Parameters on Proton Exchange Membrane Fuel Cell by using Taguchi method, Procedia Engineering, 2013, 64, Alfredo Iranzo., Miguel Munoz., Felipe Rosa. and Javier Pino., Numerical model for the performance prediction of a PEM fuel cell. Model results and experimental validation, International Journal of Hydrogen Energy, 2010, 35,