Local heat transfer coefficient in helical coils with single phase flow

The objective of the present work is to study the influence of curvature and Reynolds number on local heat transfer coefficient in a helical coil with water as the working medium. The local wall temperature is measured not only in the axial direction (along the length of coil) but also in the circumferential direction using infrared thermal imaging technique. The test sections are made of thin walled stainless steel (SS 304) tubes having an inner diameter varying from 5.4 to 7.5 mm with a thickness of 0.2 and 0.25 mm. The coil diameter to the tube diameter ratio ranges from 13.1 to 67 and coil pitch is 50 mm. The experimental results of friction factor and overall averaged total Nusselt number are compared with the available correlations in the literature. Correlations are suggested for overall averaged and local circumferentially averaged Nusselt number for inner side, outer side and total surface (inner side and outer side) of a helical coil.