Computational Fluid Dynamic Analysis of Atomization Spray Cooling Nozzle Designs for Micromachining

A recent development of cooling and lubrication technology for micromachining processes is the use of spray cooling. Atomization spray cooling systems have been shown to be more effective than traditional methods of cooling and lubrication for micromachining. Typical nozzle systems for atomization spray cooling incorporate the mixing of high speed air and atomized fluid. In a two-phase atomization spray cooling system, the atomized fluid can easily access the tool-workpiece interface, removing heat by water evaporation and lubricating the region by oil droplet spreading. The success of the system is determined in a large part by the nozzle design, which determines the droplet behavior at the cutting zone. In this study, computational fluid dynamics are used to investigate nozzle design and droplet delivery to the tool. An eccentric-angle nozzle design is evaluated through droplet flow modeling. This study focuses on the design parameters of initial droplet velocity, high speed air velocity, and the angle change between the two inlets. The system is modeled as a steady-state multiphase system without phase change. Droplet interaction with the continuous phase is dictated in the model by drag forces and fluid surface tension. The Lagragian method with a one-way coupling approach is used to analyze droplet delivery at the cutting zone. Following a factorial experimental design, deionized water droplets and a semi-synthetic cutting fluid are evaluated through model simulations. Statistical analysis of responses (droplet velocity at tool, tool positioning, and droplet density at tool) show that droplet velocity is crucial for the nozzle design and that modifying the parameters does not change droplet density in the cutting zone. Based on results, suggestions for future nozzle design are presented.