Lei Chen

Bio: Lei Chen is an academic researcher from Xi'an Jiaotong University. The author has contributed to research in topics: Proton exchange membrane fuel cell & Membrane. The author has an hindex of 8, co-authored 25 publications receiving 253 citations.

Multi-scale modeling of proton exchange membrane fuel cell by coupling finite volume method and lattice Boltzmann method

Abstract: A multi-scale modeling framework combining finite volume method (FVM) and lattice Boltzmann method (LBM) previously developed by our group is used to predict electrochemical transport reaction in proton exchange membrane fuel cell (PEMFC) cathode with a parallel gas channel (GC), a gas diffusion layer (GDL) with porous structures and a catalyst layer (CL) with idealized microstructures. In this framework, the PEMFC cathode is divided into two sub-domains, one is GC and the other contains GDL and CL. The FVM is used to simulate transport phenomena in the GC sub-domain, while the LBM is employed for pore-scale transport phenomena in the GDL and CL as well as proton conduction in the CL in the other sub-domain. Two reconstruction operators are adopted to transfer macro density, velocities and concentration in the FVM to density distribution functions and concentration distribution functions in the LBM at the interface between the two sub-domains. Simulation results show that the coupled (hybrid) simulation strategy developed is able to predict transport phenomena in the GC and to capture the pore-scale transport processes in porous GDL and CL. In addition, some techniques to save the computational resources and to improve the efficiency of the coupled (hybrid) simulation strategy are discussed.

A comprehensive review and comparison on heatline concept and field synergy principle

Abstract: A comprehensive review and comparison on heatline concept and field synergy principle have been made based on more than two hundreds of related publications. The major conclusions are as follows. Both heatline concept and field synergy principle are important contributions to the developments of single-phase convective heat transfer theories. The role and function of heat line concept is to visualize the heat transfer path while that of field synergy principle is to reveal the fundamental mechanism of heat transfer enhancement and to guide the development of enhanced structures. None of them can be used to deduce the other, nor none of them can be derived from the other. Hence, there is no problem of mutual remake between them at all. If heatlines are constructed by solving a Poisson equation additional computational work should be done; However, either the synergy number or the synergy angle both can be obtained by using numerical results without additional computational work. Further research needs for both heatline concept and field synergy principle are also provided.

The Temperature Effect on the Diffusion Processes of Water and Proton in the Proton Exchange Membrane Using Molecular Dynamics Simulation

Abstract: A molecular dynamics calculation model for the Nafion 117 membrane is constructed by Materials Studio (MS) software platform to study its transport properties. Cell structures of different water content of Nafion 117 membrane at 300 K and 353 K are obtained, respectively, and the predicted density values of simulated cell are in good agreement with available experimental data. It is found that at the same temperature, the predicted diffusion coefficients of both water molecules and hydrogen ions increase with the water content, and at the same water content the predicted diffusion coefficients of both water molecules and hydrogen ions increase with the temperature.

Mechanism of surface nanostructure changing wettability: A molecular dynamics simulation

Abstract: Molecular dynamics simulation is performed to simulate the wetting behavior of nano water droplets on flat and pillar surfaces. The result shows that the contact angle of the water droplet on the flat surface becomes smaller with the increase of the surface characteristic energy parameter e. At the same energy parameter e, the hydrophobicity is enhanced on the pillar surface compared to the flat surface. For nanostructured surfaces with different geometrical features, the sparser the surface pillars, the larger the contact angle. What’s more, we propose an equivalent potential well method, which can effectively reveal the mechanism of nanostructures changing surface wettability. The deeper the equivalent potential well, the smaller the contact angle.

Experimental and numerical studies for applying hybrid solar chimney and photovoltaic system to the solar-assisted air cleaning system

Abstract: Under the background of global energy shortage and environment deterioration, researchers of the world pay high attention to develop renewable energy. This paper proposes a hybrid solar chimney and photovoltaic system for the novel solar-assisted air cleaning system. Small-scale laboratory setups are designed and fabricated. Experimental results reveal that replacing 50.60% acrylic glass of the collector top with photovoltaic panels will reduce the thermal air flow rate only by 14%, but generate significant electric power output. A three-dimensional numerical simulation model is established and validated by experimental results (air flow rate, temperature distribution). The model includes solar ray tracing model, surface to surface radiation model, buoyancy-driven flow and heat transfer model and power generation model. Then, this model is used to predict a large-scale system based on the Manzanares pilot power plant in Spain. For the large-scale system, the electrical energy generated by the photovoltaic panels can be used to drive suction fans to increase air input. Covering the entire top surface of the collector by photovoltaic panels (113-meter-wide), the total air flow rate would increase to 2.21 times compared with the system without photovoltaic panels. And setting photovoltaic panels on the collector bottom with 113-meter-wide, the total air flow rate would increase to 2.42 times. Thus, adding photovoltaic panels for the collector can greatly improve the utilization of solar energy. It can increase the amount of air purification, or reduce land requirement for the same flow rate.

