Effect of Twin Delta-Winged Twisted-Tape on Thermal Performance of Heat Exchanger Tube

Abstract

This work aims at studying the effect of twin delta-winged twisted-tape insertion on heat transfer, pressure drop, and thermal performance characteristics of a heat exchanger tube. All twisted tapes used in this work were made of aluminum sheets twisted at a single twist ratio of 3.0. The twin delta wings were formed by extrusion of the tape at the center area at every twist length interval. For comparison, three different arrangements of the twin delta wings were: (1) the wing tips pointing upstream of the flow (TTW-up, twin delta-winged twisted tape in counterflow arrangement), (2) the wing tips pointing downstream of the flow (TTW-down, twin delta-winged twisted tape in co-flow arrangement), and (3) the wing tips pointing opposite direction (TTW-o, opposite winged twisted tape). The wing declination was arranged at an angle of 15° with respect to the tape surface. Effects of three different wing-tip angles of 20°, 40°, and 60° for a constant wing base were examined. The experiments were conducted using water as the test fluid in a uniform-heat-flux tube for Reynolds number between 5000 and 15,000. The results demonstrate that the TTW-up consistently provides greater heat transfer rate, friction factor, and thermal performance factor than the TTW-down and the TTW-o, at a similar condition. In addition, the heat transfer rate increases as the wing-tip angle decreases. Over the range investigated, the TTW-up with wing-tip angle of 20° gives the highest thermal performance factor of 1.26 along with a Nusselt number and friction factor of 2.57 and 8.55 times those of the plain tube.