<p>Nanofluids demonstrate significant application potential in the energy and chemical engineering fields due to their unique heat transfer properties. This study employed a two-step method to prepare TiO₂ nanofluids using an ethylene glycol–water mixture as the base fluid. The optimal concentration of 0.5 mass%, which exhibited the best dispersion stability as determined by absorbance measurements, was selected for experimental investigation of heat transfer performance in a hollow spiral double-tube heat exchanger. The heat transfer coefficient, heat transfer rate, and Nusselt number (<i>Nu</i>) were analyzed. Experimental results confirmed the reliability of the system, showing a deviation of less than 10% in the heat transfer rate between the water side and the nanofluid side. Within the temperature range of 303 K–328 K, the addition of TiO₂ nanoparticles significantly enhanced the heat transfer coefficient. Conversely, a reduction in the heat transfer coefficient was observed in the lower temperature range of 263 K–283 K. Meanwhile, the incorporation of TiO₂ nanoparticles led to an increase in the Nusselt number across the tested conditions. The motion and heat transport behavior of nanoparticles within the spiral flow channel were further examined from a microscopic perspective. This work provides experimental evidence and fundamental data supporting the engineering application of TiO₂–ethylene glycol nanofluids in hollow spiral double-tube heat exchangers.</p> Graphical Abstract <p></p>