Experimental investigation on the macroscopic spray and microscopic droplet diameter, velocity and temperature of R404A flashing spray

Two-phase flashing spray elicits wide interest in scientific and industrial fields. It can produce fine atomization with small size and low temperature droplets because of explosive atomization and strong evaporation. This study conducted an experimental investigation on the macroscopic spray and microscopic droplet diameter, velocity, and temperature through various measurement methods with a low saturation-temperature refrigerant R404A, which holds a special interest in laser dermatology. The spray presented a bowl spray configuration with rapid expansion at the nozzle exit. A core spray area near the nozzle field was revealed, in which the droplet Sauter mean diameter (D₃₂) and temperature (T_d) decreased rapidly while the droplet average velocity (V) exhibited an obvious acceleration with increasing axial distance. All the number distributions of droplet diameter and velocity presented Gaussian shapes. The cumulative distribution of droplet diameter followed the Rosin–Rammler correlation perfectly. The uniformity constant and characteristic droplet size were proposed for various axial and radial positions. The radial distributions of D₃₂, V, and T_d at various spray axial sections presented different profiles, among which the non-dimensional profiles of V showed a self-similar pattern. The two-dimensional thermal field presented a contractive pattern and a narrow spray width after the rapid expansion at the nozzle exit, which helped to control the spray cooling area more precisely compared with other expansion-like sprays with larger spray width. Experimental data could also provide validation data for the numerical simulation of flashing spray.