A three-dimensional numerical simulation using the volume of fluid to discrete phase model (VOF-to-DPM) approach was conducted to investigate the liquid film breakup and atomization characteristics of a liquid/liquid pintle injector under pulsating radial flow conditions. The study focused on the dynamic response of atomization parameters-such as spatial flow structures, spray angle, breakup length, and droplet size-to varying pulsation frequencies and amplitudes. Numerical results show that radial flow pulsations enhance liquid film disturbances, promoting surface wave development and accelerating film breakup. Pulsation-induced fluctuations in axial and radial velocities cause periodic spatial accumulation of droplets. The mass flow oscillations at different axial positions have the same frequency as the jet pulsations. Pulsations lead to an increased spray cone angle, with greater sensitivity to amplitude than frequency. Breakup length shows periodic fluctuations and decreases with rising pulsation frequency and amplitude. However, the decrease slows down at higher pulsation amplitudes. Droplet size initially increases and then decreases with increasing frequency and amplitude. At higher frequencies or larger amplitudes, the SMD of droplets is smaller than that under constant radial flow, and the uniformity of the droplet size is promoted. Additionally, the velocity distribution of droplets shifts from bimodal to unimodal with increased pulsation amplitude.
Spray cooling has attracted considerable attention for thermal management of high-heat-flux electronic devices owing to its high-heat dissipation capability and favorable temperature uniformity. However, the interplay between surface microstructures and mechanical vibration can markedly alter post-impingement liquid-film spreading, thereby affecting boiling heat transfer. To date, a clear understanding of how micro-pillar geometric parameters regulate liquid-film dynamics and boiling rate under vibrational conditions remains lacking. In this study, a transient numerical model for spray cooling on a vibrating surface is developed. Vibration is characterized using the vibrational Reynolds number and an acceleration number, and the mechanisms by which the micro-pillar side length, height, and spacing influence the mean liquid-film thickness, film velocity, and boiling rate are systematically investigated. The results indicate that vibration suppresses liquid-film spreading whilst promoting forced convection, leading to a non-monotonic dependence of the boiling rate on the vibrational Reynolds number, with an optimal condition at a vibrational Reynolds number of 1600. In addition, the micro-pillar geometry further modulates the boiling rate by altering the impingement blind zone, spreading pathways and the liquid-film renewal capability. Increasing the pillar side length reduces lateral splashing and enhances momentum transfer to the film, accelerating film motion and improving the boiling rate. Reducing the pillar height mitigates accumulation and blockage effects, thereby substantially enhancing the boiling rate. Increasing the pillar spacing lowers hydraulic resistance and improves mixing and renewal, strengthening boiling stability. Overall, this work elucidates the coupled regulation of liquid-film hydrodynamics and boiling rate by microstructural parameters under vibration, and it provides a theoretical basis for optimizing spray-cooling surface designs for high-heat-flux electronics operating in complex vibrational environments.
Numerical simulation was carried out to investigate the influence of protective airflow on liquid jet in crossflow, with a focus on the deformation and breakup characteristics of liquid column, flow behaviors, and atomization features of droplet. The velocity of protective airflow ranged from 0 to 160 m/s. And the velocity of the crossflow and jet liquid were kept constant at 80 and 10 m/s, respectively. The results indicated that the introduction of protective airflow prevented direct contact between crossflow and liquid column, which effectively enhanced the penetration of liquid column and mitigated the bending of it in the jet process. Furthermore, the protective airflow could induce the imbalance of the liquid inside the liquid column, intensifying its instability and promoting the breakup. Therefore, as the velocity of protective airflow increased, the windward trajectory gradually increased, and the surface breakup point gradually moves away from the nozzle while the column breakup point gradually moved closer to the nozzle. For the droplets generated by the breakup of liquid column, the protective airflow did not significantly reduce the Sauter mean diameter of droplet, but it prevents them from moving in the direction opposite to the liquid jet at the initial atomization moment.
