制冷系统融霜液击的形成机理及其预防液击冲击失效的设计准则研究

发布时间：2018-03-06 17:51

本文选题：热氨融霜　切入点：液击　出处：《南昌大学》2017年硕士论文　论文类型：学位论文

【摘要】：本文针对预防热氨制冷系统氨融霜过程液击诱发的系统爆炸事故频发的安全隐患所遇到的关键科学与技术瓶颈问题,研究构建了多相相变分层流动液击形成理论模型和相应的模拟方法,并通过数值模拟和实验研究揭示了热氨融霜过程中多相相变液击形成机理,明晰了影响液击的关键调控参数,提出了抑制液击冲击形成的关键技术和方法。基于回气总管液击冲击的安全评估,阐述了热氨制冷系统氨融霜过程液击诱发的系统爆炸事故频发的力学机理,研究结果为建立我国预防融霜过程中液击冲击失效的氨制冷装置的设计准则奠定了科学的理论基础和技术支撑。首次研究建立了综合考虑热氨融霜急剧相变影响的汽液二相分层流动液击形成机理理论模型,并依此研究建立了热氨融霜液击形成过程的虚拟仿真平台。研究发现了热氨融霜过程中回气总管液击形成的二个直接驱动力为:1)热氨总阀突然开启形成的热氨蒸汽进口流速的突变;2)高温热氨蒸汽与深冷液氨瞬间接触诱发的剧烈相变。研究建立了热氨融霜液击压力与急剧相变、热氨蒸汽进口流速突变、深冷液氨残余体积分数、热氨蒸汽气泡瞬态破裂、段塞流关联关系,明晰了热氨融霜液击压力的关键调控参数,揭示了具有相变的多相分层流动液击形成的机理,并提出了抑制液击冲击形成的关键技术和方法。构建了回气总管热氨冲霜液击形成机理的实验研究平台,研究提出了高温热氨蒸汽进口流速、突增加速度、液击压力和液位检测、显示和控制系统以及检测数据同步采集显示系统,回气总管热氨冲霜液击实验研究表明高温热氨蒸汽进口流速突变会导致回气总管在热氨冲霜过程中形成明显的液击现象,高温热氨蒸汽进口流速自动控制系统的过调纠偏导致的电动流量控制阀开启趋势的突变也会导致明显的液击,通过高温热氨蒸汽进口流速自动控制难以消除回气总管的液击现象,且实验检测的液击压强与本文理论模型按实验工况模拟预测的液击压强吻合。深冷液氨与高温热氨蒸汽的多相流动所形成的段塞流是由分层界面不稳定波动所诱发,而分层界面不稳定直接驱动力是二相流速速度差和分层界面的急剧相变。有相变与无相变多相流动液击模拟对比分析研究表明:在其他条件一定时,考虑高温热氨蒸汽与深冷液氨剧烈相变的回气总管管内第一峰值最大液击平均压强是不考虑相变情况下的管内第一峰值最大液击平均压强的四至五倍,是回气总管正常工作操作压力的65倍左右,因而热氨融霜过程诱发的液击易导致爆管与封头脱落的脆性断裂爆炸事故频发,准确预测热氨融霜液击冲击压强的理论前提是要建立综合考虑高温热氨蒸汽和深冷液氨剧烈相变的多相流动液击形成机理理论模型。
[Abstract]:This paper aims at the key scientific and technical bottleneck problems of preventing the safety hidden danger of frequent explosion accidents caused by liquid strike in ammonia melting frost process of hot ammonia refrigeration system. The theoretical model and corresponding simulation method of liquid shock formation in multiphase phase change stratified flow were established. The mechanism of liquid shock formation in the process of hot ammonia melting was revealed by numerical simulation and experimental study. The key control parameters affecting liquid impact are clarified, and the key technologies and methods to restrain the formation of liquid impact are put forward. Based on the safety evaluation of hydraulic impact of return gas manifold, The mechanical mechanism of frequent explosion accidents induced by liquid shock during ammonia defrosting in hot ammonia refrigeration system is described. The results laid a scientific theoretical foundation and technical support for the establishment of the design criteria for ammonia refrigeration units for preventing the failure of liquid impact impact in the process of defrosting. For the first time, a comprehensive consideration of the effect of rapid phase transition of hot ammonia thawing frost was established. A theoretical model for the formation mechanism of liquid shock in vapor-liquid two-phase stratified flow, The virtual simulation platform of hot ammonia thawing frost forming process was established. It was found that the two direct driving forces of hot ammonia thawing process were: 1) the hot ammonia total valve suddenly opened and formed hot ammonia steam. The abrupt change of inlet velocity of steam (2) the abrupt phase transition induced by the instantaneous contact of hot ammonia steam with cryogenic liquid ammonia. The pressure and sharp phase transition of hot ammonia melting frost-liquid were studied. The sudden change of inlet flow rate of hot ammonia steam, the residual volume fraction of cryogenic liquid ammonia, the transient rupture of hot ammonia steam bubble and the correlating relationship of slug flow reveal the key control parameters of the impact pressure of hot ammonia thawing frost. The mechanism of liquid hammer formation in multiphase stratified flow with phase transition is revealed, and the key technologies and methods to restrain liquid impact formation are proposed. An experimental research platform for the mechanism of liquid shock formation of hot ammonia scouring frost in return gas manifold is constructed. In this paper, the inlet velocity of hot ammonia steam at high temperature, sudden acceleration, liquid hammer pressure and liquid level detection, display and control system, and synchronous data acquisition and display system are proposed. The experimental study of hot ammonia scouring frost in gas return manifold shows that the sudden change of inlet velocity of hot ammonia steam at high temperature will lead to the obvious liquid hammer phenomenon in the hot ammonia scouring process of the gas return manifold. The sudden change in the opening trend of the electric flow control valve caused by the overadjustment and correction of the inlet flow rate of high temperature ammonia steam will also lead to obvious liquid hammer. Through the automatic control of inlet velocity of ammonia steam at high temperature, it is difficult to eliminate the phenomenon of liquid shock in the return gas manifold. The measured pressure coincides with that predicted by the theoretical model in this paper. The slug flow caused by the multiphase flow of cryogenic liquid ammonia and high temperature hot ammonia steam is induced by the instability of stratified interface. The direct driving force of the instability of stratified interface is the velocity difference of two phases and the sharp phase transition of the stratified interface. The comparative analysis of liquid shock simulation of multiphase flow with and without phase transition shows that: when other conditions are fixed, The average pressure of the first peak value in the return gas manifold considering the intense phase transition between the hot ammonia steam and the cryogenic liquid ammonia is four to five times that of the first maximum maximum liquid hammer average pressure in the tube without taking into account the phase change. It is about 65 times as high as the normal operating pressure of the return gas manifold. Therefore, the liquid shock induced by the hot ammonia defrosting process is liable to lead to brittle fracture and explosion accidents of the tube and the head falling off. The theoretical premise of accurately predicting the impact pressure of hot ammonia melting frost is to establish a theoretical model for the formation mechanism of liquid shock in multiphase flow considering the severe phase transition of high temperature hot ammonia steam and cryogenic liquid ammonia.
【学位授予单位】：南昌大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB657

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