Study of heat transfer in turbulent flow through tube with wire-coil inserts

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.