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.
