【作者】 郭丽华；

【导师】 陈芝久； 陈江平；

【作者基本信息】 上海交通大学 ， 制冷及低温工程， 2007， 博士

【摘要】 长期以来,适合于我国现有加工水平,以液态流体为工作介质的锯齿型错列翅片的基础研究仍然不足,限制了我国锯齿型错列翅片冷却器的自主开发与创新。本文的研究目的是综合考虑换热器的各种影响因素,得到适合于我国生产现状的换热器的设计理论与方法。紧密结合国内换热器加工工艺的实际情况,对多型锯齿型错列翅片进行试验及仿真研究;得到能够预测锯齿型错列翅片冷却器的传热及阻力性能的试验关联式;翅片性能的仿真结果用于指导翅片重要几何参数的加工公差设计;重点研究了换热器的两个重要加工工艺——翅片冲压和不锈钢真空钎焊工艺对换热器性能的影响,并探讨了量化的修正方法;最终以锯齿型翅片的板翅式机油冷却器为例进行数值模拟和性能预测。(1)搭建了以单层翅片单元为测试对象的传热及阻力性能试验台,以发动机润滑系统中常用的CD15W/40润滑油为工作介质,分别对23种HPD(High Pressure Direction)型、26种LPD(Low Pressure Direction)型、16种X(Inclined Direction)型锯齿型错列翅片在实际工况下进行试验研究,分析各几何参数对翅片传热及阻力性能的影响,得到适用于实际工程应用的各型锯齿型翅片的试验关联式,用以预测锯齿型错列翅片冷却器的传热及阻力性能。(2)采用计算流体力学仿真技术,对HPD型锯齿型错列翅片性能进行数值模拟。田口方法是田口玄一博士依据统计学原理开发出来的一种方法,是运用试验设计方法选择影响系统质量特性值的各元部件参数的最佳值及最适宜的组合,使系统的质量特性波动最小,稳定性最好的方法。引入田口方法,对HPD型锯齿型错列翅片进行参数化研究,综合考虑翅片的性能与成本,得到优化几何参数的翅片方案。引入多元质量-成本损失函数,以换热器的换热量和压降为两个质量指标,以两元质量-成本总损失为优化目标函数,对翅片的齿高、齿距几何参数进行加工容差设计,用于指导翅片加工中的公差控制,便于得到高性能、低成本的产品。(3)基于翅片-基板钎焊接头的成型机理和钎焊熔融平衡过程中的最小能量原则,对翅片-基板钎焊接头形态进行预测,定量得出翅片的焊料厚度与钎焊接头几何形态的关联式。采用有限元分析方法,对比不同参数下的翅片-基板钎焊接头的接触热阻,结果表明,翅片的焊料厚度越大,其接触热阻越小,越有利于翅片传热效率的提高。对具有在不同焊料厚度下成型的不同钎焊接头的翅片进行传热及阻力性能的CFD仿真,定量地得到不同焊料厚度时翅片传热因子和摩擦因子的修正方法。(4)材料为Cr12MoV的冷冲压模具在11种不同冲压次数时,分别采样锯齿型翅片,并对11组采样翅片的传热及阻力性能进行试验研究。分析模具磨损对翅片性能的影响,结果表明,随着模具冲压次数的变化,翅片传热因子和摩擦因子发生明显变化,可分为3个阶段分别对应于模具的初期磨损、正常磨损、过激磨损阶段。在模具过激磨损阶段时,翅片的传热及阻力性能急剧恶化。提出冷冲模具正常磨损阶段结束时为模具的一次刃磨寿命,Cr12MoV冲压模具推荐寿命的冲压次数为1,050,000次左右。建立冷冲模具在各磨损阶段内,摩擦因子、冲压次数和雷诺数的关系,用于修正翅片的阻力性能计算。(5)采用金相显微镜,对不同冲压次数时的11组翅片形状的横向和纵向剖面进行观察,在模具过激磨损阶段内,冲压翅片的表面毛刺增多,表面粗糙度增大。横向剖面的观察结果表明,随着冲压次数的增加,翅片横向截面由“长方形”逐渐向“弯月形”变化。定义“面积转移因子”判断翅片横截面积的变化情况,提出翅片加工模具不同磨损阶段的判断准则。(6)采用CFD仿真技术,利用多孔介质模型简化锯齿型错列翅片的板翅式机油冷却器的油侧芯子,仿真油冷器的换热和阻力性能。通过该型油冷器每层芯片的流量和换热量的分配规律,得到优化冷却器芯片层数的原则。结合翅片冲压模具及钎焊工艺对换热器性能的影响,采用集中参数模型,进行板翅式机油冷却器传热和阻力性能的预测。计算和试验结果的对比表明,采用试验关联式并进行相关修正的方法可以满足锯齿型错列翅片的板翅式机油冷却器性能预测的工程设计要求。综上所述,采用试验结合仿真的研究手段,进行锯齿型翅片的基础研究为锯齿型错列翅片冷却器的自主开发提供了理论基础;而紧密结合我国加工工艺特点,则使基础研究成果更快、更有效地转化,促进我国汽车零部件行业自主品牌的建设。更多还原

