【作者】 张琳；

【导师】 宣益民； 俞秀民；

【作者基本信息】 南京理工大学 ， 兵器发射理论与技术， 2006， 博士

【摘要】 换热设备的低效率和污垢沉积问题一直是一个世界性的难题。研究开发的旋转清洗扭带技术具有强化传热和污垢在线清洗的双重功效，用旋转扭带制作和改造的换热器，能够长期保持高效率运行。 本文针对旋转扭带的强化传热机理和清洗动力学，开展了许多研究工作，主要包括以下几个方面的内容： (1) 内置旋转扭带管流动和湍流特性实验研究 应用激光测试技术对内置旋转扭带管和普通光管内流体的流动进行了对比实验研究。研究结果表明：内置旋转扭带管内流体的轴向速度场、切向速度场、轴向湍流度和切向湍流度的分布规律与光管相比有着明显的不同。内置旋转扭带管内近管壁区流体的轴向速度明显比光管的大；内置旋转扭带管内流体有着明显的切向运动，而光管内流体只有随机的切向运动；内置旋转扭带管内流体的湍流强度场比光管的大。依据内置旋转扭带管和光管速度场和湍流强度场的实验结果，对旋转扭带强化传热的机理进行了初步分析。 (2) 内置扭带管流动与传热数值模拟 对内置旋转扭带管内流体的流动进行了分析，根据内置旋转扭带管流体的旋流场特点，提出了旋转扭带虚拟等效静螺距的概念，即将流体在内置旋转扭带管内的螺旋运动虚拟等效为在螺距增大的静止扭带管内的螺旋运动。 建立了内置螺旋扭带管流动和传热三维模型。应用能充分反映旋流场流动特性的RNG κ-ε模型对内置旋转扭带管、内置静止扭带管、内置旋转扭带虚拟等效静止扭带管和光管的流动和传热进行了数值模拟。 数值模拟研究结果表明：内置扭带管内流体的流动是复杂的三维螺旋流动，其速度场和湍流强度场不同于普通光管；螺旋扭带的扭率对流体流动的压力降和传热有很大的影响；模拟发现内置旋转扭带管内有二次流流动，而内置旋转扭带虚拟为螺距增大的静止扭带后，管内没有发现二次流动；内置旋转扭带虚拟等效为螺距增大的静止扭带后，二者的传热特性和阻力特性并非完全相同。速度场和湍流强度场的数值模拟结果与激光测试进行了比较，二者非常吻合。 (3) 内置旋转扭带管传热强化机理研究 在内置旋转扭带管流场的激光测试和数值模拟研究工作的基础上，提出旋转扭带强化传热的机理有：①换热管的当量直径减少效应强化；②近管壁区域流速加大效应强化；③螺旋线流动流速加大效应强化；④二次流流动流速加大效应强化。对螺旋扭带的这些强化传热机理进行了定量的理论分析研究。更多还原

【Abstract】 The question of the low efficiency and fouling deposit for heat exchangers has been a worldwide difficult problem all the time. The cleaning technology of a self-rotating twisted tape has been developed, which has double functions of heat transfer enhancement and online cleaning fouling. Heat exchangers, which are made and transformed with rotating cleaning twisted tapes, can keep running with the high efficiency.The purpose of this paper is to investigate the heat transfer enhancement mechanism and cleaning dynamics of a rotating twisted tape. The investigation is focused on the following aspects.(1) Experimental investigation of the flow and turbulent characteristics in the tube with a self-rotating twisted tape insertThe flow and turbulent characteristics in the tube with and without a self-rotating twisted tape insert are investigated experimentally by using Laser Doppler Velocimeter.The results show the flow flied of the axial velocity, the tangential velocity, the axial turbulence intensity and the tangential turbulence intensity in the tube with and without a self-rotating twisted tape insert are obviously different. The axial flow velocity near the tube wall area in the tube with a self-rotating twisted tape insert is higher than that of the smooth tube. There are distinct tangential motions in the tube with a self-rotating twisted tape insert, but there are only random tangential motions in the smooth tube. The turbulence intensity in the tube with a self-rotating twisted tape insert is higher than that of the smooth tube. According to experimental results of the velocity and turbulence intensity flied in the tube with a self-rotating twisted tape insert, the heat transfer enhancement mechanisms are initially analyzed.(2) Numerical simulation of the fluid flow and heat transfer in the tube with a twisted tape insertThe fluid flow in the tube with a self-rotating twisted tape insert is analyzed. According to the tangential motion characteristic of the swirl flow field in the tube with a self-rotating twisted tape insert, a conception of a self-rotating twisted tape being dummied as an equivalent still twisted-tape is put forward, which shows that the helix motion of the fluid in the tube with a self-rotating twisted tape insert can be dummied as the helix motion in the tube with a still twisted tape insert, which the twist ratios of the still twisted tape is augmented.更多还原