Thermal diffusivity of nanofluids: A simplified temperature oscillation approach

Thermal diffusivity is critical in optimizing processes across diverse industrial and scientific applications, including heat exchangers, electronics cooling, and energy storage systems. However, existing measurement techniques often rely on complex setups, advanced electronics, or parameter fitting, limiting their practicality for routine use. This study introduces a simplified temperature oscillation method for precise thermal diffusivity measurements that utilizes a cost-effective and reliable setup comprising a thermofoil heater and four thermocouples, requiring a small sample volume (∼1 ml). This makes it particularly well-suited for nanofluids, which are increasingly applied in advanced thermal management, innovative lubricants, pollutant remediation, and high-performance cooling systems. Experimental validation with water demonstrated excellent agreement with previously reported thermal diffusivity values, underscoring the accuracy and reliability of the technique. When applied to a luminescent nanofluid composed of NaGdF4:Yb/Er(18/2%)@NaGdF4 upconverting nanoparticles dispersed in water, the thermal diffusivity was comparable to that of distilled water challenging earlier reports of anomalous enhancements in nanofluid thermal properties.