Heat transfer coefficients in two-dimensional Yukawa systems (numerical simulations)

New data on heat transfer in two-dimensional Yukawa systems have been obtained. The results of a numerical study of the thermal conductivity for equilibrium systems with parameters close to the conditions of laboratory experiments in dusty plasma are presented. The Green-Kubo relations are used to calculate the heat transfer coefficients. The influence of dissipation (internal friction) on the heat transfer processes in nonideal systems is studied. New approximations are proposed for the thermal conductivity and diffusivity for nonideal dissipative systems. The results obtained are compared with the existing experimental and numerical data.     

Thermal Conductivity of Complex Plasmas Using Novel Evan-Gillan Approach

The thermal conductivity of complex fluid materials(dusty plasmas) has been explored through novel Evan-Gillan homogeneous non-equilibrium molecular dynamic(HNEMD) algorithm. The thermal conductivity coefficient obtained from HNEMD is dependent on various plasma parameters(Γ, κ). The proposed algorithm gives accurate results with fast convergence and small size effect over a wide range of plasma parameters. The cross microscopic heat energy current is discussed in association with variation of temperature(1/Γ) and external perturbations(P_z). The thermal conductivity obtained from HNEMD simulations is found to be very good agreement and more reliable than previously known numerical techniques of equilibrium molecular dynamic, nonequilibrium molecular dynamic simulations. Our new investigations point to an effective conclusion that the thermal conductivity of complex dusty plasmas is dependent on an extensive range of plasma coupling(Γ) and screening parameter(κ) and it varies by the alteration in these parameters.It is also shown that a different approach is used for computations of thermal conductivity in 2D complex plasmas and can be appropriate method for behaviors of complex systems.     

Heat and momentum transport to particulates injected intolow-pressure (~80 mbar) nonequilibrium plasmas

An analytical model for plasma flow around a spherical particle has been developed using a two-temperature chemical nonequilibrium approach that includes rarefaction and particle-charging effects. The contribution of each component of the plasma to the heat and momentum transfer to injected particulates is studied by simulating the plasma flow around a sphere for conditions typical of thermal spray processes at pressures from 80 mbar to 1 bar. A parametric study of the 80-mbar case is also presented for free-stream velocities in the 0-3000 m/s range and free-stream temperatures in the 8000-12000 K range for both ionization equilibrium and nonequilibrium. The results demonstrate that there are departures from kinetic and ionization equilibrium in the plasma around a particle, and that heat transfer to a particle can be enhanced by the increased ion flux to the particle surface when the surrounding plasma is in ionization nonequilibrium     

Modelling of laser surface alloying and dispersing of ceramics

Laser‐supported processes can be used to modify the electrical and thermal properties of ceramic substrates locally. These processes are characterized by a strong thermal interaction between the laser beam and the ceramic surface that leads to localized melting. During the dynamic melting process an additive material is injected into the melt pool in order to modify the physical properties. The heat and mass transfer during this dynamic melting and solidification process has been studied numerically in order to identify the dominating process parameters. Simulation tools based on a finite‐volume method have been developed to describe the heat transfer, fluid flow and the phase change during the melting and solidification of the ceramic. The results of the calculation have been validated against experimental results.     

Free convection effects and radiative heat transfer in MHD Stokes problem for the flow of dusty conducting fluid through porous medium

The present note deals with the effects of radiative heat transfer and free convection in MHD for a flow of an electrically conducting, incompressible, dusty viscous fluid past an impulsively started vertical non-conducting plate, under the influence of transversely applied magnetic field. The heat due to viscous dissipation and induced magnetic field is assumed to be negligible. The governing linear partial differential equations are solved by finite difference technique. The effects of various parameters (like radiation parameter N, Prandtl number Pr, porosity parameter K) entering into the MHD Stokes problem for flow of dusty conducting fluid have been examined on the temperature field and velocity profile for both the dusty fluid and dust particles.     

Viscosity of a dusty plasma liquid

We present the results of our experimental study of the flow of a dusty plasma liquid produced by macroparticles in an argon plasma. The dependences of shear viscosity for such a liquid on the magnitude of the external force inducing the dusty plasma liquid flow and on the plasma-generating gas pressure are analyzed. We have established that the viscosity of a dusty plasma medium decreases with increasing shear stress in it, while the viscosity of such a liquid increases with buffer gas pressure. The flow of a dusty plasma liquid under the action of an external force has been found to resemble the plastic deformation of a Bingham body. We suggest that the formation of crystal-like dusty plasma clusters in a “liquid” phase can be responsible for the non-Newtonian behavior of the dusty plasma liquid flow.     

