【作者】 韩崇刚；

【导师】 杨卫民；

【作者基本信息】 北京化工大学 ， 化工过程机械， 2012， 博士

【摘要】 管壳式换热器是许多工业生产过程的关键设备，其应用领域包括冶金、石化、能源及核能、航空等。强化换热技术是提高换热设备换热效率，减小换热体积，降低成本的关键技术。本文依托“十二五”科技支撑项目，以研发强化换热效果更高而水阻更低的“洁能芯”装置为目标，通过理论分析、数值模拟及试验对管程组合转子的强化传热特性进行了系统的研究，并在国电、中石化电厂凝汽器开展工程应用，取得了良好应用效果。本文主要研究工作如下：一、管程单元组合转子强化传热机理分析在层流和低雷诺数湍流对流传热过程中，温度梯度存在于整个流体通道截面，流体温度分布为抛物线型。因此，层流与低雷诺数湍流传热的强化应着眼于加强整个通道截面内流体的径向混合，也就是要改变流体通道内的速度场分布。增加传热方向的速度分量（横向速度），场协同数将会大幅增加进而换热强化。通道截面内的横向速度分量可引发纵向涡与横向涡。在低雷诺数湍流状态下，纵向涡具有较好的传热强化效果，并且在换热相同的情况下，纵向涡较横向涡造成的阻力压降增幅更小。管程单元组合转子可在换热管内诱导占主导地位的纵向涡，同时局部伴随有少量横向涡。随着流动雷诺数的增大，流体的流动将由层流状态渐变为湍流状态。湍流状态下，流动边界层和热边界层的厚度成一定的比例关系，减薄流动边界层与减薄热边界层是相互关联的。由此提出管程单元组合转子实现强化传热机理：①转子叶片扰动边界层；②离心流体冲击边界层；③切向流体剪切边界层。二、管程单元组合转子强化传热及阻力特性研究基于湍流区域内以破坏流体边界层的层流底层方式实现强化传热工作机理，在螺旋三叶片和叶片间断型转子的结构形式的基础上，创新提出了三种新型结构形式转子螺旋两叶片转子、螺旋阶梯两叶片转子和开槽螺旋两叶片转子，通过自行研制的强化换热综合性能实验装置，对上述五种不同结构形式的管程组合转子的强化传热特性进行实验研究。强化传热实验研究结果表明：在实验雷诺数范围内，不同结构形式及结构参数的管程组合转子可不同程度地提高换热过程的换热量、管程对流传热系数和传热努塞尔数Nu，同时也相应地增加了管程压降；增大转子外径对传热强化的贡献明显，阻力系数也相应有所增大；在不同结构形式的组合转子中，开槽螺旋叶片转子的强化传热综合性能最佳，增大转子外径对阻力系数的影响微弱，却能较大增强管程流体的换热效果；在实验研究的转子中，外径为22mm、导程为150mm的开槽螺旋叶片转子具有最佳的综合性能。三、管程单元组合转子传热及流动的数值模拟研究利用FLUENT软件对叶片外径为22mm、导程为200mm的螺旋叶片转子进行了数值模拟研究，获得了该种内置组合转子换热管管内流体的速度场和温度场分布。此外，采用数值模拟方法对外径均为22mm，导程分别为100mm、150mm和200mm的螺旋叶片组合转子进行了模拟研究，通过数值分析方法研究比较了转子导程对强化管努塞尔数和阻力系数的影响规律。数值模拟结果表明：在相同条件下，强化管的努塞尔数和阻力系数都会随着转子叶片导程的减小而增大。四、管程单元组合转子在线防垢除垢特性研究及结构创新管程单元组合转子防垢除垢实验结果表明：安装有单元组合转子的有机玻璃管与光管相比达到污垢动态平衡状态的周期更长，达到动态平衡状态后的污垢沉积程度为未安装转子有机玻璃管污垢沉积程度的50%。管程单元组合强化换热装置的在线除垢功能具体体现在：(1)破坏污垢生长的流速条件，延长污垢生长诱导期；(2)增强近壁区流体的剪切作用，加速已生成污垢的剥落；(3)减薄热边界层，增大近壁区的温度梯度，使得已生成污垢因热应力剥落；(4)增强管程中心流体对壁面污垢的冲击作用；(5)利用转子的物理磨蚀作用除垢。同时，基于湍流强化传热机理分析，以实验和数值模拟结果为依据，以改进阻垢除垢性能、增大边界层扰流、减薄边界层、提高综合换热效果为目标，再次对转子的结构进行改进，创新性的提出了边界层减薄型转子、带导热除垢纤毛螺旋两叶片转子两种新结构。五、管程单元组合转子工业应用试验蚌埠电厂以及茂名石化动力厂的凝汽器经过洁能芯节能技术改造后，凝汽器内换热效果明显提升；真空提高了0.28~2.01KPa，在真空度有一定上升的基础上，循环水的使用量也有所减少。依托茂名石化动力厂及蚌埠电厂凝汽器改造项目，充分展示本装置应用前景广阔，为后续优化装置结构和工业应用推广打下坚实的基础。更多还原