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

A Critical Review of Modeling Transport Phenomena in Polymer-Electrolyte Fuel Cells

Abstract: aLawrence Berkeley National Laboratory, Berkeley, California 94720, USA bLos Alamos National Laboratory, Los Alamos, New Mexico 87545, USA cUnited Technologies Research Center, East Hartford, Connecticut 06118, USA dSchool of Mechanical and Systems Engineering, Newcastle University, Newcastle upon Tyne NE1 7RU, United Kingdom eChemical and Biomolecular Engineering Department, University of California, Berkeley, California 94720, USA fFuel Cell Research and Development, General Motors, Pontiac, Michigan 48340, USA gBallard Power Systems, Burnaby, British Columbia V5J 5J8, Canada hFuel Cell Research Centre, Queens University, Kingston, Ontario K7L 3N6, Canada iDepartment of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA jDepartment of Mechanical Aerospace and Biomedical Engineering, University of Tennessee at Knoxville, Knoxville, Tennessee 37996, USA kDepartment of Mechanical Engineering Technology, SUNY Alfred State College, Alfred, New York 14802, USA lDepartment of Mechanical Engineering, University of Alberta, Edmonton, Alberta T6G 2G, Canada

Water absorption, desorption and transport in nafion membranes

Abstract: Abstract Water sorption, desorption, and permeation in and through Nafion 112, 115, 1110 and 1123 membranes were measured as functions of temperature between 30 and 90 °C. Water permeation increased with temperature. Water permeation from liquid water increased with the water activity difference across the membrane. Water permeation from humidified gas into dry nitrogen went through a maximum with the water activity difference across the membrane. These results suggested that the membrane was less swollen in the presence of water vapor and that a thin skin formed on the dry side of the membrane that reduced permeability to water. Permeation was only weakly dependent on membrane thickness; results indicated that interfacial mass transport at the membrane/gas interface was the limiting resistance. The diffusivity of water in Nafion deduced from water sorption into a dry Nafion film was almost two orders of magnitude slower than the diffusivity determined from permeation experiments. The rate of water sorption did not scale with the membrane thickness as predicted by a Fickian diffusion analysis. The results indicated that water sorption was limited by the rate of swelling of the Nafion. Water desorption from a water saturated film was an order of magnitude faster than water sorption. Water desorption appeared to be limited by the rate of interfacial transport across the membrane/gas interface. The analysis of water permeation and sorption data identifies different regimes of water transport and sorption in Nafion membranes corresponding to diffusion through the membrane, interfacial transport across the membrane–gas interface and swelling of the polymer to accommodate water.

Multi-phase models for water and thermal management of proton exchange membrane fuel cell: A review

Abstract: The 3D (three-dimensional) multi-phase CFD (computational fluid dynamics) model is widely utilized in optimizing water and thermal management of PEM (proton exchange membrane) fuel cell. However, a satisfactory 3D multi-phase CFD model which is able to simulate the detailed gas and liquid two-phase flow in channels and reflect its effect on performance precisely is still not developed due to the coupling difficulties and computation amount. Meanwhile, the agglomerate model of CL (catalyst layer) should also be added in 3D CFD model so as to better reflect the concentration loss and optimize CL structure in macroscopic scale. Besides, the effect of thermal management is perhaps underestimated in current 3D multi-phase CFD simulations due to the lack of coolant channel in computation domain and constant temperature boundary condition. Therefore, the 3D CFD simulations in cell and stack levels with convection boundary condition are suggested to simulate the water and thermal management more accurately. Nevertheless, with the rapid development of PEM fuel cell, current 3D CFD simulations are far from practical demand, especially at high current density and low to zero humidity and for the novel designs developed recently, such as: metal foam flow field, 3D fine mesh flow field, anode circulation etc.

Lattice Boltzmann simulation of liquid water transport in microporous and gas diffusion layers of polymer electrolyte membrane fuel cells

Abstract: In this study, the lattice Boltzmann method (LBM) is used to investigate liquid water transport in the microporous layer (MPL) and gas diffusion layer (GDL) of polymer electrolyte membrane fuel cells (PEMFCs). Two-phase LB simulations are performed with modeled porous geometries that imitate multi-layer porous transport layers (PTLs) consisting of an MPL and a GDL. The simulation conditions are closely matched to the actual liquid water transport conditions in the PEMFCs. The results indicate that invasion-percolation processes due to strong capillary effects govern liquid water transport in PEMFCs. In addition, LB simulations are conducted by varying the intrusion thickness of the MPL and the surface wettability of the PTL. The results clearly show that the liquid water content can be reduced in the PTL by employing a thicker MPL and/or more hydrophobic surfaces. The steady-state water distribution is observed to occur more rapidly as the MPL becomes thicker or as the solid surfaces become more hydrophobic. Furthermore, several dynamic liquid water transport behaviors are identified from the results and explained in detail.