Dust-ion-acoustic shock waves due to dust charge fluctuation

A dusty plasma system containing Boltzmann electrons, mobile ions and charge fluctuating stationary dust has been considered. The nonlinear propagation of the dust-ion-acoustic waves in such a dusty plasma has been investigated by employing the reductive perturbation method. It has been shown that the dust charge fluctuation is a source of dissipation and is responsible for the formation of the dust-ion-acoustic shock waves. The basic features of such dust-ion-acoustic shock waves have been identified. The implications of our results in space and laboratory dusty plasmas are discussed.     

Influences of Temperature and Average Interparticle Distance on the Properties of Two-Dimensional Dusty Plasma

The structure and single-particle motion of a two-dimensional dusty plasma have been investigated. Pair correlation function, mean square displacement, velocity autocorrelation function, and the corresponding spectrum function have been computed by molecular dynamical simulation. The results show that the coagulation of a two-dimensional dusty plasma system is strongly affected by particle density and temperature, which are discussed in details.     

Structure and phase transition of a two—dimensional dusty plasma

The structure and phase transition of a two-dimensional (2D) dusty plasma have been investigated in detail bymolecular dynamics simulation. Pair correlation function, static structure factor, mean square displacement, and bondangle correlation function have been calculated to characterize the structural properties. The variation of internalenergy, shear modulus, particle trajectories and structural properties with temperature has been monitored to studythe phase transition of the 2D dusty plasma system. The simulation results are in favour of a two-step continuoustransition for this kind of plasma.     

Overview of Hybrid Nanofluids Development and Benefits

Conventional fluids have poor heat transfer properties, but their vast applications in power generation, chemical processes, heating and cooling processes, electronics and other microsized applications make the reprocessing of those thermofluids to have better heat transfer properties quite essential. Recently, it has been shown that the addition of solid nanoparticles to various fluids can increase the thermal conductivity and can influence the viscosity of the suspensions by tens of percent. Thermophysical properties of nanofluids were shown dependent on the particle material, shape, size, concentration, the type of the base fluid, and other additives. In spite of some inconsistency in the reported results and insufficient understanding of the mechanism of the heat transfer in nanofluids, it has been emerged as a promising heat transfer fluid. In the continuation of nanofluids research, the researchers have also tried to use hybrid nanofluid recently, which is engineered by suspending dissimilar nanoparticles either in mixture or composite form. The idea of using hybrid nanofluids is to further improve the heat transfer and pressure drop characteristics by trade-off between advantages and disadvantages of individual suspension, attributed to good aspect ratio, better thermal network and synergistic effect of nanomaterials. As a conclusion, the hybrid nanofluids containing composite nanoparticles yield significant enhancement of thermal conductivity. However, the long-term stability, production process, selection of suitable nanomaterials combination to get synergistic effect and cost of nanofluids may be major challenges behind the practical applications.     

Formation of liquidlike and crystalline structures in dusty plasmas

Under certain conditions in a dusty plasma, which is a low-temperature plasma with dust grains, the strong interaction between grains can give rise to gas-liquid-solid-state phase transitions. A study is made of ordered (liquidlike and crystalline) grain structures in various kinds of dusty plasmas: a thermal plasma at atmospheric pressure, a plasma of a dc glow discharge, and a UV radiation-driven plasma. The results of experimental observations of ordered dust structures are reported, and the characteristic features of the dust structures and the conditions for their appearance are discussed.     

Effect of an Arbitrary Dust Size Distribution Dust Particles for Vortex-Like Ion Distribution Dusty Plasma

In order to investigate the effect of an arbitrary dust size distribution for vortex-like ion distribution dusty plasma, we use a reasonable polynomial-expressed function to represent an arbitrary dust size distribution. The numerical results of linear dispersion relation, nonlinear solitary wave amplitude, width and velocity for polynomial expressed dust size distribution dusty plasma with vortex-like ion distribution have been studied.     

