Laminar heat transfer and fluid flow of two various hybrid nanofluids in a helical double-pipe heat exchanger equipped with an innovative curved conical turbulator

Abstract

In the present study, the effect of inserting an innovative curved turbulator and utilizing two types of hybrid nanofluids on thermal performance in a helical double-pipe heat exchanger is evaluated numerically. The considered hybrid nanofluids include silver (Ag) and graphene (HEG) nanoparticles/water and multi-wall carbon nanotubes–iron oxide nanoparticles/water (MWCNT-Fe3O4/water). The considered innovative turbulator has 12 blades to create secondary flows. Also, a hole is considered at the end of the turbulator. The present study has two sections: In the first one, the results of utilizing hybrid nanofluids are compared with pure water (φ = 0.3%). In the second section, the hybrid nanofluid based on the first section was selected and utilized. The effect of the volume concentration of the selected hybrid nanofluid was investigated. Results show that utilizing the present innovative turbulator leads to higher heat transfer rate. As a result, the Ag-HEG/water hybrid nanofluid has better thermal performance at low mass flow rate. Also, the thermal efficiency of the considered helical heat exchanger is lowest at φ = 0.1%. In the case of highest volume concentration (φ = 0.7%), the thermal performance is maximum at low mass flow rate.