Numerical Simulation Of Evaporation Research Articles

Numerical simulation of evaporation from nanoporous arrays:

Numerical simulation of evaporation from nanoporous arrays:

Numerical simulation of WFGD wastewater with atomizing and crystallization treatment

ABSTRACTWet flue gas desulfurization (WFGD) wastewater treatments used by most coal-fired power plants have difficulty in realizing completely zero emission. An atomizing and crystallization treatment of desulfurization wastewater using high-temperature gas from SCR (selective catalytic reduction) denitrification reactors was proposed. Using ANSYS software, 3D modeling of a crystallization tower and a numerical simulation of evaporation were conducted, and the crystallization process of wastewater droplets was studied. Based on the results of the simulation, effects of four main factors on evaporation efficiency were analyzed. The results indicate that droplet group with the same initial diameter of 10 μm can evaporate entirely within a time of 0.6 s and a height of 2.4 m when the mass flow rate of 620 K flue gas increases to 2.1 kg/s. In a practical process, fluctuations in the temperature and humidity should be avoided to guarantee complete evaporation. The results provide data support for technology design of crystallization towers applied in power plants.

Numerical simulation on wastewater with flue gas in concentration tower

Most power plants equipped with limestone-gypsum wet flue gas desulphurization (FGD) system treat FGD wastewater by chemical precipitation which is not able to remove chloride ion completely. The wastewater treatment of concentrating and crystallizing piecewise by flue gas can solve this issue. Pretreating wastewater by undersaturated fuel gas and then concentrating by high temperature fuel gas is not only utilizing waste heat but also realizing “zero discharge”. By 3D-modeling of concentration tower and numerical simulation of evaporation, the evaporation process of wastewater droplet in concentration tower has been studied. Through simulation, the impact of four main factors (gas mass flow, initial droplet diameter, gas temperature and droplet temperature) to evaporation efficiency (EE) has been analyzed. Result indicates that the decrease of initial droplet diameter has greatest impact on improvement of evaporation. Furthermore, raise gas mass flow, gas temperature and droplet temperature in reasonable range can improve EE effectively. The conclusion provides reliable theoretical basis for technological design of concentration tower in power plants.

Numerical simulation of evaporation with Rayleigh convection using LBM-FDM hybrid method and proposal of the interfacial mass transfer coefficient model

The Rayleigh convection could be induced by solute evaporation in dual solvents, such as acetone-ethyl acetate and isopropanol-water system. The onset of Rayleigh convection and its evolutionary characteristics were simulated using LBM-FDM hybrid method with liquid phase random disturbance model. And the simulation results were in reasonable agreement with experimental measurements in four aspects: Rayleigh convection onset time, concentration field acquired by Schlieren and velocity field acquired by PIV, average mass transfer coefficient, and statistical average velocity distribution along the gravitational direction. It proves that the LBM-FDM hybrid method is effective in capturing the key features in this mesoscale phenomenon. Then three mass transfer model including small eddy model, surface divergence model and the new model based on theoretical parameters concentration variance, its dissipation rate and Reynolds mass flux were proposed to predict the interfacial mass transfer coefficient, and the new developed model had advantages over other two models, in the onset time of Rayleigh convection, the peak of mass transfer coefficient and tackling the non-synchronism between velocity and concentration field in fully developed convective stage. The new developed model shows its strength in determining the mass transfer coefficient in a theoretical way.

Numerical simulation of evaporation and drying of a bi-component droplet

A mathematical model to describe the evaporation and drying behavior of a single quiescent spherical bi-component droplet containing evaporating liquid and dissolved solid substance is developed with primary focus on the application of this model to study the evaporation and drying of a droplet of polymer (Polyvinylpyrrolidone – PVP) in water and Mannitol in water. The water evaporation rate is computed using a convective two-film model with modifications to account for solid layer formation. The non-ideality effect induced by the presence of PVP or Mannitol on vapor pressure of water is accounted through the calculation of activity coefficient of water in either system. The problem under consideration is governed by the continuity (diffusion) and energy equations, which are solved using a finite difference method. The effect of drying conditions such as gas velocity, temperature, and relative humidity on evaporation and drying rate is studied. It is concluded that the present model effectively captures the initial stages of single droplet drying.

Numerical analysis of the interactions between evaporating droplets in a monodisperse stream

A numerical simulation of evaporation in a monodisperse droplet stream is proposed, taking into account the transient state of the evaporation, and the non-uniform mass and heat transfer coefficients on the droplet surface. These investigations emphasize the strong interaction effects between closely spaced droplets in a dense spray, reducing significantly the transfer coefficients. Moreover, the Marangoni force becomes more significant than the viscous force, driving the internal motion of the droplet and affecting the temperature fields. Otherwise, a better understanding of the evaporation phenomenon around closely spaced droplets will help to refine the existing models used in dense sprays.

Numerical Simulation of Evaporation,Ignition and Combustion of Transient Sprays

Numerical simulations of transient sprays were made based on an Eulerian gas and a Lagrangian drop formulation coupled with chemical reactions for the gas and for soot.Computed profiles of axial and radial velocity,species and soot concentration,gas temperature,local or total heat release rate are presented to understand the overall and the internal structure of the combusting spray.Some of the computed results are compared with experiments taken in a rapid compression machine.The results indicate the following. (1) The computations predict the ignition delay,the transient configuration of the spray flame and drop penetration distance reasonably well.(2) The drops evaporate in the early stage of the spray combustion and the drop penetration distance is predicted well by taking account of the secondary breakup of the drops in the evaporating sprays. The secondary breakup is liable to occur at high pressure and high temperature atmosphere.(3) Ignition occurs at a hot spot in the off-axis region and is follo...