Research On Heat Exchange Performance Of Flouroplastic Heat Exchanger Based On Graphene Modification

As a major energy consumer in the world,China has problems such as unreasonable energy structure layout and low energy utilization rate.The low-temperature flue gas waste heat produced by fuel combustion in the industry is rich in resources,due to the difficulties of low-grade flue gas waste heat recovery and low-temperature corrosion and other issues,making this part of the resource utilization rate low cause a large number of waste of resources.Polytetrafluoroethylene(PTFE)as a polymer has the advantages of acid corrosion resistance,light weight,low surface energy and wide application temperature range.It has been used in the manufacture of heat transfer tubes for lowtemperature flue gas waste heat recovery and utilization,but the thermal conductivity of PTFE is only about 0.23 W/(m·K),which leads to high heat exchanger volume and heat transfer tube area.In order to improve the thermal conductivity of PTFE,this paper studies the effect of adding graphene on the performance of PTFE.Under different working conditions,the heat transfer performance of the PTFE heat exchanger before and after adding graphene was studied through experimental and numerical simulation methods.First,the modification of PTFE was completed by adding 5% mass fraction of graphene.The physical properties and properties of PTFE before and after the addition of graphene were tested.It was found that the thermal conductivity of modified PTFE had increased by 18.68%,the density had reduced by 10.32%,and the static contact angle had decreased by 1.35%.It had no effect on corrosion resistance in a short period of time.Secondly,based on the actual parameters of the PTFE heat exchanger,a physical model was constructed and correspondingly simplified,and the heat exchange performance of the heat exchanger before and after adding graphene modification under dry air was studied by numerical simulation.The results of the study indicate that the increase in the thermal conductivity of the material after the addition of graphene increases the heat transfer performance of the heat exchanger,and this improvement effect becomes more and more obvious with the increase of the flue gas flow rate,within the scope of this article,the highest increase is 5.62%.Through analysis,it is found that the thermal conductivity of PTFE still needs to be further improved.When the thermal conductivity of the composite material reaches at least 2.32?5.13 W/(m·K),it can be better to meet the actual application needs of the project.Next,the effects of adding graphene on the temperature gradient of condensed droplets on the surface of the heat transfer tube under mixed gas conditions were studied by experimental and numerical simulation methods.The results of the two methods verified the correctness of the simulation method.Finally,the influence of the heat exchanger before and after adding graphene on the heat exchange performance under mixed gas conditions was studied,and the difference between the phase changes of water vapor in the mixed gas was also considered.The results of the study show that the total heat transfer coefficient(taking into account the phase change)is affected not only by the flow rate of the mixed gas and material modification,but also by the inlet temperature of the mixed gas,the condensation temperature,and the water vapor content in the mixed gas.Compared with the average convective heat transfer coefficient(not considering the phase change),the total heat transfer coefficient is improved by up to about 50%.After adding graphene modification,the total heat transfer coefficient is enchanced by up to 8.3%.