Research Of Single Droplet Impacting Onto Solid Surface And Multiple Droplets Reducing Thermal Radiation

The phenomenon of single droplet impacting onto solid surface is exits broadly inthe nature and human’s social productive activities. As its significant practicalapplication value and complicated internal mechanism of action, for long time, theresearch about the impact of droplet onto solid surface is a hot issue both inhydrodynamics and physics fields.For this paper, experiments and numerical simulations of droplet impacting onsolid surface are combined to study the droplet’s variation process and its velocity andpressure fields in depth. Visualization experiment platform is built and high speedcamera Photron FASTCAM SA1.1is applied to record the empire impact process.The various influence to the droplet’s spread and oscillation of droplet’s physicalparameters, coefficient of viscosity, impact velocity and surface parameters is studiedby control variate method, and some conclusions are draw that droplet’s physicalparameters, coefficient of viscosity and surface parameters have an greater effect anddroplet of Carbopol which belongs to the shear-thinning type non-newton liquidimpact onto the solid surface has a different performance with droplet of normalnewton liquid. The numerical simulations are based on the open CFD softwareOpenFOAM, and large eddy simulation (LES) model is applied. Volume of fluid(VOF) method is used in the numerical simulations to capture the gas-liquid interface.A new segmented dynamic contact angle (SDCA) model is put forward and employedin the numerical simulations. The numerical results are consistent well with the resultsof experiments. The impacting process and the flow characteristic including thevelocity and pressure fields around the spreading droplet are analyzed. In the researchthe generation, development and dissipation processes of the vortexes that in theliquid and the surrounded air are observed, and it is obviously indicated that the localmaximum value of the spreading velocity is emerged in the gas-liquid interface, andthe local rapid flow leads to the appearance of negative pressure. The bubble isgenerated near the impact point at the impact time and then floating upward tillbreaking into the air, and the bubble generated and dissipated twice which was foundin the simulation. Furthermore, theoretical research and numerical verification is done in this paperabout the water mist’s application to reduce thermal radiation which is made up ofmultiple droplets. The theoretical model of multiple droplets reduce thermal radiationis based on the Mie’s Scattering model and combined the nozzle parameters inpractical application. The numerical verification of the theoretical model is done withCFD software Fluent. The results show that the theoretical model of multiple dropletsreduce thermal radiation could be applied in the engineering practice effectively.