Research On Heat Transfer Enhancement Method And Performance Of Polypropylene Hollow Fiber Tube Plastic Heat Exchanger

Tubular metal heat exchanger plays an important role in the fields of chemical industry,petroleum,pharmacy,energy,thermal desalination and so on.However,there are many long-term problems such as corrosion and surface scaling.In recent years,the tubular plastic heat exchanger with polymer hollow fiber tube as heat exchange element has become one of the important research directions of heat exchanger technology because it can solve the problems exist in metal heat exchanger.However,its low heat transfer performance hinders its popularization and application.Aiming at the problem of poor heat transfer performance of tubular plastic heat exchangers,in this paper,melt-spun polypropylene（PP）hollow fiber tubes are used as the base material,m-phenylenediamine and trimesyl chloride are used as active monomers.An interfacial polymerization reaction occurs on hydrophobic outer surface of the tube,and a modified PP heat transfer tube M₁ with partial attached hydrophilic polyamide composite layer was prepared,so as to construct the combined surface for steam condensation containing both hydrophilic and hydrophobic regions.Through the synergistic mechanism between the filmwise condensation on the hydrophilic region and the dropwise condensation on the hydrophobic region successfully,the heat transfer performance was enhanced.SEM,surface roughness,FT-IR,contact angle and tensile properties of M₁ were characterized.The effects of aqueous monomer content C₁,organic monomer content C₂,organic phase soaking time t₁ sweeping time t₂,and reaction time t₃ on the heat transfer performance of M₁were experimentally studied.The optimized results of interfacial polymerization modification parameters were obtained.When aqueous monomer content C₁ is 80g·L^-1,organic monomer content C₂ is 8.0 g·L^-1,organic phase soaking time t₁ and sweeping time t₁ is 60 min,sweeping time t₂ is 15 s,and reaction time t₃ is 60 s,the performance of M₁ is optimal.The total heat transfer coefficient K of steam condensation,heat transfer coefficientα_o of steam condensation outsaide the tube is as high as 2295 W·m^-2·K^-1、9619 W·m^-2·K^-1,respectively.Compared with the original tube before modification,K andα_o have increased by 87.29%and 359.8%,respectively.On the basis of the above research,the heat transfer enhancement method and performance of PP hollow fiber heat exchanger were further studied from the aspects of adding surfactant to promote the interfacial polymerization to prepare modified PP heat exchange tube M_2,heat exchanger placement,fluid flow direction,flow rate,temperature and other processes,heat exchanger loading density and.tube weaving The SEM,surface roughness and tensile properties of M₂ were characterized.In addition,the influence of preservation method of heat exchange tube on heat transfer performance of heat exchanger was also studied.When the dosage of sodium lauryl sulfate（surfactant）is 2.0 g·L-1,the performance of M₂ is the best.The total heat transfer coefficient K of heat exchanger prepared by M₂ is 106.7%and 26.20%higher than that of original tube and modified M₁.Under the conditions of 5.4%loading density,cold fluid inlet temperature 20℃and flow rate is 0.082 m·s^-1,vertical placement of heat exchanger and counter flow operation of cold and hot fluids.After the performance test of the new heat exchanger,the test was run for 12 hours after 60days of wet storage.Compared with the new made heat exchanger,the heat transfer performance did not change significantly.In this paper,a hydrophilic and hydrophobic composite surface was constructed on the outer surface of a PP hollow fiber tube successfully by an interfacial polymerization method.The heat transfer enhancement method and performance research on a PP hollow fiber controlled plastic heat exchanger were carried out.This research is of great significance to promote the development and industrial application of plastic heat exchangers.