管内波流螺旋自动清洗技术及传热性能研究

发布时间：2018-10-12 13:02

【摘要】：管内插钢丝螺旋线圈是管式换热器实现在线清洗和强化传热的一种重要手段,在节能领域具有一定的工程应用价值。本文是在换热管内插工作螺旋的基础上,提出将波动入口流速与管内运动螺旋相结合的方式应用于换热管内,利用波流驱动工作螺旋往复运动,实现换热管内在线进一步均匀清洗和强化传热的目的,主要内容如下:(1)对波流螺旋自动清洗技术及其强化传热的可行性进行了分析。基于波流螺旋自动清洗技术可行的充要条件是工作螺旋往复运动行程须超过自身一个螺距以上,对工作螺旋在管内受力进行了理论分析,在管内沿轴向方向,工作螺旋受到流体的轴向冲击力与受到柔性弹簧的约束轴向力受力平衡,推导出使螺旋能够实现往复运动的入口流速计算方法,提出一种使恒定流速转变为波动流速的阀门控制装置,验证了波流产生的现实可行性。(2)通过搭建实验平台对四种不同参数工作螺旋的起振流速及不同入口流速下螺旋的轴向伸长量进行了试验研究。结果表明不同参数的工作螺旋具有不同的起振流速;工作螺旋在不同流速作用下沿轴向平移的距离不同,验证了波流作用下的工作螺旋可以实现往复运动;波流作用下的工作螺旋达到清洗目的的初始流速应该大于螺旋的起振流速;波动流速大小则由柔性弹簧弹性系数与工作螺旋往复运动距离确定,柔性弹簧弹性系数越小,所构造的入口波动流速的波幅可以越小。(3)对管内波流螺旋清洗能力与传热性能进行了数值模拟分析。对静止螺旋在恒定入口流速流体作用下所受的轴向力大小的模拟结果显示,入口流速越大,螺旋长度越长,螺旋受到的轴向力越大;内插螺旋在流体中阻力系数随入口流速的增大而减小,随螺旋长度的增长而减小。波动流速对空管流动和传热影响的数值模拟研究显示,当波流流速变化的频率大到一定程度,管出口静压会大于入口静压,流体出现回流,基于管内综合性能评价因子随时间变化的图像显示,在所研究波流流速参数作用下,波流可以强化管内传热。建立正交实验表,分析波流的三个参数:初始流速、振动频率、流速振幅对内插螺旋换热管强化传热和清洗能力的影响,对传热效能的影响的三因素重要性排序为:初始流速、振动频率、流速振幅,波流流速大小在区间为0.1~2m/s之间变化能够强化传热;对清洗能力的影响的三因素重要性排序为:流速振幅、初始流速、振动频率,配合不同弹性系数的柔性弹簧,波流作用下的内插工作螺旋能够实现自动清洗效果。对于清洗能力的因素分析,是以使工作螺旋的往复行程达到一个螺距以上的轴向力波动差值大小作为标准,定性研究波流作用下清洗能力的强弱;对强化传热能力通过定量地分析,以管内综合性能评价因子作为评判指标。
[Abstract]:As an important means to realize on-line cleaning and heat transfer enhancement of tubular heat exchangers, inserted steel wire helical coils have certain engineering application value in the field of energy saving. On the basis of inserting the working screw into the heat transfer pipe, this paper puts forward the method of combining the fluctuating inlet velocity with the moving spiral in the tube and using the wave current to drive the working screw reciprocating motion. The main contents of the paper are as follows: (1) the technology of wave flow spiral automatic cleaning and the feasibility of heat transfer enhancement are analyzed. Based on the feasibility of wave and current spiral automatic cleaning technology, the necessary and sufficient condition is that the working screw reciprocating travel must be more than one pitch of itself, so the force of the working screw in the pipe is analyzed theoretically and along the axial direction in the pipe. The axial impact force of the working screw is balanced with the axial force of the flexible spring, and the method of calculating the inlet velocity of the helix is derived, which enables the screw to realize reciprocating motion. A valve control device for changing constant velocity to fluctuating velocity is proposed. The practical feasibility of the wave and current generation is verified. (2) the axial elongation of the helix under different inlet velocity and four different parameters working helices are studied experimentally by setting up an experimental platform. The results show that the working helix with different parameters has different starting velocity, and the distance of axial translation of the working helix under different velocity of velocity is different, which verifies that the working spiral under the action of wave and current can realize reciprocating motion. The initial velocity of the working spiral under the action of wave and current should be larger than the starting velocity of the spiral, and the magnitude of the wave velocity should be determined by the distance between the elastic coefficient of the flexible spring and the reciprocating movement of the working spiral, and the smaller the elastic coefficient of the flexible spring is, The wave amplitude of the constructed inlet wave velocity can be smaller. (3) numerical simulation analysis is carried out on the cleaning ability and heat transfer performance of the wave-current spiral in the tube. The simulation results show that the larger the inlet velocity, the longer the helical length and the greater the axial force on the helix. The drag coefficient decreases with the increase of inlet velocity and the length of spiral in fluid. The numerical simulation of the influence of wave velocity on the flow and heat transfer of air pipe shows that when the frequency of wave flow velocity changes to a certain extent, the static pressure at the outlet of the tube will be greater than the static pressure at the inlet, and the fluid will return back. Based on the image of the time varying of the comprehensive performance evaluation factor in the tube, it is shown that the wave and current can enhance the heat transfer in the tube under the action of the studied parameters of the velocity of wave and current. An orthogonal experimental table was established to analyze the effects of three parameters of wave and current: initial velocity, vibration frequency and amplitude of velocity on the enhancement of heat transfer and cleaning ability of an interpolated spiral heat exchanger tube. The order of importance of three factors to the heat transfer efficiency was as follows: initial velocity. The change of vibration frequency, velocity amplitude, wave and current velocity between 0.1~2m/s can enhance heat transfer, the order of importance of three factors on cleaning ability is as follows: velocity amplitude, initial velocity, vibration frequency, With the flexible spring with different elastic coefficients, the interpolated working spiral under the action of wave and current can realize the automatic cleaning effect. The factor analysis of cleaning ability is to make the reciprocating stroke of the working screw reach the value of axial force fluctuation of more than one pitch as the standard, and qualitatively study the strength of cleaning ability under the action of wave and current. Through the quantitative analysis of the heat transfer enhancement ability, the evaluation factor of the comprehensive performance in the tube is taken as the evaluation index.
【学位授予单位】：湘潭大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TK172

【相似文献】