【作者】 陈雪清；

【导师】 陈颖；

【作者基本信息】 广东工业大学 ， 材料学， 2013， 博士

【摘要】 目前全球的能源供求矛盾日趋突出,各种节能技术的研究及应用显得尤为重要。“分液式冷凝”是一种近年提出的通过分段冷凝中间分液实现强化凝结传热的新方法。该方法实现蒸汽和凝结液分离并将凝结液及时排出的关键装置是多孔隔板联箱。湿蒸汽进入联箱后,由于气、液相的密度相差较大,凝结液在重力和惯性力的作用下从蒸汽中分离出来并在多孔隔板上凝聚成液膜,然后通过多孔隔板上的小孔排出,在隔板上形成的液膜可阻止气体从小孔穿出,使蒸汽流进下一管程后能与管壁充分接触,利用凝结换热方式获得高传热系数,提高换热器的整体性能。目前尚未有针对这种联箱内的气液分离过程的现象和过程特性的系统研究。本文将对多孔隔板联箱内的气液分离和排液阻气过程进行深入研究,建立设计分液联箱的理论依据,并在此基础上设计分液冷凝器,对使用分液冷凝器的空调系统进行系统实验验证。首先,探索多孔隔板联箱内的气液分离和排液阻气的基本原理。搭建可视化冷态实验台,以空气和水作为工质,采用透明有机玻璃制作联箱试件,采用染色示踪和高速摄像的方法记录空气、水在联箱内的流动过程。对联箱内四种流型进行分析,揭示流速对液膜形态和运动的作用机理。并根据液膜高度的变化,引进两个临界点(溢出临界与击穿临界),划分出5种工作状态。对分液隔板上的液膜进行受力分析,引入描述气液分离特性的无量纲准则数——液体Re数和修正We数,为多孔隔板联箱结构的设计提供理论指导。在理论分析基础上,研究运行工况和结构参数对多孔隔板联箱的气液分离特性的影响。在自建的冷态实验台上,改变空气、水流速,空气压力,联箱直径,隔板与出口管间距,分液小孔直径,分液小孔数量,分液小孔的孔径和数量组合等参数,获得上述参数对分液隔板上液膜高度,漏液速率和分离效率的影响。采用PIV测速系统观测分液联箱内液体的流动轨迹,通过高速摄像的可视化结果分析流型对击穿临界和分离效率的影响。结果表明：在实验工况的条件下,多孔隔板气液分离联箱具有较好的气液分离性能；分离效率随流型变化,环状流入口和低液流速弹状流时,分离效率为45%～80%,分层流入口时,分离效率为100%。运用修正We数来讨论两个临界气液分离极限条件,获得预测临界状态下的无量纲拟合公式；液膜高度、漏液速率和分离效率随分液隔板与出口管间距增大、联箱直径增大和分液小孔直径减小、分液小孔数量减少而增加；用修正We数很好地解释了两个实验前未预测到的现象：一是增大联箱直径,气液分离联箱内的液膜高度升高,二是增加小孔的数量,漏液速率减小。通过对气液分离联箱冷态实验的结果分析,设计一体化联箱。基于维持全管程蒸汽流速基本不变,避免因蒸汽量减少造成换热弱化的优化原则,合理设计管路流程。根据漏液量与We的相关关系进行排液结构设计。在标准焓差实验室内进行分液冷凝器(LSC)对空调系统性能影响的实验研究。比较采用三个设计出来的LSC的系统的性能,将EER(制冷性能系数)最大的LSC系统与常规空调系统进行比较,并在变环境温度的条件下进一步探讨LSC系统的性能。实验结果表明多孔隔板上的小孔尺寸和多孔隔板在联箱中的位置对系统性能影响很大,三个LSC系统中,最佳的LSC的壁温分布最均匀而且进、出口压降最小,其系统的制冷量和EER分别比最差的LSC系统大8.04%和11.11%。与常规空调系统相比,虽然LSC的换热面积仅有常规L形空冷冷凝器的67%,但是在额定工况下,LSC系统的制冷量和EER仅比常规空调系统少1.6%和2.8%。更多还原

