A printed-circuit heat exchanger consideration by exploiting an Al2O3-water nanofluid: Effect of the nanoparticles interfacial layer on heat transfer

Abstract

Supercritical carbon dioxide (S-CO2) Brayton cycle is an encouraging power conversion technology pertaining to waste heat recovery applications, because of the high compactness and efficiency it presents. A key technological challenge for the commercialization of this technology is the improvement of the cooling process of these cycles. In this study, an analytical investigation of a printed-circuit heat exchanger (PCHE) used as precooler for S-CO2 Brayton cycles and employing an Al2O3-water nanofluid is presented. In particular, the heat exchanger is modeled as segments in series to investigate the nanofluid impact on the PCHE's thermal-hydraulic performance. Regarding the nanoparticles consideration, the selected theoretical model for the estimation of the thermal conductivity takes into account the radius of the nanoparticles and the nanolayer thickness which is formed around it. In brief, the maximum used nanoparticle volume fraction of 5% results in an improvement of 75% for the heat transfer coefficient leading, in turn, to a reduction of 1% for the heat exchanger length and a pressure drop increase of 8%. Finally, the increase of nanoparticle radius results in a reduced effective thermal conductivity, while the nanolayer thickness of 2 nm showed an improved heat transfer coefficient by 43% compared to the minimum nanolayer thickness of 0.5 nm. © 2020 Elsevier Ltd