Performance evaluation of shot-blasted heat exchangers with MWCNT and activated carbon nanofluids: assessing entropy, exergy, sustainability index, Grashof, Rayleigh, and Richardson numbers for solar thermal applications

This experimental study examines the exergy efficiency and entropy generation of shot-blasted heat exchangers using two types of nanofluids: solar glycol-activated carbon and solar glycol-multi-walled carbon nanotubes. The copper inner tube's external surface was roughened using pressurized mechanical shot-blasting machinery. Also, the activated carbon was prepared from biowaste using a pyrolysis process with a higher temperature sintering method. The thermal conductivity of the solar glycol-multi-walled carbon nanotubes (SG-MWCNTs)- and solar glycol-activated carbon (SG-AC)-based nanofluids increased by 22.22 and 12.73% at a nanomaterial dispersion of 0.6% and a temperature of 50 °C, compared with the base fluid respectively. The thermal exergy destruction value of SG-MWCNTs and SG-ACs rises by nearly 38.01 and 29.84% at the nanomaterial dispersion of 0.6% and MFR nanofluid of 80 g s⁻¹ compared with SG. For an SG-MWCNTs-based nanofluid volume fraction of 0.6%, the exergy efficiency was enhanced by approximately 29.15% associated with SG-AC nanofluids at an MFR nanofluid of 55 g s⁻¹. The thermal evaluation parameter of SG-MWCNTs nanofluids enhanced nearby 28.81, 24.07, and 18.15% at particle dispersion of 0.2, 0.4, and 0.6%, respectively, compared to AC-SG nanofluids at MFR of 80 g s⁻¹. This study evaluates the effects of different nanofluids on convection in shot-blasted heat exchangers by considering the Grashof, Rayleigh, and Richardson numbers. These dimensionless numbers, which are influenced by the Reynolds number, provide a comprehensive understanding of the interplay between buoyancy and inertial forces, thermal diffusivity, and the relative importance of natural and forced convection.