Clustering of magnetic microcapsules in forced convection: Effects of temperature

The development of advanced heat removal systems is highly anticipated, and functional fluids are being investigated for this purpose. In this study, we fabricated temperature-sensitive magnetic microcapsules containing ferrofluid and fluorescent dye, and investigated their flow behavior and heat transport characteristics under forced convection. A magnetic field was locally applied to a rectangular straight microchannel containing the microcapsule dispersion, and the resulting cluster formation and flow fields were visualized using PIV. We specifically examined the effects of magnetic field position, capsule concentration, and temperature. Our results showed that cluster formation occurred near the channel wall, enhancing flow locally. However, the enhancement effect weakened when the magnetic field was shifted. At higher temperatures, magnetization decreased, leading to reduced clustering. Notably, the final cluster length decreased by 27.6% when the channel temperature was increased from 25°C to 58°C. Velocity distributions near the wall also changed significantly depending on temperature, indicating that thermal conditions strongly influence cluster formation and flow dynamics. These findings highlight the feasibility of using temperature-sensitive magnetic microcapsules to achieve localized and tunable flow control, which is especially valuable in microelectronic cooling where precise heat management is essential. Furthermore, their biocompatibility and optical trackability suggest potential for non-invasive thermal control in biomedical applications, such as hyperthermia therapy or implantable devices. This study contributes to the design of multifunctional microfluidic heat transport systems with both responsiveness and adaptability.