基于气液混合层的吸附气体稳定性机理

实验表明溶解在水中的气体会在疏水表面吸附和集聚，学界普遍认为其有"纳米气泡"和"微气饼"两种存在形式。对于这两种形式，经典理论无法解释其稳定存在。本文采用分子动力学方法对气体吸附和积聚过程进行模拟，结果显示吸附气体表层覆盖着气液混合层，对该混合层的形状和特性进行分析和研究，发现该气液混合层具有较高的粘度并且对气体的扩散有明显的抑制作用。     

液态水中含有气态水的实验验证——水的蒸发量与水量的相关性理论的验证实验及其数据分析报告

气体溶质溶于水得到的水溶液可以分为两种基本形态:气液相溶态、气液相混态。气液相溶态、气液相混态符合拉乌尔定律和亨利定律的适用条件。液态的水中也存在气态的水,蒸发是这气态的水分子溢出水面的过程。液面以下的水的蒸发会产生蒸汽泡现象。水的蒸发量除了与蒸发液面的面积相关外,还与水量相关。实验证实在常温下水的蒸发量与水压、水深(水量)存在相关性。由此总结出一个新的蒸发量规律和公式。     

空间碎片超高速撞击压力容器碎片云特性数值模拟研究

 针对空间碎片超高速撞击充气压力容器问题,应用非线性动力学分析软件AUTODYN-2D,采用SPH方法对碎片云在高压气体中的运动特性进行了数值模拟研究。在建模过程中,分析比较了材料状态方程对数值模拟结果的影响,并通过与实验结果的比较,选取了适合该问题的状态方程,验证了数值模拟方法的有效性。结果表明：由于容器内压气体的存在,碎片云运动发生减速,并且碎片云的轴向扩展速度相对于碎片云的径向扩展速度减速较慢;高速撞击产生的碎片云与容器内的高压气体发生了强烈的相互作用,碎片云尖端产生的钉状物及高压气体中产生的冲击波是控制容器在撞击后发生进一步破坏的两个重要因素。     

200 kV/200 kA脉冲源的研制

研制了一台200 kV/200 kA脉冲源,脉冲源由初级储能单元、水介质整形与传输单元、气体开关和负载组成。通过优化设计由2 到1 的水介质变阻抗线、高压气体主开关和陡化开关,使得脉冲功率源在匹配负载下产生输出电压200 kV、电流200 kA、前沿40 ns、脉宽40 ns的高压脉冲。在此脉冲源平台上已开展了低阻抗1 二极管发射特性研究,并且将在高压气体开关、同步触发、二极管等离子体发射诊断等方面发挥作用。     

基于腔增强激光光谱的水中溶解甲烷传感系统

为探测水中甲烷气体浓度,研制了一种基于离轴积分腔输出光谱的水中溶解甲烷传感系统。系统由分布式反馈激光器(中心波长为1 653 nm)、激光器温度控制模块、激光器电流驱动模块、谐振腔/气室、光电探测器、数据采集模块、数据处理模块和气液分离模块构成。利用配备的甲烷气体样品和纯氮气(N2),分别开展系统有效光程标定、直接吸收光谱信号的标定和稳定性测试等实验。使用浓度为10×10-6的甲烷气体样品标定了系统有效光程,约为1 906 m。将纯氮气作为目标气体,测量系统的稳定性。Allan方差分析结果表明,当积分时间为2 s时,系统检测灵敏度为92.8×10-9,当积分时间增加到134 s,系统的灵敏度可提高到13.2×10-9。利用该系统开展自来水、雨水和湖水样品中溶解甲烷的浓度检测实验,结果证实了该技术及系统的工程实用价值。该研究及相关结果为水质检测和天然气水合物等清洁能源的勘探开发奠定了良好的基础。     