Ultra-low-frequency electrostatic and electromagnetic modes in self-gravitating magnetized dusty plasmas

A theoretical investigation has been made of ultra-low-frequency dust-electrostatic and dust-electromagnetic modes, propagating perpendicular to the external magnetic field, in a self-gravitating, warm, magnetized, two fluid dusty plasma system. It has been shown that the effects of self-gravitational field and dust thermal pressure significantly modify the dispersion properties of these ultra-low-frequency dust-modes. It is also found that under certain conditions, the self-gravitational effect can destabilize these ultra-low-frequency dust-electrostatic and dust-electromagnetic modes. However, the effects of the external magnetic field and dust and ion thermal pressures are found to play stabilizing role, i.e., these effects make these modes stable and counter the gravitational condensation of the dust grains. The implications of these results to some space and astrophysical dusty plasma systems, especially, to planetary ring-systems and cometary tails, are briefly mentioned. Received 16 December 1999     

Dynamics of macroparticles in a dusty plasma under microgravity conditions (First experiments on board the ISS)

The results of experimental investigation of macroparticle transport in the dusty plasma of a capacitive high-frequency discharge under microgravity conditions are considered. Experimental data were obtained for monodisperse polymer particles of radius a _p =1.7 mm in a wide range of plasma parameters on the International Space Station. Analysis of macroparticle dynamics for a strongly nonideal dusty plasma, including diffusion and dust vortex formation processes, is carried out.     

Effects of axial magnetic field and nonextensivity on small amplitude dust acoustic solitary waves in dusty plasma

The nonlinear propagation of small amplitude dust‐acoustic (DA) solitary waves in magnetized dusty plasma consisting of negatively charged mobile dust fluid, and Boltzmann‐distributed electrons and ions with two distinct temperatures following a q‐nonextensive distribution are investigated. In this article, a number of nonlinear equations, namely, the Korteweg–de‐Vries (K‐dV) equations, have been derived by employing the reductive perturbation technique that is valid for a small but finite amplitude limit. The effects of nonextensivity of ions with two distinct temperatures and dust concentration on the amplitude and width of DA solitary waves are investigated theoretically. It is observed that both the nonextensive and low‐temperatures ions significantly modify the basic properties and polarities of DA solitary waves. It is shown that both positive and negative potential DA solitons occur in this case. The implications of these results to some astrophysical environments and space plasmas (e.g., stellar polytropes, peculiar velocity distributions of galaxies, and collisionless thermal plasma), and laboratory dusty plasma systems are briefly mentioned.     

Measurement of the temperature of the copper plasma generated in the process of release of a shock-compressed target

The processes associated with the arrival of a strong shock wave at the surface of a metal have been considered. It has been experimentally revealed that the withdrawal of the wave from a shock-loaded sample under release is accompanied by the formation of not only a dusty flow, but also a metal plasma. The temperature of the plasma component, which is about 1 eV, has been determined from the relation of the line intensities using the spectral diagnostics of the plasma.     

Heat transport in a two-dimensional complex (dusty) plasma at melting conditions

The heat transport in a two-dimensional complex (dusty) plasma undergoing a phase transition was studied experimentally. A single layer of highly charged polymer microspheres was suspended in a plasma sheath. A part of this lattice was heated by two counterpropagating focused laser beams that moved rapidly around in the lattice and provided short intense random kicks to the particles. Above a threshold, the lattice locally melted. The spatial profiles of the particle kinetic temperature were analyzed to find a thermal conductivity, which did not depend on temperature.     

Energy transport enhancements in a transitional thermal plasmaplume

The evolution of heat and mass transfer in the initial region of a transitional plasma plume is investigated and discussed. The results show that these transport processes are controlled and limited by the plume shear layer instability. This process of laminar-turbulent transition is consecutively controlled by the plume core shear layer instability, by the “jet mode” induced by unstable shear layer, and by resonance in the jet and arc chamber. These three processes are manifested in three events. Between the first and second phase, there is a maximum of average enthalpy. The other two thresholds occur at maximum and minimum stagnation heat flux from the plume core. It seems that these processes also influence the thermal energy production in the arc chamber cavity     

纳米流体对流换热系数增大机理

纳米流体流动换热能力优于传统流体介质.研究了纳米流体热物性的提升和热散射对其对流换热系数的影响.结果表明,纳米颗粒的加入,优化了介质的热物性,增大了导热系数,强化了纳米流体内颗粒、流体以及流道管壁碰撞和相互作用,同时加强了流体的混合脉动和湍流,从而增大了对流换热系数. 关键词： 纳米流体 换热系数 热散射