纽带管内流体强化换热及抗垢特性研究

发布时间：2018-08-20 17:51

【摘要】：纽带作为一种高效强化换热的扰流元件,广泛应用于化工设备的强化换热、防垢、流体混合等领域。国内外学者针对内置纽带管内部流体流动及强化传热开展了诸多研究,但纽带的强化换热性能还需要进一步提高。本文针对纽带管研究的流动工况较少,普通纽带管强化传热综合性能欠佳,结构优化不够全面等问题,开发了三边纽带,用Fluent 15.0模拟了内置普通纽带、格栅纽带以及三边纽带在湍流(Re=5000~30000)和层流(Re=400~1500)工况下管内流体传热和阻力特性,并与圆管进行对比,结果表明三边纽带管的综合性能较好;并进一步从纽带边数n、扭率y、边长m对纽带管进行了结构参数的优化;最后模拟分析了圆管及纽带管的抗垢性能,得到的结论如下:数值模拟结果表明,内置纽带管能使流体产生螺旋流动,诱导流体产生偏离轴线方向的径向及切向流动,从而加剧近壁区流体与主流区流体的掺混,减薄流体速度和温度边界层,加速管壁热量向管内流体的传递,提高了管壁处流体的对流换热系数。湍流工况下模拟结果表明,三边纽带管的Nu较大,格栅纽带管和普通纽带管传热性能相当,Nu最小;纽带管对应的阻力系数f从高到低依次是:格栅纽带、三边纽带和普通纽带;三边纽带管的综合性能评价因子η高于其他纽带管。对纽带管结构参数的优化结果表明,Nu和f随着纽带边数和边长的增加而增加,随着扭率的增加而减小;通过对比各参数纽带管的综合性能发现,扭率y=2.0、边长m=9mm的三边纽带管的综合性能较好,综合性能评价因子η=1.33,分别比圆管和普通纽带管高出11.9%~33.2%,5.47%~5.98%。层流工况下模拟研究表明,除五边纽带管外,边数越多,Nu越大。Nu和f随边数和边长的增加而增加,随扭率的增加而减小;模拟得出y=2.0,m=9mm的三边纽带管的综合性能较好,综合性能评价因子η达到4.96。对圆管及纽带管的抗垢性能研究表明,纽带管内流体的螺旋流动冲刷管壁,使Ca Co3颗粒污垢径向分布比较均匀,在换热管内不易沉积,其抗垢性能明显优于圆管。计算得到的圆管、普通纽带管和三边纽带管的颗粒污垢不均匀系数(CV)分别为:8.72%,3.71%,3.22%,不均匀系数越小表明纽带管的抗垢性能越好;通过对比研究粒径为5um、10um和20um的颗粒污垢分布特性得出,污垢颗粒的直径影响换热管的抗垢性能,在所研究的粒径范围内,颗粒直径越大,换热管越容易结垢。
[Abstract]:As a kind of high efficiency heat transfer spoiler, tie is widely used in the fields of chemical equipment, such as enhanced heat transfer, scale prevention, fluid mixing and so on. Scholars at home and abroad have carried out a lot of research on fluid flow and enhanced heat transfer in the inner tube, but the enhanced heat transfer performance of the tie still needs to be further improved. In this paper, a trilateral tie is developed and simulated by Fluent 15.0, aiming at the problems of less flow conditions, poor comprehensive heat transfer enhancement and structural optimization of the tie tube. The characteristics of heat transfer and resistance in the tube under turbulent (Re=5000~30000) and laminar flow (Re=400~1500) conditions are compared with those of the circular tube. The results show that the comprehensive performance of the triangular-tie tube is better than that of the circular tube. Furthermore, the structural parameters of the tie tube are optimized from the following aspects: the number of the tie edges n, the torsion ratio yand the length m. Finally, the anti-fouling performance of the circular tube and the tie tube is simulated and analyzed. The conclusions are as follows: the numerical simulation results show that, The inner tie tube can make the fluid produce spiral flow, induce the fluid to produce radial and tangential flow away from the axis, and thus aggravate the mixing of the near wall fluid with the mainstream fluid, and reduce the velocity and temperature boundary layer of the fluid. The heat transfer from the tube wall to the fluid in the tube increases the convection heat transfer coefficient of the fluid in the tube wall. The simulation results under turbulent conditions show that the Nu of the triangulated tie tube is larger, the heat transfer performance of the grid tie tube and the ordinary tie tube is equivalent to that of the Nu, and the resistance coefficient f of the tie tube is in order from high to low: the grid tie, the trilateral tie and the ordinary tie. The comprehensive performance evaluation factor 畏 of trilateral tie tube is higher than that of other tie tubes. The optimization results of the structural parameters of the tie tube show that Nu and f increase with the increase of the number and length of the tie edges, and decrease with the increase of the torsion ratio. The torsion ratio is 2.0 and the side length m=9mm trilateral tie tube has better comprehensive performance, and the comprehensive performance evaluation factor 畏 1.33 is higher than that of circular tube and ordinary tie tube by 11.9and 33.2and 5.475.98, respectively. The simulation results under laminar flow condition show that the more Nu and f increase with the increase of the number of edges and the length of the edges, and the decrease with the increase of torsion ratio, the simulation results show that the comprehensive performance of the trilateral tie tube with yyong 2.0mm is better than that of the tube with 9mm. The comprehensive performance evaluation factor 畏 is 4.96. The study on the anti-fouling performance of the circular pipe and the tie tube shows that the spiral flow of the fluid in the tie tube scour the wall of the pipe, which makes the fouling distribution of Ca Co3 particles more uniform, and it is not easy to deposit in the heat transfer pipe, and its anti-fouling performance is obviously better than that of the circular tube. The calculated non-uniform coefficient of particle fouling of round tube, common tie tube and trilateral tie tube is (CV) of 8.72and 3.71and 3.22 respectively. The smaller the non-uniformity coefficient is, the better the anti-fouling performance of tie tube is. By comparing the characteristics of fouling distribution between 5um 10um and 20um particles, it is concluded that the diameter of fouling particles affects the anti-fouling performance of heat transfer tubes. The larger the particle diameter is, the easier the heat exchanger tube is to scale in the range of the studied particle diameter.
【学位授予单位】：郑州大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ055.81

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