Experimental analyses on heat transfer performance of TiO₂–water nanofluid in double-pipe counter-flow heat exchanger for various flow regimes

Nanofluids are widely used in heat transfer applications. This article presents the effect of heat transfer and pressure drop of the TiO₂–water nanofluids flowing in a double-tube counter-flow heat exchanger with various flow patterns. In this experimental work, performance of TiO₂–water nanofluid on heat transfer in three different cases such as laminar, transition and turbulent flow region were analyzed. TiO₂ nanoparticles with average diameters of 20 nm dispersed in water with three volume concentrations of 0.1, 0.3 and 0.5 vol% were used as the test fluid. The results show that the heat transfer of nanofluids is higher than that of the base liquid (water) and increased with the increase in Reynolds number and particle concentrations. The heat transfer rate of nanofluid with 0.5 vol% was 25% greater than that of base liquid, and the results also show that the heat transfer coefficient of the nanofluids at a volume concentration of 0.5 vol% was 15% higher than that of base fluid at given conditions. Pressure drop of nanofluid was increased with increase in volume concentration, and it is slightly higher than that of the base fluid.