Preparation Of PVDF Hollow Fiber Heat Exchange Tubes By Wet Spinning And Study On Heat Transfer Enhancement

The tubular heat exchanger with metal tubes as the heat exchange elements was a heat exchange equipment used widely in thermal desalination.However,the problems about corrosion of metal and fouling of tube surfaces existed for a long time in its application.In recent years,tubular plastic heat exchanger made of fluoroplastic heat exchange tubes was one of research hotspots in heat transfer field due to corrosion resistance and anti-pollution of fluoroplastics.Nonetheless,the low thermal conductivity of heat exchange tubes hindered the promotion and application of tubular plastic heat exchanger.To solve the problem that plastic heat exchange tubes presented a low thermal conductivity,the surface hydrophilic(PVDF/SPES)and surface hydrophobic(PVDF)hollow fiber heat exchange tubes with dense/non-dense layer composite structure were prepared by controlling the content and sulfonation degree of sufonated polyethersulfone(SPES)in the casting solution during the course of non-solvent induced phase separation(NIPS).The outer surface contact angle of PVDF/SPES and PVDF tubes,ere 49.8°±0.5° and 78.1°±0.3°,respectively.The outer dense layer of hollow fiber tubes was used to blocked the fluids in tube side and shell side of heat exchanger.and the non-dense layer was filled with water that had a higher thermal conductivity than PVDF matrix to improve the thermal conductivity of heat exchange tubes.In this paper.single surface hydrophobic and hydrophilic heat exchange tube were weaved together to prepare PVDF tubular plastic heat exchanger,which,on the one hand,could increased the fluid disturbance in radial direction of heat exchange tube on its surface to strengthen the convective heat transfer performance of fluids in tube side and shell side of heat exchanger,on the other hand,could built a hydrophilic/hydrophobic combination surface for steam condensation in the shell of heat exchanger to strengthen steam condensation heat transfer on the combination surface by using the synergistic effect between hydrophilic and hydrophobic areas.Finally,the heat transfer enhancement of PVDF tubular plastic heat exchanger in steam condensation process was performed by above-mentioned two methods and the means of filling water in non-dense layer of heat exchange tube to improve its thermal conductivity.In this paper,the preparation,structure and performance characterization of hollow fiber surface hydrophilic and hydrophobic heat exchange tubes,and the methods of strengthen steam condensation heat transfer by weaving hollow fiber surface hydrophilic and hydrophobic heat exchange tubes,and building hydrophilic/hydrophobic combination surface were studied deeply.The results showed that compared with hydrophobic surface of dense hollow fiber PVDF heat exchange tubes prepared by melt-spinning method,the thermal conductivity on surface hydrophilic and hydrophobic hollow fiber heat exchange tubes prepared by NIPS method were both improved about 2.7 times.Compared with the non-woven surface hydrophilic heat exchange tube.the steam condensation total heat transfer coefficient(K)of non-woven surface hydrophobic heat exchange tube was slightly higher.For a single hydrophilic or hydrophobic surface.compared with non-woven heat exchange tube,the value of K on woven heat exchange tube surface was increased by about(10.8±0.3)%.When the heat exchange tubes were woven,compared with single hydrophilic and hydrophobic surface,the value of K on hydrophilic/hydrophobic combination surface increased by(36.2±0.2)%and(27.6±0.3)%.respectively.In this paper,PVDF tubular plastic heat exchangers were developed by preparing surface hydrophilic and hydrophobic heat exchange tubes.and could strengthen its heat transfer process.This study is of great significance to promote the de?velopment of tubular plastic heat exchangers.