恒压型抽水压缩空气储能系统的热力学及经济学多目标优化

为解决可再生能源存在的间歇性和波动性等问题,考虑到现有大规模储能技术的不足,提出了一种兼具抽水蓄能技术和压缩空气储能技术特点的恒压型抽水压缩空气储能系统.首先建立其热力学模型和经济学模型,然后以能量效率和单位能量成本作为目标函数,以水气比、预置压力、增压机压比和增压机效率作为决策变量,分别针对容量为1 MW、2MW、5 MW的系统进行多目标优化。多目标优化结果表明,当水气比约为7、预置压力约为4 MPa、增压机压比约为2、增压机效率较高时,系统具有较高的能量效率和较低的单位能量成本。同时,随着系统容量的增加,单位能量成本明显降低。研究结果可为该系统的工程应用提供理论支撑。     

水合物封闭升温及降压分解气液迁移特性

水合物分解过程产生的气液固迁移特性是影响水合物分解速率的关键要素。基于此,搭建了一套可视化的水合物生长及分解特性研究实验系统,通过该系统对封闭升温及降压分解过程中气液迁移特性进行了研究。实验结果表明,水合物在封闭升温分解过程中的气液迁移主要是通过形成气体通道实现的;同时,水合物分解过程中的气液迁移会造成沉积物的体积膨胀,在封闭升温分解过程中,沉积物体积膨胀率随着分解次数的增加而增加,三次分解膨胀率依次为18. 7%,34. 7%和45. 4%。背压为0. 1 MPa的降压分解中,体积膨胀率为64. 7%,温度迅速下降,并伴随着冰的生成或水合物的再次生成阻碍分解,但是降压依然加速了水合物的分解,使得水合物的总分解速率相对于封闭升温分解提高了20. 5%。实验结果对水合物技术应用具有理论和数据支撑作用。     

容器形状和冻结行为对储能效率影响研究

本文采用计算流体力学分析方法,分析了冰储能过程中水的固-液相变行为和由此产生的自然对流现象的特征。特别地,本文着重研究了安装在冰储能器中的换热器周围的冻结行为和桥接过程对储能效率的影响。为了研究冻结行为和桥接过程中产生自然对流对储能效率的影响,改变了容器的高宽比,并采用椭圆形换热器以促进对流的形成。采用潜热与比热相结合的单域计算模型,分析了两椭圆形换热器在冻结过程中的水温分布特征、速度分布特征以及冻结率。研究发现容器内对流方向的趋势是由水的初始温度决定的,并且容器宽度越大,高度越高,冻结率效率越高。     

He气辅助熔接的全光纤型HC-PCF低压气体腔的制备

提出了一种He气辅助熔接的全光纤型空芯光子晶体光纤(HC-PCF)低压气体腔的制备方法。通过用高压待充气体冲洗HC-PCF,确保了腔内的气体纯度;通过利用光谱监测系统监测HC-PCF降压过程及He气辅助熔接过程中CO2吸收光谱的变化,研究了HC-PCF中气体动力学运动过程;通过利用He气辅助熔接方法,制备得到压强为7 k Pa、插入损耗小于2 d B、长度为10 m的全光纤型HC-PCF低压CO2气体腔。该方法也适用于更低压强的HC-PCF气体腔的研制,且制备的气体腔具有良好的气密性和长期稳定性。     

太阳能液体干燥剂除湿潜能储存热质传递过程研究

对液体干燥剂制冷和除湿能力贮存环节进行了分析,给出一种太阳能干燥剂再生转换装置传热传质数学模型．该储能方式没有因储能介质与周围环境存在温差产生的冷热损失,对ＣａＣｌ２和ＬｉＣｌ等典型液体干燥剂的分析表明,理想情况下,二者的储能密度可达１０００ ＭＪ／Ｍ３和 １４００ ＭＪ／ｍ３,远大于水和冰的蓄能密度,储能密度还受太阳辐射、面盖间距、环境条件等因素影响．     

含气量对激光空泡在刚性壁面空蚀的影响

采用强脉冲激光器设计液体环境下刚性壁面空蚀实验平台,改变液体中含气量,利用高速相机观察不同含气量条件下激光空泡在壁面附近的脉动过程,并对刚性壁面造成的空蚀结果进行了观测。实验研究发现,随着液体中相对空气含量的提高,激光空泡脉动的最大尺寸增大,空泡的膨胀运动变剧烈,溃灭运动速度降低,空泡的溃灭强度降低,从而影响到溃灭冲击波和壁面微射流对刚性壁面的冲击速度,减弱了壁面空蚀,而液体中含气量的提高能够降低激光空泡对刚性壁面的空蚀程度。     

