Effective thermal conductivity of an active suspension with gas-propelling micro-swimmers

Heat-transfer fluids with enhanced thermophysical properties are required for cooling applications in the continuously expanding computing facilities. The objective of this study is to measure the effective thermal conductivity of an active fluid based on an H2O/H2O2 mixture, where gas bubbles propel catalytic MnO2 particles. The methodology involves assessing the thermal conductivity at varying concentrations of MnO2 particles. Results indicate that the thermal conductivity of the active fluid increases by approximately 25% relative to water at a concentration of 0.2 wt% MnO2, but further increases in particle content lead to a dramatic reduction of 23%, down to 0.46 W/m⋅K. This reduction is attributed to the accumulation of gas bubbles, while the initial enhancement is due to the advective heat transfer driven by particle motion. Additionally, settling effects on particle concentration in the suspension are observed, showing a reduction of 2–7 times, along with considerations on the impact of variable concentrations of H2O2 and surfactants.