Effect of non-uniform wall corrugations on laminar convective heat transfer through rectangular corrugated tube by using graphene nanoplatelets/MWCN hybrid nanofluid

Abstract

Hybrid nanofluids and non-uniform wall corrugations have been reported to enhance convective heat transfer, which is not yet fully explored. In this study, the heat transfer efficacy of non-uniform wall corrugations on laminar convective heat transfer through a rectangular corrugated tube by using a hybrid nanofluid is investigated. Three different non-uniform wall corrugations; gradually increasing wall corrugation (GIWC), gradually decreasing wall corrugation (GDWC) and periodic wall corrugation (PWC) are investigated and compared with uniform wall corrugation (UWC). The applied hybrid nanofluid is a mixture of graphene nanoplatelets (GnP) and multi-walled carbon nanotubes (MWCN) with water, wherein the volume fractions of nanoparticles are 0.1%, 0.15%, and 0.2%. The computation is conducted under 2000 kW/m2 heat flux conditions on the heated surface of the corrugated wall with the Reynolds number in the range of 500–2000. The heat transfer efficacy and required pumping power are investigated for different wall corrugations and Reynolds numbers. The developed numerical model was validated with experimental studies from the published literature on different corrugated conduits. The computation results indicate that non-uniform wall corrugations GIWC, GDWC, and PWC provided better performance compared to uniform corrugation UWC. The average Nusselt number is the highest for PWC compared to others. At a constant Reynolds number 1000, the heat transfer was enhanced by an overall 15.61% for GDWC, 18.70% for GIWC, and 21.16% for PWC compared to UWC. In addition, PWC provided the highest increase in the pumping power requirement compared to others. At a constant Reynolds number 1000, the pumping power ratio is 1.37 for GDWC, 1.47 for GIWC, and 1.54 for PWC compared to UWC. GnP/MWCN-water hybrid nanofluid with a 0.2% volume fraction provided the highest enhancement in heat transfer compared to pure water. For PWC configuration, mixing nanoparticle volume fractions from 0.1% to 0.2%, the Nusselt number increases from 6.66% to 23.75%,while the pumping power ratio increases from 1.24 to 1.39 compared to water. It can be concluded that further experimental investigation is critical to validate the implementation of non-uniform wall corrugation for enhancing the thermal performance of rectangular corrugated tubes.