| Abstract [eng] |
The aim of the numerical study of droplet convective heating and evaporation is to simulate the phase change regimes cycle (PCRC) of a water droplet under boundary conditions typical for real water injection application cases. Based on the obtained results, to evaluate the influence of initial water injection parameters on the parameters defining the complex interaction of heat transfer and phase change, as well as on droplet evaporation duration, in order to evaluate the control capabilities of water injection technology. During this study, fuel combustion technologies using water injection are examined with the aim of improving their environmental or efficiency parameters. Based on the real parameters typical for these technologies, boundary conditions are defined under which the influence of the droplet's initial temperature, initial Reynolds number, injected droplet size, and gas temperature are investigated. For the latter two cases, the effect of radiation is also evaluated. Under these boundary conditions, water droplet PTRCs are simulated using the numerical modelling program "LAŠAS". The variation of the calculated parameters is presented graphically. The obtained results show that the initial Reynolds number (Re₀), by influencing the dynamic parameters of the PTRC, has a greater effect on the cycle duration when the droplet evaporates in high-temperature gases. During evaporation in 450 °C gases, droplets with Re₀ = 150 evaporate 10% faster than droplets with an initial Reynolds number of 5. In 1300 °C gases, the phase transition regime cycle of droplets with Re₀ = 55 is as much as 18.2% shorter than that of droplets with Re₀ = 5. Meanwhile, the initial droplet temperature has a greater influence on the PTRC duration at lower gas temperatures. Hot droplets with an initial temperature of 90 °C can evaporate up to 9% faster compared to cold droplets at 10 °C when evaporation occurs in gases at 1300 °C, or up to 12% faster when evaporation occurs in gases at 450 °C. Although droplet diameter has no effect on thermal parameters in the case of convective heating, radiation is more significant for larger droplets. For droplets with an initial diameter of 110 μm, radiation can account for up to a 6.86% difference in PTRC duration, while for droplets with an initial diameter of 20 μm it is only 0.62% (when droplets evaporate in 1300 °C gases). Gas temperature has a significant influence on droplet PTRC duration. Droplets evaporating in gases at 900 °C evaporate 2.8 times faster, and in gases at 1300 °C — as much as 5 times faster. A greater influence of radiation is also felt in higher-temperature gases. When droplets evaporate in gases at 1300 °C, the influence of the Stefan flow must be taken into account, as it suppresses heat transfer by up to 37.1%. However, in lower-temperature gases, the influence of the Stefan flow is smaller — 28.3% at 900 °C and 10.5% at a gas temperature of 450 °C. |
