Natural convection experiments on the outer surface of an inclined helical coil

摘要

Natural convection heat transfer on the outside of an inclined helical coil was investigated experimentally. For a single turn helical coil laid on the horizontal plane, the heat transfer rate was very close to that of a horizontal cylinder. The heat transfer rate decreased when the coil was tilted. For inclined helical coils with higher numbers of turns, the heat transfer rates were influenced by plumes from the lower turns, exhibiting preheating, velocity, and chimney effects. For very small pitches, the preheating effect was dominant. For moderate pitches, the velocity and chimney effects became dominant. For larger pitches, the plume effect disappeared. The angle of inclination affects the physical arrangement of the helical coil and influences the heat transfer. The study was performed using very high Pr of 2014. An empirical correlation was proposed based on the experiments.