摘要
冷却器作为一种重要的液压辅件,在液压系统正常工作过程中具有重要作用。由于风冷式冷却器与冷媒式冷却器相比,其冷却效果差,无法彻底解决液压系统油温过高的问题。因此,有必要对适应于工程机械的冷媒式冷却器及其相关组成部件进行研究。本文所研究的冷凝器及螺旋旋风分离器是为在多尘环境下工作的工程机械液压系统所用冷媒式冷却器的研发打下基础。因此,分析粉尘在冷凝器换热表面的沉积机理,采用合理的除尘方式降低气流中的含尘量对冷媒式冷却器的正常工作具有重要意义。
本文以某一应用对象的液压系统为例,根据计算所得散热功率对翅片管冷凝器的结构进行了设计计算。结合港口的大气环境,分析了港口环境对冷凝器换热效果所产生的影响。通过分析对比,本文选择螺旋旋风分离器作为多尘环境下冷媒式冷却器的除尘装置,并利用计算流体力学(CFD)分析方法,对分离器进行了数值模拟仿真。选择基于各向异性的RSM模型对螺旋旋风分离器内的三维强旋流动进行了模拟,通过仿真得出了分离器内的速度特性、压力特性及湍流特性,从而揭示了螺旋旋风分离器内的流动状态和能量损失。采用DPM模型对分离器内的气固两相流动进行了模拟,得出了分离器的分级效率,并利用相间耦合的随机轨道模型对颗粒的轨迹进行了跟踪。在改变操作参数及结构参数的基础上,分析了不同风速、螺旋圈数及锥体高度时的分离特性。为分离器的结构优化提供了依据。
利用计算得出的翅片管冷凝器结构参数,建立了翅片管的传热模型。通过数值模拟分析了翅片的对流耦合换热,并得出了翅片换热性能与风速的对应关系。本文对污垢的类别进行了阐述,建立了颗粒污垢的沉积模型,揭示了粉尘颗粒在换热表面的沉积机理,并综合分析了影响粉尘沉积的主要因素。此外,通过数值模拟得出了在不同污垢厚度下翅片管冷凝器的换热特性。结果表明,污垢的增加将导致迎面风速降低,流动阻力增加。与洁净换热表面相比,当污垢厚度达到0.25mm时,翅片管的换热量下降了16%。
As an important hydraulic accessory, the cooler has an important role during normal operation of the hydraulic system. Compared with refrigerant cooler, the air-cooled cooler has poor cooling effect and the overheat problem of hydraulic oil can't be solved completely. So, as for the refrigerant cooler used in construction machinery, it's necessary to research on the cooler and its component parts. The condenser and spiral cyclone separator studied in this paper can lay the foundation for the development of the refrigerant cooler, which will be used for the hydraulic system of the construction machinery adapted to dusty environment. Therefore, for the normal work of refrigerant cooler, it's significant to analyze the dust deposition mechanism on the heat transfer and select a reasonable method to reduce the content of dust in the air flow.
In this paper, based on the hydraulic system of an application object, the design calculation of the finned tube condenser is completed according to the calculated heat dissipation power. Combined with the atmospheric environment of the port, the impact of port environment on heat transfer performance of the condenser is analyzed. On the basis of comparison, the spiral cyclone separator is selected as the dust removal device of the refrigerant cooler used in dusty environment, and numerical simulation on the separator is completed by the computational fluid dynamics (CFD) analysis method. The three-dimensional strongly swirling flow in the separator is simulated based on the nonisotropic RSM model, the characteristics of speed, pressure and turbulence, which can reveal the flow state and energy loss inside the spiral cyclone separator, have also been obtained by simulation. The gas-solid two-phase flow inside the separator is simulated based on DPM model, the classification efficiency of the separator is obtained and the paths of particles are tracked with the coupling discrete random walk model. On the basis of changing the operation and structure parameters, the separation characteristics are analyzed when the wind speed, the number of spiral circle and the height of cone are different. These can provide basis for the structure optimization of the separator.
Based on the calculated parameters of the finned tube condenser, the heat transfer model of the finned tube is built. The coupled heat transfer of fins is analyzed by simulation, and the corresponding relation between the heat transfer performance and wind speed is obtained. The species of fouling are described in this paper, and the deposition model of particle fouling is built, at last, the mechanism of particle deposition on the heat exchanger surface is revealed and the main factors that affect the particle deposition are analyzed. In addition, the heat transfer performances of the finned tube condenser with different fouling thickness are obtained by simulation. The results show that the increase of the fouling will lead to lower wind speed and higher flow resistance. Compared with the clean heat transfer surface, the heat transfer rate of the finned tube has decreased by16%when the thickness of fouling reaches to0.25mm.
引文
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