Study On The Preparation Of PVDF Hollow Fiber Heat Exchange Tube By Gel Coating Method And Its Enhanced Heat Transfer Performance

As a kind of heat exchange equipment,heat exchanger plays an important role in industrial production.Conventional heat exchangers mostly use metal with high thermal conductivity as the material for preparing heat exchangers,but they have the disadvantages of easy corrosion,easy scaling,and unstable chemical properties.Plastic heat exchangers can overcome these shortcomings.They have been widely used in food,chemical,petroleum,medical and other industries.However,the thermal conductivity of plastic heat exchange tube is lower,which hinders the development and application of plastic heat exchange tubes.Therefore,how to improve the thermal conductivity of plastic heat transfer tubes has become one of the research hotspots in the field of heat transfer in recent years.In order to solve the problem of low thermal conductivity of plastic heat exchange tube.Gel coating method was adopted in this paper.The polyvinylidene fluoride(PVDF)ultrafiltration membrane was used as the base membrane.The PVDF composite plastic heat exchange tube with a dense skin layer and high porosity was prepared by exploring the influence factors such as polydimethylsiloxane(PDMS)concentration,PDMS molecular weight and ZnO addition amount.After hydrophilization treatment,water was filled into the pores of the heat exchange tube to improve its thermal conductivity.At the same time,the basic properties of heat exchange tube,such as porosity,thermal conductivity coefficient,gas-tightness,water flux and surface structure,were characterized.The water-steam heat transfer coefficient was test.The result showed that the porous heat exchange tube prepared by gel coating method,after hydrophilic treatment,its thermal conductivity coefficient was 2.2 times that of the solid wall heat exchange tube prepared by melting method.In order to make further improvement,the heat transfer performance of the plastic heat exchange tubes,the surface of the heat exchange tubes was roughened by the sol-gel method,and the superhydrophobic surface was obtained,which enhanced the dropwise condensation heat transfer performance of the vapor.The effects of ethyl orthosilicate content,ammonia content and reaction temperature on the hydrophobic properties and heat transfer performance of the heat transfer tubes were investigated by single factor experiments.The basic properties of the heat transfer tubes were characterized.The research showed that the outer surface contact angle of the heat exchange tube could reach 154.0±0.5°,and the total heat transfer coefficient could reach 2664.3 W m-2·K-1.Compared with that previous superhydrophobic modification,the total heat transfer coefficient was increased by 117.5%.It could be seen that the rough structure was constructed on the surface of the heat exchange tube,which could significantly improve the heat transfer performance of the heat exchange tube.In this paper,the total heat transfer coefficient of the plastic heat exchanger prepared by two-step coating method was 147.3%higher than that of prepared by melting method.Compared with the heat exchanger prepared by NIPS method,the total heat transfer coefficient increased by 85.3%.It can be seen that the plastic heat exchanger prepared by two-step coating method had better heat transfer performance.This study is of great significance to promote the development of plastic heat exchanger.