Micro-encapsulated phase change materials for advanced thermal regulation in ultrasonic reactors: A novel approach

Abstract

Ultrasonic reactors are widely employed across various technological domains, including food processing, medicine, cleaning, chemistry, and biology. However, ultrasonic wave propagation in liquids is invariably accompanied by energy dissipation in the form of heat, which is absorbed by the surrounding medium, resulting in a continuous temperature increase—often by several tens of degrees within minutes. Conventional sonochemical reactors typically rely on water-based cooling systems to manage this thermal rise. This study proposes a novel approach for in-situ thermal regulation by dispersing encapsulated phase change material (PCM) microparticles in the irradiated water. PCM spheres (RT31) of varying diameters (1 mm, 2 mm, and 3 mm) were investigated for their ability to absorb and manage heat generated during sonication, as well as their influence on acoustic pressure and velocity distributions.

The results indicate that 1 mm PCM spheres rapidly dissipate heat once saturation is reached, while 2 mm and 3 mm spheres enable a more gradual and sustained heat absorption, thereby enhancing thermal storage. Systems containing 2 mm and 3 mm PCM spheres achieved faster water temperature homogenization within the first 20 min, compared to both 1 mm spheres and systems without PCM. Beyond this period, temperature equalization occurred across all configurations. In terms of acoustic behavior, the 3 mm PCM spheres caused a noticeable but spatially confined reduction in both maximum and minimum acoustic pressures, whereas smaller spheres induced less pronounced changes. Despite these reductions, the presence of PCM spheres—especially those of 3 mm—led to a more uniform acoustic pressure distribution and enhanced nucleation of acoustic bubbles. Furthermore, the water velocity field benefited from the inclusion of PCM, with 3 mm spheres contributing to a more favorable distribution, albeit with a slight and localized reduction in peak velocities.

Overall, the incorporation of PCM spheres in sonoreactors proves beneficial for managing thermal loads, optimizing acoustic energy distribution, and improving cavitation dynamics, thereby enhancing overall reactor performance.