【作者】 李德玉；

【导师】 段雄；

【作者基本信息】 中国矿业大学 ， 流体力学， 2012， 博士

【摘要】 冰射流技术作为绿色加工新工艺，在表面清洗除垢和表面脱漆等领域表现出了巨大的应用潜力和广阔的应用前景。本论文以教育部科学技术研究重点项目“过冷水动态生成高压冰射流技术及应用”(编号：03026)为依托，以冰射流表面脱漆工程应用为背景，提出并开展了低温气体环境冰粒生成机理和射吸式冰射流喷嘴内冰粒引射机理的研究；设计并构建了低温气体环境冰粒即时制备系统和冰射流表面脱漆系统；开展了冰粒即时制备基本规律和冰射流表面脱漆试验研究。本文全面分析了冰射流技术的研究现状，重点介绍了现有技术中的冰粒制取方法，提出了低温气体环境快速制取低温球形冰粒的系统模型。利用相变动力学、传热传质及多相流理论对冰粒生成过程进行理论分析，提出了水滴凝固阶段的“冰球”物理模型，并在此基础上建立了低温气体环境冰粒生成过程数学模型。结合“温度回升法”计算分析了水滴在低温气体中的冻结成冰规律。基于液滴沸腾蒸发机理的分析，结合离散液滴多相流模型建立了液氮雾化蒸发过程数学模型。计算分析了有限空间内液氮雾化蒸发生成低温气体的温度场和速度场特点。开展了低温气体中冰粒即时制取基本规律的试验研究，重点研究了水雾化参数对生成冰粒温度、粒度分布和粘结情况的影响。基于可压缩流体动力学理论和气固两相流理论，建立了射吸式冰射流喷嘴内气体冰粒两相流动数学模型，开展了冰粒气力喷射形成冰射流机理的数值研究，计算分析了不同喷射压力下冰射流喷嘴内部气体射流特性、冰粒在喷嘴中的引射加速过程以及气体射流对冰粒速度和温度的影响。构建了冰射流表面脱漆试验系统，针对铝合金2A12和聚丙烯树脂基体开展了冰射流表面脱漆试验研究。本文的主要结论如下：①在分析冰的基本热物理属性、力学特性和粘结特性基础上，结合冰射流技术的特点，提出了适合冰射流技术使用的冰粒温度范围是-27℃到-60℃。②通过建立的低温气体环境冰粒生成过程数学模型，计算分析了水滴在低温气体中的冻结成冰规律。计算结果表明在-60℃的低温气体中，粒径为0.15mm的水滴在下落约0.4m的过程中就可生成-50℃的冰粒。针对有限空间内液氮雾化蒸发过程的数值模拟表明液氮雾化蒸发形成的低温气体空间温度场分布不均匀、不稳定，但气流组织比较简单且流速较低。③在液氮雾化沸腾蒸发制冷和冰粒生成过程计算分析的基础上，设计了可连续即时制取低温冰粒的试验系统，试验研究了冰粒制取的基本规律。结果表明该系统可以连续制取温度低于-30℃、粒径小于0.425mm的球形冰粒。④针对冰粒在射吸式冰射流喷嘴内的引射加速过程数值计算表明，被引射低温气体流量是形成冰射流的关键。低的引射气体流量容易造成冰粒驻留时间过长，引起冰粒堵塞喷嘴。⑤针对铝合金2A12和聚丙烯树脂试样的冰射流表面脱漆表明，冰射流可以有效清除两种试样的油漆涂层；压力较高时，冰射流会导致聚丙烯树脂基体表面粗化，表面粗糙度随喷射压力的增大及喷射时间的延长而增大，但没有引起铝合金基体表面的明显改变。更多还原

【Abstract】 Ice jet technology shows a promising prospect of application and extension insurface cleaning and depainting engineering because of its environment-friendlyfeature. Aimed at development and design of an effective equipment producing iceparticle, this dissertation presented mainly a comprehensive study of the ice particleproduction through experimentation and numerical methods using computational fluiddynamics and computational heat transfer and a systemic research on the depaintingby use of ice blasting technology.According to the in-depth discussions about the thermal physical properties,mechanical performance and surface behavior of ice, a conclusion could be drawn thatthe ice particles with the temperature of-27℃～-60℃should be produced for iceblasting. An “ice sphere” physical model was established and the correspondingnumerical equations were solved to obtain the basic factors influencing the freezingprocess of a water droplet. The results showed that a water droplet of0.15mm indiameter had changed into ice particle with temperature of-50℃at a falling distanceof0.4m in the atmosphere with temperature of-60℃. In order to create a cryogenicatmosphere, liquid nitrogen was used. A numerical model describing the evaporationprocess of liquid nitrogen droplets was solved to obtain the basic laws of evaporation.Furthermore, the evaporation of atomized liquid nitrogen in a specific volume wassimulated.Based on the numerical analysis of freezing of a water droplet and evaporation ofthe atomized liquid nitrogen, an experimental apparatus was established.Experimental research was made to find basic laws of producing ice particles. Resultsshowed that ice particle, ranged from0.425mm to0.075mm in diameter, withtemperature below-30℃were produced continuously by use of the apparatus.The accelerating process of ice particles in a conventional industrial siphon-typesand blasting nozzle were investigated numerically in detail. The numerical equations,including conservation equations of mass, momentum and energy of gas phase, werebuilt based on compressible fluid dynamics. The turbulent flow characteristic wasintroduced by means of RNG k-ε turbulence model and the gas-solid interactions werereflected by discrete phase model.The applications of ice blasting technology in the industrial field of depaintingwere investigated experimentally in the last part of the dissertation. The substrates of depainting samples were aluminum alloy (2A11) and poly propylene. The acrylicpaint was sprayed on the substrate surfaces. The depainting experimental resultsshowed that gas pressure of the ice jet was the most important working parameterinfluencing the de-painting effect. Even at0.2MPa blasting pressure, the two kinds ofpaint coatings samples were stripped effectively. SEM pictures showed that polypropylene surface was roughened obviously when the blasting pressure was above0.3MPa, but the aluminum alloy surface changed little under different blastingconditions.更多还原