- freely available
Energies 2013, 6(1), 204-219; https://doi.org/10.3390/en6010204
2. Model Description
2.1. Mathematical Formulation
2.2. Gel Propellant Rheology
3. Model Validations
3.1. Newtonian Droplet Coalescence
3.2. Shear-Thinning Droplet Collision
3.3. Grid and Time Step Independence Study
4. Results and Discussion
4.1. Bouncing Collision
4.2. Coalescence Collision
4.3. Reflexive Separation Collision
4.4. Evolution of the Energy Budget
4.5. Maximum Deformation
- The VOF methodology is capable of predicting the details of complex flow configurations, like the evolution of the gas-liquid free interface, gas bubbles entrapment and coalescence, and ligament formation.
- The maximum shear rate occurs at the point where the flow is redirected and accelerated, and minimum effective viscosity occurs at the corresponding point. Rebound of droplets is determined by the Weber number and viscosity of the fluid together. At the time of maximum droplet deformation, the fluid within droplets is at the stagnant state, and dynamic viscosity increases, leading to easier rebound in comparison with the base fluid droplets. The alternant appearance along with the deformation of droplets in the radial and axial direction is the main characteristic of the droplet coalescence process, and the deformation amplitude attenuates gradually. Three distinctive stages (radial expansion, recovery of the spherical shape, and the axial extension and reflexive separation) were identified for reflexive separation process of droplets.
- During the rebound process of droplets, the kinetic energy decreases remarkably, whilst the surface energy increases slightly. The kinetic energy and surface energy take on opposite variation trends for the process of droplet coalescence. The influence of Weber number on variation of surface energy is more remarkable, while the influence on variation of kinetic energy is small.
- In the case of a low Weber number, the radial velocity of rim reverses its direction towards the center of the disc; the flow within the thin disc continues to accumulate in the boundary ring, which results in the minimum central thickness of a droplet appearance later than its maximum deformation. However, this result is contrary to the case of a high Weber number, because the dimensionless center thickness δ becomes zero during the process of RH increasing.
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