【Abstract】 Shell-and-tube heat exchangers are key equipments of manyindustrial processes and are widely used in metallurgy, petrochemical,energy and nuclear power, aviation, etc. Heat transfer enhancement is thekey technology of improving heat transfer efficiency, minimizing thevolume and reducting the cost of the heat exchangers. Based on National"Twelfth Five-Year" Plan for Science&Technology Support and aimingat developing the tube side assembled rotors (TSAR) with better heattransfer enhancement performance and lower resistance, the papersystematically studied heat transfer enhancement performance of TSARthrough theoretical analysis, numerical simulation and experiment;meanwhile, TSAR were applied in condensers of guodian, sinopec powerplant and achieved good application effect. The main research studieswere listed as follows:1. Analysis of heat transfer mechanismIn laminar flow and low Reynolds number turbulent flow, there wastemperature gradient existing in the entire cross section of the tube andthe temperature distributes as a parabola. Therefore, in laminar flow andlow turbulent Reynolds number, heat transfer enhancement should focuson the strengthening of the fluid radial mixing in the whole cross sectionof the tube. That was to say, by changing the distribution of velocity fieldin the tube, velocity component (horizontal speed) in the direction of heattransfer was enhanced and the field synergy degree increased greatly, which made the heat transfer enhanced. The horizontal velocitycomponent in the cross section of the tube made many kinds of vortexessuch as longitudinal vortex and transverse vortex. In turbulent flow withlow Reynolds numbers, compared with transverse vortex, longitudinalvortex could get better heat transfer results and lower resistance increase.TSAR made many beneficial longitudinal vortexes with some transversevortexes.With the increase of Reynolds number, the fluid changed fromlaminar flow to turbulence. In case of turbulence, thinning the flowboundary layer and the thermal boundary layer, whose thicknesses areproportional to each other, was relevant. TSAR could enhance the heattransfer effect in three points summarized as follows:(1) the blade ofrotor disturbed the boundary layer of the fluid;(2) the centrifugal fluidstruck the boundary layer of the fluid;(3) the tangential fluid cut theboundary layer of the fluid.2. Experimental study on heat transfer and friction characteristicsBased on the mechanism that heat transfer enhancement wasachieved by destroying the viscous sublayer of fluid boundary layer inturbulent region and the structure styles of helical three-blade rotors andblade-discreted rotors, three new structure styles of rotors were presented:the helical blade rotor, the helical ladder rotor, and the helical blade rotorwith ladders. An experimental apparatus to test heat transfer enhancementand pressure drop characteristics of TSAR was designed and built. Fivedifferent structural forms of TSAR presented above were experimentallystudied. The experiment results showed that in the range of experimentalReynolds number, different structures forms and structure parameters ofTSAR could increase the heat transfer rate, the tube convective heattransfer coefficient and heat transfer Nusselt number, and also inevitablyincreased the pressure drop; the increase of the rotor diameter could makea significant contribution to heat transfer enhancement, but the frictionfactor correspondingly increased due to the rotation of the rotors; Thehelical blade rotor with ladders had the best heat transfer performanceduring the different structure forms of the rotors. The increase of the rotor diameter had little influence on friction factor, but enhanced heat transferof the tube side fluid; Comprehensive performance evaluation indicatedthat the helical blade rotor with ladders of22-150had the bestperformance during the experimental rotors.3. Numerical study on heat transfer and friction characteristicsThe helical blade rotor whose diameter was22mm and lead was200mm was numerically studied by the software of FLUENT. Thedistribution of the fluid velocity field and temperature field in the tubeinserted with helical blade rotors was gained. In addition, the helicalblade rotors whose outer diameters were22mm and leads were100mm,150mm and200mm respectively were also numerically studied. And theeffect of rotor lead on Nusselt number and friction factor was analysed bynumerical analysis method. The simulation results revealed that theNusselt number and friction factor of the enhanced tube increasedfollowing with the decrease of rotor lead under the same conditions.4. Fouling experimentThe anti-scale and de-scale experiments results of TSAR showedthat compared with the ordinary organic glass tube, the cycle that theorganic glass tube with rotors reached the state of fouling dynamicbalance was longer, but the dirt deposit degree is only half of that in theordinary organic glass tube after reaching the state of dynamic balance.The online cleaning performance of TSAR was listed as follows:(1) Itcould destroy the velocity conditions of fouling deposition and extend theinduction period of fouling deposition.(2) It could enhance the shearingeffect of the near wall fluid and speed up the peeling of the generatedfouling.(3) It could make thermal boundary layer thinner, increase thetemperature gradient near the wall, and make the generated dirt peelbecause of the thermal stress.(4) It could enhance the impact of the fluidin the center of the tube on the fouling of the wall.(5) It could removefouling by physical abrasion function of the rotor.Meanwhile, based on the mechanism analysis of turbulence heattransfer enhancement, according to the results of experiments andnumerical simulation, the structures of the rotors were changed with aiming at improving the performance of anti-scale and de-scale,enhancing the turbulence of boundary layer, thinning boundary layer andimproving overall heat transfer effect. Two new structures were novellypresented: the boundary layer shear rotor and helical two-blade rotor withthermal conducting and de-scaling cilia.5. Industrial applications and structure innovationAfter reformed by energy-saving technology of TSAR, the heattransfer performance of condensers in Bengbu power plant and maomingpetrochemical plant were greatly improved; the vacuum was improved by0.28~2.01KPa, and the usage of circulating water was also reduced. Thereforming projects of the condensors in maoming petrochemical plant andbengbu power plant fully displayed the wide application of TSAR, whichlaid a good foundation for the subsequent optimization and industrialapplication.更多还原