Experimental determination of single-phase pressure drop and heat transfer in a horizontal internal helically-finned tube

The single-phase pressure drop and heat transfer in an internal helically-finned tube and a plain tube are measured for aqueous ethylene glycol. Pressure drop data are collected under isothermal condition and heat transfer experiments are conducted in a flooded evaporator with R134a boiling outside the tube. The tests are performed with Prandtl number from 17 to 29 and Reynolds number from 5000 to 34,000. The main parameters of the internal helically-finned tube are nominal inside diameter (22.48 mm), fin height to the tube inside diameter ratio (0.022), number of fins (60), helix angle (45°). It is found that plain tube's results agree well with Filonenko and Gnielinski correlations. Friction factors of internal helically-finned tube increase with Re below 17,000, reaching a maximum at Recr = 17,000 and decrease above 17,000. This indicates that the conventional criterion Re > 10,000 for distinguishing turbulent flow isn't suitable for internal helically-finned tubes. A correlation is developed to predict the experimental heat transfer coefficient within 5%. In evaluation of the thermal performance, the j-factor for internal helically-finned tube is about 3.5 times of that for the plain tube and the efficiency index varies from 1.8 to 1.55. This study offers the reference on engineering design and later study.