Three-Dimensional Numerical Simulation And Transient Operation Of Underwater Oxygen PEMFC

Since the beginning of industrial age,the continuous increase of fossil energy consumption has caused long-term global concern and anxiety on energy reservation and environment protection.With the progress of science and technology,worldwide scientists and researchers are seeking for breakthroughs of energy utilization and revolution of energy structure.In recent decades,hydrogen energy has gradually attracted more and more attention.Proton Exchange Membrane Fuel Cell(PEMFC),as an efficient tool for hydrogen energy utilization,is considered to own broad application prospect.Due to its advantage of no moving parts,low noise and low emissions,PEMFC is also favored as underwater power source.Under this background,this paper established a “three-dimensional + one-dimensional”(“3D+1D”)numerical model,aiming for efficient computational fluid dynamics(CFD)simulation of underwater hydrogen-oxygen PEMFC.The model considered comprehensive physiochemical processes in PEMFC such as heat and mass transfer,electrochemical reaction and membrane water absorption/desorption and coupled with a hydrogen-oxygen permeation sub-model and a cathode recycling sub-model.In order to ensure the reliability of the proposed model,validation was carried out for both the subpart and the whole model under different inlet humidity,temperature and size of cell domain.Additionally,a data-driven surrogate method was introduced into parameter adjustment process,which achieved better efficiency.In this paper,the effects of three different cathode flow field configurations on the operation of oxygen-supplied PEMFC were explored at first,namely parallel,parallel-serpentine and interdigitated.The sensitivity analysis of the cell performance was carried out under different cathode stoichiometry.Results showed that the interdigital flow field performed the best in promoting the convective transport of reactant gas into the electrode.It was proved to be more suitable for underwater oxygen-supplied PEMFC,due to the capability of maintaining better output performance while improving fuel utilization efficiency.Secondly,to seek the balance between oxygen utilization efficiency and water management,the cathode recycling sub-model was exploited to study the performance attenuation law of PEMFC and the change of internal mass and heat transfer under different loads,efficiency of steam-water separator,circulation flow rate and operating temperature.It was found that the decay of cell performance was more severe at high current density because of faster accumulation of liquid water in flow channel.In addition,the water removal efficiency of the steam-water separator is also an important factor affecting the performance of the cathode recirculated oxygen-supplied PEMFC.Conclusion was drawn that a water removal efficiency of higher than 95% could ensure the long-term stable operation.Higher circulating flow rate accelerated the feedback of liquid water from the outlet to the inlet and caused rapid accumulation of liquid water.Higher operating temperature was beneficial to the stable operation of cathode recirculating PEMFC.Finally,this paper studied the dynamic response of the underwater oxygensupplied PEMFC during frequent load changes,and explored the effects of different cathode gas supply conditions,load change amplitudes and operating parameters on cell dynamic performance.Results showed that the cell gained smaller overshoot and faster response to variable loads when cathode was supplied with oxygen.When the amplitude of the load change increased,the fluctuation of membrane water content and oxygen concentration intensified,which increased the voltage overshoot amplitude and hindered the stable operation of cell,by increasing the overshoot amplitude of ohmic loss and the hysteresis time of mass transfer loss.This study found that too low or too high cathode stoichiometric ratio was not favored from the perspective of cell dynamic response,while increasing the relative humidity and pressure of inlet gas could improve the dynamic response capability of PEMFC.