Impact of air bubbles in a dielectric liquid when subjected to high field strengths

Abstract The dielectric breakdown of gas bubbles entrapped in liquid food flowing through the cavity of a pulsed electric field treatment chamber has been a limiting factor in this non-thermal food preservation technology. Prediction of electric field enhancement due to gas bubbles is an important tool in the design, modification, and optimization of the treatment chamber's electrode geometry and pressurization. Simulation of the electrostatic characteristics of a coaxial treatment chamber with specified voltage of 25 kV, filled with dielectric material with conductivity of 0.6 S/m containing gas bubbles, evidenced a significant perturbation in the electric field. The magnitude of electric fields generated inside the bubbles was almost two times higher than in the homogeneous food. Without pressurization (atmospheric conditions), the dielectric breakdown strength of the gas-filled bubbles was exceeded, thus indicating the risk of arcing. A system pressurization of approximately 8 atm could be sufficient to limit arcing when small gas bubbles (∼1 mm) are present. The presence of gas bubbles caused the field magnitude to decrease significantly near the boundary of the bubble, thus threatening the uniformity of the PEF treatment across the chamber gap. This perturbation in the electric field was more significant when more than one bubble was present or when smaller gaps were used. The dielectric breakdown threshold at a given pressure is more likely to be exceeded by bigger bubbles (>1 mm) entrapped in a fluid processed in smaller treatment chamber gaps (3 mm), than by smaller bubbles (