Abstract:
An experimental investigation has been carried out to study the pressure drop and
turbulent flow heat transfer to air in a tube with wire -coil -inserts. 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°) were fabricated and inserted into the smooth tube
successively. The test section was heated electrically. The Reynolds numbers were based
on inlet-inside diameter and were varied from 2.0 x 104 to 4.5 x 10 4 Air velocity, air
inlet and outlet temperatures, local wall temperature, local coil- surface temperature and
the pressure drop were collected for tubes with wire- coil- inserts to analyze the friction
factor, Nusselt number, and the heat transfer coefficient. For comparable Reynolds
numbers, friction factor for tubes with wire- coil- inserts varies from 1.50 to 4.0 folds
than that of the smooth tube. The required pumping power for tubes with wire- coilinserts
varies from 1.25 to 2.50 folds than that of the smooth tube. Heat transfer
coefficient for tubes with wire-coil-inserts increases from 1.20 to 2.0 folds than that of
the smooth tube. The heat transfer effectiveness of the exchanger was calculated for
constant wall temperature. For comparable Reynolds number the heat transfer
effectiveness for tubes with wire- coil- inserts varies from 1.50 to 2.0 folds in
comparison to smooth tube. Finally, a correlation was also developed for prediction of
heat transfer coefficient in turbulent flow for tubes with wire- coil- inserts having wire
diameter 3.25mm and also for smooth tube of70mm inner diameter.