【Abstract】 From a long time, the fundamental research is still scare on offset strip fins taken liquid fluid as working media, which is limited to independent development and innovation of domestic offset strip fin coolers. The purpose of the thesis is to get the design theory and method of heat exchangers applicable to domestic producing condition, synthetically considering each factor affecting heat exchangers. The thesis has integrated domestic heat exchanger processing technology closely and carried out the experimental and simulated research on several kinds of offset strip fins. The experimental correlations to predict the thermal and hydraulic performance on offset strip fin coolers are obtained. The simulated results on fin performance are used to instruct the processing tolerance design of important geometries for offset strip fins. The effects of two important pressing technologies, fin pressing technology and stainless steel vacuum braze, on heat exchanger performance are focused on, and the quantitatively correction methods are discussed. Lastly, the performance of plate fin oil coolers adopted offset strip fin is simulated and predicted.(1) Taken the single layer fin as test specimen, the test rig to measure the heat transfer and friction characteristics is set up. The CD15W/40 lubricant oil commonly used in engine lubricating system is taken as working media. The 23 kinds of HPD (High Pressure Direction) type, 26 kinds of LPD (Low Pressure Direction) type and 16 kinds of X (Inclined Direction) type offset strip fins are experimented respectively at actual working conditions and the effects of geometrical parameters on fin performance are analyzed. The experimental correlations on each type of offset strip fin are gained to predict the thermal and hydraulic characteristics of offset strip fin coolers, which can be used in practical engineering design.(2) Based on computational fluid dynamics simulation technique, the performance on the HPD type offset strip fins has been simulated. Taguchi method is developed by Dr. Taguchi according to statistical theory, which adopts design of experiment to select the optimal value and the combination of component parameters affecting the quality system of values, in order to make the system quality value fluctuate smallest and the stability best. Taguchi method is introduced to carry out parametrical study on the HPD type offset strip fins, and the optimum scheme is obtained, which is originated from the geometrical parameter combination based on the optimal combination of performance and cost. The multiple quality-cost loss function is introduced. Taken the heat transfer quantity and the pressure drop as two quality targets, and the whole loss of two variables as the optimum object function, the processing tolerances of fin height and fin wavelength are designed, which instructs the tolerance control in fin practical processing.(3) Based on the fin-base plate brazed joint formation mechanism and the minimum energy principle during the solder melting and balance period, the fin-base plate brazed joint topology is predicted. The correlation is quantitatively obtained on the solder thickness and geometrical topology of fin brazed joint. The finite element analysis method is adopted to compare the thermal contact resistances of fin-base plate brazed joints having different geometrical parameters. It is concluded that the thicker the solder thickness is, the smaller the thermal contact resistance is, and it is beneficial to increase the fin heat transfer efficiency. The thermal and hydraulic characteristics of fins with different brazed joints at different solder thicknesses have been simulated by CFD, and the correction methods are quantitatively gained on fin heat transfer factor and friction factor at different solder thicknesses, which is helpful to get the high performance and low cost products.(4) At different pressing times for cold pressing die made of Cr12MoV, 11 specimen offset strip fins are selected. The heat transfer and friction characteristics of 11 specimen fins are experimental researched. The effect of mould on fin performance is analyzed. The experimental results show that with the variation of mould pressing times, the heat transfer and friction performance varies obviously corresponding to the three mould wear stages, early wear stage, normal wear stage and excessive wear stage. The performance of fins pressed at excessive wear stage deteriorates sharply. The cold mould operational lifetime is recommended at the end of mould normal wear stage and the Cr12MoV cold mould lifetime is about 1,050,000 pressing times. The relations of friction factor, pressing times and Reynolds numbers are obtained at each mould wear stage, which is used to correlate the fin friction performance calculation. (5) The metallographic microscope is used to observe the longitudinal and transverse sections for 11 specimen fins pressed at different pressing times. When the mould wear stage is the excessive wear stage, fin surface burrs increase and the surface roughness becomes larger. From the transverse section observations, with the mould pressing times increasing, the fin transverse sections of‘rectangle’shape become‘meniscus’shape.‘The area transform factor’is defined to judge the area variation of fin transverse sections, and the judging criterion of mould wear stage is put forward.(6) Based on CFD simulation technique, the porous media model is adopted to simulate oil side core of plate fin oil coolers adopted offset strip fin, and the thermal and hydraulic characteristics of oil coolers are simulated. From the distribution principles of mass flow rate and heat transfer quantity at each layer core, the optimum rule for core layer numbers is obtained. Considering the effects of pressing die and braze technology on fin performance, the focus parameter model is adopted, and the heat transfer and friction characteristics for plate fin oil coolers are predicted. The comparisons between calculated results and experimental results show that the method, combined the experimental correlations and the relevant correlated methods, is met the requirement for performance prediction of plate fin oil coolers adopted offset strip fin.As a whole, based on the research means combined experiment with simulation, the fundamental research on offset strip fins provides an academic foundation for the independent development of offset strip fin coolers. The domestic processing technology is considered closely, which makes the fundamental research results transform faster and more effectively and accelerates the independent brands building for domestic automobile parts.更多还原