Research On Heat And Mass Transfer Characteristics Of Proton Exchange Membrane Fuel Cell

Proton exchange membrane fuel cell(PEMFC)has the advantages of high efficiency,fast start-up,and zero emissions,and is considered to be a very promising green energy technology.At present,durability still restricts the commercial development of PEMFCs.As an important factor affecting the durability of the PEMFC,water and thermal management need to be paid enough attention to.Aiming at the problems of water and thermal management of PEMFCs,this paper proposed a thermal management method based on vapor chamber(VC)and a water management method based on pulsating flow.The effects of the vapor chamber and pulsating flow on the electrical performance and heat and mass transfer characteristics of PEMFCs were investigated by theoretical analysis,experimental test,and numerical simulation.The main research contents are as follows:(1)A thermal management method using the vapor chamber to enhance the heat transfer of the PEMFC was proposed.The effect of structural parameters on the heat transfer performance of the vapor chamber was studied.Based on theoretical analysis,the vertical vapor chamber(VVC)and transverse vapor chamber(TVC)with thicknesses of 1.3 mm and1.32 mm were designed and fabricated,and the thermal resistance network model of the vapor chamber was established.The phenomena of water balance and water transport in the anode channel under dead-ended anode mode were analyzed theoretically,and the basic principle of pulsating flow was expounded.The results showed that the theoretical maximum heat transfer of the vapor chamber increased with the increase of the thickness of the vapor core and the wick core.When the thickness of the vapor core increased further,the theoretical maximum heat transfer tended to be stable.Pulsation frequency and pulsation amplitude were important factors affecting the pulsation intensity.Increasing the pulsation frequency or pulsation amplitude can enhance the pulsation intensity and thus enhance the effective diffusion of species.(2)A composite flow field plate structure unit based on anode plate-vertical vapor chamber-cathode plate was constructed and a test stack with VVCs(VVC-PEMFC)was successfully assembled.The temperature distribution and electrical performance of the VVC-PEMFC stack were experimentally studied,and the effect of cooling conditions on its thermal performance was emphatically investigated.The results showed that the VVC enhanced the heat transfer inside the stack so that its temperature distribution was more uniform and the output power was higher.At 0.64 A/cm~2,the maximum temperature difference of the VVC-PEMFC stack did not exceed 6°C,and the output power was about 10%higher than that of the ordinary air-cooled stack.The cooling condition had an important effect on the thermal performance of the VVC-PEMFC stack.Under proper cooling conditions,VVCs can remove nearly half of the heat produced in the stack.(3)A composite flow field plate structure unit based on anode plate-transverse vapor chamber-cathode plate was constructed and a test stack with TVCs(TVC-PEMFC)was successfully assembled.The temperature distribution and electrical performance of the TVC-PEMFC stack and the ordinary air-cooled stack were compared and analyzed.And the effects of cathode air flow rate,cooling air flow rate,current loading amplitude,and gravity on the thermal performance of the TVC-PEMFC stack were studied.The results showed that the TVC can also significantly improve the temperature distribution uniformity of the stack.Compared with the ordinary air-cooled stack,the output power of the TVC-PEMFC stack had increased by approximately 5.5%.(4)Aiming at the water flooding problem in dead-ended anode mode,a two-way hydrogen supply mode based on pulsating flow was proposed.The parameters such as voltage,pressure drop,water removal,and temperature in the dead-ended anode and two-way hydrogen supply modes were compared and analyzed,and the effects of switching period,reverse flow rate ratio,purge period,load current,and purge valve size on the two-way hydrogen supply mode were investigated.The results showed that the voltage decay rate in dead-ended anode mode increased exponentially with the increase of load current.While the two-way hydrogen supply mode effectively slowed down the voltage decay rate of the stack under high currents and significantly improved the stability and consistency of the cell voltage.The switching period and the reverse flow rate ratio significantly affected the operating characteristics of the two-way hydrogen supply mode.When the switching period was 2 s and the reverse flow rate ratio was 50%,the output performance of the stack was higher and the stability was better.(5)The effect of the two-way hydrogen supply mode on the hydrodynamic behavior in the anode channel was further studied by designing a visual stack and building a visual experimental platform.The global water distribution in anode channels in dead-ended anode mode and two-way hydrogen supply mode was compared,and the difference in the dynamic transport behavior of the droplets in the local area was investigated.The results showed that the two-way hydrogen supply mode can enhance the transfer capacity of liquid water in anode channels and effectively reduce the accumulation of liquid water.As a result,the water and gas distribution uniformity of the stack was improved,and the output performance and operation stability were improved accordingly.(6)A three-dimensional and unsteady calculation model of air-cooled PEMFC was established.The distribution of the species in the anode channel under dead-ended anode mode was investigated.The difference of operation characteristics between the two-way hydrogen supply mode and the dead-ended anode mode was compared,and the mechanism of the two-way hydrogen supply mode to improve the water management of PEMFC was revealed.The simulation results showed that the output performance of PEMFC was directly related to the liquid saturation of the gas diffusion layer and the mass transfer capacity of hydrogen.By driving the species to reciprocate,the two-way hydrogen supply mode improved the mass transfer capacity of hydrogen,which significantly improved the water and gas management and operation performance of PEMFC.