围压条件下空化磨料射流的冲蚀特性与机制分析

 磨料射流在水利水电、石油工程和海洋资源开发等领域有着广泛的应用,研究射流的冲蚀特性和破坏物料机制对提高水射流利用效率具有重要意义。利用自行研制的实验装置,研究了围压条件下自振空化、文丘里和锥形3种喷嘴形成的磨料射流冲蚀特性,分析了空化磨料射流冲蚀物料的机制。结果表明：自振空化喷嘴和文丘里喷嘴的冲蚀效果优于锥形喷嘴,空化作用有助于提高磨料射流的冲蚀效果;磨料射流的冲蚀效率随围压的增大而降低,主要原因是围压对纯水射流和空化磨料射流的压力脉动和冲击力具有抑制作用。分析认为,空化磨料射流冲蚀破碎物料的机制主要包括冲蚀、气蚀和共混磨蚀3 种作用。     

Novel cavitation fluid jet polishing process based on negative pressure effects

Traditional abrasive fluid jet polishing (FJP) is limited by its high-pressure equipment, unstable material removal rate, and applicability to ultra-smooth surfaces because of the evident air turbulence, fluid expansion, and a large polishing spot in high-pressure FJP. This paper presents a novel cavitation fluid jet polishing (CFJP) method and process based on FJP technology. It can implement high-efficiency polishing on small-scale surfaces in a low-pressure environment. CFJP uses the purposely designed polishing equipment with a sealed chamber, which can generate a cavitation effect in negative pressure environment. Moreover, the collapse of cavitation bubbles can spray out a high-energy microjet and shock wave to enhance the material removal. Its feasibility is verified through researching the flow behavior and the cavitation results of the negative pressure cavitation machining of pure water in reversing suction flow. The mechanism is analyzed through a computational fluid dynamics simulation. Thus, its cavitation and surface removal mechanisms in the vertical CFJP and inclined CFJP are studied. A series of polishing experiments on different materials and polishing parameters are conducted to validate its polishing performance compared with FJP. The maximum removal depth increases, and surface roughness gradually decreases with increasing negative outlet pressures. The surface becomes smooth with the increase of polishing time. The experimental results confirm that the CFJP process can realize a high material removal rate and smooth surface with low energy consumption in the low-pressure environment, together with compatible surface roughness to FJP.     

Liquid jet directionality and droplet behavior during emulsification of two liquids due to acoustic cavitation

The present study numerically investigates liquid-jet characteristics of acoustic cavitation during emulsification in water/gallium/air and water/silicone oil/air systems. It is found that a high-speed liquid jet is generated when acoustic cavitation occurs near a minute droplet of one liquid in another. The velocity of liquid jet significantly depends on the ultrasonic pressure monotonically increasing as the pressure amplitude increases. Also, the initial distance between cavitation bubble and liquid droplet affects the jet velocity significantly. The results revealed that the velocity takes maximum values when the initial distance between the droplet and cavitation bubble is moderate. Surprisingly, the liquid jet direction was found to depend on the droplet properties. Specifically, the direction of liquid jet is toward the droplet in the case of water/gallium/air system, and vice versa the jet is directed from the droplet in the case of water/silicone oil/air system. The jet directionality can be explained by location of the high-pressure spot generated during the bubble contraction.     

