【作者】 丛凯丽；

【导师】 李保安；

【作者基本信息】 天津大学 ， 膜科学与技术， 2010， 硕士

【摘要】 在工业生产过程中,换热器是实现能源转化和利用的最基本的设备之一。普通金属换热器易腐蚀、易结垢、价格高、重量大;用石墨、陶瓷等材料制成的换热器易碎、体积大、导热性能差和换热效率低;用贵稀金属材料制成的换热器虽然能够适应大多工况条件,但其价格昂贵,难以推广应用,仅在特定工况条件下应用;已有的塑料换热器具有体积较大,导热管管壁较粗,热阻大,传热性能较差,塑料易老化和使用温度范围较窄等缺点。提高换热器的传热性能关键是提高导热材料的导热性能。为提高换热器传热效果,扩大塑料换热器使用温度范围,本文采用耐温性较好的聚偏氟乙烯材料作为基质,并用石墨对其填充改性,制备管径小、管壁薄、导热性能好的复合材料中空纤维,并以此为导热材料制备管壳式中空纤维换热器。其中重点研究了复合材料的配方、制备条件对中空纤维力学和热学性能的影响及其规律,并对自制的导热中空纤维换热器进行“水-水”换热测试,通过改变流体流程和流量,研究流程和流量对换热器换热性能的影响及规律。研究表明,加入石墨和偶联剂之后,复合物的热稳定性提高:纯聚偏氟乙烯熔点为176℃,加入石墨后熔点升高到178℃,加入石墨和偶联剂之后熔点为178℃;偶联剂的加入使石墨起了成核的作用,促进了聚偏氟乙烯的结晶。当石墨含量分别为9%和15%时,偶联剂的最佳添加量分别为12%和15%;当石墨含量低于3%时,中空纤维的拉伸强度和断裂伸长率随着石墨含量的增加而增加;当石墨含量超过3%时,中空纤维的拉伸强度和断裂伸长率随着石墨含量的增加而降低。通过对换热器进行“水-水”换热测试,证明石墨的加入在一定程度上有利于提高聚偏氟乙烯基导热中空纤维换热器的换热性能,但是当石墨含量超过15%时,制备的中空纤维换热器的换热性能反而不如纯聚偏氟乙烯制备的,当石墨含量为3%时,换热效果最好;适当提高流体的流量有利于提高换热器的换热效果;当冷流体走换热器管程时,换热器的换热效果较好。研究表明,石墨改性聚偏氟乙烯基中空纤维换热器耐腐蚀性好、成本较低、体积小、重量轻,搬运和安装方便,单位体积内导热材料的填充率高,不易结垢、传热性能好,使用温度范围宽(可长期在120℃下使用)。更多还原

【Abstract】 Heat exchanger is one of the most basic equipment which is used to transforming and using energy in the industrial production process. Common metal heat exchangers have the disadvantage of poor corrosion resistance, poor pollution resistance, high cost and large weight; Graphite, ceramics and other materials heat exchanger have the disadvantage of fragile, bulky, poor thermal conductivity and low heat transfer efficiency; Though the heat exchanger which is made of expensive rare metal material is able to adapt to most working conditions, it has the disadvantage of high cost, be difficult to promote and be used only under certain conditions; Plastic heat exchangers has the shortcomings of bulky, thick pipe wall used to heat transfer, large thermal resistance, poor heat transfer, aging of plastic and a narrow temperature range. The key to increase the heat transfer performance of heat exchanger is improving thermal performance of heat conduction.To enhance heat transfer effects and expand the temperature range of using plastic heat exchanger, PVDF which has good temperature resistance is used as matrix and filled with graphite modification to prepare composite materials hollow fiber which has the advantage of small diameter, thin wall and good thermal conductivity in this paper. Also, using the thermal conductivity material to prepare shell and tube hollow fiber heat exchanger. The focus of study is formulation of composite materials, the influence and regularity of preparation conditions on the hollow fiber mechanical and thermal properties. Testing of "water - water" heat exchanging was made by using self-made heat conductive hollow fiber heat exchanger to research the influence and regularity of the heat exchanger performance by changing the fluid flow and flow.The results show that adding graphite and coupling agent, the thermal stability of complexes is increasing: the melting point of pure PVDF is 176℃, the melting point increased by adding graphite to 178℃, the melting point increased by adding graphite and the coupling to 178℃; Graphite played the role of nucleation by adding coupling agent, and promoted the crystallization of PVDF. When the graphite content is 9% and 15%, the optimal amount of coupling agent are 12% and 15%; when the content is less than 3%, the tensile strength and elongation of hollow fiber are as increasing as the increasing of graphite content; when the content is more than 3%, the tensile strength and elongation of hollow fiber are as decreasing as the increasing of graphite content.Through the testing of "water - water" heat exchanging, proving that adding graphite is helpful to improve thermal conductivity of PVDF-based heat conductive hollow fiber heat exchanger to a certain extent, But when the graphite content of more than 15%, the heat transfer performance of the hollow fiber is worse than that prepared by pure PVDF on the contrary. When the content of graphite is 3%, the heat transfer effect is the best; appropriately increasing the flow of fluids is helpful to improve the heat transfer effect; when the cold fluid goes though the tube of heat exchanger, the effect of heat transfer is better.The results show that graphite modified PVDF-based hollow fiber heat exchanger has the advantage of corrosion resistance, low cost, small size, light weight, easily handling and installation, the filling rate of heat conductive material in unit volume is high, anti pollution, high thermal conductivity, wide temperature range (at 120℃for long-term use).更多还原