Intensified convective energy tapping in modified tubes using Azadirachta indica brewed zinc oxide as potential thermo-fluids

Abstract

Reusing certain types of decomposed tree leaves is beneficial for biosynthesizing nanoparticles for nanofluids to meet energy sustainability and conservation. Encapsulating and reductant agents in Azadirachta indica (neem) help with fluid stability besides providing higher thermal transport properties. Sol-gel technique was adopted to prepare zinc oxide (ZnO) nanoparticles with neem solution to obtain neem-doped zinc oxide (ZnOneem) particles. According to the Debye-Scherrer relation, the size of ZnOneem was 36 nm. Optimal fluid stirring and sonication parameters were identified to synthesize and stabilize 0.05, 0.2, and 0.6% concentrated nanofluids with aqua-antifreeze (50:50) without surfactant. While the optimal stirring speed and time of 0.05, 0.2, and 0.6% nanofluids were 322 rpm and 36 min, 329 rpm and 33 min, and 334 rpm and 29 min, respectively, the optimal sonication time were 39 min, 34 min, and 32 min, respectively. However, sodium dodecyl sulphate (SDS) at a dispersion fraction of 0.6 ensured 35 months of good suspension. Pumping these turbulent fluids (Re = 5000–10000) through a microfin tube snug-fit with twisted tape inserts (twist pitch, y = 63, 84, and 105 mm) ensured the best outcomes with all the fluid samples. The Nusselt number ratio of 2.114 is the best at a penalty of 2.228 friction factor ratio with 0.6% concentrated nanofluid at Re = 10,000 circulating within the tube fit with Y = 6 tape. For this case, the Bejan number was 0.72, with the maximum Performance Evaluation Factor (PEF) and the Entropy Performance Evaluation Factor (EPEF) being 1.619 and 154.02, respectively.