| Most of the traditional heat exchangers are made of metal materials,which have many defects for application,such as poor corrosion resistance,scaling,unstable chemical properties and high cost,difficult to be applied in the corrosive environment.Plastic heat exchanger which has extraordinary chemical stability,corrosion resistance,hardness to scale,low investment costs has been widely applied in petroleum,medicine,semiconductor,chemistry and food processing industries.Therefore,the development of plastic heat exchangers has vital significance in modern industry.Aimed at the problem of low thermal conductivity of plastic heat exchangers,PVDF heat transfer tube is proposed with porous structure based on dry-wet spinning.The convective heat transfer coefficient was enhanced by the micro-convection of liquid in the pores.While the porosity of the polymer-based heat exchanger tube prepared by this method is influenced by solid content,stretching speed and so on,hence the higher solid content leads to lower the porosity and thus less heat transfer coefficient.And it is easy to produce defect holes in the strething process.In order to overcome the problems existing in the preparation of PVDF heat exchanger tubes by dry-wet spinning,hydrophobic PVDF hollow fiber microporous membrane and ultrafiltration PVDF hollow fiber microporous membrane were used to prepare the plastic heat exchanger tube with dense cortical and porous structure based on traditional and ultrafiltration interfacial polymerization method.The preparation of the heat exchanger tube not only ensures high porosity but also reduces the possibility of producing defective pores.The influences of the concentration of MPD in the aqueous solution,the concentration of TMC in the organic phase,the interface polymerization time,the blowing speed and time,and the tube vacuum on the membrane modules were investigated.And gas tightness,porosity,inner surface contact angle and mechanical properties of PVDF heat exchanger tube were characterized.The thermal conductivity of the tube on hydrophilization was calculated by Maxwell classical equation,and the water-water total heat transfer coefficient was measured.The experimental results showed that the heat conductivity coefficient of five kinds of heat exchanger tubes prepared by interfacial polymerization has increased by 553%,which is 158%higher than that by melt-spinning PVDF tubes.Meanwhile the larger the porosity and the greater the thermal conductivity of the tube were obtained after being hydrophilized.In the heat transfer performance test,the influence of inlet temperature difference and velocity between hot and cold fluid on heat transfer coefficient were investigated.The results show that the total heat transfer coefficient of heat exchanger tube increases with the increase of hot and cold fluid inlet temperature difference,and with the increasement of hot and cold fluid flow rate before they are stable.Compared with the heat exchanger tube based on ultrafiltration interfacial polymerization,the tube has a higher porosity and better heat transfer coefficient by traditional interfacial polymerization.The total heat transfer coefficient in the process of water-water heat transfer coefficient is higher than traditional interfacial polymerization,up to the same conditions ultrafiltration interfacial polymerization method 1.4 times,1286 W·m-2·K-1,but the air tightness is relatively poor. |
