Effect of coil-wire insert on heat transfer enhancement and pressure drop of the horizontal concentric tubes

In the present study, the heat transfer characteristics and the pressure drop of the horizontal double pipe with coil-wire insert are investigated. The inner and outer diameters of the inner tube are 8.92 and 9.52 mm, respectively. The coiled wire is fabricated by bending a 1 mm diameter of the iron wire into a coil with a coil diameter of 7.80 mm. Cold and hot water are used as working fluids in the shell side and tube side, respectively. The test runs are performed at the cold and hot water mass flow rates ranging between 0.01 and 0.07 kg/s, and between 0.04 and 0.08 kg/s, respectively. The inlet cold and hot water temperatures are between 15 and 20 °C, and between 40 and 45 °C, respectively. The effect of the coil pitch and relevant parameters on heat transfer characteristics and pressure drop are considered. Coil-wire insert has significant effect on the enhancement of heat transfer especially on laminar flow region. Non-isothermal correlations for the heat transfer coefficient and friction factor are proposed. There is reasonable agreement between the measured data and predicted results.