Experimental evaluation of pressure drop in round tubes provided with physically separated, multiple, short-length twisted tapes

Isothermal pressure drop tests were performed on horizontal round tubes each containing identical, physically separated, equally spaced, short-length twisted tapes (TTs). The tests investigated the dependence of the Darcy friction factor, f, on the empty tube Reynolds number Re, TT twist ratio y, and TT spacing s. The variation of f across TTs belonging to the same test section was also examined. Ranges of the experimental variables examined were: 10,000 ⩽ Re ⩽ 90,000, 1.5 ⩽ y ⩽ 6, and s = 30, 40 and 50. The number of 360° revolutions was held constant for all the tapes and equal to 1.5. Tap water at room temperature and nearly atmospheric pressure was used as the working fluid. A correlation for the Darcy friction factor, in the form f = f (Re, y, s), was developed from the collected experimental data, with excellent accuracy.