【作者】 黄冬平；

【导师】 丁国良； Hans Quack；

【作者基本信息】 上海交通大学 ， 制冷与低温工程， 2006， 博士

【摘要】 二氧化碳（CO₂）作为环保工质近年来在制冷系统中得到了越来越多的关注,在这些系统中需要安装安全阀来保障系统的超压安全。在CO₂制冷循环中CO₂是高压的超临界流体或气液混合物,其工作压力为3¹6 MPa,CO₂三相点压力介于大气压力和系统工作压力之间,在通过安全阀排放的过程中可能形成固体CO₂,即干冰,导致CO₂安全阀和下游管路的冻结和堵塞。CO₂安全阀的冻结和堵塞是推广CO₂制冷系统必须解决的问题。本文对此进行了探索性研究。为了确定安全阀和下游管路中发生冻结和堵塞的可能性及其危害,本文采用曲折管和突扩管构造了恶劣流动条件,研究了安全阀排放堵塞特性及堵塞的危害性。本文搭建了CO₂通过安全阀排放流动实验台,对常温下两相CO₂节流排放过程中发生的安全阀冻结和堵塞特性进行了实验研究。实验中利用针阀代替安全阀,研究了开度和阀前蒸气干度对安全阀冻结和堵塞特性的影响;采用同心双透明玻璃管分别模拟类似全启式安全阀、比例式安全阀和内部被堵塞的安全阀内流道,实现了阀内流动可视化,确定了三种安全阀内部结构条件下安全阀冻结和堵塞特性。实验结果表明:存在一个最优的阀开度范围,在此范围内形成的固体CO₂不容易发生沉积和堵塞;在排放高蒸汽干度的CO₂时在下游管道中形成的固体CO₂与气相CO₂摩擦产生静电,产生的静电随安全阀进口蒸汽干度增加而增加,甚至会产生电火花;安全阀下游管路中的堵塞过程呈现周期性,气液两相流和气固两相流交替流过下游管路。在此实验研究的基础上,本文利用排放过程热力分析将实验观测的堵塞特性推广到更广泛的CO₂安全阀的工作更多还原

【Abstract】 As an environment-friendly working fluid, carbon dioxide （CO₂） has gained increased interest in refrigeration applications. Safety valves are required to protect these systems from overpressures, where the fluid upstream the safety valve is supercritical fluid or vapor-liquid two-phase mixture under the pressure of 3¹6 MPa. Since the triple point pressure of CO₂ lies between the atmospheric pressure and the system working pressure, solid CO₂ might be formed and further freeze and/or block the releasing path. The freezing and blockage of the CO₂ safety valve is one of the key problems to be solved in order to marketing the CO₂ refrigeration system. This paper has done some exploratory research on it.In order to verify the possibilities of blockage during releasing, an experimental observation was made by applying meanders and sudden expansion pipe as worst releasing flow condition, and the the possibilities and danger of the blockage in the downstream pipe was studied.An experimental setup was built to study the freezing and blockage characteristics during the throttling release of two-phase CO₂ under the room temperature. Needle valves were used to substitute safety valves and study the effect of valve opening and upstream vapor quality on the freezing and blockage characteristics. Transparent double glass tubes were used to simulate更多还原