Heat transfer enhancement by combination of serpentine curves and nanofluid flow in microtube

Heat transfer and flow characteristics of Cu/water nanofluids' flow in the serpentine microtubes are investigated experimentally. The serpentine microtubes are fabricated by bending a straight copper microtube with an inner diameter of 787 μm. Also, the Cu/water nanofluids are prepared using a novel one-step technique, namely electro-exploded wire. The effects of serpentine microtubes' geometrical parameters (pitch spacing, p, and straight section, l) and nanofluid concentration (weight fraction, φ) are examined. It is found that the heat transfer enhances by decreasing both the pitch spacing and the straight section of the serpentine microtube as well as increasing the weight fraction of the nanofluid. Also, the results show that the friction factor tends to increase in the same manner. A noticeable average enhancement in the thermal performance factor of 21.8% is obtained for a specific operating condition, i.e., the nanofluid at φ = 0.3% through the serpentine microtube with p = 9.6 mm and l = 10 mm. Finally, two correlations of Nusselt number and friction factor for the Cu/water nanofluids across the serpentine microtubes are proposed.