Study On Heat Transfer Intensification And Reforming Performance Of Small-scale Reactor For Methanol Steam Reforming With Waste Heat Recovery

Today’s global vehicle ownership and demand are increasing.On the one hand,it has accelerated the consumption of petroleum resources,on the other hand,it has caused serious environmental pollution problems due to vehicle exhaust emissions.Therefore,more and more attention has been paid to the development and promotion of pollutionfree alternative energy and waste heat recovery from automobile exhaust.Studies have shown that hydrogen is one of the excellent alternative clean energy.And hydrogen can improve combustion efficiency and reduces pollutant emissions by introducing it into an internal combustion engine for combustion.However,the storage and transportation of hydrogen is extremely difficult,which has become a major obstacle for hydrogen-doped combustion during the driving of vehicles.An effective way to overcome this obstacle is to produce hydrogen as the raw material through the catalytic reforming of hydrocarbon fuels on site.Among many hydrocarbon fuels,the methanol steam reforming reaction has low reaction temperature and high hydrogen production rate,and can also be combined with the exhaust heat of automobile exhaust,which has obvious advantages.In this paper,the traditional methanol steam reforming plate reactor with waste heat recovery was optimized and a new type of fin reactor was proposed.The effects of fin reactor on heat transfer performance and reforming performance were analyzed and the influence of different fin geometric parameters and structures on reactor performance was further investigated.Due to the large heat transfer resistance of the hot air,the heat utilization of the heating channels is insufficient in the traditional plate-type reactor with waste heat recovery.In order to solve this problem,a new type of fin reactor was designed and its three-dimensional heat and mass transfer model was established.Through a comparative study with the traditional plate-type finless reactor,it was found that the heating channel temperature distribution was more uniform and the decline rate of hot air temperature was faster in the finned reactor.The average temperature of the reactants was higher.And the heat transferred from the heating channel to the reaction channel,the thermal efficiency of the reactor and the methanol conversion rate were all higher than those of the finless reactor,indicating that the finned reactor had better heat transfer performance and reforming performance.Based on the good performance of the fin reactor,the effects of fin parameters on the reactor performance was studied,and the three parameters of fin number,length and arrangement were studied.The results showed that the larger the number of fins and the longer the length of the fins,the better the heat transfer performance and reforming performance of the reactor.However,the effect of improving the reactor performance was minimal when the fin length reached a certain value.In the reactor in which the fins were arranged in parallel,wide front and narrow back,and narrow front and wide back,the reactor with fins arranged in wide front and narrow back had the highest thermal efficiency and methanol conversion,with the best heat exchange efficiency and reforming efficiency.And the difference between the heat transfer performance and reforming performance of the other two fin reactors was very small.The structure of the fins had a larger impact on the flow and heat transfer of hot air in the heating channel,which further affected the reactor performance.Therefore,the structure of the fins was optimized.Five different types of fin reactors were designed,namely straight fins,wavy fins,staggered wavy fins,perforated wavy fins and intercostal staggered wavy fins.And the distribution of temperature,velocity and species mass fraction in the reactor were compared.The results showed that among the five types fin reactors,the intercostal staggered wavy fins and the perforated wavy fins had the most obvious promoting effects on the reformer performance,followed by the staggered wavy fins and the wavy fins,which with almost same promoting effect,and the straight fin performance was the lowest.