Physical and chemical characterization of shock-induced cavitation

A strong impact on a water surface induces a shock wave propagation with a significant pressure variation leading to cavitation bubble formation. A new shock induced cavitation reactor described in this work was characterized by physical and chemical techniques. Water hammer model verification with Joukowsky approach allowed to determine the wave speed propagation and gas fraction in water submitted to shock. These values were used for frequency analysis and compared with direct bubble visualization in order to estimate the influence of the experimental parameters on the shock-induced cavitation. Thereby, the shock wave contains a broad spectrum as decomposed into frequencies. This multi-frequency nature induces heterogeneous bubbles with calculated radii of 0.01 to 3.5 mm and observed radii of 0.01 to 2.8 mm depending on experimental conditions (initial pressure, impact height, gas atmosphere). For the first time, the formation of hydroxyl radicals was proven under impact-induced cavitation. The concentration of radicals increases with increasing number of successive impacts, reaching ca. 1.3 µmol.L⁻¹ after 500 impacts in the presence of 20% O₂-Ar as saturating gas. Radical generation seems to be relatively independent of the impact height but strongly depend on the type of gas saturating water, being substantially lower in the presence of air. Moreover, radical generation increases when decreasing the initial pressure and depends on the frequency at which water is impacted by the piston. Nevertheless, yield of OH radicals during shock-induced cavitation remains much lower than that produced by power ultrasound.     

轴流式水轮机内部空化流动的数值预测

将一种完整空化模型和一种混合流体两相流模型相结合,应用于轴流式水轮机全流道内定常空化流动的数值模拟。根据模拟结果,分别预测了水轮机在正常和较低尾水位情况下运行时,流道内空化发生的部位和程度,重点考察了尾水位的降低对水轮机空化性能的影响,为水轮机在特定运行工况下的空化性能预测提供参考。     

轮背空腔-密封气对CAES向心涡轮变工况流动损失的影响

本文以国内首套MW级压缩空气储能(CAES)系统末级向心涡轮为研究对象,通过数值模拟分析了变工况条件下轮背空腔-密封气对等熵效率和流场结构的影响.结果表明:在求解中考虑轮背空腔-密封气结构能够使等熵效率数值解的偏差减小0.7%;随涡轮进口压力增加,轮背空腔泄漏流由叶片吸力面中部叶高区域逐渐向轮毂转移,流动损失先增加后减小;合理降低轮背空腔泄漏气体的轴向速度,能够减弱轮背空腔-密封气结构对等熵效率的负面影响,使向心涡轮在较宽的变工况范围内都保持高效运行.     

高温高压下湿空气的焓和熵计算

本文以湿空气透平和压缩空气储能系统中的工质-湿空气为研究对象,运用所提出的一个适合计算高温高压湿空气热力学性质的对应态维里方程,对湿空气的偏差焓和偏差熵进行了计算.在湿度0≤ W≤1 kg/kg(A),温度小于573.15 K,压力小于5 MPa时,与ASHRAE用的多项式维里方程计算得到的偏差焓和偏差熵进行了比较,误差很小.用这个对应态维里方程外推计算了温度和压力分别达到600 K和15 MPa的湿空气焓和熵.计算结果表明对湿空气而言压力和湿度越大,偏差焓和偏差熵越大;温度越高,偏差焓和偏差熵越小.     

Degradation of benzene present in wastewater using hydrodynamic cavitation in combination with air

The degradation of benzene present in wastewater using hydrodynamic cavitation (HC) alone as well as in combination with air has been studied using nozzles as cavitating device of HC reactor. Initially, the energy efficiency of the HC reactor operated at different inlet pressures was determined using the calorimetric studies. Maximum energy efficiency of 53.4% was obtained at an inlet pressure of 3.9 bar. The treatment processes were compared under adiabatic as well as isothermal conditions and it was observed that under the adiabatic condition, the extent of degradation is higher as compared to isothermal condition. Studies related to the understanding the effect of inlet pressure (range of 1.8–3.9 bar) revealed that the maximum degradation as 98.9% was obtained at 2.4 bar pressure using the individual operation of HC under adiabatic conditions and in 70 min of treatment. The combination of HC with air was investigated at different air flow rates with best results for maximum degradation of benzene achieved at air flow rate of 60 mL/sec. A novel approach of using cavitation for a limited fraction of total treatment time was also demonstrated to be beneficial in terms of the extent of degradation as well as energy requirements and cost of operation. Based on the cavitational intensity, the resonant radius of aggregates of cavitation bubbles was also determined for distilled water as well as for aqueous solution of benzene. Overall, significant benefits of using HC combined with air have been demonstrated for degradation of benzene along with fundamental understanding into cavitation effects.