Performance intensification of discontinuous twisted turbulators by using delta-winglets: Experimental study

Abstract

An experimental study is carried out on novel twisted-tapes (TTs). First, the performance of discontinuous TTs (DTTs) with both alignment (ADTT) and non-alignment (NDTT) rotations is compared to the continuous TT (CTT). The results show that the heat transfer coefficient (h) decreases by an average of 14.9% and 8.8%, as the ADTT and NDTT are used, and the pressure drop (∆p) decrements are about 23.3% and 18.6%, respectively. The average overall performance index (OPI) of CTT, ADTT, and NDTT is about 1.70, 1.55, and 1.65, respectively. Then, to enhance the performance of the DTTs, the straight sections are equipped with 1, 2, and 3 rows of delta-winglets (DWs). It is found that creating DWs increases both h and ∆p. The enhanced DTTs have two ways to disrupt the flow field, including flow disruption produced by twisting the tape and extra flow disruption produced by creating the DWs. Compared with the original DTTs, the enhanced ADTT and NDTT can effectively improve the thermal performance of the tube under identical operating condition. The values of h for the ADTT and NDTT is increased by 7.4–35.6% and 2.5–45.8%, respectively, and the corresponding OPI ranges from 1.34 to 1.95.