Effects of Dispersion on Thermal Conductivity and Viscosity in Biomass‐Based Nano Systems

Ensuring the long-term stability of nanofluids (NFs) remains a challenge due to nanoparticle aggregation, precipitation, and poor dispersion. Zeta potential (ZP) plays a crucial role in preventing agglomeration and enhancing stability. This study investigates, for the first time, the combined effect of stability and thermal conductivity (TC) enhancement in nanofluids based on biomass-derived carbon nanospheres (CNSs). CNSs synthesized from eight different biowaste sources exhibited ZP values ranging from -17.0 to -45.6 mV, influencing dispersion and fluid behavior. These NFs demonstrated exceptional stability for up to 40 days without surfactants and achieved a TC enhancement of up to 111.8%. The research also explores the influence of ZP on TC, dynamic viscosity (V), and thermal diffusivity. The NFs displayed shear-thinning, non-Newtonian behavior, with viscosity values depending on CNS concentration, reaching 0.0000000302 Pa·s. The effect of pH (3-12) on stability and TC revealed maximum performance at pH 8, while optimal TC enhancement was achieved at 0.1 wt% CNS concentration. This study bridges the gap between laboratory research and industrial applications, offering sustainable, low-cost, and high-efficiency coolant solutions for the automotive sector. It supports seven Sustainable Development Goals (SDGs) through an innovative waste-to-wealth approach.