Analysis of the Influence of Spray Pressure on Droplet Size Distribution and Coalescence Efficiency within the Spray Field

Addressing the need to enhance coal mine dust control efficiency, this study innovatively integrates conventional pressure-driven nozzles with ultrasonic atomisation technology to establish a multi-modal collaborative atomisation system platform. Through this platform, the evolution of droplet size distribution within the atomisation fields of single-type nozzles and dual-type nozzle synergistic spraying was investigated under varying spray pressures. Experiments demonstrate that as the spray pressure gradient increases (0.3–0.5 MPa air pressure / 3.0–7.0 MPa water pressure), characteristic particle size parameters (D10, D50, D90) exhibit a linear decreasing trend in both single-nozzle and dual-nozzle synergistic atomisation fields. This results in an increased volume fraction of smaller droplets and an improved uniformity index (Span value) of the particle size distribution. The authors further revealed synergistic effects through comparative analysis: within the small droplet size range (0 < d ≤ 100 µm), the water supply pressure of the 2.8 W pressure nozzle had minimal impact on droplet coalescence, whereas the air supply pressure of the JX-6 ultrasonic atomising nozzle exerted the greatest influence. Optimal droplet coalescence within the atomisation field occurred at an air pressure of 0.3 MPa. Within the large droplet size range of 200 < d ≤ 500 µm, the air supply pressure of the JX-6 ultrasonic atomising nozzle had a minor effect on droplet coalescence, whereas the water supply pressure of the 2.8 W-type nozzle exerted the greatest influence. Optimal collision coalescence was achieved at a water pressure of 7.0 MPa. Within the medium droplet size range of 100 < d < 200 µm, coalescence performance in the atomisation field was unsatisfactory across all spray pressures. This study pioneers the establishment of a ‘large-droplet-micro-droplet’ synergistic dust capture kinetic model, quantifying the interaction between droplet coalescence and pressure within the synergistic spray field of conventional pressure nozzles and ultrasonic atomisation nozzles. This achievement provides theoretical support for the design of mine spray dust suppression systems, advancing dust control technology from single-mode atomisation towards multi-scale synergistic regulation.