Preparation Of PVDF Heat Transfer Capillary By Wet Spinning And Its Properties

The metals, such as copper, aluminum, titanium and stainless steel, etc, are used for the traditional heat exchanger. The most common problems of metal heat exchangers are corrosion and fouling, especially in a caustic environment. Because of the high metal prices, many scholars use low-cost aluminum alloy material and modify its surface, and they has obtained certain effect of anti-corrosion. In recent years, scientists and engineers have studied polymer-based heat exchangers to find solutions to solve the problems of metal heat exchangers. As known, the advantages of polymers over metals as heat exchanger materials include excellent resistance to corrosion and fouling, ease of molding, manufacturing, and maintenance, etc. Now the plastic heat exchanger has been widely applied in chemical, pharmaceutical, food, petroleum, metallurgy, and semiconductor industries.The heat exchangers of polymer material have the problem of low thermal conductivity. This paper proposes PVDF heat exchange capillary tubes based on capillary wetting mechanism. It is shown that heat transfer has been promoted by the air gap of the capillary surface. However, thermal transmission is hindered by the air gap of the capillary surface for the low conductivity of air. The air gap of the micropores in the tube wall would be filled up with water after the micropores of the tubes wall being hydrophilized which means that water in the micropores would form micro-convection by the temperature difference between two sides of the tube wall. Thus the heat transfer coefficient could be significantly improved.First of all, PVDF heat exchange capillary tubes with porous structure were prepared by nonsolvent induce phase separation, the heat transfer process was intensified by wetting the air gap of the capillary surface, and their mechanical performance, inside and outside water contact angle, air tightness, internal porosity, structure and heat transfer coefficient were characterized. The heat transfer mechanism of microporous in the heat exchange capillary tube was revealed.Results showed that the heat conductivity coefficient of monolayer heat exchanger capillary tube can be improved of 270% after being hydrophilized. The heat transfer coefficient of monolayer heat exchanger capillary tube can be improved of 40% after being hydrophilized.It is difficult for the monolayer heat exchange capillary tubes to be infiltrated by water since their outer surface are relatively dense. So the dual layer heat exchange capillary tube were prepared which a hydrophilic outer layer was composited on the monolayer heat exchange tube. The dense outer layer of the monolayer heat exchange tube was removed and the porosity of the heat exchange tube was improved. Compared to the tube by TIPS, the heat conductivity coefficient of dual layer hollow fiber heat exchanger can be improved of 140% after being hydrophilized. Compared to the monolayer tube, the heat conductivity coefficient of the dual layer tube can be improved of 22% after being hydrophilized. Compared to the tube by TIPS the heat transfer coefficient of dual layer heat exchanger tube can be improved of 80% after being hydrophilized.For PVDF heat exchange capillary tubes, the heat transfer coefficient is higher when the water vapor is in the tube side than in the shell side. The heat transfer coefficient was investigated with the water vapor in the shell side. The results show that the heat transfer coefficient increases firstly and then decreases with increasing packing fraction and reaches maximum value with 15% packing fraction.