R410A在水平内螺纹管中沸腾换热实验研究

对于非共沸混合制冷剂R410A在外径9.52mm、5mm的两种不同的几何参数的内螺纹的流动沸腾换热进行了实验研究,分析讨论了制冷剂质量流速、管外水流量变化、强化管的参数、强化管的压降对换热系数影响以及其机理。试验的结果表明:换热系数随着流量的增大而增大,管径的大小对换热系数的影响较大,在相同的流量下,9.52mm的换热系数比5mm的大到110%~230%,5mm管的压降比9.52mm的大200%~300%。     

Planar Line Processes for Void and Density Statistics in Thin Stochastic Fibre Networks

Using results for the distribution of perimeters of random polygons arising from random lines in a plane, we obtain new analytic approximations to the distributions of areas and local line densities for random polygons and compute various limiting properties of random polygons. Using simulation, we show that the lengths of adjacent sides of polygons generated by random line processes in the plane are correlated with ρ=0.616±0.001.     

The Smoluchowski limit for a simple mechanical model

We consider a vertical stick constantly accelerated along thex-axis by a forceF and which elastically collides with point particles of the same mass (atoms). The atoms are initially Poisson distributed and are allowed to have four velocities only. It is shown that under suitable scaling of the system the displacementQ(t) of the stick satisfies a nontrivial CLT:Q(t)=vFt+D ^1/2 W(t) (Smoluchowski equation), where the values ofv andD depend on the fact that one atom may collide several times.     

Phase space density representations in fluid dynamics

Phase space density representations of inviscid fluid dynamics were recently discussed by Abarbanel and Rouhi. Here it is shown that such representations may be simply derived and interpreted by means of the Liouville equation corresponding to the dynamical system of ordinary differential equations that describes fluid particle trajectories. The Hamiltonian and Poisson bracket for the phase space density then emerge as immediate consequences of the corresponding structure of the dynamics. For barotropic fluids, this approach leads by direct construction to the formulation presented by Abarbanel and Rouhi. Extensions of this formulation to inhomogeneous incompressible fluids and to fluids in which the state equation involves an additional transported scalar variable are constructed by augmenting the single-particle dynamics and phase space to include the relevant additional variable.     

Electric field dependence of phase equilibria of binary Stockmayer fluid mixtures

A perturbation theory based study of the effect of an external electric field on the phase equilibrium properties of binary Stockmayer fluids is presented. The dipole–dipole interaction and the applied field are treated as independent perturbations to a Lennard–Jones mixture, and the reference fluid is treated by the van der Waals one-fluid approximation. A third-order free energy expression in the electric field strength is established, and the dielectric constant is calculated for a needle-shaped sample parallel to the field direction. We present and discuss vapour–liquid and liquid–liquid equilibrium curves at a given temperature for some dipolar mixtures exposed to an electric field, including chlorodifluoromethane +?difluoromethane and acetonitrile +?methanol. A sufficiently high electric field may result in massive shifts of vapour pressures and critical or azeotropic points, and can considerably alter the properties of coexisting phases. The vapour pressure decreases with increasing field strength.     

单级自动复叠混合工质制冷循环的实验研究

由于压缩机压比的局限,制约着单一制冷剂的压缩回热循环发展,本系统采用单一压缩机和混合工质的自复叠制冷循环系统取得了较好的制冷效果。文中对单级自动复叠制冷系统进行了理论模拟,并设计和搭建了实验台进行分析。通过理论和实验数据的分析得出混合工质组合R600a/R23,并初步得到最优配比。     

混合工质HFC134a/HCs替代R502的性能分析

针对目前R502主流替代工质R507和R404A存在的温室效应指数高、与矿物油互溶性差等缺点,提出了环保性能更好的三组近共沸混合工质R134a/R290、R134a/R1270和R134a/R290/R1270作为R502新型替代工质;并对其热物性、循环性能、安全性能和溶油性进行了计算分析。结果表明：除了压缩机排气温度偏高,这三组R134a/HCs混合工质的其它主要循环性能参数如压缩机压力比、容积制冷量和系统性能系数COP都优于R507和R404A,并且从理论上讲不存在可燃可爆的危险,同时可以与矿物油互溶,在替代R502方面更具有优势,其中R134a/R290/R1270在高热负荷下的综合性能最优良。     

Excess volumes and densities of binary mixtures of γ-butyrolactone + 1, 3, 5-trimethylbenzene or 1, 2, 4-trimethylbenzene at several temperatures

Densities of two binary mixtures formed by γ-butyrolactone with 1,3,5-trimethylbenzene and 1,2,4-trimethylbenzene have been determined over the full range of compositions over the temperature range (288.15 K to 308.15 K) and the local barometric pressure using a vibrating-tube densimeter. From these experiments, excess molar volumes () have been calculated. It is found to be positive with a maximum at about the mole fraction of 0.5. Excess volumes were also fitted to a Redlich–Kister type equation. Our result shows increases when temperature increases in the studied systems.     

Phase behaviors in a binary mixture of diblock copolymers confined between two parallel walls

The phase behaviors in a binary mixture of diblock copolymers confined between two parallel walls are investigated by using a cell dynamics simulation of the time-dependent Ginzburg-Landau theory.The morphological dependence of the wall-block interaction and the distance between walls(confinement degree) has been systematically studied,and the effect of repulsive interactions between different monomers is also discussed.It is interesting that multiple novel morphological transitions are observed by changing these factors,and various multilayered sandwich structures are formed in the mixture.Furthermore,the parametric dependence and physical reasons for the microdomain growth and orientational order transitions are discussed.From the simulation,we find that much richer morphologies can form in a binary mixture of diblock copolymers than those in a pure diblock copolymer.Our results provide an insight into the phase behaviors under parallel wall confinement and may provide guidance for experimentalists.This model system can also give a simple way to realize orientational order transition in soft materials through confinement.     

一种基于非参数贝叶斯模型的聚类算法

鉴于聚类分析是机器学习和数据挖掘领域的一项重要技术, 并且与监督学习不同的是聚类分析中没有类别或标签的指导信息, 所以如何选择合适的聚类个数(即模型选择)一直是聚类分析中的难点. 由此提出了一种基于Dirichlet过程混合模型的聚类算法, 并用collapsed Gibbs采样算法对混合模型的参数进行估计. 新算法基于非参数贝叶斯模型的框架, 能够在不断的采样过程中优化模型参数并形成合适的聚类个数. 在人工合成数据集和真实数据集上的聚类实验结果表明: 基于Dirichlet过程混合模型的聚类算法不但能够自动确定聚类个数, 而且具有较强灵活性和鲁棒性.