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This study aims at achieving improved heat transfer potential for a tube-in-tube counterflow heat exchanger using silver/water (Ag) and copper oxide/water (CuO) nanofluids. Heat transfer and rheological characteristics of prepared nanofluids containing spherical nanoparticles of average size of 12–64 nm were experimentally investigated. Based on the experimental results, for increase in nanoparticles volume proportion up to 1.0%, convective heat transfer coefficient and Nusselt number were augmented by 52% and 47.5% for Ag nanofluids, and 27.6% and 24.3% for CuO nanofluids, respectively, while compared with base fluid. Also, at higher Reynolds number typically around 7500 the heat transfer potential was also increased considerably. However, increased particle loading eventually increased the density and dynamic viscosity of nanofluids, which increased frictional pressure drop from 4% to 22.2%. The increased heat transfer rate at increased particle concentration was attributed to the thermal conductivity and diffusion of nanoparticles in fluid medium, whereas increased pressure drop was largely influenced by density and dynamic viscosity of nanofluids. Furthermore, the new correlations developed in this study based on the experimental results revealed that the mean deviation between experimental and predicted Nusselt number varied from +6% to –12% and from +3% to –7%, respectively, for Ag and CuO nanofluids. |
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