Visualization of Local Heating in Conductive Viscous Fluids Exposed to Repetitive High-Power Electrical Pulses

This study investigates the flow dynamics and temperature rise of conductive viscous fluids under pulsed electric fields (PEFs) between parallel electrodes. The aim is to enhance understanding of thermofluid dynamic phenomena, which is critical to industrial applications utilizing PEF sterilization technology. Time-resolved Schlieren and interferogram techniques are employed to visualize flow states and temperature distributions between the electrodes. Specifically, this study examines both steady states during repetitive PEF exposures and transient behaviors following a single PEF exposure under various flow conditions. In laminar flow, as low-velocity regions absorb more energy from PEFs, the temperature near the electrodes increases more significantly compared to the central region of the flow. Higher viscosity results in a greater mean flow velocity, and longer electrodes amplify the local temperature rise. By contrast, turbulent flow suppresses increases in the local temperature near the electrodes due to transverse heat transfer, even with longer electrodes. Considering excessive local temperature rises near the electrodes is crucial when processing heat-sensitive liquid foods in high-flow-rate PEF pasteurization systems, particularly for large-scale processing of protein-rich and heat-sensitive high-viscosity liquids using PEF technology.