Employing V-shaped ribs and nanofluid as two passive methods to improve second law characteristics of flow within a square channel: A two-phase approach

This research attempts to investigate the effects of simultaneous utilization of V-shaped ribs and nanofluid as two heat transfer enhancement approaches inside a square channel on the second law attributes. For this purpose, the comprehensive entropy generation and exergy destruction analyses are carried out with the aid of the two-phase mixture technique for the copper-water nanofluid flow through the channel enhanced with the 45 degrees V-shaped ribs. Firstly, a comparison is made between attack angles of 45 degrees and 60 degrees, which unveils the superiority of 45 degrees because it shows lower entropy generation. The Cu nanoparticles are utilized as the main nanoparticles. Furthermore, the nanofluids containing the Ag nanoparticles are also simulated at two volume fractions of 0.01 and 0.03 to make comparison between different nanoparticle materials. The impacts of rib configuration including the rib pitch and its height are assessed using three rib pitches and three rib heights. The total entropy generation and total exergy destruction decrease as the volume fraction increases, such that an around 31.85% reduction occurs in the total entropy generation and total exergy destruction when the volume fraction increases by 0.03 for the case of rib height of 5 mm and rib pitch of 100 mm. Thereby, the second law efficiency rises by 15.64% in the same condition. Additionally, the installed 45 degrees V-shaped ribs remarkably contribute to the total irreversibility reduction by means of creating four recirculation flows and powerful swirl flows. The results indicate that utilizing both larger rib height and smaller rib pitch (at the same time) exhibits lower exergy destruction and enhances the second law efficiency. (C) 2020 Elsevier Ltd. All rights reserved.