异型钉头管强化传热及流动特性研究

发布时间：2017-12-28 00:00

本文关键词：异型钉头管强化传热及流动特性研究　出处：《青岛科技大学》2017年博士论文　论文类型：学位论文

【摘要】：随着社会的快速发展,能源的节约和合理利用已经成为当今世界各国可持续发展的主题。强化传热能提高换热设备的效率,有效缓解能源短缺问题,一直是国内外节能减排发展关注的重点问题。钉头管作为一种高效的强化传热元件,具有扩展表面、增加流体湍流程度的作用,广泛应用于石油化工、煤化工、冶金、陶瓷、建材等领域中。异型钉头虽然已被工业界所采用,但研究主要致力于钉头形状和钉头尺寸、排列方式等,且研究参数、应用领域等各不相同,没有进行最优化分析,特别是异型钉头管应用于传热系数较低的气体侧的强化传热及流动特性,缺乏系统详细的研究数据,仍无法说明哪种钉头形状具有最好的综合性能,且对其强化传热机理还缺乏统一的认识。本文采用“理论分析—数值模拟—实验验证”相结合的研究方法,对圆形、椭圆形、滴形三种不同形状异型钉头管的传热及流动特性进行了研究。从理论方面对钉头管的传热及流动特性进行分析,为数值模拟和实验等提供指导依据。以钉头管为研究对象,在风洞背景下,以分析钉头管外侧流体流动状态和换热机理为研究目的,利用当前发展比较成熟的CFD数值模拟技术和萘升华实验进行了研究。利用正交试验设计法针对圆形钉头设计9种钉头管的计算模型,并对其进行数值模拟,获得钉头管外空气侧的压力场、温度场和速度场的分布,分析钉头管的流动与传热性能。对正交试验结果进行分析,得出在以后对钉头管流动和传热性能的研究中,工作重点主要应放在每环钉头个数和钉头高度的优化上的结论。对圆形钉头管进行数值模拟,结果表明在模拟的雷诺数范围内,钉头管的压降约为光管的1.35-2.31倍,钉头管的总表面换热系数约为光管的1.10-1.72倍。钉头管的综合性能均优于光管。当钉头高度为45mm,每环钉头个数为8,纵向间距为30mm,钉头半径为5mm时,钉头管的综合换热性能约为钉头高度为25mm,每环钉头个数为4,纵向间距为30mm,钉头半径为4mm时的1.15-1.29倍。对三种不同截面形状的钉头管进行数值模拟,通过对单位质量换热量、单位面积换热量、总表面换热系数、阻力性能、综合性能的模拟结果比较,得到滴形钉头管的传热和流动特性都是三者之中最佳,说明采用滴形钉头管,可以收到强化传热和降低流阻的双重效果。对滴形钉头管钉头高度、每环钉头个数、基管高度、钉头环数、管内壁温与入口温差以及入口空气速度等进行数值研究,并研究了钉头管空气侧流场的协同性。对钉头高度和每环钉头个数的研究表明,在每环钉头个数固定、钉头高度变化时,钉头管的单位面积换热量、总表面换热系数、阻力、综合性能大多在钉头高度为35mm时出现高峰值。对基管高度的研究表明,单位面积换热量、总表面换热系数、阻力性能、综合性能大多随着基管高度的增加而先减小后增大。对钉头环数的研究表明,单位质量换热量、总表面换热系数、阻力性能、综合性能都随着钉头环数的增加而增大,其增大的速率几乎是线性的。而单位面积换热量随钉头环数的增加而减小。对管内壁温与入口温差的研究表明,单位质量换热量、单位面积换热量、总表面换热系数、综合性能都随着管内壁温与入口空气温差的增加而增大,而阻力性能随着管内壁温与入口空气温差的增加没有变化。对入口空气速度的研究表明,单位质量换热量、单位面积换热量、总表面换热系数、综合性能都随着入口空气速度的增大而增大,而阻力性能随着入口空气速度的增大逐渐减小,动量损失率越来越小。流场协同性分析表明,滴形钉头管空气侧流场的协同优势非常明显。采用萘升华技术在吸入式风洞中对圆形、椭圆形和滴形三种不同截面形状的钉头管进行实验研究,探讨钉头纵向间距、每环钉头个数、周向角等对换热和流动特性的影响。结果表明:在雷诺数为0.5×105-4.1×105的范围内,(1)钉头表面和基管表面均在周向角Φ=90°时换热效果最好。(2)三种钉头管的换热系数均随着雷诺数的增大而增加,且均优于光管。(3)钉头形状对阻力性能影响较大,滴形钉头接近流线形,阻力较小。(4)综合考虑换热系数和阻力性能,滴形钉头管的综合换热性能指数最高。本文对异型钉头管的传热及流动特性的研究,对于指导钉头管的设计和生产实践都具有重要的意义。
[Abstract]:With the rapid development of society, energy conservation and rational utilization have become the theme of the sustainable development of all countries in the world. The enhancement of heat transfer can improve the efficiency of heat exchange equipment and effectively alleviate the problem of energy shortage. It has always been the focus of attention on the development of energy conservation and emission reduction at home and abroad. As an efficient heat transfer enhancement element, nail head pipe has the function of expanding the surface and increasing the degree of fluid turbulence. It is widely used in petrochemical, coal chemical industry, metallurgy, ceramics, building materials and other fields. Although the nail head shaped has been adopted by the industry, but the study focuses on the nail head shape and head size, arrangement, and Study on the parameter and application fields are not the same, not the optimization analysis, especially the enhancement of heat transfer and flow characteristics of gas special-shaped pin tube used in low heat transfer coefficient of the side the lack of detailed data system, still can not explain which nail head shape has the best overall performance, and the heat transfer enhancement mechanism is lack of unified understanding. In this paper, the heat transfer and flow characteristics of three different shapes of the nail head tube with circular shape, ellipse and drop shape are studied by means of theoretical analysis numerical simulation experimental verification. The heat transfer and flow characteristics of the nailed head tube are analyzed in theory, which provides guidance for numerical simulation and experiment. Taking the stud tube as the research object, in the context of wind tunnel, we analyzed the fluid flow and heat transfer mechanism outside the nail head pipe, and studied the CFD technology and naphthalene sublimation experiment. The calculation models of 9 kinds of nail head pipes are designed by orthogonal experimental design, and numerical simulation is carried out to obtain the distribution of pressure field, temperature field and velocity field on the air side outside the nail head pipe, and the flow and heat transfer performance of the nail head pipe are analyzed. After analyzing the results of orthogonal test, it is concluded that after the study of the flow and heat transfer performance of the nail head pipe, the key point should be put on the optimization of the number of nail head and the height of the nail head. The numerical simulation of the circular nail head tube shows that the pressure drop of the nail head pipe is about 1.35-2.31 times of the