Heat transfer and pressure‐drop studies were made on a series of electrically heated tubes containing full‐diameter, full‐length twisted tapes. The A nickel tubes had a nominal inside diameter of 0.4 in. (10.1 mm.) and a heated length of 12 in. (30.5 mm.). Nitrogen at 200 lb./sq.in. gauge (14.6 atm.) was the working fluid, and the tests covered the Reynolds number range from 20,000 to 200,000. Twist ratios, defined as the ratio of the tube length per 180 deg. twist to the tube diameter, were varied from 2.5 to 14. The effect of tube wall‐to‐gas temperature ratio was studied for values of up to 1.8 and the heat flux was varied from 104 to 105 B.t.u./hr. · sq.ft. (3 × 104 to 3 × 105 w./sq.m.). The results were compared with the results of previous heat transfer and pressure‐drop studies and were generally found to be in good agreement. An empirical correlation was developed for the heat transfer results that accounts for the effects of twist ratio, wall‐to‐gas temperature ratio, and tube length and includes most of the previous single‐phase results. Copyright © 1969 American Institute of Chemical Engineers
