多支管分液联箱结构优化研究

发布时间：2018-07-23 16:57

【摘要】：本文采用数值模拟的方法,利用Fluent中的VOF模型,通过研究工质为R134a的多支管分液联箱气液分离流动性能,对多支管分液联箱进行了结构优化研究。多支管分液联箱是分液冷凝器实现高效传热的关键部件,其主要作用是在换热器各管程间实现气液分离和排出冷凝液体,其工作原理是利用气液两相密度差,使得液相在多孔隔板上沉积,通过分布于多孔隔板上的各分液孔将液相排出进入下一管程,同时在隔板上部形成阻汽液膜,使气相由出口支管排出进入到下游换热管中,形成高干度传热,提高分液冷凝器的整体换热性能。分液联箱作为其中的关键部件,既要实现有效排液,又要实现有效阻汽作用,两者都需要通过结构设计自动实现。本文研究选定典型的换热器工况,首先研究了实验联箱结构下多支管分液联箱内部的气液分离流动特征,对两相工质的分布特点、联箱出口支管干度的分布特点、联箱内的压力分布和波动特点以及联箱出口支管和分液孔的流量分布均匀性进行了分析；然后研究了分液孔孔径对分液联箱各性能参数的影响,最后研究采用联箱壁面开槽结构时,槽深对分液联箱各性能参数的影响。模拟结果表明：孔径主要影响联箱的排液流动,壁面开槽主要影响联箱底部液膜的沉积。排液流动随孔径的增大而增强,壁面开槽能够显著增加联箱底部液膜的沉积。在给定工况下,孔径和槽深的变化对联箱内的压力分布基本没有影响。在给定工况下,出口支管的气相流量分配均匀性不会因孔径的变化发生明显改变,而液相流量分配的均匀性则会随着孔径的增大而变好,当孔径为0.4mm时均匀性最好；当流动达到稳定后,各出口支管的气相流量相对平均值的波动幅度随着孔径的增大保持不变,各出口支管液相流量相对平均值的波动幅度则随着孔径的增大略有减小或保持不变；在给定工况下,各分液孔的气相和流量分配均匀性均随分液孔孔径的增大而变差。当流动达到稳定后,各分液孔的气相流量相对平均值的波动幅度随着孔径的增大而减小,液相流量相对平均值的波动幅度随着孔径的增大略有减小,基本保持不变；对于开槽联箱结构,在给定工况下,出口支管的气相流量分配均匀性随槽深的变化基本保持不变,而液相流量分配的均匀性则会随着槽深的增大而变差。当槽深过小,液膜容易被气相从联箱壁面剥离,槽深过大,联箱底部的液膜容易在槽顶区域被气流冲击形成分散液滴。当槽深为0.2mm时,联箱底部沉积液膜的连续性最好,当槽深增大,各出口支管流量相对平均值的波动幅度增大。
[Abstract]:In this paper, the method of numerical simulation and the VOF model in Fluent are used to study the structure optimization of multi-branch tube separation header by studying the gas-liquid separation flowability of multi-branch tube separation header with working fluid R134a. The multi-branch tube separated liquid header is the key component of the condenser to achieve high efficiency heat transfer. Its main function is to realize gas-liquid separation and discharge of condensate liquid among the tubes of the heat exchanger. The working principle is to utilize the gas-liquid two-phase density difference. The liquid phase is deposited on the porous separator, and the liquid phase is expelled into the next tube through the holes distributed in the porous partition. At the same time, the vapor blocking liquid film is formed on the upper part of the partition, so that the gas phase is discharged from the outlet branch tube into the downstream heat transfer pipe. High dryness heat transfer is formed to improve the overall heat transfer performance of the condenser. As one of the key components, the separated liquid header is not only effective to drain liquid, but also effective to prevent steam, both of which need to be realized automatically through structural design. In this paper, the typical operating conditions of heat exchangers are studied. Firstly, the characteristics of gas-liquid separation flow in the multi-branch tube separation header under the experimental header structure are studied. The distribution characteristics of the two-phase working fluid and the dry degree of the branch pipe at the outlet of the header are studied. The characteristics of pressure distribution and fluctuation in the container and the uniformity of the flow distribution of the outlet branch pipe and the separation hole of the header are analyzed, and the influence of the pore diameter of the separate liquid hole on the performance parameters of the header is studied. Finally, the influence of groove depth on the performance parameters of liquid header was studied when the header wall was slotted. The simulation results show that the pore diameter mainly affects the discharge flow of the header, and the slotted wall mainly affects the deposition of liquid film at the bottom of the header. The efflux flow increases with the increase of pore size, and the slotted wall can increase the deposition of liquid film at the bottom of the header. Under given working conditions, the variation of aperture and groove depth has little effect on the pressure distribution in the box. Under given conditions, the gas phase flow distribution uniformity of outlet branch tubes will not change obviously because of the change of pore diameter, but the uniformity of liquid phase flow distribution will become better with the increase of pore size, and the uniformity is the best when the pore diameter is 0.4mm. When the flow reaches a stable level, the fluctuation range of the gas phase flow relative to the mean value of each outlet branch pipe remains constant with the increase of the pore size. The fluctuation range of the relative average liquid flow rate of each outlet branch pipe decreases slightly or remains unchanged with the increase of pore diameter, and the gas phase and flow distribution uniformity of each pore becomes worse with the increase of pore diameter under given operating conditions. When the flow reaches stability, the fluctuation amplitude of the relative average gas phase flow rate decreases with the increase of pore size, while the fluctuation amplitude of the relative average flow rate of liquid phase decreases slightly with the increase of pore size. For the slotted header structure, the gas phase flow distribution uniformity of the outlet branch tube remains basically unchanged with the change of the groove depth under given working conditions, but the uniformity of the liquid phase flow distribution will become worse with the increase of the groove depth. When the tank depth is too small, the liquid film is easily stripped from the header wall by the gas phase, and the tank depth is too large. The liquid film at the bottom of the tank is easily impacted by the air flow at the top of the tank to form dispersed droplets. When the channel depth is 0.2mm, the continuity of the deposition liquid film at the bottom of the header is the best, and when the channel depth increases, the relative average flow rate of each outlet branch pipe increases.
【学位授予单位】：广东工业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TK172

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