light tube in the simulated Reynolds number range, and the total surface heat transfer coefficient of the nail head tube is about 1.10-1.72 times of that of the light tube. The overall performance of the nailed head tube is better than that of the light tube. When the nail head height is 45mm, the number of nails per ring is 8, the longitudinal spacing is 30mm, and the nail head radius is 5mm. The comprehensive heat transfer performance of the nail head pipe is about 25mm, the number of nail heads per ring is 4, the longitudinal spacing is 30mm, and the nail head radius is 1.15-1.29 times of 4mm. Numerical simulation of nail head tube of three different section shapes, through the simulation results of heat transfer per unit mass per unit area, heat transfer, surface heat transfer coefficient, resistance performance and comprehensive performance comparison, get the heat transfer and flow characteristics of pin finned drop shaped tube are among the three best, the drop of nail head tube, heat transfer enhancement can receive and reduce the flow resistance of the double effect. Drop nail nail head head tube height, each ring head number, tube height, nail head ring number, tube wall temperature and the entrance temperature and air speed entrance numerical study and research the synergy of pin tube air side flow. The research on nail head height and number of nails per ring shows that when the number of nail head is fixed and the height of nail head varies, the heat transfer per unit area, the total surface heat transfer coefficient, the resistance and the comprehensive performance of the nail head pipe mostly reach a high peak value when the nail head height is 35mm. The study of the height of the tube shows that the heat transfer per unit area, the total surface heat transfer coefficient, the resistance performance and the comprehensive performance first decrease and then increase with the increase of the base height. The research on the number of nail head shows that the heat transfer per unit mass, the total surface heat transfer coefficient, the resistance performance and the comprehensive performance increase with the increase of the number of the nail head ring, and the rate of increase is almost linear. The heat transfer per unit area decreases with the increase of the number of head rings. Study on the inner wall of the tube temperature and the entrance temperature, the unit of heat, mass per unit area for heat transfer, the total surface heat transfer coefficient, comprehensive performance increases with the increase of tube wall temperature and the entrance of air temperature, and resistance with increasing tube wall temperature and the entrance of air temperature did not change. Study on the entrance of air speed show that the unit of heat, heat transfer mass per unit area and total surface heat transfer coefficient, comprehensive performance increase with the entrance of air velocity, and the resistance increases with the entrance of air velocity decreases and the momentum loss rate is more and more small. Field coordination analysis showed that the synergy of air side flow pin finned drop shaped tube is very obvious. Naphthalene sublimation technology is used to study the effects of the longitudinal distance, the number and the circumferential angle of each pin on the heat transfer and flow characteristics of the three kinds of pin shaped tubes with circular cross-section, ellipse and drop shape in the suction wind tunnel. The results show that in the range of Reynolds number of 0.5 * 105-4.1 * 105, (1) the surface of the nail head and the surface of the base tube are at the circumferential angle of =90 degrees. (2) the heat transfer coefficient of the three kinds of nailed tubes increased with the increase of Reynolds number, and all were better than those of the light tubes. (3) the nail head shape has great influence on the resistance performance, nail head drop close to streamline, small resistance. (4) considering the heat transfer coefficient and resistance performance of pin finned drop shaped tube the comprehensive heat transfer performance index is the highest. The study on the heat transfer and flow characteristics of the special-shaped nail head tube is of great significance for guiding the design and production practice of the nail head tube.
【学位授予单位】：青岛科技大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TK172

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