恒壁温工况下螺旋管内流体流动及传热性能模拟研究

发布时间：2018-06-04 04:02

本文选题：螺旋管 + 数值模拟　；参考：《兰州交通大学》2016年硕士论文

【摘要】：螺旋管即可作为缠绕管式换热器的基本结构,亦可单独作为一种换热设备,具有换热效率高、结构紧凑、可自伸缩性等优点,在石油化工、低温制冷、航空航天等领域具有广泛应用。螺旋管作为一种高效换热设备,一直是强化传热领域关注的焦点。目前对于螺旋管的相关研究主要集中在圆形截面,关于矩形截面螺旋管内流体流动及传热性能方面的研究鲜有报道,同时从场协同角度分析螺旋管强化传热内在机理的研究亦不多见。本文总结了国内外螺旋管的研究现状,简单介绍了强化传热技术及场协同理论。在前人的基础上,应用数值计算方法,建立了三维螺旋管物理及数学模型,根据Fluent软件工作流程,分别计算了恒壁温工况下,圆形截面及矩形截面螺旋管内流体在层流、湍流时的流动及传热情况,通过管内流体的平均努塞尔数Nu及进出口压降损失ΔP来评价不同几何参数下这两种截面螺旋管的传热及流阻性能。引用综合性能评价因子η,对比分析了管内流体平均速度v、螺距P、螺旋直径D及横截面积对两种截面螺旋管的流阻、传热及强化传热性能的影响。考虑了在横截面积相等的情况下,改变矩形截面形状对管内流体的流动、传热及强化传热性能的影响。从场协同的角度,对这两种截面螺旋管强化传热的内在机理进行了对比分析,并通过速度场与温度场之间的夹角对比分析了两种截面螺旋管内流体的协同性能随螺距、螺旋直径、及横截面积的变化规律。结果表明,这两种截面螺旋管内流体在层流、湍流流态下流动时均会出现二次流现象,靠近入口处,二次流对管内流体流动及传热的影响基本可忽略不计,随着转角上升,二次流作用加强,受截面形状及流态的影响,管内流体的速度、温度会呈现不同的分布形状。改变两种截面螺旋管的几何参数,管内流体的Nu、ΔP及η均会呈现不同的变化规律,相比较圆形截面螺旋管的流阻、传热、强化传热性能均要优于矩形截面。另外截面面积相等时,宽扁形矩形截面的强化传热性能要优于窄高形截面。速度场与温度场的夹角随螺旋管几何参数变化规律与管内流体流动及传热的变化规律基本相一致,说明场协同理论可解释螺旋管强化传热随几何参数变化规律的内在机理。
[Abstract]:The spiral tube can be used as the basic structure of the winding tube heat exchanger, or as a separate heat exchange equipment, with the advantages of high heat transfer efficiency, compact structure, self-scalability, etc., in petrochemical industry, low temperature refrigeration, Aerospace and other fields have a wide range of applications. Spiral tube, as an efficient heat exchanger, has always been the focus of attention in the field of heat transfer enhancement. At present, the research on helical tube is mainly focused on the circular section. There are few reports on the fluid flow and heat transfer performance in the rectangular spiral tube. At the same time, it is rare to analyze the internal mechanism of heat transfer enhancement in helical tubes from the point of view of field synergy. In this paper, the research status of helical tube at home and abroad is summarized, and the enhanced heat transfer technology and field synergy theory are briefly introduced. On the basis of previous studies, the physical and mathematical models of three-dimensional spiral tube are established by using numerical method. According to the working flow of Fluent software, the laminar flow in spiral tube with circular section and rectangular section under constant wall temperature condition is calculated, respectively. For turbulent flow and heat transfer, the heat transfer and flow resistance of the two kinds of helical tubes with different geometric parameters are evaluated by the average Nusselle number Nu of the fluid in the tube and the pressure drop loss 螖 P of the inlet and outlet. Based on the comprehensive performance evaluation factor 畏, the effects of fluid average velocity, pitch P, helical diameter D and cross sectional area on the flow resistance, heat transfer and enhanced heat transfer of two kinds of spiral tubes with different cross-sections are compared and analyzed. The effects of changing the shape of rectangular section on the flow, heat transfer and enhanced heat transfer of the fluid in the tube are considered under the condition of equal cross-sectional area. From the point of view of field synergy, the internal mechanism of heat transfer enhancement in these two kinds of spiral tubes is compared and analyzed, and the synergetic performance of the two kinds of helical tubes with helical pitch is analyzed by comparing the angle between velocity field and temperature field. The variation of spiral diameter and cross-sectional area. The results show that the secondary flow occurs in the laminar flow and turbulent flow in the two kinds of spiral tubes, and the influence of the secondary flow on the fluid flow and heat transfer in the pipe is negligible when the flow is near the entrance, and increases with the angle of rotation. Due to the influence of cross section shape and flow state, the velocity and temperature of the fluid in the tube will be distributed in different shapes. By changing the geometric parameters of the two kinds of helical tubes, the flow resistance, heat transfer and heat transfer enhancement of the circular spiral tubes are better than those of the rectangular ones. In addition, when the cross section area is equal, the heat transfer enhancement performance of wide flat rectangular section is better than that of narrow high section. The angle between velocity field and temperature field is basically consistent with the variation law of fluid flow and heat transfer in the helical tube, which indicates that the theory of field synergy can explain the inherent mechanism of the law of heat transfer enhancement of helical tube with the change of geometric parameters.
【学位授予单位】：兰州交通大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TU83

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