毕业设计论文
姓 名： 111111 学 号： 000000000 学 院： 能源与动力工程学院 专 业： 热能与动力工程 题 目： 圆形螺旋管流动和传热特性研究
指导教师：
2012 年 6 月
摘 要 摘 要
螺旋管在热力、化工、石油及核工业等领域得到了广泛应用，螺旋管换热器也具有结构简单、传热系数高等优点。它的传热系数比直管高，在相同空间里可得到更大的传热面积，布置更长的管道，减少了焊缝，提高了安全性。尽管螺旋管的流体阻力增大，压降增大，但是其传热效率的提高导致能量的节约要高于因阻力增大而消耗的能量。因此，螺旋管在许多行业得到普遍应用而倍受青睐。在工程应用中，由于工艺要求，往往需将流体加热至规定的温度范围，传热是其中的基本单元操作，所以有必要对螺旋管的传热与流动特性进行研究。从理论知识我们知道由于向心力的作用，流体从管中心部分由螺旋管内侧流向外侧壁面，因而造成了螺旋管内侧的低压区。在压差作用下，流体从外侧沿着圆管的上部和下部壁面流回内侧。这种流动是与管的轴向垂直的，也就是与流体的主体流动相垂直，称为二次流。流体的这种二次流与轴向主流复合成螺旋式的前进运动。这样，对于流体的传热传质，不仅可依靠流体的径向扩散，还有径向二次流的作用，相当于边界层进行了破坏，增强了流体传质。本文采用数值模拟的方法对圆形螺旋管的截面管进行分析，在应用FLUENT软件，对圆形螺旋管道内流体紊流流动状态下的流场进行数值模拟，分析圆形螺旋管内流场及影响因素，包括速度的分布、温度以及二次流对流场的影响。本文首先概述了圆形螺旋管的应用背景及分析意义，对GAMBIT及FLUENT进行了简单的介绍，而后进行了分析。通过在GAMBIT中建模以及划分网格定义边界条件，在FLUENT中设定初始条件进行数值模拟，进一步分析在紊流条件下流体在圆形螺旋管中换热的影响因素。通过数值模拟得出了结论，入口雷诺数对圆形螺旋管的整个流场影响较大，管道内流体压降与流体流速大小成正比。速度越大圆形螺旋管中流体压降越大。由此，我们可以增大管道雷诺数从而达到改善流场流动的目的。同时，流体入口速度的大小又影响整个管子中流体的二次流的流型。因此，选择合理的入口速度，可以使流体在流场中达到优化配置。
关键词: 圆形螺旋管；数值模拟；紊流；传热与流动
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Abstract Title The Research of Circular Spiral Pipe Flow and Heat Transfer Characteristics.
Abstract
Helical pipes in the field of thermal, chemical, oil and nuclear industry have been widely used. The helical heat exchanger also has a simple structure, the heat transfer coefficient higher merit. The heat transfer coefficient is better than straight, which enjoys greater heat transfer area in the same space, arranged a longer pipeline, reducing the weld and improve security. Although the fluid resistance of the coil and the pressure drop increase, the heat transfer efficiency of energy saving is higher than the energy consumed by the resistance increases. Therefore, helical pipes have been widely used in many industries. In engineering applications, due to process requirements, often takes the fluid heated to the specified temperature range and heat transfer is the basic unit of operation. So it is necessary to study the helical heat transfer and flow characteristics. From theoretical knowledge, we know that the role of the centripetal force, which the fluid from the tube central part of the inside by the helical flow to the outer wall, resulting in a spiral the inside area of low pressure. Under differential pressure, the fluid flows back to the inside along the upper and lower wall of the tube from the outside. This flow which is vertical to the axial of the tube is perpendicular to the main flow with the fluid, known as secondary flow. This secondary flow of the fluid is axial mainstream into a spiral forward motion. Thus, the fluid heat and mass transfer, can not only rely on the radial diffusion of the fluid, as well as the radial secondary flow, which is equivalent to the boundary layer is destroyed, and enhance the fluid mass transfer. In this paper, the numerical simulation method to analyze the cross-section of the circular spiral tube in the application of FLUENT software to simulate the flow field in the fluid turbulent flow state within the circular spiral pipe to analyze the flow field within the circular spiral and impact factors, including the velocity distribution, temperature, flow field and the secondary flow. The paper outlines the application background and analysis of the significance of the helical pipe of GAMBIT and FLUENT with a brief introduction, and we analyzed them. Divided by GAMBIT modeling and grid definition of boundary conditions and FLUENT in setting the initial conditions for
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Abstract numerical simulation, further analysis of the fluid in the turbulent conditions in a helical pipe heat transfer factor. Conclusion obtained by numerical simulation the entrance Reynolds number throughout the flow field in a helical pipe, pressure drop and fluid flow size is proportional to the fluid inside the tubes. The fluid pressure drop the greater the speed the greater the circular spiral. As a result, we can increase the pipe Reynolds number to achieve the purpose of improving the flow field. At the same time, the size of the fluid inlet velocity affects the flow pattern of the fluid in the secondary flow in the entire pipe. Therefore, the choice of reasonable inlet velocity, can achieve the optimal allocation of the fluid in the flow field.
Keywords: Helical Pipe; Numerical Simulation; Turbulence; Heat Transfer and Flow
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