Numerical simulation on partial coalescence of a droplet with different impact velocities

Partial coalescence is a complicated flow phenomenon.In the present study,the coalescence process is simulated with the volume of fluid(VOF)method.The numerical results reveal that a downward high-velocity region plays a significant role in partial coalescence.The high-velocity region pulls the droplet downward continuously which is an important factor for the droplet turning into a prolate shape and the final pinch-off.The shift from partial coalescence to full coalescence is explained based on the droplet shape before the pinch-off.With the droplet impact velocity increasing,the droplet shape will get close to a sphere before the pinch-off.When the shape gets close enough to a sphere,the partial coalescence shifts to full coalescence.The effect of film thickness on the coalescence process is also investigated.With large film thickness,partial coalescence happens,while with small film thickness,full coalescence happens.In addition,the results indicate that the critical droplet impact velocity increases with the increase of surface tension coefficient but decreases with the increase of viscosity and initial droplet diameter.And there is a maximum critical Weber number with the increase of surface tension coefficient and initial droplet diameter.

Application of entransy dissipation extremum principle in radiative heat transfer optimization

The concepts of entransy flux and entransy dissipation in radiative heat transfer were introduced based on the analogy with heat conduction and heat convection processes. Entransy will be partially dissipated during the radiative heat transfer processes due to the irreversibility. The extremum principle of entransy dissipation was developed for optimizing radiative heat transfer processes. This principle states that for a fixed boundary temperature the radiative heat transfer is optimized when the entransy dissipation is maximized, while for a fixed boundary heat flux the radiative heat transfer process is optimized when the entransy dissipation is minimized. Finally, examples for the application of the entransy dissipation extre- mum principle are presented.

Molecular dynamics study on thermal conductivity of nano-scale thin films

A simple and effective model of heat conduction across thin films is set up and molecular dynamics simulations are implemented to explore the thermal conductivity of nanoscale thin dielectric films in the direction perpendicular to the film plane. Solid argon is selected as the model system due to its reliable experimental data and potential function. Size effects of the thermal conductivity across thin films are found by computer simulations: in a film thickness range of 2-10 nm, the conductivity values are remarkably lower than the corresponding bulk experimental data and increase as the thickness increases. The consistency between the approximate solution of the phonon Boltzmann transport equation and the simulation results ascribes the thermal conductivity size effect to the phonon scattering at film boundaries.

Branching random walks with random environments in time

We consider a branching random walk on N with a random environment in time （denoted by ξ）. Let Zn be the counting measure of particles of generation n, and let Zn（t） be its Laplace transform. We show the convergence of the free energy n-llog Zn（t）, large deviation principles, and central limit theorems for the sequence of measures {Zn}, and a necessary and sufficient condition for the existence of moments of the limit of the martingale Zn（t）/E[Zn（t）ξ].

Thermal management of space stations

Thermal management aims at making full use of energy resources available in the space station to reduce energy consumption, waste heat rejection and the weight of the station. It is an extension of the thermal control. This discussion introduces the concept and development of thermal management, presents the aspects of thermal management and further extends its application to subsystems of the space station.

Two-dimensional simulation of frost formation on the NACA0012 airfoil under strong convection by using the p-VOF method

A newly developed frosting simulation method,p-VOF method,is applied to simulate the dynamic frost formation on the NACA0012 airfoil under strong convection.The p-VOF method is a pseudo VOF method of the multiphase flow simulation with phase change.By solving a simplified mass conservation equation explicitly instead of the original volume fraction equations in CFD software,the efficiency and robustness of calculation are greatly improved.This progress makes it possible to predict a long-time frost formation.The p-VOF method was successfully applied to the simulation of dynamic frosting on the two-dimensional NACA0012 airfoil under strong convection conditions with constant frost physical properties.The simulation result shows that the average thickness of the frost layer increases,and the frost bulges and flow separation appear earlier,when the airfoil surface temperature decreases or the air humidity increases.The frost bulges and flow separation appear earlier,when the air velocity is faster,the growth rate of the frost layer at the early stage is greater,but the final frost layer is thinner.

Convergence of complex martingale for a branching random walk in an independent and identically distributed environment

We consider anR^(d)-valued discrete time branching random walk in an independent and identically distributed environment indexed by time n∈N.Let W_(n)(z)(z∈C^(d))be the natural complex martingale of the process.We show necessary and sufficient conditions for the L^(α)-convergence of W_(n)(z)forα>1,as well as its uniform convergence region.