【作者】 朱登亮；

【导师】 吴金星；

【作者基本信息】 郑州大学 ， 热能工程， 2007， 硕士

【摘要】 提高换热器的换热效率和减小压降是换热器研究的主要目的，而换热器内部流体的流动状态是影响换热器综合性能的重要因素，因此，只有了解流体流动的规律才能找到提高换热效率和减小压降的方法。本文以螺旋流动为研究对象，分析了传热系数和压降的影响因素，并运用到新型换热管和换热器的开发研究，通过实验测试了新型换热器的性能，结果表明，新型换热器的综合性能明显优于折流杆换热器。本文的主要研究内容及取得的主要成果如下：(1)以管内螺旋流动为研究对象，以换热管内置扭带为模型，分别用解析和数值模拟的方法分析了管内螺旋流动，讨论了扭比和雷诺数对流体流动和传热的影响，得出螺旋流动强化传热的机理主要是：扭带使管内流体作螺旋流动，提高了流速，随之次流也增强，减薄了流动边界层和传热边界层，从而强化了管内的对流换热。螺旋流道的截面积沿轴向没有变化，流体没有产生涡和回流，流体流动连续通畅、稳定。提高雷诺数、减小扭比都可提高流体的流速，使传热系数增大，从而强化了管内的对流传热。(2)以管外螺旋流动为研究对象，以螺旋扭片套管换热器为模型，用同样的方法分析了管外螺旋流动，讨论了螺旋角和雷诺数对管外螺旋流动和传热的影响，得出管外螺旋流动与管内螺旋流动有着相同的强化传热机理，同样可以提高传热系数。管外螺旋流道的横截面积沿轴向不会变化，不会出现涡和回流，流体流动连续通畅、稳定。管外螺旋流动和管内螺旋流动不同的是扭片和扭带的作用范围，扭片的作用范围较小，对流体的影响比扭带小，做结构设计时应尽可能扩大扭片的作用范围。(3)在对螺旋流动研究的基础上，汲取螺旋折流板换热器的优点，开发出了一种新型换热管——螺旋肋片换热管和由这种换热管组装成的新型换热器——螺旋肋片自支撑管壳式换热器。对新型换热管的结构做了设计，设计了新型换热管的加工工艺。对新型换热器进行了结构设计，说明了这种换热器的组装方法。新型换热器中的螺旋肋片既增加了传热面积、诱导流体做螺旋流动，又起到支撑管束保持管间距的作用，完全取代了折流板。螺旋肋片换热器具有较高的传热系数和较低的压降，综合性能明显提高，并且结构简单、制造方便，另外，换热管上的支撑点多，约束增加，具有较好的防振和抗振性能。(4)建立了同向肋片管束和反向肋片管束的三维模型，进行了数值模拟。模拟结果表明，传热得以强化，而压降提高不大；反向肋片管束能使各单个旋流相互促进，旋流得到加强，总体性能优于同向肋片管束。通过对螺旋角的优化，确定了螺旋角的最佳取值范围为20°＜α＜25°。(5)用实验的方法测定了螺旋肋片换热器的换热和流体流动性能，并与数值模拟结果做了对比，证明了数值模拟的可行性。在相同的实验条件下做了折流杆换热器的性能实验，并与螺旋肋片换热器进行了对比。结果表明，螺旋肋片换热器总传热系数高于折流杆换热器，而流阻低于折流杆换热器，综合性能明显提高。得出了螺旋肋片换热器传热准数关联式，为工程应用奠定了基础。更多还原

【Abstract】 It is the main purpose of research on heat exchanger to increase heat transfer efficiency and reduce pressure drop. The important factor which affects the comprehensive performance of heat exchanger is fluid flow conditions in heat exchanger. So, only by understanding the law of fluid flow can it be found to improve heat transfer efficiency and reduce pressure drop. In this paper, the spiral flows have been studied as research object, the influential factors of the heat transfer coefficient and pressure drop has been analyzed, and the new type of tube and heat exchanger has been researched and developed by using the results. The performance of this new type of heat exchanger has been tested by experiment. The results show a better performance of this kind of heat exchanger than the rod baffler heat exchanger. The main works and productions in this paper are as follows:(1) The spiral flows in the tube have been analyzed by using method of numerical and analyses in which the model of tube with twisted tape inserts had been set up. The effects of twist ratio and Reynolds number on fluid flow and heat transfer have been discussed. The enhanced heat transfer mechanism of spiral flow is: twisted tape can induce spiral flow so that the flow velocity and the secondary flow are increased, the flow boundary layer and heat transfer boundary layer are thinned, and the convection heat transfer is enhanced. The cross-sectional area of spiral duct along the axis doesn’t change, and fluid doesn’t produce vortex and return fluid flow, and the movement of fluid is fluent and stable continuously. The velocity and heat transfer coefficient can be increased by increasing Reynolds and reducing twist ratio, thus convective heat transfer is enhanced.(2) Spiral flows around tube have been researched by using the same method in which the model of double-tube heat exchanger with spiral tape has been set up. The effects of helical angle and Reynolds number on fluid flow and heat transfer have been discussed. The results reveal the same mechanism of enhanced heat transfer of spiral flows both in tube and around tube. The cross-section area of spiral duct around tube along the axis will not change, so vortex and return fluid flow fluid will not be produced. The difference between spiral flow around tube and in tube is the action area. The spiral tape exert less influence on fluid than twisted tape because its small action area. It is necessary to enlarge action area of spiral tape in structure design.(3)A new type of tube, helical rib tube, and heat exchanger, helical ribbed self-support type heat exchanger, have been developed based on above research and the merits of helical baffle heat exchanger. The structure of this new type of tube has been designed. This new type of tube has been manufactured by designing a proper processing technique. The helical ribs in heat exchanger can substitute for baffle plate because it will increase heat transfer area, induce spiral flow, and support tube bundle and tube. The structure and assembly method of this new type of heat exchanger have been designed. The helical ribbed self-support type heat exchanger has the merits of higher heat transfer coefficient, lower pressure drop, good compressive performance, and simple structure. The supports and restrictions for tubes are so many that can produce the favorable antivibration capability.(4) The three dimensional models of two kind of tube bundle have been set up, the velocity field, the pressure field and temperature field have been simulated. The results reveal the enhanced heat transfer and lower pressure. The different spiral flows are promoted each other because of the tube bundle arranged ribs with the different spiral directions. The comprehensive performance of tube bundle with different spiral direction is better than the same direction. The best range of spiral angle has been determined which is from 20°to 25°by optimizing.(5) The performance of helical ribbed self-support type heat exchanger has been tested by experiment, and the results have been contrasted with the simulation results which show the feasibility of numerical simulation. The performance experiment of rod baffle exchanger with the same conditions with helical ribbed self-support type heat exchanger has been done, and the results have been contrasted. The conclusions are attained that the total transfer heat coefficient of helical ribbed self-support type heat exchanger is higher than that of rod baffle heat exchanger and the pressure drop is lower than its, the comprehensive performance is heightened distinctly. The relationship formula of heat transfer has been attained by disposing the data of experiments, and can provide reference for engineering application.更多还原