太阳能两级喷射式制冷系统性能的模拟及其分析

讨论了一种新型的太阳能制冷系统——带回热器的太阳能两级喷射式制冷系统。该系统最大的特点是将两个喷射器串联在一起,以提高整个太阳能制冷系统的性能系数。分别采用R134a、R152a、R245ca和R227ea为制冷工质下系统性能系数COP随两级间总压比分配度不同的变化关系。这四种制冷剂的两级压缩比的变化对总喷射系数的影响各有不同,并提出了气体喷射器的总压缩比1.2—2.8之间两级压缩比的不均匀分配原则。     

应用R236fa作为制冷剂的喷射制冷系统性能分析

分析了R236fa工作介质的特点,研究了其作为喷射制冷系统制冷剂的适用性.通过对系统的热力学分析计算,比较R141b、R123、R134a和R236fa作为喷射制冷系统制冷剂的工作特性,得出了R236fa作为喷射制冷系统工作介质的优点和特点.给出了以R236fa作为制冷剂的喷射制冷系统在不同工作条件下的运行性能.重点分析了以R236fa作为工作介质的喷射制冷系统的泵功率、COP和喷射器关键几何尺寸.当系统制冷量为1 000kW时,最大泵功率仅为58kW,混合室直径仅为152 mm,COP最大可达到0.35.研究结果表明,以R236fa作为制冷剂的喷射制冷系统具有更好的经济性,并且在大型化制冷系统的设计、加工和制造中具有明显的优势.     

Review on mathematical analysis of some two-phase flow models

The two-phase flow models are commonly used in industrial applications, such as nuclear, power, chemical-process, oil-and-gas, cryogenics, bio-medical, micro-technology and so on. This is a survey paper on the study of compressible nonconservative two-fluid model, drift-flux model and viscous liquid-gas two-phase flow model. We give the research developments of these three two-phase flow models, respectively. In the last part, we give some open problems about the above models.     

锅炉启动疏水回收至除氧器的降噪实验研究

将超临界直流锅炉启动疏水引入除氧器,可同时回收疏水工质及其热量.启动疏水在进入除氧器时,由于压力的骤降会产生巨大动能会冲击并损害除氧器内件,且伴随有近100 dB(A)的蒸汽水下喷射噪声.针对这一问题,设计了蒸汽喷射器和小孔喷注消声器作为降噪装置进行对比实验.结果表明,蒸汽在蒸汽喷射器内被冷凝,使得蒸汽水下喷射噪声被降低至80 dB(A)以下.小孔喷注消声器则不能使蒸汽在进入过冷水之前被冷凝,其蒸汽水下喷射噪声最低也在80 dB(A)以上.因此蒸汽喷射器在降低蒸汽水下喷射噪声方面要优于小孔喷注消声器.     

超临界二氧化碳类液-类气区边界线数值分析

超临界二氧化碳(S-CO₂)因在萃取、沉淀、热力循环及化学反应等方面有着十分广阔的应用前景,逐渐成为学术界的重要研究课题.由于在近临界区,可以观察到随温度或压力变化出现大量的物性异变现象,使得各国学者对流体临界点附近区域的研究产生了浓厚兴趣.随着分子动力学模拟技术的快速发展,该技术可辅助传统实验方法用于研究近临界流体的相关物性.为确定S-CO₂在近临界区Widom线范围及类液-类气区的分子结构特征,本文通过分子动力学模拟技术结合聚类分析,研究了温度和压力范围分别在300—350 K和5.5—18.5 MPa下,CO₂密度时间序列变异系数及偏度同Widom线和类液-类气区间的关系.结果表明:S-CO₂在近临界区Widom线的确定可通过连接密度时间序列曲线变异系数极大值点来确定,Widom线沿着临界点开始延伸直到350 K时停止;S-CO₂类液区和类气区的分子分布结构可以用数密度分布的偏度来区分,偏度在类气态时为正值,在类液态时为负值,而在Widom线上达到最大值.     

