Second law analysis of turbulent convection flow of boehmite alumina nanofluid inside a double-pipe heat exchanger considering various shapes for nanoparticle

摘要

The main objective of this research is to study the effects of nanoparticle shape on the entropy generation characteristics of boehmite alumina nanofluid flow in a horizontal double-pipe heat exchanger. The examined boehmite alumina nanofluids include dispersed cylindrical, brick, blade, platelet and spherical nanoparticles in a mixture of water/ethylene glycol. The nanofluid and water flow through the tube side and annulus side of the heat exchanger, respectively. Two-phase mixture model is applied to precisely simulate the behavior of nanofluid. The effects of the various Reynolds numbers, nanoparticle concentrations and nanoparticle shapes on the frictional, thermal and total entropy generation rates as well as the Bejan number are numerically investigated. The results indicated that the highest and lowest frictional entropy generation rate belongs to the nanofluids with platelet shape and spherical shape nanoparticles, respectively, while the nanofluid containing spherical shape and platelet shape nanoparticles represented the maximum and minimum thermal and total entropy generation rates. Furthermore, it was inferred that the frictional entropy generation rate is enhanced with an increase in nanoparticle concentration, whereas except for nanofluid with spherical shape nanoparticles, the opposite is true for thermal and total entropy generation rates and Bejan number.