Study of heat transfer through a tube with wire-coil-inserts at low turbulent flow

Abstract

An experimental investigation has been carried out to study the pressure drop and convective heat transfer in a tube with wire-coil-inserts of varying pitch in turbulent flow at low Reynolds number. Four mild steel wire coils of different pitches (pitch, P=12mm, 24mm, 40mm, and 50mm with corresponding helix angles, a =10°, 20°, 35°, and 45° respectively) were fabricated and inserted into the smooth tube successively. The test section was heated electrically. The Reynolds number was chosen based on inlet diameter of the tube and was varied in the range of 6.0 x 10 3 to 2.2 x 104 . Coil surface temperatures, wall temperatures and pressure drops along the axial length of the test section and velocity of the airflow were measured to analyze the friction factor, Nusselt number, and the heat transfer coefficient. From the measured data and their subsequent analysis, it is clear that with wire-coil-inserts, the heat transfer coefficient is enhanced with corresponding increase in friction factor and pumping power. For 2 folds enhancement of heat transfer coefficient in a coil inserted tube, the friction factor and pumping power are found to be increased by 3.5 folds and 3 folds respectively, compared to smooth tube at comparable Reynolds number. The effectiveness for the constant wall temperature of the coil-inserted tube increases as much as 1.25 folds than the smooth tube. A correlation has been proposed for the prediction of heat transfer coefficient for tubes with wire- coil- inserts.