引射器用作化学氧碘激光器压力恢复系统的探讨

探讨了引射器在化学氧碘激光器（ＣＯＩＬ）压力恢复系统中的使用问题。为减小引射器的规模而达到较高的扩压比Ｐｒｅｃ／Ｐ′，引射工质应采用分子量和比热比小的气体。提高引射气体的温度及马赫数，也可增加扩压比     

Stability and evolution of liquid-gas interfaces on superhydrophobic surfaces

超疏水表面功能材料在防污、流动减阻等领域具有重要应用,其中液-气界面的稳定性是关系到该种材料性能发挥的关键因素.微结构液-气界面的稳定性主要体现在浸润状态转变过程,浸润状态恢复过程和气泡形态演化过程三个方面.在压强变化、气体扩散等多种因素作用下,液-气界面会发生失稳现象,并以不同的形态变化方式进行演化发展.该文首先总结了三类液-气界面稳定性问题.在不同的演化阶段,液-气界面具有不同的位置和形状,体现出不同的稳定性.然后,分别针对液滴系统和水下浸没系统,考虑了几种主要的影响因素,综述了目前国内外关于超疏水微结构液-气界面稳定性研究的主要进展,总结液-气界面的演化机制.最后,展望了该领域中存在的主要科学问题.     

A numerical and experimental study of a collapsing bubble-induced droplet ejector

This paper aims to study a novel drop-on-demand droplet generation mechanism in which the oscillation and deformation of a non-equilibrium bubble in close proximity to a free surface induce an axisymmetric liquid spike on the free surface. The evolution of the liquid spike and its deformation due to the effect of surface tension force lead to the formation of a droplet. The free surface can be accorded by either a circular hole on a horizontal flat plate or by the top opening/nozzle of a vertical cylinder. A high-speed camera capable of obtaining images at a frame rate of 15,000 fps is utilized to observe the droplet formation process. Numerical simulations corresponding to the experiments are performed using the boundary integral spatial solution coupled with the time integration, i.e., a mixed Eulerian–Lagrangian method. In the experiments the bubble is generated using a very low voltage (only 55 V) in contrast to the relatively much higher voltages usually employed in reported works. This is very attractive from a safety viewpoint and accords great simplification of the setup. A comparison is made between the numerical and experimental results. A reasonable agreement has been found. The influences of the main design parameters, namely, the bubble-free surface distance and the dimension of the hole/nozzle on the bubble dynamics and on the droplet formation process are discussed and the conditions of the bubble dynamics under which a satellite-free droplet can be generated are sought. Furthermore, the effects of different geometries, namely, the horizontal flat plate and the vertical cylinder on the bubble dynamics and on the droplet features are examined. One important feature of the proposed actuation mechanism is the capability of producing droplets much smaller than the nozzle size. The possible applications of this mechanism are those where the accurate direction of the ejected droplet is of great importance such as inkjet printing.      

热核物质液气相变的临界温度和三体核力效应

通过引入微观三体核力, 扩展了有限温度Brueckner-Hartree-Fock方法. 利用这一扩展的理论模型, 研究了热核物质的状态方程和液气相变现象并计算了临界温度, 讨论了三体核力对液气相变临界点性质的影响并与Dirac-Brueckner-Hartree-Fock方法的理论预言进行了比较. 结果表明：三体核力对热核物质状态方程提供一个随密度和温度增大而增强的排斥贡献, 而且三体核力的排斥效应导致热核物质液气相变的临界温度明显降低.     

蒸汽喷射式制冷系统模型建立与仿真

对蒸汽喷射制冷工作过程中能量转化进行了深入分析,建立了制冷系统中的三个关键部件——喷射器、冷凝器及蒸发器的热力学模型.以此为基础,结合运行参数,采用Matlab软件,对喷射系数、蒸汽消耗量以及循环水耗量进行仿真计算.探讨了以喷射系数为评定标准时,工作蒸汽压力Pg、冷凝温度Tc、蒸发温度Te对系统性能的影响.分析结果表明...