Aggregation Effects on Heat Transfer in Viscoplastic Nanofluid Entrance Flows

Abstract

This study numerically investigates heat transfer enhancement in laminar, incompressible viscoplastic nanofluid flow through the entrance region of a circular cylinder with a uniformly heated wall, including the effects of both, non-aggregation and aggregation of nanoparticles. Nanofluid properties are modeled using Brinkman and Maxwell models in the case of non-aggregation, and Krieger-Dougherty, Maxwell-Bruggeman models in the case of aggregation, while the viscoplastic behavior is described by the Bingham-Papanastasiou model. The governing boundary layer equations are solved using a finite-difference method. The effects of yield stress and nanoparticle volume fraction (up to 5%) on friction, pressure drop, and Nusselt number are analyzed, and performance evaluation criteria are evaluated to identify the optimal volume fraction for maximum efficiency.