Three-dimensional analysis of combined thermal-solutal buoyancy and capillary convection of water-based micropolar multi-walled carbon nanotubes nanofluids

International audienceA parametric numerical investigation has been performed of three-dimensional combined thermal-solutal capillary and buoyancy convection performances of micropolar multi-walled carbon nanotubes-water nanofluid. The governing equations are given based on vorticity-vector potential formulation and numerically resolved with finite volume method. The effects of Rayleigh number (10(4) <= Ra <= 10(6)), micropolar parameter (0 <= K <= 5), buoyancy ratio (- 2 <= N <= 0), Marangoni number (0 <= Ma <= 1000), and nanofluid concentration (0.0055% <= phi <= 0.557%) on Sherwood/averaged Nusselt number are examined along with their impact on the streamlines, isotherms, and isoconcentrations. The results imply the significant impact of surface tension on the heat/mass transfer rate, in low Rayleigh number in particular Besides, the averaged Nusselt and Sherwood numbers are improved significantly due to arise in the Marangoni number originated from unidirectional effects of surface tension and buoyancy for the thermal-dominated regime. Within solutal-buoyancy governed zone, however, an opposite trend is evidenced. Heat/mass transfer rate is overestimated when the micropolar theory is not taken into consideration. Also, the performance of multi-walled carbon nanotubes/water nanofluid depends on the nanoparticles volume concentration. Hence, there is a critical nanofluid concentration beyond which the intensity of flow increases and then declines

Improving the thermal-hydraulic performance of parabolic solar collectors using absorber tubes equipped with perforated twisted tape containing nanofluid

The thermal and hydraulic efficiency of a parabolic trough solar collector is investigated in this study. The collector absorber tube is equipped with twisted tape with circular holes containing water-copper oxide nanofluid with three nanoparticles volume fractions of 1%, 2% and 4%. In three modes (d/W = 0.5, 0.7, 0.9), circular holes are constructed for the ratio of the circle's diameter to the twisted tape's breadth. All turbulent flow simulations were done using the SIMPLEC algorithm, FVM and RNG k-ε model in three Reynolds numbers as 10,000, 20,000 and 30,000. Studies have shown inserting twisted tape with a circular hole increases the pressure drop and the heat transfer rate compared to a pipe without twisted tape. The highest coefficient of thermal performance occurs in Reylond number of 10,000 and a nanoparticles volume fraction of 4%. The findings indicate that using nanoparticles improves the solar collector's energy and exergy efficiency. As a result, the best collector performance was obtained when using nanofluids with an nanoparticles volume fraction of 4%.The Deanship of Scientific Research at King Khalid University, Abha, Saudi Arabia.http://www.elsevier.com/locate/seta2024-04-11hj2023Mechanical and Aeronautical Engineerin