Natural convection from a horizontal cylinder at moderate grashof numbers

Abstract

This chapter discusses the role of non-Newtonian flow characteristics of structured fluids—within the framework of continuum mechanics—on the hydrodynamic and convective heat and mass transport processes for bluff bodies of various shapes immersed in streaming (unconfined or confined) or quiescent fluids in different flow regimes. It focuses on the steady and laminar vortex shedding regimes of the flow over long cylinders of circular, elliptic, semicircular, square, and triangular cross sections. Within this framework, the flow invariably tends to be two-dimensional and laminar. The unconfined or free flow past a circular cylinder exhibits a rich variety of flow regimes depending upon the intrinsic nature of the flow. The simple flow is governed by the Reynolds number that is based upon the diameter of the cylinder, kinematic viscosity of the fluid, and the faraway uniform velocity. Most non-Newtonian fluids tend to be far more viscous than their Newtonian counterparts like air and water and, therefore, laminar flow conditions prevail more often in such fluids than that in Newtonian fluids like air. The chapter describes the flow regimes and fluid mechanical aspects related to circular, elliptical, semicircular, triangular, and square cylinders, together with the critical values of the Reynolds number denoting the transition from one flow regime to another. These values are strongly influenced not only by the rheological characteristics but also by the shape of the bluff body, its orientation with regard to the mean direction of flow, and its extent and type of confinement. The scaling considerations that are used to extract the pertinent dimensionless parameters which influence the detailed and macroscopic momentum and heat transfer characteristics for each shape of the bluff body have also been highlighted.