Anomalous increase in the thermal conductivity of water on the addition of liquid-exfoliated magnesium diboride sheets

Abstract

Low thermal conductivity constraints heat transfer fluids (HTFs) from becoming an energy-efficient technology. Nanomaterial-dispersed HTFs, commonly known as nanofluids, have garnered enormous attention by providing anomalous rises in the thermal transport properties due to their unique dimensional and conformational features within the fluid medium. Herein, we study the thermal transport properties of highly stable liquid-exfoliated magnesium diboride sheet-based nanofluids. Following the Maxwell (Hashin-Shtrikman) mean-field theory for the prediction of the effective thermal conductivity (k_eff) of well-dispersed magnesium diboride (MgB₂) particles in the fluid medium, the result indicates a k_eff value in the range of 0.63 W m⁻¹ K⁻¹ and 0.26 W m⁻¹ K⁻¹ for water and ethylene glycol respectively at a volume fraction of ϕ = 0.020. However, experimental observations yield k_eff of 0.74 W m⁻¹ K⁻¹ and 0.29 W m⁻¹ K⁻¹, respectively, at ϕ = 0.020, representing a deviation from Maxwell's prediction. The article explains this anomalous behaviour of the MgB₂ dispersed system by considering two effective thermal transport mechanisms: geometrical configurations and micro-convection.