【Abstract】 The contradiction between supply and demand of global energy becomes increasingly prominent at present. It is particularly important to research and apply energy saving technology. Recently, an innovatory idea called "Liquid-vapor separation condensing" was proposed to enhance the condensation heat transfer by separating liquid from gas-liquid mixture during condensing. This method realized the liquid separation of steam and condensate and timely discharge of the condensate by a special setting of the header with porous baffles. When the wet steam enter into the header, the condensate separate from the steam and flow down to the baffle due to the effects of the gravity and inertia force because the density difference between the gas and liquid is very large. Then a liquid film accumulates on the porous baffle plate and the liquid flows through the holes on the baffle. The liquid film could prevent gas to flow out from the holes, so the steam could better contact with the tube wall when flowed into the next tube pass. Higher heat transfer coefficient was obtained by using condensation heat transfer process, and then high performance of the heat exchanger would be achieved. Up till now, there was no systematical research of the phenomenon and process characteristics during liquid-gas separation process in this kind of header. In this study, liquid-gas separation and liquid discharged process were investigated in-depth to established the theory basis for the header design and the design of the liquid-vapor separation condenser (LSC), and the system characters of an air conditioning system with LSC was verified.Firstly, the basic principle of liquid-gas separation and liquid discharge process were explored. A visualization cold state test system was set up, using air and water as the working fluids. The header was manufactured from transparent acrylic resin. The method of dyeing tracer and high-speed camera were adopted to record the gas and water flow process in the header. The results of four kinds of flow pattern in the header were analyzed, and the mechanism of the effects of gas and liquid superficial velocities on the morphology and movement of the liquid film was revealed. Based on the change of the liquid level height, two limits (flooding limit and drain limit) were introduced and the working condition was divided into five situations. The dimensionless Re and modified We number were introduced by forces analyzing to describe the gas-liquid separation characteristics. The results could provide theoretical guidance for the header design.On the basis of theoretical analysis, effects of operation conditions and structure parameters on the gas-liquid separation characteristics of the header were studied. The effects of the operation conditions and structure parameters on liquid level height, water seepage flow rate and liquid separation efficiency were discussed at different gas and liquid superficial velocities, air pressure, header diameter, space between the baffle and the outlet pipe, diameter of the liquid-gas separation hole, number of the liquid-gas separation hole, combined effects of the diameter and number of the liquid-gas separation holes on the self-built cold state test system. The flow characteristics in the header were observed by a PIV velocity measuring system to analyze the influence of flow patterns on the drain limit and the liquid separation. The results showed that under the experimental condition, the header showed capabilities of good liquid-gas separation; the liquid separation efficiency changed with different inlet flow patterns; it was higher than45%and80%respectively for annular flow inlet and for slug flow inlet at low liquid inlet superficial velocities, and close to100%for a stratified flow inlet. Modified We number were used to discuss the two limit conditions, and dimensionless correlations were obtained for predicting the limits. It was found that the liquid level height, water seepage flow rate and liquid separation efficiency increased with increased header diameter, spacing between baffle and outlet pipe and reduced diameter of the liquid-gas separation hole, number of the liquid-gas separation hole, The modified We number was suitable for analyzing two unexpected phenomenon:one was the increase of liquid level height with increasing header diameter at the same inlet conditions. The other was the decrease of water seepage flow rate with increasing the number of the liquid-gas separation holes.Headers were designed according to the analysis of the results of gas-liquid separation characteristics of the header in the cold state experiments. The tube path was reasonable designed based on the principle that maintaining all the steam flow rates basically remain unchanged to avoid heat transfer weakening caused by reduced steam. The baffles with liquid-gas separation holes were designed according to the relationship between water seepage flow rate and modified We number. The system performance characteristics of air conditioning systems with liquid-vapor separation condenser (LSC) were invested in a standard air enthalpy difference test room. The results indicate that, the designs of refrigerant flow path and the holes in the baffles of the LSC affected the system performance, among three tested LSC systems, the best LSC had the most uniform wall temperature distribution and the smallest pressure drop. The cooling capacity and EER(Energy Efficiency Ratio) of the best LSC system were8.04%and11.11%higher than those of the worst of the three tested LSC systems. Compared to the baseline system, although the LSC had only67%of the heat transfer area of the baseline condenser, the cooling capacity and EER of the LSC system were only1.6%and2.8%less than those of the baseline system at the nominal operating condition.更多还原