Numerical Studies On The Two-phase Flow In The Effervescent Atomizer

The fuels with the low flash point such as light diesel is safe to use and easy to store, so more and more attention was paid to them in the application of some special field. However, because of the low flash point, the high pressure have to be provided to finish the atomization when use the conventional pressure atomization method, which will increase the mass of the whole mechine. The effervescent atomizer which belongs to the twin-fluid atomizer will atomize the liquid in relative low pressure.In addition, the effervescent atomizer have some advantages comparing with other twin-fluid atomizer, such as the small gas flow rate, hard to clogging, etc., and all of this advantages make effervescent atomizer meet the requirement of liquid atomization in the dynamic machine used in some special fields.This thesis focused on the effervescent atomizer, established the geometry model and mathematical models which could describe the gas-liquid flow, then finished the mesh generation and confirmation of boundary condition. Base on the models, this thesis finished the study on the gas-liquid flow in the effervescent atomizer and the spray field of atomizer downstream.Aiming at the pattern of bubble flowing in the atomizer, this thesis studied the bubble pattern and the bubble characteristic parameters when the single bubble flows through the atomizer using the VOF method. The bubble pattern characteristic in different condition was investigated by changing the bubble size, liquid mass flow rate, liquid viscosity, nozzle Shrinkage angle and the nozzle length/diameter ratio. Based on this, the effect of different parameters on the bubble characteristic parameter was studied through comparing bubble characteristic parameters under different condition.In order to understand the characteristic of the two phase flow structure in the different working condition, the flow structures in the atomizer under different GLR was compared. The two phase flow parameters at exit in different GLR and different liquid mass flow rates was investigated through calculating the exit parameters. The result indicates:the exit flow parameter fluctuates with time in every condition. In addation, the GLR and the liquid mass flow rate have a notable effect on the exit flow parameter.Finally, using the exit two phase flow parameter and the Euler-Lagrange method, the gas-droplet coupled spray field of the effervescent atomizer was modeled. Geometry of the computed domain was established and the mesh was generated. Than the droplet size after primary atomization in different condition was calculated, which was imported into the model as the boundary contidion. The distribution of the droplet size and droplet velocity was investigated, and the effect of GLR and liquid mass flow rate on the distribution was studied through changing in GLR and liquid mass flow rate.