Heat transfer, friction factor and exergy efficiency analysis of nanodiamond-Fe3O4/water hybrid nanofluids in a tube with twisted tape inserts

In the present study, the Nusselt number, exergy efficiency, entropy generation and themal performance factor of nanodiamond-Fe3O4/water hybrid nanofluids in a tube with twisted tape inserts have been con-ducted experimentally. The experiments have been performed under turbulent flow regime in different Reynolds number ranging from 2000 to 22000, volume loadings from 0 to 0.2 %, and twisted tape inserts, HID of 5, 10, and 15, respectively. It is found that, compared to water plain tube, the Nusselt number and exergy efficiency of 0.2 % vol. of nanofluid in a tube is raised by 29.55 % and 18.13 % with twisted tape insert, HID of 5, the Nusselt number and exergy efficiency is further raised by 73.04 % and 161.31 % at a Reynolds number of 20,095 with a maximum friction factor penalty of 61.93 %. The thermal entropy generation is dropped by 30.72 % for 0.2 % vol. of nanofluid in a tube and with twisted tape insert, HID of 5, the thermal entropy generation is further dropped by 48.58 % compared to water. Maximum increase of frictional entropy generation is about 74.81 % at 0.2 % vol. of nanofluid with twisted tape insert of HID = 5 over base fluid. New Nusselt number and friction factor correlations were developed.(c) 2022 THE AUTHORS. Published by Elsevier BV on behalf of Faculty of Engineering, Ain Shams Uni-versity. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/ by-nc-nd/4.0/).

Automated summary

The present study experimentally investigated the Nusselt number, exergy efficiency, entropy generation, and thermal performance factor of nanodiamond-Fe3O4/water hybrid nanofluids in a tube with twisted tape inserts. The experiments were conducted under turbulent flow regime with different Reynolds numbers, volume loadings, and twisted tape inserts. The results showed that the addition of nanofluids and twisted tape inserts significantly improved the heat transfer and energy efficiency, while reducing thermal entropy generation. New correlations for Nusselt number and friction factor were proposed.