The primary factors are surface tension (γ), the Qd/Qc flow rate ratio, and the viscosity of both phases. Lower surface tension and higher continuous-phase flow rates produce smaller droplets. The Weber number (We = ρv²L/σ) and Capillary number (Ca = μv/σ) are the key dimensionless parameters governing droplet formation and the transition between flow regimes.

Breakup frequency is the rate at which new droplets form from the dispersed phase, in Hz (droplets/second). It is calculated by dividing the dispersed phase flow rate by single-droplet volume. Higher frequencies produce more uniform spray patterns with better temporal consistency — critical for fuel injection, pharmaceutical coating, and precision humidification where droplet timing matters.

Surface tension (γ) is the interfacial force between dispersed and continuous phases that resists droplet breakup. Higher surface tension promotes larger droplets by requiring more energy to create new surface area. Surfactants reduce surface tension by adsorbing at the interface; elevated temperature also reduces γ. Water-air surface tension is approximately 72 mN/m at 25°C, while oil-water systems are typically 10–50 mN/m.

The 30–150 μm range suits fine misting, pharmaceutical spray drying, precision coating, and humidification where small droplets and minimal drift are required. The 60–300 μm range covers general industrial spraying, agricultural applications, and cooling. The 90–450 μm range applies to high-volume washing, fire suppression, and processes where larger droplets reduce evaporation loss or improve surface penetration.

Correlation-based models typically achieve accuracy within 10–25% of measured values under steady-state Newtonian conditions. Real-world deviation is caused by nozzle orifice geometry, turbulence, temperature gradients, non-Newtonian behavior, and transient startup effects. For critical applications, validate using laser diffraction (LDSA) or phase Doppler anemometry (PDA).