Abstract
Numerous investigations were conducted to enhance heat transfer in smooth tubes. They have used both active and passive methods. However, very rare investigations have reported the simultaneous usage of active and passive methods. Furthermore, the investigations on entropic behaviors are very rare too. Through present paper, effect of air bubble injection (as active method) together with spring wire turbulator (as the passive method) is probed. The pipe was subjected to a constant heat flux. Spring pitch and fluids flow rates were variable parameters of this study. Four flow levels of 2, 3, 4, and 5 were intended for water and air. The studied parameters were Nusselt number, cost-performance coefficient, and dimensionless exergy destruction. The flow patterns were also assessed. To calculate the Nusselt number and exergy destruction, ambient temperature, pipe surface temperature, water inlet, and outlet temperatures were measured. Results showed that reducing the induced rotational flow by the pitch, affects two-phase flow and leads significant changes flow pattern and two-phase flow motion model. Air bubble injection increased Nu by 40% and dimensionless exergy destruction by 36%.