Enhanced tubes with internally helical fins have been extensively used in the large heat exchangers. This paper experimentally determined the single-phase friction factor and heat transfer coefficients in an internal helically-finned tube. Parameters of the test tubes are nominal inside diameter (22.48mm), fin height to the tube inside diameter ratio (0.022), number of fins (60), and helix angle (45°). Pressure drop data were collected under isothermal condition and heat transfer experiments are conducted in a flooded evaporator. The aqueous ethylene glycol was used as the working fluid and the tests are performed with the Prandtl number from 18.1 to 29.5 and Reynolds number from 7,000 to 37,000. The heat transfer enhancement ratio hi-en/hi-p and friction enhancement ratio fen/fp increased with Reynolds number and reached maximum at Re>17,000, while efficiency index (hi-en/hi-p)/(fen/fp) decreased with Reynolds number and reached the minimum at Re>17,000. The maximum friction enhancement ratio of 2.13 and the maximum heat transfer enhancement ratio of 3.47 were obtained, while the corresponding minimum efficiency index was 1.62. The maximum efficiency index of 1.86 occurred at the minimum Re in the heat transfer experiments. This study offers a reference on the design of the heat exchangers.
Papers presented at the 13th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Portoroz, Slovenia on 17-19 July 2017 .