A comprehensive second law analysis for a heat exchanger tube equipped with the rod inserted straight and twisted tape and using water/CuO nanofluid

Thermohydraulic performance and second law analysis was applied on the experimental results by using water/CuO nanofluid, and the rod inserted straight tape (RIST) and the rod inserted twisted tape (RITT) for a heat exchanger tube under constant heat flux and turbulent flow conditions. The experiments were conducted for the Reynolds number ranging from 5000 to 29,000, the nanofluid mass fraction of 0, 1.0 and 2.0%, the pitch ratios of the rods on the tapes (L/p) of 10, 20 and 40. The experimental results were comprehensively evaluated according to Nusselt number, friction factor, thermohydraulic performance criteria, entropy generation rate, Bejan number, entropy generation number, exergy destruction rate and second law efficiency. The results showed that although the RITT cases are superior for the thermal performance than the counterparts of the RIST, there was no significant influence by the cases of RITT and RIST on the second law efficiency due to greater frictional losses. However, the use of nanofluid contributes a significant influence on increasing the second law efficiency. As a conclusion, the highest thermohydraulic performance criteria of 1.377 and the highest second law efficiency of 0.439 was observed by the case of R/TTL/p=40 and the nanofluid mass fraction of 2.0% at Reynolds number of 6572.