Conclusions
Simulations are carried out for finding out optimum crosssectional shape for double pipe helical coil using 4 shapes which are circular, rectangular, triangular, and square. It was found that rectangular cross-section was having best heat transfer properties followed by triangular, square and circular. But pressure drop was highest for rectangular shape and least for circular shape. Various simulations are carried out for finding out how the taper angle on helical coil influences heat transfer and pressure drop properties. It was found that as the coil taper angle increases, the heat transfer rate increases considerably, while pressure drop also increases with taper angle. After carrying out various simulations for finding out optimum coil, it was found out that a rectangular crosssection coil (Fig. 12) with maximum possible taper angle can give best heat transfer characteristics. The extent of taper angle is limited by coil length increase which would demand more space, and also the pressure drop and pumping power. This rectangular cross-section coil with a fixed taper angle of 30 is used for comparison with double pipe straight tube. It was observed that heat transfer in the optimized helical coil was nearly twice more than that of straight tube. The friction factor was higher in the helical coil than straight tube which implies more pumping power requirement for helical coil.
