| Summary: | The curved geometry of a coiled flow inverter (CFI) promotes chaotic mixing through a combination of coils and bends. Besides the heat exchanger geometry, the heat transfer can be enhanced by improving the thermophysical properties of the working fluid. In this work, aqueous solutions of dispersed TiO<sub>2</sub> nanometer-sized particles (i.e., nanofluids) were prepared and characterized, and their effects on heat transfer were experimentally investigated in a CFI heat exchanger inserted in a forced convective thermal loop. The physical and transport properties of the nanofluids were measured within the temperature and volume concentration domains. The convective heat transfer coefficients were obtained at Reynolds numbers (<i>N<sub>Re</sub></i>) and TiO<sub>2</sub> nanoparticle volume concentrations ranging from 1400 to 9500 and 0–1.5 <i>v</i>/<i>v</i>%, respectively. The Nusselt number (<i>N<sub>Nu</sub></i>) in the CFI containing 1.0 <i>v</i>/<i>v</i>% nanofluid was 41–52% higher than in the CFI containing pure base fluid (i.e., water), while the 1.5 <i>v</i>/<i>v</i>% nanofluid increased the <i>N<sub>Nu</sub></i> by 4–8% compared to water. Two new correlations to predict the <i>N<sub>Nu</sub></i> of TiO<sub>2</sub>–water nanofluids in the CFI at Reynolds numbers of 1400 ≤ <i>N<sub>Re</sub></i> ≤ 9500 and nanoparticle volume concentrations ranges of 0.2–1.0 <i>v</i>/<i>v</i>% and 0.2–1.5 <i>v</i>/<i>v</i>% are proposed.
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