TEMPERATURE AND CONCENTRATION TRACES OF SPRAY FLOWS DURING MOTION IN A FLAME

Heat and mass transfer models are developed on the base of experimental data and using Ansys Fluent software. These models allow prediction of the temperature and concentration traces of droplets. Transfer mechanisms of water droplets from different flames of flammable liquid (ethanol, kerosene и benzine) with temperature gases 450–850 К are analyzed. The paper considers aerosol flows with droplets sizes of 0.04– 0.4 mm and concentration of 3.8·10 –10.3·10 m of droplets/m of gas. The maximum gas temperature reduction in the trace of a moving liquid is ranged from 850 K to 600 K. The times of keeping the low temperature of the gas-vapor mixture in the droplets trace are from 13 s to 25 s relative to the initial gas temperature.


Introduction
At the present time gas-vapor-droplet technologies are used in various industries [1][2][3], for example, in firefighting, thermal treatment of liquids, ignition of liquid fuels.However, to talk about the broad and active use of high-temperature (over 1000 K) gas-vapor droplet technologies is quite difficult due to a rather limited information base (particularly, the reliable experimental).
Over the last yers researches are conducted [4,5].The main objective of various development and research are improving the efficiency of means and methods of atomization in high-temperature heat technology.Unfortunately, the fact is not taken account that the water droplets during motion in high-temperature gases reserve temperature and concentration traces which reduce the temperature in the combustion zone due to the evaporation of water droplets.
The goal of the present work is numerical analyses of heat and mass transfer processes at researches of temperature and concentration traces of spray flows during motion in a typical flame with using Ansys Fluent software.

Physical model of heat transfer
When setting heat and mass transfer problems considered that initial water temperature equals T w0 =300 K, initial temperature gases equals T g0 =300 K.It was assumed that the thermal characteristics of the materials are not dependent on temperature.Fig. 1 shows the scheme of solution area for spray flow during motion in a flame.
The simulation used Ansys package.To solve this problem used time steps Δτ = 0.01 s and grid Δx = 0.01 mm.Fig. 3 indicates a satisfactory correlation between the maximum temperatures (T g ') in the trace of the aerosol droplets obtained by experiment and when simulating.This allows us to make some conclusions.Firstly, the Ansys Fluent models can be used to predict of temperatures T g ' at different parameters (size, concentration, velocity, initial droplets temperature) of the aerosol and combustion products (temperature and velocity).Secondly, in the case of the aerosol, water evaporation is a determining mechanism for reducing the temperature in the trace.For small R d difference between the experimental and theoretical values of τ grows.This can be explained mainly by the fact that the experiments [6] showed rather intense deceleration and turn of small droplets.As consequence, the experimental times τ are longer than those obtained by the mathematical simulation.

Conclusion
According to the experimental results, physical and mathematical models of heat and mass transfer have been developed using the Ansys Fluent software.These models can be used in predicting gas temperatures, concentrations of vapor and gases in the trace of aerosol drip flows, as well as times of keeping low temperatures τ.Researches show satisfactory correlation of simulation results and experimental data.

Fig. 1 .
Fig. 1.Scheme of solution area for spray flow during motion in a flame: 1high-temperature of the gas-vapor mixture, 2spray flows.

Fig. 2
Fig.2shows temperature fields in the channel after injection of aerosol for typical flame (ethanol, kerosene and benzine).

Fig. 4
Fig.4shows times of keeping temperature trace depending on droplet size for typical flame: ethanol, kerosene and benzine.
coordinate of the spherical systems; R dradius of droplet, m; T gtemperature of gases, K; U gvelocity of high-temperature gases, m/s 2 ; U wvelocity of spray flow, m/s 2 ; T atemperature of air, К.In this formulation of the problem there are adiabatic horizontal and vertical walls with constant temperature 1170 К Where ttime, s; Ttemperature, K; T g0initial temperature of gases, K; T woinitial temperature of water, K; C wconcentration of water; C g -concentration of high-rotation vector velocity, s -1 ; ψflow function, m 2 /s; x, y coordinates of the Cartesian coordinate system, m; H, Ldimensions of solution area, m; r, φa U .