空气源热泵机组结霜问题的实验分析

基于空气源热泵在低温寒冷地区运行中遇到的结霜问题,对不同风速工况下,结霜过程中设备性能的变化进行分析,以换热量、换热系数为指标对不同翅型换热器的换热特性进行研究。实验结果显示:换热器结霜过程中,换热过程主要分为初始增加段、换热平稳段、缓慢衰减段、后期平稳等四段,结晶体在增加空气湍流度强化换热的同时,也增加了换热热阻使换热效果变差,因此换热效果本质而言是两种换热效果的综合体现;空气阻力随风速的增大、结霜量的增加而增大,而蒸发压力随着风速的增加而升高、随结霜量的增大而减小;百叶窗翅片表面结霜量大于平翅片,因此平翅片翅型当量换热系数更大,翅片结霜量、当量换热系数随风速的增加而增大,风速由1 m/s增至4 m/s时,结霜量、当量换热系数增加约三倍。     

Confinement effects on the electronic structure of M‐shell atoms: A study with explicitly correlated wave functions

The ground and some excited states of Na and Mg atoms confined at the center of a spherical box with impenetrable walls are studied. Variational wave functions including dynamic correlations and configuration mixing have been obtained. Level crossings induced by confinement have been analyzed in terms of the energy of the occupied orbitals of the M shell and the weight of the different configurations. Confinement effects on the correlation energy have been studied. The parameterized optimized effective potential and the variational Monte Carlo methods have been employed. A cut off‐factor has been included to account for the hard wall confinement.     

A stability study of Navier-Stokes equations (III)

In this paper, the necessary conditions of the existence of C² solutions in some initial problems of Navier-Stokes equations are given, and examples of instability of initial value (at t=0) problems are also given. The initial value problem of Navier-Stokes equation is one of the most fundamental problem for this equation various authors studies this problem and contributed a number of results. J. Lerav, a French professor, proved the existence of Navier-Stokes equation under certain defined initial and boundary value conditions. In this paper, with certain rigorously defined key concepts, based upon the basic theory of J. Hadamard partial differential equations¹, gives a fundamental theory of instability of Navier-Stokes equations. Finally, many examples are given, proofs referring to Ref. [4].     

线性船舶兴波阻力边界元新方法

采用常数边界元对船舶与流体界面进行离散，求解船舶兴波势及船舶兴波阻力。这种方法可避免在船舶与流体自由面交线上安置节点，因而避免了这些节点建立补充方程。因为满足自由面条件的Ｈａｖｅｌｏｃｋ源函数的源点和场点不能同时在自由面上，使得自由面上的节点无法用Ｈａｖｅｌｏｃｋ源函数的建立方程。如对自由面交线上的节点建立补充方程，则要对线性自由面条件中包含的未知势函数的二阶导数用差分形式表达，引入较大误差。     

Forced convection of gaseous slip-flow in porous micro-channels under Local Thermal Non-Equilibrium conditions

Steady laminar forced convection gaseous slip-flow through parallel-plates micro-channel filled with porous medium under Local Thermal Non-Equilibrium (LTNE) condition is studied numerically. We consider incompressible Newtonian gas flow, which is hydrodynamically fully developed while thermally is developing. The Darcy–Brinkman–Forchheimer model embedded in the Navier–Stokes equations is used to model the flow within the porous domain. The present study reports the effect of several operating parameters on velocity slip and temperature jump at the wall. Mainly, the current study demonstrates the effects of: Knudsen number (Kn), Darcy number (Da), Forchheimer number (Γ), Peclet number (Pe), Biot number (Bi), and effective thermal conductivity ratio (K _R) on velocity slip and temperature jump at the wall. Results are given in terms of skin friction (C _f Re ^*) and Nusselt number (Nu). It is found that the skin friction: (1) increases as Darcy number increases; (2) decreases as Forchheimer number or Knudsen number increases. Heat transfer is found to (1) decreases as the Knudsen number, Forchheimer number, or K _R increases; (2) increases as the Peclet number, Darcy number, or Biot number increases.     

Similarity solutions for the flow behind an exponential shock in a non-ideal gas

Similarity solutions for the flow of a non-ideal gas behind a strong exponential shock driven out by a piston (cylindrical or spherical) moving with time according to an exponential law are obtained. Similarity solutions exist only when the surrounding medium is of constant density. Solutions are obtained, in both the cases, when the flow between the shock and the piston is isothermal or adiabatic. It is found that the assumption of zero temperature gradient brings a profound change in the density distribution as compare to that of the adiabatic case. Effects of the non-idealness of the gas on the flow-field between the shock and the piston are investigated. The variations of density-ratio across the shock and the location of the piston with the parameter of non-idealness of the gas are also obtained.     

变分原理分析开裂简支箱梁剪力滞效应

变分原理通常应用于箱形截面梁剪力滞效应弹性分析,本文基于换算截面法,运用变分原理推导了预应力混凝土简支箱梁均布荷载作用、钢筋混凝土简支箱梁集中荷载作用的剪力滞系数计算公式,考虑了混凝土开裂对箱梁剪力滞效应的影响,并与试验结果和规范方法进行了对比分析。变分原理分析开裂混凝土箱梁剪力滞效应方法力学概念明确,是其弹性分析适用范围的拓展,亦可推广应用到混凝土连续箱梁开裂后的剪力滞效应分析,具有广阔的应用前景。     

Poroacoustic solitary waves under the unidirectional Darcy–Jordan model

Working in the context of poroacoustics, we present new, physically relevant, explicit solutions to the Cauchy problem for the model we term the (1D) damped Riemann equation. The solitary waveforms that evolve from both Lorentzian ($C^{\infty }$-smooth) and symmetric-exponential ($C^0$-smooth) initial conditions are analyzed, the focus being on wave overturning and the evolution/structure of the shocks which develop thereafter. In addition to those for both the multi- and single-valued forms of each solution, expressions for the shock amplitude, velocity, and critical values of the physical parameters are derived/compared. Lastly, links to other areas of continuum physics, and possible follow-on investigations, are noted.     

On the boundary value problem of elastostatics in terms of stresses

The boundary value problem of elastostatics in terms of six components of the stress consists of nine equations and three boundary conditions. In this paper, we distinguished between the possible cases and impossible cases, i.e., the problem is or is not equivalent to a boundary value problem of six equations and six boundary conditions.     

Mixed Formulations of Bending Problems for Homogeneous Elastic Plates and Beams

Mixed formulations of bending problems for homogeneous plates (beams) are proposed, whose essence is that the deformation of a plate (beam) near its fixed boundary is described by the threedimensional elasticity equations, and the remaining part by the conventional equations of plate (beam) bending. At the interface between these regions, the solutions of these equations are joined. The mixed formulation allows one to describe the threedimensional stress state in the neighborhood of the fixed boundaries of plates (beams) and take into account the complex nature of the fixing conditions. Finiteelement implementation is more efficient for the mixed formulations of plate (beam) bending problems than for the wellknown threedimensional formulations.