【作者】 蒋斌；

【导师】 付祥钊；

【作者基本信息】 重庆大学 ， 供热、供燃气、通风及空调工程， 2010， 博士

【摘要】 为了充分吸引客流,地铁站总是设置在闹市区。在寸土寸金的闹市区,在满足冷却塔设置要求的前提下,又要与周围的环境协调共存,很难找到一个合适的位置安置冷却塔。因此,迫切需要一种高效换热设备替代常规冷却塔,将冷却塔移入地铁站排风通道内,解决地铁站等地下建筑设置冷却塔的问题。本文提出采用全膜流板式蒸发冷却器代替冷却塔的构想,并对该换热设备的关键技术进行了理论和实验研究。主要包括以下内容:论文阐述了全膜流板式蒸发冷却器的运行环境、系统构成以及工作原理。通过对顺流、逆流、叉流条件下的模拟计算以及该设备安装位置的比较分析,指出不论从提高设备换热性能方面,还是从设备安装和日后的运行维护方面在地铁排风道水平段设置全膜流板式蒸发冷却器都是最佳方案。全膜流板式蒸发冷却器至少包括板式蒸发换热器和全膜流蒸发布液器,板式蒸发换热器与对应的全膜流蒸发布液器构成冷却单元,实际工程应用中,可根据换热量增减冷却单元数量。通过对模拟计算结果与实验结果的关联分析,指出均匀布膜技术和研制适用于地铁站排风道环境的板式蒸发换热器是全膜流板式蒸发冷却器的核心技术;换热板片之间的间距、储液槽与换热板之间的夹角以及储液槽下边缘与换热板片之间的缝宽是全膜流板式蒸发冷却器的关键参数。建立全膜流板式蒸发冷却器液膜在气体外掠条件下液膜流动和传热特性的数学模型,探讨了气液界面切应力协同条件下层流液膜非线性温度分布的液膜传热性能,分析液膜厚度和传热系数沿液膜流动方向上的变化趋势,讨论界面切应力、界面对流换热强度和雷诺数等因素的对液膜换热的影响。结果表明:随着液膜雷诺数的增加,无量纲液膜厚度逐渐增大,无量纲液膜换热系数逐渐减小;同向界面切应力对液膜有推动拉伸作用,液膜传热系数随同向界面切应力的增加不断增大;反向界面切应力对液膜流动有阻碍作用,液膜传热系数随反向界面切应力的增加不断减小,并且反向界面切应力对液膜换热的影响比同向界面切应力显著。分析湍流液膜涡旋粘性和速度分布,对涡旋粘性、界面切应力和雷诺数对液膜厚度和液膜传热系数的影响进行讨论,结果表明:涡旋粘性随着界面切应力的增大逐渐增大,并且随着界面切应力的增大,涡旋粘性的最大值逐渐向气液界面靠近;无量纲速度分布随着距离壁面间距的增加不断增大。在气液叉流条件下,采用VOF两相流模型,考虑表面张力源项和气液两相传质源项,编写UDF程序,建立了三维全膜流板式蒸发冷却器数理模型,对实验条件和恒定壁面热流密度条件液膜流动的传热传质性能进行模拟计算,考察表面张力、固液接触角等因素对液膜流动状态和传热传质性能的影响,结果表明:随着表面张力系数和固液接触角的增大,液膜的不稳定性增强,边界发生波动,在实际工程应用中,应当采取一些物理或化学方法,降低液相表面张力,以促进连续液膜的形成。自行设计和搭建实验台,综合考察了叉流条件下液膜流量、液膜温度、外掠空气温度、相对湿度、流动速度以及换热器内热流体流动方式等因素对液膜传热传质性能的影响。结果表明:在液膜雷诺数增加的过程中,存在最佳雷诺数,使得液膜的换热热阻最小,换热系数最大;雷诺数较小时,热量传递受温度的影响较大,雷诺数较大时,流动状态对液膜换热系数的影响远大于温度对液膜换热系数的影响。更多还原

【Abstract】 For sake of getting more passengers, the subway station is always located at down town. In order to meet setting demand of cooling tower and not to destroy urban landscape, it is very difficult to find an appropriate location to install cooling tower. Hence, there is an impatient need to find an efficient heat exchanger to substitute the cooling tower, move the cooling tower into the subway station and solve the problem that there is no place for installing the cooling tower of the underground buildings. The paper presents a novel subway station plate evaporative cooler as an alternative to cooling tower, and the key technology of it was investigated experimentally and theoretically. The main contents of the present paper include:The working environment, system composition and working principle of subway station plate evaporative cooler were expatiated. Based on the simulated results of concurrent flow counterflow and cross flow and comparative analysis of install location in subway station exhaust airway, it is pointed out that the optimal install location is horizontal segment of subway station exhaust airway, not only from the aspect of installing, but also from the aspect of running attention.The subway station plate evaporative cooler comprises plate evaporative heat exchanger and liquid film distributor at least. Plate evaporative heat exchanger and liquid film distributor in corresponding compose the cooling unit. The number of cooling unit could be increased or decreased according to the heat transfer rate in practical application. Based on relevance analysis of simulated results and experimental results, it is indicated that the uniform liquid film technique and the developing of plate evaporative heat exchanger suitable for subway station exhaust airway are the key technology. It is pointed out that the spacing between heat exchange flat, the angle between reservoir and heat exchanges flat and the spacing between reservoir lower limb and heat exchanges flat are the key parameters.Under the gas stream sweeping condition, the hydrodynamics and heat transfer model of subway station plate evaporative cooler was established. The heat transfer performance of laminar liquid film under nonlinear temperature distribution with interfacial shear stress was discussed. The change of liquid film thickness and heat transfer coefficient along with the flow direction of liquid film was discussed. The effects of interfacial shear stress and the intensity of interfacial convection heat transfer and Reynolds number on hydrodynamics and heat transfer are explained. The results indicate that with a rise in Reynolds number the dimensionless liquid film thickness increases and heat transfer coefficient decreases. The cocurrent shear stress plays the roles on thinning film thickness and enhancing heat transfer, and the countercurrent shear has inverse effect. And the effect of countercurrent is more remarkable than that of cocurrent shear stress. The effects of eddy viscosity, interfacial shear stress and Reynolds number on heat transfer of turbulent liquid film were discussed. The results indicate that eddy viscosity increases with a rise in interfacial shear stress. And the eddy viscosity maximal value gets close to gas-liquid interface gradually as the interfacial shear stress increases. The dimensionless velocity distribution increases with the increasing of distance from wall.Based on volume of fluid (VOF) method, the three-dimensional model of subway station plate evaporative cooler was set up under gas-liquid cross-flow condition. By compiling user-defined functions, the surface tension source and mass transfer source were taken into account. The heat transfer of liquid film under experimental condition and constant heat flux condition was investigated. The effects of surface tension and liquid solid contact angle on heat transfer of liquid film were investigated. The results show that with the increasing of surface tension and liquid solid contact angle the instability of liquid film strengthens and liquid film brim begins to fluctuate. Hence, in practical engineering physical or chemical methods should be taken into account to reduce the surface tension source.By designing and founding the experimental apparatus and collecting the data of liquid film flow rate, inlet and outlet water temperatures and the air velocity, the heat transfer of liquid film was investigated. The experimental results indicate that as the increasing of Reynolds number there was an optimal liquid Reynolds number which minimize thermal resistance and maximize heat transfer coefficient of liquid film. Temperature plays an important role in heat transfer of laminar flow liquid film. Whereas, the heat transfer of turbulence liquid film flow is not sensitive to liquid film inlet temperature.更多还原